Fighting a losing battle: Vigorous immune response countered by pathogen suppression of host defenses in the chytridiomycosis-susceptible frog Atelopus zeteki

Ellison, Amy, Savage, A. E., DiRenzo, G. V., Langhammer, P., Lips, K. R. and Zamudio, K. R. 2014. Fighting a losing battle: Vigorous immune response countered by pathogen suppression of host defenses in the chytridiomycosis-susceptible frog Atelopus zeteki. G3: Genes | Genomes | Genetics 4 (7) , pp. 1275-1289. 10.1534/g3.114.010744

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Abstract

The emergence of the disease chytridiomycosis caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd) has been implicated in dramatic global amphibian declines. Although many species have undergone catastrophic declines and/or extinctions, others appear to be unaffected or persist at reduced frequencies after Bd outbreaks. The reasons behind this variance in disease outcomes are poorly understood: differences in host immune responses have been proposed, yet previous studies suggest a lack of robust immune responses to Bd in susceptible species. Here, we sequenced transcriptomes from clutchmates of a highly susceptible amphibian, Atelopus zeteki, with different infection histories. We found significant changes in expression of numerous genes involved in innate and inflammatory responses in infected frogs despite high susceptibility to chytridiomycosis. We show evidence of acquired immune responses generated against Bd, including increased expression of immunoglobulins and major histocompatibility complex genes. In addition, fungal-killing genes had significantly greater expression in frogs previously exposed to Bd compared with Bd-naïve frogs, including chitinase and serine-type proteases. However, our results appear to confirm recent in vitro evidence of immune suppression by Bd, demonstrated by decreased expression of lymphocyte genes in the spleen of infected compared with control frogs. We propose susceptibility to chytridiomycosis is not due to lack of Bd-specific immune responses but instead is caused by failure of those responses to be effective. Ineffective immune pathway activation and timing of antibody production are discussed as potential mechanisms. However, in light of our findings,suppression of key immune responses by Bd is likely an important factor in the lethality of this fungus.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Biosciences
Subjects:	Q Science > Q Science (General)
Uncontrolled Keywords:	Batrachochytrium dendrobatidis; Immunogenomics; Atelopus zeteki; Acquired immunity; Immunosuppression; Genetics of immunity; Innate immunity; Complex genetics; Tolerance; Complex immunity; Infection; Resistance
Publisher:	Genetics Society of America
ISSN:	2160-1836
Date of First Compliant Deposit:	29 November 2016
Date of Acceptance:	15 May 2014
Last Modified:	06 May 2023 07:36
URI:	https://orca.cardiff.ac.uk/id/eprint/95747

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