Immunoglobulin alpha Fc receptor (CD89) (FCAR)

The Immunoglobulin alpha Fc receptor (CD89), encoded by the FCAR gene, is a transmembrane glycoprotein and a member of the immunoglobulin superfamily that serves as the primary receptor for the Fc region of immunoglobulin A (IgA). It is predominantly expressed on myeloid cells, including neutrophils, monocytes, macrophages, and eosinophils, where it mediates critical immune effector functions such as phagocytosis, degranulation, and antibody-dependent cellular cytotoxicity (ADCC). In the context of disease, CD89 plays a pivotal role in the pathogenesis of IgA nephropathy (IgAN), where the formation of complexes between soluble CD89 and galactose-deficient IgA1 leads to glomerular deposition and inflammation. Therapeutic strategies targeting this pathway include monoclonal antibodies designed to block the IgA-CD89 interaction or to deplete CD89-expressing cells, as well as the use of IgA1 proteases to cleave the pathogenic ligand. While no CD89-targeted therapies are currently approved, the receptor remains a significant focus for treating autoimmune and inflammatory conditions where IgA-mediated pathology is central. Additionally, CD89 is being explored as a target for cancer immunotherapy to harness the potent cytotoxic capabilities of neutrophils against tumor cells.

Other names

CD89Fc-alpha-RIFc fragment of IgA receptorFcalphaRIImmunoglobulin alpha Fc receptor

The Immunoglobulin alpha Fc receptor (CD89) binds to the Fc region of IgA antibodies, triggering intracellular signaling through the associated Fc receptor gamma chain (FcRγ). This interaction mediates effector functions such as phagocytosis and degranulation. In IgA nephropathy, drugs aim to block the binding of pathogenic IgA1 complexes to CD89 or to cleave the IgA1 hinge/Fc region to prevent receptor activation and subsequent tissue damage.