Epinephrine-treated SS RBCs adhere to Lu-Fc in an integrin α₄β₁–dependent manner under flow conditions. (A) AA and SS RBCs (.005 [0.5%] hematocrit) were either untreated or incubated with 20 nM epinephrine (Epi) for 1 minute at room temperature, then injected into a Lu-Fc–coated microslide (0.3 mg/mL) at 0.2 dyne/cm² for 10 minutes before applying 5-minute washout steps at 0.4, 1, 2, and 4 dyne/cm². Cells were counted after each wash in 6 areas along the microslide centerline. (B) AA (AA1 and AA2), SS (SS1-SS6), and high-reticulocyte control (C1-C3) RBC samples (.005 [0.5%] hematocrit) were either untreated or incubated with 20 nM epinephrine with or without preincubation with 10 μg/mL blocking antibody anti–integrin β₁ (mAb 13), or with 1 μg/mL activating antibody anti–integrin β₁ TS2/16. Injection and washouts were carried out as for panel A. The graph shows results at 1 dyne/cm². Each value is a mean of 6 measures. (**P < .01; in panel B, ▧ and ▪ are compared with □, and ⊡ is compared with ▪). Error bars represent SD.