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SummarySevere COVID-19 is linked to both dysfunctional immune response and unrestrained immunopathogenesis, and it remains unclear if T cells also contribute to disease pathology. Here, we combined single-cell transcriptomics and proteomics with mechanistic studies to assess pathogenic T cell functions and inducing signals. We identified highly activated, CD16+ T cells with increased cytotoxic functions in severe COVID-19. CD16 expression enabled immune complex-mediated, T cell receptor-independent degranulation and cytotoxicity not found in other diseases. CD16+ T cells from COVID-19 patients promoted microvascular endothelial cell injury and release of neutrophil and monocyte chemoattractants. CD16+ T cell clones persisted beyond acute disease maintaining their cytotoxic phenotype. Age-dependent generation of C3a in severe COVID-19 induced activated CD16+ cytotoxic T cells. The proportion of activated CD16+ T cells and plasma levels of complement proteins upstream of C3a correlated with clinical outcome of COVID-19, supporting a pathological role of exacerbated cytotoxicity and complement activation in COVID-19.

The incidence of inflammatory bowel disease with its two main manifestations, colitis ulcerosa and Crohn's disease, is rising globally year after year. There is still a tremendous need to study the underlying pathomechanisms and a well-established tool in order to better understand the disease are colitis models in rodents. Since the concept of the 3Rs was proposed by Russell and Burch, this would include pain medication in animal models of intestinal inflammation as a reduction of suffering. This review argues against pain medication because the administration of pain medication in its current form has an impact on the inflammatory process and the immune response, thus falsifying the results and the reproducibility and therefore leading to misconceptions.Colitis models are a good tool to study underlying pathomechanisms of inflammatory bowel disease. Pain medication to fulfill the concept of the 3Rs has to be considered carefully. This review discusses influences of pain medication on the immune system, functional structures, and inflammatory processes.

Severe COVID-19 is linked to both dysfunctional immune response and unrestrained immunopathogenesis, and it remains unclear if T cells contribute to disease pathology. Here, we combined single-cell transcriptomics and proteomics with mechanistic studies assessing pathogenic T cell functions and inducing signals. We identified activated, CD16+ T cells with increased cytotoxic functions in severe COVID-19. CD16 expression enabled immune complex-mediated, T cell receptor-independent degranulation and cytotoxicity not found in other diseases. CD16+ T cells from COVID-19 patients promoted microvascular endothelial cell injury and release of neutrophil and monocyte chemoattractants. CD16+ T cell clones persisted beyond acute disease maintaining their cytotoxic phenotype. Age-dependent generation of C3a in severe COVID-19 induced activated CD16 + cytotoxic T cells. The proportion of activated CD16+ T cells and plasma levels of complement proteins upstream of C3a correlated with clinical outcome, supporting a pathological role of exacerbated cytotoxicity and complement activation in COVID-19. Funding: This work was supported by the German Research Foundation (DFG): SA1383/3-1 to B.S.; SFB-TR84 114933180 to L.E.S., S.B., P.G., S.H. and W.M.K. INST 37/1049-1, INST 216/981- 1, INST 257/605-1, INST 269/768-1, INST 217/988-1, INST 217/577-1, and EXC2151- 390873048 to J.L.S.; GRK 2168 – 272482170, ERA CVD (00160389 to J.L.S.; SFB 1454 – 432325352 to A.C.A. and J.L.S.; SFB TR57 and SPP1937 to J.N.; GRK2157 to A.-E.S.; and ME 3644/5-1 to H.E.M.; RTG2424 to N.B.; SFB-TRR219 322900939, BO3755/13-1 Project- ID 454024652 to P.B.; the Berlin University Alliance (BUA) (PreEP-Corona grant to L.E.S. and V.M.C.); the Berlin Institute of Health (BIH) (to L.E.S., V.M.C.,B.S. and W.M.K.); Helmholtz- Gemeinschaft Deutscher Forschungszentren, Germany (sparse2big to J.L.S.), EU projects SYSCID (733100 to J.L.S.); European Research Council Horizon 2020 (grant agreement No 101001791 to P.B.); the DZIF, Germany (TTU 04.816 and 04.817 to J.N.); the Hector Foundation (M89 to J.N.); the EU projects ONE STUDY (260687), BIO-DrIM (305147) and INsTRuCT (860003) to B.S.); German Registry of COVID-19 Autopsies through Federal Ministry of Health (ZMVI1-2520COR201 to P.B.); Federal Ministry of Education and Research (DEFEAT PANDEMICs, 01KX2021 and STOP-FSGS-01GM1901A to P.B.); the Berlin Senate to German Rheumatism Research Centre (DRFZ); the Berlin Brandenburg School for regenerative Therapies (BSRT) to C.B.; the German Federal Ministry of Education and Research (BMBF) projects RECAST (01KI20337) to B.S., V.M.C., L.E.S and M.R.; VARIPath (01KI2021) to V.M.C.; NUM COVIM (01KX2021) to L.E.S., V.M.C., F.K., J.L.S., J.N. and B.S.; RAPID to and S.H.,; SYMPATH to N.S. and W.M.K.; PROVID to S.H. and W.M.K.; ZissTrans (02NUK047E) to N.B; National Research Node ‘Mass spectrometry in Systems Medicine (MSCoresys) (031L0220A) to M.R. and N.B.; Diet–Body–Brain (DietBB) (01EA1809A) to J.L.S.; the UKRI/NIHR through the UK Coronavirus Immunology Consortium (UK-CIC), the Francis Crick Institute through the Cancer Research UK (FC001134), the UK Medical Research Council (FC001134), the Wellcome Trust (FC001134 and IA 200829/Z/16/Z) to M.R.; a Charite 3R project (to B.S., S.H., W.M.K.); and an intramural grant from the Department of Genomics & Immunoregulation at the LIMES Institute to A.C.A. We are grateful to the patients and donors volunteering to participate in this study making this research possible in the first place and wish for a speedy and full recovery. Conflict of Interest: V.M.C. is named together with Euroimmun GmbH on a patent application filed recently regarding SARS-CoV-2 diagnostics via antibody testing. A.R.S. and H.E.M. are listed as inventors on a patent application by the DRFZ Berlin in the field of mass cytometry. Ethical Approval: The study was approved by the Institutional Review board of Charite (EA2/066/20).

