TOXOPLASMA-GONDII - REDISTRIBUTION OF TACHYZOITE SURFACE PROTEIN DURING HOST-CELL INVASION AND INTRACELLULAR DEVELOPMENT

Immunoperoxidase localisation of antigen at the electron microscope le vel confirms that parasite surface proteins, in association with membr ane, are shed from the surface of the zoite on invasion, while varying amounts are also internalised. SAG 1 is stable on intracellular zoite s for up to 48 h, although new protein is also synthesised. SAG1 is pr esent on the surface of daughter zoites and is found throughout the in fected cell in distinct vacuoles; these vacuoles represent either dire ct extensions of the parasitophorous vacuole or true export of parasit e surface material. Conflicting reports exist concerning the presence of SAG1 on the developing intraphagosomal membrane (IPM) network immed iately post-invasion (Sibley et al. 1986; Dubremetz et al. 1993). It i s not known whether the molecule continues to be expressed during intr acellular development. The current study follows the fate of SAG1 duri ng invasion and over the first 48 h of parasite multiplication within the host cell, using pre- and post-invasion labeling techniques at the electron microscope level.