Researchers are currently involved in a strong effort to find a safe and effective vaccine against highly pathogenic avian influenza H5N1 viruses. Toward that goal, we obtained soluble recombinant flagellin (FliC) of Salmonella typhimurium to be used as a mucosal adjuvant for H5HA subunit vaccine development. Intranasal immunization of H5HA antigen with recombinant FliC protein in an oil-in-water emulsion increased H5HA-specific IgG and IgA titers in sera, bronchoalveolar lavage fluids (BALFs), and nasal washes. Use of FliC adjuvant for intranasal immunization further augmented B-cell responses in mucosal environments via increased IgA titers in BALFs and nasal washes. Increases in IgA and IgG titers through the use of FliC adjuvant in intranasal immunization correlated with higher neutralizing antibody titers in sera and BALFs and higher numbers of IgG- and IgA-secreting B cells in spleen and cervical lymph nodes. High levels of IL-17A cytokine production were also found in stimulated T cells of spleen and cervical lymph node cells, only by intranasal immunization particularly with the use of FliC adjuvant in oil-in-water emulsions. These findings may provide useful information toward the development of H5HA mucosal influenza vaccines.
