TNF activation of NF-κB is essential for development of single-positive thymocytes

NF-κB regulated expression of A20 controls IKK dependent repression of RIPK1 induced cell death in activated T cells

IKK signalling is essential for survival of thymocytes by repressing RIPK1 induced cell death rather than its canonical function of activating NF-κB. The role of IKK signalling in activated T cells is unclear. To investigate this, we analysed activation of IKK2 deficient T cells. While TCR triggering was normal, proliferation and expansion was profoundly impaired. This was not due to defective cell cycle progression, rather dividing T cells became sensitised to TNF induced cell death, since inhibition of RIPK1 kinase activity rescued cell survival. Gene expression analysis of activated IKK2 deficient T cells revealed defective expression of Tnfaip3, that encodes A20, a negative regulator of NF-κB. To test whether A20 expression was required to protect IKK2 deficient T cells from cell death, we generated mice with T cells lacking both A20 and IKK2. Doing this resulted in near complete loss of peripheral T cells, in contrast to mice lacking one or other gene. Strikingly, this phenotype was completely reversed by inactivation of RIPK1 kinase activity in vivo. Together, our data show that IKK signalling in activated T cells protects against RIPK1 dependent death, both by direct phosphorylation of RIPK1 and through NF-κB mediated induction of A20, that we identify for the first time as a key modulator of RIPK1 activity in T cells.

The CD4 Versus CD8 T Cell Fate Decision: A Multiomics-Informed Perspective

The choice of developing thymocytes to become CD8+ cytotoxic or CD4+ helper T cells has been intensely studied, but many of the underlying mechanisms remain to be elucidated. Recent multiomics approaches have provided much higher resolution analysis of gene expression in developing thymocytes than was previously achievable, thereby offering a fresh perspective on this question. Focusing on our recent studies using CITE-seq (cellular indexing of transcriptomes and epitopes) analyses of mouse thymocytes, we present a detailed timeline of RNA and protein expression changes during CD8 versus CD4 T cell differentiation. We also revisit our current understanding of the links between T cell receptor signaling and expression of the lineage-defining transcription factors ThPOK and RUNX3. Finally, we propose a sequential selection model to explain the tight linkage between MHC-I versus MHC-II recognition and T cell lineage choice. This model incorporates key aspects of previously proposed kinetic signaling, instructive, and stochastic/selection models.

Single-cell multiomic analysis of thymocyte development reveals drivers of CD4+ T cell and CD8+ T cell lineage commitment

The development of CD4+ T cells and CD8+ T cells in the thymus is critical to adaptive immunity and is widely studied as a model of lineage commitment. Recognition of self-peptide major histocompatibility complex (MHC) class I or II by the T cell antigen receptor (TCR) determines the CD8+ or CD4+ T cell lineage choice, respectively, but how distinct TCR signals drive transcriptional programs of lineage commitment remains largely unknown. Here we applied CITE-seq to measure RNA and surface proteins in thymocytes from wild-type and T cell lineage-restricted mice to generate a comprehensive timeline of cell states for each T cell lineage. These analyses identified a sequential process whereby all thymocytes initiate CD4+ T cell lineage differentiation during a first wave of TCR signaling, followed by a second TCR signaling wave that coincides with CD8+ T cell lineage specification. CITE-seq and pharmaceutical inhibition experiments implicated a TCR-calcineurin-NFAT-GATA3 axis in driving the CD4+ T cell fate. Our data provide a resource for understanding cell fate decisions and implicate a sequential selection process in guiding lineage choice.

IKK promotes naïve T cell survival by repressing RIPK1-dependent apoptosis and activating NF-κB

The inhibitor of κB kinase (IKK) complex regulates the activation of the nuclear factor κB (NF-κB) family of transcription factors. In addition, IKK represses extrinsic cell death pathways dependent on receptor-interacting serine/threonine-protein kinase 1 (RIPK1) by directly phosphorylating this kinase. Here, we showed that peripheral naïve T cells in mice required the continued expression of IKK1 and IKK2 for their survival; however, the loss of these cells was only partially prevented when extrinsic cell death pathways were blocked by either deleting Casp8 (which encodes the apoptosis-inducing caspase 8) or inhibiting the kinase activity of RIPK1. Inducible deletion of Rela (which encodes the NF-κB p65 subunit) in mature CD4⁺ T cells also resulted in loss of naïve CD4⁺ T cells and in reduced abundance of the interleukin-7 receptor (IL-7R) encoded by the NF-κB target Il7r, revealing an additional reliance upon NF-κB for the long-term survival of mature T cells. Together, these data indicate that the IKK-dependent survival of naïve CD4⁺ T cells depends on both repression of extrinsic cell death pathways and activation of an NF-κB-dependent survival program.

