Immune response against ovalbumin in rats colonized with an ovalbumin-producing Escherichia coli and the influence of feeding ovalbumin.

The influence of feeding ovalbumin (OA) on the development of IgE/IgG antibodies and delayed-type hypersensitivity (DTH) against OA was studied in rats colonized from birth with an Escherichia coli genetically manipulated to produce OA. At 21 days of age, colonized pups and pups with a normal intestinal flora were weaned onto either an OA-containing or a conventional diet without OA. At 2 months of age the colonized rats showed an increased DTH reaction to OA, but they did not have any anti-OA antibodies in serum. The rats were then immunized intracutaneously with OA in Freund's complete adjuvant. After immunization the colonized rats fed the conventional diet had a significantly higher DTH reaction to OA and significantly higher serum levels of IgE anti-OA antibodies than the uncolonized rats on the same diet. The colonized rats eating the OA-containing diet showed a 73% decrease in the DTH reaction to OA and also significantly lower levels of IgE and IgG antibodies against OA compared with the colonized rats fed conventional diet. The dams colonized as adults by the OA-producing E. coli developed IgE anti-lipopolysaccharide antibodies in serum while the pups colonized via the dams at birth did not. Neonatal colonization with an E. coli strain producing OA resulted in increased DTH reactivity against OA and priming for secondary IgE anti-OA response. Feeding the animals an OA-containing diet from weaning abrogated this intestinally induced hypersensitivity and rendered the animals orally tolerant to OA.