[Frontiers in Bioscience 5, d880-893, November 1, 2000]

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Dr C van Kooten,
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Basic science, Immunology, CD40, CD40-L, Signal transduction, Review

Versions: 1997, 2000

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Copyright © Frontiers in Bioscience, 1995

IMMUNE REGULATION BY CD40-CD40-L INTERACTIONS - 2; Y2K UPDATE

Cees van Kooten

Dept of Nephrology, Leiden University Medical Center, Leiden, the Netherlands

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Immune regulation by CD40-CD40-L interactions
3.1. Structure and expression of CD40 and its ligand
3.2. CD40 signal transduction
3.2.1 Kinases
3.2.2 TNF-R Associated Factors (TRAF)
3.2.3 Genetic inactivation of TRAF molecules
3.2.4 CD40 signaling and EBV
3.2.5 Mechanisms of transducing signals
3.3. Functions of CD40 in vitro
3.3.1. B lymphocytes
3.3.2. Monocytes and dendritic cells
3.3.3. Non-hematopoietic cells
3.4. In vivo functions of CD40/CD40-L interactions
3.4.1. Hyper-IgM syndrome
3.4.2. CD40/CD40L: humoral immune responses
3.4.3 CD40/CD40L: priming of T cell responses
3.4.3. CD40/CD40L: role in autoimmunity
3.4.4. CD40/CD40L: role in transplantation
3.4.5 CD40/CD40L: role in inflammation
4. Concluding remarks
5. References

1. ABSTRACT

CD40 is a cell surface receptor, which belongs to the TNF-R family, and which was first identified and functionally characterized on B lymphocytes. However, in recent years it has become clear that CD40 is expressed much broader, including expression on monocytes, dendritic cells, endothelial cells and epithelial cells. Therefore it is now thought that CD40 plays a more general role in immune regulation. The present paper reviews recent developments in this field of research, with main emphasis on CD40 signal transduction and on in vivo functions of CD40/CD40-L interactions.

2. INTRODUCTION

After the identification of CD40 in 1985, research has for a long time been focussed around the regulation of humoral immune responses. CD40 was identified as a molecule expressed during all stages of B cell development and differentiation, which plays a pivotal role in T cell-dependent B cell responses. The in vivo relevance was proven by the finding that patients suffering from the X-linked hyper-IgM syndrome (HIGM), were characterized by mutations in the gene coding for the ligand of CD40 (CD40L or CD154).

After this breakthrough finding, research on CD40-CD40L has expanded in various directions. It was found that both CD40 and CD40L expression is much broader than initially thought. For instance, it has become clear that on dendritic cells (DC) CD40 is one of the critical steps in its final maturation into a fully competent antigen presenting cell. CD40 is also widely expressed on non-hematopoietic cells, including endothelial cells, fibroblasts and epithelial cells, where it seems involved in the amplification and regulation of inflammatory responses. Interference with CD40-CD40L interaction might represent a new target to treat patients with unwanted immune-activation such as autoimmunity or transplant rejection, and has resulted in respective phase II clinical trials.

CD40 and CD40L belong to the TNF-R and TNF family, an emerging group of receptor-ligand pairs. Families are characterized by structural homologies, clustered chromosome location, shared signal transduction pathways and overlapping biological activities in processes such as cell growth, differentiation and death. In the present review we will mainly concentrate on two aspects of CD40 biology: i) mechanisms of signal transduction via the CD40 receptor, since this integrates the receptor with other members of the TNF-R family and might provide clues how this receptor can have such diverse effects; ii) the in vivo role of CD40-CD40L and the implications for its use in therapeutic settings. Other subjects will be briefly summarized and for more detail readers are referred to the 1996 version of this review (1), or to several extensive overviews (2-9).

3. IMMUNE REGULATION BY CD40-CD40-L INTERACTIONS

3.1. Structure and expression of CD40 and its ligand

The CD40 antigen is a 45-50 kDa glycoprotein of 277 AA, which belongs to the Tumor Necrosis Factor Receptor family (10). The extracellular segment of CD40, in particular the 22 cysteine residues, are homologous to other members of the TNF-R family, which at the moment includes at least 20 members (11, 12). Initially it was suggested that these cysteins form 4 predicted protein domains of about 40 AA. More recently the modularity of the TNF-receptor family has been refined, suggesting that every domain is built of two modules, with 5 different forms of modules being identified (13). Although the structure of CD40 has not been resolved, a model has been built using homology modeling, mutagenesis, X-ray structures of TNF-R and allignment of the TNF-R family (14). The mouse CD40 gene, composed of nine exons that span a 16.3 kb of genomic DNA, is located on the distal region of chromosome 2 which is syntenic to human chromosome 20q11-q13 where the human CD40 gene is located.

CD40 is expressed by multiple cell types. In the hematopoietic system, it is expressed on CD34+ hematopoietic progenitors, B cell progenitors, mature B Iymphocytes, plasma cells, monocytes, dendritic cells, eosinophils, basophils and on some T Iymphocytes. CD40 is also expressed on non-hematopoietic cells such as endothelial cells, fibroblasts and epithelial cells (6, 9).

Expression cloning using a CD40-Fc fusion protein allowed the isolation of a CD40-ligand (CD40-L) from activated T cells (15). Human CD40-L is a polypeptide of 261 AA including a 215 AA extracellular domain with five cysteins. The structure of the TNF-like region of human CD40L (a soluble form spanning from Gly116 to Leu261) has been resolved by X-ray crystallography at 2 Å resolution (16). CD40L is a sandwich of two beta sheets with jelly roll topology and forms a 3-fold symmetric homotrimer. The three-dimensional organization is similar to that described for the TNF-alpha and LT-alpha proteins, and as predicted by initial modelling studies. The gene for CD40-L is located on the X-chromosome at position q26.3-q23.1. It spans over 12-13 kb and consists of five exons.

CD40-L is expressed on activated but not on resting T cells, as demonstrated with either CD40-Ig fusion proteins or specific monoclonal antibodies. CD40-L can be induced on Th0, Th1 and Th2 cells and is primarily restricted to CD4+ T cells, although a small population of CD8+ T cells also expresses CD40-L. Apart from T lymphocytes, both primary cells and cell lines of mast cells, basophils and eosinophils stain positive with CD40-Ig or CD40L antibodies (17). Similarly, expression of CD40L has been demonstrated on B cells and B cell lines, NK cells, monocytes/macrophages and dendritic cells under certain conditions (18-21). Finally, pre-formed CD40L was demonstrated to be present in intracellular stores of thrombocytes (22).

CD40L is produced as a type II transmembrane protein, but may be expressed on the cell surface as a heteromultimeric complex (23). The molecule can excist in two shorter versions of 31 kD and 18 kD (24, 25). These shorter soluble forms of CD40L retain their ability to form trimers, to bind CD40 and to deliver biological signals, thus indicating that CD40L might also act as a "cytokine" (24-26). Qualitative differences between the soluble and membrane bound forms may yet exist.

3.2. CD40 signal transduction

3.2.1. Kinases

Like all other members of the TNF-R family, CD40 has no kinase domain and no known consensus sequence for binding to kinases. Yet, CD40 ligation activates several second messenger systems, including activation of protein tyrosine kinases (PTK; lyn, syk and Jak3), protein kinase A (PKA), phosphoinositide-3 kinase (PI-3 kinase) and phospholipase C (6). In recent years many studies have concentrated on the involvement of serine / threonine kinases: stress activated protein kinase / c-jun aminoterminal kinase (JNK/SAPK), p38 MAPK and extracellular signal-regulated mitogen activated protein kinase (ERK) (27-30). Since contrasting results have been obtained regarding JNK, p38 or ERK activation, general conclusions should be taken with care.

An important reason for different experimental results might be that studies often have used different cell types or models of transfected cells. This might have important consequences for signal transduction pathways. For instance, although the NF-kB inducing kinase (NIK) was shown to be essential for B cell activation, it seems to be dispensable for activation of dendritic cells (31). Alternatively, TRAF6 (see below) is an intermediate in CD40-induced NF-kB activation in 293 epithelial cells, but not in B cells (32). Finally, comparing members of the NF-kB family upon CD40 ligation showed a difference in p50 (B cells and monocytes) or p65 (B cells only) induction (33). The same study showed that in both B cells and monocytes, CD40 is associated with JAK3, but only in monocytes CD40 triggering results in activation of STAT5a. This might contribute to the finding that CD40 signaling seems to be normal in monocytes of patients with non-X-linked hyper IgM syndrom (34), a B cell deficiency not based on the absence of functional CD40L.

3.2.2. TNF-R Associated Factors (TRAF)

In recent years it has been established that members of the TNF-R family associate intracellularly with different families of signalling molecules. This includes the 'death domain' family for receptors involved in apoptosis induction (12). For CD40, coupling of the receptor to different signaling pathways has been better understood by the identification of another family of associated proteins: TRAF (TNF-R Associated Factor)(for review (11)). Most of these factors have been identified by the technique of the two-hybrid system, and at the moment 6 members of the TRAF family have been cloned and identified. The TRAF proteins are well conserved during evolution and TRAF-like proteins have been found in C. elegans and Drosophila. The proteins contain several functional domains which might be involved in signal transduction (RING finger domain, Isoleucine zipper, Zinc finger). In addition the TRAF-C domain plays a role in protein-protein interactions, either to associate with CD40 or other TNF-R members, or to form homo- / heterodimers. Crystallography of this TRAF-C domain of TRAF2, with peptides of either TNF-R2 or CD40, showed a spontaneous trimeric self-association (35, 36).

In general, there is little cross reactivity between the extracellular ligands and members of the TNF-R family, with the exception of TNF and LT, TRAIL and it's receptors and the interaction between BAFF/TALL-1 and TACI or BCMA (37). In contrast, the intracellular ligands seem to be much more promiscuous and form a complex network of homo- and hetero-dimers and interact with many members of the TNF-R family (11).

