MPO and mixed connective tissue disease: Non-specifically reacting with MPO also may occur in the course of non-specific inflammatory bowel diseases (in 60–70% of patients with ulcerative colitis and 10% of individuals with Crohn’s disease), autoimmune liver diseases (in 90% of patients with primary sclerosing cholangitis and 70% of patients with autoimmune hepatitis), and HIV infections (18%), as well as in patients with connective tissue diseases (in 20–25% of patients with systemic lupus erythematosus, 20% of patients with mixed connective tissue disease) [10,67,68].