Cell mediated immune response against virus in Atlantic salmon measured by T cell interferon gamma production

There is a need for more and better methods to test viral vaccine efficacy in Atlantic salmon. The adaptive immune responses mounted after vaccination of vertebrates against pathogens are classified as humoral (antibody mediated) and cell mediated immune (CMI) mechanisms. Humoral immune mechanisms have been well studied in fish and assays for antibody production exists for Atlantic salmon and other species. In contrast, CMI mechanisms in fish have received little attention despite their importance in prot ection against viral infection. This is mainly due to the lack of proper analysis methods. CMI responses against viruses are mediated by cytotoxic T-cells (CTLs), which kill virus-infected cells specifically and secrete large amounts of interferon gamma, a cytokine which induces antiviral activity in cells. Measurement of blood leukocytes, which secreteinterferon gamma upon challenge with virus, is frequently used to estimate CTL responses in mammals vaccinated against virus. At present, the ELISPOT metho d is the simplest and most sensitive method for enumerating antigen-specific CTLs. CTL mediated immune responses are known to exist in fish, but convenient assays of CTL activity for vaccine testing in Atlantic salmon and other fish species are lacking. A major goal of the present project is to establish an ELISPOT assay for interferon gamma secreting CTLs in Atlantic salmon. Such a methods could be of major importance for future testing of viral vaccines in this economically important species. The assay will be tested in fish surviving infections with IPN-virus or ISA-virus and in fish immunized with various IPN vaccines.