Differential Regulation of chTLR3 by Infectious Bursal Disease Viruses with Different Virulence In Vitro and In Vivo.

Toll-like receptor 3 (TLR3) is one of the TLRs whose ligand is double-stranded RNA (dsRNA). Infectious bursal disease virus (IBDV) is a dsRNA virus that could be recognized by TLR3. The purpose of this study was to determine the role of the virulence of IBDV on the expression of chicken TLR3 (chTLR3). For this purpose, the levels of chTLR3 expression and its downstream effectors, Interferon beta (IFN-beta) and Interleukin 8 (IL-8), were detected and analyzed after infection of IBDV field isolates with differential virulence in vitro (chicken embryo fibroblast and/or chicken peripheral blood mononuclear cells) and in vivo (commercial Three-Yellow chicken). The results showed that chTLR3 was activated by IBDV, resulting in the expression of antiviral IFN-beta and chemokine IL-8. The expression of chTLR3, IFN-beta, and IL-8 correlated well with the virulence of IBDV as the more virulent the IBDV strain that was used, the more pronounced was the expression of chTLR3, IFN-beta, and IL-8. These results suggest that chTLR3 is involved in the pathogenesis of IBDV in commercial chickens and its downstream effectors (IFN-beta and IL-8) might play an important role in this process.