28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Increases In Short Term In Vivo Expression Of Natural Resistance-Associated Macrophage Protein, Nramp, In Striped Bass (Morone saxatilis) Following Mycobacterial Challenge Erin J. Burge1, David T. Gauthier1, Christopher A. Ottinger2, Peter A. Van Veld1 1 College of William & Mary, Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062; 2 U.S. Geological Survey, Leetown Science Center, Fish Health Branch, 1700 Leetown Road, Kearneysville, WV 25430 Mycobacteriosis in wild, Chesapeake Bay striped bass (Morone saxatilis) is an emerging disease with important implications for the viability of a large commercial and recreational fishery.  Striped bass and its hybrids are among the most important species currently produced by governmental and private aquaculture and outbreaks of mycobacteriosis in cultured populations are problems for mass production.  The natural resistance-associated macrophage protein 1 gene, Nramp1, has been shown to encode an integral membrane protein that confers resistance to mycobacterial infection in mice. The striped bass genome also contains an Nramp-like gene (MsNramp) that is highly expressed during experimental infection with mycobacteria.  Laboratory-reared striped bass were injected intraperitoneally with 1.4x106 colony forming units (cfu) of Mycobacterium marinum, 9.3x105 cfu of M. shottsii or sterile carrier and sacrificed one, three or 15 days post-injection.  Peritoneal macrophages, anterior kidney, spleen and white muscle were assayed for the expression of MsNramp by semiquantitative reverse transcription-PCR (qRT-PCR) using fluorescent-labelled hybridization probes.  Results of these experiments showed that within one day of infection levels of MsNramp were 17-fold higher in peritoneal macrophages of fish injected with M. marinum relative to controls.  Levels of MsNramp were increased three- and six-fold on days three and 15, respectively.  Injection with M. shottsii resulted in two-, five-, and three-fold increases in gene expression in peritoneal macrophages over the time course.  Levels of MsNramp expression in mycobacteria-injected fish were not significantly different from control fish for the anterior kidney or spleen until 15 days post-injection, at which time small (two-fold) increases were observed. Muscle tissue showed no significant induction of MsNramp in any fish during the 15-day challenge period. Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page