The immune enhancement effects of recombinant NDV expressing chicken granulocyte‐macrophage colony‐stimulating factor on the different avian influenza vaccine subtypes

Avian influenza is an acute and highly contagious infectious disease that is caused by the influenza virus. Avian influenza has been widely spread all over the world, has caused property loss and has threatened human life and security. In this study, the recombinant plasmid rClone30‐chGM‐CSF was constructed and rescued to the recombinant virus rClone30‐chGM‐CSF successfully. After 8 days of immunization with the recombinant virus, the titre of NDV HI (haemagglutination inhibition) antibodies in SPF chickens reached its peak. The average titre of the rClone30‐chGM‐CSF group reached 6 log2 and was significantly higher than the protection critical value of 4 log2; the titres of the rClone30 group and the blank group were 2.86 log2 and 1 log2, respectively, indicating that the recombinant virus can effectively improve the NDV antibody titre. Then, SPF chickens were co‐immunized with the recombinant virus and with three different vaccine subtypes of inactivated avian influenza. The results indicated that the SPF chickens that were immunized with the vaccine plus rClone30‐chGM‐CSF showed significantly higher avian influenza antibody levels than those in the single vaccine groups. Furthermore, the SPF chickens in the vaccine plus rClone30‐chGM‐CSF group elicited stronger CD4+ and CD8+ T‐cell proliferative responses and also had upregulated transcriptional levels of interleukin‐1β (IL‐1β), IL‐4, IL‐6 and IL‐17 compared with those in the single vaccine groups. This study has shown that the recombinant virus expressing chicken granulocyte‐macrophage colony‐stimulating factor (chGM‐CSF) can be used not only as an NDV vaccine to effectively improve the titre of NDV antibodies but also as a biological adjuvant to enhance the immune effects of the avian influenza vaccine. Therefore, this recombinant virus can also be used as a biological adjuvant for other poultry vaccines.