‘Severe Acute Respiratory Syndrome - Coronavirus-2’ (SARS-CoV-2) infection causes Coronavirus Disease 2019 (COVID-19), a mild to moderate respiratory tract infection in the majority of patients. A subset of patients, however, progresses to severe disease and respiratory failure with acute respiratory distress syndrome (ARDS). Severe COVID-19 has been associated with increased neutrophil counts and dysregulated immune responses. The mechanisms of protective immunity in mild forms and the pathogenesis of dysregulated inflammation in severe courses of COVID-19 remain largely unclear. Here, we combined two single-cell RNA-sequencing technologies and single-cell proteomics in whole blood and peripheral blood mononuclear cells (PBMC) to determine changes in immune cell composition and activation in two independent dual-center patient cohorts (n=46+n=54 COVID-19 samples), each with mild and severe cases of COVID-19. We observed a specific increase of HLA-DRhiCD11chiinflammatory monocytes that displayed a strong interferon (IFN)-stimulated gene signature in patients with mild COVID-19, which was absent in severe disease. Instead, we found evidence of emergency myelopoiesis, marked by the occurrence of immunosuppressive pre-neutrophils and immature neutrophils and populations of dysfunctional and suppressive mature neutrophils, as well as suppressive HLA-DRtomonocytes in severe COVID-19. Our study provides detailed insights into systemic immune response to SARS-CoV-2 infection and it reveals profound alterations in the peripheral myeloid cell compartment associated with severe courses of COVID-19.

