Reaction of lectins with human erythrocytes: I. Factors governing the agglutination reaction

Abstract

At low concentrations of concanavalin A (conA), binding of the lectin to the erythrocytes appears to be the rate-limiting step in the agglutination of these cells. At higher concentrations of lectin the rate of agglutination is concentration-independent, indicating that the aggregation reaction is rate-determining. Only 5 to 7% of the 1.2 × 10 5 receptor sites need be occupied by con A in order for agglutination to take place. Although trypsin-treated cells bind 30% less 125I-conA, they agglutinate better than untreated cells. At high lectin concentrations, erythrocyte agglutination by wheat germ agglutinin (WGA) is more than 8 times faster than the conA-mediated reaction. Lowering of the temperature to 0 °C reduces the rate but not the extent of the agglutination by both lectins. Mechanical shear reduced the conA-mediated agglutination of native cells by more than 160-fold and that of trypsinized and neuraminidase-treated cells 6-fold and 4-fold, respectively. It is concluded that metabolic activity, receptor mobility (i.e. cluster or patch formation) and cytochalasin B-sensitive processes, all of which have been reported to be involved in the lectin-mediated agglutination of fibroblasts and other cells, do not play a role in erythrocyte agglutination. Lectin-mediated erythrocyte agglutination appears to be governed primarily by the rate and extent of binding of lectin to the cell surface, the cell surface charge (modifiable by enzyme treatments or polycations) and the shear forces in the suspension. Morphological studies confirm and amplify these conclusions.