Neonatal colonization of rats induces immunological tolerance to bacterialantigens

We wanted to investigate the immunological events occurring in rats intesti nally colonized from birth (neonatally) or at adult age with an ovalbumin ( OVA)-producing Escherichia coil O6K13 strain, carrying type 1 pill. The neo natally colonized animals responded with lower delayed type hypersensitivit y (DTH) against OVA and lower levels of IgG antibodies against OVA, O6 lipo polysaccharide (LPS) and type 1 pill compared to age-matched controls. The IgG antibody response against the bystander antigen, human serum albumin (H SA), was lower in the neonatally colonized animals than in the controls co- immunized with HSA and E.coli, indicating a release of suppressive factors induced by the bacterial antigens. The adult colonized animals showed an in creased DTH and antibody response against OVA after immunization. They also had high pre-immunization levels of IgG anti-O6 LPS antibodies compared to controls. However, the relative increase in IgG anti-O6 LPS antibody level s after the immunization with dead E. coli was much lower in the adult colo nized animals. The present results suggest that neonatal animals develop to lerance against antigen on bacterial colonizers of the intestine. In additi on, this tolerance contains components of suppression.