Effects of oral administration of hydroxyurea on leukocyte recruitment in TNF-α–treated SCD mice. HU (250 mg/kg) was given orally to SCD mice at the time of TNF-α administration. (A) Leukocyte rolling; (B) adhesion; (C) extravasation; and (D) quantification of RBC-WBC interactions were determined at 180 minutes after TNF-α (*P < .05 compared with vehicle; n = 3-5 mice per group).