Anti-MDA5 antibody is one of the dermatomyositis-specific autoantibodies and anti-MDA5-potsitive patients show characteristic clinical features, such as hypomyositis, high prevalence of acute/subacute interstitial pneumonia (A/ SIP) with poor prognosis, hyperferritinemia and elevated hepatobiliary enzyme. We found that serum IL-6, IL-18, M-CSF and IL-10 were significantly higher and serum IL-12 and IL-22 were significantly lower in anti-MDA5-posi-tive patients than in anti-MDA5-negative patients before treatment. Taking together these serological findings, we hypothesized that monocyte and macrophage activation may underlie in the pathophysiology of anti-MDA5-positive patients. They rarely survive after they become to need oxygenation, and so need to be treated as soon as possible once the diagnosis has been made. Intensive regimen of combined immunosuppressive therapy (high-dose corticosteroids, oral cyclosporin and intravenous cyclophosphamide (IVCY, 900-1000 mg/m&lt
sup&gt
2&lt
/sup&gt
in every other week)) improved the survival rate of anti-MDA5-positive patients. Especially, the serum ferritin levels tended to go down about 14 days after IVCY, suggesting that IVCY might be a key drug in the treatment of anti-MDA5-positive A/SIP patients. © 2013 The Japan Society for Clinical Immunology.