CD36-dependent adhesion and knob expression of the transmission stages of Plasmodium falciparum is stage specific.

Plasmodium falciparum trophozoites sequester from the peripheral circulation by adherence to host endothelium. Gametocytes, also sequester during maturation. Analysis of the adhesion phenotype of stage I to V gametocytes of several isolates/clones was assessed by binding of infected cells to C32 melanoma cells (C32MC) and the purified adhesion proteins, leucocyte differentiation antigen (CD36) and intercellular adhesion molecule-1 (ICAM-1). These cells and proteins, have previously been shown to be receptors for adherence of trophozoites. Early gametocytes (stages I-IIA) were found to bind to C32MC as well as the purified receptor CD36 but not to ICAM-1. Early gametocytes bound to C32MC via CD36 and the parasite ligand involved in this binding was trypsin sensitive. Stage IIB to V gametocytes did not adhere to C32MC, CD36 nor ICAM-1. Electron-dense protruberances known as knobs and histidine rich protein 1 (HRP 1) expression have been associated with trophozite adhesion to CD36. Knobs were present at the surface of early but not late gametocyte infected cells. Stage-specific patterns of HRP 1 expression, consistent with a role for this molecule in CD36 adhesion of early gametocytes, were also observed. The adhesion phenotype of these young gametocytes was indistinguishable from that of the trophozoites by all criteria examined. These data support the hypothesis that other host receptors mediate the binding of late gametocytes.