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Abstract:
Vertebrate innate immunity is the first line of defense against an invading pathogen and has long been assumed to be
largely unspecific with respect to parasite/pathogen species. However, recent phenotypic evidence suggests that
immunogenetic variation, i.e. allelic variability in genes associated with the immune system, results in host-parasite
genotype-by-genotype interactions and thus specific innate immune responses. Immunogenetic variation is common in all
vertebrate taxa and this reflects an effective immunological function in complex environments. However, the underlying
variability in host gene expression patterns as response of innate immunity to within-species genetic diversity of
macroparasites in vertebrates is unknown. We hypothesized that intra-specific variation among parasite genotypes must be
reflected in host gene expression patterns. Here we used high-throughput RNA-sequencing to examine the effect of
parasite genotypes on gene expression patterns of a vertebrate host, the three-spined stickleback (Gasterosteus aculeatus).
By infecting naı¨ve fish with distinct trematode genotypes of the species Diplostomum pseudospathaceum we show that
gene activity of innate immunity in three-spined sticklebacks depended on the identity of an infecting macroparasite
genotype. In addition to a suite of genes indicative for a general response against the trematode we also find parasite-strain
specific gene expression, in particular in the complement system genes, despite similar infection rates of single clone
treatments. The observed discrepancy between infection rates and gene expression indicates the presence of alternative
pathways which execute similar functions. This suggests that the innate immune system can induce redundant responses
specific to parasite genotypes.
