Using an antibody raised against the NC1 domain of the ColIVα5 polypeptide (Gly1461 ∼ Thr1685), spanning the pentastatin sequence (Leu1516 ∼ Phe1535) (Supplemental Fig. S1, displaying proteolytic cleavage sites), we detected the presence of NC1- ColIVα5 fragments in pulmonary arteries of healthy donors and patients with end-stage IPAH (Supplemental Fig. S9A). This evidence concerns the gene COL18A1 and idiopathic pulmonary arterial hypertension.