Major histocompatibility complex (MHC) genes are among the most polymorphic in the vertebrate genome. The high allele diversity is believed to be maintained primarily by sexual and pathogen-mediated balancing selection. The number of MHC loci also varies greatly across vertebrates, most notably across birds. MHC proteins play key roles in presenting antigens on the cell surface for recognition by T cells, with class I proteins specifically targeting intracellular pathogens. Here, we explore the hypothesis that MHC class I diversity (measured as loci number) coevolves with haemosporidian parasite burden of the host. Using data on 54 bird species, we demonstrate that high-MHC class I diversity is associated with significantly lower richness of Plasmodium, Haemoproteus as well as overall haemosporidian parasite lineages, the former thus indicating more efficient protection against intracellular pathogens. Nonetheless, the latter associations were only detected when MHC diversity was assessed using cloning and not 454 pyrosequencing-based studies, nor across all genotyping methods combined. Our results indicate that high-MHC class I diversity might play a key role in providing qualitative resistance against diverse haemosporidian parasites in birds, but further clarification is needed for the origin of contrasting results when using different genotyping methods for MHC loci quantification.

主要组织相容性复合体 (MHC) 基因是脊椎动物基因组中多态性最多的基因之一。高等位基因多样性被认为主要是通过性和病原体介导的平衡选择来维持的。MHC 基因座的数量在脊椎动物之间也有很大差异，尤其是在鸟类之间。MHC 蛋白在细胞表面呈递抗原以供 T 细胞识别方面发挥关键作用，I 类蛋白专门针对细胞内病原体。在这里，我们探讨了 MHC I 类多样性（以基因座数测量）与宿主的血孢子虫寄生虫负担共同进化的假设。使用 54 种鸟类的数据，我们证明高 MHC I 类多样性与疟原虫、嗜血杆菌属的丰富度显着降低有关以及整个血孢子寄生虫谱系，前者因此表明对细胞内病原体的更有效保护。尽管如此，仅当使用克隆评估 MHC 多样性时才检测到后一种关联，而不是 454 项基于焦磷酸测序的研究，也不是所有基因分型方法相结合。我们的结果表明，高 MHC I 类多样性可能在提供对鸟类多种血孢子虫寄生虫的定性抗性方面发挥关键作用，但当使用不同的基因分型方法进行 MHC 基因座量化时，需要进一步澄清对比结果的来源。