肾移植术后持续BK病毒感染受者的特异性细胞免疫反应的动态变化

Kinesis of cellular immune response to persistent infection with BK virus after renal transplantation

目的探讨肾移植术后持续BK病毒（BKV）感染的受者特异性细胞免疫反应的动态变化规律。方法选择2011年2月至2012年1月接受同种异体肾移植手术的受者46例，术后每3个月定期监测尿液和血液的BK病毒DNA载量，随访术后持续性病毒感染（连续2次尿液或血液样本检出BK病毒DNA载量阳性）受者，并提取其外周血单核淋巴细胞，并分别与包含BK病毒特异性5种肽段的重叠肽池（VP1、VP2、VP3、LT-Ag及st-Ag）进行混合培养，采用流式细胞仪检测体外分别由γ-干扰素（IFN-γ）、白细胞介素2（IL-2）和肿瘤坏死因子-α（TNF-α）诱导的T淋巴细胞增殖情况，分析病毒特异性免疫反应的变化规律。结果随访期间，46例受者中出现持续性病毒尿症6例，其中3例同时出现持续性病毒血症，2例经病理学检查证实为BK病毒性肾病（BKVN），均表现为持续性病毒尿症和持续性病毒血症。3例术后发生持续性病毒血症的受者在5种BK病毒特异性蛋白体外刺激后，IL-2、IFN-γ、TNF-α诱导类型的CD4^＋T淋巴细胞反应强度呈明显下降趋势。持续性病毒尿症受者无此类似现象发生。结论肾移植受者发展至病毒血症阶段时，抗BK病毒特异性细胞免疫反应受到严重抑制，若机体不能及时恢复抗病毒的能力，则持续性病毒血症极易发展为BKVN，而导致移植肾功能受损甚至丧失。

Objective To analyze and discuss the dynamics of cellular immune response to persistent infection with BK virus after renal transplantation. Methods The recipients of renal transplantation in our center were selected and BK virus load in urine and blood was regularly observed. The victims of persistent infection with BK virus （defined as two successive positive results of BK virus load in urine or blood） were followed up and peripheral blood mononuclear cells （PBMCs） were collected for mixed cultivation with overlapping peptide pool, which contained peptide fragments （VP1, VP2, VP3, LT-Ag and st-Ag） extracted from BK virus. Flow cytometry was used to examine the in vitro proliferation of IFN-γ/IL-2/TNF-α-induced T cells and analyze the dynamics of cellular immune response to BK virus. Results A total of 46 recipients of renal transplantation were enrolled and 6 victims of persistent viruria were identified. Of the 6 victims, 3 were complicated with persistent viremia, and 2 were diagnosed as BK virus nephropathy by biopsy, presenting with persistent viruria and viremia. The victims of persistent BK viremia after renal transplantation showed a significantly decreasing trend in cellular immune response to 5 BKV-specific proteins, according to the proliferation of TNF-γ/IL-2/TNF-α-induced T cells. However, this trend was not observed in the victims of persistent BK viruria. Conclusion At the stage of viremia, the victims of BKV infection after renal transplantation have seriously inhibited specific immune response to BKV. Thus, if the antiviral mechanisms are not restored in time, these recipients suffering persistent viremia are prone to virus nephropathy （BKVN）, delayed graft function, and even graft loss.