Specific mucosal immunity and enhanced nasopharyngeal clearance of nontypeable Haemophilus influenzae after intranasal immunization with outer membrane protein P6 and cholera toxin.

Nontypeable Haemophilus influenzae (NTHi) is one of the leading pathogens in otitis media. Studies of vaccines against NTHi have focused on outer membrane proteins (OMPs). One outer membrane protein P6 is highly conserved among strains and is an attractive candidate for a subunit bacterial vaccine. In this study, mucosal immunity induced by intranasal immunization with P6 and cholera toxin (CT) was investigated in a mouse model. Intranasal immunization with P6 and CT evoked a good mucosal IgA as well as a systemic IgG response against P6. On the other hand, intranasal immunization with P6 alone induced a weak mucosal IgA response. Enzyme linked immunospot assay detected anti-P6 specific antibody producing cells in the nasopharyngeal mucosa of immunized mice. The protective response of intranasal immunization was demonstrated by enhancement of nasopharyngeal clearance of NTHi and inhibition of adherence of NTHi to cultured human epithelial cells. Based on these results, intranasal immunization with P6 and CT may be an effective approach to protect human from H. influenzae infections in the upper respiratory tract.