Elicitation of protective immunity to Entamoeba histolytica--an experimental study.

Immunization of hamsters with plasma membrane (PM) antigens of virulent subline of axenic Entamoeba histolytica (NIH: 200 V) entrapped in multilamellar phosphatidyl choline liposomes conferred 100% protection to a subsequent intrahepatic amoebic challenge. In contrast, vaccination of hamsters with live amoebic trophozoites injected intradermally failed to protect any of the animals. The protected animals had significantly high levels of anti-PM anti-amoebic antibodies, cellular sensitization and macrophage-mediated antibody-dependent cytotoxicity against amoebic trophozoites. However, none of the intradermally immunized animals had anti-PM anti-amoebic antibodies at the time of challenge. Such animals also had significantly low macrophage-mediated antibody-dependent cellular cytotoxicity. The data indicate the potential prophylactic use of PM antigens against hepatic amoebic infection.