Effect ofAeromonas hydrophila enterotoxins on function of mouse phagocytes

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Abstract
Two enterotoxins produced byAeromonas hydrophila isolate SSU have been characterized in this laboratory. One is a cholera toxin cross-reactive cytolytic enterotoxin (CTC toxin) and the other is a non-cholera toxin cross-reactive cytotonic enterotoxin (non-CTC toxin). The two enterotoxins are capable of causing fluid accumulation in animal models; however, only the CTC toxin is lethal to mice and expresses hemolytic as well as cytotoxic activities. In this study, we have investigated the effects of these two toxins on mouse phagocytes. Four hours after intraperitoneal injection of a sublethal dose (460 μg/kg of body weight) of CTC toxin, the chemiluminescence (CL) response of phagocytes in mouse blood was depressed significantly when compared with that observed for controls (intraperitoneal injection of only Hanks' balance salt solution, non-CTC toxin or before treatment with CTC toxin). When fresh whole blood was incubated with various concentrations (2.3, 11.5, 23, 230, 2300 ng/ml) of CTC toxin for 1.5 hr at 37° C, the CL response of blood phagocytes was reduced strikingly in a dose-dependent fashion; however, non-CTC toxin did not inhibit the CL response. The inhibitory effect induced by CTC toxin of the phagocytic function not only was abolished completely, but phagocytosis was enhanced in the presence of interferon-gamma (IFN-γ). In addition, IFN-γ alone induced the largest enhancement of the CL response in mouse phagocytes. These results demonstrated that CTC toxin inhibits the phagocytic ability of phagocytes eitherin vivo orin vitro and that IFN-γ pretreatment can overcome this toxic effect. The direct inhibitory effect on phagocytic activity by CTC toxin may be one of the pathological mechanisms associated with someAeromonas-mediated diseases, whereas IFN-γ may play a protective role for the host against these diseases.