IgA antibodies are synthesized in plasma cells underneath epithelial basement membranes of the respiratory epithelia, the gut, tear and salivary glands, and the lactating gland. The IgA dimer diffuses across the basement membrane while the poly-Ig receptors binds to the epithelial cell. The complex undergoes transcytosis and then is transported in a vesicle through the cell. The poly-Ig receptor then leaves the IgA-binding component (as the secretory component). The rest of the poly-Ig receptor is degraded, and IgA is then transported across the epithelia.