Smallbone Willow, Ellison Amy, Poulton Simon, van Oosterhout Cock, Cable Joanne
School of Biosciences, Cardiff University, Cardiff, UK.
School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, UK.
Mol Ecol. 2021 Feb;30(3):736-746. doi: 10.1111/mec.15763. Epub 2020 Dec 22.
The major histocompatibility complex (MHC) plays an important role in infectious disease resistance. The presence of certain MHC alleles and functionally similar groups of MHC alleles (i.e., supertypes) has been associated with resistance to particular parasite species. Farmed and domesticated fish stocks are often depleted in their MHC alleles and supertype diversity, possibly as a consequence of artificial selection for desirable traits, inbreeding (loss of heterozygosity), genetic drift (loss of allelic diversity) and/or reduced parasite biodiversity. Here we quantify the effects of depletion of MHC class II genotype and supertype variation on resistance to the parasite Gyrodactylus turnbulli in guppies (Poecilia reticulata). Compared to the descendants of wild-caught guppies, ornamental fish had a significantly reduced MHC variation (i.e., the numbers of MHC alleles and supertypes per individual, and per population). In addition, ornamental fish were significantly more susceptible to G. turnbulli infections, accumulating peak intensity 10 times higher than that of their wildtype counterparts. Four out of 13 supertypes were associated with a significantly reduced parasite load, and the presence of some supertypes had a dramatic effect on the intensity of infection. Remarkably, the ornamental and wildtype fish differed in the supertypes that were associated with parasite resistance. Analysis with a genetic algorithm showed that resistance-conferring supertypes of the wildtype and ornamental fish shared two unique amino acids in the peptide-binding region of the MHC that were not found in any other alleles. These data show that the supertype demarcation captures some, but not all, of the variation in the immune function of the alleles. This study highlights the importance of managing functional MHC diversity in livestock, and suggests there might be some immunological redundancy among MHC supertypes.
主要组织相容性复合体（MHC）在抗感染疾病中发挥着重要作用。某些MHC等位基因以及功能相似的MHC等位基因组（即超型）的存在与对特定寄生虫物种的抗性相关。养殖和驯化的鱼类种群的MHC等位基因和超型多样性往往会减少，这可能是人工选择优良性状、近亲繁殖（杂合性丧失）、遗传漂变（等位基因多样性丧失）和/或寄生虫生物多样性降低的结果。在此，我们量化了MHC II类基因型和超型变异的减少对孔雀鱼（孔雀鱼）抵抗寄生虫旋毛虫的影响。与野生捕捞孔雀鱼的后代相比，观赏鱼的MHC变异显著减少（即每个个体和每个种群的MHC等位基因和超型数量）。此外，观赏鱼对旋毛虫感染的易感性显著更高，累积峰值强度比野生型同类高出10倍。13种超型中有4种与寄生虫负荷显著降低相关，某些超型的存在对感染强度有显著影响。值得注意的是，观赏鱼和野生型鱼在与寄生虫抗性相关的超型方面存在差异。遗传算法分析表明，野生型和观赏鱼的抗性超型在MHC的肽结合区域共享两个独特的氨基酸，这在任何其他等位基因中都未发现。这些数据表明，超型划分捕获了等位基因免疫功能变异的一部分，但不是全部。这项研究强调了管理家畜功能性MHC多样性的重要性，并表明MHC超型之间可能存在一些免疫冗余。
