CD32 expression and signaling is down-regulated by transforming growth factor-β1 on human monocytes

CD32 (FcγRII) is the most abundantly distributed class of IgG Fc receptors in the human body. In this study, we analyzed the effect of transforming growth factor (TGF)-β1, a cytokine with strong immunosuppressive function, on the expression and function of CD32 on freshly isolated peripheral blood monocytes and three human monocytic cell lines, U937, THP-1 and Mono mac-6. We found that TGF-β1 down-regulates CD32 expression on monocytes and all monocytic cell lines in a dose- and time-dependent fashion. A mean down-regulation of CD32 expression on THP-1 cells of 54 ± 3.2% after 24 h was found at a concentration of 1 ng/ml TGF-β1. At the mRNA level, TGF-β1 induced a twofold down-regulation of CD32. Cross-linking of CD32 induced an increase in the concentration of intracellular Ca²⁺, which was reduced by 50% by TGF-β1, suggesting a decreased downstream signaling mediated by the receptor.