Publisher Correction: Tumor-necrosis factor impairs CD4+ T cell-mediated immunological control in chronic viral infection.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Tumor-necrosis factor impairs CD4(+) T cell-mediated immunological control in chronic viral infection.

Persistent viral infections are characterized by the simultaneous presence of chronic inflammation and T cell dysfunction. In prototypic models of chronicity--infection with human immunodeficiency virus (HIV) or lymphocytic choriomeningitis virus (LCMV)--we used transcriptome-based modeling to reveal that CD4(+) T cells were co-exposed not only to multiple inhibitory signals but also to tumor-necrosis factor (TNF). Blockade of TNF during chronic infection with LCMV abrogated the inhibitory gene-expression signature in CD4(+) T cells, including reduced expression of the inhibitory receptor PD-1, and reconstituted virus-specific immunity, which led to control of infection. Preventing signaling via the TNF receptor selectively in T cells sufficed to induce these effects. Targeted immunological interventions to disrupt the TNF-mediated link between chronic inflammation and T cell dysfunction might therefore lead to therapies to overcome persistent viral infection.

Enzymatic Activity of HPGD in Treg Cells Suppresses Tconv Cells to Maintain Adipose Tissue Homeostasis and Prevent Metabolic Dysfunction.

Regulatory T cells (Treg cells) are important for preventing autoimmunity and maintaining tissue homeostasis, but whether Treg cells can adopt tissue- or immune-context-specific suppressive mechanisms is unclear. Here, we found that the enzyme hydroxyprostaglandin dehydrogenase (HPGD), which catabolizes prostaglandin E2 (PGE2) into the metabolite 15-keto PGE2, was highly expressed in Treg cells, particularly those in visceral adipose tissue (VAT). Nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ)-induced HPGD expression in VAT Treg cells, and consequential Treg-cell-mediated generation of 15-keto PGE2 suppressed conventional T cell activation and proliferation. Conditional deletion of Hpgd in mouse Treg cells resulted in the accumulation of functionally impaired Treg cells specifically in VAT, causing local inflammation and systemic insulin resistance. Consistent with this mechanism, humans with type 2 diabetes showed decreased HPGD expression in Treg cells. These data indicate that HPGD-mediated suppression is a tissue- and context-dependent suppressive mechanism used by Treg cells to maintain adipose tissue homeostasis.

Repression of the genome organizer SATB1 in regulatory T cells is required for suppressive function and inhibition of effector differentiation.

Regulatory T cells (T(reg) cells) are essential for self-tolerance and immune homeostasis. Lack of effector T cell (T(eff) cell) function and gain of suppressive activity by T(reg) cells are dependent on the transcriptional program induced by Foxp3. Here we report that repression of SATB1, a genome organizer that regulates chromatin structure and gene expression, was crucial for the phenotype and function of T(reg) cells. Foxp3, acting as a transcriptional repressor, directly suppressed the SATB1 locus and indirectly suppressed it through the induction of microRNAs that bound the SATB1 3' untranslated region. Release of SATB1 from the control of Foxp3 in T(reg) cells caused loss of suppressive function, establishment of transcriptional T(eff) cell programs and induction of T(eff) cell cytokines. Our data support the proposal that inhibition of SATB1-mediated modulation of global chromatin remodeling is pivotal for maintaining T(reg) cell functionality.

iRhom2 inhibits bile duct obstruction-induced liver fibrosis.

Chronic liver disease can induce prolonged activation of hepatic stellate cells, which may result in liver fibrosis. Inactive rhomboid protein 2 (iRhom2) is required for the maturation of A disintegrin and metalloprotease 17 (ADAM17, also called TACE), which is responsible for the cleavage of membrane-bound tumor necrosis factor-α (TNF-α) and its receptors (TNFRs). Here, using the murine bile duct ligation (BDL) model, we showed that the abundance of iRhom2 and activation of ADAM17 increased during liver fibrosis. Consistent with this, concentrations of ADAM17 substrates were increased in plasma samples from mice after BDL and in patients suffering from liver cirrhosis. We observed increased liver fibrosis, accelerated disease progression, and an increase in activated stellate cells after BDL in mice lacking iRhom2 (Rhbdf2-/- ) compared to that in controls. In vitro primary mouse hepatic stellate cells exhibited iRhom2-dependent shedding of the ADAM17 substrates TNFR1 and TNFR2. In vivo TNFR shedding after BDL also depended on iRhom2. Treatment of Rhbdf2-/- mice with the TNF-α inhibitor etanercept reduced the presence of activated stellate cells and alleviated liver fibrosis after BDL. Together, these data suggest that iRhom2-mediated inhibition of TNFR signaling protects against liver fibrosis.

The IDO1-induced kynurenines play a major role in the antimicrobial effect of human myeloid cells against Listeria monocytogenes.

Induction of indoleamine 2,3-dioxygenase (IDO1) is an established cellular response to infection with numerous pathogens. Several mechanisms, such as IDO1-mediated tryptophan (Trp) depletion, but also accumulation of Trp catabolites, have been associated with the antimicrobial effects of IDO(+) cells. Recent findings of IDO1 as an immunoinhibitory and signaling molecule extended these previous observations. Using infection of professional phagocytes with Listeria monocytogenes (L.m.) as a model, we illustrate that IDO1 induction is a species-specific event observed in human, but not murine myeloid, cells. Knockdown and inhibition experiments indicate that IDO1 enzymatic activity is required for the anti-L.m. effect. Surprisingly, the IDO1-mediated antimicrobial effect is less prominent when Trp is depleted, but can be significantly amplified by tryptophan excess, leading to increased accumulation of catabolites that promote enhanced bactericidal activity. We observed a pathogen-specific pattern with kynurenine and 3-hydroxy-kynurenine being most potent against L.m., but not against other bacteria. Hence, apparent discrepant findings concerning IDO1-mediated antimicrobial mechanisms can be reconciled by a model of species and pathogen-specificity of IDO1 function. Our findings highlight the necessity to consider species- and pathogen-specific aspects of host-pathogen interactions when elucidating the individual role of antimicrobial proteins such as IDO1.

Efficient genome engineering by targeted homologous recombination in mouse embryos using transcription activator-like effector nucleases.

Generation of mouse models by introducing transgenes using homologous recombination is critical for understanding fundamental biology and pathology of human diseases. Here we investigate whether artificial transcription activator-like effector nucleases (TALENs)-powerful tools that induce DNA double-strand breaks at specific genomic locations-can be combined with a targeting vector to induce homologous recombination for the introduction of a transgene in embryonic stem cells and fertilized murine oocytes. We describe the generation of a conditional mouse model using TALENs, which introduce double-strand breaks at the genomic locus of the special AT-rich sequence-binding protein-1 in combination with a large 14.4 kb targeting template vector. We report successful germline transmission of this allele and demonstrate its recombination in primary cells in the presence of Cre-recombinase. These results suggest that TALEN-assisted induction of DNA double-strand breaks can facilitate homologous recombination of complex targeting constructs directly in oocytes.