TLR4 signaling in effector CD4+ T cells regulates TCR activation and experimental colitis in mice

Investigation of immunomodulatory and cytotoxic effects of shed snake skin (Elaphe sauromates) extract

Introduction

Shed snake skin (SSS) is commonly used empirically in ethnomedicine to treat psoriasis, acne, warts, eczema, scabies, open wounds, hemorrhoids, and glaucoma. Although a few studies exist, SSS extracts' in vitro immunological effects have yet to be well described. Therefore, we aimed to investigate the immunomodulatory effects of SSS extract on murine lymphocytes and T cells.

Methods

Hexane, methanol, and chloroform extractions were conducted in collected SSS samples. Protein concentrations in the SSS extract were measured. The cytotoxic and anticancer activities were measured using L929 Fibroblast and SK MEL 30 Cell Lines via MTT assay as described in TS EN ISO 10993-5. Immunomodulatory activities of SSS extract on total lymphocytes or enriched CD4+ T cell cultures, their cell-specific pro-inflammatory cytokines (IL-6, IL-1β. IL-12p40, IL-23p19, TNF-α, IL-17A, IFN-γ, IL-10, TGFβ1) levels were measured via FACS ARIA III analysis and related gene expression with Real-Time Quantitative Polymerase Chain Reaction (Rt-qPCR).

Results

Hexane, methanol, and chloroform-extracted SSS were tested on SK-MEL-30 cells via MTT and revealed a superior anti-proliferative effect for hexane extract of SSS at low concentrations. SSS treatment of murine lymphocytes augmented Tnf-α and IFN-γ levels produced by CD3+ T cells when lymphocytes were activated with anti-CD3/CD28 or LPS stimulation. This effect required the presence of non-T cells, possibly antigen-presenting cells, and was not observed on purified CD4+ T cells. Additionally, SSS significantly blocked suppressive cytokine Tgfb gene expression (but not Il10) without altering in vitro Treg generation/or expansion.

Discussion

This is the first in vitro study investigating SSS's anti-tumor and immunomodulatory effects. Our data provide evidence for SSS's anti-proliferative activity on SK-MEL-30 cells and its pro-inflammatory role on murine lymphocytes, which warrants further investigation of the potential use of SSS extract with in vivo disease models.

Pattern-Recognition Receptors and Immunometabolic Reprogramming: What We Know and What to Explore

BACKGROUND

Evolutionarily, immune response is a complex mechanism that protects the host from internal and external threats. Pattern-recognition receptors (PRRs) recognize MAMPs, PAMPs, and DAMPs to initiate a protective pro-inflammatory immune response. PRRs are expressed on the cell membranes by TLR1, 2, 4, and 6 and in the cytosolic organelles by TLR3, 7, 8, and 9, NLRs, ALRs, and cGLRs. We know their downstream signaling pathways controlling immunoregulatory and pro-inflammatory immune response. However, the impact of PRRs on metabolic control of immune cells to control their pro- and anti-inflammatory activity has not been discussed extensively.

SUMMARY

Immune cell metabolism or immunometabolism critically determines immune cells' pro-inflammatory phenotype and function. The current article discusses immunometabolic reprogramming (IR) upon activation of different PRRs, such as TLRs, NLRs, cGLRs, and RLRs. The duration and type of PRR activated, species studied, and location of immune cells to specific organ are critical factors to determine the IR-induced immune response.

KEY MESSAGE

The work herein describes IR upon TLR, NLR, cGLR, and RLR activation. Understanding IR upon activating different PRRs is critical for designing better immune cell-specific immunotherapeutics and immunomodulators targeting inflammation and inflammatory diseases.

Identification, expression and molecular polymorphism of T-cell receptors α and β from the glacial relict Hucho bleekeri

The T-cell receptor (TCR) is a specific molecule on the surface of all T cells that mediates cellular adaptive immune responses to antigens. Hucho bleekeri is a critically endangered species and is regarded as a glacial relict that has the lowest-latitude distribution compared with any Eurasian salmonid. In the present study, two TCR genes, namely, TCR α and β, were identified and characterized in H. bleekeri. Both TCR α and TCR β have typical TCR structures, including the IgV domain, IgC domain, connecting peptide, transmembrane and cytoplasmic domains. The two TCR genes were constitutionally expressed in various tissues, with the highest expression found in the spleen for TCR α and in the trunk kidney for TCR β. Challenge of H. bleekeri with LPS or poly(I:C) resulted in significant upregulation of both TCR α and β expression in headkidney and spleen primary cells, indicating their potential roles in the immune response. Molecular polymorphism analysis of the whole ORF regions of TCR α and β in different individuals revealed high diversity of IgV domains of these two genes, especially in complementarity-determining region (CDR) 3. The ratio of nonsynonymous substitution occurred at a significantly higher frequency than synonymous substitution in the CDR of TCR α and β, demonstrating the existence of positive selection. The results obtained in the present study enhance our understanding of TCR roles in regulating immune mechanisms and provide new information for the study of TCR lineage diversity in fish.

Recombinant 60-kDa heat shock protein from Paracoccidioides brasiliensis induces the death of mouse lymphocytes in a mechanism dependent on Toll-like receptor 4 and tumor necrosis factor

Paracoccidioides fungi are thermodimorphic microorganisms that cause paracoccidioidomycosis (PCM), an autochthonous disease from Latin America, with most cases in Brazil. Humans become infected by inhaling conidia or mycelial fragments that transform into yeast at body temperature. These fungi cause chronic-granulomatous inflammation, which may promote fibrosis and parenchyma destruction in the lungs. In response to stress imposed by the host, fungi Paracoccidioides spp. increase the expression of heat shock proteins (HSP), which protect them by sustaining cellular proteostasis. Our group has studied the role of HSP60 in PCM, and previous data show that the recombinant HSP60 (rHSP60) has a deleterious effect when used in a single dose as therapy for experimental PCM. Here, we investigated the mechanism by which rHSP60 could worsen the disease. We found that rHSP60 caused the viability loss of splenic or lymph node cells from both immunized and non-immunized mice, including in splenic T lymphocytes under polyclonal stimulation with concanavalin A, probably by undergoing apoptosis. Among analyzed splenic cells, lymphocytes were indeed the main cells to die. When we investigated the death mechanisms, remarkably, we found that there was no viability loss in rHSP60-stimulated splenic cells from mice deficient in Toll-like receptor 4, TRIF adapter protein, and TNF receptor 1(TNFR1), as well as rHSP60-stimulated WT cells incubated with anti-TNF antibody. Besides, caspase-8 inhibitor IETD-CHO blocked the rHSP60 effect on splenic cells, suggesting that rHSP60 induces the extrinsic apoptosis pathway dependent on signaling via TLR4/TRIF and TNFR1.

Post-operative cognitive dysfunction is exacerbated by high-fat diet via TLR4 and prevented by dietary DHA supplementation

Post-operative cognitive dysfunction (POCD) is an abrupt decline in neurocognitive function arising shortly after surgery and persisting for weeks to months, increasing the risk of dementia diagnosis. Advanced age, obesity, and comorbidities linked to high-fat diet (HFD) consumption such as diabetes and hypertension have been identified as risk factors for POCD, although underlying mechanisms remain unclear. We have previously shown that surgery alone, or 3-days of HFD can each evoke sufficient neuroinflammation to cause memory deficits in aged, but not young rats. The aim of the present study was to determine if HFD consumption before surgery would potentiate and prolong the subsequent neuroinflammatory response and memory deficits, and if so, to determine the extent to which these effects depend on activation of the innate immune receptor TLR4, which both insults are known to stimulate. Young-adult (3mo) & aged (24mo) male F344xBN F1 rats were fed standard chow or HFD for 3-days immediately before sham surgery or laparotomy. In aged rats, the combination of HFD and surgery caused persistent deficits in contextual memory and cued-fear memory, though it was determined that HFD alone was sufficient to cause the long-lasting cued-fear memory deficits. In young adult rats, HFD + surgery caused only cued-fear memory deficits. Elevated proinflammatory gene expression in the hippocampus of both young and aged rats that received HFD + surgery persisted for at least 3-weeks after surgery. In a separate experiment, rats were administered the TLR4-specific antagonist, LPS-RS, immediately before HFD onset, which ameliorated the HFD + surgery-associated neuroinflammation and memory deficits. Similarly, dietary DHA supplementation for 4 weeks prior to HFD onset blunted the neuroinflammatory response to surgery and prevented development of persistent memory deficits. These results suggest that HFD 1) increases risk of persistent POCD-associated memory impairments following surgery in male rats in 2) a TLR4-dependent manner, which 3) can be targeted by DHA supplementation to mitigate development of persistent POCD.

