IL-1-Alpha and TNF-Alpha Differentially Regulate CD4 and Mac-1 Expression in Mouse Microglia

The regulatory effects of the proinflammatory cytokines, interleukin-1α (IL-1α) and tumor necrosis factor-α (TNF-α) were investigated on CD4 and Mac-1 expression in mouse microglial cultures. The identity of the microglia in cultures was confirmed by multiple indices including morphology, uptake of acetylated low-density lipoprotein and lectin RCA 120 staining. Microglia growing on a monolayer of astrocytes (astrocyte-supported microglia) were both CD4- and Mac-1 positive (out of 94.5% Mac-1-positive cells, 85.3% were also CD4 positive). When astrocyte-supported microglia were replated directly onto culture dishes (plate-supported microglia), the percentage of CD4- and Mac-1-positive cells decreased to 12–29 and 20–25% resepctively. The addition of IL-1α or TNF-α to plate-supported microglia led to an upregulation of Mac-1 expression in a time- and dose-dependent manner with different EC50s (0.5 ng/ml for IL-1α and 2 ng/ml for TNF-α) but exhibited similar time-to-peak responses (over 12 h). The addition of IL-1α, but not TNF-α, also led to an increase in CD4 expression on plate-supported microglia with a similar dose response and time course. IL-1α treatment gave rise to an increase in the level of CD4 mRNA as assessed by RT-PCR. The possibility that cell proliferation was responsible for the observed effects on microglia was excluded by an analysis of 3H-thymidine incorporation. Our results suggest that cultured mouse microglia express CD4 molecules which can be upregulated by IL-1α while Mac-1 can be upregulated by both IL-1α and TNF-α.