An immunogenic 30-kDa surface antigen of pathogenic clinical isolates of Entamoeba histolytica.

A 30-kDa surface antigen was identified by Western blots with human immune sera in all 15 isolates of E. histolytica from patients with invasive amebiasis (pathogenic) but not in 15 strains from asymptomatic patients (nonpathogenic). This antigen is highly immunogenic in naturally infected humans and was recognized by sera from 22 patients with invasive disease but not by sera from 13 patients harboring nonpathogenic strains. Its surface location is supported by its differential extraction in the detergent phase of Triton X-114 and by surface immunofluorescence of live trophozoites. Unlike previously described amebic surface antigens, this 30-kDa antigen is undetectable in axenic strains that were originally isolated from patients with invasive disease but have been adapted to grow without bacteria. Affinity-purified antibody to the 30-kDa antigen did not promote lysis of complement-resistant pathogenic strains. This surface antigen may be diagnostically important in the identification of pathogenic clinical isolates.