Severe CD8+ T Lymphopenia in WHIM Syndrome Caused by Selective Sequestration in Primary Immune Organs

Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is an ultra-rare combined primary immunodeficiency disease caused by heterozygous gain-of-function mutations in the chemokine receptor CXCR4. WHIM patients typically present with recurrent acute infections associated with myelokathexis (severe neutropenia due to bone marrow retention of mature neutrophils). Severe lymphopenia is also common, but the only associated chronic opportunistic pathogen is human papillomavirus and mechanisms are not clearly defined. In this study, we show that WHIM mutations cause more severe CD8 than CD4 lymphopenia in WHIM patients and WHIM model mice. Mechanistic studies in mice revealed selective and WHIM allele dose-dependent accumulation of mature CD8 single-positive cells in thymus in a cell-intrinsic manner due to prolonged intrathymic residence, associated with increased CD8 single-positive thymocyte chemotactic responses in vitro toward the CXCR4 ligand CXCL12. In addition, mature WHIM CD8+ T cells preferentially home to and are retained in the bone marrow in mice in a cell-intrinsic manner. Administration of the specific CXCR4 antagonist AMD3100 (plerixafor) in mice rapidly and transiently corrected T cell lymphopenia and the CD4/CD8 ratio. After lymphocytic choriomeningitis virus infection, we found no difference in memory CD8+ T cell differentiation or viral load between wild-type and WHIM model mice. Thus, lymphopenia in WHIM syndrome may involve severe CXCR4-dependent CD8+ T cell deficiency resulting in part from sequestration in the primary lymphoid organs, thymus, and bone marrow.

Phosphorylation of RIPK1 serine 25 mediates IKK dependent control of extrinsic cell death in T cells

The Inhibitor of Kappa B Kinase (IKK) complex is a critical regulator of NF-κB activation. More recently, IKK has also been shown to repress RIPK1 dependent extrinsic cell death pathways by directly phosphorylating RIPK1 at serine 25. In T cells, IKK expression is essential for normal development in the thymus, by promoting survival of thymocytes independently of NF-κB activation. RIPK1 undergoes extensive phosphorylation following TNF stimulation in T cells, though which targets are required to repress RIPK1 has not been defined. Here, we show that TNF induced phosphorylation of RIPK1 at S25 is IKK dependent. We test the relevance of this phosphorylation event in T cells using mice with a RIPK1^S25D phosphomimetic point mutation to endogenous RIPK1. We find that this mutation protects T cells from TNF induced cell death when IKK activity is inhibited in vitro, and can rescues development of IKK deficient thymocytes in vivo to a degree comparable with kinase dead RIPK1^D138N. Together, these data show that phosphorylation of RIPK1S25 by IKK represents a key regulatory event promoting survival of T cells by IKK.

The dichotomous outcomes of TNFα signaling in CD4+ T cells

TNFa blocking agents were the first-in-class biologic drugs used for the treatment of autoimmune disease. Paradoxically, however, exacerbation of autoimmunity was observed in some patients. TNFa is a pleiotropic cytokine that has both proinflammatory and regulatory effects on CD4+ T cells and can influence the adaptive immune response against autoantigens. Here, we critically appraise the literature and discuss the intricacies of TNFa signaling that may explain the controversial findings of previous studies. The pleiotropism of TNFa is based in part on the existence of two biologically active forms of TNFa, soluble and membrane-bound, with different affinities for two distinct TNF receptors, TNFR1 and TNFR2, leading to activation of diverse downstream molecular pathways involved in cell fate decisions and immune function. Distinct membrane expression patterns of TNF receptors by CD4+ T cell subsets and their preferential binding of distinct forms of TNFα produced by a diverse pool of cellular sources during different stages of an immune response are important determinants of the differential outcomes of TNFa-TNF receptor signaling. Targeted manipulation of TNFa-TNF receptor signaling on select CD4+ T cell subsets may offer specific therapeutic interventions to dampen inflammation while fortifying immune regulation for the treatment of autoimmune diseases.

