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

Abstract

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 (HA₁) 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-HA₁ IgA antibody in the intestine and specific anti-HA₁ IgG antibody in the serum (p < 0.05). Additionally, when the splenic lymphocytes isolated from immunized mice were stimulated by HA₁ 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-HA₁-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.

Keywords:

• avian influenza
• hemagglutinin
• Lactococcus lactis
• mucosal immunity

Acknowledegments

The authors gratefully acknowledge J Kok from University of Groningen in The Netherlands for providing the Lactococcus lactis MG1363 strain and pMG36E plasmid and sharing his expertise.

Financial & competing interests disclosure

This work was supported by the Doctoral Program Research Fund of National Higher Education (No. 20060307013), Youth Science and Technology Innovation Grand of Nanjing Agricultural University (No. 090600321) and Research Fund for the Doctoral Program of Higher Education of China (No. 20100097120007 and No. B200606). This work was also supported by the National Science Grant of China (No. 30871858). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Additional information

Funding

This work was supported by the Doctoral Program Research Fund of National Higher Education (No. 20060307013), Youth Science and Technology Innovation Grand of Nanjing Agricultural University (No. 090600321) and Research Fund for the Doctoral Program of Higher Education of China (No. 20100097120007 and No. B200606). This work was also supported by the National Science Grant of China (No. 30871858). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript