Partial characterization of a 36-kDa antigen of Entamoeba histolytica and its recognition by sera from patients with amoebiasis.

A 36-kDa antigen of axenically grown pathogenic Entamoeba histolytica (HM1-IMSS) was eluted from the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)-resolved crude amoebic extract antigens. The immunoreactivity of this partially purified 36-kDa antigen with monoclonal antibody (MoAb) 3D(10) altered significantly (P<0.01) after heat and trypsin treatment but remained unaltered after treatment with sodium metaperiodate (P0.5), thereby indicating the protein nature of the epitope recognized by MoAb 3D(10). The epitope was found to be localized on the surface as well as in the cytoplasm of the E. histolytica trophozoites with the majority of it in the cytoplasm. In addition, this epitope was also found to be present on the cyst form of the parasite. The 36-kDa molecule was recognized by the sera from 29 (85%) of the 34 patients with amoebic liver abscess and five (83%) of the six patients with amoebic colitis. No serum samples from asymptomatic cyst passers, from patients with non-amoebic hepatic or intestinal disorders and apparently healthy subjects had antibodies that reacted with this 36-kDa molecule. The immune responses in man to this 36-kDa amoebic molecule indicate a potential specific role for this molecule in invasive amoebiasis.