Cysteine proteinase in Trypanosoma cruzi: immunocytochemical localization and involvement in parasite-host cell interaction.

A monospecific polyclonal antibody obtained against a cysteine proteinase isolated from epimastigotes of Trypanosoma cruzi was used for the immunocytochemical localization of the protein by electron microscopy and to analyse the role played by cysteine proteinase in the process of T. cruzi-host cell interaction. Cytoplasmic structures that correspond to elements of the endosomal-lysosomal (reservosome) system found in epimastigote, amastigote and trypomastigote forms reacted intensely with colloidal gold-labelled antibodies using on-section indirect labelling. The surface of most of the tissue culture-derived trypomastigotes was not labelled. However, the flagellar pocket of this form was labelled. All epimastigotes obtained from axenic cultures and amastigote-like forms found in the supernatant of vertebrate cells heavily infected with T. cruzi had their surface intensely labelled, indicating also the surface localization of the protein. Incubation of the parasites in the presence of a sub-agglutinating concentration of the anti-cysteine proteinase antibody led to a marked increase in their uptake by macrophages. In contrast, addition of the F(ab')2 portion of the same antibody significantly reduced the uptake of the parasites by the macrophages. The results obtained strongly suggest an important participation of cysteine proteinase in the process of T. cruzi-macrophage interaction.