Toll-like receptors and interferon associated immune factors responses to spring viraemia of carp virus infection in common carp (Cyprinus carpio)

Pattern recognition receptor (PRR) toll-like receptors (TLRs), antiviral agent interferon (IFN) and the effector IFN stimulated genes (ISGs) play a fundamental role in the innate immune response against viruses among all vertebrate classes. Common carp is a host for spring viraemia of carp virus (Rhabdovirus carpio, SVCV), which belong to Rhabdoviridae family. The present in-vivo experiment was conducted to investigate the expression of these innate immune factors in early phase as well as during recovery of SVCV infection by real-time quantitative reverse transcriptase polymerase chain reaction. A less lethal SVCV infection was generated in common carp (Cyprinus carpio) and was sampled at 3, 6, 12 h post infection (hpi), 1, 3, 5, 7 and 10 days post infection (dpi). At 3 hpi, the SVCV N gene was detected in all three fish and all three fish showed a relative fold increase of TLR2, TLR3 and TLR7, IFNa1, ISG15 and Vig1. Viral copies rapidly increased at 12 hpi then remained high until 5 dpi. When viral copy numbers were high, a higher expression of immune genes TLR2, TLR3, TLR7, IFNa1, IFNa2, IFNa1S, IFN regulatory factor 3 (IRF3), IRF7, interleukin 1β (IL1β), IL6, IL10, ADAR, ISG15, Mx1, PKR and Vig1 were observed. Viral copies were gradually reduced in 5 to 10 dpi fish, and also the immune response was considerably reduced but remained elevated. A high degree of correlation was observed between immune genes and viral copy number in each of the sampled fish at 12 hpi. The quick and prolonged elevated expression of the immune genes indicates their crucial role in survival of host against SVCV.