As will be discussed later, MAIT cell frequencies are very sensitive to therapeutic corticosteroids, which cause a rapid decrease in MAIT cell frequencies.44, 45 Indeed Cho et al. 19 observed decreased MAIT cell frequencies only in patients with SLE or RhA, of which 90% were receiving corticosteroids, but no deficiency in two other autoimmune diseases also studied – ankylosing spondylitis and Behçet's disease – in which no patients were receiving steroids. The gene discussed is DHX9; the disease is systemic lupus erythematosus.