In PAH patients there is an increased number of activated macrophages around the pulmonary blood vessels that could induce the release of IL-1, IL-6, IL-10, TNF-α, CCL2 (MCP-1) CXCL1 (fractalkine) and CCL5 (RANTES) [157,164,165]. The gene discussed is CCL2; the disease is pulmonary arterial hypertension.