Abstract
Highly pathogenic avian influenza (HPAI) H5N1 viruses cause serious infection in both human and avian, and it is necessary to provide a safe and effective mucosal vaccine for protection of respiratory route. In our study, we used the recombinant proteins of type IIb heat labile enterotoxin B subunit (LTIIb-B5) and flagellin (FliC) as mucosal or systemic adjuvants to investigate recombinant H5N1 subunit HA (rH5HA) vaccine development. Three -doses immunizations were conducted in BALB/c mice through intranasal (i.n.) or intramuscular (i.m.) immunization. Our results showed that LTIIb-B5 as an adjuvant induced higher neutralization antibodies and enhanced IgA secretion in respiratory route through nasal administration. Combined with the inactivated H5N1 virus vaccine (NIBRG-14), rH5HA proteins coupled with LTIIb-B5 and FliC were also investigated for a prime-boost immunization (i.m./i.n.) strategy. Inactivated vaccine priming followed by rH5HA coupled with LTIIb-B5 boosting elicited higher neutralization antibodies against homologous and heterologous clades of H5N1 virus strains. Taken together, the study demonstrated that LTIIb-B5 is a potential and useful molecular adjuvant that can be used with subunit vaccines to elicit both mucosal and systemic immunities against multiple subtypes of H5N1 influenza viruses.