Epithelial ovarian cancer is the leading cause of death from malignant gynaecologic tumours. At the time of diagnosis approximately 75% of patients with ovarian carcinoma have advanced intraperitoneal metastatic disease. 1 The tumours often remain confined to the peritoneum both as peritoneal implants and as floating tumour cells within the ascitic fluid frequently causing death without development of distant met- astases. Ovarian cancer-associated ascites contains various cytokines such as TNF-α, IL-1 and IL-6 which may significantly affect tumour biology. 2–4 IL-6 levels in particular have been shown to be markedly elevated in these fluids. 2,4–6 IL-6 is an extremely pleiotropic polypeptide exerting diverse effects including B-cell differentiation, immunoglobulin production, mega- karyopoiesis and the stimulation of acute phase protein synthesis by the liver. 7,8 In addition, there is increasing evidence that IL-6 affects important tumour cell func- tions including adhesion, invasion, proliferation and neoangiogenesis. 9–11 IL-6 is produced by a variety of cell types such as monocytes, lymphocytes, fibroblasts, and various tumour cells including epithelial ovarian can- cer cells. 2,7,12,13 Recently, it has been demonstrated that peritoneal mesothelial cells are also able to secrete bioactive IL-6. 14 However, the source of ascitic IL-6 and the importance of diverse cell types for IL-6 production in ovarian cancer associated ascites is not well defined. To elucidate this question and to better define the role of the mesothelium as a possible source of ascitic IL-6 we have compared the IL-6 secretion by human ovar- ian cancer cell lines and human peritoneal mesothelial cells. Moreover, we investigated the regulation of its production by the inflammatory cytokines IL-1β, TNF-α and IFN-γ. RESULTS Purity of mesothelial cell cultures To confirm the purity of the mesothelial cell cul- tures single cell suspensions of HPMC were analysed 542 / Offner et al. CYTOKINE, Vol. 7, No. 6 (August 1995: 542–547) 542 CYTOKINE, Vol. 7, No. 6 (August), 1995: pp 542–547 IL-6 SECRETION BY HUMAN PERITONEAL MESOTHELIAL AND OVARIAN CANCER CELLS Felix Albert Offner, 1 Peter Obrist, 1 Sylvia Stadlmann, 1 Hans Feichtinger, 1 Paul Klingler, 2 Manfred Herold, 3 Heinz Zwierzina, 3 Anton Hittmair, 1 Gregor Mikuz, 1 Burghard Abendstein, 5 A. Zeimet, 4 Christian Marth 4 Malignant ascites of epithelial ovarian cancer patients contains high levels of interleukin 6 (IL-6). The present study was conducted to compare the secretion of IL-6 by seven different human ovarian cancer cell lines (OVCA) and cultured human peritoneal mesothelial cells (HPMC) and to examine the regulation of its production by other cytokines. IL-6 was detected in supernatant medium of all mesothelial cell cultures (8/8) and 6/7 ovarian cancer cell lines. Levels of IL-6 secreted by HPMC (median 27 100 pg/1  10 5 cells; range 3870–168 200) were 590-fold higher ( P  0.01) than those secreted by OVCA (median 46 pg/1  10 5 cells; range 0–16 450). Treatment with TNF-α or IL-1β (both 10 ng/ml) for both types of cells and both cytokines resulted in a significant ( P  0.05) elevation of IL-6 pro- duction. In OVCA IL-6 secretion was increased 7- and 39-fold and in HPMC 6- and 8-fold, respectively. Under TNF-α treatment IL-6-levels secreted by HPMC were 149-fold higher ( P  0.01) than those generated by OVCA . Similarly, IL-1β-induced IL-6 levels were 102-fold higher in HPMC (median 288 800 pg/1  10 5 cells; range 93 125–552 800) than in OVCA. IFN-γ (10 ng/ml) increased IL-6 generation in OVCA (6-fold) but not HPMC. The proliferation of both cell types however, was significantly ( P  0.05) inhibited by IFN-γ. Our results suggest that peritoneal mesothelial cells may be a prominent source of IL-6 in ovarian cancer-related ascites. © 1995 A cademic Press Limited. From the Departments of 1 Pathology, 2 Surgery-II, 3 Internal Medicine and 4 Obstetrics and Gynecology, University of Innsbruck; 5 Department of Obstetrics and Gynecology, General Hospital, Hall in Tirol, Austria Correspondence to F.A. Offner MD, Department of Pathology, University of Innsbruck, Muellerstrasse 44, A-6020 Innsbruck, Austria Received 11 November 1994; accepted for publication 25 January 1995 © 1995 Academic Press Limited 1043-4666/95/060542+6 $12.00/0 KEY WORDS: interleukin 6/mesothelial cells/ovarian carcinoma