Banked normal AARBCs stored for 30 days failed to reduce SSRBC adhesion to the vascular endothelium and vaso-occlusion in vivo. (A-M) Microscopic observations of postcapillary venules were conducted by using 10× and 20× magnification through implanted dorsal skin-fold window chambers after infusion of human SSRBCs into the tail vein of nude mice. Vessels without adherent cells appear gray, due to the blurred fluorescence of rapidly moving SSRBCs. Mice received infusion of vehicle-treated SSRBCs, Epi-treated SSRBCs, or Epi-treated SSRBCs mixed with fresh AARBCs or AARBCs stored for 14 or 30 days. Vehicle-treated SSRBCs adhered minimally to the endothelium in vivo (A-B), whereas Epi dramatically increased SSRBC adhesion (indicated by black arrows) and vaso-occlusion (indicated by white arrows) (C-D). Infusion of either fresh (“0 day”) AARBCs mixed with epi-treated SSRBCs (E-G), or AARBCs stored for 14 days mixed with Epi-treated SSRBCs (H-J), dramatically reduced SSRBC adhesion and vascular stasis compared with Epi-stimulated SSRBCs alone. In contrast, admixture with AARBCs stored for 30 days (K-M) failed to decrease adherence of Epi-activated SSRBCs to the endothelium (indicated by black arrows) and vascular occlusion (indicated by white arrows). (N) Fluorescence intensity (pixels) representative of human SSRBC adhesion to vessels. Movies (20× magnification) were used to quantify fluorescence intensity induced by adherent human SSRBCs in animals infused with fluorescence-labeled SSRBCs treated as described in panels A-M (n = 5 for each treatment). The values were averaged among groups of animals to represent the mean fluorescence intensity. Error bars show SEM. **P < .05 for Epi-treated SS vs vehicle-treated SS, and Epi-treated SS + fresh AA vs Epi-treated SS. ***P < .05 for Epi-treated SS + 14-day-old AARBCs vs Epi-treated SS.