TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Immunoregulation Of Innate Immunity In Tilapia: Activation Of Nonspecific Cytotoxic Cells By Cytokine-Like Factors Liliana Jaso-Friedmann, J. Ruiz, G.R. Bishop and D. L. Evans. Department of Medical Microbiology and Parasitology, University of Georgia, Athens, GA. 30602 Exposure of tilapia (Oreochromis sp) to water temperatures of 5-15 C for 3-5 minutes produces physiological stress responses characterized by immediate phenotypic and immunological changes. In the present study, this general stress response was utilized as a model system to study innate immunity mediated by soluble factors and cytotoxic cells. Acute innate cytotoxic responses of NCC in the PBL, AK and SPL were measured. Following temperature stress, the levels of NCC activity depended on the presence of soluble factors and on the cell compartments from which the NCC were obtained. NCC from PBL of stressed tilapia had 30x or greater cytotoxic activitiy compared to nonstressed PBLs from controls. NCC from the AK and SPL of stressed tilapia had lower cytotoxicity than controls. Flow cytometric analysis of NCC concentrations in each tissue indicated that increased cytotoxicity was not produced by increased numbers of NCC. To determine the mechanism of amplification of cytotoxicity, NCC from nonstressed tilapia were passively treated with serum from temperature stressed tilapia. Serum containing the "stress activated serum factor" (SASF) passively increased naive NCC cytotoxicity (from PBL) 100-400%. SASF had no activating effects on AK or splenic NCC from naïve fish. SASF required only 15 min pre-incubation with naive NCC to activate cytotoxicity. Activation was nonreversible and concentration dependent. Pretreatment of NCC with SASF reduced the assay time required to amplify target cell cytotoxicity from 12-24h to 6h. SASF amplification of NCC cytotoxicity was not restricted by different histological types of target cells. Determination on the NCC subset or compartment from which the NCC were obtained. Research supported by a Bard grant. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page