Mucosal TLR5 activation controls healthspan and longevity

Addressing age-related immunological defects through therapeutic interventions is essential for healthy aging, as the immune system plays a crucial role in controlling infections, malignancies, and in supporting tissue homeostasis and repair. In our study, we show that stimulating toll-like receptor 5 (TLR5) via mucosal delivery of a flagellin-containing fusion protein effectively extends the lifespan and enhances the healthspan of mice of both sexes. This enhancement in healthspan is evidenced by diminished hair loss and ocular lens opacity, increased bone mineral density, improved stem cell activity, delayed thymic involution, heightened cognitive capacity, and the prevention of pulmonary lung fibrosis. Additionally, this fusion protein boosts intestinal mucosal integrity by augmenting the surface expression of TLR5 in a certain subset of dendritic cells and increasing interleukin-22 (IL-22) secretion. In this work, we present observations that underscore the benefits of TLR5-dependent stimulation in the mucosal compartment, suggesting a viable strategy for enhancing longevity and healthspan.

Disulfide-HMGB1 signals through TLR4 and TLR9 to induce inflammatory macrophages capable of innate-adaptive crosstalk in human liver transplantation

Ischemia-reperfusion injury (IRI) during orthotopic liver transplantation (OLT) contributes to graft rejection and poor clinical outcomes. The disulfide form of high mobility group box 1 (diS-HMGB1), an intracellular protein released during OLT-IRI, induces pro-inflammatory macrophages. How diS-HMGB1 differentiates human monocytes into macrophages capable of activating adaptive immunity remains unknown. We investigated if diS-HMGB1 binds toll-like receptor (TLR) 4 and TLR9 to differentiate monocytes into pro-inflammatory macrophages that activate adaptive immunity and promote graft injury and dysfunction. Assessment of 106 clinical liver tissue and longitudinal blood samples revealed that OLT recipients were more likely to experience IRI and graft dysfunction with increased diS-HMGB1 released during reperfusion. Increased diS-HMGB1 concentration also correlated with TLR4/TLR9 activation, polarization of monocytes into pro-inflammatory macrophages, and production of anti-donor antibodies. In vitro, healthy volunteer monocytes stimulated with purified diS-HMGB1 had increased inflammatory cytokine secretion, antigen presentation machinery, and reactive oxygen species production. TLR4 inhibition primarily impeded cytokine/chemokine and costimulatory molecule programs, whereas TLR9 inhibition decreased HLA-DR and reactive oxygen species production. diS-HMGB1-polarized macrophages also showed increased capacity to present antigens and activate T memory cells. In murine OLT, diS-HMGB1 treatment potentiated ischemia-reperfusion-mediated hepatocellular injury, accompanied by increased serum alanine transaminase levels. This translational study identifies the diS-HMGB1/TLR4/TLR9 axis as potential therapeutic targets in OLT-IRI recipients.

S100A8/A9-alarmin promotes local myeloid-derived suppressor cell activation restricting severe autoimmune arthritis

Immune-suppressive effects of myeloid-derived suppressor cells (MDSCs) are well characterized during anti-tumor immunity. The complex mechanisms promoting MDSC development and their regulatory effects during autoimmune diseases are less understood. We demonstrate that the endogenous alarmin S100A8/A9 reprograms myeloid cells to a T cell suppressing phenotype during autoimmune arthritis. Treatment of myeloid precursors with S100-alarmins during differentiation induces MDSCs in a Toll-like receptor 4-dependent manner. Consequently, knockout of S100A8/A9 aggravates disease activity in collagen-induced arthritis due to a deficit of MDSCs in local lymph nodes, which could be corrected by adoptive transfer of S100-induced MDSCs. Blockade of MDSC function in vivo aggravates disease severity in arthritis. Therapeutic application of S100A8 induces MDSCs in vivo and suppresses the inflammatory phenotype of S100A9ko mice. Accordingly, the interplay of T cell-mediated autoimmunity with a defective innate immune regulation is crucial for autoimmune arthritis, which should be considered for future innovative therapeutic options.

Protein arginine N-methyltransferase 4 (PRMT4) contributes to lymphopenia in experimental sepsis

BACKGROUND

One hallmark of sepsis is the reduced number of lymphocytes, termed lymphopenia, that occurs from decreased lymphocyte proliferation or increased cell death contributing to immune suppression. Histone modification enzymes regulate immunity by their epigenetic and non-epigenetic functions; however, the role of these enzymes in lymphopenia remains elusive.

METHODS

We used molecular biological approaches to investigate the high expression and function of a chromatin modulator protein arginine N-methyltransferase 4 (PRMT4)/coactivator-associated arginine methyltransferase 1 in human samples from septic patients and cellular and animal septic models.

RESULTS

We identified that PRMT4 is elevated systemically in septic patients and experimental sepsis. Gram-negative bacteria and their derived endotoxin lipopolysaccharide (LPS) increased PRMT4 in B and T lymphocytes and THP-1 monocytes. Single-cell RNA sequencing results indicate an increase of PRMT4 gene expression in activated T lymphocytes. Augmented PRMT4 is crucial for inducing lymphocyte apoptosis but not monocyte THP-1 cells. Ectopic expression of PRMT4 protein caused substantial lymphocyte death via caspase 3-mediated cell death signalling, and knockout of PRMT4 abolished LPS-mediated lymphocyte death. PRMT4 inhibition with a small molecule compound attenuated lymphocyte death in complementary models of sepsis.

CONCLUSIONS

These findings demonstrate a previously uncharacterised role of a key chromatin modulator in lymphocyte survival that may shed light on devising therapeutic modalities to lessen the severity of septic immunosuppression.

Neutrophil extracellular traps primed intercellular communication in cancer progression as a promising therapeutic target

In addition to the anti-infection response, neutrophils are linked to tumor progression through the secretion of inflammation components and neutrophil extracellular traps (NETs) formation. NET is a web-like structure constituted by a chromatin scaffold coated with specific nuclear and cytoplasmic proteins, such as histone and granule peptides. Increasing evidence has demonstrated that NETs are favorable factors to promote tumor growth, invasion, migration, and immunosuppression. However, the cell-cell interaction between NETs and other cells (tumor cells and immune cells) is complicated and poorly studied. This work is the first review to focus on the intercellular communication mediated by NETs in cancer. We summarized the complex cell-cell interaction between NETs and other cells in the tumor microenvironment. We also address the significance of NETs as both prognostic/predictive biomarkers and molecular targets for cancer therapy. Moreover, we presented a comprehensive landscape of cancer immunity, improving the therapeutic efficacy for advanced cancer in the future.

Mitogen-Activated Protein Kinase Phosphatases: No Longer Undruggable?

Phosphatases and kinases maintain an equilibrium of dephosphorylated and phosphorylated proteins, respectively, that are required for critical cellular functions. Imbalance in this equilibrium or irregularity in their function causes unfavorable cellular effects that have been implicated in the development of numerous diseases. Protein tyrosine phosphatases (PTPs) catalyze the dephosphorylation of protein substrates on tyrosine residues, and their involvement in cell signaling and diseases such as cancer and inflammatory and metabolic diseases has made them attractive therapeutic targets. However, PTPs have proved challenging in therapeutics development, garnering them the unfavorable reputation of being undruggable. Nonetheless, great strides have been made toward the inhibition of PTPs over the past decade. Here, we discuss the advancement in small-molecule inhibition for the PTP subfamily known as the mitogen-activated protein kinase (MAPK) phosphatases (MKPs). We review strategies and inhibitor discovery tools that have proven successful for small-molecule inhibition of the MKPs and discuss what the future of MKP inhibition potentially might yield.

