The IgA dimer, with its linking J chain, emerges from the plasma cell and binds to the poly-Ig receptor on the submucosal tissue side of an epithelial cell. The bound IgA is endocytosed, transported across the cell in a vesicle and is released at the mucosal surface, by cleavage of the poly-Ig receptor. The segment of the receptor that remains bound to the Fc portions of the secreted IgA dimer is the secretory component, which helps prevent enzymic degradation of the antibody. The other segment remains in the membrane.