Interleukin (IL-)27 is a member of the IL-12 cytokine family. Although recent analyses of WSX-1 (IL-27 receptor x chain)-deficient mice as well as in vitro studies using recombinant IL-27 revealed the immonosuppressive function of IL-27, in vivo role and therapeutic potential of IL-27 remain poorly elucidated. Here we investigated the effect of IL-27 administration on delayed-type hypersensitivity (DTH). While WSX-1-deficient mice showed higher DTH responses as shown by the degree of footpad swelling administration of IL-27 significantly ameliorated the footpad swelling. Since the activation status of the draining lymph node cells were not affected by IL-27 deficiency, it was suggested that IL-27 affected the effector phase of the response. These results collectively indicate that IL-27 has a suppressive effect on activated T cells in the experimental model and also has a therapeutic potential for some diseases caused by immune disorder. (c) 2008 Elsevier Inc. All rights reserved.