Single-cell transcriptome landscape and antigen receptor dynamic during SARS-CoV-2 vaccination

Vaccination by inactivated vaccine is an effective strategy to prevent the COVID-19 pandemic. However, the detailed molecular immune response at single-cell level is poorly understood. In this study, we systematically delineated the landscape of the pre- and post-vaccination single-cell transcriptome, TCR (T cell antigen receptor) and BCR (B cell antigen receptor) expression profile of vaccinated candidates. The bulk TCR sequencing analysis of COVID-19 patients was also performed. Enrichment of a clonal CD8⁺ T cell cluster expressing specific TCR was identified in both vaccination candidates and COVID-19 patients. These clonal CD8⁺ T cells showed high expression of cytotoxicity, phagosome and antigen presentation related genes. The cell–cell interaction analysis revealed that monocytes and dendritic cells could interact with these cells and initiate phagocytosis via ICAM1-ITGAM and ITGB2 signaling. Together, our study systematically deciphered the detailed immunological response during SARS-CoV-2 vaccination and infection. It may facilitate understanding the immune response and the T-cell therapy against COVID-19.

Transcriptome analysis reveals fluid shear stress (FSS) and atherosclerosis pathway as a candidate molecular mechanism of short-term low salinity stress tolerance in abalone

Background

Transcriptome sequencing is an effective tool to reveal the essential genes and pathways underlying countless biotic and abiotic stress adaptation mechanisms. Although severely challenged by diverse environmental conditions, the Pacific abalone Haliotis discus hannai remains a high-value aquaculture mollusk and a Chinese predominantly cultured abalone species. Salinity is one of such environmental factors whose fluctuation could significantly affect the abalone’s cellular and molecular immune responses and result in high mortality and reduced growth rate during prolonged exposure. Meanwhile, hybrids have shown superiority in tolerating diverse environmental stresses over their purebred counterparts and have gained admiration in the Chinese abalone aquaculture industry.

The objective of this study was to investigate the molecular and cellular mechanisms of low salinity adaptation in abalone. Therefore, this study used transcriptome analysis of the gill tissues and flow cytometric analysis of hemolymph of H. discus hannai (DD) and interspecific hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) during low salinity exposure. Also, the survival and growth rate of the species under various salinities were assessed.

Results

The transcriptome data revealed that the differentially expressed genes (DEGs) were significantly enriched on the fluid shear stress and atherosclerosis (FSS) pathway. Meanwhile, the expression profiles of some essential genes involved in this pathway suggest that abalone significantly up-regulated calmodulin-4 (CaM-4) and heat-shock protein90 (HSP90), and significantly down-regulated tumor necrosis factor (TNF), bone morphogenetic protein-4 (BMP-4), and nuclear factor kappa B (NF-kB).

Also, the hybrid DF showed significantly higher and sustained expression of CaM and HSP90, significantly higher phagocytosis, significantly lower hemocyte mortality, and significantly higher survival at low salinity, suggesting a more active molecular and hemocyte-mediated immune response and a more efficient capacity to tolerate low salinity than DD.

Conclusions

Our study argues that the abalone CaM gene might be necessary to maintain ion equilibrium while HSP90 can offset the adverse changes caused by low salinity, thereby preventing damage to gill epithelial cells (ECs).

The data reveal a potential molecular mechanism by which abalone responds to low salinity and confirms that hybridization could be a method for breeding more stress-resilient aquatic species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08611-8.

Mapping the developing human immune system across organs

Single-cell genomics studies have decoded the immune-cell composition of several human prenatal organs but were limited in understanding the developing immune system as a distributed network across tissues. We profiled nine prenatal tissues combining single-cell RNA sequencing, antigen-receptor sequencing, and spatial transcriptomics to reconstruct the developing human immune system. This revealed the late acquisition of immune effector functions by myeloid and lymphoid cell subsets and the maturation of monocytes and T cells prior to peripheral tissue seeding. Moreover, we uncovered system-wide blood and immune cell development beyond primary hematopoietic organs, characterized human prenatal B1 cells, and shed light on the origin of unconventional T cells. Our atlas provides both valuable data resources and biological insights that will facilitate cell engineering, regenerative medicine, and disease understanding.

Effects of Human RelA Transgene on Murine Macrophage Inflammatory Responses

The NFκB transcription factors are major regulators of innate immune responses, and NFκB signal pathway dysregulation is linked to inflammatory disease. Here, we utilised bone marrow-derived macrophages from the p65-DsRedxp/IκBα-eGFP transgenic strain to study the functional implication of xenogeneic (human) RelA(p65) protein introduced into the mouse genome. Confocal imaging showed that human RelA is expressed in the cells and can translocate to the nucleus following activation of Toll-like receptor 4. RNA sequencing of lipid A-stimulated macrophages, revealed that human RelA impacts on murine gene transcription, affecting both non-NFκB and NFκB target genes, including immediate-early and late response genes, e.g., Fos and Cxcl10. Validation experiments on NFκB targets revealed markedly reduced mRNA levels, but similar kinetic profiles in transgenic cells compared to wild-type. Enrichment pathway analysis of differentially expressed genes revealed interferon and cytokine signaling were affected. These immune response pathways were also affected in macrophages treated with tumor necrosis factor. Data suggests that the presence of xenogeneic RelA protein likely has inhibitory activity, altering specific transcriptional profiles of key molecules involved in immune responses. It is therefore essential that this information be taken into consideration when designing and interpreting future experiments using this transgenic strain.

