COPD AMs are defective in their ability to phagocytose apoptotic cells (“efferocytosis”), and this defect is potentially linked to the sphingosine-1 phosphate (S1P) system, in particular, the sphingosine-1 phosphate receptor 5 (S1PR5) and antagonizing SIRP5 significantly improves phagocytosis (41). Here, S1PR5 is linked to chronic obstructive pulmonary disease.