INVASIVE PHENOTYPE OF TRYPANOSOMA-CRUZI RESTRICTED TO A POPULATION EXPRESSING TRANS-SIALIDASE

Trypanosoma cruzi expresses a developmentally regulated trans-sialdase implicated in the pathogenesis of Chagad disease. On inhabitation of the extracellular milieu of cultured cells by infective trypomastigote s, the enzyme is restricted to a small (20 to 30%) population of paras ites. The biological significance of trans-sialidase expression on thi s subset, termed TS+, and not on the majority (70 to 80%) of morpholog ically similar trypanosomes, named TS-, is unknown. To determine the r oles of the TS+ and TS- subsets in T. cruzi invasion, we prepared pure populations of TS- and TS+ trypanosomes using magnetic beads coated w ith a monoclonal antibody specific for the tandem repeat unit of the t rans-sialidase C terminus. After removal of nonadherent TS- trypomasti gotes, the TS+ trypomastigotes were isolated from the beads by specifi c elusion with a synthetic peptide epitope of the trans-sialidase mono clonal antibody. Confirmation of TS+ and TS- phenotypes was obtained b y immunofluorescence, immunoblotting, and sialidase or sialyl transfer ase activity measurements. The TS+ trypanosomes were highly invasive, as they attached to, penetrated, and thrived in cultured mammalian cel ls much more efficiently than did unfractionated parasites. The critic al role of the trans-sialidase in invasion was underscored by the obse rvation that infection was neutralized by human antibodies to trans-si alidase. What's more, the TS- parasites, in sharp contrast to their TS + counterparts, were extremely inefficient in invading epithelial cell s and fibroblasts. Further, introduction of small amounts of exogenous trans-sialidase into suspensions of nonpenetrating TS- parasites conv erted them to a highly invasive phenotype indistinguishable from that of the TS+ population. Rescue of the invasive phenotype was specific f or the T. cruzi enzyme, for it didn't happen with bacterial and viral sialidases. The in vitro results were confirmed in the murine model of Chagas' disease, as TS- trypomastigotes were relatively avirulent whi le TS+ trypomastigotes were more virulent than unfractionated parasite s.