SPNS2 and chronic obstructive pulmonary disease: A potential limitation of our study is the relatively small numbers in some groups; however, despite this we were able to support our hypothesis by showing a significant increase in Spns2 immunofluorescence in COPD alveolar macrophages compared to those from non-COPD patients and healthy controls, and a significant correlation between epithelial expression of Spns2 and macrophage phagocytic capacity in mouse.