Koprak S, Sirotina A, Ok H, Dumont F J
Department of Immunology, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
Transplantation. 1996 Mar 27;61(6):926-32. doi: 10.1097/00007890-199603270-00015.
FK506 blocks T cell activation by preventing the transcription of lymphokine genes through binding to the intracellular protein FKBP12 and formation of complex that inhibits the phosphatase activity of calcineurin. Beside exerting potent suppressive activity on cellular and humoral immune responses, in vivo treatment with FK506 in rodent models induces thymic alterations characterized by a selective reduction of mature CD4+8- cells. The potential relationship between such thymic alterations and the immunosuppressive and calcineurin inhibitory activities of FK506 has not been defined. Here, we took advantage of the availability of FK506 analogs with different immunosuppressive potencies to address this question. Intravenous daily administration of FK506 in Sprague-Dawley rats for 4 days was found to be sufficient to cause a depletion of CD4+8- thymocytes with an ED50=0.06 mg/kg/day. Under the same conditions, L-683,590 which is 2-3-fold less potent than FK506 in inhibiting T cell activation and calcineurin function gave an ED50=0.17 mg/kg/day. In contrast, the nonimmunosuppressive, calcineurin noninhibitory antagonist L-685,818, failed to deplete the CD4+8- thymocyte subset but could reverse the reducing effect of FK506 on this subset. Another analog, L-688,617, which does not completely inhibit T cell activation in vitro, also behaved as a partial agonist of CD4+8- cell depletion. Therefore, the ability of FK506 analogs to deplete the CD4+8- thymocytes subset correlates with their immunosuppressive and calcineurin inhibitory potencies. This suggests that calcineurin is involved in the intra-thymic maturation processes of CD4+8- T cells. Moreover, the short-term treatment protocol described here provides a rapid and quantitative assay to determine the immunosuppressive potency of FK506-like compounds in vivo
FK506通过与细胞内蛋白FKBP12结合并形成抑制钙调神经磷酸酶磷酸酶活性的复合物，阻止淋巴因子基因的转录，从而阻断T细胞活化。除了对细胞免疫和体液免疫反应具有强大的抑制活性外，在啮齿动物模型中用FK506进行体内治疗会引起胸腺改变，其特征是成熟CD4+8-细胞选择性减少。这种胸腺改变与FK506的免疫抑制和钙调神经磷酸酶抑制活性之间的潜在关系尚未明确。在此，我们利用具有不同免疫抑制效力的FK506类似物来解决这个问题。发现在Sprague-Dawley大鼠中每日静脉注射FK506 4天足以导致CD4+8-胸腺细胞耗竭，ED50=0.06 mg/kg/天。在相同条件下，L-683,590在抑制T细胞活化和钙调神经磷酸酶功能方面的效力比FK506低2-3倍，其ED50=0.17 mg/kg/天。相比之下，非免疫抑制性、非钙调神经磷酸酶抑制性拮抗剂L-685,818未能耗尽CD4+8-胸腺细胞亚群，但可逆转FK506对该亚群的减少作用。另一种类似物L-688,617在体外不能完全抑制T细胞活化，在耗尽CD4+8-细胞方面也表现为部分激动剂。因此，FK506类似物耗尽CD4+8-胸腺细胞亚群的能力与其免疫抑制和钙调神经磷酸酶抑制效力相关。这表明钙调神经磷酸酶参与了CD4+8-T细胞的胸腺内成熟过程。此外，此处描述的短期治疗方案提供了一种快速定量测定方法，以确定FK506类化合物在体内的免疫抑制效力
