Data from: Sustained immune activation is associated with susceptibility to the amphibian chytrid fungus

The disease chytridiomycosis caused by the fungus Bd has devastated
amphibian populations worldwide. Functional genomic contributions to host
susceptibility remain enigmatic and vary between species and populations.
We conducted experimental Bd infections in Rana yavapaiensis, a species
with intraspecific variation in chytridiomycosis susceptibility, to assess
the skin and spleen transcriptomic response to infection over time. We
predicted that increased immune gene expression would be associated with a
positive disease outcome, but we instead found that surviving frogs had
significantly reduced immune gene expression compared to susceptible frogs
and to uninfected controls. MHC class II gene expression was also
significantly higher in susceptible frogs compared to surviving frogs.
Furthermore, susceptible frogs expressed a significantly larger number of
distinct class II alleles, demonstrating a negative correlation between
class II expression, functional diversity, and survival. Expression of
the MHC class II locus previously associated with Bd disease outcomes was
a significant predictor of Bd infection intensity at early infection
stages but not at late infection stages, suggesting initial MHC-linked
immune processes are important for ultimate disease outcomes. We infer
through disease association and phylogenetic analysis that certain MHC
variants are linked to the immune expression that was negatively
associated with survival, and we hypothesize that frogs that did not
express these alleles could better survive infections. Our study finds
that MHC expression at early and late infection stages predicts Bd
infection intensity, and suggests that generating a sustained immune
response against Bd may be counterproductive for surviving
chytridiomycosis in this partially susceptible species.