CRC - Red Blood Cell Aggregation
|Publication Date:||28 September 2011|
PHENOMENON OF RED BLOOD CELL AGGREGATION
Human red blood cells (RBC), as well as RBC from most mammals, have a tendency to form aggregates that initially consist of face-to-face linear structures that resemble a stack or roll of coins (Chien and Jan 1973; Chien and Sung 1987; Fåhraeus 1929). Such individual linear structures are often termed rouleau, with rouleaux being the plural. Figure 1.1 shows a representative assortment of rouleaux for normal human RBC in autologous plasma, where it is obvious that (1) the number of RBC per rouleau can vary widely, and (2) side-to-side or side-to-end branching can occur. While Figure 1.1 represents normal aggregation in a thin two-dimensional geometry (i.e., between a microscope slide and cover slip), rouleaux can form threedimensional structures under appropriate conditions (Branemark 1971; Cokelet and Goldsmith 1991). As anticipated, the formation of these larger structures is affected by factors such as available space and the level of cell-cell attractive forces.
The aggregates shown in Figure 1.1 were photographed under static, no-flow conditions after sufficient time had elapsed for the aggregates to reach a stable configuration. However, as will be detailed in other sections of this monograph, RBC aggregation involves relatively weak attractive forces (Neu and Meiselman 2002; Neu et al. 2003; Skalak and Zhu 1990). Hence, it is possible to disperse aggregates into smaller structures or individual cells by the application of forces resulting from fluid flow or mechanical shear (Rampling 1990; Schmid-Schönbein et al. 1969). It is important to recognize that RBC aggregation is a reversible process: aggregates will reform when external forces are reduced or eliminated. The reversible nature of RBC aggregation is different from blood coagulation in which the soluble plasma protein fibrinogen forms a network of insoluble strands and in which RBC and blood platelets can become enmeshed. The distinction between aggregation and blood coagulation can be initially unclear because fibrinogen is a major determinant of RBC aggregation and also participates in coagulation (Meiselman 2009; Rampling 1990). Unlike coagulation, fibrinogen remains soluble during aggregation.