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 as cites from patients diagnosed with advanced epithelial ovarian cancer. Methods: Ascites samples from advanced ovarian cancer patients and pe ritoneal fluid from normal controls and endometriosis patients were te sted for the presence of IL-12 by ELISA. Two different IL-12 ELISA kit s were used. One ELISA kit detected the bioactive heterodimeric form o f the IL-12 cytokine composed of the p40 and p35 subunits, while the s econd kit detected both the bioactive form and the p40 subunit of IL-1 2. Results: The first ELISA, which tested for only the bioactive heter odimer of IL-12, was negative in all 28 ovarian cancer patients. The s econd 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 mo nomer 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 con tains significantly higher levels of the IL-12 p40 subunit than perito neal 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 v ivo suppression of lymphocytes by IL-12 p40 in ovarian cancer patients has not yet been demonstrated.