Amphibian mast cells serve as barriers to chytrid fungus infections.

Abstract

Global amphibian declines are compounded by deadly disease outbreaks caused by the chytrid fungus, <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>). Much has been learned about the roles of amphibian skin-produced antimicrobial components and microbiomes in controlling <i>Bd</i>, yet almost nothing is known about the roles of skin-resident immune cells in anti-<i>Bd</i> defenses. Mammalian mast cells reside within and serve as key immune sentinels in barrier tissues like skin. Accordingly, we investigated the roles of <i>Xenopus laevis</i> frog mast cells during <i>Bd</i> infections. Our findings indicate that enrichment of <i>X. laevis</i> skin mast cells confers anti-<i>Bd</i> protection and ameliorates the inflammation-associated skin damage caused by <i>Bd</i> infection. This includes a significant reduction in infiltration of <i>Bd</i>-infected skin by neutrophils, promoting mucin content within cutaneous mucus glands, and preventing <i>Bd</i>-mediated changes to skin microbiomes. Mammalian mast cells are known for their production of the pleiotropic interleukin-4 (IL4) cytokine and our findings suggest that the <i>X. laevis</i> IL4 plays a key role in manifesting the effects seen following cutaneous mast cell enrichment. Together, this work underscores the importance of amphibian skin-resident immune cells in anti-<i>Bd</i> defenses and illuminates a novel avenue for investigating amphibian host-chytrid pathogen interactions.