Antibodies Against Entamoeba histolytica Hemolysin HLY4 in Sera from Patients with Invasive Amebiasis

In the city of Leon, Nicaragua, nearly 20% of the population carries cysts of Entamoeba histolytica / Entamoeba dispar (1) and 30% have antibodies against E. histolytica . Few cases of invasive amebiasis with liver abscess formation are seen yearly in Leon. Thus, E. histolytica is present in the population, but it is not known to what extent the antibody titers reflect infection with E. histolytica. Because conventional assays, such as indirect immunofluorescence and ELISA using crude or semipurified E. histolytica fractions as antigen, do not differentiate between E. histolytica and E. dispar , and additionally, the latter, nonpathogenic parasite seems to be immunogenic in infected individuals, we wanted to develop an E. histolytica -specific serological assay. E. histolytica has the capacity to lyse red cells. We have studied the hemolytic activity of recombinant hemolysin HLY4. AntiE. histolytica reactivity to the recombinant hemolysin HLY4 was demonstrated in rabbit antisera against the HM1:IMSS strain and standardized by ELISA. Patient antiE. histolytica serum reactivity was specifically quantified in ELISA and a hemolysis-inhibition assay was developed. Hemolysins of E. histolytica are recognized as important molecules of this parasite, and appear to be linked to the pathogenicity of this parasite (2). Thus, hemolysins seem to be markers for E. histolytica that are able to distinguish this species from the apathogenic E. dispar. Antibodies against E. histolytica hemolysins are, therefore, potential markers for infection with E. histolytica and invasive amebiasis. The recombinant hemolysin HLY4 was used in the present study to develop a specific assay to detect antiamebic hemolysin antibodies in sera from patients suffering from invasive amebiasis.