Studies on falciparum malaria with atomic-force and surface-potential microscopes.

Atomic-force microscopy (AFM) was used to examine the structure of the knobs on unfixed erythrocytes infected with Plasmodium falciparum. Although each knob appears as a cone when chemically fixed and viewed by transmission electron microscopy, AFM revealed that each consisted of two subunits, and that, unlike the remainder of the erythrocytic surface, which was negatively charged, the knob surface has a positive electrical charge. Each of these factors might be central to the phenomenon of cyto-adherence in falciparum malaria.