The nature of human blood group A3 erythrocytes.

A population of human erythrocytes (free A3 cells) which was entirely unagglutinable with anti-A hemagglutinins was successfully separated from human blood group A3 erythrocytes by affinity chromatography on a column of lima bean anti-A hemagglutinin (LBH)-Sepharose. The hemagglutinating and the binding properties of free A3 cells with purified LBH and purified eel serum anti-H hemagglutinin (ESH) were investigated. It has been revealed that there exists a bulk of H antigens on free A3 cells, whereas the number of A antigens on a free A3 cell is only 9% of that on an A1 cell. However, no appreciable difference was observed in the binding constants of A1 and free A3 cells to LBH and ESH. From these results it is assumed that the structure of the A antigens on free A3 cells is identical with, or at least similar to, that on A1 cells, but the density of the antigens on the surface of free A3 cells is too low to induce the agglutination of the cells with LBH or anti-A serum.