Summary Coronavirus Disease 2019 (COVID-19) is a mild to moderate respiratory tract infection, however, a subset of patients progresses to severe disease and respiratory failure. The mechanism of protective immunity in mild forms and the pathogenesis of severe COVID-19, associated with increased neutrophil counts and dysregulated immune responses, remains unclear. In a dual-center, two-cohort study, we combined single-cell RNA-sequencing and single-cell proteomics of whole blood and peripheral blood mononuclear cells to determine changes in immune cell composition and activation in mild vs. severe COVID-19 (242 samples from 109 individuals) over time. HLA-DRhiCD11chi inflammatory monocytes with an interferon-stimulated gene signature were elevated in mild COVID-19. Severe COVID-19 was marked by occurrence of neutrophil precursors, as evidence of emergency myelopoiesis, dysfunctional mature neutrophils, and HLA-DRlo monocytes. Our study provides detailed insights into the systemic immune response to SARS-CoV-2 infection and it reveals profound alterations in the myeloid cell compartment associated with severe COVID-19., Highlights ● SARS-CoV-2 infection induces profound alterations of the myeloid compartment ● Mild COVID-19 is marked by inflammatory HLA-DRhiCD11chi CD14+ monocytes ● Dysfunctional HLA-DRloCD163hi and HLA-DRloS100Ahi CD14+ monocytes in severe COVID-19 ● Emergency myelopoiesis with immature and dysfunctional neutrophils in severe COVID-19

Group 2 innate lymphoid cells (ILC2s) are innate effectors playing an important role in the defense against helminthic infections and in the pathogenesis of allergic inflammation. Cytokines have been identified as the major stimuli driving ILC2 activation and expansion. Conversely, it is unclear whether costimulatory molecules contribute to regulation of ILC2 functions. ILC2s display high expression of inducible T-cell costimulator (ICOS), which belongs to the CD28 superfamily, and which has been shown to control late effector T-cell functions, and is of utmost importance for the humoral immune response. However, the biological function of ICOS expression on ILC2s is unknown. Here, we show that ICOS signaling in mice regulates ILC2 homeostasis independently of T cells and B cells, by promoting proliferation and accumulation of mature ILC2s in lung and intestine. In a model of IL-33-induced airway inflammation, ICOS controls ILC2 activation and eosinophil infiltration in the lung. Our data identify a role of ICOS in innate immunity and indicate that not only cytokines, but also costimulatory pathways such as those involving ICOS, can contribute to regulate the ILC2 pool. Thus, ICOS costimulation blockade, which is currently under clinical evaluation for inhibiting the humoral immune response, could also target innate inflammatory circuits.

Monocytes and macrophages link the innate and adaptive immune systems and protect the host from the outside world. In inflammatory disorders their activation leads to tissue damage. Galectins have emerged as central regulators of the immune system. However, if they regulate monocyte/macrophage physiology is still unknown. Binding of Gal-1, Gal-2, Gal-3 and Gal-4 to monocytes/macrophages, activation, cytokine secretion and apoptosis were determined by FACS, migration by Transwell system and phagocytosis by phagotest. Supernatants from macrophages co-cultured with galectins revealed their influence on T-cell function. In our study Gal-1, Gal-2, Gal-4, and partly Gal-3 bound to monocytes/macrophages. Galectins prevented Salmonella -induced MHCII upregulation. Cytokine release was distinctly induced by different galectins. T-cell activation was significantly restricted by supernatants of macrophages co-cultured in the presence of Gal-2 or Gal-4. Furthermore, all galectins tested significantly inhibited monocyte migration. Finally, we showed for the first time that galectins induce potently monocyte, but not macrophage apoptosis. Our study provides evidence that galectins distinctively modulate central monocyte/macrophage function. By inhibiting T-cell function via macrophage priming, we show that galectins link the innate and adaptive immune systems and provide new insights into the action of sugar-binding proteins.

Group 2 innate lymphoid cells (ILC2s) are innate effectors playing an important role in the defense against helminthic infections and in the pathogenesis of allergic inflammation. Cytokines have been identified as the major stimuli driving ILC2 activation and expansion. Conversely, it is unclear whether costimulatory molecules contribute to regulation of ILC2 functions. ILC2s display high expression of inducible T-cell costimulator (ICOS), which belongs to the CD28 superfamily, and which has been shown to control late effector T-cell functions, and is of utmost importance for the humoral immune response. However, the biological function of ICOS expression on ILC2s is unknown. Here, we show that ICOS signaling in mice regulates ILC2 homeostasis independently of T cells and B cells, by promoting proliferation and accumulation of mature ILC2s in lung and intestine. In a model of IL-33-induced airway inflammation, ICOS controls ILC2 activation and eosinophil infiltration in the lung. Our data identify a role of ICOS in innate immunity and indicate that not only cytokines, but also costimulatory pathways such as those involving ICOS, can contribute to regulate the ILC2 pool. Thus, ICOS costimulation blockade, which is currently under clinical evaluation for inhibiting the humoral immune response, could also target innate inflammatory circuits.

