Expression of cytokines during glial differentiation.

Astrocytes and microglia produce a variety of cytokines, some of which may have roles in the proliferation and differentiation of glial cells during development in the central nervous system. Cytokine mRNAs and activities were therefore assayed during glial development in mixed glial cell cultures from newborn mouse brain. Cytokine mRNAs were also measured in mouse brain during postnatal development in vivo. Macrophage colony-stimulating factor(M-CSF) mRNA, interleukin-1 beta (IL-1 beta) mRNA and tumor necrosis factor alpha (TNF alpha) mRNA were all detected on the in vitro cultures and each showed a distinct time course of expression. IL-6 and granulocyte-macrophage colony-stimulating factor(GM-CSF) mRNAs were not detected in the cultured cells. Measurements of cytokine activity in culture supernatants as well as cytokine mRNAs in vivo gave similar results. The data suggest that IL-1, TNF alpha and M-CSF are produced in the period of gliogenesis, and that M-CSF rather than GM-CSF may promote the generation and proliferation of microglia. Although IL-6 and GM-CSF exhibit neurotrophic effects, these cytokines may not function as neurotrophic factors during early postnatal development.