[Frontiers in Bioscience 15, 25-34, January 1, 2010]

Beneficial effects of Bacteroides fragilis polysaccharides on the immune system

Erin B. Troy1,2, Dennis L. Kasper1,2

1Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA, 2Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115, USA

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Bacteroides fragilis
4. Correction of CD4+ T cell deficiencies in germ-free mice
5. Antigen Presentation of PSA
6. Establishing a Th1/Th2 balance
7. Innate immunity and PSA
8. Prevention of inflammatory disease
8.1. Repression of pro-inflammatory cytokines associated with the Th17 lineage
8.2. IL-10 is required for the PSA mediated anti-inflammatory response
9. Conclusion
10. Acknowledgements
11. References

1. ABSTRACT

Bacterial colonization of the intestine is critical for the normal function of the mammalian immune system. However, the specific molecules produced by commensal bacteria that contribute to the modulation of the host immune system are largely uncharacterized. Polysaccharide A (PSA) produced by the ubiquitous human commensal, Bacteroides fragilis is a model symbiosis factor. PSA is capable of activating T cell-dependent immune responses that can affect both the development and homeostasis of the host immune system. Colonization of previously germ-free mice with B. fragilis alone is sufficient to correct the splenic Th1/Th2 imbalance found in germ-free mice. In addition, PSA can provide protection in animal models of colitis through repression of pro-inflammatory cytokines associated with the Th17 lineage. This review provides an overview of the immunologic properties of PSA including the mechanisms of immune system activation and the resulting immunomodulatory effects.