PAI-1 promoter directs expression of a β-Gal reporter to fibroblasts juxtaposed to endothelial cells. (A) Fibroblasts transfected with a PAI promoter-LacZ plasmid. (B) Fibroblasts transfected with an L16 promoter-LacZ plasmid. See Materials and Methods for details. L-fibroblasts (L); LE-II endothelial cells (E).