Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.
Am Nat. 2010 Nov;176(5):613-24. doi: 10.1086/656496.
Most hosts are infected with multiple parasites, and responses of the immune system to co-occurring parasites may influence disease spread. Helminth infection can bias the host immune response toward a T-helper type 2 (Th2) over a type 1 (Th1) response, impairing the host’s ability to control concurrent intracellular microparasite infections and potentially modifying disease dynamics. In humans, immune-mediated interactions between helminths and microparasites can alter host susceptibility to diseases such as HIV, tuberculosis (TB), and malaria. However, the extent to which similar processes operate in natural animal populations and influence disease spread remains unknown. We used cross-sectional, experimental, and genetic studies to show that gastrointestinal nematode infection alters immunity to intracellular microparasites in free-ranging African buffalo (Syncerus caffer). Buffalo that were more resistant to nematode infection had weaker Th1 responses, there was significant genotypic variation in nematode resistance, and anthelminthic treatment enhanced Th1 immunity. Using a disease dynamic model parameterized with empirical data, we found that nematode-induced immune suppression can facilitate the invasion of bovine TB in buffalo. In the absence of nematodes, TB failed to invade the system, illustrating the critical role nematodes may play in disease establishment. Our results suggest that helminths, by influencing the likelihood of microparasite invasion, may influence patterns of disease emergence in the wild.
大多数宿主都会感染多种寄生虫，而免疫系统对同时存在的寄生虫的反应可能会影响疾病的传播。蠕虫感染会使宿主的免疫反应偏向 Th2 型（辅助性 T 细胞 2 型）而不是 Th1 型（辅助性 T 细胞 1 型），从而削弱宿主控制同时发生的细胞内微寄生虫感染的能力，并可能改变疾病的动态。在人类中，蠕虫和微寄生虫之间的免疫介导相互作用可以改变宿主对 HIV、结核病（TB）和疟疾等疾病的易感性。然而，在自然动物种群中，类似的过程在何种程度上起作用并影响疾病的传播仍不清楚。我们使用横断面、实验和遗传研究表明，胃肠道线虫感染会改变自由放养的非洲野牛（Syncerus caffer）对细胞内微寄生虫的免疫反应。对线虫感染更具抵抗力的野牛 Th1 反应较弱，线虫抗性存在显著的基因型变异，驱虫治疗增强了 Th1 免疫。使用参数化的经验数据的疾病动态模型，我们发现线虫诱导的免疫抑制可以促进牛型结核分枝杆菌在野牛中的入侵。如果没有线虫，结核病就无法入侵系统，这说明了线虫在疾病建立过程中可能起关键作用。我们的研究结果表明，寄生虫通过影响微寄生虫入侵的可能性，可能会影响野生环境中疾病的出现模式。
