This study examines the influence of insoluble matrix components of glioma (astrocytoma) cells on LPS-mediated inducible nitric oxide (NO)/NO synthase (iNOS) induction in microglia cells. Insoluble matrix components prepared from C6 rat glioma cells strongly suppressed iNOS induction and subsequent NO release induced by LPS. Matrices prepared from several glioma cell lines displayed similar inhibitory effects on LPS-induced NO/iNOS induction, whereas matrices from primary cultured rat astrocytes had a minimal influence. Of the various purified ECM materials examined, collagen suppressed LPS-mediated iNOS/NO induction in microglia. C6 matrices potentiated LPS-induced NF-kappaB DNA binding/transcriptional activity, suggesting that the suppression of LPS-induced iNOS by C6 matrices is NF-kappaB independent. C6 matrices inhibited LPS-mediated activation of p38 and JNK MAP kinases. This study shows that non-diffusible factors derived from astrocytoma cells in the brain are critically involved in the suppression of microglial cell activation. Our results indicate that activation of microglia can be regulated by various cellular and pathological environmental conditions, not only through cell-cell contact or soluble factors, but also via insoluble matrix components.