We briefly review our recent studies on in vitro and in vivo virus-specific cell-mediated cytotoxicity in clonal ginbuna crucian carp. We have demonstrated specific cell-mediated cyototxicity against virus-infected cells, employing clonal ginbuna crucian carp (S3n clone) and the syngeneic cell lines (CFS) established from the S3n clone. Moreover, we have demonstrated an in vivo role of specific cytotoxic cells against viral infection, using CHNV which has a virulence to ginbuna. We found that 1) there is an inverse relationship between cytotoxic activity and viral load and 2) adoptive transfer of immune leukocytes prevented viral infection. Viral titers of tissues from infected fish were remarkably reduced 8 days after infections when specific cytotoxic activity reached a peak. This result suggested that specific cytotoxic cells were responsible for the early control of CHNV replication. On the other hand, CHNV-specific antibody increased after virus was eliminated by cytotoxic activities. These results suggested that specific cytotoxic cells of fish play an important role in specific immunity to viruses.
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