A rhoptry-derived P falciparum parasite molecule binds to the surface of normal and infected erythrocytes. Staining of nEs and IEs from FCR3^CSA parasites using mAb B4 (green) in IFA. Parasite DNA is stained with DAPI (blue). (A-D) L-IFA analysis. (E-H) AD-IFA analysis. (A) Merozoite binding to the membrane of an nE stained with anti–RSP-2. (B) Surface staining of an nE (left) and rIE (right). (C) Transfer of RSP-2 from merozoite to the entire erythrocyte surface. (D) A mature trophozoite-stage parasite is not stained by mAb B4. AD-IFA using B4 in young rIEs. (E) Endoplasmic reticulum (ER) in 26 ± 2–hour-old parasites. (F) Rhoptries in 34 ± 2–hour-old schizont stage (G) and surface of free merozoites at 44 ± 2 hours (H). Scale bars measure 10 μm.