Trypanosoma cruzi: separation of broad and slender trypomastigotes using a continuous hypaque gradient

Trypanosoma cruzi trypomastigotes occur as a mixture of morphologically distinct forms in natural and experimental infections. We have been able to separate mixed populations into slender and broad forms using a continuous gradient composed of 12.5-25.0% hypaque in culture media. Previously, comparisons could only be made by using various strains of T. cruzi which show a predominance of either form. This separation procedure gave recoveries of 88-98% and had no effect on the viability of the parasites. Infectivity studies showed that slender forms were much more infectious to cultured muscle cells than were broad forms. However, studies with macrophages from CFW mice showed both forms to be equally capable of infection. It is concluded that the mechanism by which each form infects host cells is different; slender forms being capable of infecting both by penetration and by phagocytosis, while broad forms are only capable of infecting through phagocytosis.