GM‐CSF and M‐CSF modulate β‐chemokine and HIV‐1 expression in microglia

Significant numbers of patients with acquired immunodeficiency syndrome (AIDS) develop CNS infection primarily in macrophages and microglial cells. Therefore, the regulation of human immunodeficiency virus type 1 (HIV‐1) infection and activation of the brain mononuclear phagocytes subsequent to infection are important areas of investigation. In the current report, we studied the role of granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) and macrophage‐CSF (M‐CSF) in the expression of antiviral β‐chemokines and HIV‐1 p24 in cultures of primary human fetal microglia. We found that stimulation with GM‐CSF or M‐CSF induced macrophage inflammatory proteins (MIP‐1α and MIP‐1β) and augmented RANTES expression, after HIV‐1 infection of microglia. This was not due to the effect of GM‐CSF on viral expression because GM‐CSF was neither necessary nor stimulatory for viral infection, nor did GM‐CSF enhance the expression of env ‐pseudotyped reporter viruses. Blocking GM‐CSF‐induced microglial proliferation by nocodazole had no effect on β‐chemokine or p24 expression. The functional significance of the GM‐CSF‐induced β‐chemokines was suggested by the finding that, in the presence of GM‐CSF, exogenous β‐chemokines lost their anti‐HIV‐1 effects. We further show that although HIV‐1‐infected microglia produced M‐CSF, they failed to produce GM‐CSF. In vivo, GM‐CSF expression was localized to activated astrocytes and some inflammatory cells in HIV‐1 encephalitis, suggesting paracrine activation of microglia through GM‐CSF. Our results demonstrate a complex interplay between CSFs, chemokines, and virus in microglial cells and may have bearing on the interpretation of data derived in vivo and in vitro. GLIA 39:174–183, 2002. © 2002 Wiley‐Liss, Inc.