THROMBOSPONDIN-RELATED ADHESIVE PROTEIN (TRAP) OF PLASMODIUM-FALCIPARUM - EXPRESSION DURING SPOROZOITE ONTOGENY AND BINDING TO HUMAN HEPATOCYTES

Plasmodium sporozoites collected from oocysts, haemocoel and salivary glands of the mosquito show profound differences in their biological p roperties such as motility, ability to induce protective immune respon se and infectivity for vertebrate host cells. Sporozoites from salivar y glands are much more infectious than those from oocysts and haemocoe l. Differential expression of proteins, such as the circumsporozoite ( CS) protein and the thrombospondin-related adhesive protein (TRAP), im plicated in sporozoite recognition and entry into hepatocytes may acco unt for the development of infectivity during ontogeny. We have carrie d out a series of experiments to: (i) analyse the expression and local ization of TRAP in P.falciparum sporozoites during development in the mosquito; and (ii) elucidate the biochemical and adhesive properties o f recombinant TRAP. Our data indicate that TRAP is not expressed in oo cysts, whereas variable amounts of CS protein are found in this parasi te developmental stage. Hemocoel sporozoites display the distinct phen otypes TRAP CS protein(+) and TRAP(+) CS protein(+) at a frequency of 98.5 and 1.5% respectively. Salivary gland sporozoites are all TRAP(+) CS protein(+). We also provide experimental evidence showing that rec ombinant TRAP binds to the basolateral cell membrane of hepatocytes in the Disse's space and that sulfated glycoconjugates function as TRAP ligands on human hepatocytes.