Phospholipid synthesis in HeLa cells exposed to immunoglobulin G and complement.

1. HeLa cells were cultured in the presence of heterologous immunoglobulin G and guinea-pig serum together with [(32)P]phosphate. 2. Incorporation of [(32)P]phosphate was significantly stimulated by anti-HeLa immunoglobulin G and complement-sufficient serum compared with immunoglobulin G from unimmunized rabbits and complement. Within 2.5h heat-inactivated guinea-pig serum and anti-HeLa immunoglobulin G stimulated [(32)P]phosphate incorporation to the same extent as heat-inactivated complement and immunoglobulin G from unimmunized rabbits. 3. Compared with cells exposed to immunoglobulin G from unimmunized rabbits together with complement, anti-HeLa immunoglobulin G with complement increased the phospholipid content of HeLa cells twofold within 5h of incubation. 4. Exposure of HeLa cells to anti-HeLa immunoglobulin G and complement for 5-22h resulted in a twofold increase in the net accumulation of [(32)P]phosphate in sphingomyelin and phosphatidylcholine and a 50% increase in the net accumulation of [(32)P]phosphate in phosphatidylethanolamine, compared with cultures exposed to immunoglobulin G from unimmunized rabbits and complement. 5. A transient accumulation of (32)P-labelled lysophosphoglycerides in HeLa cells exposed to antibody and complement was detected, confirming previous findings (Güttler & Clausen, 1969b). 6. The stimulation of [(32)P]phosphate turnover occurred in cells filling up their cytoplasma with vacuoles. This supports the suggestion that the accumulation of phospholipid in these cells may be concerned with the synthesis and function of cytomembranes.