S1PR1 and chronic obstructive pulmonary disease: It is thus likely that the defective efferocytosis in COPD that persists despite smoke cessation could be mediated by S1PR5, possibly in association with S1PR1. Interestingly, in our previous study the relative mRNA for S1PR5 was significantly lower in whole lung tissue of patients with COPD compared to controls without COPD [16].