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We have previously shown that monoclonal antibodies directed to the 90 kDa glycoprotein and the 35/50 kDa glycoconjugate, present on the surface of Trypanosoma cruzi metacyclic trypomastigotes, inhibited host cell invasion. Here we investigated whether these molecules could be the ligands for the target cell receptor. Binding assays were performed by incubating Vero cells with sonicated parasite extract. Detection of bound parasite components was carried out by using monoclonal antibodies (MoAbs) IG7 and 10D8, which recognize the 90 kDa and the 35/50 kDa antigens respectively. These experiments revealed that the 35/50 kDa glycoconjugate of metacyclic forms, but not the 1G7-reactive antigen, binds to Vero cells. The purified 35/50 kDa antigen bound to Vero cells and inhibited the entry of metacyclic forms in a dose-dependent manner. Although to a lesser extent, an immunologically related 35/50 kDa antigen of non-infective epimastigotes also bound to Vero cells but it was unable to inhibit parasite penetration at a concentration (100 micrograms/ml) in which metacyclic antigen exhibited more than 60% inhibition. All these data suggest that the metacyclic 35/50 kDa surface glycoconjugate is a ligand to the host cell in the process of T. cruzi invasion.