Cathepsin G is a serine protease that plays an important role in inflammation and the immune reaction and works by modifying chemokines, cytokines, and cell surface receptors, controlling blood pressure and inducing thrombogenesis. Recent studies suggest that it is a key factor in the pathogenesis of several autoimmune diseases, and anti-cathepsin G IgG antibodies are found in patients with systemic vasculitis, inflammatory rheumatic diseases (e.g., SLE, Sjögren’s syndrome, Felty’s syndrome), autoimmune hepatitis, and chronic inflammatory bowel diseases.