Murine monoclonal antibodies (mAbs) were produced against an n-octyl-beta-D-glucopyranoside-extracted fraction of trophozoites of Entamoeba histolytica HM-1:IMSS. Four of the mAbs were reactive with a 150-kDa surface antigen characterized by Western-immunoblot analysis under nonreducing conditions. When the reactivity of the four mAbs with nine reference strains of E. histolytica was examined by an indirect fluorescence antibody test, two of the mAbs (EH3015 and EH3023) were found to react with all nine strains and the other two mAbs (EH3056 and EH3126) reacted with seven strains. The four mAbs did not react with any E. dispar reference strain or with other enteric protozoan parasites. The reactivity of EH3015 and EH3023 with numerous isolates of E. histolytica and E. dispar collected in our laboratories was also examined. The 2 mAbs reacted with all of the 37 E. histolytica isolates tested but did not react with any of the 33 isolates of E. dispar. These results indicate that common antigenic epitopes of E. histolytica are on the 150-kDa surface molecule and that mAbs can distinguish between E. histolytica and E. dispar.

Bithionol, dichlorophene, and hexachlorophene, which are used in treating some helminthic infections, killed trophozoites of Giardia lamblia and Trichomonas vaginalis in modified BI-S-33 and Asami media, respectively. Virtually all G. lamblia and T. vaginalis cells were killed within 24 h with a 0.42 mM concentration of these compounds, except that 0.93 mM dichlorophene was required for sterilizing T. vaginalis in the same period. In modified BI-S-33 and Asami media from which bovine and human sera were omitted, respectively, the inhibitory actions of the compounds against in vitro growth of these protozoa were significantly enhanced. Trophozoites of G. lamblia and T. vaginalis could be killed in shorter than 10 min with 0.074 mM dichlorophene and 0.0025 mM hexachlorophene, respectively, in serum-free media. G. lamblia, which was incubated in the complete medium containing dichlorophene, showed a characteristic swelling of the ventral side which led to disruption of the parasite, whereas bithionol caused a thin crack in the cytoplasm of T. vaginalis incubated in Asami medium. The crack appeared to enlarge and result in vacuolization of T. vaginalis. These observations suggest that bithionol, dichlorophene, and hexachlorophene merit further evaluation to ascertain whether they are useful for treatment of giardiasis and trichomoniasis.