At least 4 TRAF molecules have been demonstrated to associate with the CD40 cytoplasmic tail (TRAF2, TRAF3, TRAF5, TRAF6), and three of these were cloned using CD40 as bait in the two-hybrid system. TRAF3 was the first identified CD40-associated TRAF molecule and was simultaneously found by several groups as CRAF1, CD40bp, LAP1 and CAP1 (38-41). TRAF3 is a 62 kD intracellular protein which is expressed in almost all cell types. CD40 also associates with TRAF2, a molecule first identified as an addaptor molecule bound to TNF-R2 (42). Finally, both TRAF5 and TRAF6 were cloned by yeast two-hybrid using CD40 as bait (43, 44).

Early mutagenesis studies already suggested a critical role for the Thr residue at position 254 (complete coding sequence)(45), and this residue was implicated in TRAF3 binding (39). Deletion mutants of the intracellular region indeed showed association of TRAF2, TRAF3 and TRAF5 to one region (residue 246-269), whereas TRAF6 associated with a separate domain (residue 230-245)(44). Such a separation of the TRAF members in two groups is supported by the more distant amino acid homology of TRAF4 and TRAF6 compared to TRAF1,2,3,5 which are more homologous (11). A comparable difference in binding domain of TRAF6 has been demonstrated for RANK (46). In accordance, pepscan analysis of CD40 identified PVQET (residue 250-254) as the minimal unit for TRAF1, TRAF2 and TRAF3 binding, and QEPQEINF (residue 231-238) as the minimum for TRAF6 binding (47). In this study, TRAF5 binding could only be demonstrated indirectly via TRAF3, which was confirmed by others (48). Binding and signaling of TRAF6 could even be optimized by generating a N237D mutant (49). Using wild-type CD40 and a mutant only containing the binding site for TRAF6, it was demonstrated that CD40 activates ERK both by a ras-dependent pathway and a ras-independent pathway involving TRAF6 (50).

3.2.3. Genetic inactivation of TRAF molecules

To unravel this complex network and to understand the in vivo role of the different TRAF molecules, several members have been genetically inactivated in mice. TRAF3 knock out mice appear normal at birth, but die around the age of 10 days (51). B cells from these mice show an apparantly normal proliferation and signaling in B cells, suggesting that the action of TRAF3 might be compensated by other TRAF molecules. In contrast, it was found that T cell activation is impaired, but signaling via which receptor is responsible for this defect is not clear (51).

Inactivation of TRAF2 showed that mice were born normal, although at lower frequency, but they also died early in life (52). Initial experiments had suggested that TRAF2 was both critical for JNK and NF-kB activation, but analysis of embryonic fibroblasts of these TRAF2-KO mainly showed hampered JNK activation, but almost normal NF-kB. A similar observation was made in transgenic mice, overexpressing a dominant negative form of the TRAF2 molecule (53).

Inactivation of TRAF5 resulted in a milder phenotype and no gros abnormalities of the mice (54). Stimulation of TRAF5 -/- B cells via several receptors (CD40, CD27, TNF) resulted in normal NF-kB and JNK activation. Nevertheless, the same cells showed defects in CD40-mediated proliferation and expression of CD23, CD54, CD80, CD86 and Fas/CD95 (54), suggesting a critical role for TRAF5 in CD40 signaling.

After it's initial cloning as a CD40 associated molecule, the role of TRAF6 has become more complex. It was found that TRAF6, via two additional adaptor molecules (IRAK and MyD88), is also critical in the signal transduction induced by the Toll / IL1-R family (55-58). Within the TNF-R family, association with TRAF6 is restricted to CD40, RANK and the p75 NGF-R (11). Generation of TRAF6 KO mice showed low birth rates of -/- mice and early death (59, 60). Importantly, these mice exhibited severe osteopetrosis, confirming the critical role of RANK-OPGL in bone remoddeling (61). In line with it's role in different signaling pathways, absence of TRAF6 not only interfered with CD40-mediated B cell proliferation, but also B cell proliferation induced by LPS or induction of iNOS in macrophages by IL-1 or LPS (59, 60). These recent observations of TRAF6, which link immune regulation (CD40) and inflammation (IL-1/LPS), might be helpfull in understanding the role of CD40 expression on cells outside the immune system.

3.2.4. CD40 signaling and EBV

TRAF3 was also cloned by screening for proteins which can interact with the EBV transforming gene product LMP1 (latent infection membrane protein-1)(40). It is thought that TRAF mediated signals will be launched by trimerization of surface receptors. After EBV transformation, it is likely that the oligomerization of these molecules is obtained by the spontaneous aggregation capacity of the LMP1 molecule. This indicates that EBV utilizes the CD40 signalling pathway to activate and immortalize B lymphocytes. Continuous expression of LMP1 is essential for the proliferation of the EBV-immortalized B cells (62, 63). Generation of chimeric proteins suggested that CD40-induced and LMP1-induced pathways are overlapping (64), although it has been shown that TRAF6 can not associate with the LMP-1 molecule (44). In vivo experiments showed that transgenic overexpression of LMP-1 in a CD40 deficient background resulted in extrafollicular B cell proliferation and Ig production, but not in the generation of germinal centers (65). Although this points to differences in signal transduction, an alternative explanation might be the absence of CD40-CD40L interaction and subsequent "CD40L triggering" which has been suggested to be important for GC formation (66).

3.2.5. Mechanisms of transducing signals

Despite the wealth of new information on molecules implicated in CD40 signaling, the exact mechanism how signals are transmitted is still not clear. For a long time it has been assumed that the trimeric configuration of the different ligands, as proven by chrystallography of TNF, LT and CD40L (16, 67-69), will trimerize the receptor and thereby launch the signal machinery. This resembles the concept of signaling by other cytokines and growth factors. However, crystallography of the TRAF-C domain of TRAF2 which showed spontaneous trimerization already complicated this picture (35, 36). Moreover, recent studies identified a domain (pre-ligand assambly domain; PLAD) in the extracellular parts of TNF-R members, including CD40, which was responsible for the assembly of a trimeric receptor complex in the absence of ligand (70). Whether there is a signaling function for ligand-independent trimers and what is the consequence of ligand binding remains to be determined. For instance different levels of crosslinking might have different biological consequences as shown by functional differences in IL-6 production after anti-CD40 antibody or membrane bound CD40L exposure (71).

A constitutive association between CD40 and TRAF2 has been described (72). Others described that CD40 activation in B cells results in translocation of TRAF2 from cytoplasm to the membrane (73). More importantly, it seems that upon activation, CD40 together with associated TRAF2 and TRAF3 move to lipid microdomains which brings them in close vicinity of different src kinases (73). Interaction between TRAF2 and these kinases can be prevented by TRAF mutants or zinc chelators. Similar results on the importance of membrane rafts for CD40 signaling has been demonstrated in dendritic cells (74). These exciting new developments might provide clues to the exact mechanisms of signal transduction, explaining the array of different activities and differences between cell types.

3.3. Functions of CD40 in vitro

3.3.1. B Iymphocytes

Extensive studies on CD40 activation of B cells in vitro, have demonstrated that CD40 activation has major effects on many steps of the B cell natural history (2, 5, 6). CD40 ligation activates resting B cells as shown by increase in size and expression of new surface molecules involved in homotypic and heterotypic aggregation (CD23, VLA-4), T cell costimulation (CD80/CD86) and increased expression of MHC class I, MHC class II and TAP transporter (75). Furthermore, CD40-activated B cells secrete a panel of cytokines which may act as autocrine and paracrine growth and differentiation factors (76, 77). These molecules, which all contribute to the biological function of the B cells, have also provided the tools to study signal transduction pathways in more detail. For most processes, CD40 acts in concert with either cytokines or other receptor-ligand interactions.

An important example of such cooperation is the process of isotype switching, which is initiated by CD40, but for which the specificity of the isotype is determined by cytokines. In human, IL-4/IL-13 induce switch to IgE and IgG4, IL-10 induces switch to IgG1 and IgG3, whereas combinations of IL-10 and TGF-beta promote switch to IgA. More recently, it has become clear that also other molecular interactions, like interaction with dendritic cells, might enhance the level of Ig production (78), or even directly promote the switch to a specific isotype (IgA)(79).

For selection of high affinity memory B cells, a complex network of interactions exists, involving CD40, Fas, B cell Antigen-receptor (BCR) and cytokines. CD40 crosslinking induces Fas expression and sensitivity for Fas-mediated apoptosis (80-82). However, the simultaneous triggering of the BCR increases the resistance to Fas-induced apoptosis (83). In contrast, apoptosis of germinal center B cells can be induced by prolonged crosslinking of the BCR, an effect which can be prevented by the addition of IL-4 (84, 85). The interplay of these various signalling pathways has been confirmed in vivo using HEL transgenic mice (86).

Dual triggering of resting B Iymphocytes through their CD40 and antigen receptor induces a phenotype characteristic of cells from germinal centers (87, 88), the anatomical site where B cells undergo somatic mutation, selection, isotype switching and become either plasma or memory cells. Prolonged triggering of CD40 skews the maturation of B cells into memory cells while interruption of CD40 signalling allows plasma cell differentiation (89, 90).

