Meeting Abstract

10.1  Wednesday, Jan. 4  Paralysis of amphibian lymphocyte functions by products of the chytrid fungus, Batrachocytrium dendrobatidis FITES, J. Scott; RAMSEY, Jeremy P.; ROLLINS-SMITH, Louise A.*; Vanderbilt University, Nashville TN; James Madison University, Harrisonburg VA; Vanderbilt University Med. Center, Nashville TN

Batrachochytrium dendrobatidis (Bd) is a pathogenic chytrid fungus that infects the keratinized epithelium of amphibian skin. Severe infections cause lethal chytridiomycosis in many amphibian species, contributing to the decline of amphibian populations globally. Although amphibians have several types of immune defenses against Bd, the role of adaptive immunity in resistance to chytridiomycosis is unclear. Our previous studies of the effects of X-irradiation in Xenopus laevis suggested that adaptive immunity is an important component of resistance to Bd infection in this species. However, lack of extensive lymphocyte infiltration in diseased skin suggests an impaired immune response. We show here that mature Bd sporangia, but not zoospores, have the capacity to inhibit the proliferation of mitogen-stimulated B and T lymphocytes from X. laevis and Rana pipiens. This inhibition occurs even when the cells are separated from the lymphocytes by a cell-impermeable membrane in a transwell assay. One mechanism of inhibition is by induction of lymphocyte apoptosis. Supernatant factors shed by the fungus also inhibit lymphocyte proliferation and induce apoptosis. The active factors are heat-resistant, acid-resistant, and protease-resistant suggesting that the inhibitory factors are not proteins. Because the factors are released by mature sporangia containing cell walls and not by zoospores that lack a cell wall, we hypothesize that the inhibitory factors are cell wall components. Support: NSF 0843207.