Trickle infection and immunity to Trichuris muris

The majority of experiments investigating the immune response to gastrointestinal helminth infection use a single bolus infection. However, in situ individuals are repeatedly infected with low doses. Therefore, to model natural infection, mice were repeatedly infected (trickle infection) with low doses of Trichuris muris. Trickle infection resulted in the slow acquisition of immunity reflected by a gradual increase in worm burden followed by partial expulsion. Flow cytometry revealed that the CD4+ T cell response shifted from Th1 dominated to Th2 dominated, which coincided with an increase in Type 2 cytokines. The development of resistance following trickle infection was associated with increased worm expulsion effector mechanisms including goblet cell hyperplasia, Muc5ac production and increased epithelial cell turn over. Depletion of CD4+ T cells reversed resistance confirming their importance in protective immunity following trickle infection. In contrast, depletion of group 2 innate lymphoid cells did not alter protective immunity. T. muris trickle infection resulted in a dysbiotic mircrobiota which began to recover alpha diversity following the development of resistance. These data establish trickle infection as a robust and informative model for analysis of immunity to chronic intestinal helminth infection more akin to that observed under natural infection conditions and confirms the importance of CD4+ T cell adaptive immunity in host protection.当前绝大多数探究胃肠道蠕虫感染（gastrointestinal helminth infection）免疫应答的实验，均采用单次冲击感染（single bolus infection）模型。但自然感染情境下的宿主实则会反复接触低剂量的病原体，因此为了模拟真实自然的感染过程，本研究采用低剂量鼠鞭虫（Trichuris muris）反复感染小鼠的模型，即滴注感染（trickle infection）。滴注感染可使宿主缓慢获得免疫保护，表现为虫荷（worm burden）逐渐升高后伴随部分虫体被清除。流式细胞术（flow cytometry）检测结果显示，CD4阳性T细胞（CD4+ T cell）应答从以Th1型为主转向以Th2型为主，这与2型细胞因子（Type 2 cytokines）水平的升高相契合。滴注感染后宿主抗性的形成，与虫体清除相关效应机制的增强有关，包括杯状细胞增生（goblet cell hyperplasia）、Muc5ac蛋白产生以及上皮细胞更新（epithelial cell turn over）加快。清除CD4阳性T细胞可逆转宿主的抗性，证实了其在滴注感染后保护性免疫中的关键作用；与之相反，清除2型先天淋巴细胞（group 2 innate lymphoid cells）并不会改变宿主的保护性免疫能力。鼠鞭虫滴注感染会引发宿主菌群失调（dysbiotic microbiota），而在宿主形成抗性后，菌群的α多样性（alpha diversity）开始逐步恢复。本研究数据证实，滴注感染模型可作为一种稳健且信息丰富的研究工具，用于分析更贴近自然感染情境的慢性肠道蠕虫感染免疫应答，同时验证了CD4阳性T细胞适应性免疫在宿主防御中的重要性。