Immunosuppressive activity of ascitic fluid from patients with cancer metastatic to the peritoneum.

We have examined the immunosuppressive effects of ascitic fluids from patients with advanced cancer metastatic to the peritoneum and compared them with noncancerous abdominal or pleural effusions, serum from cancer patients, or the proteins human serum albumin and bovine gamma-globulin. The ascitic fluids from cancer patients produce a nontoxic, dose-dependent suppression of DNA and protein synthesis of phytohemagglutinin-stimulated human peripheral blood lymphocytes. This suppression reached 100% with an ascitic protein concentration of 4 to 6 mg/ml, whereas control effusions, serum from cancer patients, or added extraneous proteins were not suppressive. Ascitic proteins also suppress the mixed lymphocyte reaction and the response of human peripheral blood lymphocytes to the antigen keyhold limpet hemocyanin, in vivo, the primary plaque-forming response to sheep red blood cells in mice could be suppressed, and this suppression was not due to antigenic competition.