No NETs no TIME: Crosstalk between neutrophil extracellular traps and the tumor immune microenvironment

The tumor immune microenvironment (TIME) controls tumorigenesis. Neutrophils are important components of TIME and control tumor progression and therapy resistance. Neutrophil extracellular traps (NETs) ejected by activated neutrophils are net-like structures composed of decondensed extracellular chromatin filaments decorated with a plethora of granules as well as cytoplasmic proteins. Many of these harbour post translational modifications. Cancer cells reportedly trigger NET formation, and conversely, NETs alter the TIME and promote tumor cell proliferation and migration. The specific interactions between NETs and TIME and the respective effects on tumor progression are still elusive. In certain tumors, a CD4+ T helper (Th) 2 cell-associated TIME induces NETs and exerts immunosuppressive functions via programmed death 1 (PD-1)/PD-L1, both associated with poorer prognosis. In other cases, NETs induce the proliferation of Th1 cells, associated with an improved prognosis in cancer. In addition, NETs can drive macrophage polarization and often rely on macrophages to promote cancer cell invasion and metastasis. In turn, macrophages can swiftly clear NETs in an immunologically silent manner. The aim of this review is to summarize the knowledge about the mutual interaction between NETs and TIME and its impact on tumor growth and therapy.

Ferroptosis promotes T-cell activation-induced neurodegeneration in multiple sclerosis

While many drugs are effective at reducing the relapse frequency of multiple sclerosis (MS), there is an unmet need for treatments that slow neurodegeneration resulting from secondary disease progression. The mechanism of neurodegeneration in MS has not yet been established. Here, we discovered a potential pathogenetic role of ferroptosis, an iron-dependent regulated cell death mechanism, in MS. We found that critical ferroptosis proteins (acyl-CoA synthetase long-chain family member 4, ACSL4) were altered in an existing genomic database of MS patients, and biochemical features of ferroptosis, including lipid reactive oxygen species (ROS) accumulation and mitochondrial shrinkage, were observed in the experimental autoimmune encephalitis (EAE) mouse model. Targeting ferroptosis with ferroptosis inhibitors or reducing ACSL4 expression improved the behavioral phenotypes of EAE mice, reduced neuroinflammation, and prevented neuronal death. We found that ferroptosis was an early event in EAE, which may promote T-cell activation through T-cell receptor (TCR) signaling in vitro and in vivo. These data indicate that ferroptosis may be a potential target for treating MS.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Absent in Melanoma 2 (AIM2) Regulates the Stability of Regulatory T Cells

Absent in melanoma 2 (AIM2) is a cytosolic dsDNA sensor that has been broadly studied for its role in inflammasome assembly. However, little is known about the function of AIM2 in adaptive immune cells. The purpose of this study was to investigate whether AIM2 has a cell-intrinsic role in CD4+ T cell differentiation or function. We found that AIM2 is expressed in both human and mouse CD4+ T cells and that its expression is affected by T cell receptor (TCR) activation. Naïve CD4+ T cells from AIM2-deficient (Aim2−/−) mice showed higher ability to maintain forkhead box P3 (FOXP3) expression in vitro, while their capacity to differentiate into T helper (Th)1, Th2 or Th17 cells remained unaltered. Transcriptional profiling by RNA sequencing showed that AIM2 might affect regulatory T cell (Treg) stability not by controlling the expression of Treg signature genes, but through the regulation of the cell’s metabolism. In addition, in a T cell transfer model of colitis, Aim2−/−-naïve T cells induced less severe body weight loss and displayed a higher ability to differentiate into FOXP3+ cells in vivo. In conclusion, we show that AIM2 function is not confined to innate immune cells but is also important in CD4+ T cells. Our data identify AIM2 as a regulator of FOXP3+ Treg cell differentiation and as a potential intervention target for restoring T cell homeostasis.

PMN-MDSCs accumulation induced by CXCL1 promotes CD8+ T cells exhaustion in gastric cancer

Myeloid-derived suppressor cells (MDSCs) accumulation in multiple tumor is associated with immune checkpoint inhibitors (ICIs) resistance. However, mechanisms of MDSCs in ICIs resistance of gastric cancer (GC) have not been thoroughly explored. In this study, we found that the PMN-MDSCs frequency rather than the M-MDSCs frequency was correlated with the survival of GC patients and CXCL1 induced PMN-MDSCs accumulation in GC. S100A8/A9 heterodimer, a hallmark of MDSCs, upregulated the CXCL1 expression in GC cells through the TLR4/p38 MAPK/NF-κB pathway. Notably, PMN-MDSCs exerted immunosuppressive effect through S100A8/A9. Mechanically, S100A8/A9 led to CD8⁺ T cells exhaustion including inhibiting CD8⁺ T cells glycolysis, proliferation and TNF-α and IFN-γ production, which was dependent on TLR4/AKT/mTOR pathway. In tumor-bearing mice, the CXCR2 antagonist SB225002 decreased PMN-MDSCs accumulation, increased CD8⁺ T cells infiltration in GC and further enhanced anti-tumor efficacy of anti-PD-1. Taken together, our study identified that CXCL1 induced PMN-MDSCs accumulation in GC, and unveiled how PMN-MDSCs promoted CD8⁺ T cells exhaustion, which may provide a potential therapeutic strategy for GC.

Regulatory T-cell and neutrophil extracellular trap interaction contributes to carcinogenesis in non-alcoholic steatohepatitis

BACKGROUND & AIMS

Regulatory T-cells (Tregs) impair cancer immunosurveillance by creating an immunosuppressive environment that fosters tumor cell survival. Our previous findings demonstrated that neutrophil extracellular traps (NETs), which are involved both in innate and adaptive immunity, are abundant in livers affected by non-alcoholic steatohepatitis (NASH). However, how NETs interact with Tregs in the development of NASH-associated hepatocellular carcinoma (NASH-HCC) is not known.

METHODS

A choline-deficient, high-fat diet+diethylnitrosamine mouse model and the stelic animal model were utilized for NASH-HCC and a western diet mouse model was used for NASH development. Treg depletion was achieved using FoxP3-DTR mice. RNA sequencing was used to explore the mechanism by which NETs could regulate Treg differentiation. Bioenergetic analyses of naïve CD4⁺ T-cells were assessed by Seahorse.

RESULTS

Although the absolute number of CD4⁺ T-cells is lower in NASH livers, the Treg subpopulation is selectively increased. Depleting Tregs dramatically inhibits HCC initiation and progression in NASH. There is a positive correlation between increased NET and hepatic Treg levels. RNA sequencing data reveals that NETs impact gene expression profiles in naïve CD4⁺ T-cells, with the most differentially expressed genes being those involved in mitochondrial oxidative phosphorylation. By facilitating mitochondrial respiration, NETs can promote Treg differentiation. Metabolic reprogramming of naïve CD4⁺ T-cells by NETs requires toll-like receptor 4. Blockade of NETs in vivo using Pad4^-/- mice or DNase I treatment reduces the activity of Tregs.

CONCLUSIONS

Tregs can suppress immunosurveillance in the premalignant stages of NASH. NETs facilitate the crosstalk between innate and adaptive immunity in NASH by promoting Treg activity through metabolic reprogramming. Therapies targeting NETs and Treg interactions could offer a potential strategy for preventing HCC in patients with NASH.

LAY SUMMARY

Regulatory T-cells (Tregs) can promote tumor development by suppressing cancer immunosurveillance, but their role in carcinogenesis during non-alcoholic steatohepatitis (NASH) progression is unknown. Herein, we discovered that selectively increased intrahepatic Tregs can promote an immunosuppressive environment in NASH livers. Neutrophil extracellular traps (NETs) link innate and adaptive immunity by promoting Treg differentiation via metabolic reprogramming of naïve CD4⁺ T-cells. This mechanism could be targeted to prevent liver cancer in patients with NASH.

