The anti-inflammatory effects of the recently identified cytokine interleukin (IL)-13 on collagen-induced arthritis (CIA) was explored and compared to those of IL-4 using systemic administration of these cytokines via two injections of xenogeneic vector cells transfected with a plasmid construct. CIA was induced in DBA/I mice by immunization with native bovine type II collagen (CII). Chinese hamster ovary (CHO) fibroblasts transfected with the mouse IL-13 or IL-4 genes were inoculated subcutaneously on days 10 and 25 post-priming with CII and mice were monitored for signs of arthritis by observers unaware of the status of the animal. Incidence and severity of CIA were significantly reduced in the groups of mice treated with IL-13 and IL-4 gene-transfected CHO cells compared to control groups receiving nontransfected cells. Expression of various cytokines in spleen cells from individual mice was assessed by quantitative reverse transcriptase-polymerase chain reaction at different times after immunization. Our data show that IL-13-induced suppression of CIA coincided with a decreased TNF-alpha mRNA expression in the spleen of treated animals. This may explain at least partially the anti-inflammatory effects of IL-13 in CIA. Thus, our results may have important implications for the clinical use of T helper (Th)1/TH2 modulatory cytokines as therapeutic agents in the treatment of autoimmune diseases.