Preliminary Report on a Hemagglutination Test for Entamoebae.

Abstract

Previous serologic tests for amebiasis utilized antigens prepared from amebae grown symbiotically in cultures with mixed or single species of bacteria isolated from the intestinal tract of man or animals. From such cultures it has been difficult to isolate stable and highly specific amebic antigens. In the current study the value of a test antigen prepared by growing amebae with microbial symbionts that do not occur in the intestinal tract has been attempted. Entamoeba invadens and Entamoeba histolytica (DKB strain) were each grown in Phillips, medium with the symbiont, Trypanosoma cruzi, and the amebae separated by washing and centrifugation. Test antigens prepared from such amebae have exhibited marked sensitivity and high specificity with homologous antisera in the hemagglutination and complement fixation tests. The hemagglutination test employed was a modification of Boyden''S procedure using human O cells tanned at 2[degree] C, as developed in this laboratory for toxoplasmosis. As significantly higher titers both with rabbit antisera and with human sera from clinical cases of amebiasis were obtained with the test antigen prepared from E. histolytica (DKB strain), than with antigen prepared from E. invadens, the antigen from E. histolytica was selected for subsequent tests with 144 human sera. Ninety-eight per cent of the sera from persons with clinical amebiasis were positive while only 2% of the sera from individuals without amebiasis were positive. Sera from "carriers" showed variable results. Complement fixation tests were performed successfully on 111 of the sera previously tested by the hemagglutination procedure. Ninety-six per cent of 48 sera negative by the hemagglutination test were also negative by the complement fixation test. As the hemagglutination test titers increased, the percentage of positive complement fixation tests also increased. Thus, all sera with hemagglutination titers of 1:32000 or above produced positive complement fixation tests. The exact relationship and significance of the 2 tests in amebiasis requires further study.