Alhagi pseudalhagi Extract Exerts Protective Effects Against Intestinal Inflammation in Ulcerative Colitis by Affecting TLR4-Dependent NF-κB Signaling Pathways

Alhagi pseudalhagi Desv. Extract (APE) is the major active fraction extracted from the aerial part of Alhagi pseudalhagi Desv. In view of its application in Uyghur medicine, it may be beneficial for the treatment of ulcerative colitis (UC). The aim of the present study was to investigate the possible beneficial effects of APE on UC mice and detect the possible mechanisms underlying these effects.

Methods: An acute UC model was established in mice using dextran sulfate sodium. Sixty mice were randomly divided into six groups: normal, UC model, sulfasalazine (200 mg/kg), high-dose APE (APE-H, 2.82 g/kg), middle-dose APE (APE-M, 1.41 g/kg), and low-dose APE (APE-L, 0.70 g/kg) groups. Drugs were administered by gavage for 10 days after the induction of colitis. Serum and colon tissue samples were collected from the mice during the experiment, and survival signs, body weight changes, disease activity index (DAI), colon length, and colon wet weight in mice were determined after the treatment. UC-induced damage, including inflammation and ulceration of colon mucosa, were observed by the naked eye as well as using hematoxylin and eosin staining (H&E) and scanning electron microscopy and scored according to Wallace and Keean’s criteria. We measured the levels of tumor necrosis factor α (TNF-α), interleukin (IL)-1β, IL-6, and IL-10 in the serum and colon tissues using ELISA. Additionally, the relative protein levels of toll-like receptor 4 (TLR₄), nuclear factor-kappa B p65 (NF-κB p65), phosphorylated NF-κB p65 at Ser536 (p-p65 Ser536), inhibitor kappa B-kinase ß (IK-Kβ), and phosphorylated IK-Kβ (Ser176/180) (p-IK-Kβ) in colonic mucosal epithelial tissues were detected using western blotting. The main functional components of APE were analyzed and confirmed by UPLC-MS/MS.

Results: APE treatment repaired the UC-induced colon mucosa injury, reduced the weight loss, attenuated DAI, colon macroscopic damage index, and histological inflammation, and significantly downregulated the levels of inflammatory markers, including TNF-α, IL-1β, and IL-6, in the serum and colon tissues. Additionally, APE treatment reduced the levels of TLR₄ and phosphorylation of p-NF-κB and p-IK-Kβ. The main components of APE are taxifolin, 3,5-dihydroxy-2-(4-hydroxyphenyl)-7-[(2R,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl) oxan-2-yl] oxychromen-4-one, hyperoside, rutin, kaempferol, isorhamnetin, 7,8-dihydroxyflavone, and kaempferide.

Conclusions: To the best of our knowledge, the present study is first to demonstrate that APE exerts a protective effect against intestinal inflammation in UC by affecting TLR₄-dependent NF-κB signaling pathways.

The soluble cytoplasmic tail of CD45 regulates T-cell activation via TLR4 signaling

The soluble cytoplasmic tail of CD45 (ct-CD45) is a cleavage fragment of CD45, that is generated during the activation of human phagocytes. Upon release to the extracellular space, ct-CD45 binds to human T cells and inhibits their activation in vitro. Here, we studied the potential role of TLR4 as a receptor for ct-CD45. Treatment of Jurkat TLR4/CD14 reporter cells with ct-CD45 induced the upregulation of the reporter gene NFκB-eGFP and could be blocked by inhibitors of TLR4 signaling. Conversely, ct-CD45 did not promote the NFκB-controlled eGFP induction in reporter cells expressing TLR1, TLR2, and TLR6 transgenes and did not lead to the activation of the transcription factors NFκB, AP-1, and NFAT in a Jurkat reporter cell line expressing endogenous TLR5. Moreover, ct-CD45 binds to recombinant TLR4 in an in vitro assay and this association was reduced in the presence of oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine. Blockade of TLR4 with mAb HTA125 partially reversed the ct-CD45-mediated inhibition of T-cell proliferation. Interestingly, targeting of TLR4 with mAb W7C11 also suppressed T-cell proliferation. In summary, the results of this study demonstrate that ct-CD45 acts via a noncanonical TLR4 activation pathway on T cells, which modulates TCR signaling.

Direct tissue-sensing reprograms TLR4+ Tfh-like cells inflammatory profile in the joints of rheumatoid arthritis patients

CD4⁺ T cells mediate rheumatoid arthritis (RA) pathogenesis through both antibody-dependent and independent mechanisms. It remains unclear how synovial microenvironment impinges on CD4⁺ T cells pathogenic functions. Here, we identified a TLR4⁺ follicular helper T (Tfh) cell-like population present in the blood and expanded in synovial fluid. TLR4⁺ T cells possess a two-pronged pathogenic activity whereby direct TLR4⁺ engagement by endogenous ligands in the arthritic joint reprograms them from an IL-21 response, known to sponsor antibody production towards an IL-17 inflammatory program recognized to fuel tissue damage. Ex vivo, synovial fluid TLR4⁺ T cells produced IL-17, but not IL-21. Blocking TLR4 signaling with a specific inhibitor impaired IL-17 production in response to synovial fluid recognition. Mechanistically, we unveiled that T-cell HLA-DR regulates their TLR4 expression. TLR4⁺ T cells appear to uniquely reconcile an ability to promote systemic antibody production with a local synovial driven tissue damage program.

In order to identify how the synovial microenvironment impinges on CD4+ T cells pathogenic functions in Rheumatoid Arthritis (RA), Amaral-Silva examined RA patient blood and synovial fluif and identified the presence of a TLR4+ follicular helper T (Tfh) cell-like population. They provided mechanistic insight into how TLR4⁺ T cells uniquely reconcile an ability to promote systemic antibody production with a local synovial driven-tissue damage program.

Increased Expression of Proatherogenic Proteins in Immune Cell Subtypes in Tobacco Cigarette Smokers But Not in Electronic Cigarette Vapers

It is unclear how oxidative stress triggered by smoking and vaping may alter specific immune cell subsets. In this study, we showed that tobacco cigarette smoking, but not electronic-cigarette vaping, is associated with increased expression of major proteins in the toll-like receptor 4 (TLR4) inflammasome-interleukin (IL)-6 signalling axis in monocyte subtypes and T cells. TLR4 senses oxidative stress in immune cells caspase-1 is a key protein of inflammasome activation, and IL-6R-α is the receptor for IL-6 that drives proatherogenic IL-6 signalling. These findings implicate the non-nicotine, pro-oxidant toxicants in tobacco cigarette smoke as instigators of increased expression of key proteins in the TLR4-inflammasome-IL-6 axis that contribute to atherogenesis.

IgE-activated mast cells enhance TLR4-mediated antigen-specific CD4+ T cell responses

Mast cells are potent mediators of allergy and asthma, yet their role in regulating adaptive immunity remains ambiguous. On the surface of mast cells, the crosslinking of IgE bound to FcεRI by a specific antigen recognized by that IgE triggers the release of immune mediators such as histamine and cytokines capable of activating other immune cells; however, little is known about the mast cell contribution to the induction of endogenous, antigen-specific CD4⁺ T cells. Here we examined the effects of specific mast cell activation in vivo on the initiation of an antigen-specific CD4⁺ T cell response. While CD4⁺ T cells were not enhanced by FcεRI stimulation alone, their activation was synergistically enhanced when FcεRI activation was combined with TLR4 stimulation. This enhanced activation was dependent on global TLR4 stimulation but appeared to be less dependent on mast cell expressed TLR4. This study provides important new evidence to support the role of mast cells as mediators of the antigen-specific adaptive immune response.

