Reactivity of antibodies against conserved regions of pilins of Haemophilus influenzae type b.

To identify epitopes on pilins of Haemophilus influenzae type b (Hib) that may also be immunologically available on assembled pili, antisera were developed against eight synthetic peptides that represent conserved and hydrophilic regions of Hib pilin. Seven of the eight peptides were immunogenic. Binding of the anti-peptide antibodies to purified pili of Hib strain Eagan was weak. However, when the purified pili were denatured by heating, binding of the anti-peptide antibodies improved considerably, suggesting that the epitopes defined by the peptides were more available for anti-peptide antibody binding on the denatured pilins than on purified pili. On Western blot analysis, strain variation was seen in the binding of some of the anti-peptide antibodies, notably those directed against peptides in the N-terminal half of the pilin. Thus, when pilins are assembled into pili, the epitopes defined by the seven immunogenic peptides appear to be altered so that binding of the anti-peptide antibodies is greatly reduced.