Virus infections are controlled by innate and adaptive cell-mediated cytotoxicity (CMC) in mammals. The cellular part of the innate immune system is represented by non-specific cytotoxic cells (NCC) and NK (natural killer) cells. These cells are able to kill xenogenic, allogenic and virus infected cells. However, virus infected cells are largely controlled by adaptive CMC, too. During this, virus-infected cells present MHC class I bound viral peptides on their surface to the T cell receptor (TCR) of CD8+ cytotoxic T cells (CTLs) [figure]
Sequence homologies between the piscine and mammalian MHC class I, TCR and its co-receptor CD8, suggest that antigen presentation in fish is MHC class I restricted like in mammals. While the expression of most immune-related molecules can only be indirectly determined through mRNA expression we have developed monoclonal antibodies to MHC class I and CD8alpha.
In most fish species, cytotoxicity has not been studied due to the lack of suitable methods and tools. In collaboration with Japanese and French partners we have established cytotoxicity assays using clonal rainbow trout and infected MHC class I matched target cells. For the generation of cytotoxic effector cells clonal rainbow trout are infected or are immunized by DNA encoding immunogenic viral proteins. Population-specific antibodies are used to enrich cytotoxic cells, and real time RT-PCR is used to determine the expression of immune-related genes.