SEB诱导的CD4^+ T细胞无能、凋亡及MHC-I类分子表达下调

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

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一2Kb)表达的变化。用琼脂糖凝胶电泳,观察不同时问段凋亡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DNA ladder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ConA而逆转。在SEB刺激后,CD4+ T细胞表面MHC-I类分子(H-2Kb)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的表达下凋有关。

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.