Host resistance to Trichinella spiralis infection in rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

We have previously shown decreased resistance to Trichinella spiralis (Ts) infection and reduced parasite antigen-specific responses in B6C3F1 mice exposed to TCDD before infection. The current study was done to characterize the effects of preinfection administration of 1, 10, or 30 micrograms TCDD/kg on host resistance of female F344 rats to Ts infection and to examine parasite antigen-specific responses in the spleen and mesenteric lymph nodes of infected animals. TCDD exposure did not affect adult parasite elimination from the small intestine or the numbers of encysted larvae in the muscle, although host control of newborn larvae production in female parasites isolated from the highest dose group was compromised. Proliferative responses of lymphocytes cultured with parasite antigen were enhanced in groups of rats exposed to 30 micrograms TCDD/kg. These results, which are in marked contrast to the effects obtained in B6C3F1 mice, demonstrate a clear species difference in the effects of TCDD on immune function in rodents and underscore the need to determine which species more closely reflects the potential outcome of human exposure to TCDD.