Fc alpha receptor I (CD89) (FCAR)

The Immunoglobulin A (IgA) receptor pathway is a complex signaling and transport system centered on the interaction of IgA antibodies with specific cell-surface receptors, most notably the Fc alpha receptor I (CD89) and the polymeric immunoglobulin receptor (pIgR) (UniProt P24071, P01833). CD89 is primarily expressed on myeloid cells, such as neutrophils and monocytes, where it triggers potent effector functions including phagocytosis, respiratory burst, and the release of pro-inflammatory cytokines upon binding to IgA immune complexes (PubMed 23782171). pIgR plays a vital role in mucosal immunity by facilitating the transcytosis of dimeric IgA across epithelial layers to the mucosal surface, where it serves as the first line of defense against pathogens (PubMed 31113977). In pathological conditions like IgA nephropathy, the pathway is characterized by the accumulation of galactose-deficient IgA1 (Gd-IgA1), which forms pathogenic immune complexes that deposit in the renal mesangium, leading to inflammation and progressive kidney damage (Nature Reviews Nephrology, 2023). Current therapeutic strategies targeting this pathway focus on reducing IgA levels through the inhibition of B-cell activating factors like APRIL and BLyS, or by utilizing IgA-specific proteases and complement inhibitors to mitigate the downstream effects of IgA deposition (ClinicalTrials.gov NCT04287985). Additionally, the transferrin receptor (CD71) has been identified as an alternative IgA1 receptor on mesangial cells that contributes to renal injury.

Other names

CD89Fc alpha receptorFCARPolymeric immunoglobulin receptorpIgRFc alpha/mu receptorCD71Transferrin receptorImmunoglobulin A receptor pathway

Inhibition of B-cell activating factors (APRIL and BLyS) to reduce IgA production, enzymatic cleavage of IgA antibodies, blockade of IgA-receptor binding, and inhibition of downstream complement activation.