A paradigm of cancer immunotherapy based on 2-[18F]FDG and anti-PD-L1 mAb combination to enhance the anti-tumor effect

PURPOSE

Efforts have been devoted to select eligible candidates for PD-1/PD-L1 immune checkpoint blocker (ICB) immunotherapy. Here, we have a serendipitous finding of positron emitting tomography (PET) imaging tracer 2-[18F]FDG as a potential immunomodulator. Therefore, we hypothesize that 2-[18F]FDG could induce PD-L1 expression change and create an immune-favorable microenvironment for tumor immunotherapy.

EXPERIMENTAL DESIGN

We designed a series of assays to verify PD-L1 upregulation, and tested immunotherapy regimens based on 2-[18F]FDG and anti-PD-L1 mAb, as monotherapy and in combination, in fully immunocompetent mice of MC38 and CT26 models. PD-L1 expression and tumor microenvironment (TME) changes were analyzed by western blot, transcriptomics study and flow-cytometric analysis.

RESULTS

PD-L1 was upregulated in a time- and dose-dependent manner after being induced by 2-[18F]FDG. The activation of NF-κB/IRF3 pathway and STAT1/3-IRF1 pathway play crucial parts in modulating PD-L1 expression after DNA damage and repair. Improved αPD-L1 mAb utilization rate and significant tumor growth delay were observed when the personalized therapeutic alliance of 2-[18F]FDG stimulation and ICB were employed. In addition, combination of 2-[18F]FDG with αPD-L1 mAb could reprogram a TME from "cold" to "hot", to make low immunoactivity tumors sensitive to ICB therapy.

CONCLUSIONS

In summary, this promising paradigm has the potential to expand the traditional tumor theranostics. [18F]FDG-based ICB immunotherapy is highly significant in enhancing anti-tumor effect.

Mice transgenic for human CTLA4-CD28 fusion gene show proliferation and transformation of ATLL-like and AITL-like T cells

CTLA4-CD28 gene fusion has been reported to occur in diverse types of T cell lymphoma. The fusion event is expected to convert inhibitory signals to activating signals and promote proliferation and potentially transformation of T cells. To test the function of the CTLA4-CD28 fusion gene in vivo, we generated a murine model that expresses the gene in a T cell-specific manner. The transgenic mice have shorter life spans and display inflammatory responses including lymphadenopathy and splenomegaly. T cells in turn show higher levels of activation and infiltrate various organs including the lung and skin. T cells, in particular CD4+ helper T cells, were also readily transplantable to immunocompromised mice. Transcriptomic profiling revealed that the gene expression pattern in CD4 + T cells closely resembles that of adult T cell leukemia/lymphoma (ATLL) and that of angioimmunoblastic T cell lymphoma (AITL) tissues. Consistently, we detected supernumerary FOXP3+ cells and PD-1+ cells in transgenic and transplanted mice. This is the first report demonstrating the transforming activity of the CTLA4-CD28 fusion gene in vivo, and this murine model should be useful in dissecting the molecular events downstream to this mutation.

Nicaraven inhibits TNFα-induced endothelial activation and inflammation through suppression of NF-κB signaling pathway

Inflammation-induced activation and dysfunction of endothelial cells play an important role in the pathology of multiple vascular diseases. Nicaraven, a potent hydroxyl radical scavenger, has recently been found to have anti-inflammatory roles; however, the mechanism of its action is not fully understood. Here we investigated the effects of Nicaraven on tumor necrosis factor α (TNFα) - induced inflammatory response in human umbilical vein endothelial cells and we explore the underlying mechanisms related to the nuclear factor-κB (NF-κB) signaling pathway. Our results showed that Nicaraven significantly reduced the reactive oxygen species production after TNFα stimulation. Nicaraven suppressed TNFα-induced mRNA expression of multiple adhesion molecules and pro-inflammatory cytokines, including vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), E-selectin, MCP-1, TNFα, interleukin-1β (IL-1β), IL-6, and IL-8. In addition, Nicaraven inhibited monocyte adhesion and reduced the protein levels of VCAM-1 and ICAM-1. Mechanistically, Nicaraven prevented TNFα-induced activation of NF-κB signaling pathway by suppressing the phosphorylation of NF-κB p65, IκBα, and IκB kinase (IKK)α/β, stabilizing IκBα, and inhibiting the translocation of p65 from cytosol to nucleus. Finally, we showed that Nicaraven improved the functions of endothelial cells, seen as the upregulation of endothelial nitric oxide synthase and increased nitric oxide levels. Our findings indicated that Nicaraven effectively inhibits TNFα-induced endothelial activation and inflammatory response at least partly through inhibiting NF-κB signaling pathway.

