Oral administration of Escherichia coli in enteric coated microparticles induces serum antibodies against lipopolysaccharide antigens

Abstract

Heat-killed Escherichia coli O55:B5 were encapsulated in microcapsules coated with a pH-sensitive enteric coating (methacrylic acid copolymer). Oral immunization of C57BI/6 x DBA/2 (BDF1) mice with encapsulated bacteria resulted in a humoral immune response directed against bacterial lipopolysaccharide (LPS). This response was greatly boosted by a second series of immunization and differed both quantitatively and qualitatively from that induced by intraperitoneal immunization with non-encapsulated heat-killed bacteria. The anti-LPS response following oral immunization was comprised almost exclusively of IgG1 subclass antibodies and was highly specific for the LPS of the immunizing bacteria. The anti-LPS response following intraperitoneal immunization consisted mainly of IgM and IgG2a antibodies which were crossreactive with several bacterial strains. Our results demonstrate that whole killed bacteria, encapsulated by an enteric coating and administered orally, effectively induces an antibody response to LPS in mice which shows a typical memory response following secondary challenge.