FIGURE 1

Endoglin is expressed in the veins, distal arteries and capillaries of the pulmonary vasculature. Pulmonary veins are supported by distinctive myocardial muscle cells (arrows) that are recognizable in H&E-stained sections (a), and confirmed by cardiac -actinin staining (b). Pulmonary arteries are recognized by their position within a bronchiovascular bundle in H&E-stained sections (c). Endoglin is expressed in the pulmonary artery valve leaflets (arrow) and surrounding endothelium (d); but expression is lost (arrows) as the pulmonary artery divides into the left and right pulmonary arteries (e). (Inset in d shows an example of negative staining in no primary antibody controls). Expression remains low in arteries within the lung parenchyma, until the distal arteries where there is a transition to positive expression (arrows; f, g). Endoglin is expressed throughout the venous (arrows) and capillary endothelium (h, i). Abbreviations: a, artery; al, alveolus; br, bronchiole; da, distal artery; dv, distal vein; lpa, left pulmonary artery; rpa, right pulmonary artery; s-br, small bronchiole; v, vein. Scale bars: 100 m.