CCL2 and pulmonary arterial hypertension: In CTD-PAH, various pro-inflammatory molecules, such as interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-α and chemokines (such as chemokine ligand 2(CCL2)/monocyte chemoattractant protein-1 (MCP-1), RANTES chemokines or fracta) are synthesized by fibroblasts, ECs and vascular SMCs (9, 29, 30).