Polymeric Pathogen-Like Particles-Based Combination Adjuvants Elicit Potent Mucosal T Cell Immunity to Influenza A Virus

Eliciting durable and protective T cell-mediated immunity in the respiratory mucosa remains a significant challenge. Polylactic-co-glycolic acid (PLGA)-based cationic pathogen-like particles (PLPs) loaded with TLR agonists mimic biophysical properties of microbes and hence, simulate pathogen-pattern recognition receptor interactions to safely and effectively stimulate innate immune responses. We generated micro particle PLPs loaded with TLR4 (glucopyranosyl lipid adjuvant, GLA) or TLR9 (CpG) agonists, and formulated them with and without a mucosal delivery enhancing carbomer-based nanoemulsion adjuvant (ADJ). These adjuvants delivered intranasally to mice elicited high numbers of influenza nucleoprotein (NP)-specific CD8+ and CD4+ effector and tissue-resident memory T cells (T_RMs) in lungs and airways. PLPs delivering TLR4 versus TLR9 agonists drove phenotypically and functionally distinct populations of effector and memory T cells. While PLPs loaded with CpG or GLA provided immunity, combining the adjuvanticity of PLP-GLA and ADJ markedly enhanced the development of airway and lung T_RMs and CD4 and CD8 T cell-dependent immunity to influenza virus. Further, balanced CD8 (Tc1/Tc17) and CD4 (Th1/Th17) recall responses were linked to effective influenza virus control. These studies provide mechanistic insights into vaccine-induced pulmonary T cell immunity and pave the way for the development of a universal influenza and SARS-CoV-2 vaccines.

iRGD conjugated nimbolide liposomes protect against endotoxin induced acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a deadly respiratory illness associated with refractory hypoxemia and pulmonary edema. The recent pandemic outbreak of COVID-19 is associated with severe pneumonia and inflammatory cytokine storm in the lungs. The anti-inflammatory phytomedicine nimbolide (NIM) may not be feasible for clinical translation due to poor pharmacokinetic properties and lack of suitable delivery systems. To overcome these barriers, we have developed nimbolide liposomes conjugated with iRGD peptide (iRGD-NIMLip) for targeting lung inflammation. It was observed that iRGD-NIMLip treatment significantly inhibited oxidative stress and cytokine storm compared to nimbolide free-drug (f-NIM), nimbolide liposomes (NIMLip), and exhibited superior activity compared to dexamethasone (DEX). iRGD-NIMLip abrogated the LPS induced p65 NF-κB, Akt, MAPK, Integrin β3 and β5, STAT3, and DNMT1 expression. Collectively, our results demonstrate that iRGD-NIMLip could be a promising novel drug delivery system to target severe pathological consequences observed in ARDS and COVID-19 associated cytokine storm.

Multi-Omic Data Integration Allows Baseline Immune Signatures to Predict Hepatitis B Vaccine Response in a Small Cohort

Background

Vaccination remains one of the most effective means of reducing the burden of infectious diseases globally. Improving our understanding of the molecular basis for effective vaccine response is of paramount importance if we are to ensure the success of future vaccine development efforts.

Methods

We applied cutting edge multi-omics approaches to extensively characterize temporal molecular responses following vaccination with hepatitis B virus (HBV) vaccine. Data were integrated across cellular, epigenomic, transcriptomic, proteomic, and fecal microbiome profiles, and correlated to final HBV antibody titres.

Results

Using both an unsupervised molecular-interaction network integration method (NetworkAnalyst) and a data-driven integration approach (DIABLO), we uncovered baseline molecular patterns and pathways associated with more effective vaccine responses to HBV. Biological associations were unravelled, with signalling pathways such as JAK-STAT and interleukin signalling, Toll-like receptor cascades, interferon signalling, and Th17 cell differentiation emerging as important pre-vaccination modulators of response.

Conclusion

This study provides further evidence that baseline cellular and molecular characteristics of an individual's immune system influence vaccine responses, and highlights the utility of integrating information across many parallel molecular datasets.

Toll-Like Receptor-4 Is Involved in Mediating Intestinal and Extra-Intestinal Inflammation in Campylobacter coli-Infected Secondary Abiotic IL-10-/- Mice

Human Campylobacter infections are emerging worldwide and constitute significant health burdens. We recently showed that the immunopathological sequelae in Campylobacter jejuni-infected mice were due to Toll-like receptor (TLR)-4 dependent immune responses induced by bacterial lipooligosaccharide (LOS). Information regarding the molecular mechanisms underlying Campylobacter coli-host interactions are scarce, however. Therefore, we analyzed C. coli-induced campylobacteriosis in secondary abiotic IL-10^−/− mice with and without TLR4. Mice were infected perorally with a human C. coli isolate or with a murine commensal Escherichia coli as apathogenic, non-invasive control. Independent from TLR4, C. coli and E. coli stably colonized the gastrointestinal tract, but only C. coli induced clinical signs of campylobacteriosis. TLR4^−/− IL-10^−/− mice, however, displayed less frequently fecal blood and less distinct histopathological and apoptotic sequelae in the colon versus IL-10^−/− counterparts on day 28 following C. coli infection. Furthermore, C. coli-induced colonic immune cell responses were less pronounced in TLR4^−/− IL-10^−/− as compared to IL-10^−/− mice and accompanied by lower pro-inflammatory mediator concentrations in the intestines and the liver of the former versus the latter. In conclusion, our study provides evidence that TLR4 is involved in mediating C. coli-LOS-induced immune responses in intestinal and extra-intestinal compartments during murine campylobacteriosis.

Δ42PD1-TLR4 Augments γδ-T Cell Activation of the Transitional Memory Subset of CD4+ T Cells

TLR ligands can contribute to T cell immune responses by indirectly stimulating antigen presentation and cytokines and directly serving as co-stimulatory signals. We have previously reported that the human endogenous surface protein, Δ42PD1, is expressed primarily on (Vγ9)Vδ2 cells and can interact with TLR4. Since Vδ2 cells possess antigen presentation capacity, we sought to further characterize if the Δ42PD1-TLR4 interaction has a role in stimulating T cell responses. In this study, we found that stimulation of Vδ2 cells not only upregulated Δ42PD1 expression but also increased MHC class II molecules necessary for the antigen presentation. In a mixed leukocyte reaction assay, upregulation of Δ42PD1 on Vδ2 cells elevated subsequent T cell proliferation. Furthermore, the interaction between Δ42PD1-TLR4 augments Vδ2 cell stimulation of autologous CMV pp65-or TT-specific CD4⁺ T cell proliferation and IFN-γ responses, which was specifically and significantly reduced by blocking the Δ42PD1-TLR4 interaction. Furthermore, confocal microscopy analysis confirmed the interaction between Δ42PD1⁺HLA-DR⁺Vδ2 cells and TLR4⁺CD4 T cells. Interestingly, the subset of CD4⁺ T cells expressing TLR4 appears to be PD-1⁺ CD45RO⁺CD45RA⁺ transitional memory T cells and responded to Δ42PD1⁺HLA-DR⁺Vδ2 cells. Overall, this study demonstrated an important biological role of Δ42PD1 protein exhibited by Vδ2 antigen-presenting cells in augmenting T cell activation through TLR4, which may serve as an additional co-stimulatory signal.

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Δ42PD1 is co-expressed with MHC-II on activated Vδ2 cells

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Δ42PD1⁺MHC-II⁺Vδ2 cells interact directly with TLR4⁺CD4⁺T cells in 3D imaging

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TLR4 is highly expressed on the PD-1⁺CD45RO⁺CD45RA⁺CD4⁺T cell subset

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Δ42PD1-TLR4 selectively activates this subset of Ag-specific CD4⁺ T cells

Programming Multifaceted Pulmonary T Cell Immunity by Combination Adjuvants

Induction of protective mucosal T cell memory remains a formidable challenge to vaccinologists. Using a combination adjuvant strategy that elicits potent CD8 and CD4 T cell responses, we define the tenets of vaccine-induced pulmonary T cell immunity. An acrylic-acid-based adjuvant (ADJ), in combination with Toll-like receptor (TLR) agonists glucopyranosyl lipid adjuvant (GLA) or CpG, promotes mucosal imprinting but engages distinct transcription programs to drive different degrees of terminal differentiation and disparate polarization of T_H1/T_C1/T_H17/T_C17 effector/memory T cells. Combination of ADJ with GLA, but not CpG, dampens T cell receptor (TCR) signaling, mitigates terminal differentiation of effectors, and enhances the development of CD4 and CD8 T_RM cells that protect against H1N1 and H5N1 influenza viruses. Mechanistically, vaccine-elicited CD4 T cells play a vital role in optimal programming of CD8 T_RM and viral control. Taken together, these findings provide further insights into vaccine-induced multifaceted mucosal T cell immunity with implications in the development of vaccines against respiratorypathogens, including influenza virus and SARS-CoV-2.

