Antigens on human tumor cells assayed by complement fixation with allogeneic sera.

A well-documented report showed that human tumor cells acquired a new antigen, heterologous membrane antigen (HMAg), from heterologous serum-supplemented media. Cellular cytotoxicity and immune adherence as says that involve human tumor cells grown in fetal calf serum (PCS) have been shown to be influenced by the presence of this antigen on target cells. This report describes the effect of HMAg on the detec tion of cellular antigens of human tumor cells by human serum antibodies in the complement-fixation assay. PCS and/or partially purified HMAg (P-HMAg) were used as the HMAg source. The P-HMAg was extracted from PCS by 75% ethanol. The cellular antigenic extract was prepared from human osteosarcoma (SA2) cells grown in FCS-supplemented medium by freeze-thaw and ultrasonic extrac tion. The cellular extract contained HMAg by the immune adherence inhibition assay. Complement fixation detected the incidences of natural antibody to HMAg in 51 of 100 (51%) of sarcoma patients' sera and 32 of 62 (52%) of normal donors' sera (p = 0.94). Reactivity of sarcoma sera to the FCS-grown SA2 extract was much higher, 54 of 63 (86%), than in normal donors' sera, 18 of 55 (33%) (p < 0.0001). Some sera reacted to both antigens, while others reacted to P-HMAg but not to the cellular antigens, and wee versa. Quantitative absorp tion with insolubilized PCS or sheep erythrocytes of the serum samples that reacted to both antigens completely removed antibody activity to P-HMAg or PCS, whereas reactivity against cellular antigens remained unaffected. Antigen extracts prepared from agamma human serumgrown SA2 cells and a biopsied liposarcoma specimen were free of HMAg. Antibody reactivity of the test sera to these antigens was essentially the same as that to the antigens prepared from FCS-grown SA2 cells. There was an almost complete reciprocity of antibody titer to these three antigenic extracts. Therefore it may be inferred that the presence of HMAg on cultured human tumor cells does not influence the results of complement fixation.