Medullary stromal cells synergize their production and capture of CCL21 for T-cell emigration from neonatal mouse thymus

The release of newly selected αβT cells from the thymus is key in establishing a functional adaptive immune system. Emigration of the first cohorts of αβT cells produced during the neonatal period is of particular importance, because it initiates formation of the peripheral αβT-cell pool and provides immune protection early in life. Despite this, the cellular and molecular mechanisms of thymus emigration are poorly understood. We examined the involvement of diverse stromal subsets and individual chemokine ligands in this process. First, we demonstrated functional dichotomy in the requirement for CCR7 ligands and identified CCL21, but not CCL19, as an important regulator of neonatal thymus emigration. To explain this ligand-specific requirement, we examined sites of CCL21 production and action and found Ccl21 gene expression and CCL21 protein distribution occurred within anatomically distinct thymic areas. Although Ccl21 transcription was limited to subsets of medullary epithelium, CCL21 protein was captured by mesenchymal stroma consisting of integrin α7+ pericytes and CD34+ adventitial cells at sites of thymic exit. This chemokine compartmentalization involved the heparan sulfate-dependent presentation of CCL21 via its C-terminal extension, explaining the absence of a requirement for CCL19, which lacks this domain and failed to be captured by thymic stroma. Collectively, we identified an important role for CCL21 in neonatal thymus emigration, revealing the importance of this chemokine in initial formation of the peripheral immune system. Moreover, we identified an intrathymic mechanism involving cell-specific production and presentation of CCL21, which demonstrated a functional synergy between thymic epithelial and mesenchymal cells for αβT-cell emigration.

The thymus medulla and its control of αβT cell development

αβT cells are an essential component of effective immune responses. The heterogeneity that lies within them includes subsets that express diverse self-MHC-restricted αβT cell receptors, which can be further subdivided into CD4⁺ helper, CD8⁺ cytotoxic, and Foxp3⁺ regulatory T cells. In addition, αβT cells also include invariant natural killer T cells that are very limited in αβT cell receptor repertoire diversity and recognise non-polymorphic CD1d molecules that present lipid antigens. Importantly, all αβT cell sublineages are dependent upon the thymus as a shared site of their development. Ongoing research has examined how the thymus balances the intrathymic production of multiple αβT cell subsets to ensure correct formation and functioning of the peripheral immune system. Experiments in both wild-type and genetically modified mice have been essential in revealing complex cellular and molecular mechanisms that regulate thymus function. In particular, studies have demonstrated the diverse and critical role that the thymus medulla plays in shaping the peripheral T cell pool. In this review, we summarise current knowledge on functional properties of the thymus medulla that enable the thymus to support the production of diverse αβT cell types.

NF-κB and Extrinsic Cell Death Pathways - Entwined Do-or-Die Decisions for T cells

NF-κB signaling is required at multiple stages of T cell development and function. The NF-κB pathway integrates signals from many receptors and involves diverse adapters and kinases. Recent advances demonstrate that kinases controlling NF-κB activation, such as the IKK complex, serve dual independent functions because they also control cell death checkpoints. Survival functions previously attributed to NF-κB are in fact mediated by these upstream kinases by novel mechanisms. This new understanding has led to a refined view of how NF-κB and cell death signaling are interlinked and how they regulate cell fate. We discuss how NF-κB activation and control of cell death signaling by common upstream triggers cooperate to regulate different aspects of T cell development and function.

25 years of research put RIPK1 in the clinic

Receptor Interacting Protein Kinase 1 (RIPK1) is a key regulator of inflammation. To warrant cell survival and appropriate immune responses, RIPK1 is post-translationally regulated by ubiquitylations, phosphorylations and caspase-8-mediated cleavage. Dysregulations of these post-translational modifications switch on the pro-death function of RIPK1 and can cause inflammatory diseases in humans. Conversely, activation of RIPK1 cytotoxicity can be advantageous for cancer treatment. Small molecules targeting RIPK1 are under development for the treatment of cancer, inflammatory and neurogenerative disorders. We will discuss the molecular mechanisms controlling the functions of RIPK1, its pathologic role in humans and the therapeutic opportunities in targeting RIPK1, specifically in the context of inflammatory diseases and cancers.

