Scanning electron microscope-analysis of the protrusions (knobs) present on the surface of Plasmodium falciparum-infected erythrocytes.

Abstract

The nature of the surface deformations of erythrocytes infected with the human malaria parasite Plasmodium falciparum was analyzed using scanning electron microscopy at two stages of the 48-h parasite maturation cycle. Infected cells bearing trophozoite-stage parasites (24-36 h) had small protrusions (knobs), with diameters varying from 160 to 110 nm, and a density ranging from 10 to 35 knobs x tLm -2. When parasites were fully mature (schizont stage, 40-44 h), knob size decreased (100-70 nm), whereas density increased (45-70 knobs x pm-2). Size and density of the knobs varied inversely, suggesting that knob production (a) occurred throughout intraerythrocytic parasite development from trophozoite to schizont and (b) was related to dynamic changes of the erythrocyte membrane. Variation in the distribution of the knobs over the red cell surface was observed during parasite maturation. At the early trophozoite stage of parasite development, knobs appeared to be formed in particular domains of the cell surface. As the density of knobs increased and they covered the entire cell surface, their lateral distribution was dispersive (more-than-random); this was particularly evident at the schizont stage. Regional surface patterns of knobs (rows, circles) were seen throughout parasite development. The nature of the dynamic changes that occurred at the red cell surface during knob formation, as well as the nonrandom distribution of knobs, suggested that the red cell cytoskeleton may have played a key role in knob formation and patterning.

Cytoadhesion of Plasmodium falciparum–infected erythrocytes to chondroitin-4-sulfate is cooperative and shear enhanced

“…29,35 To obtain quantitative data on knob number and distribution, we performed atomic force microscopy on erythrocytes infected with FCR3 CSA . A significant increase in knob density from 9 6 1 to 14 6 1 mm 22 (P 5 .02) and a decrease in basal knob diameter from 73 6 3 to 64 6 2 nm (P 5 .004) were observed as the parasite developed from trophozoites to schizonts (supplemental Figure 2A).…”

PfEMP1 expression is reduced on the surface of knoblessPlasmodium falciparuminfected erythrocytes

“…Perhaps the most obvious modification to the host erythrocyte is the development of several thousand knob-like protrusions (~100 nm diameter) from approximately 16-18 hours post-invasion (Gruenberg et al, 1983;Langreth et al, 1978;Nagao et al, 2000). These electron dense structures act as sites for anchoring PfEMP1 on the outer face of the plasma membrane and are thus implicated in mediating IE cytoadhesion (Baruch et al, 1995;Cooke et al, 2000).…”

Identification of Novel Membrane Structures in Plasmodium falciparum Infected Erythrocytes

“…The fact that these structures are not detectable on schizontinfected erythrocytes either by transmission (Langreth et al 1978, Atkinson & Aikawa 1990 or SEM (Gruenberg et al 1983), suggests that the formation of such membrane modifications might be functionally related to the release of merozoites from infected erythrocytes.…”

“…Membranous structures were then processed either for transmission (Winograd & Sherman 1989) or scanning electron microscopy (SEM) (Gruenberg et al 1983) and observations were either carried out on a Phillips transmission electron microscope Model CM10 or a Phillips scanning electron microscope Model 515.…”