Trypanosoma cruzi is the etiologic agent of
Chagas' disease. It is known that amastigotes derived from trypomastigotes in the extracellular milieu are infective
in vitro and in vivo. Extracellular amastigotes (EAs) have a stage-specific
surface antigen called
Ssp-4, a GPI-anchored
glycoprotein that is secreted by the
parasites. By
immunoprecipitation with the
Ssp-4-specific
monoclonal antibodies (mAb) 2C2 and 1D9, we isolated the
glycoprotein from EAs. By
mass spectrometry, we identified the core
protein of
Ssp-4 and evaluated
mRNA expression and the presence of
Ssp-4 carbohydrate epitopes recognized by mAb1D9. We demonstrated that the
carbohydrate epitope recognized by mAb1D9 could promote host
cell invasion by EAs. Although infectious EAs express lower amounts of
Ssp-4 compared with less-infectious EAs (at the
mRNA and
protein levels), it is the
glycosylation of
Ssp-4 (identified by mAb1D9
staining only in infectious
strains and recognized by
galectin-3 on host
cells) that is the determinant of EA invasion of host
cells. Furthermore,
Ssp-4 is secreted by EAs, either free or associated with
parasite vesicles, and can participate in host-
cell interactions. The results presented here describe the possible
role of a
carbohydrate moiety of T. cruzi
surface glycoproteins in host
cell invasion by EA forms, highlighting the potential of these moieties as
therapeutic and
vaccine targets for the
treatment of
Chagas' disease.