Tuder found that macrophages, T cells, B cells and other inflammatory cells infiltrate surrounding injured vessels in PAH patients with pulmonary plexiform lesions [35], and many studies have found significantly increased levels of inflammatory markers in the blood of PAH patients, including C-reactive protein (CRP), interleukins (IL, such as IL-1, IL-6, IL-8, and IL-10), monocyte chemotactic protein 1 (MCP-1), tumor necrosis factor-α (TNF-α), and high mobility group box chromosomal protein 1 (HMGB1) [36]. Here, CCL2 is linked to pulmonary arterial hypertension.