[Entamoeba histolytica: II. Effect of humoral immune mechanisms on cytotoxic activity].

The time dependency of the cytotoxic action of E. histolytica against tissue culture cells of mammalian origin was assessed in a 51Cr-release assay. Obviously, the amebae-dependent cytotoxic activity within the first 30-60 min of the assay against K562 (an erythroleukemic cell line) and MH1C1 (a rat hepatoma cell line) correlated with the pathogenicity of the respective amebae in vivo as measured by the hamster liver infectivity test. The in vivo apathogenic strain of E. histolytica (HK9) exhibited a delayed cytotoxic action in comparison with the in vivo pathogenic strain (SFL3), which revealed approximately 50% of maximum 51Cr-release after 10 min of the assay. Peripheral blood lymphocytes and HeLa cells proved to be not suitable to discriminate between pathogenic and apathogenic strains in vitro. Human antibodies directed against E. histolytica were capable of inhibiting the cytotoxic action of pathogenic amebae against K562 and MH1C1 within the first 30-60 min of the assay, revealing a kinetic pattern nearly identical with that observed with apathogenic amebae against K562. Possibly, this antibody-mediated inhibition of the cytotoxic action of E. histolytica against target cells reflects one of the defence mechanisms of the host against invasive amebiasis.