Evaluation of Adjuvant Effect of Cytosine-Guanosine-Oligodeoxynucleotide in Meat-Type Chickens Coadministered In Ovo with Herpesvirus of Turkey Vaccine

Abstract

Herpesvirus of turkey (HVT) increases activation of T cells in 1-day-old chickens when administered in ovo. This study evaluated whether adding cytosine-guanosine oligodeoxynucleotides (CpG ODNs) to the HVT vaccine could enhance the adjuvant effect of HVT. We used a CpG ODN dose of 10 μg per egg. The experimental groups were (1) diluent-only control (sham), (2) HVT, (3) HVT+CpG ODN, (4) HVT+non-CpG ODN, (5) CpG ODN, and (6) non-CpG ODN control. Cellular response evaluation included measuring the frequencies of macrophages (KUL01⁺MHC-II⁺), gamma delta T cells (γδTCR⁺MHC-II⁺), CD4⁺, and CD8⁺ T cell subsets, including double-positive (DP) cells. In addition, CD4⁺ and CD8⁺ T cell activation was evaluated by measuring the cellular expression of major histocompatibility complex class II (MHC-II), CD44 or CD28 costimulatory molecules. An adjuvant effect was considered when HVT+CpG ODN, but not HVT+non CpG ODN, or CpG ODN, or non-CpG ODN, induced significantly increased effects on any of the immune parameters examined when compared with HVT. The findings showed that (1) HVT vaccination induced significantly higher frequencies of γδ⁺MHC-II⁺ and CD4⁺CD28⁺ T cells when compared with sham chickens. Frequencies of DP and CD4⁺CD28⁺ T cells in HVT-administered birds were significantly higher than those observed in the non-CpG ODN group. (2) Groups receiving HVT+CpG ODN or CpG ODN alone were found to have significantly increased frequencies of activated CD4⁺ and CD8⁺ T cells, when compared with HVT. Our results show that CpG ODN administration in ovo with or without HVT significantly increased frequencies of activated CD4⁺ and CD8⁺ T cells.

Keywords: cellular immunity; chickens; herpesvirus of turkey; immunocompetence; in ovo vaccination; toll-like receptor 21.