KILLED CAMPYLOBACTER ELICITS IMMUNE-RESPONSE AND PROTECTION WHEN ADMINISTERED WITH AN ORAL ADJUVANT

The heat-labile toxin (HLT) of enterotoxigenic Escherichia coli (ETEC) is a potent oral adjuvant. We determined whether the ETEC HLT could b e mixed with killed campylobacter to induce an immune response protect ive upon subsequent challenge with live pathogens. Mice were immunized orally three times with 10(9) sonicated campylobacter with or without 25 mug of ETEC HLT, and humoral immune responses in intestinal lavage fluids measured by, ELISA. Whereas 10(9) live bacteria induced strong intestinal IgA responses, killed bacteria did not unless ETEC HLT was also added. The magnitude of the antibody, response was dependent on the amount of antigen given. The ETEC HLT given with bacteria also ind uced a potent cross-reaction with cholera toxin. The latter had an adj uvant effect in mice similar to that of ETEC HLT. Protection against c olonization was studied in mice and rabbits. In contrast to non-immune animals, those given live organisms or sonicated cells mixed with ETE C HLT quickly cleared homologous, but not heterologous, Lior serotypes of Campylobacter upon challenge. These data show for the first time t hat ETEC HLT can potentiate an immune response to killed campylobacter that promotes a rapid clearance of live pathogens from the intestine.