CHARACTERIZATION OF EXTREME APICAL ANTIGENS FROM TOXOPLASMA-GONDII

We have isolated 26 monoclonal antibodies which specifically recognize the extreme apex of Toxoplasma gondii, a protozoan parasite which att aches to and invades host cells via its specialized apical end. The un ique apical organelles which define the phylum Apicomplexa are thought to be involved in mechanical and enzymatic aspects of invasion. Immun oblots, immunofluorescent morphology, and immunogold labeling define s ix classes of apically localized antigens recognized by these antibodi es. Three of the classes are detergent insoluble and localize to the c onoid and the cytoplasmic face of the apical membrane, suggesting that they may be part of the parasite's membrane cytoskeleton. The remaini ng three classes extract with detergent and are associated with intern al membrane bounded vesicles (micronemes and the upper necks of rhoptr ies). One class of micronemal antigens appears to be cell cycle regula ted. This antigen localizes to the cytoplasm, especially the perinucle ar region, in thin (recently replicated) parasites, but is apical in l arger parasites. (C) 1994 Academic Press, Inc.