Serological Comparison of Selected Parasitic and Free‐Living Amoebae in vitro, Using Diffusion‐Precipitation and Fluorescent‐Antibody Technics*

SYNOPSIS. The present study has been directed to a serological comparison of three closely similar species of Entamoeba: E. histolytica, E. invadens and E. moshkovskii , and two free‐living soil amoebae: Hartmannella rhysodes and Mayorella palestinensis. Except for E. histolytica and E. moshkovskii , the other amoebae used here were grown axenically; this is the first report of the use of antigenic extracts from axenic cultures of parasitic amoebae. The method described here provides a potent antigen that elicits a good antibody titer and is generally applicable to both parasitic and free‐living amoebae. Amoebae pooled from well‐grown cultures were thoroughly washed, sonicated and mixed with Freund's Adjuvant; this antigenic preparation was injected into rabbits. Two subcutaneous injections were given at three‐week intervals, and 2‐3 weeks thereafter blood was withdrawn to obtain antiserum. Agar‐gel diffusion, cellulose acetate paper and fluorescent antibody technics were used to test the antigen‐antibody (Ag‐Ab) reactions. Results of the Ag‐Ab reactions can be summarized as follows: 1) The homologous Ag‐Ab reaction was obtained in all cases tested. 2) There was no serological reaction between the parasitic and free‐living amoebae tested. 3) There was a definite serological reaction between H. rhysodes and M. palestinensis. 4) Multiple antigens were found in E. invadens (PZ strain) and E. histolytica (DKB strain) when they were tested against anti‐PZ serum and anti‐DKB serum, respectively, and no reaction was found when the other test antigens were exposed to these two antisera in gel‐diffusion tests. 5) With the fluorescent antibody technic, E. histolytica (Laredo strain), E. moshkovskii (DSR strain) and E. histolytica (DKB strain) showed some degree of serological reaction in descending order when they were stained with conjugated anti‐ E. invadens serum.