For instance metalloproteinase-9 (MMP9) is augmented in the sera of systemic lupus erythematosus patients (36) and dipeptidyl peptidase-4/CD26 (DPP4/CD26) in sera of type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus and inflammatory bowel disease (37). Here, DPP4 is linked to rheumatoid arthritis.