Identification and functional study of immortalized mouse thymic epithelial cells

As the key cells in a three-dimensional scaffold within the thymus, Thymic epithelial cells (TECs) play critical roles in the homing, migration and differentiation of T cell precursors through adhesive interactions and the release of various cytokines. In this study, primary cultures of mouse TECs were isolated and identified with TEC-specific antibodies CK5 and CK8. These TECs were immortalized by retroviral transduction of simian virus (SV) 40 large T antigen. We then compared the functions of TECs and immortalized TECs (iTECs). Cell morphology and the proliferative capacity of TECs and iTECs were observed by inverted microscope photography and crystal violet assay after passage. A soft agar assay was then performed to observe their clone formation ability. The expression levels of epithelial cell related factors, such as IL-7, Lptin, Pax-9, Sema3A and et al., were detected by IF and qPCR. TECs were co-cultured with human acute monocytic leukemia cells (THP-1), and the effect of TECs on promoting THP-1 proliferation was observed with flow cytometry and CFSE labeling. Senescence-associated β-galactosidase assay was measured to detect the anti-aging capabilities of the cells. Cell cycle distribution was analyzed by propidium iodide (PI) staining, and paclitaxel (PTX)-induced apoptosis was detected by Annexin V-PI staining to evaluate the anti-apoptotic ability of the cells. Throughout, we found that the immortalized TECs still retain the characteristics of primary TECs, such as the morphology, function and epithelial characteristics; however, iTECs have stronger capabilities in proliferation and anti-aging. Our research suggests that the iTECs were successfully immortalized by SV40 large T antigen, and that the biological characteristics and functions of iTECs were similar to the original TECs. This immortalized cell can be used as an efficient cell model in functional research of the thymus substituting primary TECs with iTECs.

Self-enforcing HMGB1/NF-κB/HIF-1α Feedback Loop Promotes Cisplatin Resistance in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is ranked the sixth most common cancer and the fourth leading cause of cancer-related death worldwide, and its incidence is expected to increase in the future. Cisplatin has been widely used in chemotherapy and transarterial chemoembolization in treatment for HCC. However, the main obstacle to the clinical use of cisplatin is the development of resistance, the mechanisms of which are poorly defined. Therefore, it is imperative to investigate the cellular mechanisms mediating cisplatin resistance in HCC. Here, we demonstrated that high mobility group box 1 (HMGB1) is upregulated in patients with cancer, and implicated in a tumor-supportive role. Further, we showed that HMGB1 has an important role in mediating cisplatin resistance via an HMGB1/ nuclear factor kappa-B (NF-κB)/ hypoxia inducible factor-1α (HIF-1α) feedback loop. The study findings reveal an unappreciated molecular mechanism of HMGB1-mediated cisplatin resistance and may provide a new clue in cancer therapy.

Intestinal mucosal injury induced by obstructive jaundice is associated with activation of TLR4/TRAF6/NF-κB pathways

OBJECTIVES

To investigate the role of TLR4/TRAF6/NF-κB pathways in intestinal mucosal injury induced by obstructive jaundice (OJ).

METHODS

A total of 100 male C57BL/6J mice were randomly assigned to two groups: (I) sham operation (SH); (II) OJ. The mice were sacrificed before operation and on the 1st, 3rd, 5th and 7th day after operation. The blood and terminal ileum were simultaneously collected under the aseptic condition for further detection.

RESULTS

In the SH group, TLR4 protein and mRNA rarely expressed in the intestinal mucosa of the mice and there were no significant differences at different time points (p>0.05). By contrast, in the OJ group TLR4 protein (0.12±0.06, 0.16±0.08, 0.27±0.10, 0.35±0.12 and 0.41±0.13, respectively) and mRNA (0.49±0.19, 0.62±0.23, 0.98±0.32, 1.42±0.41 and 1.72±0.49, respectively) increased gradually with the extension of time (p<0.05). Also in the OJ group, the levels of DAO and endotoxin in plasma as well as the expressions of NF-κB and caspase-3 increased gradually with the extension of time, showing positive correlation with the expression of TLR4 (p<0.05).

CONCLUSIONS

The expression of TLR4 was significantly up-regulated in the distal ileum of mice with OJ. Activation of the TLR4/TRAF6/NF-κB pathways was involved in the occurrence and development of intestinal mucosal injury and endotoxemia in mice with OJ.

