Transforming growth factor beta's 1, 2 and 3 inhibit proliferation of ramified microglia on an astrocyte monolayer.

The transforming growth factor beta's (TGFbeta) are a multipotent family of cytokines with strong immunosuppressive and neurotrophic effects. In the current study, we examined the effect of the TGFbeta's 1, 2 and 3 on the proliferation of ramified microglia cultured on top of a confluent astrocyte monolayer. All three TGFbeta isoforms inhibited proliferation. PCR analysis also showed the presence of mRNA for the TGFbeta receptors type I and II and for all 3 TGFbeta isoforms in microglia, astrocytes and in co-cultures. Moreover, removal of this endogenous TGFbeta activity with antibodies against TGFbeta1 and TGFbeta3 strongly stimulated microglial proliferation. These inhibitory effects on the proliferation of ramified microglia suggest that TGFbeta's may play an important role in the regulation of the microglial population under normal conditions and after injury or disease in the central nervous system.