TREM2 and idiopathic pulmonary fibrosis: In our annotations, we refer to SPP1+ macrophages as CHI3L1+ macrophages, resembling previously identified TREM2+ macrophages (36), define the airway macrophage niche (Fig. 2A), which, together with C1Qhi macrophages (36), was nearly exclusively found in IPF tissue (fig.