Genetic variation is associated with differences in disease resistance and susceptibility among individuals within a population. To date, molecular genetic analyses of host responses have relied on extraction of genomic DNA from whole blood or tissue samples. However, such samples are not routinely collected during large-scale field studies. We demonstrate that cell-free genomic DNA (cfDNA) may be extracted and amplified from archived plasma samples, allowing retrospective analysis of host genetic diversity. This technique was also applicable to archived serum samples up to 35 years old and to different ruminant species. As proof of concept, we used this cfDNA approach to genotype the major histocompatibility complex (MHC) class II DRB1 locus of 224 Merino sheep which had participated in field trials of a commercial Haemonchus contortus vaccine, Barbervax®, in Australia. This identified a total of 51 different DRB1 alleles and their relative frequencies. This is the first study to examine host MHC diversity using DNA extracted from archived plasma samples, an approach that may be applied to retrospective analyses of genetic diversity and responses to vaccination or infection across different species and populations.

中文翻译：

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使用从存档的绵羊血清和血浆中提取的无细胞DNA，对疫苗或感染反应进行回顾性遗传分析的新技术。

遗传变异与人群中个体之间的抗病性和易感性差异有关。迄今为止，宿主反应的分子遗传学分析依赖于从全血或组织样品中提取基因组DNA。但是，在大规模的田野研究期间，通常不会收集此类样品。我们证明无细胞的基因组DNA（cfDNA）可以从存档的血浆样品中提取和扩增，从而可以对宿主遗传多样性进行回顾性分析。该技术还适用于35岁以下的存档血清样本以及不同的反刍动物。作为概念的证明，我们使用了这种cfDNA方法对224头美利奴羊的主要组织相容性复合体（MHC）II类DRB1基因座进行基因分型，这些人参加了商业化的Haemonchus contortus疫苗的田间试验，澳大利亚的Barbervax®。这样鉴定出总共51个不同的DRB1等位基因及其相对频率。这是第一项使用从存档血浆样品中提取的DNA检验宿主MHC多样性的研究，该方法可用于回顾性分析遗传多样性以及不同物种和种群对疫苗接种或感染的反应。