Review article: Epithelial disposition of antigen.

Exogenous antigens can impinge upon the luminal surface of mucous membranes and to a limited degree, can even penetrate into the lamina propria. As a result of infection, microbial antigens can be present in mucosal epithelium or lamina propria. At all three levels (lumen, epithelium, lamina propria), locally produced antibodies, principally immunoglobulin A (IgA), can combine with antigens. As a result, antigens can be prevented from attaching to the epithelium, viruses can be neutralized inside epithelial cells and immune complexes in the lamina propria can be excreted into the lumen. As the Fc portion of IgA is specialized to facilitate epithelial transport of IgA rather than to activate inflammatory mediator systems (as is the case with other classes of immunoglobulin), the predominance of IgA among mucosal antibodies serves to limit the degree of local inflammation following antigen-antibody reactions.