Abstract
Marek's disease is an immune suppressive disease that threatens poultry industry. It is controlled by vaccination against MDV. However, the post-vaccination immune mechanisms remain vague. Therefore, the objective of this study was to examine the transcripts of the cellular immune responses of two commercial vaccines (CVI988 and HVT strains) compared to control non-vaccinated chickens through the analyses of several cytokine responses. The mRNA was extracted from the bursa of Fabricius and thymus, sampled at 7, 14 and 21 days post-immunization (PI) of both vaccinated and control groups. Several pro-inflammatory and anti-inflammatory cytokine gene expressions were analyzed using RT-PCR. Early significant up-regulation of IFN-γ, a pro-inflammatory cytokine was observed. Also, upregulation of other cytokines like IL-1β and IL-6 was observed at different time points along with minimal non-significant expression of inducible nitric oxide synthase (iNOS) in both of vaccinated groups. Meanwhile, a late upregulation of the anti-inflammatory cytokine, IL-10 was only noticed by 21 day PI. These findings show that both vaccinal strains mimic the natural infection by inducing early cell-mediated inflammatory responses, while devoid the long-term immune suppressive effect of natural infection. Additionally, vaccination triggers anti-tumor cell-mediated responses as indicated by the late increase of IL-10 expression. Furthermore, the observed cytokine responses following CV1988 strain supports its previously reported efficacy over HVT strain, making the Rispens vaccine more suitable candidate for Egyptian field conditions. Additionally, the early observed up-regulation of IFN-γ cytokine nominates its administration as an adjuvant with the Rispens vaccine; this may provide synergistic immunomodulatory capacities to the available vaccines and better levels of protection.

Key words: Marek's disease vaccines, Pro-inflammatory Cytokines, RT-PCR, Chicken