Polymeric immunoglobulin receptor (pIgR)

The **polymeric immunoglobulin receptor** (pIgR) is a transmembrane glycoprotein expressed predominantly on the basolateral surface of epithelial cells lining mucosal surfaces. It belongs to the immunoglobulin superfamily and functions as an Fc receptor specialized for binding polymeric forms of immunoglobulins—specifically dimeric IgA and pentameric IgM—produced by local plasma cells in subepithelial tissues. Upon binding these antibodies via their J-chain, pIgR mediates their transcytosis from the basolateral side through epithelial cells to the apical surface. There, proteolytic cleavage releases its extracellular domain—the "secretory component"—either free or complexed with antibody into mucus secretions. This process results in formation of **secretory IgA** (SIgA) and **secretory IgM** (SIgM), which play critical roles in immune defense by neutralizing pathogens at mucosal barriers without triggering inflammation. The secretory component also protects these antibodies from proteolytic degradation within harsh luminal environments and can itself bind bacteria non-specifically, contributing further to host defense. Genetic variation in PIGR has been associated with diseases such as **IgA nephropathy**, while deficiency impairs secretion of SIgA/SIgM leading to increased risk for infections at mucosal sites. The magnitude of pIgR-mediated transport is highest in intestinal epithelium but occurs throughout various glandular tissues including respiratory tract, mammary glands, liver bile ducts, etc.[1][3][4][6]

Other names

pIgRSecretory component (refers to the cleaved extracellular domain)PIGR (gene symbol)

Not applicable; there are no approved drugs that act directly on this receptor. Its function is primarily physiological—mediating antibody transport and immune exclusion.