免疫功能是影响动物个体适合度的重要因素之一，也是防御病原体入侵的重要途径，对动物的生存至关重要。种群密度与寄生物感染都能影响动物的免疫功能。本实验通过2×2析因实验设计，测定了母体密度应激+球虫感染、母体密度应激+未球虫感染、未母体密度应激+球虫感染、未母体密度应激+未球虫感染等4个处理对根田鼠粪便皮质酮、球虫感染率、白细胞总数、各型白细胞的百分比、淋巴细胞亚型计数（CD4，CD8计数）等指标。结果表明，高密度母体应激处理可显著降低CD4数量、CD4/CD8比例、淋巴细胞数、嗜酸性粒细胞数、白细胞数，母体应激与球虫的耦合可使上述免疫指标进一步降低，说明母体密度应激和球虫感染对于根田鼠的免疫具有负的叠加效应。

The immune function of animal is an important factors to influence animal  fitness. As it is a crucial way to defend against bacterial pathogens such as viruses, the immune system play a key role in animal’s survival. Both population density and parasitization are known to deteriorate individuals’ immune function. This experiment using 2×2 factorial experiment design to measure the indexes of four treatments(maternal density stress+coccidian infection, not maternal density stress+not coccidian infection, maternal density stress+not coccidian infection, not maternal density stress+coccidian infection), including the fecal corticosterone metabolite(FCM), coccidian infection rate,blood parameters, lymphocyte subsets counts(CD4, CD8 counts). The results show that the density-induced maternal stress can significantly reduce the number of CD4, rate of CD4/CD8, Lymphocytes, Eosinophils, white cell. The effects were further deteriorated when maternally stressed offspring infected with coccidian. Our results showed that the interaction of density-induced maternal stress and coccidian infection has negatively synergistic effect on the immune of root vole．