The F41 adhesin of enterotoxigenic Escherichia coli: inhibition of adhesion by monoclonal antibodies.

The anti-adhesive properties of 23 specific monoclonal antibodies (MAbs) against the F41 adhesive fimbrial antigen of enterotoxigenic Escherichia coli (ETEC) were studied in brush border adhesion inhibition tests and haemag-glutination inhibition tests with four F41-positive E. coli strains and purified F41 antigen. These MAbs recognize five epitope clusters, F41-1 to F41-5. It was proven that these epitope clusters were located on the 29 kDa F41 major fimbrial subunits. All nine MAbs against epitope cluster 1 inhibited the adhesion of F41-positive strains to brush border preparations of calf and pig intestines and the haemagglutination of sheep and guinea pig erythrocytes by the F41-positive strains and purified F41 antigen. The fourteen MAbs against the other four epitope clusters showed very little to no blocking of adhesion and haemagglutination. The results indicate that the adhesion of F41 to intestinal epithelial cells is mediated by the same domain of the 29 kDa F41 major fimbrial subunit(s) as the adhesion of F41 to erythrocytes. Irrespective of their epitope specificity F41 MAbs protected infant mice against a challenge with F41-positive ETEC. MAbs against all epitope clusters partly protected piglets against challenge with F41-positive ETEC in a similar way. Therefore, we conclude that direct blocking of the receptor binding site located on the major fimbrial subunit is not the main mechanism how antibodies protect against ETEC infection.