Primary Immune Responses by Cord Blood CD4(+) T Cells and NK Cells Inhibit Epstein-Barr Virus B-Cell Transformation In Vitro

Epstein-Barr virus (EBV) transformation of B cells from fetal cord blood in vitro varies depending on the individual sample. When a single preparation of EBV was simultaneously used to transform fetal cord blood samples from six different individuals, the virus transformation titer varied from less than zero to 10(5.9). We show that this variation in EBV transformation is associated with a marked primary immune response in cord blood samples predominately involving CD4(+) T cells and CD16(+) CD56(+) NK cells. After virus challenge both CD4(+) T cells and NK cells in fetal cord blood cultures expressed the lymphocyte activation marker CD69. The cytotoxic response against autologous EBV-infected lymphoblastoid cell line (LCL) targets correlated with the number of CD16(+) CD69(+) cells and was inversely correlated with the virus transformation titer. Although NK activity was detected in fresh cord blood and increased following activation by the virus, killing of autologous LCLs was detected only following activation by exposure to the virus. Both activated CD4(+) T cells and CD16(+) NK cells were independently able to kill autologous LCLs. Both interleukin-2 and gamma interferon were produced by CD4(+) T cells after virus challenge. The titer of EBV was lower when purified B cells were used than when whole cord blood was used. Addition of monocytes restored the virus titer, while addition of resting T cells or EBV-activated CD4(+) T-cell blasts reduced the virus titer. We conclude that there are primary NK-cell and Th1-type CD4(+) T-cell responses to EBV in fetal cord blood that limit the expansion of EBV-infected cells and in some cases eliminate virus infection in vitro.EB病毒（Epstein-Barr virus, EBV）体外转化胎儿脐血来源B淋巴细胞的效率存在显著个体样本差异。当使用同一批次的EB病毒制剂同时转化6名不同个体的胎儿脐血样本时，病毒转化滴度范围从低于0到10^5.9。本研究证实，EB病毒转化效率的上述差异与胎儿脐血样本中以CD4阳性T淋巴细胞和CD16阳性CD56阳性自然杀伤（NK）细胞为主的显著初次免疫应答密切相关。经病毒感染攻击后，胎儿脐血培养物中的CD4阳性T淋巴细胞与NK细胞均可表达淋巴细胞活化标记物CD69。针对自体EB病毒感染淋巴母细胞系（Lymphoblastoid cell line, LCL）靶细胞的细胞毒性应答，与CD16阳性CD69阳性细胞数量呈正相关，而与病毒转化滴度呈负相关。尽管在新鲜脐血中即可检测到NK细胞活性，且经病毒活化后该活性进一步增强，但仅在病毒暴露活化后，方可检测到对自体LCL的杀伤作用。活化的CD4阳性T淋巴细胞与CD16阳性NK细胞均可独立杀伤自体LCL。病毒感染攻击后，CD4阳性T淋巴细胞可产生白细胞介素-2（interleukin-2, IL-2）与γ干扰素（gamma interferon, IFN-γ）。使用纯化B细胞时测得的EB病毒滴度低于使用全脐血时的滴度。添加单核细胞可恢复病毒滴度，而添加静息T细胞或EB病毒活化的CD4阳性T细胞母细胞则会降低病毒滴度。本研究得出结论：胎儿脐血中存在针对EB病毒的初次NK细胞应答与Th1型CD4阳性T细胞应答，这类应答可限制EB病毒感染细胞的增殖，在部分体外实验中甚至可清除病毒感染。