An Immunogenic 30-kDa Surface Antigen of Pathogenic Clinical Isolates of Entamoeba histolytica

Abstract

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.

A Redescription of Entamoeba Histolytica Schaudinn, 1903 (Emended Walker, 1911) Separating It From Entamoeba Dispar Brumpt, 19251

“…A 30-kDa surface antigen was identified by Western blots with human serum in 15 P isolates and was absent in 15 NP isolates. This particular antigen of E. histolytica differed from the others described in that it was not detected in amebae cul-tivated axenically, despite the amebae having been originally isolated from patients with invasive disease [2].…”

A monoclonal antibody for distinction of invasive and noninvasive clinical isolates of Entamoeba histolytica

“…Nevertheless, MAb 20/7D recognizes an epitope with interesting features. The 81-and 84-kDa protein bearing the epitope is not equivalent to those already described (2,22,24,27,40,44). Furthermore, the fact that it is present in both invasive and noninvasive isolates, as shown by Western blotting, but differentially recognized by IFA suggests that this epitope is expressed and processed in such a way that it is accessible to MAb 20/7D only in nondenatured E. histolytica antigens of the invasive zymodemes.…”

“…Immunofluorescence analysis of living parasites. Immunofluorescence analysis of live E. histolytica trophozoites was carried out as previously described by Blakely et al (2) with some modifications. Briefly, axenic HM-1:IMSS trophozoites were harvested and washed in cold 0.9% saline with 0.2% glucose and 2 mM CaCl2-1 mM ascorbic acid (no.…”

Complement Resistance of Parasites

“…In addition to the secreted protease and the adhesin other suggested virulence factors affecting C activation include variation in surface polysaccharides, hydrophobicity of the trophozoites [56] and a 30 kDa surface protein [57]. However, the possible C regulatory activities of these factors have not been well established.…”