Alkaline CDase, SK, Sph, and S1P in SCD. (A) ACER1 expression in RBCs and (B) plasma. (C-D) SK1 and SK2 expression from equal amounts of RBC protein. (E-F) SK2 levels from equal amounts of plasma protein. (G-I) Sphingosine and S1P levels in whole blood (G), plasma (H), and RBCs (I). *P < .05 measured with a Student t test relative to AA.