IMMORTALIZATION OF FISH LYMPHOCYTES AND F ISH INTERFERON GENE

Fish interferon (FIFN) is expected to have a potential to play an impo rtant role in the prevention of viral infections in fish farming. Sinc e a very small amount of FIFN is produced in fish body, it is quite di fficult to purify it. Therefore, we first tried to immortalize lymphoc ytes of the Japanese flounder using a variety of oncogenes and found t hat the cotransfection of c-sa-ras and c-fos was most effective. One o f these immortalized lymphocyte cell lines, HL8, produced FIFN which w as a glycoprotein of about 16 kDa. The cloned FIFN cDNA is composed of a signal peptide region coding 30 amino acids and a structure gene co ding a 108 amino acid chain including a potential Asn-linked glycosila tion site. The recombinant FIFN (rFIFN) produced by mammalian BHK-21 c ells inhibited the propagation of three fish viruses in cell lines and infection with hirame rhabdovirus in rainbow trout by oral administra tion. The minimum effective amount of the rFIFN was 200 pg/g-body weig ht.