Cell growth-dependent variation in the sensitivity of human and mouse tumor cells to complement-mediated killing

Cells removed from asynchronous cultures during lag, log, and stationary phases of growth were found to differ in their sensitivity to antibody/complement-mediated killing. The human lymphoblastoid line, Raji, was relatively more susceptible to killing by human anti-HLA antibody plus rabbit complement during the lag and log phases of growth, while the human lymphoid cell line, PY, was relatively more susceptible to rabbit antilymphocyte serum or human anti-HLA plus rabbit complement during the log and late-log phases of growth. The mouse mastocytoma cell line, P815, was relatively resistant to killing by rabbit anti-P815 plus guinea pig complement during the middle log phase of growth. The variation in sensitivity of the three cell lines was dependent upon the concentration of antibody used to sensitize the cells but not due to differences in antigen expression, antigen density, or net synthesis of DNA, RNA, protein, complex carbohydrate, or lipid-containing macromolecules. These data suggest that the variability in susceptibility of the cells for complement-mediated killing is due to changes in physiological and/or physicochemical properties of the cells which either affect the ability of the cells to repair complement-mediated damage or nullify the activity of cell-bound complement.