Neurotoxicity and immunotoxicity assessment in CBA/J mice with chronic Toxoplasma gondii infection and multiple oral exposures to methylmercury

The present study was conducted to determine the effect of multiple low doses of methylmercury (MeHg) on the course of a chronic Toxoplasma gondii infection. Four groups of 6-wk-old female CBA/J mice either were fed 25 T. gondii tissue cysts of the ME-49 strain or were vehicle control. Six weeks later, half of each group was orally gavaged with 8-mg/kg body weight doses of MeHg on days 0, 2, 4, 7, 10, and 13, totaling 4 experimental groups. Mice were killed on day 17 or 18 after MeHg exposure. Flow cytometric analysis of lymphocyte subpopulations in the thymus demonstrated a significant increase in the percentage of CD4- CD8+ T-cells in mice exposed to MeHg with a concurrent T. gondii infection. Groups of mice exposed to MeHg showed a decrease in total thymic cellularity and cellularity of all T-cell subpopulations when compared with control mice, but viability of these cells was unaffected. Splenic cell viability was decreased in mice exposed to MeHg, but alterations in T-cell subpopulations were not noted. These data indicate that multiple low doses of MeHg may not exacerbate chronic toxoplasmosis, but MeHg-induced effects on the immune system were evident.