Protection against Mucosal Infections by Secretory IgA

In the past decade, several model systems have been developed to study the details of the production of secretory IgA by the mucosal surface. Until recently, most attention in vaccine research has been directed toward establishing a vigorous systemic (predominantly IgG) humoral immune response to the infectious agent. With the recognition, however, that secretory IgA is overwhelmingly the predominant immunoglobulin along mucosal surfaces and likely responsible for host defense, much work has been directed at understanding initiation of the secretory IgA response and to establishing a secretory IgA memory response. Also, the mechanisms by which secretory IgA affects protection are being sought. Unlike IgG, secretory IgA does not opsonize for phagocytosis or efficiently activate complement for cell destruction by membrane damage. Rather, secretory IgA seems to afford protection by preventing attachment of microorganisms and/or their toxic product to the delicate surface epithelium that lines the mucosa.