Surface Of Human Red Cells Research Articles

Erythroid cell adhesion molecules Lutheran and LW in health and disease

The Lutheran and LW glycoproteins are blood group-active proteins found at the surface of human red cells. The Lutheran glycoprotein (Lu gp) is a member of the immunoglobulin superfamily (IgSF) that binds the extracellular matrix protein laminin, in particular, laminin isoforms containing the α5 subunit. The LW glycoprotein (LW gp), also an IgSF member, has substantial sequence homology with the family of intercellular adhesion molecules (ICAMs). LW gp binds the integrin very late antigen-4 (VLA-4, α4β1) and αV-containing integrins. Studies on the expression of LW and Lu gps during erythropoiesis utilizing in vitro cultures of haemopoietic progenitor cells have shown that LW gp expression precedes that of Lu gp. These observations have led to the suggestion that LW gp on erythroblasts may interact with VLA-4 on macrophages to stabilize erythroblastic islands in normal bone marrow and that Lu gp may facilitate trafficking of more mature erythroid cells to the sinusoidal endothelium where α5-containing laminins are known to be expressed. Levels of Lu gp and LW gp expression on sickle red cells are greater than on normal red cells and sickle red cells adhere to α5-containing laminins. These data suggest that the Lu and LW molecules may contribute to the vaso-occlusive events associated with episodes of acute pain in sickle cell disease.

MONOCLONAL ANTI‐LWab AND ANTI‐D REAGENTS RECOGNIZE A NUMBER OF DIFFERENT EPITOPES

Monoclonal antibodies (mAbs) which detect antigens on human red cells are also suitable for testing cells of other species. Such studies may reveal previously unrecognized heterogeneity in antibodies which apparently detect the same antigen on the human red cell surface. Information is also provided on specificities shared amongst several species. Here three anti-LWab and a variety of Rh-related antibodies have been tested against the red cells of various primates. One monoclonal anti-LWab antibody, BS46, reacted with the red cells of gorillas and rhesus monkeys but not those of orang-utans, baboons or marmosets. In contrast, BS56 and NIM-M8 reacted with the cells of all these species. Chimpanzee cells, however, reacted only with NIM-M8. Use of primate cells has shown that all three monoclonal anti-LWab antibodies recognize different epitopes. These observations may explain early conflicting data concerning primate cells. The difference between the monoclonal anti-D, D4, and three other anti-D antibodies, 8G2, 8D6 and 7D10, has been confirmed. The D antigen is apparently confined to the red cells of apes and humans. D4 recognizes a polymorphism in chimpanzees and 8G2, 8D6 and 7D10 recognize a polymorphism in gorillas. Two Rh-related mAbs, R6A and K70, were also investigated. R6A fails to react with Rhnull cells and reacts more weakly with homozygous-D-cells than with cells of common Rh phenotypes. K70 reacts weakly with Rhnull and -D-/-D- cells. The antigen detected by R6A is confined to the red cells of humans, gorillas and chimpanzees, while the antigen detected by K70 shows a wider species distribution. In some primates LW antigens are expressed in the absence of the determinant recognized by R6A. This phenotype has never been known to occur in humans.

The inhibition of Na,K-activated adenosinetriphosphatase by a large molecule derivative of p-chloromercuribenzoic acid at the outer surface of human red cell

A large mercurial compound was newly synthesized from Aminoethyldextran (mean MW 250,000) and p-chloromercuribenzoic acid with dicyclohexylcarbodiimide. The reagent inhibited Na, K-activated ATPase of the red cell membrane when applied to intact cells, but not the ouabain-insensitive-ATPase, whereas both were inhibited when it was applied to the membrane preparations. The active transport of rubidium in intact cells was inhibited, but was not the passive transport. The reagent may be a useful tool for studying the polarity and orientation of Na,K-ATPase and other proteins in the cell membranes.

Tracer exchange vs. net uptake of glucose through human red cell surface. New evidence for carrier-mediated diffusion.

Previous kinetic studies of net sugar movements through the human erythrocyte surface (in response to concentration gradients) have led to postulation of a special "carrier" system for transfer of monosaccharides in these cells. But alternatively some sort of non-specific depression of cell permeability at high sugar concentrations has been suggested as a possible basis for the saturation kinetics and the competitive phenomena observed. New theoretical calculations show that these two interpretations predict entirely different orders of magnitude for the relative rate of tracer glucose exchange at such high sugar levels. Therefore, the speeds of gross chemical equilibration and of tracer glucose equilibration were compared by means of serial analyses on quickly separated cells and media, in thick red cell suspensions. Glucose was first added to glucose-free suspensions, and its entry into the cells followed; then C14-glucose was added after attainment of chemical equilibrium, and the tracer equilibration similarly followed. The speed of the tracer movement in relation to the speed of net uptake was on the order of 50 to 100 times greater than would be found in an uncomplicated diffusion process, regardless of what depressant effect might be occasioned by the high sugar levels. In contrast, the comparative rates observed are predicted by the previously proposed facilitated-diffusion mobile-carrier model for monosaccharide transfer, if the glucose-carrier complex is assigned a dissociation constant (at 20 degrees C.) in the neighborhood of 1 mM.

The mechanism of glucose transfer into and out of the human red cell.

1. The kinetics of the movements of glucose in both directions across the surface of the human red cell were studied by optical recording (Ørskov method) of resultant cell volume changes. 2. A wide experimental variety was arranged in the relations between the several quantitative factors contributing to the glucose gradient and the volume changes expected, in order to provide a maximum variety of systematic relations between those factors and the rate of glucose transfer. 3. The kinetics were shown to follow the patterns predicted on the basis of a simple carrier system, involving formation of a highly undissociated complex between the sugar and some factor in the cell surface, provided the glucose concentrations used did not exceed about 3/4 isosmotic. Certain simple properties of this system are derived from the data. 4. At very high glucose concentrations, this system apparently gradually fails to operate; this failure is reversible upon lowering of the excessive glucose concentration. 5. An empirical correction was derived for a previously known but uncalibrated optical disturbance complicating the use of the Ørskov method with media containing appreciable concentrations of non-electrolytes.