Studies with ferritin-labelled Dolichos biflorus lectin on the numbers and distribution of A sites on A 1 and A 2 erythrocytes, and on the nature of its specificity and enhancement by enzymes.

Abstract

Summary. 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 A1 and A2 red cells; there were five times as many ferritin‐labelled lectin molecules on A1 as on A2 cells (about 800,000: 150,000). The arrangement of sites on both A1 and A2 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‐A1 saline test activity shown by the Dolichos reagent is due to the inefficiency of the small lectin molecules to bring about agglutination of the A2 cells. A2 cells have fewer sites and consequently a larger mean distance between their A sites than have A1 cells. Thus the probability of ‘bridging’ between the A sites of adjacent cells is reduced. Enzyme treatment increased lectin uptake and the A2 and B cells both bound over 8 million molecules per cell. The A2 cells gave agglutination reactions like untreated A1 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.