[Detection of interferon-gamma in malignant peritoneal effusion in ovarian cancer patients]

Concanavalin A-induced human and mouse T cell proliferation assay was used to detect the suppressive activity of ascitic fluid (AF) in ovarian cancer patients. About 80% of AF specimens were found to be suppressive. However, when later tested for AF's effect on NK cell activity, instead of suppression, marked enhancement was observed. As IL-2 was barely detectable in AF, attention was focused on interferon (IFN). Its presence was then examined and confirmed by the ability of AF to protect HEp-2 cells from the cytopathic effect of vesicular stomatitis virus (VSV). As the protective effect against VSV was abolished by low pH treatment and by anti-human interferon gamma monoclonal antibodies (MAb), the IFN identified in AF was of the gamma type (IFN-gamma). The MAb could markedly inhibit not only AF's NK-enhancing effect but T cell suppressing effect as well. After removal of the IFN-gamma from AF by affinity chromatography, both activities of AF were lost. The possible clinical implication of this new finding with regards to host's anti-tumor resistance and prognosis is discussed.