Kai C, Sármay G, Ramos O, Yefenof E, Klein E
Department of Tumor Biology, Karolinska Instituet, Stockholm, Sweden.
Cell Immunol. 1988 May;113(2):227-34. doi: 10.1016/0008-8749(88)90022-6.
The majority of cell lines derived from Burkitt lymphomas carry CR2 on their plasma membrane cell lines of haematopoietic origin can activate C3 present in human serum through the alternative pathway. However, only the lines that carry CR2 were shown to bind C3 fragments. This bond can be either fixation to acceptor sites or attachment to the CR. Our studies with Raji cells showed that when the possibility for the covalent acceptor bond was eliminated by using methylamine (MA)- or zymosan-treated serum, considerably lower amounts of C3 were bound. In the zymosan-treated serum C3 fragments are present that can bind to receptors but their capacity for acceptor bond is absent. These results indicate that when Raji cell are incubated in human serum some of the generated C3 fragments are bound to acceptors and a lower proportion through the specific interaction with complement receptors. Pretreatment of the CR2 carrying cell lines with human serum elevated their sensitivity to the lytic effect of human blood lymphocytes. We showed in this work that MA-treated serum did not induce this elevation. Zymosan-treated serum under conditions that excluded activation of the residual native C3 molecules, i.e., in the presence of EDTA, did not have the enhancing effect either. These results suggest that the increased lytic efficiency imposed by human serum was due to cleavage of C3 molecules by Raji and fixation of the C3 fragments by acceptor sites. Natural killer cells carry CR3; therefore it is likely that the attached C3 fragments bind also to the effector cells. The C3 molecules could elevate thereby the avidity between the target and the lytic lymphocytes. The observation that C3 fragments are not bound to the surface of CR2 negative lines in spite of their capacity to activate C3 suggests that the receptor molecule is either involved in the activation and/or serves also as an acceptor.
大多数源自伯基特淋巴瘤的细胞系在其质膜上携带CR2，造血来源的细胞系可通过替代途径激活人血清中存在的C3。然而，只有携带CR2的细胞系被证明能结合C3片段。这种结合可以是固定到受体位点或附着到CR上。我们用拉吉细胞进行的研究表明，当使用甲胺（MA）或酵母聚糖处理的血清消除共价受体结合的可能性时，结合的C3量会显著降低。在酵母聚糖处理的血清中存在可与受体结合的C3片段，但它们没有受体结合能力。这些结果表明，当拉吉细胞在人血清中孵育时，一些产生的C3片段会与受体结合，而通过与补体受体的特异性相互作用结合的比例较低。用人血清预处理携带CR2的细胞系可提高它们对人血淋巴细胞裂解作用的敏感性。我们在这项工作中表明，MA处理的血清不会诱导这种提高。在排除残留天然C3分子激活的条件下，即在EDTA存在的情况下，酵母聚糖处理的血清也没有增强作用。这些结果表明，人血清引起的裂解效率提高是由于拉吉细胞对C3分子的裂解以及受体位点对C3片段的固定。自然杀伤细胞携带CR3；因此，附着的C3片段很可能也与效应细胞结合。由此，C3分子可提高靶细胞与裂解淋巴细胞之间的亲和力。尽管CR2阴性细胞系有激活C3的能力，但C3片段却不与它们的表面结合，这一观察结果表明，受体分子要么参与激活过程，要么也作为受体起作用。
