Anti-TRAIL antibody treatment prevents the development of PAH at day 21 in the MCT rat model. (A–D) Bar graphs show RVSP (A), RVEDP (B), left ventricular end-systolic pressure (LVESP; C), and LVEDP (D), measured in mm Hg. (E–H) PA AT (E), cardiac index (F), ePVRi (G), and RVH (H) are shown. (I) The degree of medial wall thickness as a ratio of total vessel size (Media/CSA). (J and K) Quantification of the percentage of proliferating cells (PCNA positive; J) and apoptotic (TUNEL positive; K) separated into pulmonary arteries <50 µm in diameter, vessels from 51 to 100 µm in diameter, and vessels >100 µm in diameter. (L) Representative photomicrographs of serial lung sections from IgG and anti-TRAIL–treated MCT-induced rats 21 d after injection. Sections were stained with Alcian Blue Elastic van Gieson (ABEVG) or immunostained for α-SMA, von Willebrand factor (vWF), PCNA, or TUNEL. Error bars represent mean ± SEM, n = 4 animals per group. *, P < 0.05; **, P < 0.01; ***, P < 0.001, compared with IgG-treated rats. Arrows point to PCNA- or TUNEL-positive cells. Bars, 50 µm.