TNF-α suppresses dendritic cell death and the production of reactive oxygen intermediates induced by plasma withdrawal

Mature dendritic cells (DCs) were generated by culturing human peripheral blood monocytes for 7 days and, then, treating them with a cytokine cocktail for 2 days. The viability of the mature DCs (Day 9) obtained was approximately 60-70%, and this gradually declined when they were recultured in X-VIVO 15 media containing 2% human plasma (40% viability after 3 days of reculture). DC death accelerated on withdrawing plasma from the culture (20% viability after 3 days). However, the addition of tumor necrosis factor-α (TNF-α) to the medium completely restored DC viability in the absence of plasma. Such a protective effect was not afforded by other cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-1α (IL-1α), IL-4, IL-6 and prostaglandin E₂ which are used for the maturation of DCs. These results indicate that TNF-α is specifically required to maintain the viability of mature DCs. The withdrawal of plasma rapidly (within 15 min elevated cellular levels of reactive oxygen intermediates (ROIs), which have been proposed to regulate the ability of DCs to control inflammatory reactions. The possibility that ROIs act as mediators of DC death was eliminated by the observation that scavengers of ROIs, such as catalase, N-acetylcysteine, glutathione, failed to prolong DC life span in the absence of plasma. Interestingly, TNF-α was found to almost completely abolish the production of ROIs induced by plasma withdrawal. To summarize, our results suggest that TNF-α controls not only the inflammatory functions of DCs but also their survival.