Polymeric immunoglobulin receptor.

The surface of mucosal sites, such as the intestinal tract, are covered by epithelial cells. To protect the intestinal environment from invading pathogens and maintain homeostasis, the human body developed an exquisite acquired immune system, referred to as the mucosal immune system, in which epithelial cells and lymphocytes function cooperatively. The main player in this immune system is the polymeric immunoglobulins (pIgs), in particular dimeric IgA (dIgA). To exert its protective effect, dIgA produced in the lamina propria must be transported to the intestinal lumen across epithelial cells. This process is called transcytosis and is mediated by polymeric immunoglobulin receptor (pIgR), which is exclusively produced by intestinal epithelial cells (IECs). DIgA is captured by pIgR on the basolateral surface of IECs and transcytosed to the opposite side of IECs. The dIgA-pIgR complex is expressed on the apical surface of IECs and proteolytically cleaved to generate secretory IgA (SIgA). This review describes the current understanding and recent progress in this research field.