Toll-like receptors (TLRs) are key components of the innate immune system that trigger antimicrobial host defense responses. The aim of the present study was to analyze the effects of probiotic Escherichia coli Nissle strain 1917 in experimental colitis induced in TLR-2 and TLR-4 knockout mice. Colitis was induced in wild-type (wt), TLR-2 knockout, and TLR-4 knockout mice via administration of 5% dextran sodium sulfate (DSS). Mice were treated with either 0.9% NaCl or 10 7 E. coli Nissle 1917 twice daily, followed by the determination of disease activity, mucosal damage, and cytokine secretion. wt and TLR-2 knockout mice exposed to DSS developed acute colitis, whereas TLR-4 knockout mice developed significantly less inflammation. In wt mice, but not TLR-2 or TLR-4 knockout mice, E. coli Nissle 1917 ameliorated colitis and decreased proinflammatory cytokine secretion. In TLR-2 knockout mice a selective reduction of gamma interferon secretion was observed after E. coli Nissle 1917 treatment. In TLR-4 knockout mice, cytokine secretion was almost undetectable and not modulated by E. coli Nissle 1917, indicating that TLR-4 knockout mice do not develop colitis similar to the wt mice. Coculture of E. coli Nissle 1917 and human T cells increased TLR-2 and TLR-4 protein expression in T cells and increased NF-κB activity via TLR-2 and TLR-4. In conclusion, our data provide evidence that E. coli Nissle 1917 ameliorates experimental induced colitis in mice via TLR-2- and TLR-4-dependent pathways.

Local photodynamic therapy was used to prevent neointimal hyperplasia after stenting. Slotted tube stents were placed with 16 atmospheres in porcine femoral arteries with the external diameter to match the diameter at 10 atmospheres. Animals were randomly allocated to Group 1 (stenting only); or Group 2 with stenting, local drug delivery of a photosensitizer (5 mg Photofrin) and subsequent exposure to light (photodynamic therapy, 100 J). Fourteen days later, all vessels were excised, fixed and processed for histology. Tissue hyperplasia was observed after stenting in vessels from Group 1. In Group 2 with photodynamic therapy, the myoproliferative response was significantly reduced. Tissue hyperplasia after stenting was effectively suppressed by photodynamic therapy.

Group 3 innate lymphoid cells (ILC3s) are defined by the expression of the transcription factor RORγt, which is selectively required for their development. The lineage-specified progenitors of ILC3s and their site of development after birth remain undefined. Here we identified a population of human CD34(+) hematopoietic progenitor cells (HPCs) that express RORγt and share a distinct transcriptional signature with ILC3s. RORγt(+)CD34(+) HPCs were located in tonsils and intestinal lamina propria (LP) and selectively differentiated toward ILC3s. In contrast, RORγt(-)CD34(+) HPCs could differentiate to become either ILC3s or natural killer (NK) cells, with differentiation toward ILC3 lineage determined by stem cell factor (SCF) and aryl hydrocarbon receptor (AhR) signaling. Thus, we demonstrate that in humans RORγt(+)CD34(+) cells are lineage-specified progenitors of IL-22(+) ILC3s and propose that tonsils and intestinal LP, which are enriched both in committed precursors and mature ILC3s, might represent preferential sites of ILC3 lineage differentiation.

Pancreatic autoantibodies are Crohn disease-specific serologic markers. The function and immunological role of their recently identified autoantigen, glycoprotein 2 (GP2), are unknown. We therefore investigated the impact of GP2 on modulation of innate and adaptive immune responses to evaluate its potential therapeutic use in mucosal inflammation. Our data indicate a previously unknown function for GP2 as an immunomodulator. GP2 was ubiquitously expressed on cells vital to mucosal immune responses. The expression of GP2 was upregulated on activated human T cells, and it was further influenced by pharmaceutical TNF-α inhibitors. Recombinant GP2 significantly decreased human intestinal epithelial cells, mucosal and peripheral T cell proliferation, apoptosis, and activation, and it distinctly modulated cytokine secretion. Furthermore, intestinal epithelial cells stimulated with GP2 potently attracted T cells. In conclusion, we demonstrate a novel role for GP2 in immune regulation that could provide a platform for new therapeutic interventions in the treatment of Crohn disease.

