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 (ILl 4) 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% respectively. 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.