可溶性CD22作为B细胞活化标志物对移植排斥反应的预警意义及机制研究

Current identification of graft rejection depends on clinical evidence of graft dysfunction, pathological changes in graft and alloantibodies in serum. However, the diagnostic criteria can only identify rejection after the graft injury or the alloantibody production, and there is a lack of forewarning marker in graft rejection. CD22 is a B-cell associated membrane protein, which plays an important role in inhibiting B-cell activation. Following B-cell activation, CD22 turns from masked form to unmasked form. Soluble CD22 (sCD22) is the soluble extracellular domain of CD22 molecule. In our previous studies, we detected sCD22 in the serum of kidney transplant recipients, and found that the levels of sCD22 were associated with the immune status of the recipients. We presumed that the level of sCD22 was associated with B-cell activation, and served as a forewarning marker of rejection. The potential mechanism of sCD22 production was that B-cell activation made cell-surface CD22 molecule turn to unmasked form, which was more prone to be cleaved. In this study, we plan to identify the structure of sCD22, and perform experiments in vitro or in vivo. The purpose is to reveal the relationship between sCD22 and B-cell activation as well as the unmasked form, and to determine the mechanism of sCD22 production. We also will detect sCD22 in a large number of transplant recipients, in order to investigate the forewarning significance of sCD22 in graft rejection.

目前移植排斥反应的诊断主要依靠移植物功能不全临床表现、移植物病理改变或同种异体抗体检测，这些方法均滞后于排斥反应的发生，目前尚缺乏对排斥反应具有预警意义的标志物。CD22是特异性表达于B细胞的膜分子，具有负性调控作用，当B细胞活化时CD22可由"遮蔽态"转化为"暴露态"进而抑制BCR信号。CD22胞外段可发生断裂而形成可溶性CD22（sCD22）。我们在前期研究中从肾移植受者血清中检测到sCD22，并发现其与受者的免疫状态有明显相关性。我们推测sCD22可能是B细胞活化标志物，对排斥反应具有预警意义，其产生的机制可能是B细胞活化而导致CD22转化为更易断裂的"暴露态"。本研究拟对sCD22进行分离鉴定，并通过体外实验和动物实验研究其与B细胞活化及CD22"暴露态"的相关性，揭示sCD22升高的机制，同时对大样本量的器官移植受者血清sCD22进行检测，探讨sCD22对排斥反应的预警意义。

目前移植排斥反应的诊断主要依靠移植物功能不全的临床表现、移植物病理改变或同种异体抗体检测，这些方法均滞后于排斥反应的发生，目前尚缺乏对排斥反应具有预警意义的标志物。CD22是特异性表达于B细胞的膜分子，具有负性调控作用，当B细胞活化时CD22可由“遮蔽态”转化为“暴露态”进而抑制BCR信号。CD22胞外段可发生断裂而形成可溶性CD22（sCD22）。我们在前期研究中从肾移植受者血清中检测到sCD22，并发现其与受者的免疫状态有明显的相关性。我们推测sCD22可能是B细胞活化标志物，对排斥反应具有预警意义，其产生的机制可能是B细胞活化而导致CD22转化为更易断裂的“暴露态”。此外，我们发现在脓毒症患者血清中sCD22是一种非特异性炎症因子，对革兰氏阴性细菌性脓毒症具有诊断意义，其诊断价值与PCT和IL-6相当，并且sCD22在预后评估方面可能比PCT和IL-6具有更高的应用价值。在进一步机制研究发现，sCD22与B细胞活化具有明显地相关性，可以作为B细胞活化的标志物。sCD22的产生是由于B细胞活化使细胞表面CD22的表达水平增加，同时使CD22转化为“暴露态”，增加了CD22分子胞外段的断裂几率，进而导致sCD22水平的升高。