Final answer:
Dimeric IgA is transported across mucosal epithelium via the polymeric immunoglobulin receptor and released into secretions such as saliva and tears, bound to the secretory component. This process allows IgA to neutralize and trap pathogens, providing essential immune defense at mucosal surfaces.
Step-by-step explanation:
Dimeric IgA is a crucial component of the immune defense system associated with mucosal surfaces. It is secreted by plasma cells located in mucosal tissues and is the most common and abundant antibody class found in mucus secretions. The dimeric form of IgA is joined by a protein structure called the secretory component. This secretory component not only helps to transport IgA across the mucosal epithelium but also protects it from being degraded by enzymes in the secretions. Once synthesized, dimeric IgA binds to a polymeric immunoglobulin receptor (pIgR) on the basolateral surface of mucosal epithelial cells. The IgA-pIgR complex is then transported across the cell to the apical surface. There, the complex is cleaved, releasing the IgA into the lumen of the mucosa bound to a portion of the pIgR, known as the secretory component. This process allows IgA to be present in bodily secretions such as saliva, tears, and breast milk, where it can neutralize pathogens and prevent infection by trapping pathogens in mucus to be eliminated from the body.