Oral Immunization with Recombinant Lactococcus Lactis Expressing the Hemagglutinin of the Avian Influenza Virus Induces Mucosal and Systemic Immune Responses

Aims: The aim of the study in this article is to explore a safe, convenient and effective oral mucosal vaccine candidate against highly pathogenic avian influenza.

Materials & Methods: We have constructed an oral mucosal vaccine, LL36EH, by use of the genetically stable θ-replicating vector pMG36E, which expressed the fusion protein hemagglutinin 1 (HA(1)) in a live carrier, Lactococcus lactis MG1363. LL36EH was administered orally to mice three times at 2-week intervals. The specific serum IgG and mucosal IgA antibodies were detected and evaluated at different time points after immunization.

Results: The results showed that LL36EH could significantly induce specific anti-HA(1) IgA antibody in the intestine and specific anti-HA(1) IgG antibody in the serum (p < 0.05). Additionally, when the splenic lymphocytes isolated from immunized mice were stimulated by HA(1) antigen in vitro, splenic lymphocyte proliferative reaction and secretions of the cytokines IFN-γ and IL-4 were also significantly increased. Most importantly, the mice that were immunized with LL36EH were protected to some extent against lethal challenge of the H5N1 virus.

Conclusion: LL36EH triggered the anti-HA(1)-specific humoral and cellular immune responses and protective immunity. Therefore, oral immunization with LL36EH could be a valuable strategy against highly pathogenic avian influenza for humans and animals.