Although most normal and malignant B cells proliferate in response to CD40 engagement, plasma cells appear unresponsive (91). Furthermore, CD40 ligation appears to inhibit the proliferation of diffuse B cell Iymphomas, thus illustrating a possible negative role of CD40 on cell proliferation (92, 93)

3.3.2. Monocytes and dendritic cells

The expression of CD40 on antigen presenting cells like monocytes and dendritic cells is well established now (94, 95). Activation of the CD40 receptors is one of the critical signals which allow the full maturation of dendritic cells into the most powerfull antigen presenting cells (96). CD40 ligation on monocytes and dendritic cells results in: i) increased expression of costimulatory molecules such as CD54/ICAM-1, CD58/LFA-3, CD80/B7-1, CD86/B7-2; ii) the secretion of cytokines (such as IL1, IL6, IL8, IL10, IL12, TNFa, MIP1a) and enzymes such as matrix metalloproteinase (MMP); iii) an enhanced survival of these cells; iv) enhanced monocyte tumoricidal activity; v) NO synthesis; vi) promote differentiation of DC from CD34+ hematopoietic progenitors. Therefore the interaction between CD40 and CD40L has important consequences for both APC function and T cell function. The full impact of CD40 for DC biology is outside the scope of this paper and is reviewed elsewhere (96-98).

3.3.3. Endothelial cells, epithelial cells and fibroblasts

Apart from hematopoietic cells, the expression of CD40 has now been observed on many other cell lineages. Although the expression is generally low in normal tissues, the molecule is clearly upregulated under various pathological conditions. In accordance, expression can be observed on many cultured cell types including endothelial cells, epithelial cells and fibroblasts. Increased expression of CD40 is observed after in vitro activation, notably after stimulation with IL-1, IL-17 or IFN-gamma. The functional relevance of the CD40 molecule on these cells is relatively less investigated. Most likely, CD40 expression on non-hematopoietic cells might be relevant for inflammatory responses. Initial in vitro studies, using various cell types, have demonstrated prominent effects of CD40 crosslinking on the production of cytokines and chemokines. Moreover, also other inflammatory mediators are increased, including expression of adhesion molecules, production of matrix metalloproteinases (MMP) and procoaggulant activity.

Alternatively, on some cell types, including carcinomas, it has been demonstrated that CD40 activation results in an induction of cell death (99-101).

3.4. In vivo functions of CD40/CD40-L interactions

3.4.1. Hyper IgM Syndrome

The first demonstration of the critical role of CD40/CD40-L interactions in vivo came from the discovery that the hyper IgM syndrome, an X-linked immunodeficiency, is due to a genetic alteration of the CD40-L (102). This disease is characterized by a severe impairment of T cell dependent antibody responses with no B cell memory and no circulating IgG, IgA and IgE (103, 104). The demonstration of preformed CD40L in platelets has been instrumental in the development of an easy diagnostic tool (105). Next to patients with the X-linked form of hyper-IgM, who have mutations in CD40L and normal B cells, other patients have been described who have a similar immunodeficiency caused by deficiencies in CD40 signalling (106).

Patients with hyper-IgM syndrome have an enhanced susceptibility to opportunistic infections, such as Pneumocystis carinii pneumonia and Cryptosporidium diarrhea. This indicates a role for CD40-CD40-L interactions in cell-mediated immune responses. Indeed, CD40-L knockout mice display a considerable impairment of antigen specific T cell priming (107) and appear particularly susceptible to Leishmania infection (108-110). This most likely results from a defective Th1 response which is related to an impaired production of IL12 by antigen presenting cells.

3.4..2 CD40-CD40L: humoral immune responses

The role of CD40L for B cell proliferation and germinal center formation was demonstrated in vivo by simultaneous tracking of antigen specific T and B cells after immunization (111). The generation of CD40 and CD40-L knockout mice revealed a phenotype comparable to that of the patients suffering from the hyper IgM syndrome (112-114).

In view of the critical role of CD40-CD40L interactions in humoral immune responses, strategies have been developed to either decrease or increase these responses. Blocking anti-CD40L antibodies have been used in animal models to inhibit situations of unwanted antibody production. Anti-CD40L treatment inhibits production of autoantibodies in models of collagen-induced arthritis, SLE nephritis and experimental autoimmune encephalomyelitis (EAE). On the other hand, administration of agonistic anti-CD40 antibodies can result in strong, isotype-switched, antibody responses against pneumococcal polysaccharides (115). Similarly, an expression plasmid containing the CD40L-trimer has been administered together with Leishmania Ag, and was successfull in controling infection with Leishmania major (116). Therefore, administration of CD40 stimulating agents might be used for future vaccination strategies against weakly immunogenic, T cell-independent, antigens, or to boost immune responses in immunecompromized individuals.

3.4.3. CD40-CD40L: priming of T cell responses

The contribution of CD40-CD40L interactions to the process of T cell priming, differentiation and effector functions has been extensively reviewed (95, 117-119). The notion that CD40 is expressed on (professional) antigen presenting cells has been a break through in this field. There has been some controversy whether antigen presentation in the absence of CD40-CD40L interaction leads to tolerance (120). In some models, like the cellular immunity against LCMV or VSV virus, T cell priming seems to be independent of CD40L (121), although differences might exist between the induction of the CTL response and maintenance of CTL memory (122, 123). The difference in CD40L-dependence has not been fully explained, but factors like TCR occupancy, antigen persistence and simultaneous inflammation have been proposed.

For a long time, it has been realized that in many cases, CD4+ T cells are required to induce efficient CD8+ cytotoxic T cell responses, a process termed 'cross-priming'. It has become clear that CD40-CD40L interaction between the CD4+ T cell and the professional APC (dendritic cell), stimulates the DC in such a way that it aquires the capacity to subsequently stimulate CD8+ cytotoxic T cells (124-126). The molecular mechanism underlying this capacity of the APC is at present unknown. However, it seems that other signals, like TNF, LPS or viral infection may substitute for the CD40L-mediated signals, explaining the existence of CD4-independent CD8 T cell responses (127). Stimulating CD40 antibodies have been used to convert a tolerogenic peptide vaccine into strong CTL priming, and to show regression of established tumors (128-130).

3.4.4. CD40-CD40L: role in autoimmunity

Administration of blocking anti-CD40L has been demonstrated to be benificial in several models of autoimmunity, including spontaneous diseases like lupus nephritis in SNF1 mice or diabetes in NOD mice or in experimentally induced forms of disease like collagen-induced arthritis or experimental allergic encephalomyelitis (EAE)(131). In patients with SLE, an increased expression of CD40L was observed on circulating lymphocytes (132, 133), and CD40L positive cells could also be demonstrated in kidney sections of SLE patients (134). Moreover, serumlevels of soluble CD40L seem to be increased in patients with SLE (135). Similarly, activated helper T cells expressing CD40-L surface protein are detected in multiple sclerosis patient brain sections where CD40 bearing antigen presenting cells can be found (136).

Since most diseases will have a complex pathophysiology, the levels at which the anti-CD40L might potentially interfere are diverse (antigen presentation, Ig production, inflammatory responses). Interestingly, both for lupus nephritis and EAE it was demonstrated that anti-CD40L could also interfere with ongoing disease, confirming the role of CD40-CD40L in the effector phase of the disease (136, 137). Part of the mechanism has been suggested to relate to a block in Th1 development and diminished IFN-gamma production (138).

3.4.5. CD40-CD40L: role in transplantation

Interference with CD40 activation prolongs the survival of experimentally transplanted organs. These models have been mostly limited to murine models, since only blocking anti-murine CD40L antibodies are at present available, and include allografts of heart, skin, aorta and pancreatic islets, as well as the respective xenografts (139-142). Although treatment with anti-CD40L alone prolongs graft survival, better results have been obtained by combined treatment, either with donor splenocytes or CTLA4-Ig. Simultaneous blocking of the CD40 and CD28 pathways resulted in long-term acceptance of skin and cardiac allografts (143). However, it has been shown that the results are strongly dependent on the strain combinations used. In several cases, rejection seems to occur indendent of CD40-CD40L and are mediated by CD8 positive T cells (144, 145). Moreover, it has been shown that the Th1 or Th2 background of the mice affects the result of anti-CD40L blockade (146).

The treatment regimen has been different in the various studies, ranging from once at the time of transplantation until continuous administration every 72 hours to prevent chronic rejection in aortic allografts (147). In the latter case, also CD40L effector functions operating within the transplanted graft might be of importance (see 3.4.4). Local expression of CD40L has been found in human renal and heart allografts, and expression seems to correlate with rejection (148, 149).

Studies with a humanized anti-CD40L antibody have been performed in renal allotransplantation in rhesus monkeys. An extended course of anti-CD40L as the only treatment over a 6 months period resulted in long-term survival (150, 151). Importantly, the organs were not rejected when treatment was stopped, and graft survival reached up to 10 months post-treatment. Combinations of current immunosuppressive drugs, including steroids, MMF, and tracolimus, seems to counteract the benificial effect of anti-CD40L. The same humanized Ab has been used in a primate model of cardiac transplantation, showing improved survival and less vascular pathology (152).

Although the present data do not provide sufficient evidence to show permanent transplant tolerance, these data are promising for the development and use of blocking CD40L reagents. These studies have resulted in a phase-II human clinical trial in renal allograft recipients. However, this trial has been discontinued, due to adverse effects, specifically thrombo-embolic complications (153). It is expected that these trials will be resumed, but it underlines the need for further detailed analysis of the mechanism of action of CD40L blockade in basal studies.

3.4.6. CD40/CD40-L: role in inflammation

Long lasting, chronic, inflammatory responses, which are characteristic of many diseases, ultimately lead to severe histological changes and loss of normal function. Generally, these situations, such as atherosclerosis or fibrosis, are characterized by the local presence of infiltrating mononuclear cells, including T cells, B cells and monocytes (154, 155).

Administration of soluble CD40L in the lung was demonstrated to induce pulmonary inflammation (156), whereas the use of CD40L KO mice prevented the development of lung inflammation and fibrosis (157). Treatment with anti-CD40L was shown to prevent pulmonary inflammation and fibrosis as a consequence of oxygen-induced respiratory distress syndrom (158). In a chimeric model, it was shown that CD40 positive bone marrow derived cells paly a critical role in this process (159).