Fold-Change Detection of NF-κB at Target Genes with Different Transcript Outputs

The transcription factor nuclear factor (NF)-κB promotes inflammatory and stress-responsive gene transcription across a range of cell types in response to the cytokine tumor necrosis factor (TNF). Although NF-κB signaling exhibits significant variability across single cells, some target genes supporting high levels of TNF-inducible transcription exhibit fold-change detection of NF-κB, which may buffer against stochastic variation in signaling molecules. It is unknown whether fold-change detection is maintained at NF-κB target genes with low levels of TNF-inducible transcription, for which stochastic promoter events may be more pronounced. Here, we used a microfluidic cell-trapping device to measure how TNF-induced activation of NF-κB controls transcription in single Jurkat T cells at the promoters of integrated HIV and the endogenous cytokine gene IL6, which produce only a few transcripts per cell. We tracked TNF-stimulated NF-κB RelA nuclear translocation by live-cell imaging and then quantified transcript number by RNA FISH in the same cell. We found that TNF-induced transcript abundance at 2 h for low- and high-abundance target genes correlates with similar strength with the fold change in nuclear NF-κB. A computational model of TNF-NF-κB signaling, which implements fold-change detection from competition for binding to κB motifs, could reproduce fold-change detection across the experimentally measured range of transcript outputs. However, multiple model parameters affecting transcription had to be simultaneously varied across promoters to maintain fold-change detection while also matching other trends in the single-cell data for low-abundance transcripts. Our results suggest that cells use multiple biological mechanisms to tune transcriptional output while maintaining robustness of NF-κB fold-change detection.

Survival of Single Positive Thymocytes Depends upon Developmental Control of RIPK1 Kinase Signaling by the IKK Complex Independent of NF-κB

NF-κB (nuclear factor κB) signaling is considered critical for single positive (SP) thymocyte development because loss of upstream activators of NF-κB, such as the IKK complex, arrests their development. We found that the compound ablation of RelA, cRel, and p50, required for canonical NF-κB transcription, had no impact upon thymocyte development. While IKK-deficient thymocytes were acutely sensitive to tumor necrosis factor (TNF)-induced cell death, Rel-deficient cells remained resistant, calling into question the importance of NF-κB as the IKK target required for thymocyte survival. Instead, we found that IKK controlled thymocyte survival by repressing cell-death-inducing activity of the serine/threonine kinase RIPK1. We observed that RIPK1 expression was induced during development of SP thymocytes and that IKK was required to prevent RIPK1-kinase-dependent death of SPs in vivo. Finally, we showed that IKK was required to protect Rel-deficient thymocytes from RIPK1-dependent cell death, underscoring the NF-κB-independent function of IKK during thymic development.

Modulation of T-cell responses by anti-tumor necrosis factor treatments in rheumatoid arthritis: a review

Tumor necrosis factor (TNF) is a pleiotropic cytokine involved in many aspects of immune regulation. Anti-TNF biological therapy has been considered a breakthrough in the treatment of chronic autoimmune diseases, such as rheumatoid arthritis (RA). In this review, because of the major involvement of T cells in RA pathogenesis, we discuss the effects of anti-TNF biotherapy on T-cell responses in RA patients. We also outline the potential fields for future research in the area of anti-TNF therapy in RA.This could be useful to better understand the therapeutic efficiency and the side effects that are encountered in RA patients. Better targeting of T cells in RA could help set more specific anti-TNF strategies and develop prediction tools for response.

Aire controls the recirculation of murine Foxp3+ regulatory T-cells back to the thymus

In the thymus, medullary thymic epithelial cells (mTEC) determine the fate of newly selected CD4+ and CD8+ single positive (SP) thymocytes. For example, mTEC expression of Aire controls intrathymic self-antigen availability for negative selection. Interestingly, alterations in both Foxp3+ Regulatory T-cells (T-Reg) and conventional SP thymocytes in Aire-/- mice suggest additional, yet poorly understood, roles for Aire during intrathymic T-cell development. To examine this, we analysed thymocytes from Aire-/- mice using Rag2GFP and Foxp3 expression, and a recently described CD69/MHCI subset definition of post-selection CD4+ conventional thymocytes. We show that while Aire is dispensable for de novo generation of conventional αβT-cells, it plays a key role in controlling the intrathymic T-Reg pool. Surprisingly, a decline in intrathymic T-Reg in Aire-/- mice maps to a reduction in mature recirculating Rag2GFP- T-Reg that express CCR6 and re-enter the thymus from the periphery. Furthermore, we show mTEC expression of the CCR6 ligand CCL20 is reduced in Aire-/- mice, and that CCR6 is required for T-Reg recirculation back to the thymus. Collectively, our study re-defines requirements for late stage intrathymic αβT-cell development, and demonstrates that Aire controls a CCR6-CCL20 axis that determines the developmental makeup of the intrathymic T-Reg pool.

