Modulation of cell-mediated resistance to listeriosis in mice given T-2 toxin.

The modulating effect of preinoculation and postinoculation treatment with a single oral 4.0 mg/kg dosage of T-2 toxin on cell-mediated resistance was studied in mice inoculated with Listeria monocytogenes. Toxin treatment caused significant decreases in thymus and spleen weights, bone marrow cellularity, and in the total number of circulating leukocytes, lymphocytes, and neutrophils. Enhancement or suppression of resistance to listeriosis was dependent on the time of toxin administration relative to the time of Listeria challenge. Preinoculation treatment on Day 2 or 4 prior to Listeria challenge significantly enhanced resistance and decreased mortality due to listeriosis by as much as 50%. In contrast, resistance was suppressed and mortality was increased by 50% in mice that were treated with toxin after Listeria challenge. Enhanced resistance to listeriosis was accompanied by a significant increase in the influx of macrophages into Listeria-elicited peritoneal exudates. In addition, in vivo phagocytosis of sheep red blood cells by peritoneal macrophages was significantly increased in toxin-treated mice that were sensitized with sheep erythrocytes. The data indicate that T-2 toxin has a modulating effect on cell-mediated resistance and that enhancement of resistance to listeriosis in mice pretreated with T-2 toxin is associated with increased migration/activation of macrophage effector cells.