Heterozygote advantage at MHC DRB may influence response to infectious disease epizootics

The effect of MHC polymorphism on individual fitness variation in the wild remains equivocal; however, much evidence suggests that heterozygote advantage is a major determinant. To understand the contribution of MHC polymorphism to individual disease resistance or susceptibility in natural populations, we investigated two MHC class II B loci, DQB and DRB, in the New Zealand sea lion (NZSL, Phocarctos hookeri). The NZSL is a threatened species which is unusually susceptible to death by bacterial infection at an early age; it has suffered three bacterial induced epizootics resulting in high mortality levels of young pups since 1997. The MHC DQB and DRB haplotypes of dead NZSL pups with known cause of death (bacteria, enteritis or trauma) were sequenced and reconstructed, compared to pups that survived beyond 2 months of age, and distinct MHC DRB allele frequency and genotype differences were identified. Two findings were striking: (i) one DRB allele was present only in dead pups, and (ii)...

野外环境中，主要组织相容性复合体（MHC）多态性对个体适合度变异的影响仍存在争议；不过大量证据表明，杂合子优势是其主要决定因素。为阐明MHC多态性对自然种群中个体抗病性或易感性的贡献，我们对新西兰海狮（NZSL, *Phocarctos hookeri*）的两个MHC II类B基因座DQB与DRB展开了研究。新西兰海狮属于受威胁物种，其幼崽极容易在幼年时期因细菌感染死亡；自1997年以来，该种群已爆发三次由细菌引发的兽疫，造成幼崽死亡率居高不下。我们对已知死亡原因（细菌感染、肠炎或外伤）的新西兰海狮幼崽的MHC DQB与DRB单倍型进行了测序与重构，并将其与存活超过2个月的幼崽进行对比，最终鉴定出MHC DRB等位基因频率与基因型的显著差异。有两项发现尤为引人注目：（i）某一DRB等位基因仅在死亡幼崽中存在；（ii）……