Molecular heterogeneity of human IgA antibodies during an immune response.

Human IgA occurs in multiple molecular forms (polymeric and monomeric) and two subclasses which show differential distribution between the mucosal and circulatory compartments of the immune system. However, the molecular form and subclass of specific IgA antibodies are influenced, especially during an immune response, by the type of antigen and duration of the response as well as by the route of exposure. These considerations question previously held notions that polymeric IgA and an increased representation of the IgA2 subclass among circulating antibodies or antibody-secreting cells signify their mucosal origin. Although the functional properties of different molecular forms and subclasses of IgA antibodies are incompletely understood, it appears that there is physiological benefit in the diversity of the IgA immune system.