Review of the Amphibian Immune Response to Chytridiomycosis, and Future Directions

Grogan, Laura F., Robert, Jacques, Berger, Lee, Skerratt, Lee F., Scheele, Benjamin C., Castley, J. Guy, Newell, David A., and McCallum, Hamish I. (2018) Review of the Amphibian Immune Response to Chytridiomycosis, and Future Directions. Frontiers in Immunology, 9. 2536.

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Abstract

The fungal skin disease, chytridiomycosis (caused by Batrachochytrium dendrobatidis and B. salamandrivorans), has caused amphibian declines and extinctions globally since its emergence. Characterizing the host immune response to chytridiomycosis has been a focus of study with the aim of disease mitigation. However, many aspects of the innate and adaptive arms of this response are still poorly understood, likely due to the wide range of species' responses to infection. In this paper we provide an overview of expected immunological responses (with inference based on amphibian and mammalian immunology), together with a synthesis of current knowledge about these responses for the amphibian-chytridiomycosis system. We structure our review around four key immune stages: (1) the naive immunocompetent state, (2) immune defenses that are always present (constitutive defenses), (3) mechanisms for recognition of a pathogen threat and innate immune defenses, and (4) adaptive immune responses. We also evaluate the current hot topics of immunosuppression and immunopathology in chytridiomycosis, and discuss their respective roles in pathogenesis. Our synthesis reveals that susceptibility to chytridiomycosis is likely to be multifactorial. Susceptible amphibians appear to have ineffective constitutive and innate defenses, and a late-stage response characterized by immunopathology and Bd-induced suppression of lymphocyte responses. Overall, we identify substantial gaps in current knowledge, particularly concerning the entire innate immune response (mechanisms of initial pathogen detection and possible immunoevasion by Bd, degree of activation and efficacy of the innate immune response, the unexpected absence of innate leukocyte infiltration, and the cause and role of late-stage immunopathology in pathogenesis). There are also gaps concerning most of the adaptive immune system (the relative importance of B and T cell responses for pathogen clearance, the capacity and extent of immunological memory, and specific mechanisms of pathogen-induced immunosuppression). Improving our capacity for amphibian immunological research will require selection of an appropriate Bd-susceptible model species, the development of taxon-specific affinity reagents and cell lines for functional assays, and the application of a suite of conventional and emerging immunological methods. Despite current knowledge gaps, immunological research remains a promising avenue for amphibian conservation management.

Item ID: 56272
Item Type: Article (Research - C1)
ISSN: 1664-3224
Keywords: chytridiomycosis, immune, innate, adaptive, frogs, declines, amphibian, Batrachochytrium dendrobatidis
Copyright Information: Copyright © 2018 Grogan, Robert, Berger, Skerratt, Scheele, Castley, Newell and McCallum. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Funders: Australian Research Council (ARC), National Institute of Allergy and Infectious Diseases (NIAID), National Science Foundation (NSF)
Projects and Grants: ARC DP180101415, ARC LP110200240, NIH/NIAID, R24-AI-059830, NSF IOS-1456213
Date Deposited: 28 Nov 2018 07:57
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060804 Animal Immunology @ 100%
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