Tumor necrosis factor-alpha (TNF alpha) is a potent pro-inflammatory cytokine that plays a major role in the pathogenesis of acute and chronic inflammatory disorders such as septic shock and arthritis, respectively. Leukocytes stimulated with inflammatory signals such as lipopolysaccharide (LPS) are the predominant producers of TNFa, and thus control of TNF alpha release from stimulated leukocytes represents a potential therapeutic target. Here, we report that leptomycin B (LMB), a specific inhibitor of CRM1-dependent nuclear protein export, inhibits TNF alpha release from LPS-stimulated human peripheral blood neutrophils and mononuclear cells. In addition, immunofluorescence confocal microscopy and immunoblotting analysis indicate that TNF alpha is localized in the nucleus of human neutrophils and mononuclear cells. This study demonstrates that the cellular release of TNFa from stimulated leukocytes is mediated by the CRM1-dependent nuclear export mechanism. Inhibition of CRM1-dependent cellular release of TNF alpha could thus provide a novel therapeutic approach for disorders involving excessive TNF alpha release. (c) 2006 Elsevier Inc. All rights reserved.