IL‐22 is up‐regulated in patients with rheumatoid arthritis,31, 32 Crohn's disease,33, 34 psoriasis35, 36 and atopic dermatitis,37, 38 whereas it is down‐regulated in the serum of patients with sarcoidosis and systemic lupus erythematosus. Here, IL22 is linked to rheumatoid arthritis.