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 molecularlevel. However, very little is known about their effecton 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 1 beta (IL- 1 beta) and transforming growth factor (TGF-beta), the CXC chernokine 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-1 beta 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 ill 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 signi fie ant increase occurred in the spleen and liverat day 7 post-infection. No effect of the virus on MHC II expression was ever observed while NOS 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. (c) 2004 Elsevier Ltd. All rights reserved.