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Antigens in electron-dense granules from Entamoeba histolytica as possible markers for pathogenicity

In vitro interaction of Entamoeba histolytica with collagen induces intracellular formation and release of electron-dense granules (EDG) and stimulation of collagenolytic activity. Purified EDG contain 1.66 U of collagenase per mg of protein. Thus, EDG may participate in tissue destruction during invasive amebiasis. Monoclonal antibodies (MAbs) L1.1 and L7.1 reacted specifically with EDG in enzyme-linked immunosorbent assay (ELISA) and immunofluorescence and immunoelectron microscopy. MAb L7.1 immunoprecipitated three polypeptides with molecular weights of 95,000, 68,000, and 28,000 from lysates of biosynthetically labeled E. histolytica. Both MAbs recognized the pathogenic E. histolytica axenic strains HM1:IMSS, HM38:IMSS, and HK-9 but failed to react in ELISA with Entamoeba moshkovskii, Entamoeba invadens, and E. histolytica-like Laredo. In addition, MAb L7.1 reacted with one E. histolytica isolate from a symptomatic patient but did not react with four of five isolates from asymptomatic patients. EDG antigens were detected by a MAb L7.1-based ELISA in E. histolytica-containing fecal samples from symptomatic, but not asymptomatic, individuals. These results suggest that the EDG antigen detected with MAb L7.1 may be differentially expressed in pathogenic and nonpathogenic E. histolytica.