Trout VH Gene Specificity For IHNV; Applications To Disease Resistance Studies   Stephen L. Kaattari1 and Teresa D. Lewis2   1Dept. of Environmental Sciences, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062, USA; 2Present address:  Dept. of Microbiology, Oregon State University, Corvallis, OR 97331         The germline repertoire of antibody genes produces the initial complement of antibody binding sites for any animal. This repertoire is expanded and refined in specificity via somatic hypermutation during mammalian immune responses.  Many have postulated that fish; however, may not be capable of somatic hypermutation. If this is so, the capacity of a fish to resist infection may be completely dependent upon this original germline repertoire. Therefore the characterization of this repertoire and the potential differences among various stocks may serve as useful genetic markers for ascertaining resistant and susceptible fish. We have initiated these studies by examining the antibody (VH) genes encoding specificities for two antigens, a common haptenic antigen, trinitrophenyl- (TNP), and infectious hematopoietic necrosis virus, IHNV, an economically important salmonid pathogen.  VH gene sequences were identified by producing VH cDNA from immunoadsorbed, or 'panned', antigen-reactive trout lymphocytes obtained over the course of the specific immune response. Sequence analysis enabled us to ascertain that TNP-specific antibodies employed the VH gene family V, whereas antibodies recognizing IHNV (ostensibly the G protein) employed VH gene family IV. Quantitative gene titration indicated that family IV possesses many more VH genes than does family V (~30 vs. 5). Implications of these results on antibody repertoire development and assessment, with a view towards stock evaluation are discussed.  This work was supported by N.R.I. (U.S.D.A.) grants #97-03915 and 95-37024