An Improved Method for Assessing Antigen Presentation on the Surface of Plasmodium falciparum-Infected Erythrocytes by Immuno-Electron Microscopy.

Immuno-electron microscopy can detect and localize antigens in cells or tissues at a resolution of several nanometers. In the case of P. falciparum-infected erythrocytes, immuno-EM studies are frequently hampered by the electron-dense nature of the hemoglobin and access of antibodies to antigenic sites, particularly if the targeted protein is presented on the host cell surface or lies in proximity to the host cell cytoskeleton. Here, we describe an improved immuno-EM protocol that overcomes these problems. The improved signal to noise ratio and the enhanced access to antigenic sites now allows one to obtain information regarding target density and distribution and, hence, additional insights into the architecture and function of parasite-induced, or -affected, structures.

KAHRP dynamically relocalizes to remodeled actin junctions and associates with knob spirals in Plasmodium falciparum-infected erythrocytes.

The knob-associated histidine-rich protein (KAHRP) plays a pivotal role in the pathophysiology of Plasmodium falciparum malaria by forming membrane protrusions in infected erythrocytes, which anchor parasite-encoded adhesins to the membrane skeleton. The resulting sequestration of parasitized erythrocytes in the microvasculature leads to severe disease. Despite KAHRP being an important virulence factor, its physical location within the membrane skeleton is still debated, as is its function in knob formation. Here, we show by super-resolution microscopy that KAHRP initially associates with various skeletal components, including ankyrin bridges, but eventually colocalizes with remnant actin junctions. We further present a 35 Å map of the spiral scaffold underlying knobs and show that a KAHRP-targeting nanoprobe binds close to the spiral scaffold. Single-molecule localization microscopy detected ~60 KAHRP molecules/knob. We propose a dynamic model of KAHRP organization and a function of KAHRP in attaching other factors to the spiral scaffold.