Development of atherosclerosis is thought to be dependent on local communication within the vessel wall, possibly orchestrated by activated T cells. In vitro studies already indicated that vascular cells, like endothelial cells and smooth muscle cells (SMC) are responsive to CD40 signaling. CD40 activation of both cell types results in an increased expression of adhesion molecules, cytokines, matrix metalloproteinases and tissue factor (160-163). More importantly it was shown that CD40-CD40L is also relevant for the process of atherosclerosis in vivo. Treatment with anti-CD40L in hyperlipidemic mice (lacking LDL receptor) reduced the size of atherosclerotic lesions (162, 164). Evenmore, in models with progressive atherosclerosis, delayed treatment with anti-CD40L was still able to change the composition of the plaque and reduced further disease development (165, 166). These data were confirmed in a model of ApoE and CD40L double knock-out mice (167). Finally, transplant arteriosclerosis, occurring during chronic rejection, was prevented by anti-CD40L treatment and was associated with an increased expression of the protective, anti-apoptotic genes heme oxygenase-1, Bcl-xL and A20 (168).

4. CONCLUDING REMARKS

In recent years, the focus of CD40 research has been shifted from the study of B cell regulation (humoral immunity), to the study of a general regulator of immune and inflammatory processes. Multiple disease states appear to be improved by interruption of CD40/CD40-L interactions. This is presently accomplished by preventing the association of the receptor with its ligand using specific antibodies and has resulted in phase II clinical trials. However, for long term clinical applications, such reagents may not be optimal. The identification of small synthetic chemical agents preventing the interaction of CD40 with its ligand would be of interest. Recently important progress has been made in unravelling the signal transduction pathways of CD40 in different target cells. This might allow the development of pharmacologic agents which will specifically block the intracellular pathways turned on after ligation of either CD40 or CD40-L.

5. REFERENCES

1 C. Van Kooten & J. Banchereau: Immune regulation by CD40-CD40L interactions. Front Biosci2, 358-368 (1997)

2 J. Banchereau, F. Bazan, D. Blanchard, F. Briere, J. P. Galizzi, C. Van Kooten, Y. J. Liu, F. Rousset & S. Saeland: The CD40 antigen and its ligand. Annu. Rev. Immunol. 12, 881-922 (1994)

3 E. A. Clark & J. A. Ledbetter: How B and T cells talk to each other. Nature 367, 425-428 (1994)

4 D. Hollenbaugh, H. D. Ochs, R. J. Noelle, J. A. Ledbetter & A. Aruffo: The role of CD40 and its ligand in the regulation of the immune response. Immunol Rev 138, 23-37 (1994)

5 T. M. Foy, A. Aruffo, J. Bajorath, J. E. Buhlmann & J. Noelle: Immune regulation by CD40 and its ligand gp39. Annu. Rev. Immunol. 14, 591-617 (1996)

6 C. Van Kooten & J. Banchereau: CD40-CD40 ligand: a multifunctional receptor-ligand pair. Adv. Immunol. 61, 1-77 (1996)

7 R. J. Noelle: CD40 and its ligand in host defense. Immunity 4, 415-419 (1996)

8 I. S. Grewal & R. A. Flavell: CD40 and CD154 in cell-mediated immunity. Annu. Rev. Immunol. 16, 111-135 (1998)

9 C. Van Kooten & J. Banchereau: CD40-CD40 ligand. J. Leuk. Biol. 67, 2-17 (2000)

10 C. A. Smith, T. Farrah & R. G. Goodwin: The TNF receptor superfamily of cellular and viral proteins: Activation, costimulation and death. Cell 76, 959-962 (1994)

11 J. Inoue, T. Ishida, N. Tsukamoto, N. Kobayashi, A. Naito, S. Azuma & T. Yamamoto: Tumor necrosis factor receptor-associated factor (TRAF) family: adapter proteins that mediate cytokine signaling. Exp Cell Res 254, 14-24 (2000)

12 S. J. Baker & E. P. Reddy: Modulation of life and death by the TNF receptor superfamily. Oncogene 17, 3261-70 (1998)

13 J. H. Naismith & S. R. Sprang: Modularity in the TNF-receptor family. TIBS 23, 74-79 (1998)

14 J. Singh, E. Garber, H. Van Vlijmen, M. Karpusas, Y. M. Hsu, Z. Zheng, J. H. Naismith & D. Thomas: The role of polar interactions in the molecular recognition of CD40L with its receptor CD40. Protein Science 7, 1124-1135 (1998)

15 R. J. Armitage, W. C. Fanslow, L. Strockbine, T. A. Sato, K. N. Clifford, B. M. Macduff, D. M. Anderson, S. D. Gimpel, T. Davis-Smith, C. R. Maliszewski, E. A. Clark, C. A. Smith, K. H. Grabstein, D. Cosman & M. K. Spriggs: Molecular and biological characterization of a murine ligand for CD40. Nature 357, 80-2 (1992)

16 M. Karpusas, Y. M. Hsu, J. H. Wang, J. Thompson, S. Lederman, L. Chess & D. Thomas: 2A crystal structure of an extracellular fragment of human CD40 ligand. Structure 3, 1031-1039 (1995)

17 J. F. Gauchat, S. Henchoz, D. Fattah, G. Mazzei, J. P. Aubry, T. Jomotte, L. Dash, K. Page, R. Solari, D. Aldebert, M. Capron, C. Dahinden & J. Y. Bonnefoy: CD40 ligand is functionally expressed on human eosinophils. Eur. J. Immunol. 25, 863-865 (1995)

18 L. M. Pinchuk, S. J. Klaus, D. M. Magaletti, G. V. Pinchuk, J. P. Norsen & E. A. Clark: Functional CD40 ligand expressed by human blood dendritic cells is up-regulated by CD40 ligation. J. Immunol. 157, 4363-4370 (1996)

19 A. C. Grammer, M. C. Bergman, Y. Miura, K. Fujita, L. S. Davis & P. E. Lipsky: The CD40 ligand expressed by human B cells costimulates B cells responses. J. Immunol. 154, 4996-5010 (1995)

20 F. Mach, U. Schonbeck, G. K. Sukhova, T. Bourcier, J. Y. Bonnefoy, J. S. Pober & P. Libby: Functional CD40 ligand is expressed on human vascular endothelial cells, smooth muscle cells, and macrophages: implications for CD40-CD40 ligand signaling in atherosclerosis. Proc. Natl, Acad. Sci. USA 94, 1931-1936 (1997)

21 E. Carbone, G. Ruggiero, G. Terrazzano, C. Palomba, C. Manzo, S. Fontana, H. Spits, K. Karre & S. Zappacosta: A new mechanism of NK cell cytotoxicity activation: the CD40-CD40 ligand interaction. J Exp Med 185, 2053-2060 (1997)

22 V. Henn, J. R. Slupsky, M. Grafe, I. Anagnostopoulos, R. Forster, G. Muller-Berghaus & R. A. Kroczek: CD40 ligand on activated platelets triggers an inflammatory reaction of endothelial cells. Nature 391, 591-594 (1998)

23 Y. M. Hsu, J. Lucci, L. Su, B. Ehrenfels, E. Garber & D. Thomas: Heteromultimeric complexes of CD40 ligand are present on the cell surface of human T lymphocytes. J. Biol. Chem. 272, 911-915 (1997)

24 D. Graf, S. Muller, U. Korthauer, C. van Kooten, C. Weise & R. A. Kroczek: A soluble form of TRAP (CD40 ligand) is rapidly released after T cell activation. Eur J Immunol 25, 1749-1754 (1995)

25 G. J. Mazzei, M. D. Edgerton, C. Losberger, S. Lecoanet-Henchoz, P. Graber, A. Durandy, J. F. Gauchat, A. Bernard, B. Allet & J. Y. Bonnefoy: Recombinant soluble trimeric CD40 ligand is biologically active. J. Biol. Chem. 270, 7025-7028 (1995)

26 B. Ludewig, V. Henn, J. M. Schroder, D. Graf & R. A. Krozcek: Induction, regulation, and function of soluble TRAP (CD40 ligand) during interaction of primary CD4+CD45RA+ T cells with dendritic cells. Eur. J. Immunol. 26, 3137-3143 (1996)

27 I. Berberich, G. Shu, F. Siebelt, J. R. Woodgett, J. M. Kyriakis & E. A. Clark: Cross-linking CD40 on B cells preferentially induces stress-activated protein kinases rather than mitogen-activated protein kinases. EMBO J. 15, 92-101 (1996)

28 A. C. Grammer, J. L. Swantek, R. D. McFarland, Y. Miura, T. Geppert & P. E. Lipsky: TNF receptor-associated factor-3 signaling mediates activation of p38 and Jun N-terminal kinase, cytokine secretion, and Ig production following ligation of CD40 on human B cells. J Immunol 161, 1183-1193 (1998)

29 J. M. Purkerson & D. C. Parker: Differential coupling of membrane Ig and CD40 to the extracellularly regulated kinase signaling pathway. J Immunol 160, 2121-2129 (1998)

30 A. Craxton, G. Shu, J. D. Graves, J. Saklatvala, E. G. Krebs & E. A. Clark: p38 MAPK is required for CD40-induced gene expression and proliferation in B lymphocytes. J Immunol 161, 3225-3236 (1998)

31 N. Garceau, Y. Kosaka, S. Masters, J. Hambor, R. Shinkura, T. Honjo & R. J. Noelle: Lineage-restricted function of nuclear factor kappaB-inducing kinase (NIK) in transducing signals via CD40. J Exp Med 191, 381-6 (2000)

