NF-κB plays a key role in the production of cytokines in inflammatory diseases. The effects of a novel T cell-specific NF-κB inhibitor, SP100030, were evaluated in cultured Jurkat cells and in murine collagen-induced arthritis (CIA). Chemical libraries were screened for NF-κB-inhibitory activity. SP100030, a compound identified in this process, inhibited NF-κB activation in PMA/PHA-activated Jurkat cells by EMSA at a concentration of 1 μM. Jurkat cells and the monocytic cell line THP-1 were transfected with an NF-κB promotor/luciferase construct and activated. SP100030 inhibited luciferase production in the Jurkat cells (IC 50= 30 nM). ELISA and RT-PCR confirmed that IL-2, IL-8, and TNF-α production by activated Jurkat and other T cell lines were inhibited by SP100030. However, cytokine expression was not blocked by the compound in THP-1 cells, fibroblasts, endothelial cells, or epithelial cells. Subsequently, DBA/1J mice were immunized with type II collagen. Treatment with SP100030 (10 mg/kg/day ip beginning on day 21) significantly decreased arthritis severity from onset of clinical signs to the end of the study on day 34 (arthritis score, 5.6±1.7 for SP100030 and 9.8±1.5 for control; p< 0.001). Histologic evaluation demonstrated a trend toward improvement in SP100030-treated animals. EMSA of arthritic mouse ankles in CIA showed that synovial NF-κB binding was suppressed in the SP100030-treated mice. SP100030 inhibits NF-κB activation in T cells, resulting in reduced NF-κB-regulated gene expression and decreased CIA. Its selectivity for T cells could provide potent immunosuppression with less toxicity than other NF-κB inhibitors.