Nasal-associated lymphoid tissue immunity and vaccine development.

Nasal vaccination is an effective therapeutic regimen for preventing upper respiratory infectious diseases. In the development of nasal vaccine, an appropriate adjuvant is required. In the present study, we examined the efficacy of fms-like tyrosine kinase receptor-3 ligand (Flt3L) as a mucosal adjuvant. Mice were immunized intranasally with Flt3L and P6 protein of nontypeable Haemophilus influenzae (NTHi), and P6-specific immune responses were examined. In addition, NTHi challenges were performed and the level of NTHi was quantified in nasal washes. Nasal vaccination with P6 and Flt3L induced an increase in the number of dendritic cells in nasal-associated lymphoid tissue. P6-specific nasal wash immunoglobulin (Ig)A and serum IgG titers were elevated significantly after nasal immunization. Enhanced NTHi clearance from the nasopharynx was also observed. These results indicate the potential of Flt3L as an effective mucosal adjuvant and suggest that nasal vaccination with P6 and Flt3L might be an effective regimen for the induction of NTHi-specific protective immunity.