NON-SPECIFIC CYTOTOXIC CELLS (NCCS) ARE A UNIQUE GROUP OF CELLS THAT ARE PRESENT IN FISH AND AMPHIBIANS, BUT NOT MAMMALS. THESE CELLS ARE INNATE IMMUNE CELLS AND HAVE FUNCTIONS SIMILAR TO NATURAL KILLER (NK) CELLS AND T CYTOTOXIC CELLS. WE HAVE DETERMINED THAT CATFISH NCCS DIRECTLY BIND BACTERIA. DIRECT BACTERIAL KILLING BY CYTOTOXIC CELLS HAS BEEN DEMONSTRATED IN ONE MAMMALIAN CELL MODEL BUT NOT IN ANY FISH MODEL. WE HYPOTHESIZE THAT DIRECT NCC:BACTERIA BINDING AND KILLING IS AN IMPORTANT IMMUNE MECHANISM IN FISH. THIS PROJECT HAS TWO OBJECTIVES: 1. DETERMINE HOW NCCS DIRECTLY KILL BACTERIA AFTER THEY BIND. WE WILL USE TWO BACTERIA: EDWARDSIELLA ICTALURI AND EDWARDSIELLA PISCICIDA. 2. VISUALIZE HOW NCCS AND BACTERIA BIND. BECAUSE HYBRID CATFISH ARE IMPORTANT IN THE INDUSTRY, THESE EXPERIMENTS WILL BE REPEATED WITH HYBRIDS. RAG1-/- MUTANT ZEBRAFISH WILL BE USED FOR ADOPTIVE NCC TRANSFERS UNDER A DIFFERENT IACUC PROTOCOL. COMPLETION OF THIS PROJECT WILL PROVIDE KEY INFORMATION ABOUT HOW CATFISH NCCS KILL BACTERIA. THESE RESULTS WILL INCREASE OUR UNDERSTANDING OF HOW CATFISH FIGHT BACTERIAL DISEASES AND WILL LEAD TO USEFUL METHODS TO PREVENT OR REDUCE DISEASE LOSS IN THE CATFISH INDUSTRY.