الفهرس 
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Abstract
The present study was planned to: 1) Detection of direct antibacterial activity of T cell subpopulation especially at low E:T ratio (1:1000) and long incubation period 4 hours. 2) Investigation of the Contact requirement between effectors and targets for direct antibacterial activity. 3) Identification of NK-lysin gene in ginbuna fish. 4) Expression analysis of NK-lysin in different cell populations (CD8+ , CD4+ and sIgM+ cells). 5) characterization of antimicrobial activity of NK-lysin synthetic peptide. 6) Expression of NK-lysin in tissues before and after challenge with E.tarda.
The results could be summarized as follow:
• CD8α+T cells collectedfrom ginbuna immunized with inactivated E. tarda showed high killing activity against both E. tardaand S. iniae at 98.8 ± 1.2% and 99.6%, respectively. Similar but lower killing activity against E. coli (70.3 ± 4.2%) by CD8α+T cells from immunized ginbuna was observed. There was a significant difference in the killing activity of CD8α+T cells between non-immunized and immunized ginbuna against E. tarda and S. iniae.
• CD4+ cells from immunized fish were found to kill 100% and 99.6% of E. tarda and S. iniae, respectively. CD4+ T cells also showed higher direct killing activity against E. tarda and S. iniae than against E. coli (21.3 ± 2.4%). Immunized CD4+ T cells showed significantly higher killing activities against E. tarda, S. iniae and E. coli than non-immunized CD4+ T cells .