The effect of proteolytic enzymes and protease inhibitors on the interaction Trypanosoma cruzi-fibroblasts.

It has been shown previously that the capability to adhere to and infect fibroblastic cells by Trypanosoma cruzi is expressed only partially in trypomastigotes recently liberated from infected fibroblasts, but these parasites can increase several-fold their adhesion and infectivity by a time-dependent extracellular incubation. It is now shown that polyacrylamide gel electrophoresis patterns of 125I-labelled surface proteins of the parasites change during the activation process and that protease inhibitors of diverse specificity can block both these changes and the development of adhesion and infectivity. Treatment of fresh trypomastigotes with different proteases increases immediately adhesion and infection. The effect of trypsin has been studied in detail and it was found that this protease stimulates adhesion 4- to 6-fold, even in trypomastigotes obtained and assayed in the absence of serum. Trypomastigotes incubated for various periods and then exposed to trypsin increase their adhesion to values similar to those attained by prolonged incubation of trypomastigotes alone, but infection is stimulated in fresh trypomastigotes only. Trypomastigotes whose development of activation has been inhibited either by protease inhibitors, puromycin, and tunicamycin, and are thereafter trypsinized, show respectively, that: adhesion and infection are restored immediately to the same high values obtained when untreated controls are trypsinized, adhesion is restored, but not infection, and infection is not restored. These results suggest that the adhesion step of T. cruzi trypomastigotes to fibroblastic cells depends on a membrane protein(s) that is (are) already present in an inactive or hidden form in parasites recently liberated from infected fibroblasts. Upon extracellular maturation of these trypomastigotes this proteins(s) is activated or unmasked, probably through an endogenous proteolytic process, whose expression requires protein synthesis. The penetration step requires biosynthesis of a tunicamycin-sensitive glycoprotein(s) of the parasite and its full expression necessitates serum.