Maximum β₁ level of activation as determined by 8A2 prestimulation of β₁ (9EG7 epitope). The percentage expression of the activation epitope of β₁ recognized by the 9EG7 antibody, before and after incubation with β₁-activating antibody 8A2, ranged from 6% to 100% in a subset of 24 AML patients.