Direct lysis of Trypanosoma cruzi: a novel effector mechanism of protection mediated by human anti-gal antibodies.

Anti-gal antibodies directed against a carbohydrate epitope present in mouse laminin (galactosyl alpha 1-3 galactose) and detected in high levels in sera from patients in the acute phase of Chagas disease are responsible for the direct lysis (DL) of Trypanosoma cruzi blood forms independent of either the classic or alternative complement pathways. Furthermore, the lectins Euonymus europaeus (EE) specific for the carbohydrates gal alpha 1-3 gal present a similar lytic activity against T. cruzi at the same concentrations of purified anti-gal antibodies. The DL activity was tested with several other lectins but Concanavalin A (Con A) specific for alpha-D-mannose and alpha-D-glucose was the only one also presenting lytic activity. The lectins and anti-gal antibodies lytic activity can be inhibited by specific carbohydrates suggesting that this phenomenon is related to the capability of these lectins or anti-gal antibodies to bind to a crucial surface component of T. cruzi. Moreover, the infectivity of T. cruzi blood forms to mice was clearly inactivated by incubation with acute chagasic sera (ACS) but not by ACS absorbed by immunoaffinity chromatography with mouse laminin, a strong evidence that high levels of anti-gal antibodies participate in the decline of the parasitaemia from the acute to the chronic phase in Chagas disease.