Transfusion of stored RBCs induces an acute phase response.(A) SAA1-luciferase reporter mice were transfused with 200 μL of either fresh RBCs (< 24-hour storage) or stored RBCs (2-week storage) and luciferase activity measured by noninvasive bioluminescence imaging at multiple times up to 24 hours after transfusion (n = 3 per group). Results are representative of 2 experiments. (B) Bioluminescence was quantified over the hepatosplenic region of SAA1-luciferase reporter mice transfused with fresh RBCs (n = 6; ) or stored RBCs (n = 6; ■); *P < .01. (C) Circulating SAA1 protein levels in SAA1-luciferase reporter mice 24 hours after transfusion with fresh RBCs or stored RBCs (n = 6 per group); *P < .01. Results are combined from 2 separate experiments.