Summary Many studies have examined pathways controlling effector T cell differentiation, but less is known about the fate of individual CD8+ T cells during infection. Here, we examined the antiviral and anti-bacterial responses of single CD8+ T cells from the polyclonal repertoire. The progeny of naïve clonal CD8+ T cells displayed unique profiles of differentiation based on extrinsic pathogen-induced environmental cues, with some clones demonstrating extreme bias towards a single developmental pathway. Moreover, even within the same animal, a single naïve CD8++ T cell exhibited distinct fates that were controlled by tissue-specific events. However, memory CD8+ T cells relied on intrinsic factors to control differentiation upon challenge. Our results demonstrate that stochastic and instructive events differentially contribute to shaping the primary and secondary CD8+ T cell response. and provide insight into the underlying forces that drive effector differentiation and protective memory formation.

NK cells are the main cells of the innate immune system that produce IFN-γ, and they express this cytokine at early stages of maturation in response to cytokine stimulation. Conversely, acquisition of IFN-γ-competence in CD4 + T helper cells requires a differentiation process from naïve toward type 1 (Th1) cells, which is associated with epigenetic remodeling at the IFNG locus. In the present study, we show that the ability of NK cells to produce IFN-γ in response to activating receptor (actR) engagement is gradually acquired during terminal differentiation and is accompanied by progressively higher NF-κB activation in response to actR triggering. Moreover, during the differentiation process NK cells gradually display increasing expression of IFNG and TBX21 (encoding T-bet) transcripts and demethylation at the IFNG promoter. This study provides new insights in the molecular mechanisms underlying NK-cell ability to express IFN-γ upon actR engagement. Thus, we propose that in order to efficiently produce IFN-γ in response to infected or transformed cells, NK cells gain Th1-like features, such as higher IFN-γ competence and epigenetic remodeling of the IFNG promoter, during their terminal differentiation.Keywords: Cell differentiation r Chromatin remodeling r IFN-γ r NK cells Additional supporting information may be found in the online version of this article at the publisher's web-site Introduction IFN-γ is a cytokine critically involved in protection against intracellular pathogens and is expressed primarily by T-cell and NK-cell Correspondence: Dr. Chiara Romagnani e-mail: romagnani@drfz.de lineages. Naïve CD4 + T helper (Th) cells must endure a detailed program of proliferation and differentiation in the periphery toward type 1 (Th1) cells before they are competent to transcribe the IFNG gene [1,2]. Differentiation of naïve T cells toward a Th1 phenotype requires at least two phases: an early TCR/IFN-γ/ STAT1-dependent programing, which induces low levels of the T-box transcription factor T-bet (encoded by TBX21) and upregulation of IL-12Rβ2, followed by an IL-12/STAT4/T-bet-dependent C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2014. 44: 2074-2084 Innate immunity 2075 commitment, during which IL-12 further enhances T-bet expression and heightens IFNG gene expression [3][4][5]. Once T-bet and IL-12Rβ2 are expressed, IFNG transcriptional activity is acutely promoted by TCR triggering or combined stimulation with IL-12 and IL-18. Both stimuli induce the activation of NF-κB p65 (RelA), which can couple either with STAT4 (selectively induced by or with TCR-induced NFAT. These complexes bind to the correspondent accessible sites of the IFNG locus, thus enhancing IFN-γ transcription in Th1 cells [6,7]. A key mechanism by which this transcription factor network stabilizes Th1-lineage commitment is epigenetic imprinting, resulting in heritable DNA and histone modifications of IFNG cis-elements, such as the promoter and several conserved noncoding sequences. Similarly, effector/...

The nuclear pregnane X receptor (PXR) plays a central role in regulating xenobiotic metabolism. We now report a novel role for PXR as a critical negative regulator of innate immunity after infection. Pxr−/− mice exhibited remarkably elevated pro-inflammatory cytokine and chemokine production following infection with Listeria monocytogenes (Lm). Despite the more robust innate immune response, Pxr−/− mice were highly susceptible to Lm infection. Surprisingly, disruption of the Toll-like receptor 4 (TLR4) but not TLR2 signaling restored the inflammation to normal levels and the ability to clear Lm in Pxr−/− mice. Mechanistically, the heightened inflammation in Pxr−/− mice resulted in the death of inflammatory monocytes that led to the enhanced susceptibility to Lm infection. These data demonstrated that PXR regulated pathogen-induced inflammation and host defense against Lm infection through modulating the TLR4 pathway. In summary, we discovered an apical role for PXR in regulating innate immunity. In addition, we uncovered a remarkable negative impact of the TLR4 pathway in controlling the quality of the inflammatory response and host defense against a gram-positive bacterial infection.

The respiratory mucosa is a major site for pathogen invasion and, hence, a site requiring constant immune surveillance. The type I, semi-invariant natural killer T (NKT) cells are enriched within the lung vasculature. Despite optimal positioning, the role of NKT cells in respiratory infectious diseases remains poorly understood. Hence, we assessed their function in a murine model of pulmonary tularemia—because tularemia is a sepsis-like proinflammatory disease and NKT cells are known to control the cellular and humoral responses underlying sepsis. Here we show for the first time that respiratory infection with Francisella tularensis live vaccine strain resulted in rapid accumulation of NKT cells within the lung interstitium. Activated NKT cells produced interferon-γ and promoted both local and systemic proinflammatory responses. Consistent with these results, NKT cell-deficient mice showed reduced inflammatory cytokine and chemokine response yet they survived the infection better than their wild type counterparts. Strikingly, NKT cell-deficient mice had increased lymphocytic infiltration in the lungs that organized into tertiary lymphoid structures resembling induced bronchus-associated lymphoid tissue (iBALT) at the peak of infection. Thus, NKT cell activation by F. tularensis infection hampers iBALT formation and promotes a systemic proinflammatory response, which exacerbates severe pulmonary tularemia-like disease in mice.

The respiratory mucosa is a major site for pathogen invasion and, hence, a site requiring constant immune surveillance. The semi-invariant natural killer T (NKT) cells are enriched within the lung vasculature. Despite optimal positioning for border patrol, the role of NKT cells in respiratory infectious diseases remains poorly understood. Hence, we assessed their function in a murine model of pulmonary tularemia—because tularemia is a sepsis-like proinflammatory disease and NKT cells are known to control the cellular and humoral responses underlying sepsis. Here we show for the first time that respiratory infection with Francisella tularensis live vaccine strain results in rapid recruitment of NKT cells to the lung interstitium. Interstitial NKT cell activation resulted in protective interferon-γ production, and affected both local and systemic proinflammatory responses. Hence, NKT cell-deficient mice showed reduced inflammatory cytokine and chemokine response yet survived the infection whilst their wild type counterparts did not. Strikingly, NKT cell-deficient mice had increased lymphocytic infiltration in the lungs that organized into structures resembling induced bronchus-associated lymphoid tissue (iBALT) at the peak of infection. Thus, NKT cell activation by F tularensis infection hampers iBALT formation, which in conjunction with NKT cell-dependent proinflammatory response causes severe pulmonary tularemia-like disease in mice.