Redefining thymus medulla specialization for central tolerance

During αβT cell development, the thymus medulla represents an essential microenvironment for T cell tolerance. This functional specialization is attributed to its typical organized topology consisting of a branching structure that contains medullary thymic epithelial cell (mTEC) networks to support negative selection and Foxp3+ T-regulatory cell (T-reg) development. Here, by performing TEC-specific deletion of the thymus medulla regulator lymphotoxin β receptor (LTβR), we show that thymic tolerance mechanisms operate independently of LTβR-mediated mTEC development and organization. Consistent with this, mTECs continue to express Fezf2 and Aire, regulators of intrathymic self-antigens, and support T-reg development despite loss of LTβR-mediated medulla organogenesis. Moreover, we demonstrate that LTβR controls thymic tolerance by regulating the frequency and makeup of intrathymic dendritic cells (DCs) required for effective thymocyte negative selection. In all, our study demonstrates that thymus medulla specialization for thymic tolerance segregates from medulla organogenesis and instead involves LTβR-mediated regulation of the thymic DC pool.

α7 nAChR mediated Fas demethylation contributes to prenatal nicotine exposure-induced programmed thymocyte apoptosis in mice

This study aimed to investigate the effects of prenatal nicotine exposure (PNE) on thymocyte apoptosis and postnatal immune impairments in vivo and further explore the epigenetic mechanisms of the pro-apoptotic effect of nicotine in vitro. The results showed that PNE caused immune impairments in offspring on postnatal day 49, manifested as increased IL-4 production and an increased IgG1/IgG2a ratio in serum. Enhanced apoptosis of total and CD4+SP thymocytes was observed both in fetus and in offspring. Further, by exposing thymocytes to 0–100 μM of nicotine in vitro for 48 h, we found that nicotine increased α7 nicotinic acetylcholine receptor (nAChR) expression, activated the Fas apoptotic pathway, and promoted thymocyte apoptosis in concentration-dependent manners. In addition, nicotine could induce Tet methylcytosine dioxygenase (TET) 2 expression and Fas promoter demethylation, which can be abolished by TET2 siRNA transfection. Moreover, the α7 nAChR specific antagonist α-bungarotoxin can abrogate nicotine-induced TET2 increase, and the following Fas demethylation and Fas-mediated apoptosis. In conclusion, our findings showed, for the first time, that α7 nAChR activation could induce TET2-mediated Fas demethylation in thymocytes and results in the upregulation of Fas apoptotic pathway, which provide evidence for elucidating the PNE-induced programmed thymocyte apoptosis.

A type 2 cytokine axis for thymus emigration

In the thymus, stromal microenvironments support a developmental program that generates mature T cells ready for thymic exit. The cellular and molecular specialization within thymic stromal cells that enables their regulation of specific stages of thymocyte development is poorly understood. Here, we show the thymic microenvironment expresses the type 2 IL-4R complex and is functionally responsive to its known ligands, IL-4 and IL-13. Absence of IL-4Rα limits thymocyte emigration, leading to an intrathymic accumulation of mature thymocytes within medullary perivascular spaces and reduced numbers of recent thymic emigrants. Thymus transplantation shows this requirement maps to IL-4Rα expression by stromal cells, and we provide evidence that it regulates thymic exit via a process distinct from S1P-mediated migration. Finally, we reveal a cellular mechanism by which IL-4⁺IL-13⁺ invariant NKT cells are necessary for IL-4Rα signaling that regulates thymic exit. Collectively, we define a new axis for thymic emigration involving stimulation of the thymic microenvironment via type 2 cytokines from innate T cells.

Linear ubiquitin chain assembly complex coordinates late thymic T-cell differentiation and regulatory T-cell homeostasis

The linear ubiquitin chain assembly complex (LUBAC) is essential for innate immunity in mice and humans, yet its role in adaptive immunity is unclear. Here we show that the LUBAC components HOIP, HOIL-1 and SHARPIN have essential roles in late thymocyte differentiation, FOXP3⁺ regulatory T (Treg)-cell development and Treg cell homeostasis. LUBAC activity is not required to prevent TNF-induced apoptosis or necroptosis but is necessary for the transcriptional programme of the penultimate stage of thymocyte differentiation. Treg cell-specific ablation of HOIP causes severe Treg cell deficiency and lethal immune pathology, revealing an ongoing requirement of LUBAC activity for Treg cell homeostasis. These data reveal stage-specific requirements for LUBAC in coordinating the signals required for T-cell differentiation.

LUBAC is a ubiquitin ligase complex of HOIL-1, HOIP and SHARPIN important for signal transduction of a range of stimuli. Here the authors define the function of all three LUBAC components in T cell development and homeostasis.