10 O - Expression of inducible nitric oxide synthase mRNA in human tumor-associated macrophages

The enzyme inducible Nitric oxide synthase (iNOS) is known to catalyse the release of Nitric oxide from L-arginin. Expression of iNOS is readily induced in macrophases of various mammals, but the presence of this enzyme in human monocytes and macrophages has not been entirely clarified. In this study we tested wbether iNOS mRNA and protein can be detected in human tumor-assiociated macrophages (TAMs). TAMs were isolated from malignant effusions of cancer patients (n = 4) by gradient separation. The reverse transcription polymerase chain reaction (oligonucleotide primers derived from human hepatocyte iNOS mRNA) and immuncytochemistry (anti-macNOS) were used. Stimulalion of TAMs was achieved by incubating the cells with rh-GM-CSF and rh. IFN-g and a combination of these cytokines. iNOS specific mRNA as well as iNOS protein could be detected in TAMs. The mRNA signal was induced in 10/14 samples and increased in 4/14 following stimulation with the cytokines GM-CSF and IFN-g. This stimulalion correlated with enhancement of TNF-a production and ceIl mediated cytotoxicity of TAMs against tumor targets. Our finding that iNOS is detectable and can be stimulated in human TAMs supports the notion that iNOS/NO are important molecules in antitumoral effector mechanisms.