Combination adjuvants stimulate potent T_RM cell immunity in the respiratory tract

Differentiation and functional programming depend on adjuvant and TCR signaling

Vaccine-induced T cell immunity to influenza requires CD4 and CD8 T cells

CD4 T cells regulate optimal positioning and programming of CD8 T_RM in lungs

Bystander CD4+ T cells: crossroads between innate and adaptive immunity

T cells are the central mediators of both humoral and cellular adaptive immune responses. Highly specific receptor-mediated clonal selection and expansion of T cells assure antigen-specific immunity. In addition, encounters with cognate antigens generate immunological memory, the capacity for long-term, antigen-specific immunity against previously encountered pathogens. However, T-cell receptor (TCR)-independent activation, termed “bystander activation”, has also been found. Bystander-activated T cells can respond rapidly and secrete effector cytokines even in the absence of antigen stimulation. Recent studies have rehighlighted the importance of antigen-independent bystander activation of CD4⁺ T cells in infection clearance and autoimmune pathogenesis, suggesting the existence of a distinct innate-like immunological function performed by conventional T cells. In this review, we discuss the inflammatory mediators that activate bystander CD4⁺ T cells and the potential physiological roles of these cells during infection, autoimmunity, and cancer.

Immune cells that become activated in the absence of antigen stimulation could be harnessed in the fight against infection, autoimmunity, and cancer. Je-Min Choi and colleagues from Hanyang University in Seoul, South Korea, review how the immune system can deploy helper T cells through an unusual process called bystander activation. Most T cells become activated only after receptors on their surface bind to specific cognate antigen. In contrast, bystander T cells are activated non-specifically in response to cytokines and other pro-inflammatory mediators. Studies have shown that this cell population has a variety of protective and pathogenic functions, for example, guarding against multiple sclerosis, aggravating the symptoms of parasitic infections and promoting antitumor immunity. A better understanding of these immune cells could lead to new therapeutic options for these diseases.

MAP3K2 augments Th1 cell differentiation via IL-18 to promote T cell-mediated colitis

T cell-mediated immunity in the intestine is stringently controlled to ensure proper immunity against pathogenic microbes and to prevent autoimmunity, a known cause of inflammatory bowel disease. However, precisely how T cells regulate intestine immunity remains to be fully understood. In this study, we found that mitogen-activated protein kinase kinase kinase 2 (MAP3K2) is required for the CD4⁺ T cell-mediated inflammation in the intestine. Using a T cell transfer colitis model, we found that MAP3K2-deficient naïve CD4 T cells had a dramatically reduced ability to induce colitis compared to wild type T cells. In addition, significantly fewer IFN-γ- but more IL-17A-producing CD4⁺ T cells in the intestines of mice receiving MAP3K2-deficient T cells than in those from mice receiving wild type T cells was observed. Interestingly, under well-defined in vitro differentiation conditions, MAP3K2-deficient naïve T cells were not impaired in their ability to differentiate into Th1, Th17 and Treg. Furthermore, the MAP3K2-regulated colitis severity was mediated by Th1 but not Th17 cells in the intestine. At the molecular level, we showed that MAP3K2-mediated Th1 cell differentiation in the intestine was regulated by IL-18 and required specific JNK activation. Together, our study reveals a novel regulatory role of MAP3K2 in intestinal T cell immunity via the IL-18-MAP3K2-JNK axis and may provide a novel target for intervention in T cell-mediated colitis.

Innate Immune Sensing by Cells of the Adaptive Immune System

Sensing of microbes or of danger signals has mainly been attributed to myeloid innate immune cells. However, T and B cells also express functional pattern recognition receptors (PRRs). In these cells, PRRs mediate signaling cascades that result in different functions depending on the cell's activation and/or differentiation status, on the environment, and on the ligand/agonist. Some of these functions are beneficial for the host; however, some are detrimental and are exploited by pathogens to establish persistent infections. In this review, we summarize the available literature on innate immune sensing by cells of the adaptive immune system and discuss possible implications for chronic infections.

Toll-like Receptors from the Perspective of Cancer Treatment

Toll-like receptors (TLRs) represent a family of pattern recognition receptors that recognize certain pathogen-associated molecular patterns and damage-associated molecular patterns. TLRs are highly interesting to researchers including immunologists because of the involvement in various diseases including cancers, allergies, autoimmunity, infections, and inflammation. After ligand engagement, TLRs trigger multiple signaling pathways involving nuclear factor-κB (NF-κB), interferon-regulatory factors (IRFs), and mitogen-activated protein kinases (MAPKs) for the production of various cytokines that play an important role in diseases like cancer. TLR activation in immune as well as cancer cells may prevent the formation and growth of a tumor. Nonetheless, under certain conditions, either hyperactivation or hypoactivation of TLRs supports the survival and metastasis of a tumor. Therefore, the design of TLR-targeting agonists as well as antagonists is a promising immunotherapeutic approach to cancer. In this review, we mainly describe TLRs, their involvement in cancer, and their promising properties for anticancer drug discovery.

Macrophage migration inhibitory factor regulates TLR4 expression and modulates TCR/CD3-mediated activation in CD4+ T lymphocytes

Toll-like receptor 4 (TLR4) is involved in CD4+ T lymphocyte-mediated pathologies. Here, we demonstrate that CD4+ T lymphocytes express functional TLR4 that contributes to their activation, proliferation and cytokine secretion. In addition, we demonstrate that TLR4-induced responses are mediated by macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine. We also demonstrate that MIF regulates suboptimal TCR/CD3-mediated activation of T lymphocytes. On one hand, MIF prevents excessive TCR/CD3-mediated activation of CD4+ T lymphocytes under suboptimal stimulation conditions and, on the other hand, MIF enables activated CD4+ T lymphocytes to sense their microenvironment and adapt their effector response through TLR4. Therefore, MIF appears to be a major regulator of the activation of CD4+ T lymphocytes and the intensity of their effector response. TLR4-mediated activation is thus an important process for T cell-mediated immunity.

Dual-Specificity Phosphatases in Immunity and Infection: An Update

Kinase activation and phosphorylation cascades are key to initiate immune cell activation in response to recognition of antigen and sensing of microbial danger. However, for balanced and controlled immune responses, the intensity and duration of phospho-signaling has to be regulated. The dual-specificity phosphatase (DUSP) gene family has many members that are differentially expressed in resting and activated immune cells. Here, we review the progress made in the field of DUSP gene function in regulation of the immune system during the last decade. Studies in knockout mice have confirmed the essential functions of several DUSP-MAPK phosphatases (DUSP-MKP) in controlling inflammatory and anti-microbial immune responses and support the concept that individual DUSP-MKP shape and determine the outcome of innate immune responses due to context-dependent expression and selective inhibition of different mitogen-activated protein kinases (MAPK). In addition to the canonical DUSP-MKP, several small-size atypical DUSP proteins regulate immune cells and are therefore also reviewed here. Unexpected and complex findings in DUSP knockout mice pose new questions regarding cell type-specific and redundant functions. Another emerging question concerns the interaction of DUSP-MKP with non-MAPK binding partners and substrate proteins. Finally, the pharmacological targeting of DUSPs is desirable to modulate immune and inflammatory responses.

