Blocking of the activating Fcγ receptor CD32a abrogates the IVIg-mediated regulation of CD1 expression on dendritic cells. The effect of blocking the Fcγ receptors CD16, CD32a, CD32b, and CD64 using 2 μg/mL of each antibody (in the presence of 0.5 mg/mL IVIg) on CD1 expression on DCs was determined. The graphs show the relative MFI expression of CD1a, CD1b, CD1c, and CD1d cell surface expression (± standard deviation) from 9 individual donors after 6 days of culture (A). The reference line indicates the relative CD1 expression on DCs cultured in FCS and IVIg. The statistical difference between the CD1 expression on DCs grown in FCS and IVIg and DCs cultured in FCS, IVIg, and blocking FcγR antibodies was determined by paired t test or signed rank test if normality test failed. The surface expression of the activating Fcγ receptor CD32a (B) and the inhibitory Fcγ receptor CD32b (C) on CD14⁺ monocytes and on DCs cultured in IL-4, GM-CSF, and FCS for the indicated times was determined by flow cytometry. The histograms show the CD32 expression in black and the isotype control in gray. Statistical differences were considered significant when P < .05; *P < .05 and **P < .01.