Complement-mediated killing of myeloma tumor cells: Differences in susceptibility to lysis by antibodies and complement are independent of antigen expression and antibody binding

The susceptibility to lysis by antibodies (Ab) and complement (C) of several murine myeloma tumour sublines was studied. Significant differences in the degree of C-mediated lysis were observed and found to be independent of the expression of antigens on the cell surface and their accessibility to react with Ab. Several experiments correlate the presence and amount of a 160 kilo dalton cell-surface glycoprotein (gp160) and the diminished susceptibility to C attack observed with some of these tumour sublines. Different sources of Ab and C were tested and similar results were obtained, although the effect was most apparent when mouse Ab and rabbit C were used in the cytotoxicity assays. These results suggest that gp160, when present in large amounts on the cell surface, could be interfering with the generation of the C-induced membrane lesions.