Identification of the inhibitory p40 subunit of interleukin 12 from the ascitic fluid of patients with advanced carcinoma of the ovary

Objective: To determine the levels of interleukin 12 (IL-12) in the ascites from patients diagnosed with advanced epithelial ovarian cancer. Methods: Ascites samples from advanced ovarian cancer patients and peritoneal fluid from normal controls and endometriosis patients were tested for the presence of IL-12 by ELISA. Two different IL-12 ELISA kits were used. One ELISA kit detected the bioactive heterodimeric form of the IL-12 cytokine composed of the p40 and p35 subunits, while the second kit detected both the bioactive form and the p40 subunit of IL-12. Results: The first ELISA, which tested for only the bioactive heterodimer of IL-12, was negative in all 28 ovarian cancer patients. The second ELISA assay, which reacts with both the p40 subunit monomer and the heterodimer of IL-12, showed detectable levels of IL-12 in all 28 cancer patients and all 29 benign patients. Since no IL-12 heterodimer was detected in the first assay, these results represented the p40 monomer levels. A significantly higher median level of IL-12 monomer was found in malignant ascites compared to all benign control groups (P < 0.05). Conclusions: Ascites from advanced ovarian cancer patients contains significantly higher levels of the IL-12 p40 subunit than peritoneal fluid from normal patients, but contains no measurable bioactive IL-12 heterodimer. The secreted p40 subunit has been shown to inhibit IL-12 mediated activation of T and natural killer cells in vitro. In vivo suppression of lymphocytes by IL-12 p40 in ovarian cancer patients has not yet been demonstrated.