Immunoglobulin A: Strategic Defense Initiative at the Mucosal Surface

Abstract

IgA is the predominant immunoglobulin in the external secretions of humans. Specific IgA-producing cells home to mucosal epithelia through­ out the body to provide humoral protection as a frontline defense against pathogens borne in aerosols, the environment, and the diet. Much of the recent research on IgA has been directed toward three central questions: (a) What are the factors that account for the localization and regulation of IgA-producing cells at the mucosae; (b) What is the nature of the mechanism that selectively transports secretory IgA to the mucosal lumen; and (c) What are the physiologically important roles of IgA, both in blood and in the exocrine environment. Regulation of IgA production is an extensive topic in itself and will be touched on here only briefly. We concentrate on the fate and function of IgA after synthesis and try to assess which of its experimentally described properties are essential for IgA to contribute to the well-being of the host.