Differential Expression Of Toll-like Receptor Genes Between Lymphoid Tissues Of Marek’s Disease Virus Infected And Noninfected Chickens

Chicken Toll-like receptors have been extensively studied in response to infection of pathogens. This demonstrates that TLRs play pivotal roles in resisting the invasion of pathogens. However, limited work has been done to investigate the role of TLRs against MDV infection. In this study, we aimed at investigating the response of TLRs and down-stream genes to Marek’s disease virus (MDV) infection. Forty one-day-old chicks were randomly divided into two groups, with20chicks infected with MDV-GA strain and20chicks mock-infected. Four chickens were euthanized respectively from infected and age-matched non-infected groups at4,7,14,21, and28days post-infection (dpi). Bursas, spleens, and thymuses were removed. The differential expression of TLR genes, including TLR3, TLR5, TLR7, TLR15, and TLR21, and down-stream gene of TLR7, MyD88gene in lymphoid tissues of MDV-infected and non-infected chickens was determined by real-time PCR at five time points. Meanwhile expression of down-stream genes of MyD88in spleens, including TRAF3, TRAF6, IFNA, IFNB, and IL6gene was detected by real-time PCR at14and28dpi. The results are as follows:1) In spleens, expression of TLR7and MyD88gene was up-regulated at14dpi and down-regulated at28dpi in MDV-infected compared to non-infected spleens. Furthermore, expression of TRAF6and IFNB gene was up-regulated, and TRAF3, IFNA, IL6gene showed increasing trends in MDV-infected compared to non-infected spleens at14dpi. The results indicated that TLR7and its down-stream genes were response to MDV infection at14dpi. However, the function of TLRs was impaired when infection enter tumor transformation phase in spleens.2) In bursas, TLR3and TLR15gene were up-regulated at7and4dpi, respectively. While the expression of TLR3and TLR15gene was down-regulated in MDV-infected compared to non-infected spleens at28dpi. It indicated that TLR3and TLR15might be involved in response to MDV infection in bursa at early phases. However, the function of TLRs was inhibited when infection enter tumor transformation phase in spleens.3) No differential expression of TLR5and TLR21gene was observed between MDV-infected and non-infected lymphoid tissues, which indicated that TLR5and TLR21were not involved in response to MDV infection.4) Compared to spleens and bursas, no differential expression of TLR genes was observed between MDV-infected and non-infected thymuses, which indicated that thymus was not response to MDV infection mediated by TLRs.