Figure 1.

Tissue architecture and mesenchymal lineages in the lung. A: Electron microscopy photomicrographs of normal mouse lung showing fibroblast processes abutting epithelium and pericyte processes attached to endothelium and within a loose capillary basement membrane. Fluorescence images of inflated lung (B) and scheme (C) showing FoxD1 lineage pericytes (red) and cells producing collagen (Col) 1 (green). Note extensive mesenchymal cell populations in normal lung. In disease, both pericyte-derived cells and Col1⁺, platelet-derived growth factor receptor-α⁺ resident fibroblast–derived cells contribute to Col1 production in the foci of fibrosis. Scale bars: 1 μm (A); 50 μm (B and C). a, alveolus; c, capillary; cbm, capillary basement membrane; ec, endothelial cell; epi, epithelial cell; f, fibroblast; p, pericyte; rbc, red blood corpuscle.