Molecular mechanisms for generation and maintenance of memory CD8T cells following bacterial infection.

在细胞内病原体的急性感染过程中，抗原特异性T细胞在扩增期增殖，然后大多数T细胞在随后的收缩期因凋亡而死亡，但少数存活的T细胞成为记忆细胞并持续很长一段时间。记忆性CD 8 T细胞被迅速激活以抵抗再感染并消除病原体。通过将表达OVA_1<257-264>/K_1b特异性T细胞受体的OT-I细胞过继转移到对照、IL-15敲除（KO）和IL-15转基因（Tg）小鼠中，然后用表达OVA的重组单核细胞增生李斯特菌（Listeria monocytogenes）攻击，我们发现IL-15在记忆性CD_8 T细胞的产生、维持和再活化中的作用如下：（1）效应期：IL-15在细菌感染后被激活以产生效应性CD_8 T细胞。(2)收缩期：IL-15通过诱导抗凋亡分子在微生物感染后的收缩期保护效应CD 8 ^+T细胞免于凋亡中起关键作用。(3)维持期：IL-15通过诱导稳态增殖在记忆性CD 8 ^+ T细胞的长期维持中发挥重要作用。(4)再活化：IL-15通过诱导再感染时的细胞毒性分子，在记忆性CD 8 ^+ T细胞的早期活化中发挥重要作用。

During the course of acute infection with an intracellular pathogen, antigen-specific T cells proliferate in the expansion phase, and then most of the T cells die by apoptosis in the following contraction phase, but the few that survive become memory cells and persist for a long period of time. Memory CD8T cells are activated rapidly against re-infection and eliminate pathogens. Using an adoptive transfer system of OT-I cells expressing OVA_<257-264>/K^b-specific T cell receptor into control, IL-15 knockout (KO) and IL-15 transgenic (Tg) mice followed by challenge with recombinant Listeria monocytogenes expressing OVA, we found the roles of IL-15 in generation, maintenance and reactivation of memory CD8T cells as follows :(1) Effector phase : IL-15 is dispensable for generation of effector CD8T cells following bacterial infection.(2) Contraction phase : IL-15 plays a critical role in protecting effector CD8^+T cells from apoptosis during the contraction phase following a microbial infection via inducing anti-apoptotic molecules.(3) Maintenance phase : IL-15 plays an important role in long-term maintenance of memory CD8^+ T cells through induction of homeostatic proliferation.(4) Reactivation : IL-15 plays an important role in early activation of memory CD8^+ T cells through induction of cytotoxic molecules upon re-infection.