The role of interleukin-12 (IL-12) in T cell activation and IL-12 receptor-mediated signaling

（1）IL-12的产生机制：IL-12的产生是由抗原呈递细胞/巨噬细胞通过活化T细胞上表达的CD 40配体或脂多糖（LPS）刺激介导的。我们已经证明，通过这两种途径产生的IL-12受体液免疫中涉及的细胞和可溶性组分、B细胞和Th 2型细胞因子（IL-10、IL-6和IL-4）的调节。(2)IL-12应答性T细胞克隆（2D 6）的建立：我们成功地建立了可以对少量rIL-12应答并在单独使用rIL-12的体外培养物中维持的T细胞克隆。建立该克隆使我们不仅能够制备能够定量IL-12的量的高灵敏度生物测定系统，而且还可以研究以下研究。(3)通过IL-12受体（IL-12 R）进行信号传导。用IL-12刺激T细胞导致两种Janus激酶（TYK 2和JAK 2）和两种STAT蛋白（STAT 4和STAT 3）的磷酸化。2D 6细胞可以用IL-12或IL-2（分别命名为2D 6 <IL-12>μ或2D 6 μ<IL-2>）维持。我们发现用IL-12刺激2D 6除了激活上述信号分子外还激活STAT 5。使用这两个2D 6亚系，我们观察到IL-12刺激诱导两个亚系中的增殖，但IFN-γ产生仅在2D 6中<IL-12>。我们的研究还表明TYK 2和STAT 4/STAT 3是IL-12 R信号传导到IFN-γ产生所必需的，而JAK 2和STAT 5负责包括2D 6细胞的增殖。

Through our 2-year investigations, the following were revealed :(1) Mechanisms underlying IL-12 production : IL-12 production is mediated by antigen-presenting cells/macrophages through stimulation with either CD40 ligand expressed on activated T cells or lipopolysaccharide (LPS). We have demonstrated that IL-12 production via these two pathways is regulated by cellular and soluble components involved in humoral immunity ; B cells and Th2 type cytokines (IL-10, IL-6 and IL-4).(2) Establishment of an IL-12-responsive T cell clone (2D6) : We succeeded in establishing a T cell clone which can respond to a small amount of rIL-12 and be maintained in vitro cultures with rIL-12 alone. Establishing this clone permitted us not only to prepare a high-sensitive bioassay system capable of quantitating the amounts of IL-12 but also to investigate the following study.(3) Signaling through IL-12-receptor (IL-12R). Stimulation of T cells with IL-12 rsults in the phosphorylation of two Janus kinases (TYK2 and JAK2) and two STAT proteins (STAT4 and STAT3). 2D6 cells could be maintained with either IL-12 or IL-2 (designated 2D6^<IL-12>, or 2D6^<IL-2> respectively). We found that stimulation of 2D6 with IL-12 activates STAT5 in addition to the above signaling molecules. Using these two 2D6 sublines, we observed that IL-12 stimulation induces proliferation in both sublines, but IFN-gamma production only in 2D6^<IL-12>. Our study also showed that TYK2 and STAT4/STAT3 are required for IL-12R signaling to IFN-gamma production whereas JAK2 and STAT5 are responsible for including the proliferation of 2D6 cells.