Abstract
In recent years, the H9N2 subtype of LPAI has become one of the most widespread diseases in poultry in the world, and infected poultry usually show no obvious symptoms, mainly in the form of reduced performance. However, when secondary infection with other pathogenic bacteria occurs, it can significantly increase the morbidity and mortality of poultry, causing huge losses to the poultry industry. At present, vaccination is still the most common way to prevent and control avian influenza, but the traditional vaccine has deficiencies such as short duration of maintaining immunity, poor mucosal immunity and re-enforcement of virulence. Probiotics for feeding have the advantages of green, safe, non-polluting, etc., and have become a more ideal antibiotic substitute for livestock and poultry farming. Microecological preparations using lactic acid bacteria as carriers to deliver antigenic proteins via the mucosal route have a wide range of applications. These products are safe and non-toxic, can be taken orally directly to stimulate the body to produce mucosal immunity, and have the probiotic effect of lactic acid bacteria. In this study, the HA2 gene, the main protective antigen of H9N2 AIV, was introduced into the constitutive and inducible expression systems of Lactobacillus casei, and the constitutive recombinant Lactobacillus casei pSIP409-p32-HA2/NC8 and inducible recombinant Lactobacillus casei pNZ8149-HA2/NZ3900 were constructed, and both of them were able to express the HA2 protein of avian influenza virus successfully. After immunisation of SPF chicks, both recombinant Lactobacillus strains induced mucosal and humoral immune responses in the organism and were able to effectively reduce viral emissions. Taken together, the constitutive pSIP409-p32-HA2/NC8 recombinant Lactobacillus is easy to produce and has a non-significant difference in immunocompetence from the inducible recombinant Lactobacillus pNZ8149-HA2/NZ3900, which is expected to be a novel agent for the prevention and control of H9N2 AIV.