Heterologous expression of Trypanosoma cruzi trans-sialidase in Leishmaniamajor enhances virulence

Earlier studies showed that mice primed for a few hours with the trans-sial idase (TS) of Trypanosoma cruzi, the agent of Chagas' disease, become highl y susceptible to trypanosomal infection. These studies suggest that TS affe cts parasite virulence independent of antigenic stimulation. Potentially, T S could enhance or reduce the virulence of heterologous microbes depending on the mechanism of TS action and on the type of immune response elicited b y the particular parasite. We tested this hypothesis by expressing heterolo gous TS in Leishmania major, a protozoan parasite that causes cutaneous lei shmaniasis and lacks TS and the TS product alpha 2-3-linked sialic acid. Le ishmania cells transfected with a T. cruzi TS expression construct made hig h levels of active enzyme, which was present in the promastigotes and shed into the extracellular milieu. TS expression did not affect L. major bindin g to and entry into cultured macrophages or its tropism for macrophage infe ction in vivo. However, TS-expressing L. major exhibited elevated virulence in BALB/c mice, as determined by lesion progression, parasite numbers, and macro- and microscopic examination of cutaneous lesions. Several genetic t ests proved that the enhanced virulence was directly attributable to TS exp ression. The results are consistent with TS functioning to sabotage the mou se immune system to confer a growth advantage on T. cruzi and transgenic L. major. These data suggest that heterologous expression of T. cruzi virulen ce factors in Leishmania may provide a new approach for dissecting their fu nction in vivo.