“…4) PN-1 is a serpin and shares considerable structural homology to ATIII, a-1-proteinase inhibitor, C1-inhibitor, and plasminogen activator inhibitor 1 (209,210). While PN-1 is not found in plasma at significant concentrations, it is synthesized by a number of cells including fibroblasts (21 I), smooth-and skeletal muscle cells (21 1-213), neuronal and glial cells (214), and platelets (215). Endothelial cells express PN-1 only upon stimulation with phorbol esters (21 1).…”