TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Nonspecific Cytotoxicity In Channel Catfish, Ictalurus punctatus, After DNA Vaccination C. Chitmanat, L. Jaso-Friedman, D. Evans, and Steven Poet Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602 American fish consumption has dramatically increased at the same time that wild fish stocks are in decline. For this reason, the commercial catfish farming industry is rapidly growing in order to provide sufficient high quality fish protein. Unfortunately, channel catfish virus can cause serious losses for catfish farmers. Without effective antiviral therapies, vaccination and quarantine are the only options for controlling channel catfish virus disease. DNA vaccination is a novel method to produce immunizing protein, in vivo, that elicits both humoral and cellular immunity. As nonspecific immunity is the first line of antiviral host defense, the objective of this study was to determine if DNA vaccines could induce a nonspecific cytotoxic response in channel catfish. Channel catfish fingerlings were immunized with either a plasmid encoding a reporter gene (pCMV-b), a plasmid without a gene insert [pcDNA 3.1 (+)], or saline as control. Nonspecific cytotoxicity in the two plasmid-injected groups was increased compared with saline-injected fish, but there was no difference in cytotoxicity between the plasmid-injected groups. These results suggest that unmethylated CpG-like motifs in the plasmid backbone of DNA vaccines are able to induce nonspecific cytotoxic activity. To test this hypothesis, catfish were injected with either unmethylated plasmid or DNase treated plasmid. Catfish injected with DNase treated plasmid had decreased nonspecific cytoxicity when compared with catfish injected with intact plasmid. These findings suggest that the plasmid backbone of DNA vaccines can enhance nonspecific cytotoxicity in channel catfish. Further studies are underway to evaluate the role of plasmid CpG motifs in channel catfish DNA vaccines. Additionally, the cooperation between the nonspecific immune enhancement from the plasmid vector and the specific immune induction from an expressed antigen gene insert will be elucidated. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page