Major histocompatibility complex variation and the evolution of resistance to amphibian chytridiomycosis

• Published in: Immunogenetics (New York) Vol. 69; no. 8-9; pp. 529 - 536
• Main Authors: Fu, Minjie, Waldman, Bruce
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.08.2017; Springer Nature B.V
• Subjects: Adaptive systems; Alleles; Allergology; Amphibians; Amphibians - genetics; Amphibians - immunology; Animals; Batrachochytrium; Biomedical and Life Sciences; Biomedicine; Cell Biology; Chytridiomycosis; Chytridiomycota - immunology; Environmental conditions; Epizootics; Fungi; Gene Function; Genes, MHC Class I; Genes, MHC Class II; Genetic diversity; Genetic Predisposition to Disease; Genetic Variation; Human Genetics; Immune response; Immune system; Immunogenetics; Immunologic Memory; Immunology; Life history; Major histocompatibility complex; Mycoses - genetics; Mycoses - immunology; Mycoses - veterinary; Pathogens; Population decline; Reptiles & amphibians; Review; Toll-Like Receptors - physiology; Topical Collection on MHC/KIR in Health and Disease; Transcription; Virulence; Amphibian population declines; Major histocompatibility complex; Chytridiomycosis; Life-history trade-offs; Heterozygosity; Batrachochytrium dendrobatidis
• DOI: 10.1007/s00251-017-1008-4
• ISSN: 0093-7711; 1432-1211

Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has been implicated in population declines and species extinctions of amphibians around the world. Susceptibility to the disease varies both within and among species, most likely attributable to heritable immunogenetic variation. Analyses of transcriptional expression in hosts following their infection by Bd reveal complex responses. Species resistant to Bd generally show evidence of stronger innate and adaptive immune system responses. Major histocompatibility complex (MHC) class I and class II genes of some susceptible species are up-regulated following host infection by Bd, but resistant species show no comparable changes in transcriptional expression. Bd-resistant species share similar pocket conformations within the MHC-II antigen-binding groove. Among susceptible species, survivors of epizootics bear alleles encoding these conformations. Individuals with homozygous resistance alleles appear to benefit by enhanced resistance, especially in environmental conditions that promote pathogen virulence. Subjects that are repeatedly infected and subsequently cleared of Bd can develop an acquired immune response to the pathogen. Strong directional selection for MHC alleles that encode resistance to Bd may deplete genetic variation necessary to respond to other pathogens. Resistance to chytridiomycosis incurs life-history costs that require further study.