Fc fragment of IgG receptor IIb (coded by FCGR2B gene) is a low affinity inhibitory receptor for the Fc region of immunoglobulin gamma (IgG). The receptor inhibits the functions of activating FcγRs, such as phagocytosis and pro-inflammatory cytokine release, mainly by clustering of FCGR2B with different activating FCGR receptors or with the BCR by immune complexes. FCGR2B regulates B cell activation by increasing the BCR activation threshold and suppressing B cell mediated antigen presentation to T cells through the ITIM-dependent inhibitory mechanism. FCGR2B expression on follicular dendritic cells (FDCs) is important for capturing the antigen-containing immune complexes which are essential for the germinal center response.
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