ANCHORING OF AN IMMUNOGENIC PLASMODIUM-FALCIPARUM CIRCUMSPOROZOITE PROTEIN ON THE SURFACE OF DICTYOSTELIUM-DISCOIDEUM

The circumsporozoite protein (CSP), a major antigen of Plasmodium falc iparum, was expressed in the slime mold Dictyostelium discoideum. Fusi on of the parasite protein to a leader peptide derived from Dictyostel ium contact site A was essential for expression. The natural parasite surface antigen, however, was not detected at the slime mold cell surf ace as expected but retained intracellularly. Removal of the last 23 a mino acids re suited in secretion of CSP, suggesting that the C-termin al segment of the CSP, rather than an ectoplasmic domain, was responsi ble for retention, Cell surface expression was obtained when the CSP C -terminal segment was replaced by the D. discoideum contact site A gly cosyl phosphatidylinositol anchor signal sequence. Mice were immunized with Dictyostelium cells harboring CSP at their surface, The raised a ntibodies recognized two different regions of the CSP, Anti-sporozoite titers of these sera were equivalent to anti-peptide titers detected by enzyme-linked immunosorbent assay, Thus, cell surface targeting of antigens can be obtained in Dictyostelium, generating sporozoite-like cells having potentials for vaccination, diagnostic tests, or basic st udies involving parasite cell surface proteins.