Studies with Ferritin‐Labelled Dolichos biflorus Lectin on the Numbers and Distribution of A Sites on A₁ and A₂ Erythrocytes, and on the Nature of its Specificity and Enhancement by Enzymes

Abstract

S ummary . The conjugation of Dolichos biflorus extract with ferritin produced an electron dense anti‐A reagent that was used to study the number and distribution of A sites on A 1 and A 2 red cells; there were five times as many ferritin‐labelled lectin molecules on A 1 as on A 2 cells (about 800,000: 150,000). The arrangement of sites on both A 1 and A 2 cells was diffuse but not random, as pattern analysis of the ferritin molecules revealed a contagious distribution of the sensitized A sites. It is suggested that the anti‐A 1 saline test activity shown by the Dolichos reagent is due to the inefficiency of the small lectin molecules to bring about agglutination of the A 2 cells. A 2 cells have fewer sites and consequently a larger mean distance between their A sites than have A 1 cells. Thus the probability of ‘bridging’ between the A sites of adjacent cells is reduced. Enzyme treatment increased lectin uptake and the A 2 and B cells both bound over 8 million molecules per cell. The A 2 cells gave agglutination reactions like untreated A 1 cells but the B cells were not agglutinated. In areas of agglutination between the cells lectin molecules probably occurred mainly as a monolayer; however, in the other areas they occurred in multiple layers and only the first layer was in contact with cell membrane sites.