Research On Expression Level Of Correlated Gene Of ILTV In Latency

In this study, three pair of primers flanking the ICP4 gene were designed according to the published nucleotide sequence of the ILTV strain SA2. The ICP4 gene of the ILTV strain WG was obtained by PCR and the nucleotides of the ICP4 gene ware sequenced. Nucleotide sequence and the deduced amino acid comparisons of the ICP4 gene of ILTV strain WG with that of ILTV strain SA2 and different Alphaherpesvirus found that the ICP4 gene was relatively conserved among different ILTV strains, the homology of the nucleotide sequence and the deduced amino acid were 99.7% and 99.1%, but very low between different Alphaherpesvirus. Detection of virus gene in latently infected trigeminal ganglia(TG) indicate that ICP4-specific RNA was present on days 10 to 60 after infected with ILTV strain WG, but gB, gC and TK specific RNA was absent.SPF chickens were infected with ILTV strain WG and intravenously injected with Dexamethasone (DEX) at 39 days post infection to initiates reactivation. Infectious virus was detected at 5,9,10,11,12,39 days post infection and DEX treatment (1, 2, 3, 5, 6, 7, 8 days) by detecting virus genome DNA. Trigeminal ganglion (TG) was collected from sacrificed chickens before infection and at day 6, 10, 20 and 30 post-infection as well as at day 2, 4, 7, 10 and 30 after DEX treatment. Samples were subjected to nucleic acid extraction and processed for real-time RT-PCR to quantification analysis the expression of ICP4, IFN-γand IL-18 transcripts. The results indicate that SPF chickens were infected and reactivated successfully. Low-level of ICP4 gene expressed in the absence of detectable reactivation, this low-level expression of ICP4 gene provide antigenic stimulus to maintain inflammatory cells response and trigger IFN-γand IL-18 secretion in ganglia, so this can maintain virus in latent state and not reactivate to infect other healthy host. After DEX treatment, the expression of IFN-γwas at a maximum level on day 2, so we concluded that IFN-γfunction to suppression the reactivated ILTV infection. Although there is no obvious difference in IL-18 expression before and after DEX treatment, we hypothesize that IFN-γfunctions to rapid suppression of ILTV with IL-18 once virus was reactivated. So this study will be a method to confirm whether the poultry is in latency and all kinds of vaccines lead to latency, as well as provide a framework for further studying the function of ICP4 gene, confirming latency-related gene and the relativity of persistent expression of ILTV antigen and cell immunity in trigeminal ganglia in latently.