SUPPRESSION OF MICROBICIDAL ACTIVITY OF PERITONEAL-EXUDATE BY SUBLETHAL DIELDRIN EXPOSURE OF OUTBRED AND INBRED MICE

The effects of sublethal exposure to the organochlorine insecticide dieldrin on susceptibility to bacterial infection were studied in inbred and outbred mice. The possible alterations to natural resistance by the pesticide were evaluated. Three genetically distinct mouse strains were used in a model of Salmonellosis bacterial infection: the A/J strain, which is resistant to Salmonella byphimurium; Swiss, which is semiresistant; and C57Bl/6, which is susceptible. Mice received a sublethal (0.4 < LD50 < 0.6) intraperitoneal dose of dieldrin in 0.1 ml corn oil used as vehicle. Seven days after treatment, the in vivo susceptibility; and antibody production to S. typhimurium were determined, as well as the in vitro phagocytosis and intracellular killing of bacteria by peritoneal exudate cells. Our study showed that dieldrin rendered mice significantly more susceptible to S. typhimurium and, in vitro, dieldrin significantly suppressed phagocytosis and intracellular killing of bacteria, while the vehicle had no effect on the immune system. The in vitro results support the in vivo findings in that dieldrin inhibits the natural resistance of mice to bacterial infection.