Background Tumour necrosis factor alpha (TNF alpha) inhibitors such as adalimumab and infliximab are frequently prescribed for inflammatory bowel disease (IBD). Despite the clinical success of TNF alpha inhibitors, their physiological mode of action is not fully understood. The aim of this study was to investigate the mode of action of anti-TNF alpha agents in IBD. Methods It was hypothesised that Notch mediates anti-TNF alpha action in T cells. A study was carried out to identify Notch-1 as a link by which anti-TNF alpha antibodies mediate their inhibitory functions. Results TNF alpha inhibitors induced T cell apoptosis, inhibited activation, reduced cytokine secretion and restricted cell cycling. TNF alpha blockade at several levels showed that TNF alpha is responsible for inducing apoptosis by anti-TNF alpha but not for cell cycle restriction. By linking Notch and TNF alpha it was shown that (1) Notch-1 mucosal expression differs in inflamed and non-inflamed mucosa and increases in response to anti-TNF alpha treatment; (2) Notch-1 function is regulated by TNF alpha inhibitors; (3) Notch-1 binds to TNF alpha; and (4) Notch-1 inhibition prevents anti-TNF alpha-induced T cell cycle arrest but not apoptosis. Conclusions TNF alpha inhibitors potently inhibit T cell function. By demonstrating for the first time that Notch-1 mediates the inhibitory effects of adalimumab and infliximab on T cell cycling, this study reveals a new mode of action and also an underlying signalling pathway by which biological agents act in IBD.

Galectin-4 is a carbohydrate-binding protein belonging to the galectin family. Here we provide novel evidence that galectin-4 is selectively expressed and secreted by intestinal epithelial cells and binds potently to activated peripheral and mucosal lamina propria T-cells at the CD3 epitope. The carbohydrate-dependent binding of galectin-4 at the CD3 epitope is fully functional and inhibited T cell activation, cycling and expansion. Galectin-4 induced apoptosis of activated peripheral and mucosal lamina propria T cells via calpain-, but not caspase-dependent, pathways. Providing further evidence for its important role in regulating T cell function, galectin-4 blockade by antisense oligonucleotides reduced TNF-alpha inhibitor induced T cell death. Furthermore, in T cells, galectin-4 reduced pro-inflammatory cytokine secretion including IL-17. In a model of experimental colitis, galectin-4 ameliorated mucosal inflammation, induced apoptosis of mucosal T-cells and decreased the secretion of pro-inflammatory cytokines. Our results show that galectin-4 plays a unique role in the intestine and assign a novel role of this protein in controlling intestinal inflammation by a selective induction of T cell apoptosis and cell cycle restriction. Conclusively, after defining its biological role, we propose Galectin-4 is a novel anti-inflammatory agent that could be therapeutically effective in diseases with a disturbed T cell expansion and apoptosis such as inflammatory bowel disease.