The Innate Immune Sensor NLRC3 Acts as a Rheostat that Fine-Tunes T Cell Responses in Infection and Autoimmunity

Appropriate immune responses require a fine balance between immune activation and attenuation. NLRC3, a non-inflammasome-forming member of the NLR innate immune receptor family, attenuates inflammation in myeloid cells and proliferation in epithelial cells. T lymphocytes express the highest amounts of Nlrc3 transcript where its physiologic relevance is unknown. We show that NLRC3 attenuated interferon-γ and TNF expression by CD4⁺ T cells and reduced T helper 1 (Th1) and Th17 cell proliferation. Nlrc3^-/- mice exhibited increased and prolonged CD4⁺ T cell responses to lymphocytic choriomeningitis virus infection and worsened experimental autoimmune encephalomyelitis (EAE). These functions of NLRC3 were executed in a T-cell-intrinsic fashion: NLRC3 reduced K63-linked ubiquitination of TNF-receptor-associated factor 6 (TRAF6) to limit NF-κB activation, lowered phosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), and diminished glycolysis and oxidative phosphorylation. This study reveals an unappreciated role for NLRC3 in attenuating CD4⁺ T cell signaling and metabolism.

Toll-Like Receptor 4 Promotes Th17 Lymphocyte Infiltration Via CCL25/CCR9 in Pathogenesis of Experimental Autoimmune Encephalomyelitis

Toll-like receptor 4 (TLR4) is a key component in innate immunity and has been linked to central nervous system (CNS) inflammation diseases, such as multiple sclerosis (MS), an inflammatory disorder induced by autoreactive Th17 cells. In our study, we found that TLR4 deficient (TLR4^-/-) mice were inadequate to induce experimental autoimmune encephalomyelitis (EAE), characterized by low clinic score and weight loss, alleviative demyelinating, as well as decreased inflammatory cell infiltration in the spinal cord. In the lesion area of EAE mice, loss of TLR4 down-regulated the secretion of inflammatory cytokines and chemokine CCL25. Furthermore, the expression of CCR9 was decreased and chemotactic migration was attenuated in TLR4^-/- Th17 cells. Our results demonstrate that TLR4 may mediate Th17 infiltration through CCL25/CCR9 signal during pathogenesis of EAE. Graphical Abstract Immunofluorescent staining of RORγt (green) and CCR9 (red) in spinal cords. TLR4 deficiency down-regulates CCR9 expression in infiltrating lymphocytes.

ST2/MyD88 Deficiency Protects Mice against Acute Graft-versus-Host Disease and Spares Regulatory T Cells

Acute graft-versus-host disease (aGVHD) hinders the efficacy of allogeneic hematopoietic cell transplantation (HCT). Plasma levels of soluble membrane-bound ST2 (ST2) are elevated in human and murine aGVHD and correlated to type 1 T cells response. ST2 signals through the adapter protein MyD88. The role of MyD88 in T cells during aGVHD has yet to be elucidated. We found that knocking out MyD88 in the donor T cells protected against aGVHD independent of IL-1R and TLR4 signaling in two murine HCT models. This protection was entirely driven by MyD88^-/- CD4 T cells. Transplanting donor MyD88^-/- conventional T cells (Tcons) with wild-type (WT) or MyD88^-/- regulatory T cells (Tregs) lowered aGVHD severity and mortality. Transcriptome analysis of sorted MyD88^-/- CD4 T cells from the intestine 10 d post-HCT showed lower levels of Il1rl1 (gene of ST2), Ifng, Csf2, Stat5, Batf, and Jak2 Transplanting donor ST2^-/- Tcons with WT or ST2^-/- Tregs showed a similar phenotype with what we observed when using donor MyD88^-/- Tcons. Decreased ST2 was confirmed at the protein level with less secretion of soluble ST2 and more expression of ST2 compared with WT T cells. Our data suggest that Treg suppression from lack of MyD88 signaling in donor Tcons during alloreactivity uses the ST2 but not the IL-1R or TLR4 pathways, and ST2 represents a potential aGVHD therapeutic target sparing Tregs.

Protein Tyrosine Phosphatases: Regulators of CD4 T Cells in Inflammatory Bowel Disease

Protein tyrosine phosphatases (PTPs) play a critical role in co-ordinating the signaling networks that maintain lymphocyte homeostasis and direct lymphocyte activation. By dephosphorylating tyrosine residues, PTPs have been shown to modulate enzyme activity and both mediate and disrupt protein-protein interactions. Through these molecular mechanisms, PTPs ultimately impact lymphocyte responses to environmental cues such as inflammatory cytokines and chemokines, as well as antigenic stimulation. Mouse models of acute and chronic intestinal inflammation have been shown to be exacerbated in the absence of PTPs such as PTPN2 and PTPN22. This increase in disease severity is due in part to hyper-activation of lymphocytes in the absence of PTP activity. In accordance, human PTPs have been linked to intestinal inflammation. Genome wide association studies (GWAS) identified several PTPs within risk loci for inflammatory bowel disease (IBD). Therapeutically targeting PTP substrates and their associated signaling pathways, such as those implicated in CD4⁺ T cell responses, has demonstrated clinical efficacy. The current review focuses on the role of PTPs in controlling CD4⁺ T cell activity in the intestinal mucosa and how disruption of PTP activity in CD4⁺ T cells can contribute to intestinal inflammation.

Immunoproteasome Inhibition Impairs T and B Cell Activation by Restraining ERK Signaling and Proteostasis

Immunoproteasome (IP) inhibition holds potential as a novel treatment option for various immune-mediated pathologies. The IP inhibitor ONX 0914 reduced T cell cytokine secretion and Th17 polarization and showed pre-clinical efficacy in a range of autoimmune disorders, transplant-allograft rejection, virus-mediated tissue damage, and colon cancer progression. However, the molecular basis of these effects has remained largely elusive. Here, we have analyzed the effects of ONX 0914 in primary human and mouse lymphocytes. ONX 0914-treatment impaired primary T cell activation in vitro and in vivo. IP inhibition reduced ERK-phosphorylation sustainment, while leaving NF-κB and other signaling pathways unaffected. Naïve T and B cells expressed nearly exclusively immuno- or mixed proteasomes but no standard proteasomes and IP inhibition but not IP-deficiency induced mild proteostasis stress, reduced DUSP5 expression and enhanced DUSP6 protein levels due to impaired degradation. However, accumulation of DUSP6 did not cause the reduced ERK-phosphorylation in a non-redundant manner. We show that broad-spectrum proteasome inhibition and immunoproteasome inhibition have distinct effects on T cell activation at the molecular level. Notably, ONX 0914-treated T cells recovered from proteostasis stress without apoptosis induction, apparently via Nrf1-mediated up-regulation of standard proteasomes. In contrast, B cells were more susceptible to apoptosis after ONX 0914-treatment. Our data thus provide mechanistic insights how IP inhibition functionally impedes T and B cells likely accounting for its therapeutic benefits.

Human Bone Marrow-Resident Natural Killer Cells Have a Unique Transcriptional Profile and Resemble Resident Memory CD8+ T Cells

Human lymphoid tissues harbor, in addition to CD56^bright and CD56^dim natural killer (NK) cells, a third NK cell population: CD69⁺CXCR6⁺ lymphoid tissue (lt)NK cells. The function and development of ltNK cells remain poorly understood. In this study, we performed RNA sequencing on the three NK cell populations derived from bone marrow (BM) and blood. In ltNK cells, 1,353 genes were differentially expressed compared to circulating NK cells. Several molecules involved in migration were downregulated in ltNK cells: S1PR1, SELPLG and CD62L. By flow cytometry we confirmed that the expression profile of adhesion molecules (CD49e⁻, CD29^low, CD81^high, CD62L⁻, CD11c⁻) and transcription factors (Eomes^high, Tbet^low) of ltNK cells differed from their circulating counterparts. LtNK cells were characterized by enhanced expression of inhibitory receptors TIGIT and CD96 and low expression of DNAM1 and cytolytic molecules (GZMB, GZMH, GNLY). Their proliferative capacity was reduced compared to the circulating NK cells. By performing gene set enrichment analysis, we identified DUSP6 and EGR2 as potential regulators of the ltNK cell transcriptome. Remarkably, comparison of the ltNK cell transcriptome to the published human spleen-resident memory CD8⁺ T (Trm) cell transcriptome revealed an overlapping gene signature. Moreover, the phenotypic profile of ltNK cells resembled that of CD8⁺ Trm cells in BM. Together, we provide transcriptional and phenotypic data that clearly distinguish ltNK cells from both the CD56^bright and CD56^dim NK cells and substantiate the view that ltNK cells are tissue-resident cells, which are functionally restrained in killing and have low proliferative activity.

