Transfusion of stored RBCs induces dose-responsive proinflammatory cytokine responses. (A) Hemoglobinemia, as detected by absorbance, was observed in all mice (n = 8) transfused with stroma-free lysate derived from stored RBCs. Representative spectra of plasma (diluted 1:4 with PBS) obtained from mice 2 hours after transfusion with fresh RBCs (< 24-hour storage), stored RBCs (2-week storage), or stroma-free lysate derived from stored RBCs are shown. (B) Untransfused C57BL/6 mice (n = 13) or mice transfused with fresh RBCs (1u = 200 μL, n = 5; [ie, 1 human equivalent unit = 200 μL]; 2u = 400 μL, n = 17), stored RBCs (1u = 200 μL, n = 5; 2u = 400 μL, n = 17), washed stored RBCs (400 μL; n = 13), stored RBC-derived supernatant (SN, 400 μL, n = 12), ghosts prepared from stored RBCs (400 μL, n = 8), and stroma-free lysate derived from stored RBCs (400 μL, n = 8) were killed 2 hours after transfusion, and plasma cytokine levels were measured (as labeled); *P < .05; **P < .01; ***P < .001 compared with fresh RBCs.