Evaluation of outer membrane protein P2 of nontypeable Haemophilus influenzae as a potential vaccine antigen
Ostberg, Karen Lynn
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Nontypeable Haemophilus influenzae (NTHI) is an important human pathogen. This organism is a significant cause of otitis media in children and exacerbations in adults with chronic obstructive pulmonary disease. A vaccine to prevent infection by NTHI would have a great impact on the morbidity and mortality associated with these diseases, as well as reduce healthcare costs. Outer membrane protein P2 was originally considered as a potential vaccine antigen for NTHI because it is a target of the human immune response. In addition, animal studies showed P2 induced bactericidal antibodies, which are correlated with protection. Further investigation indicated that infection with NTHI largely induces strain specific immune responses, and this strain specificity was linked to the antigenic heterogeneity of P2. As a result, interest in P2 as a vaccine antigen quickly waned. However, several studies have indicated that P2 is capable of inducing cross-reactive antibody responses. The goal of this work was to investigate further the possibility of overcoming strain specific immune responses to NTHI through immunization with recombinant P2. Initial experiments involving whole cell immunization confirmed the ability of NTHI to induce cross-reactive antibody responses and identified three strains which induced antibodies with a broad range of cross-reactivity. Cloning of the ompP2 gene from these three strains resulted in recombinant P2. Purified recombinant P2 was administered to mice either subcutaneously or intranasally. Both routes of immunization were immunogenic by quantitative ELISA. Whole cell ELISA and flow cytometry indicated that mucosal immunization induced antibodies to epitopes on the surface of NTHI, while subcutaneous immunization induced antibodies to non-surface exposed epitopes. Furthermore, antibodies induced by mucosal immunization recognized epitopes on multiple strains of NTHI. These studies are the first to examine either systemic or mucosal immunization with a purified recombinant P2. My results show that mucosal immunization with recombinant P2 induces cross-reactive antibodies, despite the strain specificity commonly seen following infection or immunization with the whole organism. These results have important implications for the potential use of P2 as a vaccine antigen for NTHI and indicates that further study of P2 as a vaccine antigen is warranted.