32 S. V. Jalukar, B. S. Hostager & G. A. Bishop: Characterization of the roles of TNF receptor-associated factor 6 in CD40-mediated B lymphocyte effector functions. J Immunol 164, 623-30 (2000)

33 P. Revy, C. Hivroz, G. Andreu, P. Graber, C. Martinache, A. Fischer & A. Durandy: Activation of the Janus kinase 3-STAT5a pathway after CD40 triggering of human monocytes but not of resting B cells. J Immunol 163, 787-93 (1999)

34 P. Revy, F. Geissmann, M. Debre, A. Fischer & A. Durandy: Normal CD40-mediated activation of monocytes and dendritic cells from patients with hyper-IgM syndrome due to a CD40 pathway defect in B cells. Eur J Immunol 28, 3648-54 (1998)

35 Y. C. Park, V. Burkitt, A. R. Villa, L. Tong & H. Wu: Structural basis for self-association and receptor recognition of human TRAF2. Nature 398, 533-538 (1999)

36 S. M. McWhirter, S. S. Pullen, J. M. Holton, J. J. Crute, M. R. Kehry & T. Alber: Crystallographic analysis of CD40 recognition and signaling by human TRAF2. Proc Natl Acad Sci U S A 96, 8408-8413 (1999)

37 J. A. Gross, J. Johnston, S. Mudri, R. Enselman, S. R. Dillon, K. Madden, W. Xu, J. Parrish-Novak, D. Foster, C. Lofton-Day, M. Moore, A. Littau, A. Grossman, H. Haugen, K. Foley, H. Blumberg, K. Harrison, W. Kindsvogel & C. H. Clegg: TACI and BCMA are receptors for a TNF homologue implicated in B-cell autoimmune disease. Nature 404, 995-9 (2000)

38 G. Cheng, A. M. Cleary, Z. S. Ye, D. I. Hong, S. Lederman & D. Baltimore: Involvement of CRAF1, a relative of TRAF, in CD40 signaling. Science 267, 1494-1498 (1995)

39 H. M. Hu, K. O'Rourke, M. S. Boguski & V. M. Dixit: A novel RING finger protein interacts with the cytoplasmic domain of CD40. J Biol Chem 269, 30069-30072 (1994)

40 G. Mosialos, M. Birkenbach, R. Yalamanchili, T. VanArsdale, C. Ware & E. Kieff: The Epstein-Barr virus transforming protein LMP1 engages signaling proteins for the tumor necrosis factor family. Cell 80, 389-399 (1995)

41 T. Sato, S. Irie & J. C. Reed: A novel member of the TRAF family of putative signal transducing proteins binds to the cytoplasmic domain of CD40. FEBS Letters 358, 113-118 (1995)

42 M. Rothe, V. Sarma, V. M. Dixit & D. V. Goeddel: TRAF2-mediated activation of NF-kB by TNF receptor 2 and CD40. Science 269, 1424-1427 (1995)

43 T. Ishida, T. Tojo, T. Aoki, N. Kobayashi, T. Ohishi, T. Watanabe, T. Yamamoto & J. Inoue: TRAF5, a novel tumor necrosis factor receptor-associated factor family protein, mediates CD40 signaling. Proc. Natl Acad. Sci. USA 93, 9437-9442 (1996)

44 T. Ishida, S. Mizushima, S. Azuma, N. Kobayashi, T. Tojo, K. Suzuki, S. Aizawa, T. Watanabe, G. Mosialos, E. Kieff, T. Yamamoto & J. Inoue: Identification of TRAF6, a novel tumor necrosis factor receptor-associated factor protein that mediates signaling from an amino-terminal domain of the CD40 cytoplasmic region. J. Biol. Chem. 271, 28745-28748 (1996)

45 S. Inui, T. Kaisho, H. Kikutani, I. Stamenkovic, B. Seed, E. A. Clark & T. Kishimoto: Identification of the intracytoplasmic region essential for signal transduction through a B cell activation molecule, CD40. Eur J Immunol 20, 1747-53 (1990)

46 L. Galibert, M. E. Tometsko, D. M. Anderson, D. Cosman & W. C. Dougall: The involvement of multiple tumor necrosis factor receptor (TNFR)-associated factors in the signaling mechanisms of receptor activator of NF-kappaB, a member of the TNFR superfamily. J Biol Chem 273, 34120-7 (1998)

47 S. S. Pullen, H. G. Miller, D. S. Everdeen, T. T. A. Dang, J. J. Crute & M. R. Kehry: CD40-tumor necrosis factor receptor-associated factor (TRAF) interactions: regulation of CD40 signaling through multiple TRAF binding sites and TRAF hetero-oligomerization. Biochemistry 37, 11836-11845 (1998)

48 E. Leo, K. Welsh, S. Matsuzawa, J. M. Zapata, S. Kitada, R. S. Mitchell, K. R. Ely & J. C. Reed: Differential requirements for tumor necrosis factor receptor-associated factor family proteins in CD40-mediated induction of NF-kappaB and Jun N-terminal kinase activation. J Biol Chem 274, 22414-22 (1999)

49 S. S. Pullen, T. T. Dang, J. J. Crute & M. R. Kehry: CD40 signaling through tumor necrosis factor receptor-associated factors (TRAFs). Binding site specificity and activation of downstream pathways by distinct TRAFs. J Biol Chem 274, 14246-54 (1999)

50 M. Kashiwada, Y. Shirakata, J. I. Inoue, H. Nakano, K. Okazaki, K. Okumura, T. Yamamoto, H. Nagaoka & T. Takemori: Tumor necrosis factor receptor-associated factor 6 (TRAF6) stimulates extracellular signal-regulated kinase (ERK) activity in CD40 signaling along a ras-independent pathway. J Exp Med 187, 237-244 (1998)

51 Y. Xu, G. Cheng & D. Baltimore: Targeted disruption of TRAF3 leads to postnatal lethality and defective T-dependent immune responses. Immunity 5, 407-415 (1996)

52 W. C. Yeh, A. Shahinian, D. Speiser, J. Kraunus, F. Billia, A. Wakeham, J. L. de la Pompa, D. Ferrick, B. Hum, N. Iscove, P. Ohashi, M. Rothe, D. V. Goeddel & T. W. Mak: Early lethality, functional NF-kappaB activation, and increased sensitivity to TNF-induced cell death in TRAF2-deficient mice. Immunity 7, 715-25 (1997)

53 S. Y. Lee, A. Reichlin, A. Santana, K. A. Sokol, M. C. Nussenzweig & Y. Choi: TRAF2 is essential for JNK but not NF-kappaB activation and regulates lymphocyte proliferation and survival. Immunity 7, 703-13 (1997)

54 H. Nakano, S. Sakon, H. Koseki, T. Takemori, K. Tada, M. Matsumoto, E. Munechika, T. Sakai, T. Shirasawa, H. Akiba, T. Kobata, S. M. Santee, C. F. Ware, P. D. Rennert, M. Taniguchi, H. Yagita & K. Okumura: Targeted disruption of Traf5 gene causes defects in CD40- and CD27- mediated lymphocyte activation. Proc Natl Acad Sci U S A 96, 9803-9808 (1999)

55 Z. Cao, J. Xiong, M. Takeuchi, T. Kurama & D. V. Goeddel: TRAF6 is a signal transducer for interleukin-1. Nature 383, 443-6 (1996)

56 F. L. Rock, G. Hardiman, J. C. Timans, R. A. Kastelein & J. F. Bazan: A family of human receptors structurally related to Drosophila Toll. Proc Natl Acad Sci U S A 95, 588-93 (1998)

57 O. Adachi, T. Kawai, K. Takeda, M. Matsumoto, H. Tsutsui, M. Sakagami, K. Nakanishi & S. Akira: Targeted disruption of the MyD88 gene results in loss of IL-1- and IL-18-mediated function. Immunity 9, 143-50 (1998)

58 T. Kawai, O. Adachi, T. Ogawa, K. Takeda & S. Akira: Unresponsiveness of MyD88-deficient mice to endotoxin. Immunity 11, 115-22 (1999)

59 M. A. Lomaga, W. C. Yeh, I. Sarosi, G. S. Duncan, C. Furlonger, A. Ho, S. Morony, C. Capparelli, G. Van, S. Kaufman, A. van der Heiden, A. Itie, A. Wakeham, W. Khoo, T. Sasaki, Z. Cao, J. M. Penninger, C. J. Paige, D. L. Lacey, C. R. Dunstan, W. J. Boyle, D. V. Goeddel & T. W. Mak: TRAF6 deficiency results in osteopetrosis and defective interleukin-1, CD40, and LPS signaling. Genes Dev 13, 1015-24 (1999)

60 A. Naito, S. Azuma, S. Tanaka, T. Miyazaki, S. Takaki, K. Takatsu, K. Nakao, K. Nakamura, M. Katsuki, T. Yamamoto & J. Inoue: Severe osteopetrosis, defective interleukin-1 signalling and lymph node organogenesis in TRAF6-deficient mice. Genes Cells 4, 353-62 (1999)

61 Y. Y. Kong, H. Yoshida, I. Sarosi, H. L. Tan, E. Timms, C. Capparelli, S. Morony, A. J. Oliveira-dos-Santos, G. Van, A. Itie, W. Khoo, A. Wakeham, C. R. Dunstan, D. L. Lacey, T. W. Mak, W. J. Boyle & J. M. Penninger: OPGL is a key regulator of osteoclastogenesis, lymphocyte development and lymph-node organogenesis. Nature 397, 315-23 (1999)

62 U. Zimber-Strobl, B. Kempkes, G. Marshall, R. Zeidler, C. Van Kooten, J. Banchereau, G. W. Bornkamm & W. Hammerschmidt: Epstein-Barr virus latent membrane protein (LMP1) is not sufficient to maintain proliferation of B cells but both it and activated CD40 can prolong their survival. EMBO J. 15, 7070-7078 (1996)

