Siemasko K, Chong A S, Jäck H M, Gong H, Williams J W, Finnegan A
Department of Immunology/Microbiology, Rush-Presbyterian-St. Luke's Medical Center, Chicago, IL 60612, USA.
J Immunol. 1998 Feb 15;160(4):1581-8.
Leflunomide is an immunosuppressive drug capable of inhibiting T and B cell responses in vivo. A number of studies demonstrate that leflunomide functions both as a pyrimidine synthesis inhibitor and as a tyrosine kinase inhibitor. We previously reported that leflunomide inhibits LPS-stimulated B cell proliferation, cell cycle progression, and IgM secretion. This inhibition can be reversed by the addition of exogenous uridine, suggesting that leflunomide functions as a pyrimidine synthesis inhibitor in B cells. We report here that while the addition of uridine restored proliferation and IgM secretion to leflunomide-treated LPS-stimulated B cells, as determined by metabolic labeling and immunoprecipitation, it did not completely restore secretion of IgG Ab. We hypothesized that leflunomide inhibits LPS-induced IgG secretion by inhibiting tyrosine kinase activity required for isotype switch. We tested this hypothesis in a well-defined model of isotype switch, LPS plus IL-4 induction of IgG1. Leflunomide inhibited IgG1 secretion in this model in a dose-dependent manner. The signal transduction pathway utilized by IL-4 to induce IgG1 involves tyrosine phosphorylation of the IL-4 receptor, JAK1, JAK3, and STAT6 proteins induced by IL-4 binding to the IL-4R. Leflunomide diminished the tyrosine phosphorylation of JAK3 and STAT6 in the absence or presence of uridine. In gel mobility shift studies, STAT6 binding to the STAT6 DNA binding site in the IgG1 promoter decreased in the presence of leflunomide or leflunomide plus uridine. Taken together, these data suggest that leflunomide acts as a tyrosine kinase inhibitor to block IgG1 production.
来氟米特是一种免疫抑制药物，能够在体内抑制T细胞和B细胞反应。多项研究表明，来氟米特兼具嘧啶合成抑制剂和酪氨酸激酶抑制剂的功能。我们之前报道过来氟米特可抑制脂多糖（LPS）刺激的B细胞增殖、细胞周期进程及IgM分泌。添加外源性尿苷可逆转这种抑制作用，这表明来氟米特在B细胞中作为嘧啶合成抑制剂发挥作用。我们在此报告，虽然添加尿苷可使来氟米特处理的LPS刺激的B细胞恢复增殖和IgM分泌（通过代谢标记和免疫沉淀法测定），但它并未完全恢复IgG抗体的分泌。我们推测来氟米特通过抑制同种型转换所需的酪氨酸激酶活性来抑制LPS诱导的IgG分泌。我们在一个明确的同种型转换模型（LPS加IL-4诱导IgG1）中验证了这一假设。来氟米特在该模型中以剂量依赖性方式抑制IgG1分泌。IL-4诱导IgG1所利用的信号转导途径涉及IL-4与IL-4受体结合后诱导的IL-4受体、JAK1、JAK3和STAT6蛋白的酪氨酸磷酸化。无论有无尿苷存在，来氟米特都会减少JAK3和STAT6的酪氨酸磷酸化。在凝胶迁移率变动分析中，在存在来氟米特或来氟米特加尿苷的情况下，STAT6与IgG1启动子中STAT6 DNA结合位点的结合减少。综上所述，这些数据表明来氟米特作为酪氨酸激酶抑制剂来阻断IgG1的产生。
