Immunoglobulin alpha Fc receptor (FcαRI) (CD89)

Immunoglobulin alpha Fc receptor (FcαRI), also known as CD89, is a type I transmembrane glycoprotein expressed exclusively on cells of the myeloid lineage, including neutrophils, monocytes, macrophages, and eosinophils (UniProt P24071). It serves as the primary receptor for the Fc region of Immunoglobulin A (IgA), the most prevalent antibody class in mucosal secretions and the second most abundant in serum. Upon binding to IgA-antigen complexes, CD89 associates with the Fc receptor gamma chain (FcRγ) to initiate intracellular signaling via immunoreceptor tyrosine-based activation motifs (ITAMs), triggering potent effector functions such as phagocytosis and antibody-dependent cellular cytotoxicity (ADCC) (PubMed: 29434067). In modern drug development, CD89 is being targeted as a novel checkpoint for cancer immunotherapy, utilizing engineered multimeric IgA or IgA/IgM-mediated complexes. These complexes leverage the J-chain multimerization mechanism—naturally found in both IgA and IgM—to achieve high-avidity binding to CD89, thereby potently recruiting and activating neutrophils to eliminate tumor cells that may be resistant to traditional IgG-based therapies (IGM Biosciences).

Other names

FCARFc alpha receptor ICD89 antigenBlood group Bes-related

The mechanism involves the recruitment and activation of myeloid effector cells, particularly neutrophils, through the high-avidity binding of multimeric IgA or IgA/IgM-hybrid complexes to the FcαRI (CD89) receptor. This binding induces the phosphorylation of ITAMs on the associated FcRγ signaling subunits, triggering a cascade that leads to the destruction of target cells (e.g., tumor cells) via ADCC, trogocytosis, or phagocytosis.