Immunogenicity of RNA-protein fraction isolated from axenic Entamoeba histolytica (NIH:200)

The immunogenicity of Entamoeba histolytica RNA (EhRNA) was studied in guinea-pigs. Animals immunized with a single dose of EhRNA and Freund's complete adjuvant (FCA) showed a high level of cell-mediated immune response (CMIR) as assessed by percent leucocyte migration inhibition (74.8 +/- 2.9) after 1 week of immunization. This response faded away gradually and by week 5 after immunization the percent leucocyte migration inhibition was 27.1 +/- 8.27, which is quite close to control values. The immunogenic activity of EhRNA was found to be specific, since yeast RNA failed to elicit immunological responses, and was RNase-sensitive. The CMIR could be maintained at its high level by giving boosters or multiple doses. Anti-EhRNA antibodies (haemagglutinins or precipitins) could not be demonstrated at any stage.