Recombinant Lactobacillus plantarum expressing HA2 antigen elicits protective immunity against H9N2 avian influenza virus in chickens

Low pathogenic H9N2 subtype avian influenza virus (AIV) can lead to moderate respiratory symptoms and low egg production rates in poultry. Due to its immunologic suppression, other various infectious pathogens give rise to the co-infection of hosts, causing heavy economic losses in the commercial poultry industry in both China and worldwide. Therefore, it is time to explore a novel, safe, and effective vaccine. We have already made use of the surface of Lactobacillus plantarum to display AIV HA2 (NC8-pSIP409-pgsA'-HA2), which demonstrated that it has a good immunogenicity. In this study, by evaluating the immune protection effect of NC8-pSIP409-pgsA'-HA2 on chickens, we found that the hemagglutination inhibition (HI) antibodies, specificity IgG antibody in chickens, the sIgA titer in broncho alveolar lavage fluids (BALF), and the T cell response were increased notably after oral vaccination with NC8-pSIP409-pgsA'-HA2. In addition, weight loss, lung titers, and lung pathologies were improved when chickens were orally vaccinated with NC8-pSIP409-pgsA'-HA2 after challenge with H9N2 AIV. This strategy lays the foundation for the development of recombinant L. plantarum oral vaccines in the prevention of AIV.