SURVIVAL OF BLASTOCYSTIS-HOMINIS CLONES AFTER EXPOSURE TO A CYTOTOXICMONOCLONAL-ANTIBODY

Our previous studies have shown that monoclonal antibodies (MAbs) to B lastocystis hominis react mainly with carbohydrate epitopes, while 1 M Ab (1D5) reacts specifically with a protein of 30,5 kDa. In the presen t study, 3 monoclonal antibodies (1D5, 1E7 and 4F7) were used in immun ogold localization. 1E7 and 4F7 were found to react primarily with the surface coat, while 1D5 was plasma membrane-specific. In the presence of complement, only IDS exhibited a cytotoxic effect on B. hominis wh ereas 1E7 and 4F7 did not, suggesting that the surface coat of B. homi nis could serve as an immunological barrier against host antibodies. U sing a recently described agar plating method, only 1D5 exhibited sign ificant (P < 0.01) complement-independent cytotoxicity to B. hominis, inhibiting colony growth at low concentrations. Parasites that had bee n exposed to 1D5 were morphologically smaller than those that were not exposed to this MAb. Colonies that grew in the presence of 1D5 were i solated and grown in liquid medium containing increasing amounts of th e cytotoxic MAb. Two clones that grew well in liquid medium containing 1D5 were also able to develop into colonies in soft agar. This study has shown that the 30.5 kDa protein found on the plasma membrane of B. hominis is a functionally important protein and that not all cells wi thin a certain population would be susceptible to the cytotoxic effect s of 1D5. These findings suggest that a heterogenous population exists in continuously maintained cultures of B. hominis. (C) 1997 Australia n Society for Parasitology. Published by Elsevier Science Ltd.