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

Abstract

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-alpha (TNF-alpha) 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-1alpha (IL-1alpha), IL-4, IL-6 and prostaglandin E2 which are used for the maturation of DCs. These results indicate that TNF-alpha 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-alpha was found to almost completely abolish the production of ROIs induced by plasma withdrawal. To summarize, our results suggest that TNF-alpha controls not only the inflammatory functions of DCs but also their survival.

Activation of the aryl hydrocarbon receptor promotes allograft-specific tolerance through direct and dendritic cell–mediated effects on regulatory T cells

“…Alternatively, mature tolerogenic DCs may display a prolonged life span in inflammatory conditions and mediate active tolerance toward donor antigens. 45 In summary, this study translates the initial in vitro observations, which showed that VAF347 acts as immunomodulatory compound into an in vivo clinically relevant setting of allogeneic islet transplantation. Results provide direct experimental evidence that VAF347 generates tolerogenic DCs, and improves the survival of Tr cells.…”

Autocrine TNF Is Critical for the Survival of Human Dendritic Cells by Regulating BAK, BCL-2, and FLIPL

“…The exogenous addition of TNF has previously been found to improve the survival of dermal Langerhans cells and to increase the viability of immature and of mature Mo-DCs cultured under serumfree conditions (35)(36)(37). In other reports, improved DC viability has been attributed to the differentiation and maturation process rather than to a direct antiapoptotic effect of TNF (31,32,38).…”

CD40 ligation during dendritic cell maturation reduces cell death and prevents interleukin‐10‐induced regression to macrophage‐like monocytes

“…The results obtained by counting viable trypan blue exclusing cells on day 8 and 11 could be confirmed by analyzing the extent of cell necrosis by staining day 11 DCs with propidium iodide and submitting cells to flow cytometry. Recently, TNF‐α could be identified as a key factor for suppression of cell death after withdrawal of human plasma from DC‐cultures (42). It was shown that no other single agent contained in ICC is able to induce a death‐protective effect comparable to TNF‐α (42).…”

“…Recently, TNF‐α could be identified as a key factor for suppression of cell death after withdrawal of human plasma from DC‐cultures (42). It was shown that no other single agent contained in ICC is able to induce a death‐protective effect comparable to TNF‐α (42). Interestingly, in the present work, the highest resistance to cell death was achieved by a combination of ICC and CD40‐L, which points to an additive effect of both TNF‐α and CD40‐L.…”