Effects of ligands for Toll-like receptors 3, 4, and 21 as adjuvants on the immunogenicity of an avian influenza vaccine in chickens.

Avian influenza viruses (AIV) are of great concern to the worldwide community as well as the poultry industry. Although existing vaccines are successful in limiting the spread of the virus, these vaccines do not eliminate virus shedding into the environment. As a result, it is of great importance to enhance the efficacy of existing AIV vaccines. Therefore, the objective of the present study was to utilize the immunostimulatory Toll-like receptor ligands poly I:C, lipopolysaccharide (LPS), and CpG DNA motifs, either alone or in combination with each other, as adjuvants to enhance the immunogenicity of an inactivated AIV vaccine. Chickens were vaccinated twice, 14 days apart. Antibody-mediated responses were assessed by collected sera and lacrimal secretions, while cell-mediated immunity was assessed by stimulating splenocytes from vaccinated chickens in vitro with the vaccine antigen. The results suggest that CpG alone served as the best single-ligand adjuvant compared to poly I:C or LPS, as it significantly enhanced antibody-mediated responses, as determined by enzyme-linked immunosorbant assay. Furthermore, upon combining CpG with poly I:C, a robust antibody-mediated and cell-mediated immune response was elicited, resulting in an enhanced hemagglutination inhibition titer and splenocyte proliferation respectively. Future studies may be aimed at assessing the efficacy of the poly I:C and CpG combination adjuvant in protecting against AIV infection.