Immunity to heat-labile enterotoxins of porcine and human Escherichia coli strains achieved with synthetic cholera toxin peptides.

Antiserum to a synthetic peptide, CTP3, consisting of residues 50 to 64 of the B subunit of cholera enterotoxin (CT), a sequence which is conserved in heat-labile enterotoxins from Escherichia coli strains of human (H-LT) or porcine (P-LT) origin, cross-reacted with and neutralized all three enterotoxins. It also cross-reacted with genetically engineered chimeric B subunit proteins in which H-LT amino acids had been substituted for the corresponding residues in P-LT. Antisera against another CT peptide, CTP1, consisting of residues 8 to 20, were weakly cross-reactive with H-LT but not with P-LT, whereas antisera against four other CT peptides were not cross-reactive with the heterologous enterotoxins. A single dose of CTP3-linked tetanus toxoid, by itself nonimmunogenic, primed rabbits to a vigorous immune response to subsequent administration of single, small, subimmunizing doses of any of the three enterotoxins.