SEB诱导的CD4+ T细胞无能、凋亡及MHC-I类分子表达下调

目的：探讨超抗原金黄色葡萄球菌肠毒素（SEB）体外诱导外周T细胞免疫耐受的作用机制。方法：采用SEB体外刺激C57BL/6J（B6）小鼠的脾细胞后，以MTT比色法检测脾细胞的增殖，并用PI染色后以流式细胞术（FCM）分析不同时间段处于S期，G0-G1期的细胞及无能T细胞的凋亡，测定T细胞亚群及MHC-I（H-2K^b)表达的变化。用琼脂糖凝胶电泳，观察不同时间段凋亡T细胞的DNA特征。结果：部分去除CD8^ T细胞后。SEB可刺激B6小鼠脾细胞中CD4^ T细胞大量增殖，在SEB刺激后第3天，CD4^ T细胞中处于S期的比率最大，此后开始下降；而处于G0-G1期的CD4^ T细胞变化则相反，在初次刺激后第3天，增殖的CD4^ T细胞出现无能，FCM检测及用琼脂糖凝胶电泳检查DNAladder证实，在第7天，无能CD4^ T细胞出现凋亡，且凋亡细胞的比率逐渐增多，不因加入抗CD3抗体或CoN A而逆转，在SEB刺激后，CD4^ T细胞表面MHC-I类分子（H-2K^b)的表达，随细胞无能的出现而明显下调。结论：SEB诱导的T细胞免疫耐受，可能与CD4^ T细胞的无能，凋亡及细胞表面分子MHC-I的表达下调有关。

Anergy, apoptosis and decreased MHC class Ⅰmolecule expression of C57BL/6J mouse CD4+ T cells induced by SEB

AIM: To study the mechanism of peripheral T cell tolerance induced by superantigen staphylococus aureus enterotoxin B (SAgSEB). METHODS: Splenocytes from C57BL/6J (B6) mice were stimulated with SEB in vitro. The proliferation of lymphocytes was determined by MTT colorimetry. The apoptosis of anergic T cells, the cells being in the S and G0 ~ G1 phase and MHC-I (H-2Kb) expression of T cells were analyzed by flow cytometry (FCM). Apoptosis of anergic T cells was also demonstrated by DMA electrophore-sis ladder. RESULTS; SEB could induce strong proliferation of CD4+ T cells and the maximal percentage of CD4+ T cells in S phase appeared on 3th day after SEB stimulation and then decreased, but the changes of percentage of CD4+ T cells in G0 ~G1 phase was opposite to that in S phase. CD4+ T cells became anergy on 3th day and apoptosis of anergic CD4+ T cell appeared on 5th day. Percentage of apoptosis cells increased gradually and could not be reversed by addition of anti-CD3 Ab and ConA. Expression of MHC-I(H-2Kb) was marginally declined accom panied by CD4+ T cell anergy after SEB exposure. CONCLUSION; SEB-induced tolerance may have relation to anergy and apoptosis of CD4+ T cells, and down-regulation of MHC-I molecules.