VIPER regulates naive T cell activation and effector responses: Implication in TLR4 associated acute stage T cell responses

Naive T cells are known to express the modest level of TLR4 while it is known to go down during TCR activation. However, information towards the requirement of TLR4 signaling during TCR or mitogenic activation of naive wild-type T cells remains scanty. Here we have investigated the endogenous functional expression of TLR4 in naive mice T cells during TCR and mitogenic stimulation in presence of VIPER peptide (VP), an established inhibitor of TLR4 signaling. As expected we found that TLR4 expression goes down during TCR and mitogenic activation. Interestingly, we observed that VP treatment restores TLR4 expression on those activated T cells. Moreover, VP was found to regulate such activation of naive T cell as evident by reduction of CD25, CD69 expression, effector cytokines (IL-2, IFN-γ, TNF) production, T cell proliferation and down-regulation of T cell activation-dependent Fas (CD95), FasL (CD95L) expression. Together, our current observation highlights a possible requirement of TLR4 responses in T cells, which might have possible implication towards the pathogenic acute phase activation of naive T cells.

STING-Dependent Signaling Underlies IL-10 Controlled Inflammatory Colitis

Intestinal immune homeostasis is preserved by commensal bacteria interacting with the host to generate a balanced array of cytokines that are essential for wound repair and for combatting infection. Inflammatory bowel disease (IBD), which can lead to colitis-associated cancer (CAC), is thought to involve chronic microbial irritation following a breach of the mucosal intestinal epithelium. However, the innate immune pathways responsible for regulating these inflammatory processes remain to be fully clarified. Here, we show that commensal bacteria influence STING signaling predominantly in mononuclear phagocytes to produce both pro-inflammatory cytokines as well as anti-inflammatory IL-10. Enterocolitis, manifested through loss of IL-10, was completely abrogated in the absence of STING. Intestinal inflammation was less severe in the absence of cGAS, possibly suggesting a role for cyclic dinucleotides (CDNs) indirectly regulating STING signaling. Our data shed insight into the causes of inflammation and provide a potential therapeutic target for prevention of IBD.

The spectrum of T cell metabolism in health and disease

In healthy individuals, metabolically quiescent T cells survey lymph nodes and peripheral tissues in search of cognate antigens. During infection, T cells that encounter cognate antigens are activated and - in a context-specific manner - proliferate and/or differentiate to become effector T cells. This process is accompanied by important changes in cellular metabolism (known as metabolic reprogramming). The magnitude and spectrum of metabolic reprogramming as it occurs in T cells in the context of acute infection ensure host survival. By contrast, altered T cell metabolism, and hence function, is also observed in various disease states, in which T cells actively contribute to pathology. In this Review, we introduce the idea that the spectrum of immune cell metabolic states can provide a basis for categorizing human diseases. Specifically, we first summarize the metabolic and interlinked signalling requirements of T cells responding to acute infection. We then discuss how metabolic reprogramming of T cells is linked to disease.

The TRPA1 ion channel is expressed in CD4+ T cells and restrains T-cell-mediated colitis through inhibition of TRPV1

OBJECTIVE

Transient receptor potential ankyrin-1 (TRPA1) and transient receptor potential vanilloid-1 (TRPV1) are calcium (Ca²⁺)-permeable ion channels mostly known as pain receptors in sensory neurons. However, growing evidence suggests their crucial involvement in the pathogenesis of IBD. We explored the possible contribution of TRPA1 and TRPV1 to T-cell-mediated colitis.

DESIGN

We evaluated the role of Trpa1 gene deletion in two models of experimental colitis (ie, interleukin-10 knockout and T-cell-adoptive transfer models). We performed electrophysiological and Ca²⁺ imaging studies to analyse TRPA1 and TRPV1 functions in CD4+ T cells. We used genetic and pharmacological approaches to evaluate TRPV1 contribution to the phenotype of Trpa1^-/- CD4+ T cells. We also analysed TRPA1 and TRPV1 gene expression and TRPA1⁺TRPV1⁺ T cell infiltration in colonic biopsies from patients with IBD.

RESULTS

We identified a protective role for TRPA1 in T-cell-mediated colitis. We demonstrated the functional expression of TRPA1 on the plasma membrane of CD4+ T cells and identified that Trpa1^-/- CD4+ T cells have increased T-cell receptor-induced Ca²⁺ influx, activation profile and differentiation into Th1-effector cells. This phenotype was abrogated upon genetic deletion or pharmacological inhibition of the TRPV1 channel in mouse and human CD4+ T cells. Finally, we found differential regulation of TRPA1 and TRPV1 gene expression as well as increased infiltration of TRPA1⁺TRPV1⁺ T cells in the colon of patients with IBD.

CONCLUSIONS

Our study indicates that TRPA1 inhibits TRPV1 channel activity in CD4+ T cells, and consequently restrains CD4+ T-cell activation and colitogenic responses. These findings may therefore have therapeutic implications for human IBD.

T cell-intrinsic TLR2 stimulation promotes IL-10 expression and suppressive activity by CD45RbHi T cells

While Toll-like receptors (TLRs) represent one of the best characterized innate immune pathways, evidence suggests that TLRs are not restricted to innate leukocytes and some epithelial cells, but are also expressed in T cells. Specifically, published evidence focusing on FoxP3⁺ regulatory T cells demonstrate that they express functional TLR2, which is already known among the TLR family for its association with immune suppression; however, little is known about the relationship between T cell-intrinsic TLR2 binding and cytokine production, T cell differentiation, or T cell receptor (TCR) stimulation. Here, we demonstrate that TCR and TLR2 co-stimulation provides a T cell-intrinsic signal which generates a dramatic, synergistic cytokine response dominated by IL-10. Importantly, the response was not seen in either CD4⁺CD25⁺ or CD4⁺FoxP3⁺ Tregs, yet resulted in the expansion of a suppressive CD4⁺CD25⁺CD62L^-CD44⁺CD45Rb^hi effector/memory T cell subset not typically associated with immune inhibition. This study reveals the striking ability of a prototypical innate immune receptor to trigger a potent and suppressive IL-10 response in effector/memory T cells, supporting the notion that TLR2 is a co-regulatory receptor on T cells.

House Dust Mite Allergens: New Discoveries and Relevance to the Allergic Patient

PURPOSE OF REVIEW

Recent findings on house dust allergens and their contribution to knowledge that will significantly impact on current and future allergy treatments are appraised.

RECENT FINDINGS

Quantitation of IgE binding to a spectrum of allergen components in several independent studies in varying locations has largely affirmed the main components as the groups 1 and 2 and possibly 23 allergens with mid-tier contributions from the groups 4, 5, 7, and 21. Prevalent binding to Der p 23 has been recapitulated sometimes with low titers. The IgE of non-asthmatic atopic subjects binds at lower titer and to fewer components than that of asthmatics, and their IgG binding relative to IgE is higher especially for children hospitalized for exacerbation. The higher IgG ratios were associated with increased IL-10 a cytokine more readily induced from T cells of allergic subjects. Peptides representing the groups 1 and 2 allergens can be used to stimulate ex vivo T cells showing responses correlating with IgE binding and providing a valuable tool for ascertaining the contribution of IgE and T cells to disease. Also, the induction of Th2 and follicular helper T cells are shown to make different contributions in mice. Cross-reactivity of IgE binding assays with high-titer cross-reactive antibodies induced by scabies is a problem in the many areas of the world where scabies is highly prevalent and endemic and from recent increases in immigration. In the last few years, allergen research has produced results that warrant rapid translation into diagnostic tools and the formulation of allergen components for immunotherapy.