Department of Biology, Lund University, Lund, SE-22362, Sweden.
Centre for Ecology and Conservation, University of Exeter, Penryn, TR10 9FE, United Kingdom.
Evolution. 2022 Sep;76(9):2067-2075. doi: 10.1111/evo.14590. Epub 2022 Aug 9.
MHC genes are extraordinarily polymorphic in most taxa. Host-pathogen coevolution driven by negative frequency-dependent selection (NFDS) is one of the main hypotheses for the maintenance of such immunogenetic variation. Here, we test a critical but rarely tested assumption of this hypothesis-that MHC alleles affect resistance/susceptibility to a pathogen in a strain-specific way, that is, there is a host genotype-by-pathogen genotype interaction. In a field study of bank voles naturally infected with the tick-transmitted bacterium Borrelia afzelii, we tested for MHC class II (DQB) genotype-by-B. afzelii strain interactions for infection prevalence between 10 DQB alleles and seven strains. One allele (DQB37) showed an interaction, such that voles carrying DQB37 had higher prevalence of two strains and lower prevalence of one strain than individuals without the allele. These findings were corroborated by analyses of strain composition of infections, which revealed an effect of DQB*37 in the form of lower β diversity among infections in voles carrying the allele. Taken together, these results provide rare support at the molecular genetic level for a key assumption of models of antagonistic coevolution through NFDS.
MHC 基因在大多数分类单元中具有极高的多态性。由负频率依赖性选择（NFDS）驱动的宿主-病原体协同进化是维持这种免疫遗传变异的主要假设之一。在这里，我们检验了该假设的一个关键但很少被检验的假设，即 MHC 等位基因以菌株特异性的方式影响对病原体的抗性/易感性，也就是说，存在宿主基因型-病原体基因型相互作用。在一项对自然感染 tick 传播细菌 Borrelia afzelii 的 bank voles 的实地研究中，我们针对 10 个 DQB 等位基因和 7 个菌株之间的感染流行率，测试了 MHC 类 II（DQB）基因型与 B. afzelii 菌株的相互作用。一个等位基因（DQB37）表现出相互作用，携带 DQB37 的田鼠对两种菌株的感染流行率较高，而对一种菌株的感染流行率较低，而没有该等位基因的个体则没有这种相互作用。这些发现通过对感染菌株组成的分析得到了证实，分析结果表明 DQB*37 以携带该等位基因的田鼠感染之间β多样性降低的形式发挥作用。综上所述，这些结果从分子遗传水平上为通过 NFDS 拮抗协同进化模型的一个关键假设提供了罕见的支持。
