Immune regulation by Fcα/μ receptor (CD351) on marginal zone B cells and follicular dendritic cells

Summary Although both Fcα/μ receptor (Fcα/μR) and polymeric Ig receptor (poly‐IgR) are Fc receptors for IgA and IgM and are functionally and genetically related, the expression profile of Fcα/μR is unique. Unlike poly‐IgR, Fcα/μR is expressed on marginal zone ( MZ ) B cells and follicular dendritic cells, suggesting that Fcα/μR plays an important role in humoral immune responses. Fcα/μR mediates endocytosis of the IgM immune complex ( IC ). Recent research demonstrated that Fcα/μR downregulated retention of the IgM IC with a T‐independent ( TI ) antigen on MZ B cells and follicular dendritic cells due to endocytosis of the IgM IC , suppressing germinal center formation, affinity maturation, and memory B‐cell generation in response to TI antigen challenge. In addition, Fcα/μR physically associates with Toll‐like receptor 4 ( TLR 4) and augments TLR 4 oligomerization and signaling in MZ B cells upon lipopolysaccharide (LPS) challenge, leading to increased proinflammatory cytokine production by MZ B cells. Thus, Fcα/μR is a unique Fc receptor that is involved in humoral immune responses and inflammation.