TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Mechanisms Of Anti-Bacterial Immunity In Tilapia: Role Of Nonspecific Cytotoxic Cells Don L. Evans, S. L. Taylor, G. R. Bishop and L. Jaso-Friedmann. Department of Medical Microbiology and Parasitology, University of Georgia, Athens, GA 30602 The immediate innate cytotoxic and cytokine mediated immunological responses of tilapia to environmental or microbial stressors may be the model for studies of teleost survival. In aquatic species the tissue compartment containing the greatest potential for exposure to high levels of bacterial insult is the peripheral blood (PB). In the present study, we demonstrate that I. V. injection of S. iniae into the caudal vein of tilapia (within minutes) initiates increased NCC cytotoxicity of PBL. However, increased cytotoxic responses are not seen in anterior kidney or splenic tissue. This activity is also observed following exposure of tilapia to short term (3-10 min) cold water (5-10C) shock. Both types of stressors activate PB cytotoxicity and cause the release of soluble factors that passively activate naive NCC from non-stressed tilapia. Results of in vitro studies of the same S. iniae isolate that activates in vivo cytotoxicity suggest that the production of the altered innate cytotoxicity in tilapia may be determined by whether Streptococci produce apoptosis or necrosis responses of NCC. We predict that the streptococcal isolates that decrease in vitro apoptosis while increasing necrosis, may generate active inflammatory responses in vivo and augment antigen processing and the development of acquired immunity. Research supported by a Bard grant. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page