Membrane knobs are required for the microcirculatory obstruction induced by Plasmodium falciparum-infected erythrocytes.

Abstract

We have studied the pathophysiology of the vascular obstruction induced by Plasmodumfalkiparum-parasitized erythrocytes with the use of an ex vivo microcirculatory preparation perfused with red cells infected with knobless and knobby dones of the FCR-3 strain. We find that parasitized erythrocyte membrane knobs are indispensable for the generation of the circulatory obstruction. Uninfected erythrocytes incubated in culture and erythrocytes infected with early or late forms of the knobless dones or the early forms of the knobby done all failed to obstruct the microcirculation, although exhibiting various effects on bulk viscosity and peripheral resistance during flow. In contrast, late forms of the knobby clone produced significantly higher peripheral resistance during flow and significant obstruction as detected by changes in time of pressure flow recovery as well as by direct videorecorded microscopic observation. Optical and electron microscopy showed that the adherence of parasitized cells to the endothelium was limited to the venules and involved the knobs in junctions. In addition, we were able to follow the sequence of events during obstruction: initial red-cell adherence to the venular endothelium (sometimes only transitory) followed by progressive recruitment at the venule surface, finally leading to total obstruction that involved parasitized and nonparasitized erythrocytes. Sometimes, retrograde aggregation would extend the obstruction to the capillaries or even precapillary arterioles. These results show that knobs are necessary and sufficient to produce vascular obstruction and that other factors (spleen, immunological, etc.) can only have a modulating role. These results also exclude the possibility that the exclusive adherence to venules is the consequence of "plasma factors"found in the malaric patients.The infection caused by Plasmodium falciparum produces the most severe form of human malaria (1) The mechanism of the P. falciparum-induced microvascular obstruction is not clearly understood; both the capability of malaria parasite-infected erythrocytes to produce aggregates through cell-cell interactions (4) as well as parasitized erythrocyte-endothelial cell interaction (5, 6) have been suggested as mechanisms for the vascular entrapment of parasitized cells. Knobs found in the membranes of malariainfected erythrocytes (7) have been proposed as the specific structures involved in both possible mechanisms. Decreased red cell deformability secondary to increased viscosity of parasitized red cells may also play a role in obstruction (8).The work presented here attempts to dissect the differential contribution of erythrocyte membrane knobs, decreased deformability, and aggregation (clumping of parasitized and nonparasitized cells) to the pathophysiology of the microcirculation obstruction induced by P. falciparum malaria infection. Our experimental design makes use of an isolated vasculature preparation of the rat mesoappendix [Baez preparation (9)] artificially perfused with P. falciparum-...

New Ultrastructural Analysis of the Invasive Apparatus of the Plasmodium Ookinete

“…Previously, similar fixation and embedding in LXR112 was used to study the TEM of knob and knobless P. falciparuminfected erythrocytes. 47 The ultrastructure findings of the apical complex structures required new fixation and embedding methods and materials. It is noteworthy to observe that the apical end of the mature ookinete protrudes as a sucker-like structure, which might enable effective attachment and targeted secretion of enzymes, such as proteases and chitinases, to dissolve down peritrophic matrix (PM) barrier as previously visualized.…”

PfEMP1 expression is reduced on the surface of knoblessPlasmodium falciparuminfected erythrocytes

“…It has been suggested that the biological function of knobs is to augment PfEMP1 adhesion under flow (Cooke et al, 2002a;Crabb et al, 1997;Raventos-Suarez et al, 1985). KAHRP interacts directly with both the cytoplasmic tail of PfEMP1 as well as components of a modified IE cytoskeleton (Magowan et al, 2000;Oh et al, 2000;Waller et al, 1999;Waller et al, 2002).…”

Chromatin structure determines the sites of chromosome breakages in Plasmodium falciparum

“…The KAHRP gene product is a component of the knob structure on the surface of parasitized erythrocytes that are responsible for cytoadherence (12,13). Chromosomal breakage events disrupting the KAHRP gene result in parasite mutants that are knobless and cytoadherentdeficient (14,15,16).…”