Induction of human secretory and serum immune responses: molecular properties of IgA antibodies

Abstract

The level and properties of antibodies (polymeric/monomeric forms and IgA subclasses) induced in various external secretions and in blood by systemic or oral immunizations with protein and/or polysaccharide antigens were examined in human volunteers. The purpose of these studies was to determine the influence of immunization routes and of antigen composition on the induction of IgA1 and IgA2 responses. Systemic immunization with polysaccharide and/or protein antigens induced a transient appearance of specific antibody-secreting cells of IgA, IgG, and IgM isotypes in the peripheral blood, followed by specific antibodies in serum and in saliva. While the protein antigens induced predominantly IgAl responses, the polysaccharide-specific antibodies were mainly present in the IgA2 subclass. Most of the serum IgA specific for injected antigens occurred in a polymeric form. Although the response was weaker than after systemic immunization, oral immunization with influenza virus induced both secretory and to a lesser degree systemic antibodies. Previous exposure by mucosal or systemic routes influenced the quantity and quality of the immune response stimulated by oral or systemic immunizations.