CD89 (FcαRI), encoded by the FCAR gene, is an IgA-specific receptor primarily expressed on myeloid cells (e.g., neutrophils, monocytes/macrophages). It mediates immune defense functions by binding to the Fc region of IgA (with a preference for polymeric forms), facilitating phagocytosis, antibody-dependent cellular cytotoxicity (ADCC), and inflammation regulation. Its signaling relies on the ITAM motif of the FcRγ chain, enabling dual immunoregulatory roles in both activation and suppression. Clinically, CD89 is implicated in IgA nephropathy, pathogen immune evasion, and tumor immunity. Targeted therapies, such as the bispecific antibody MOR202, are under development for diseases like multiple myeloma, highlighting its therapeutic potential as a bridge between mucosal and systemic immunity.