The term “normobaric oxygen paradox” (NOP), describes the response to the return to normoxia after a hyperoxic event, sensed by tissues as oxygen shortage, and resulting in up-regulation of the Hypoxia-inducible factor 1α (HIF-1α) transcription factor activity. The molecular characteristics of this response have not been yet fully characterized. Herein, we report the activation time trend of oxygen-sensitive transcription factors in human peripheral blood mononuclear cells (PBMCs) obtained from healthy subjects after one hour of exposure to mild (MH), high (HH) and very high (VHH) hyperoxia, corresponding to 30%, 100%, 140% O2, respectively. Our observations confirm that MH is perceived as a hypoxic stress, characterized by the activation of HIF-1α and Nuclear factor (erythroid-derived 2)-like 2 (NRF2), but not Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB). Conversely, HH is associated to a progressive loss of NOP response and to an increase in oxidative stress leading to NRF2 and NF-kB activation, accompanied by the synthesis of glutathione (GSH). After VHH, HIF-1α activation is totally absent and oxidative stress response, accompanied by NF-κB activation, is prevalent. Intracellular GSH and Matrix metallopeptidase 9 (MMP-9) plasma levels parallel the transcription factors activation pattern and remain elevated throughout the observation time. In conclusion, our study confirms that, in vivo, the return to normoxia after MH is sensed as a hypoxic trigger characterized by HIF-1α activation. On the contrary, HH and VHH induce a shift toward an oxidative stress response, characterized by NRF2 and NF-κB activation in the first 24 h post exposure.

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T cells chronically stimulated by a persistent antigen often become dysfunctional and lose effector functions and proliferative capacity. To identify the importance of micro-RNA-155 (miR-155) in this phenomenon, we analyzed mouse miR-155-deficient CD4 + T cells in a model where the chronic exposure to a systemic antigen led to T-cell functional unresponsiveness. We found that miR-155 was required for restoring function of T cells after programmed death receptor 1 blockade. Heme oxygenase 1 (HO-1) was identified as a specific target of miR-155 and inhibition of HO-1 activity restored the expansion and tissue migration capacity of miR-155 −/− CD4 + T cells. Moreover, miR-155-mediated control of HO-1 expression in CD4 + T cells was shown to sustain in vivo antigen-specific expansion and IL-2 production. Thus, our data identify HO-1 regulation as a mechanism by which miR-155 promotes T-cell-driven inflammation.Keywords: Adaptive tolerance r Heme oxygenase 1 (HO-1) r Immunoregulation r Micro-RNA r Th1Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionT lymphocytes are a crucial part of the immune system and are a major cell type involved in the adaptive immune response. Usually, T cells expand rapidly in response to antigenic stimulation, and then, as a result of antigen clearance, they die by apoptosis. However, in situations of chronic antigenic exposure, such as those observed in cancer, chronic infections, or autoimmunity, antigen-specific T cells may persist for extended periods of time and these conditions are often associated with T-cell Correspondence: Dr. Michel Y. Braun e-mail: mbraun@ulb.ac.be dysfunction, such as decreased cytokine expression and effector function. Recent experimental evidence indicates that this unresponsive state is maintained by the inhibition of signaling events, particularly downstream proximal signals of the T-cell receptor, that in turn promotes T-cell dysfunction [1][2][3][4]. Since the attenuation of T-cell effector functions by the programmed death receptor 1 (PD-1) pathway has been demonstrated in various chronic infectious diseases and cancer and in the control of autoimmune T cells, the modulation of this inhibitory pathway is considered a promising means to control the function of T cells or enhance immune responses in patients.Micro-RNAs (miRNAs) are small genome-encoded RNAs that regulate gene expression by targeting complementary messenger RNAs (mRNAs) and block their translation [5,6]. The first C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 830Jinyu Zhang et al. Eur. J. Immunol. 2015. 45: 829-842 evidence for the involvement of miRNAs in regulating T-cell differentiation and function came from the observation that the specific deletion of the endoribonuclease DICER, a RNaseIII-like enzyme required for generating miRNAs, in the CD4 + T-cell lineage resulted in impaired T-cell development and aberrant Th1-cell differentiation and cytokine production [7]. Among miRNAs the mo...

Aim To model in vitro the contact between adult dental pulp stem cells (DPSCs) and lipoteichoic acid (LTA), a cell wall component expressed at the surface of most Gram‐positive bacteria. Methodology Human DPSCs obtained from impacted third molars were cultured and exposed to various concentrations of S. aureus LTA (0.1, 1.0 and 10 µg mL−1). The effects of LTA on DPSCs proliferation and apoptosis were investigated by MTT assay and flow cytometry. Mineralization of DPSCs was evaluated by alizarin red staining assay. Migration was investigated by microphotographs of wound‐healing and Transwell migration assays. Reverse transcription polymerase chain reaction was used to examine the effects of LTA on p65 NF‐κB translocation and TLR1, TLR2 or TLR6 regulation. Enzyme‐linked immunosorbent assay was used to investigate LTA‐stimulated DPSCs cytokine production. One‐way or two‐way ANOVA and Tukey post hoc multiple comparison were used for statistical analysis. Results DPSCs expressed TLR1, TLR2 and TLR6 involved in the recognition of various forms of LTA or lipoproteins. Exposure to LTA did not up‐ or down‐regulate the mRNAs of TLR1, TLR2 or TLR6 whilst LPS acted as a potent inducer of them [TLR1 (P ≤ 0.05), TLR2 (P ≤ 0.001) and TLR6 (P ≤ 0.001)]. Translocation of p65 NF‐κB to the nucleus was detected in LTA‐stimulated cells, but to a lesser extent than LPS‐stimulated DPSCs (P ≤ 0.001). The viability of cells exposed to LTA was greater than unstimulated cells, which was attributed to an increased proliferation and not to less cell death [LTA 1 μg mL−1 (P ≤ 0.001) and 10 μg mL−1 (P ≤ 0.01)]. For specific doses of LTA (1.0 µg mL−1), adhesion of DPSCs to collagen matrix was disturbed (P ≤ 0.05) and cells enhanced their horizontal mobility (P ≤ 0.001). LTA‐stimulated DPSCs released IL‐6 and IL‐8 in a dose‐dependent manner (P ≤ 0.0001). At all concentrations investigated, LTA did not influence osteogenic/odontoblastic differentiation. Conclusions Human DPSCs were able to sense the wall components of Gram‐positive bacteria likely through TLR2 signalling. Consequently, cells modestly proliferated, increased their migratory behaviour and contributed significantly to the local inflammatory response through cytokine release.