FIG 1.

Schematic representation of IgA transcytosis and secretory IgA (SIgA) formation. SIgA is delivered into intestinal secretions through a process involving intestinal epithelial cells themselves. Specifically, B cells located in the gut mucosa secrete dimeric IgA (dIgA), which is recognized by the polymeric immunoglobulin receptor (pIgR) on the basolateral surfaces of intestinal epithelial cells. The pIgR transports dIgA from basolateral to apical cell surfaces, where dIgA is then released into the intestinal lumen in complex with secretory component (SC), an ~70 kDa proteolytic fragment of pIgR. Thus, in its final form, SIgA is an assemblage of two IgA monomers and SC.