Multiple neutrophil-derived proteolytic enzymes have been shown to be elevated in periodontitis compared to healthy controls, including myeloperoxidase (GCF) [22] and matrix metalloproteinases (e.g., MMP-2 and MMP-9) whose major source in the periodontium is the neutrophil [23]–[25]. The gene discussed is MMP9; the disease is periodontitis.