Stear Michael J, Fitton Lesley, Innocent Giles T, Murphy Lisa, Rennie Kerry, Matthews Louise
Institute of Comparative Medicine, University of Glasgow, Bearsden Road, Glasgow G61 1QH, UK.
J R Soc Interface. 2007 Oct 22;4(16):767-76. doi: 10.1098/rsif.2007.1104.
The interaction between sheep and the nematode Teladorsagia circumcincta is one of the best understood of all host-parasite interactions. Following infection, there is considerable variation among lambs in the number of nematode eggs produced, the number of early fourth-stage larvae and the number of adult worms in the mucosa. These traits have a high variance to mean ratio (i.e. they are overdispersed or aggregated among hosts), they are skewed and approximately negative binomially distributed. The sources of overdispersion are differences among lambs in the ingestion of infective larvae and the immune response. Both forces can produce aggregation but their relative importance is unknown. The key components of variation can be identified by variance analysis. The sum of the average effects of polymorphic genes is known as additive genetic variation and this increases essentially from zero at one month of age to quite high values at six months of age. The major mechanism underlying genetic variation appears to be the differences among individuals in immune responses. Two of the major sources of variation in immune responses are differences in antigen recognition and differences in the type of cytokines produced. Genes that influence both these sources of variation are associated with differences in resistance to nematode infection. Therefore, much of the heterogeneity among animals in parasite transmission appears to be due to genetic variation in immune responsiveness.
绵羊与环形泰勒线虫之间的相互作用是所有宿主 - 寄生虫相互作用中理解最为深入的之一。感染后，羔羊在产生的线虫卵数量、早期第四阶段幼虫数量以及黏膜中成虫数量方面存在相当大的差异。这些性状具有高方差均值比（即它们在宿主间过度分散或聚集），呈偏态分布且近似负二项分布。过度分散的来源是羔羊在摄入感染性幼虫和免疫反应方面的差异。这两种因素都可导致聚集，但它们的相对重要性尚不清楚。变异的关键组成部分可通过方差分析来识别。多态基因的平均效应之和称为加性遗传变异，其基本上从1月龄时的零增加到6月龄时的相当高的值。遗传变异的主要潜在机制似乎是个体在免疫反应方面的差异。免疫反应变异的两个主要来源是抗原识别差异和产生的细胞因子类型差异。影响这两个变异来源的基因与对线虫感染抗性的差异相关。因此，动物在寄生虫传播方面的许多异质性似乎是由于免疫反应性的遗传变异所致。
