Respiratory Syncytial Virus Inhibits Granulocyte Apoptosis through a Phosphatidylinositol 3-Kinase and NF-κB-Dependent Mechanism

Abstract

Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract disease in children. It is associated with increased neutrophil numbers in the airway. In this study, we assessed whether this ssRNA virus can directly influence granulocyte longevity. By culturing RSV with granulocytes, it was observed that virus delays both constitutive neutrophil and eosinophil apoptosis. Using pharmacological inhibitors, the RSV-induced delay in neutrophil apoptosis was found to be dependent on both PI3K and NF-κB, but not p38 MAPK or MEK1/MEK2 activation. Using blocking Abs and a reporter cell line, we were able to exclude TLR4 as the receptor responsible for mediating RSV-induced delay in neutrophil apoptosis. The antiapoptotic effect was abrogated by preincubation with the lysosomotropic agent chloroquine, indicating the requirement for endolysosomal internalization. Furthermore, addition of ssRNA, a ligand for the intracellular TLR7/TLR8, also inhibited neutrophil apoptosis, suggesting that intracellular TLRs could be involved in induction of the antiapoptotic effect. Using the BioPlex cytokine detection assay (Bio-Rad), we found that IL-6 was present in supernatants from RSV-exposed neutrophils. IL-6 was found to inhibit neutrophil apoptosis, suggesting that there is an autocrine or paracrine antiapoptotic role for IL-6. Finally, RSV treatment of neutrophils resulted in increased expression of the antiapoptotic Bcl-2 protein Mcl-1. Taken together, our findings suggest involvement of multiple intracellular mechanisms responsible for RSV-induced survival of granulocytes and point toward a role for intracellular TLRs in mediating these effects.

Triggering of TLR7 and TLR8 expressed by human lung cancer cells induces cell survival and chemoresistance

“…We observed that lung cancer cells displayed prolonged survival and reduced cell death when stimulated with TLR7 or TLR8 agonists. These effects were not caused by modification of the cell cycle, demonstrating tumor cell survival rather than proliferation, and were consistent with the observations of Lindemans et al (63), who demonstrated that TLR7 or TLR8 stimulation by respiratory syncitial virus inhibits apoptosis of neutrophils via a NF-κB-dependent mechanism. Thus, we conclude that the expression of TLR7 or TLR8 by human lung cancer cells represents an advantage to tumor growth when TLRs are stimulated.…”

A Nonredundant Role for Canonical NF-κB in Human Myeloid Dendritic Cell Development and Function

“…Canonical NF-kB plays a crucial role in antiapoptosis by the induction of antiapoptotic genes (41). Accordingly, its activity has been associated with augmented cell survival in various cell types (42)(43)(44)(45). In line, in this study, we show that during development of human myeloid DCs, either from monocytes or from CD34 + HPCs, cell survival is strongly dependent on intact canonical NF-kB activation.…”

Chromatin remodelling and autocrine TNFα are required for optimal interleukin-6 expression in activated human neutrophils

“…These comprise cell shape changes, CD62L shedding, priming for enhanced respiratory burst 17,[47][48][49] , chemotaxis, phagocytosis 17,50 and neutrophil extracellular trap formation induction 51 , lipid mediator production 18 , prolonged survival 49,52 and cytokine production (using, however, less pure neutrophil populations than in this study), including TNFa 53 and IL-6 (refs 48,53,54). Similarly, two studies 55,56 have reported that human neutrophils cultured in the presence of infectious respiratory syncytial virus produce IL-6 at 1 ng ml À 1 per 5 Â 10 6 cells per 3 h (498% neutrophil purity 55 ), or at 100 pg ml À 1 per 5 Â 10 5 cells per 12 h (497% purity 56 ). Even though these data require corroboration using highly purified neutrophils, it is likely that, being a single-stranded RNA virus, respiratory syncytial virus activates neutrophil TLR8 to ultimately induce IL-6 expression.…”