Immunoglobulin α Fc Receptor (IgA Fc Receptor) is a member of the immunoglobulin gene superfamily. It is a transmembrane glycoprotein present on the surface of myeloid lineage cells such as neutrophils, monocytes, macrophages, and eosinophils, where it mediates immunologic responses to pathogens through the charged arginin residue within its transmembrane domain. IgA Fc Receptor binds both IgA1 and IgA2 with similar affinity. The site of interaction between FCAR and IgA was identified in the first extracellular domain of FCAR and the C2/C3 junction of IgA. It interacts with IgA-opsonized targets and triggers several immunologic defense processes, including phagocytosis, antibody-dependent cell-mediated cytotoxicity, and stimulation of the release of inflammatory mediators. FCAR is also expressed on Kupffer cells in the liver, where it was suggested to provide a second line of defense.