Up-regulation of cytokine production is mediated by FcγRIIa. (A) FcγR expression on immature DCs was measured by FACS. Black line indicates expression; and gray line, control. Data shown are from one representative experiment of 3 experiments with different donors. (B) DC were preincubated for 30 minutes with or without a blocking Ab against FcγRIIa, after which cells were stimulated with IgG-opsonized or nonopsonized S aureus. Cytokine levels were determined in the supernatant by ELISA. Data shown are from 1 representative experiment of 3 experiments with different donors. (C) DCs were preincubated for 2 hours with DMSO or 10μM Cytochalasin D, after which cells were stimulated with S aureus that was preincubated or not in human serum (HS) or purified IgG. Cytokine levels were determined in the supernatant by ELISA. Data shown are from 1 representative experiment of 3 experiments with different donors. Error bars indicate SEM; *P < .05, **P < .01; ns indicates not significant; paired t test.