Does Concanavalin a Treatment of Host Cells Enhance or Inhibit Their Association with Trypanosoma cruzi Trypomastigotes?

Abstract

Concanavalin A (Con A) has frequently been used as a probe of cell surface molecules that mediate cell-cell interactions. There have been conflicting reports that Con A treatment of vertebrate host cells can subsequently increase or reduce the level of association (surface attachment and penetration) of Trypanosoma cruzi trypomastigotes with these cells. In this work, we have established that the type of effect produced by treatment of host cells with Con A depended on whether or not fetal bovine serum was present during the interaction of trypomastigotes and host cells; Con A treatment reduced host cell association with T. cruzi in the presence of the serum, but increased it when the serum was absent. In addition, ovalbumin, a glycoprotein with a high mannose content and the ability to specifically bind to Con A, was found capable of altering the effect of Con A treatment of host cells on parasite association levels in a manner similar to fetal bovine serum. These results suggested that glycoproteins present in the serum can modulate the effect of Con A, possibly by blocking free sites remaining on the Con A molecules which had bound to the surface of host cells. If free binding sites on the Con A molecule remained unblocked, they could conceivably form bridges between host cells and parasites resulting in an artifactual enhancement of their level of association in serum-free medium.