KILLING OF EDWARDSIELLA-ICTALURI BY MACROPHAGES FROM CHANNEL CATFISH IMMUNE AND SUSCEPTIBLE TO ENTERIC SEPTICEMIA OF CATFISH

The role of peritoneal macrophages in immunity to enteric septicemia o f catfish (ESC) after infection with live Edwardsiella ictaluri was in vestigated. Channel catfish macrophage-mediated bacteriocidal activity was dependent on the macrophage:bacteria ratio. Ratios of 1:1 to 1:12 exhibited significant differences (P less than or equal to 0.05) in k illing between macrophages from immune fish when compared to killing b y macrophages from susceptible fish at 2.5 h. At 5 h, macrophages from immune fish were capable of effective killing (83.3%) at a 1:24 effec tor:target ratio, whereas macrophages from susceptible fish killed sig nificantly (P less than or equal to 0.05) less (56.9%). Macrophage bac teriocidal activity was significantly greater (P less than or equal to 0.05) in macrophages from individual immune fish (93.4%) compared to macrophages from individual susceptible fish (85.4%). The kinetics of macrophage killing showed a linear increase in bacteriocidal activity from 1 to 3 h. Opsonization with immune serum enabled macrophages from immune fish to kill bacteria more effectively (93.8 vs. 75.9%) at 2.5 h. Opsonization of E. ictaluri with immune serum significantly suppre ssed the killing ability of macrophages from susceptible fish (46.2%) at 2.5 h. The results suggest that macrophages from fish immune to ESC had a greater capacity to kill E. ictaluri than macrophages from susc eptible fish especially when E. ictaluri were opsonized with anti-E. i ctaluri antibody. (C) 1997 Published by Elsevier Science B.V.