Production of interferon-gamma by microglia.

Neural cells do not usually interact with immune cells because of the lack of major histocompatibility complex (MHC) antigen expression. Interferon-gamma (IFN-gamma) enables this interaction via induction of MHC antigen expression in neural cells. Thus, IFN-gamma is a critical cytokine for the development of central nervous system (CNS) pathologies. IFN-gamma, however, is considered to be produced exclusively by lymphoid cells. Here, we show for the first time that murine microglia produce IFN-gamma in response to IL-12 and/or IL-18, using RT-PCR detection of IFN-gamma mRNA and Western blotting and immunohistochemical analysis for cytoplasmic expression of IFN-gamma. Stimulation of microglia with IL-12 and IL-18 resulted in MHC class II mRNA expression in microglia. Since IL-12 and IL-18 are produced in the CNS by glial cells, these cytokines may play a critical role in the initiation of neural-immune cell interaction and the induction of autoimmune processes in the CNS via induction of IFN-gamma and MHC antigens.