Trypanosoma cruzi, the causative agent of Chagas' disease, exists in nature as a complex and highly variable population (1). Thus, a variety of strains and clones isolated and used by different laboratories display very distinct biological properties (1-3). Properties such as tissue tropism (4), resistance to complement lysis (5), virulence (6), and infectivity in different animal models (7) were extensively examined using either metacyclic or tissue culture-derived trypomastigotes, regarded as the classic infective form of the parasite. Several studies attempting to correlate strain and clone polymorphism with biological properties of trypomastigotes have implicated specific surface antigens (8-12). Tissue culture-derived trypomastigotes may differentiate extracellularly into amastigotes that resemble the proliferative intracellular forms in many aspects (13). T. cruzi amastigotes have also been shown to be infective, both for phagocytic (14-16) and non-phagocytic cells (14,17,18). Although it has been reported that amastigotes express specific membrane components that might be involved in their uptake by phagocytes (16,19), the parasite molecules involved in cell invasion, particularly of non-professional phagocytes, are still unknown. Detailed work by Andrews et al. (13,20) showed that both intracellular and extracellular forms express a major surface glycoprotein designated Ssp-4 that is bound to the membrane via a GPI anchor. Another T. cruzi amastigote-specific component named amastin was recently isolated by Teixeira et al. (21). Although its relation to Ssp-4 is unclear at the moment, the analysis of the amastin sequence indicates that it is a hydrophobic polypeptide lacking the characteristic GPI-anchor sequence (22) that would be expected for Ssp-4. Other amastigote specific antigens that have recently been cloned and sequenced based on previously published amino-terminal sequence data (23) were shown to belong to the trans-sialidase/sialidase superfamily (24). In the present study we show that T. cruzi amastigotes from distinct strains and clones express different epitopes in a polymorphic manner, similar to that described for epitopes defined for other parasite stages.
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