经口灌胃感染弓形虫诱导的BALB/c小鼠肠道粘膜免疫应答(英文)

GUT MUCOSAL IMMUNE RESPONSE INDUCED BY TOXOPLASMA GONDII TACHYZOITE IN ORALLY INFECTED BALB/c MICE

目的研究BALB/c小鼠经口感染（灌胃）弓形虫速殖子后肠液IgA抗体分泌的动态变化及肠道粘膜组织诱导与效应部位T淋巴细胞亚群的变化，探讨肠道粘膜免疫应答机制。方法将6-8周龄BALB/c小鼠100只随机分为对照组和感染组。感染组经口感染（灌胃）弓形虫RH株速殖子5×10^4个/只，对照组给予等量PBS。于感染后第2、4、6、8、10、13、16、19、22、25d处死小鼠，每次5只。收集各时间点肠道冲洗液，用ELISA法测定肠液IgA水平;分离第2、4、6、8、10dPeyer’s Patches（PP）、肠系膜淋巴结（MLN）及小肠上皮内淋巴细胞（IEL），制备悬液并涂片，用免疫细胞化学方法测定CD4^＋、CD8^＋T细胞亚群水平。结果在感染后第4、6、8、13d实验组的肠液IgA抗体分泌显著高于对照组（P〈0.01）。实验组PP结CD4＋T细胞水平在6、8、10d显著高于对照组（P〈0.05）;CD8^＋T细胞水平与对照组无显著性差异，CD4^＋/CD8^＋比值在6、8、10d显著升高（P〈0.05）。肠系膜淋巴结的CD4^＋、CD8＋及CD4^＋/CD8^＋比值各时间点均无显著变化。感染后第6、8、10d，效应部位小肠上皮内淋巴细胞CD8^＋T细胞增高显著（P〈0.01）、CD4^＋/CD8^＋比值倒置（P〈0.05）。结论经口感染弓形虫BALB/c小鼠的肠道产生高水平的IgA抗体，作为局部首道屏障，发挥着重要的抗虫作用。诱导部位PPCD4^＋T细胞水平明显增高，诱导对弓形虫抗原的处理提呈作用;效应部位IELCD8^＋T细胞亚群增殖明显，在清除虫体的过程中起主导作用。

Objective To investigate the mucosal immune responses following Toxoplasma gondii oral infection, including the responses of IgA antibodies in intestinal secretions and proliferation of T lymphocyte subsets in gut mucosa-associated tissues in BALB/c mice. Methods One hundred 6- to 8-week-old BALB/c mice were divided into two groups： control group and infected group. 5 × 10^4 tachyzoites of RH strain were administered orally to all animals of infected group by gavage while the control group was given PBS solution instead. Five mice in each group were killed 2, 4, 6, 8, 10, 13, 16, 19, 22 and 25 day after infection, respectively, after administration. The titer of IgA antibody in intestinal secretions was determined By ELISA. The levels of CD4^＋ and CD8^＋ T cells in Peyer＇s patches （PP）, mesenteric lymph node （MLN） and intestinal mucosal epithelial tissues were determined 2, 4, 6, 8 and 10 days after infection by streptavidin-biotin-peroxidase complex （SABC） immunohistochemistry. Results The IgA antibody levels in intestinal secretions changed greatly, there was significant difference between control group and infected group on days 4, 6, 8 and 13. In mucosal inductive sites PP, the CD4^＋ T cells increased significantly 6, 8 and 10 day after infection. However, the levels of CD8^＋ T cells didn＇t change much and the ration of CD4^＋/CD8^＋ was up-regulated. There were no obvious changes in MLN. The proliferation of CD8^＋ T cells in intestinal epithelia was significant 6, 8 and 10 days after infection, the ratio of CD4/CD8^＋ was reversed with significant difference （P〈0.05）. Conclusion The IgA antibody response induced in the intestinal secretions after infection with T. gondii provided as the first protective barrier for defending the invade of this parasite. Besides, cellular immunity also plays the important role in the local protection. The CD4^＋T cells in PP induced the parasite antigen to be processed and presented, and CD8^＋ T cell subsets of the effector site were the primary immune components for the elimination of parasites.