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The members of the tumor necrosis factor (TNF) family play pivotal roles in the regulation of the immune system. LIGHT is a type II transmembrane protein belonging to the TNF family that was originally identified as a weak inducer of apoptosis. This cytokine has been extensively studied for its role in T cell regulation. Recently, we identified its role in inducing maturation of dendritic cells, such as LIGHT upregulated CD86 expression on dendritic cells in our previous report. However, the signal transduction pathway on this regulation remains unknown. In this study, we found that LIGHT activated NF-κB, p44/42 MAPK, but not JNK. LIGHT upregulates CD86 expression on DCs through activation of NF-κB, but not p44/42 signal pathway, because inhibition of NF-κB activity by its inhibitor could blunt the effect of LIGHT in up-regulation of CD86 expression, but neither inhibitor of p44/42 MAPK nor JNK inhibitor has this effect. Thus we demonstrate that LIGHT regulates CD86 expression through NF-κB signal transduction pathway but neither p44/42 MAPK nor JNK/AP-1 signaling pathway. We conclude that NF-κB signal plays a key role in LIGHT-mediated upregulation of CD86 expression. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]