In vitro tests of natural allelic variation of innate immune genes (avian β‐defensins) reveal functional differences in microbial inhibition

Abstract

Allelic variation in immune genes might result from, and contribute to, host–pathogen evolution. Functional allelic variation in the innate immune system has received little attention. Here, we investigate whether naturally occurring allelic variation within the avian innate immune system (β‐defensins) is associated with variation in antimicrobial activity. We tested differences in in vitro antimicrobial properties of the synthesized products of two alleles of avian β‐defensin 7, both of which occur at high frequency in natural populations of the great tit (Parus major). Only one allele strongly inhibited the growth of the gram‐positive bacterium Staphylococcus aureus, but both alleles strongly inhibited growth of the gram‐negative bacterium Escherechia coli. Our data demonstrate functional allelic variation in natural defensin genes, and we discuss how differences in efficacy against microbial species might contribute to maintaining this variation.