Complement-dependent lysis of Erhlich ascites tumor cells by human serum (ascitolysin) in lowered in cancer patients and raised in pregnant women

Abstract

Normal human serum has been shown to contain IgM antibodies that are lytic to Ehrlich ascites tumor cells in the presence of complement. We call this activity ascitolysin (AL). Using a 51Cr release assay, the AL titers of 164 normal sera, 211 sera from patients with non-malignant disease, 62 sera from 25 pregnant women and 170 sera from cancer patients were estimated. The patient sera were taken preoperatively, and were assigned to the cancer or non-cancer group after histological diagnosis. In normals, higher titers were found in sera of A and O blood groups but not B and AB. The difference was due to a fraction absorbed by B red blood cells. Sera from untreated cancer patients showed significantly reduced titers when compared to normal, benign tumor, chronic and other non-malignant disease groups. In pregnancy, titers were positively correlated with duration and remained elevated for at least 6 weeks post partum. About 30% of AL activity was absorbed by the free galactose groups of agarose. This fraction was significantly lower in untreated cancer patients. Anti-T antigen antibodies do not contribute to AL levels. Galactophilic blocking factors were also found; eight times more frequently in cancer sera than in normals. The non-absorbed fraction was also lower in cancer sera. The data suggest that AL antibodies may be directed against human oncofetal antigens.