S1PR5 and chronic obstructive pulmonary disease: Although we did not find significantly increased expression of S1PR1 in alveolar macrophages from either smokers or COPD subjects, this receptor was found to be strongly correlated with S1PR5. Taken together with our findings of a negative correlation with lung function and phagocytosis of apoptotic cells, these data suggest that both receptors may be associated with COPD progression and defective macrophage function in COPD either by a link between the two or common downstream effectors.