Rheological analysis of the formation of rosettes by red blood cells parasitized by Plasmodium falciparum

Abstract

Red blood cells infected by mature malarial parasites of the species Plasmodium falciparum can adhere to non-parasitized red cells (rosetting) and also to endothelial cells (cytoadhesion). To investigate how the circulation might influence rosetting, we studied formation of rosettes in cell suspensions sheared in a cone-and-plate viscometer, and the ability of flowing non-parasitized cells to bind to parasitized cells already adherent to a surface. After rosettes of strain R29 had been disrupted with fucoidan, they reformed slowly under stationary conditions but more rapidly in suspensions sheared at low stress (about 0.1-0.2 Pa). Strain Malayan Camp gave a lower rosetting frequency which actually increased at low shear. Increasing shear stress was associated with reduction in rosette formation, although rosetting occurred at >1 Pa, suggesting that rosettes could form in the systemic circulation. Rosetting inhibited adhesion of flowing parasitized cells to immobilized platelets (which express the cytoadhesion receptor CD36), as evidenced by increased adhesion after disruption of rosettes. The de-rosetted adherent cells parasitized by R29 supported only a low level of rosetting when non-parasitized cells were flowed over them at a wall shear of 0.1 Pa, with little increase if the stress was decreased to 0.05 Pa. Rosettes formed in the circulation might obstruct microvessels and inhibit cytoadhesion if they reached venules. However, if cytoadhesion occurred before rosetting, then adherent cells should not efficiently form rosettes.

The Effect of Anti-Rosetting Agents against Malaria Parasites under Physiological Flow Conditions

“…Using this system, we found that, in agreement with previous work [5], [30], [31], [32], rosettes do exist under physiologically relevant shear stresses (Figs. 1 and 2).…”

“…Despite the time-consuming nature of the image analysis in the new flow assay, it does have some advantages compared to methods previously used to assess rosetting under shear stresses, including the plate-cone viscometer [30], [31] and LORCA [32]. These assays, whilst subjecting rosettes to shear stress, ultimately calculate rosette frequency from a standard wet preparation.…”

“…The IEs are subjected to continuous flow of the vascular system, with shear stresses ranging from 0.5–5.0 dyn/cm 2 within the microvasculature, to >10 dyn/cm 2 on the arterial side of the circulation [29]. The rheological properties of rosettes have been examined previously using a variety of techniques including perfusion of ex vivo rat microvasculature [5], micropipette manipulation and use of a cone-plate viscometer [30], [31] and use of a Laser-Assisted Optical Rotational Cell Analyser (LORCA) [32]. Using these techniques it has been shown that rosettes can withstand shear forces equivalent to those found in the microvasculature [5], [30], [31], [32].…”

Blood group and size dependent stability of P. falciparum infected red blood cell aggregates in capillaries

“…9 Rowe et al 10 found reduced rosetting in blood group O patient isolates in compliance with a 66% lower chance of severity of blood group O patients, and variable rosetting levels in relation to the ABO blood type of the RBCs have been reported in in vitro studies. 9,11,12 The cohesion within rosettes and their formation was studied during the 1990s by Nash et al using cone-and-plate viscometers 13,14 or micropipets. 13 They found strong binding between infected and uninfected RBCs and assumed that rosettes can both survive 13 and even form 14 in the circulation.…”

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“…Yet, even if rosettes are only partially being formed during the passage through the venules, they would still slow down blood flow and thereby enhance cytoadherence, in as much as reduced flow is known to increase it [36]. However, if cytoadherence occurred before rosetting, then adherent cells should not efficiently form rosettes [37]. …”