Protection of chickens against H9N2 avian influenza virus challenge with recombinant Lactobacillus plantarum expressing conserved antigens

Avian influenza virus (AIV) is spreading worldwide and is a serious threat to the health of poultry and humans. In many countries, low pathogenic AIVs, such as H9N2, have become an enormous economic burden on the commercial poultry industry because they cause mild respiratory disease and decrease egg production. A recombinant Lactobacillus plantarum NC8 strain expressing NP-M1-DCpep from H9N2 AIV has been studied in a mouse model. However, it remains unknown whether this L. plantarum strain can induce an immune response and provide protection against H9N2 AIV in chickens. In this study, chickens that were orally vaccinated with NC8-pSIP409-NP-M1-DCpep exhibited significantly increased T cell-mediated immune responses and mucosal sIgA and IgG levels, which provided protection against H9N2 AIV challenge. More importantly, compared with oral administration of NC8-pSIP409-NP-M1-DCpep, intranasal administration induced stronger immune responses and provided effective protection against challenge with the H9N2 virus by reducing body weight loss, lung virus titers, and throat pathology. Taken together, these findings suggest that L. plantarum expressing NP-M1-DCpep has potential as a vaccine to combat H9N2 AIV infection.