Agglutination, cell erythrocytes

The hemagglutinin agglutinates human erythrocytes without regard to type. The toxin, on the other hand, agglutinates cells only after addition of antiricin antiserum, or at high concentrations, where dimer formation occurred.147... 

Some surface assays are based on whole cells and thus have the benefit that they can measure biological activity on biological surfaces. Hemagglutination assays involve observation of the agglutination of erythrocytes by bacteria, viruses. 

The flexibility of surfaces and the formation in the cells of pseudopodia with small terminal radii of curvature will obviously complicate the application of theory. In the agglutination of erythrocytes and the adsorption of erythrocytes to virus-infected cells, projections of small radius of curvature have been observed. Such highly curved regions could well account for local penetration of the energy barrier and strong adhesion at the primary minimum. 

Interestingly, erythrocytes that had lost (2—>3)-sialyl residues were still agglutinable by influenza viruses.531 In similar experiments with Madin-Darby, bovine kidney-cells and Sendai viruses, (2— 3)-sialyl residues as components of the oligosaccharide sequence a-Neu5Ac-(2— 3)-/3-Gal-(T 3)-GalNAc constitute specific receptors for these... 

The role of carbohydrates in biological communication is well illustrated by the human blood types.a b According to the ABO system first described by Landsteiner in 1900, individuals are classified into types A, B, AB, and O. Blood of individuals of the same type can be mixed without clumping of cells, but serum from a type O individual contains antibodies that agglutinate erythrocytes of persons of types A and B. Serum of persons of type B causes type A cells to clump and vice versa. Individuals of none of the four types have antibodies against type O erythrocytes. For this reason, persons with type O blood are sometimes inaccurately described as "universal donors."... 

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