Susceptibility of amphibians to chytridiomycosis is associated with MHC class II conformation

Proc Biol Sci. 2015 Apr 22;282(1805):20143127. doi: 10.1098/rspb.2014.3127.

Abstract

The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) can cause precipitous population declines in its amphibian hosts. Responses of individuals to infection vary greatly with the capacity of their immune system to respond to the pathogen. We used a combination of comparative and experimental approaches to identify major histocompatibility complex class II (MHC-II) alleles encoding molecules that foster the survival of Bd-infected amphibians. We found that Bd-resistant amphibians across four continents share common amino acids in three binding pockets of the MHC-II antigen-binding groove. Moreover, strong signals of selection acting on these specific sites were evident among all species co-existing with the pathogen. In the laboratory, we experimentally inoculated Australian tree frogs with Bd to test how each binding pocket conformation influences disease resistance. Only the conformation of MHC-II pocket 9 of surviving subjects matched those of Bd-resistant species. This MHC-II conformation thus may determine amphibian resistance to Bd, although other MHC-II binding pockets also may contribute to resistance. Rescuing amphibian biodiversity will depend on our understanding of amphibian immune defence mechanisms against Bd. The identification of adaptive genetic markers for Bd resistance represents an important step forward towards that goal.

Keywords: conservation; disease resistance; emerging infectious disease; major histocompatibility complex; peptide-binding domain; pocket residue.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptive Immunity*
  • Amino Acid Sequence
  • Amphibian Proteins / chemistry
  • Amphibian Proteins / genetics*
  • Amphibian Proteins / metabolism
  • Animals
  • Anura* / genetics
  • Anura* / metabolism
  • Chytridiomycota / physiology*
  • Disease Resistance
  • Disease Susceptibility
  • Histocompatibility Antigens Class II / chemistry
  • Histocompatibility Antigens Class II / genetics*
  • Histocompatibility Antigens Class II / metabolism
  • Molecular Sequence Data
  • Mycoses / genetics
  • Mycoses / immunology
  • Mycoses / microbiology
  • Mycoses / veterinary*
  • Sequence Alignment / veterinary

Substances

  • Amphibian Proteins
  • Histocompatibility Antigens Class II

Associated data

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  • GENBANK/KJ679287
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