Importance of an immunodominant surface-exposed loop on outer membrane protein P2 of nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHI) frequently causes recurrent infections of the respiratory tract in humans, Previous indirect evidence suggested that a strain-specific immune response occurs following infection and that this: immune response is directed at an immunodominant epitope on the bacterial surface, To test this hypothesis, mice and rabbits were immunized with whole cells of a strain of NTHI and the antiserum was characterized the identify the antigens to which antibodies were directed. All animals made a prominent antibody response to the loop 5 region of the P2 molecule, which is the major outer membrane protein. Rabbit serum showed complement-dependent bactericidal activity. Adsorption of the immune serum with the loop 5 fusion peptide removed bactericidal activity and also abolished reactivity to PZ detected blv an immunoblot assay, an enzyme-linked immunosorbent assay, and a radioimmunoprecipitation assay. These data indicate that immunization with whole cells of NTHI results in a prominent antibody response which is directed at epitopes on the loop 5 region of the P2 molecule, Thus, a strain-specific immune response to NTHI occurs as a result of the expression of an immunodominant epitope on the P2 molecule.