MICROGLIAL CELLS INDUCE CYTOTOXIC EFFECTS TOWARD COLON-CARCINOMA CELLS - MEASUREMENT OF TUMOR-CYTOTOXICITY WITH A GAMMA-GLUTAMYL-TRANSPEPTIDASE ASSAY

Activated macrophages have been shown to exert cytostatic and cytotoxi c effects toward tumor cells via nitric oxide (NO) release. In the CNS , microglial cells are considered to be the main resident population o f immune effector cells. In this study, cytotoxic activity of NII, an immortalized murine microglial cell line, toward rat progressive DHD/P ROb and regressive DHD/REGb colon carcinoma cells was examined in para llel with NO production. Cytotoxicity was evaluated using a novel meth od, the gamma-glutamyl transpeptidase (gamma-GTP) assay, based on the fact that DHD tumor cells expressed high levels of gamma-GTP activity, while no gamma-GTP activity was found in cells of the monocyte/macrop hage lineage. Results showed that activation of NII cells by interfero n-gamma plus either lipopolysaccharide or tumor necrosis factor-alpha induced high amounts of NO release and cytotoxic effects toward DHD/PR Ob as well as DHD/REGb cells. NO release by activated NII cells was au gmented by addition of tumor cell-conditioned medium. Both NO release by NII cells and cytotoxicity were blocked by addition of N-G-monometh yl-L-arginine (L-NMA), an inhibitor of NO synthase, suggesting that cy totoxicity was mediated by NII-derived NO. However, in the presence of L-NMA an increased production of interleukin-6 was also observed. In conclusion, in opposition to information obtained with brain-derived e ndothelial cells, brain-derived microglial cells did not differentiate between progressive and regressive clones of colon carcinoma cells. O ur results point to a specific role for both endothelial and microglia l cell types in the context of brain metastasis. Microglial cells can be cytotoxic for tumor cells, and this cytotoxicity is mediated by NO. (C) 1997 Wiley-Liss, Inc.