The growth and infectivity of Leishmania major is not altered by in vitro exposure to 2,3,7,8-tetrachlorodibenzo- p -dioxin

The numbers of Leishmania major parasites in foot lesions of C57Bl/6, BALB/c or SCID mice can be significantly reduced by pre-exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). One potential mechanism to explain this enhanced resistance to infection is that TCDD is directly toxic to L. major. This potential mechanism was addressed by exposing L. major promastigotes and amastigotes to TCDD in vitro and examining their subsequent proliferation and infectivity. We found no significant change in the rate of in vitro L. major proliferation (promastigotes or amastigotes) after TCDD exposure at concentrations up to 100 nM. Moreover, in vitro TCDD exposure did not significantly alter the ability of L. major to infect mice, trigger lesion formation, or survive in those lesions.