[Frontiers in Bioscience S1, 68-91, June 1, 2009]

Immune defenses of Xenopus laevis against Batrachochytrium dendrobatidis

Louise A. Rollins-Smith1,2, Jeremy P. Ramsey1, Laura K. Reinert1, Douglas C. Woodhams1,3, Lauren J. Livo4, Cynthia Carey4

1Department of Microbiology and Immunology, 2Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232 USA, 3Department of Biology, James Madison University, Harrisonburg VA 22807 USA, 4Department of Integrative Physiology, University of Colorado, Boulder, CO 80309


1. Abstract
2. Introduction
3. Biology of B. dendrobatidis
4. Impact of B. dendrobatidis on populations of X. laevis (a resistant species) compared to a more sensitive species (Bufo boreas)
5. Overview of immune defenses in X. laevis.
5.1. Innate immune defenses in X. laevis
5.1.1. Complement and lysozyme
5.1.2. Phagocytic cells and natural killer cells
5.1.3. Toll-like receptors
5.1.4. Antimicrobial peptides (AMPs)
5.2. Adaptive immune defenses in X. laevis
5.2.1. Lymphoid organs
5.2.2. Major histocompatibility complex (MHC)
5.2.3. Antibody classes
5.2.4. Cytokines and chemokines
5.2.5. T cell-mediated immunity
6. Immune defenses against B. dendrobatidis
6.1. Antimicrobial peptide defenses against B. dendrobatidis
6.2. Antibody-mediated defenses against B. dendrobatidis
6.3. T cell-mediated defenses against B. dendrobatidis
7. Can amphibians be immunized to protect them from infection by B. dendrobatidis?
8. Future directions for research
8.1. Alternative immunization strategies
8.2. Focus on the skin
9. Perspective and concluding remarks
10. Acknowledgements
11. References


Amphibian populations are declining at an unprecedented rate worldwide. A number of declines have been linked to a pathogenic skin fungus, Batrachochytrium dendrobatidis. Although amphibians have robust immune defenses, many species seem to be very susceptible to infection by this fungus and to development of the lethal disease called chytridiomycosis. One species that is relatively resistant to B. dendrobatidis is Xenopus laevis. Because X. laevis has been used as a model for studies of immunity in amphibians and because it is relatively resistant to chytridiomycosis, it is a good model to examine immune defenses against B. dendrobatidis. Although much less is known about immune defenses in Bufo boreas, it serves as a second model species because it is very susceptible to B. dendrobatidis. Here we review what is known about innate antimicrobial peptide defenses in the skin and the development of immune responses following experimental immunization with heat-killed fungal cells. Development of an immunization protocol in X. laevis that induces effective defenses may suggest better strategies for protecting vulnerable species such as B. boreas.