Fluorescence histograms of platelets treated with human anti-A,B.

In this assay, O platelets (A) could not be distinguished from A₂ platelets (B). The platelets from most A₁donors (C) gave a broad histogram that overlapped the histograms of group O and group A₂ platelets. However, some A₁ platelet preparations (D) gave a broad histogram similar in shape to that of normal-expresser A₁ platelets, but shifted to the right, and (E) 2 of 100 donors gave a sharp peak consisting of platelets expressing much higher levels of A antigen. The histograms shown are referred to as Type I (D) and Type II (E) high expresser.