PLASMODIUM-VIVAX - A MONOCLONAL-ANTIBODY RECOGNIZES A CIRCUMSPOROZOITE PROTEIN-PRECURSOR ON THE SPOROZOITE SURFACE

The major surface circumsporozoite (CS) proteins are known to play a r ole in malaria sporozoite development and invasion of invertebrate and vertebrate host cells. Plasmodium vivax CS protein processing during mosquito midgut oocyst and salivary gland sporozoite development was s tudied using monoclonal antibodies which recognize different CS protei n epitopes. Monoclonal antibodies which react with the CS amino acid r epeat sequences by ELISA recognized a 50-kDa precursor protein in imma ture oocyst and additional 47- and 42-kDa proteins in older oocysts. A 42-kDa CS protein was detected after initial sporozoite invasion of m osquito salivary glands and an additional 50-kDa precursor CS protein observed later in infected salivary glands. These data confirm previou s results with other Plasmodium species, in which more CS protein prec ursors were detected in oocysts than in salivary gland sporozoites. A monoclonal antibody (PvPCS) was characterized which reacts with an epi tope found only in the 50-kDa precursor CS protein. PvPCS reacted with all P. vivax sporozoite strains tested by indirect immunofluorescent assay, homogeneously staining the sporozoite periphery with much lower intensity than that produced by anti-CS repeat antibodies. Immunoelec tron microscopy using PvPCS showed that the CS protein precursor was a ssociated with peripheral cytoplasmic vacuoles and membranes of sporob last and budding sporozoites in development oocysts. In salivary gland sporozoites, the CS protein precursor was primarily associated with m icronemes and sporozoite membranes. Our results suggest that the 50-kD a CS protein precursor is synthesized intracellularly and secreted on the membrane surface, where it is proteolytically processed to form th e 42-kDa mature CS protein. These data indicate that differences in CS protein processing in oocyst and salivary gland sporozoites developme nt may occur. (C) 1998 Academic Press.