Fc alpha/mu Receptor  

The Fc alpha/mu receptor (Fcα/μR, CD351) is a receptor that has dual specificity for IgA and IgM. Fcα/μR binds IgM with high affinity and IgA with a 10-fold lower affinity. Fcα/μR is expressed by both hematopoietic and non-hematopoietic cells, and has been shown to play an important role in humoral immune responses, especially in pro-inflammatory functions of marginal zone B cells in sepsis. Fcα/μR is a type I transmembrane protein that belongs to the immunoglobulin (Ig) superfamily and contains one Ig-like domain in the extracellular portion and a motif in the Ig-like domain conserved in the first Ig-like domain of the human, bovine and rodent poly-IgR. Mouse Fcα/μR contains a dileucine motif at residues 519 and 520 in the cytoplasmic portion that is involved in receptor internalization. However, since the human Fcα/μR does not have a di-leucine motif in its cytoplasmic domain, it remains unclear whether and how it transduces a signal in humans.