63 E. Kilger, A. Kieser, M. Baumann & W. Hammerschmidt: Epstein-Barr virus-mediated B-cell proliferation is dependent upon latent membrane protein 1, which simulates an activated CD40 receptor. EMBO J 17, 1700-1709 (1998)

64 E. Hatzivassiliou, W. E. Miller, N. Raab-Traub, E. Kieff & G. Mosialos: A fusion of the EBV latent membrane protein-1 (LMP1) transmembrane domains to the CD40 cytoplasmic domain is similar to LMP1 in constitutive activation of epidermal growth factor receptor expression, nuclear factor-kappa B, and stress-activated protein kinase. J Immunol 160, 1116-1121 (1998)

65 J. Uchida, T. Yasui, Y. Takaoka-Shichijo, M. Muraoka, W. Kulwichit, N. Raab-Traub & H. Kikutani: Mimicry of CD40 signals by Epstein-Barr virus LMP1 in B lymphocyte responses. Science 286, 300-3 (1999)

66 D. Van Essen, H. Kikutani & D. Gray: CD40 ligand-transduced co-stimulation of T cells in the development of helper function. Nature 378, 620-623 (1995)

67 M. J. Eck & S. R. Sprang: The structure of tumor necrosis factor-alpha at 2.6 A resolution. Implications for receptor binding. J Biol Chem 264, 17595-605 (1989)

68 M. J. Eck, M. Ultsch, E. Rinderknecht, A. M. de Vos & S. R. Sprang: The structure of human lymphotoxin (tumor necrosis factor-beta) at 1.9-A resolution. J Biol Chem 267, 2119-22 (1992)

69 D. W. Banner, A. D'Arcy, W. Janes, R. Gentz, H. J. Schoenfeld, C. Broger, H. Loetscher & W. Lesslauer: Crystal structure of the soluble human 55 kd TNF receptor-human TNF beta complex: implications for TNF receptor activation. Cell 73, 431-45 (1993)

70 F. K. Chan, H. J. Chun, L. Zheng, R. M. Siegel, K. L. Bui & M. J. Lenardo: A domain in TNF receptors that mediates ligand-independent receptor assembly and signaling [see comments]. Science 288, 2351-4 (2000)

71 M. Baccam & G. A. Bishop: Membrane-bound CD154, but not CD40-specific antibody, mediates NF-kappaB-independent IL-6 production in B cells. Eur J Immunol 29, 3855-66 (1999)

72 A. Chaudhuri, S. Orme, S. Eilam & B. J. Cherayil: CD40-mediated signals inhibit the binding of TNF receptor-associated factor 2 to the CD40 cytoplasmic domain. J Immunol 159, 4244-4251 (1997)

73 B. S. Hostager, I. M. Catlett & G. A. Bishop: Recruitment of CD40 and tumor necrosis factor receptor-associated factors 2 and 3 to membrane microdomains during CD40 signaling. J Biol Chem 275, 15392-8 (2000)

74 P. O. Vidalain, O. Azocar, C. Servet-Delprat, C. Rabourdin-Combe, D. Gerlier & S. Manie: CD40 signaling in human dendritic cells is initiated within membrane rafts. Embo J 19, 3304-3313 (2000)

75 R. Khanna, L. Cooper, N. Kienzle, D. J. Moss, S. R. Burrows & K. K. Khanna: Engagement of CD40 antigen with soluble CD40 ligand up-regulates peptide transporter expression and restores endogenous processing function in Burkitt's lymphoma cells. J Immunol 159, 5782-5785 (1997)

76 N. Burdin, C. Van Kooten, L. Galibert, J. S. Abrams, J. Wijdenes, J. Banchereau & F. Rousset: Endogenous IL-6 and IL-10 contribute to the differentiation of CD40-activated human B lymphocytes. J Immunol 154, 2533-44 (1995)

77 N. Burdin, L. Galibert, P. Garrone, I. Durand, J. Banchereau & F. Rousset: Inability to produce IL-6 is a functional feature of human germinal center B cells. J Immunol 156, 4107-4113 (1996)

78 B. Dubois, B. Vanbervliet, J. Fayette, C. Massacrier, C. Van Kooten, F. Briere, J. Banchereau & C. Caux: Dendritic cells enhance growth and differentiation of CD40-activated B lymphocytes. J. Exp. Med. 185, 941-951 (1997)

79 J. Fayette, B. Dubois, S. Vandenabeele, J. M. Bridon, B. Vanbervliet, I. Durand, J. Banchereau, C. Caux & F. Briere: Human dendritic cells skew isotype switching of CD40-activated naive B cells towards IgA1 and IgA2. J Exp Med 185, 1909-1918 (1997)

80 P. Garrone, E. M. Neidhardt, E. Garcia, L. Galibert, C. van Kooten & J. Banchereau: Fas ligation induces apoptosis of CD40-activated human B lymphocytes. J. Exp. Med. 182, 1265-1273 (1995)

81 E. J. Schattner, K. B. Elkon, D. H. Yoo, J. Tumang, P. H. Krammer, M. K. Crow & S. M. Friedman: CD40 ligation induces Apo-1/Fas expression on human B lymphocytes and facilitates apoptosis through the Apo-1/Fas pathway. J. Exp. Med. 182, 1557-1565 (1995)

82 S. M. Lens, K. Tesselaar, B. F. den Drijver, M. H. van Oers & R. A. van Lier: A dual role for both CD40-ligand and TNF-alpha in controlling human B cell death. J. Immunol. 156, 507-514 (1996)

83 T. L. Rothstein, J. K. M. Wang, D. J. Panka, L. C. Foote, Z. Wang, B. Stanger, H. Cui, S. T. Ju & A. Marshak-Rothstein: Protection against Fas-dependent Th1-mediated apoptosis by antigen receptor engagement in B cells. Nature 374, 163-165 (1995)

84 L. Galibert, N. Burdin, C. Barthelemy, G. Meffre, I. Durand, E. Garcia, P. Garrone, F. Rousset, J. Banchereau & Y. J. Liu: Negative selection of human germinal center B cells by prolonged BCR cross-linking. J Exp Med 183, 2075-2085 (1996)

85 C. Van Kooten, L. Galibert, B. K. Seon, P. Garrone, Y. L. Liu & J. Banchereau: Cross-linking of antigen receptor via Ig-beta (B29-CD79b) caninduce both positive and negative signals in CD40-activated human B cells. Clin. Exp. Immunol. 110, 509-515 (1997)

86 J. C. Rathmell, S. E. Townsend, J. C. Xu, R. A. Flavell & C. C. Goodnow: Expansion or elimination of B cells in vivo: dual roles for CD40 and Fas (CD95)-ligands modulated by the B cell antigen receptor. Cell 87, 319-329 (1996)

87 L. Galibert, N. Burdin, B. de Saint-Vis, P. Garrone, C. Van Kooten, J. Banchereau & F. Rousset: CD40 and B cell antigen receptor dual triggering of resting B lymphocytes turns on a partial germinal center phenotype. J Exp Med 183, 77-85 (1996)

88 K. Wheeler & J. Gordon: Co-ligation of surface IgM and CD40 on naive B lymphocytes generates a blast population with an ambiguous extrafollicular/germinal centre cell phenotype. Int Immunol 8, 815-828 (1996)

89 C. Arpin, J. Dechanet, C. Van Kooten, P. Merville, G. Grouard, F. Briere, J. Banchereau & Y. J. Liu: Generation of memory B cells and plasma cells in vitro. Science 268, 720-722 (1995)

90 A. Silvy, C. Lagresle, C. Bella & T. Defrance: The differentiation of human memory B cells into specific antibody-secreting cells is CD40 independent. Eur. J. Immunol. 26, 517-524 (1996)

91 P. Merville, J. Dechanet, A. Desmouliere, I. Durand, O. de Bouteiller, P. Garrone, J. Banchereau & Y. J. Liu: Bcl-2+ tonsillar plasma cells are rescued from apoptosis by bone marrow fibroblasts. J. Exp. Med. 183, 227-236 (1996)

92 W. J. Murphy, S. Funakoshi, M. Beckwith, S. E. Rushing, D. K. Conley, R. J. Armitage, W. C. Fanslow, H. C. Rager, D. D. Taub, F. W. Ruscetti & D. L. Longo: Antibodies to CD40 prevent Epstein-Barr virus-mediated human B cell lymphomagenesis in severe combined immune deficient mice given human peripheral blood lymphocytes. Blood 86, 1946-1953 (1995)

93 R. T. Costello, J. A. Gastaut & D. Olive: What is the real role of CD40 in cancer immunotherapy? Immunol Today 20, 488-93 (1999)

94 R. D. Stout & J. Suttles: The many roles of CD40 in cell-mediated inflammatory responses. Immunol. Today 17, 487-492 (1996)

95 I. S. Grewal & R. A. Flavell: A central role of CD40 ligand in the regulation of CD4+ T cell responses. Immunol. Today 17, 410-414 (1996)

96 J. Banchereau & R. M. Steinman: Dendritic cells and the control of immunity. Nature 392, 245-252 (1998)

97 P. J. Lane & T. Brocker: Developmental regulation of dendritic cell function. Curr Opin Immunol 11, 308-13 (1999)

98 J. Banchereau, F. Briere, C. Caux, J. Davoust, S. Lebecque, Y. J. Liu, B. Pulendran & K. Palucka: Immunobiology of dendritic cells. Annu. Rev. Immunol. 18, 767-811 (2000)

99 S. Hess & H. Engelmann: A novel function of CD40: induction of cell death in transformed cells. J Exp Med 183, 159-167 (1996)

