Adjuvant effects of bacterium-like particles in the intranasal vaccination of chickens against Newcastle disease

Given that the respiratory mucosa is an important site for the initial replication of Newcastle disease virus (NDV), developing intranasal vaccines for chickens is an effective strategy to protect against this disease. The low immunogenicity of inactivated NDV administered by the mucosal route motivated us to identify a safe and potent adjuvant. Previous studies have shown that bacterium-like particles (BLPs), which serve as mucosal adjuvants, induce effective local and systemic immune responses through TLR2 signaling in both mammals and humans. Here, we report that BLPs could activate the innate immune system of chickens in a manner that was dependent on the combination of chicken TLR2 type 1 (chTLR2t1) and chicken TLR1 type 1 (chTLR1t1). The chicken macrophage-like HD11 cell line was stimulated with BLPs, resulting in the production of nitric oxide and the expression of the proinflammatory cytokines IFN-γ, IL-1β and IL-6. Chickens intranasally immunized with inactivated NDV vaccines mixed with BLP adjuvants exhibited significantly increased levels of local SIgA in their tracheal lavage fluid and as well as hemagglutination-inhibiting antibodies in serum samples. The strong systemic and local immune responses induced by BLP-adjuvanted vaccines provided 100 % protection against intranasal challenge with a lethal dose of virulent NDV without showing any signs of disease. These results indicate that BLPs should be considered for use as a potential mucosal adjuvant for inactivated NDV vaccines and other vaccines for poultry.