Characterization of the gene encoding a 26-kilodalton protein (OMP26) fromnontypeable Haemophilus influenzae and immune responses to the recombinantprotein

A 26-kDa protein (OMP26) isolated and purified from nontypeable Haemophilus influenzae (NTHI) strain 289 has been shown to enhance clearance of infect ion following pulmonary challenge with NTHI in rats. DNA sequence analysis revealed that it was 99% identical to a gene encoding a cell envelope prote in of the H. influenzae Rd strain (TIGR accession no. HI0916). The deduced amino acid sequence revealed a hydrophilic polypeptide rich in basic amino acids. Restriction fragment length polymorphism analysis suggested that the OMP26 gene was relatively conserved among isolates of NTHI. Analysis of th e deduced amino acid sequence of the OMP26 gene from 20 different isolates showed that similarity with NTHI-289 ranged from 96.5% (1 isolate) to 99.5% (14 isolates), Two recombinant forms of OMP26, a full length 28-kDa protei n (equivalent to preprotein) and a 26-kDa protein lacking a 23-amino-acid l eader peptide (equivalent to processed protein), were assessed in immunizat ion studies for the ability to induce an immune response that would be as e ffective as the native protein in enhancing the clearance of NTHI following pulmonary challenge in rats. Immunization with the recombinant protein tha t included the leader peptide was more effective in enhancing pulmonary cle arance, and it induced a better cell-mediated response and higher titers of systemic and mucosal antibody. This study has characterized a 26-kDa prote in from NTHI that shows significant potential as a vaccine candidate.