100 L. S. Young, A. G. Eliopoulos, N. J. Gallagher & C. W. Dawson: CD40 and epithelial cells: across the great divide [In Process Citation]. Immunol Today 19, 502-506 (1998)

101 A. Hirano, D. L. Longo, D. D. Taub, D. K. Ferris, L. S. Young, A. G. Eliopoulos, A. Agathanggelou, N. Cullen, J. Macartney, W. C. Fanslow & W. J. Murphy: Inhibition of human breast carcinoma growth by a soluble recombinant human CD40 ligand. Blood 93, 2999-3007 (1999)

102 R. A. Kroczek, D. Graf, D. Brugnoni, S. Giliani, U. Korthuer, A. Ugazio, G. Senger, H. W. Mages, A. Villa & L. D. Notarangelo: Defective expression of CD40 ligand on T cells causes "X-linked immunodeficiency with hyper-IgM (HIGM1)". Immunol Rev 138, 39-59 (1994)

103 L. D. Notarangelo & M. C. Peitch: CD40Lbase: a database of CD40L gene mutations causing X-linked hyper-IgM syndrome. Immunol. Today 17, 511-516 (1996)

104 L. D. Notarangelo & A. R. Hayward: X-linked immunodeficiency with hyper-IgM (XHIM). Clin Exp Immunol 120, 399-405 (2000)

105 D. P. Inwald, M. J. Peters, D. Walshe, A. Jones, E. G. Davies & N. J. Klein: Absence of platelet CD40L identifies patients with X-linked hyper IgM syndrome. Clin Exp Immunol 120, 499-502 (2000)

106 A. Durandy, C. Hivroz, F. Mazerolles, C. Schiff, F. Bernard, E. Jouanguy, P. Revy, J. P. DiSanto, J. F. Gauchat, J. Y. Bonnefoy, J. L. Casanova & A. Fischer: Abnormal CD40-mediated activation pathway in B lymphocytes from patients with hyper-IgM syndrome and normal CD40 ligand expression. J Immunol 158, 2576-2584 (1997)

107 I. S. Grewal, J. Xu & R. A. Flavell: Impairment of antigen-specific T-cell priming in mice lacking CD40 ligand. Nature 378, 617-620 (1995)

108 M. Kamanaka, P. Yu, T. Yasui, K. Yoshida, T. Kawabe, T. Horii, T. Kishimoto & H. Kikutani: Protective role of CD40 in Leishmania major infection at two distinct phases of cell-mediated immunity. Immunity 4, 275-281 (1996)

109 K. A. Campbell, P. J. Ovendale, M. K. Kennedy, W. C. Fanslow, S. G. Reed & C. R. Maliszewski: CD40 ligand is required for protective cell-mediated immunity to Leishmania major. Immunity 4, 283-289 (1996)

110 L. Soong, J. C. Xu, I. S. Grewal, P. Kima, J. Sun, B. Longley, Jr., N. H. Ruddle, D. McMahon-Pratt & R. A. Flavell: Disruption of CD40-CD40 ligand interactions results in an enhanced susceptibility to Leishmania amazonensis infection. Immunity 4, 263-273 (1996)

111 P. Garside, E. Ingulli, R. R. Merica, J. G. Johnson, R. J. Noelle & M. K. Jenkins: Visualization of specific B and T lymphocyte interactions in the lymph node. Science 281, 96-99 (1998)

112 B. R. Renshaw, W. r. Fanslow, R. J. Armitage, K. A. Campbell, D. Liggitt, B. Wright, B. L. Davison & C. R. Maliszewski: Humoral immune responses in CD40 ligand-deficient mice. J Exp Med 180, 1889-1900 (1994)

113 J. Xu, T. M. Foy, J. D. Laman, E. A. Elliott, J. J. Dunn, T. J. Waldschmidt, J. Elsemore, R. J. Noelle & R. A. Flavell: Mice deficient for the CD40 ligand. Immunity 1, 423-431 (1994)

114 T. Kawabe, T. Naka, K. Yoshida, T. Tanaka, H. Fujiwara, S. Suematsu, N. Yoshida, T. Kishimoto & H. Kikutani: The immune responses in CD40-deficient mice: impaired immunoglobulin class switching and germinal center formation. Immunity 1, 167-178 (1994)

115 P. Dullforce, D. C. Sutton & A. W. Heath: Enhancement of T cell-independent immune responses in vivo by CD40 antibodies. Nat Med 4, 88-91 (1998)

116 S. Gurunathan, K. R. Irvine, C. Y. Wu, J. I. Cohen, E. Thomas, C. Prussin, N. P. Restifo & R. A. Seder: CD40 ligand/trimer DNA enhances both humoral and cellular immune responses and induces protective immunity to infectious and tumor challenge [In Process Citation]. J Immunol 161, 4563-4571 (1998)

117 R. D. Stout, J. Suttles, J. Xu, I. S. Grewal & R. A. Flavell: Impaired T cell-mediated macrophage activation in CD40 ligand-deficient mice. J Immunol 156, 8-11 (1996)

118 M. F. Mackey, R. J. Barth, Jr. & R. J. Noelle: The role of CD40/CD154 interactions in the priming, differentiation, and effector function of helper and cytotoxic T cells. J Leukoc Biol 63, 418-428 (1998)

119 W. R. Heath & F. R. Carbone: Cytotoxic T lymphocyte activation by cross-priming. Curr Opin Immunol 11, 314-8 (1999)

120 J. E. Buhlmann, T. M. Foy, A. Aruffo, K. M. Crassi, J. A. Ledbetter, W. R. Green, J. C. Xu, L. D. Shultz, D. Roopesian, R. A. Flavell, L. Fast, R. J. Noelle & F. H. Durie: In the absence of a CD40 signal, B cells are tolerogenic. Immunity 2, 645-653 (1995)

121 A. Oxenius, K. A. Campbell, C. R. Maliszewski, T. Kishimoto, H. Kikutani, H. Hengartner, R. M. Zinkernagel & M. F. Bachmann: CD40-CD40 ligand interactions are critical in T-B cooperation but not for other anti-viral CD4+ T cell functions. J Exp Med 183, 2209-2218 (1996)

122 P. Borrow, A. Tishon, S. Lee, J. Xu, I. S. Grewal, M. B. Oldstone & R. A. Flavell: CD40L-deficient mice show deficits in antiviral immunity and have an impaired memory CD8+ CTL response. J Exp Med 183, 2129-2142 (1996)

123 A. R. Thomsen, A. Nansen, J. P. Christensen, S. O. Andreasen & O. Marker: CD40 ligand is pivotal to efficient control of virus replication in mice infected with lymphocytic choriomeningitis virus. J Immunol 161, 4583-4590 (1998)

124 S. R. Bennett, F. R. Carbone, F. Karamalis, R. A. Flavell, J. F. Miller & W. R. Heath: Help for cytotoxic-T-cell responses is mediated by CD40 signalling. Nature 393, 478-480 (1998)

125 J. P. Ridge, F. Di Rosa & P. Matzinger: A conditioned dendritic cell can be a temporal bridge between a CD4+ T-helper and a T-killer cell. Nature 393, 474-478 (1998)

126 S. P. Schoenberger, R. E. Toes, E. I. van der Voort, R. Offringa & C. J. Melief: T-cell help for cytotoxic T lymphocytes is mediated by CD40-CD40L interactions. Nature 393, 480-483 (1998)

127 Z. Lu, L. Yuan, X. Zhou, E. Sotomayor, H. I. Levitsky & D. M. Pardoll: CD40-independent pathways of T cell help for priming of CD8(+) cytotoxic T lymphocytes. J Exp Med 191, 541-50 (2000)

128 R. R. French, H. T. Chan, A. L. Tutt & M. J. Glennie: CD40 antibody evokes a cytotoxic T-cell response that eradicates lymphoma and bypasses T-cell help. Nat Med 5, 548-553 (1999)

129 L. Diehl, A. T. den Boer, S. P. Schoenberger, E. I. van der Voort, T. N. Schumacher, C. J. Melief, R. Offringa & R. E. Toes: CD40 activation in vivo overcomes peptide-induced peripheral cytotoxic T-lymphocyte tolerance and augments anti-tumor vaccine efficacy. Nat Med 5, 774-779 (1999)

130 E. M. Sotomayor, I. Borrello, E. Tubb, F. M. Rattis, H. Bien, Z. Lu, S. Fein, S. Schoenberger & H. I. Levitsky: Conversion of tumor-specific CD4+ T-cell tolerance to T-cell priming through in vivo ligation of CD40. Nat Med 5, 780-787 (1999)

131 S. K. Datta & S. L. Kalled: CD40-CD40 ligand interaction in autoimmune disease. Arthritis Rheum 40, 1735-1745 (1997)

132 A. Desai-Mehta, L. Lu, R. Ramsey-Goldman & S. K. Datta: Hyperexpression of CD40 ligand by B and T cells in human lupus and its role in pathogenic autoantibody production. J Clin Invest 97, 2063-2073 (1996)

133 M. Koshy, D. Berger & M. K. Crow: Increased expression of CD40 ligand on systemic lupus erythematosus lymphocytes. J Clin Invest 98, 826-837 (1996)

134 M. J. Yellin, V. D'Agati, G. Parkinson, A. S. Y. Han, A. Szema, D. Baum, D. Estes, M. Szabolzs & L. Chess: Immunohistologic analysis of renal CD40 and CD40L expression in lupus nephritis and other glomerulonephritides. Arthritis & Rheumatism 40, 124-134 (1997)

135 K. Kato, E. Santana-Sahagun, L. Z. Rassenti, M. H. Weisman, N. Tamura, S. Kobayashi, H. Hashimoto & T. J. Kipps: The soluble CD40 ligand sCD154 in systemic lupus erythematosus. J Clin Invest 104, 947-55 (1999)

