Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/3/1997
Publication Date: N/A
Citation: Interpretive Summary: Resistance to Edwardsiella ictaluri is poorly understood in cultured catfish. Previously, we found that catfish that survived exposure to E. ictaluri were resistance to reexposure. Antibody specific for E. ictaluri was shown not be responsible for this resistance. We next studied the role of macrophages in resistance. Macrophages from the resistant catfish were found to have a greater capacity to kill e. ictaluri than macrophage from susceptible catfish. The killing capacity of macrophages from resistant catfish was enhanced when the E. ictaluri was reacted with the specific antibody. Our results show that macrophages and specific antibody together play a major role in resistance to E. ictaluri, the cause of enteric septicemia of catfish (ESC). These findings are important in the development of ESC vaccines and the selection of genetically superior catfish resistance to ESC.
Technical Abstract: Abstract The role of peritoneal macrophages in immunity to enteric septicemia of catfish (ESC) after immersion vaccination with live Edwardsiella ictaluri was investigated. Channel catfish macrophage-mediated bacterial killing was dependent on macrophage:bacteria ratio. Ratios of 1:1 to 1:12 exhibited significant differences (p < 0.05) in killing between macrophages from immunized fish when compared to killing by macrophages from susceptible fish at 2.5 hrs. At 5 hrs, macrophages from immunized fish were capable of effective killing (83.3%) at a 1:24 effector to tart ratio; whereas macrophages from susceptible fish killed significantly (p < 0.05) less (56.9%). Macrophage bactericidal activity was significantly greater (p < 0.05) in macrophages from individual immunized fish (93.4%) compared to macrophages from individual susceptible fish (85.4%). The kinetics of macrophage killing showed a linear increase in bactericidal activity from 1 to 3 hrs. Differences in macrophage bactericidal activity occurred at 1.5, 2.5 and 3.0 hrs; with macrophages obtained from immunized fish having a higher killing ability. Opsonization of E. ictaluri with serum from immune fish enable macrophages from immunized fish to kill more effectively (93.8%) at 2.5 hrs. In comparison, killing of non-opsonized bacteria incubated with macrophages from immunized fish was 75.9% at 2.5 hrs. Opsonization of E. ictaluri with serum significantly suppressed the killing ability of macrophages from susceptible fish (46.2%) at 2.5 hrs. The results suggest that macrophages from fish immune to ESC had a greater capacity to kill E. ictaluri than macrophages from susceptible fish