The activation of the antiviral pathway in ILP cells correlated to the virulence of IBDV at the early stage of infection was further investigated by detecting the expressions of TLR3, IRF7, IFN-α/β, PKR, OAS and Mx in birds infected with the attenuated vaccine strain B87 and then compared with those in the birds infected with the HLJ0504-like vvIBDV strain NN1172. This evidence concerns the gene MX1 and infection.