Progression of visceral leishmaniasis due to Leishmania infantum in BALB/c mice is markedly slowed by prior infection with Trichinella spiralis.

We investigated in BALB/c mice the influence of the immunological environment created by the nematode Trichinella spiralis on the course of visceral leishmaniasis due to Leishmania infantum. On the day of Leishmania inoculation (day 0), mice, T. spiralis infected 7 days earlier, presented increased gamma interferon (IFN-gamma), interleukin-4 (IL-4), and IL-5 mRNA levels locally and systemically and increased the potential of spleen cells to synthesize IFN-gamma and IL-4 after activation in vitro. Eighteen days after Leishmania inoculation (day 18), corresponding to the acute phase of leishmaniasis, the hepatic amastigote burden in mice coinfected with L. infantum and T. spiralis (LT mice) was significantly lower (P < 0.001) than that in mice infected with L. infantum only (L mice). IFN-gamma and IL-4 mRNAs were overexpressed in livers of LT and L mice. On day 70, corresponding to the chronic phase, the splenic amastigote load was significantly lower (P = 0.004) in LT mice than it was in L mice. Splenic IFN-gamma transcripts were overexpressed in both L and LT mice. After Leishmania-specific in vitro stimulation, cytokine production was enhanced in both groups, but spleen cells from L mice produced significantly more IFN-gamma than did spleen cells from LT mice. Our data (i) generalize previous results indicating the lack of a clear-cut correlation between the outcome of murine visceral leishmaniasis and the type of cytokine pattern and (ii) demonstrate that in LT mice, leishmaniasis takes a markedly milder course than it does in L mice, providing information on the potential consequences of coinfection in a mammalian host.