In addition, it has been shown that levels of certain inflammatory cytokines and chemokines, including tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin-1beta (IL-1β), interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-18 (IL-18), interleukin-10 (IL-10), matrix metalloproteinase 9 (MMP9), CC Motif Chemokine Ligand 5 (CCL5), or monocyte chemotactic protein 1 (MCP-1), are elevated in patients with PAH and may correlate with disease severity, and thus monitoring their changes may be diagnostically useful in patients with PAH [18,22]. The gene discussed is MMP9; the disease is pulmonary arterial hypertension.