Inhibition by Lipopolysaccharide (Endotoxin) of Antibody Response of Rabbit to Common Antigen of Enterobacteriaceae.

A common antigen (CA) is present in many species and serogroups of enteric bacteria, but only the antigen from E. coli O14 engenders CA antibodies in the rabbit upon intravenous injection. The ethanol soluble fraction of the former, however, induces the formation of CA antibodies. The present study has revealed that lipopolysaccharides (endotoxins) inhibit this CA antibody response. This inhibition was observed regularly when CA and lipopolysaccharides were injected as mixtures, but not when administered separately, although simultaneously, into different veins. Injection of mixtures prepared in ethanol were even less immunogenic than those prepared in water. A single preparation of lipoid A also inhibited the CA antibody response. It is postulated that the poor immunogenicity of enteric bacteria, other than E. coli O14, is due to the inhibitory effect of the lipopolysaccharide on the fully immunogenic CA.