Expression of genes related to the early immune response in rainbow trout (Oncorhynchus mykiss) after viral haemorrhagic septicemia virus (VHSV) infection.

In the last few years, many cytokine and other immune related genes have been identified in different teleost species, thus allowing their study at a molecular level. However, very little is known about their effect on fish antiviral responses. In the current work, we have studied the effect of viral haemorrhagic septicemia virus (VHSV) infection on the expression of different immune genes in rainbow trout (Oncorhynchus mykiss) through semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). We have studied the effect of the viral infection on the expression of different cytokines such as interleukin 1beta (IL-1beta) and transforming growth factor beta (TGF-beta), the CXC chemokine IL-8, and other immune genes such as inducible nitric oxide synthase (iNOS) and the class II major histocompatibility complex (MHC II). The virus induced an increased transcription of IL-1beta in the spleen, and to a lesser extent in the head kidney and liver at early times post-infection. IL-8 transcription was also significantly induced with the virus in the spleen at early times post-infection. TGF-beta transcription was significantly induced in VHSV infection in the spleen and liver. In the spleen, a significant induction of TGF-beta at day 1 post-infection was observed. A further significant increase occurred in the spleen and liver at day 7 post-infection. No effect of the virus on MHC II expression was ever observed while iNOS was induced in the spleen, head kidney and liver of VHSV-infected fish mostly at day 7 post-infection. These results constitute a first step towards the understanding of which molecules may have a role in antiviral defence in fish.