136 K. Gerritse, J. D. Laman, R. J. Noelle, A. Aruffo, J. A. Ledbetter, W. J. A. Boersma & E. Claassen: CD40-CD40 ligand interactions in experimental allergic encephalomyelitis and multiple sclerosis. Proc Natl Acad Sci USA 93, 2499-2504 (1996)

137 S. L. Kalled, A. H. Cutler, S. K. Datta & D. W. Thomas: Anti-CD40 ligand antibody treatment of SNF1 mice with established nephritis: preservation of kidney function. J. Immunol. 160, 2158-2165 (1998)

138 L. M. Howard, A. J. Miga, C. L. Vanderlugt, M. C. Dal Canto, J. D. Laman, R. J. Noelle & S. D. Miller: Mechanisms of immunotherapeutic intervention by anti-CD40L (CD154) antibody in an animal model of multiple sclerosis. J. Clin. Invest. 103, 281-290 (1999)

139 C. P. Larsen & T. C. Pearson: The CD40 pathway in allograft rejection, acceptance, and tolerance. Curr. Opin. Immunol. 9, 641-647 (1997)

140 M. H. Sayegh & L. A. Turka: The role of T-cell costimulatory activation pathways in transplant rejection. N. Engl. J. Med. 338, 1813-1821 (1998)

141 H. Gudmundsdottir & L. A. Turka: T cell costimulatory blockade: new therapies for transplant rejection. J. Am. Soc. Nephrol. 10, 1356-1365 (1999)

142 C. Van Kooten: Blockade of costimulatory pathways of T cell activation: the solution to acute and chronic rejection? Curr. Opin. Nephrol. Hypertens. 8, 675-680 (1999)

143 C. P. Larsen, E. T. Elwood, D. Z. Alexander, S. C. Ritchie, R. Hendrix, C. Tucker-Burden, H. R. Cho, A. Aruffo, D. Hollenbaugh, P. S. Linsley, K. J. Winn & T. C. Pearson: Long-term acceptance of skin and cardiac allografts after blocking CD40 and CD28 pathways. Nature 381, 434-438 (1996)

144 J. Trambley, A. W. Bingaman, A. Lin, E. T. Elwood, S. Y. Waitze, J. Ha, M. M. Durham, M. Corbascio, S. R. Cowan, T. C. Pearson & C. P. Larsen: Asialo GM1(+) CD8(+) T cells play a critical role in costimulation blockade-resistant allograft rejection. J Clin Invest 104, 1715-22 (1999)

145 N. D. Jones, A. Van Maurik, M. Hara, B. M. Spriewald, O. Witzke, P. J. Morris & K. J. Wood: CD40-CD40 ligand-independent activation of CD8+ T cells can trigger allograft rejection. J Immunol 165, 1111-8 (2000)

146 K. Kishimoto, V. M. Dong, S. Issazadeh, E. V. Fedoseyeva, A. M. Waaga, A. Yamada, M. Sho, G. Benichou, H. Auchincloss, Jr., M. J. Grusby, S. J. Khoury & M. H. Sayegh: The role of CD154-CD40 versus CD28-B7 costimulatory pathways in regulating allogeneic Th1 and Th2 responses in vivo. J Clin Invest 106, 63-72 (2000)

147 H. Sun, V. Subbotin, C. Chen, A. Aitouche, L. A. Valdivia, M. H. Sayegh, P. S. Linsley, J. J. Fung, T. E. Starzl & A. S. Rao: Prevention of chronic rejection in mouse aortic allografts by combined traetment with CTLA4-Ig and anti-CD40 ligand monoclonal antibody. Transplantation 64, 1838-1843 (1997)

148 R. M. Reul, J. C. Fang, M. D. Denton, C. Geehan, C. Long, R. N. Mitchell, P. Ganz & D. M. Briscoe: CD40 and CD40 ligand (CD154) are coexpressed on microvessels in vivo in human cardiac allograft rejection. Transplantation 64, 1765-1774 (1997)

149 X. X. Zheng, A. D. Schachter, L. Vasconcellos, J. Strehlau, Y. Tian, M. Shapiro, H. W. & T. B. Strom: Increased CD40 ligand gene expression during human renal and murine islet allograft rejection. Transplantation 65, 1512-1515 (1998)

150 A. D. Kirk, D. M. Harlan, N. N. Armstrong, T. A. Davis, Y. Dong, G. S. Gray, X. Hong, D. Thomas, J. H. Fechner & S. J. Knechtle: CTLA4-Ig and anti-CD40 ligand prevent renal allograft rejection in primates. Proc. Natl. Acad. Sci. USA 94, 8789-8794 (1997)

151 A. D. Kirk, L. C. Burkly, D. S. Batty, R. E. Baumgartner, J. D. Berning, K. Buchanan, J. H. Fechner, Jr., R. L. Germond, R. L. Kampen, N. B. Patterson, S. J. Swanson, D. K. Tadaki, C. N. TenHoor, L. White, S. J. Knechtle & D. M. Harlan: Treatment with humanized monoclonal antibody against CD154 prevents acute renal allograft rejection in nonhuman primates. Nat. Med. 5, 686-693 (1999)

152 R. N. r. Pierson, A. C. Chang, M. G. Blum, K. S. Blair, M. A. Scott, J. B. Atkinson, B. J. Collins, J. P. Zhang, D. W. Thomas, L. C. Burkly & G. G. Miller: Prolongation of primate cardiac allograft survival by treatment with ANTI-CD40 ligand (CD154) antibody. Transplantation 68, 1800-5 (1999)

153 T. Kawai, D. Andrews, R. B. Colvin, D. H. Sachs & A. Benedict Cosimi: Thromboembolic complications after treatment with monoclonal antibody against CD40 ligand. Nat. Med. 6, 114 (2000)

154 J. D. Laman, B. J. de Smet, A. Schoneveld & M. van Meurs: CD40-CD40L interactions in atherosclerosis. Immunol Today 18, 272-277 (1997)

155 R. P. Phipps: Atherosclerosis: the emerging role of inflammation and the CD40-CD40 ligand system. Proc Natl Acad Sci U S A 97, 6930-2 (2000)

156 J. A. Wiley, R. Geha & A. G. Harmsen: Exogenous CD40 ligand induces a pulmonary inflammation response. J Immunol 158, 2932-8 (1997)

157 X. Lei, Y. Ohkawara, M. R. Stampfli, C. Mastruzzo, R. A. Marr, D. Snider & Z. Xing: Disruption of antigen-induced inflammatory responses in CD40 ligand knockout mice. J. Clin. Invest. 101, 1342-1353 (1998)

158 A. Adawi, Y. Zhang, R. Baggs, J. Finkelstein & R. P. Phipps: Disruption of the CD40-CD40 ligand system prevents an oxygen-induced respiratory distress syndrom. Am. J. Pathol. 152, 651-657 (1998)

159 J. A. Wiley & A. G. Harmsen: Bone marrow-derived cells are required for the induction of a pulmonary inflammatory response mediated by CD40 ligation. Am J Pathol 154, 919-26 (1999)

160 U. Schonbeck, F. Mach, J. Y. Bonnefoy, H. Loppnow, H. D. Flad & P. Libby: Ligation of CD40 activates Interleukin 1-converting enzyme (caspase-1) activity in vascular smooth muscle and endothelial cells and promotes elaboration of active Interleukin 1b. J. Biol. Chem. 272, 19569-19574 (1997)

161 U. Schonbeck, F. Mach, G. K. Sukhova, C. Murphy, J. Y. Bonnefoy, R. P. Fabunmi & P. Libby: Regulation of matrix metalloproteinase expression in human vascular smooth muscle cells by T lymphocytes: a role for CD40 signaling in plaque rupture? Circ Res 81, 448-54 (1997)

162 U. Schonbeck, F. Mach, G. K. Sukhova, E. Atkinson, E. Levesque, M. Herman, P. Graber, P. Basset & P. Libby: Expression of stromelysin-3 in atherosclerotic lesions: regulation via CD40-CD40 ligand signaling In vitro and In vivo. J Exp Med 189, 843-853 (1999)

163 F. Mach, U. Schonbeck, R. P. Fabunmi, C. Murphy, E. Atkinson, J. Y. Bonnefoy, P. Graber & P. Libby: T lymphocytes induce endothelial cell matrix metalloproteinase expression by a CD40L-dependent mechanism: implications for tubule formation. Am. J. Pathol. 154, 229-238 (1999)

164 F. Mach, U. Schonbeck, G. K. Sukhova, E. Atkinson & P. Libby: Reduction of atherosclerosis in mice by inhibition of CD40 signalling. Nature 394, 200-203 (1998)

165 E. Lutgens, K. B. Cleutjens, S. Heeneman, V. E. Koteliansky, L. C. Burkly & M. J. Daemen: Both early and delayed anti-CD40L antibody treatment induces a stable plaque phenotype. Proc Natl Acad Sci U S A 97, 7464-9 (2000)

166 U. Schonbeck, G. K. Sukhova, K. Shimizu, F. Mach & P. Libby: Inhibition of CD40 signaling limits evolution of established atherosclerosis in mice. Proc Natl Acad Sci U S A 97, 7458-63 (2000)

167 E. Lutgens, L. Gorelik, M. J. Daemen, E. D. de Muinck, I. S. Grewal, V. E. Koteliansky & R. A. Flavell: Requirement for CD154 in the progression of atherosclerosis. Nat Med 5, 1313-6 (1999)

168 W. W. Hancock, R. Buelow, M. H. Sayegh & L. A. Turka: Antibody-induced transplant arteriosclerosis is prevented by graft expression of anti-oxidant and anti-apoptotic genes. Nat Med 4, 1392-6 (1998)