SPP1 and idiopathic pulmonary fibrosis: Upper lobes from patients with IPF had more FABP4+ alveolar macrophages and fewer IPF-associated profibrotic SPP1+ macrophages than the lower lobes but similarly elevated numbers of CMKLR1+ macrophages (IPF upper lobe: 8.4% and lower lobe: 8.9% versus control upper lobe: 2.3% and lower lobe: 0.8%).