FIG. 4.

Expression of MIP-1α in microglia from FcγR-deficient mice. Murine microglia were isolated from the neonates of WT (wt), FcγRI α-chain-deficient (RI KO), FcγRIII α-chain-deficient (RIII KO), FcγRII-deficient (RII KO), and the common γ-chain-deficient (γ KO) mice as described in the text. (A) Murine microglial cells in enriched cultures were examined for the expression of CD11b, CD16, GSA lectin, and GFAP by immunohistocytochemistry as described in Materials and Methods. Mouse microglia express CD11b (CR3), CD16 (FcγRIII), and GSA lectin. Cultures were highly pure as demonstrated by lack of astrocytes (GFAP⁺). (B) Murine microglia were exposed to medium only (media), C. neoformans, MAb (18B7), or C. neoformans plus 18B7, as described for human microglia experiments. ELISA specific for murine MIP-1α was used to determine chemokine levels. Each data point represents three to six wells (mean ± standard deviation). All except γ KO mouse microglia showed induction of MIP-1α after exposure to C. neoformans plus 18B7. RIII KO microglia produced significantly less MIP-1α than did WT microglia. *, P < 0.05 versus WT. (C) Giemsa staining of the WT microglia showed that C. neoformans phagocytosis occurred in the presence of specific antibody 18B7. A decrease in phagocytosis of 18B7-opsonized C. neoformans was observed in RI KO and RIII KO microglia but not in RII KO microglia. In γ KO microglia, C. neoformans cells were attached to the surface, but no phagocytosis occurred. The results are representative of five independent experiments with similar results.