Elevated plasma adenosine induces erythrocyte SphK1 activity increase in vivo. (A) Schematic representation of mouse treatment strategy. (B) Plasma adenosine and (C) erythrocyte SphK1 activity in Ada^+/−, Ada^−/− with PEG-ADA treatment, Ada^−/− without PEG-ADA treatment, and Ada^−/− rescue. Values shown represent the mean ± SEM (n = 6 for each group). *P < .05 Ada^−/− vs Ada^−/−+ PEGADA;**P < .05 Ada^−/− vs Ada^−/− rescue.