SMase activity in SCD. (A) Neutral SMase activity in plasma and (B) RBCs. (C) Acid SMase activity in plasma and (D) RBCs. (E) Acid SMase expression in plasma and RBCs. (F) Acid SMase activity in high- and low-density RBCs (labeled “high ρ” and “low ρ, ” respectively), and (G) representative SEM images of RBCs. (H) Acid SMase activity in whole blood of AS/SS mice immediately after 8 hours normoxic/hypoxic conditioning. *P < .05 measured with an analysis of variance (ANOVA) relative to AA or AS normoxia.