Metabolic labeling of Entamoeba histolytica antigens: characterization of a 28-kDa major intracellular antigen.

The in vivo incorporation of radiolabeled amino acids into antigens of Entamoeba histolytica, HM-1:IMSS, is reported. Immunoprecipitation with sera from patients with invasive amebiasis revealed a 28-kDa antigen present in whole cell lysates of E. histolytica. This antigen was of cytoplasmic origin, as indicated by cell fractionation and Triton X-114 detergent-phase separation. Immunoprecipitation, using sera from patients with invasive amebiasis and symptomless cyst passers, revealed the 28-kDa antigen as the major antigen recognized by the sera tested. Immunoprecipitation analysis using radiolabeled-released proteins instead of whole cell lysates showed a number of bands, including the 28-kDa antigen. The data suggest that the 28-kDa antigen is of cytoplasmic origin or is released from the cytoplasmic compartment.