A study of weak subgroups of blood group A with an antiglobulin-latex test.

The distribution of the blood group A antigen on subgroups A1, A2, A3, Ax, and Ae1 was studied by means of a highly sensitive and specific antiglobulin-latex test. Marked variability in the cell to cell expression of A antigen was observed in A1 and A2 cells. The weaker subgroups (A3, Ax, and Ae1) were characterized by a minor population of cells containing A antigen and a major population with no detectable A sites. Comparison of the antiglobulin-latex test with the fluorescent antibody technique indicates that the former is approximately 10,000 times more sensitive in detecting cell bound antibody, and thereby membrane antigens. The results of this study demonstrate that within each of the A subgroups (with the possible exception of A1) there exist erythrocytes that apparently lack recognizable A antigen sites. The number of such cells is greatest in the weakest subgroups (Ax and Ae1).