Pruett S B, Lackey A
Department of Biological Sciences, Mississippi State University 39762.
Clin Exp Immunol. 1987 Sep;69(3):624-31.
A number of investigators have reported that human serum inhibits the proliferation of IL-2-dependent mouse cells in IL-2 bioassays, but the mechanism of inhibition has not been carefully examined. We noticed that IL-2-dependent mouse cells (CTLL-2) are killed within 30 min in the presence of a 1/10 dilution of human serum. However, CTLL-2 cells totally deprived of IL-2 did not begin to die until at least 6 h in culture. Thus, even complete inhibition of IL-2 by human serum could not account for the rapid cytotoxicity caused by human serum. Since humans have 'natural' antibodies which react with mouse cells, it seemed possible that the cytotoxicity was due to antibody/complement-mediated cell lysis. This was supported by the observation that EDTA (at a concentration sufficient to inhibit complement) protected CTLL-2 cells from the cytotoxic effects of human sera from four normal donors. In addition, preincubation of CTLL-2 cells with heat-inactivated human sera at 4 degrees C rendered them much more susceptible to lysis with rabbit complement than cells which were preincubated with complete culture medium. The cytotoxicity of human serum is not limited to IL-2-dependent mouse cells but was also observed with EL4 and Ag8.653 cells as well as normal splenocytes. The cytotoxic effect of human serum was lost upon removal of IgM, but not upon removal of IgG. These results strongly suggest that the inhibition of proliferation of IL-2-dependent mouse cells by human serum is due to antibody/complement-mediated lysis of those cells. In addition, non-heat-inactivated human serum did not inhibit the IL-2-mediated proliferation of human PHA blasts, indicating that there is no inherent inhibitory activity in human serum apart from the cytotoxic effect on xenogeneic cells. Thus the reported IL-2 inhibitory activity of whole human serum is probably not biologically relevant.
一些研究人员报告称，在白细胞介素-2（IL-2）生物测定中，人血清会抑制依赖IL-2的小鼠细胞增殖，但抑制机制尚未得到仔细研究。我们注意到，在存在1/10稀释度人血清的情况下，依赖IL-2的小鼠细胞（CTLL-2）在30分钟内就会死亡。然而，完全缺乏IL-2的CTLL-2细胞在培养至少6小时后才开始死亡。因此，即使人血清完全抑制了IL-2，也无法解释人血清引起的快速细胞毒性。由于人类具有与小鼠细胞反应的“天然”抗体，细胞毒性似乎可能是由于抗体/补体介导的细胞裂解。这一观点得到了以下观察结果的支持：乙二胺四乙酸（EDTA，浓度足以抑制补体）可保护CTLL-2细胞免受来自四名正常供体的人血清的细胞毒性作用。此外，将CTLL-2细胞在4℃下与人血清热灭活物预孵育，会使其比用完全培养基预孵育的细胞更容易被兔补体裂解。人血清的细胞毒性不仅限于依赖IL-2的小鼠细胞，在EL4和Ag8.653细胞以及正常脾细胞中也观察到了这种现象。去除IgM后人血清的细胞毒性消失，但去除IgG后则不会。这些结果有力地表明，人血清对依赖IL-2的小鼠细胞增殖的抑制作用是由于抗体/补体介导的这些细胞的裂解。此外，未热灭活的人血清不会抑制人PHA刺激的淋巴细胞的IL-2介导的增殖，这表明除了对异种细胞的细胞毒性作用外，人血清中没有内在的抑制活性。因此，所报道的全人血清的IL-2抑制活性可能与生物学无关。
