Cell-mediated resistance induced by axenic amoebal RNA--protein fraction

Immunologically potent, RNA protein fraction could be isolated from axenic Entamoeba histolytica (NIH: 200) using a phenol extraction method. Immunization of animals with amoebal RNA protein (Eh RNA) fraction evoked an intense cellular sensitization. In immunized animals the percent leucocyte migration inhibition was found to be 73.7 +/- 6.9. In control groups where the animals were treated with Freund's complete adjuvant, yeast RNA and amoebal RNA treated with RNase, the percent leucocyte migration inhibition was 15.8 +/- 2.9, 16.8 +/- 6.2 and 14.0 +/- 4.0 respectively. Anti Eh RNA antibodies (haemagglutinins and precipitins) could not be demonstrated in immunized animals at any stage of observations. The cellular immunity could be maintained at its high level by giving three immunization doses of Eh RNA and also a high degree (95.45%) of protection against experimental challenge with virulent strain of E. histolytica could be obtained in immunized animals. The immunogenic and protective capabilities of Eh RNA were found to be specific since they were abolished by the RNase treatment. Further, the yeast RNA failed to elicit immunity.