CELLULAR LOCATION AND TEMPORAL EXPRESSION OF THE PLASMODIUM-FALCIPARUM SEXUAL STAGE ANTIGEN PFS16

The temporal expression during gametogenesis and the cellular location of the sexual stage specific protein Pfs16, a putative integral membr ane protein of Plasmodium falciparum, was investigated using two monoc lonal antibodies, 2G7 and 93A3A2. Using sorbitol synchronised, in vitr o gametocyte cultures along with immunofluorescence assays, the time a t which Pfs16 is first expressed during gametogenesis has been estimat ed to 35 hours post merozoite invasion. By immunofluorescence assays o n thin blood smears monoclonal antibodies specific for Pfs16 react str ongly with the gametocyte and also with vesicles within the red blood cell cytoplasm, many of which connect with the gametocyte cell. Purifi cation of parasitophorous vacuole membranes from mature and immature g ametocytes and immunoelectron microscopy on gametocytes during gametog enesis have allowed us to locate Pfs16 to the parasitophorous vacuole membrane. During gametogenesis this membrane is shed along with the re d blood cell membrane. Immunofluorescence assays and immunoelectron mi croscopy studies of emerged gametes indicate that in a minority of cas es the parasitophorous vacuole membrane along with Pfs16 can be retain ed to some extent on the gamete surface.