Immunoprotective behaviour of plasma-membrane-associated antigens of axenic Entamoeba histolytica.

Immunisation of golden hamsters with plasma-membrane-associated antigens of a virulent subline of axenic Entamoeba histolytica strain NIH 200 V, entrapped in multilamellar phosphatidylcholine liposomes (MPL) or Freund's complete adjuvant (FCA), afforded protection against intrahepatic challenge with axenic amoebic trophozoites of the same strain. Amoebic liver abscess developed in 86% and 80% of the animals that received empty liposomes or buffer emulsified in FCA but in none of the animals that received plasma-membrane-antigen vaccines. All the immunised animals had significantly higher levels (p less than 0.001) of antibodies to plasma-membrane components and significantly higher levels (p less than 0.001) of cellular sensitisation. Antibody-dependent macrophage-mediated cytotoxicity against trophozoites was also found to be significantly greater (p less than 0.001) in immunised animals. Liposome-entrapped antigens stimulated the immune system of the host as well as, or better than, antigens administered with FCA.