Background: Inflammatory bowel diseases (IBDs) are characterized by various degrees of mucosal surface damage and subsequent impairment of the intestinal barrier function. Resealing of the epithelial barrier requires intestinal cell migration and proliferation. Galectins are increasingly recognized as novel regulators of inflammation. Thus, we aimed to explore the effect of galectin-2 (Gal-2) and Gal-4 on epithelial cell function and wound healing. Methods: Binding of Gal-2 and Gal-4 was determined by flow cytometric analysis and binding sites by SDS-PAGE electrophoresis. Cell migration by Gal-1, -2, and -4 was determined by a wound-healing assay. Cell cycle analysis and detection of apoptosis were determined by flow cytometric analysis. Results: Gal-2 and Gal-4 bind to epithelial cells at the E-cadherin/β-catenin complex. Both galectins significantly enhanced intestinal epithelial cell restitution in vitro. This enhancement of epithelial cell restitution was TGF-β-independent. In contrast, Gal-1 decreased epithelial cell migration TGF-β dependently. By performing cell cycle analysis, we show that Gal-2 and Gal-4 increased cyclin B1 expression and consequently cell cycle progression, while Gal-1 inhibited cell cycling. Determining the influence of Gal-2 and Gal-4 on epithelial cell apoptosis, we showed no induction of apoptosis, whereas Gal-1 significantly induced apoptosis of epithelial cells caspase-independently. Conclusions: Gal-2 and Gal-4 bind to intestinal epithelial cells and promote their restitution. Thus, our study provides for the first time evidence that these galectins play a significant role in intestinal wound-healing processes and might exert beneficial effects in diseases characterized by epithelial barrier disruption like IBDs. (Inflamm Bowel Dis 2008)

Nutritional support is an established element of therapy for various indications. However, its impact on the mucosal barrier function is not well understood. We investigated the influence of EN and PN on intestinal epithelial cells and peripheral blood (PBMC) and lamina propria mononuclear cells (LPMC), all of which are involved in the mucosal defense against bacterial translocation and systemic inflammation. Integrity of epithelial cells was measured as transepithelial electrical resistance (TER) of confluent Caco-2 monolayers in the presence of 1% EN, PN and a parenteral amino acid mixture (AM). To determine wound healing capacities, an established migration model with IEC-6 cells was used. Furthermore, we investigated apoptosis, cell activation, proliferation and cytokine secretion of Caco-2, HT29 and of stimulated PBMC and LPMC cultured with or without 1 and 5% EN, AM or PN. We demonstrated that EN, AM and PN promoted the integrity of the epithelial monolayer and reconstituted epithelial cell continuity TGF-β-dependently and -independently. Interestingly, only PN induced apoptosis and decreased the mitochondrial membrane potential. The activation status of PBMC was significantly reduced by EN and AM. Specifically, EN leads to an increased apoptosis rate, inhibited cell cycle progression and increased pro-inflammatory cytokine secretion. Both EN and PN reduced the activation status and the release of pro- and anti-inflammatory cytokines. Our study provides evidence that by promoting wound healing and regulating T cell function, EN, AM, and PN potently interact with the intestinal barrier and immune system, thus justifying its use in diseases accompanied by impaired mucosal barrier function.

Galectins have recently emerged as central regulators of the immune system. We have previously demonstrated that carbohydrate-dependent binding of galectin-2 induces apoptosis in activated T cells. Here, we investigate the potential therapeutic effect of galectin-2 in experimental colitis. Galectin-2 expression and its binding profile were determined by immunohistochemistry. Acute and chronic colitis was induced by dextran sodium sulfate administration and in a T-cell transfer colitis model. Apoptosis was assessed by TdT-mediated dUTP-biotin nick-end labeling, and cytokine secretion was determined by cytometric bead array. We show that galectin-2 was constitutively expressed mainly in the epithelial compartment of the mouse intestine and bind to lamina propria mononuclear cells. During colitis, galectin-2 expression was reduced, but could be restored to normal levels by immunosuppressive treatment. Galectin-2 treatment induced apoptosis of mucosal T cells and thus ameliorated acute and chronic dextran-sodium-sulfate-induced colitis and in a T-helper-cell 1-driven model of antigen-specific transfer colitis. Furthermore, the pro-inflammatory cytokine release was inhibited by galectin-2 treatment. In preliminary toxicity studies, galectin-2 was well tolerated. Our study provides evidence that galectin-2 induces apoptosis in vivo and ameliorates acute and chronic murine colitis. Furthermore, galectin-2 has no significant toxicity over a broad dose range, suggesting that it may serve as a new therapeutic agent in the treatment of inflammatory bowel disease.

SummaryRORγt+ innate lymphoid cells (ILCs) are crucial players of innate immune responses and represent a major source of interleukin-22 (IL-22), which has an important role in mucosal homeostasis. The signals required by RORγt+ ILCs to express IL-22 and other cytokines have been elucidated only partially. Here we showed that RORγt+ ILCs can directly sense the environment by the engagement of the activating receptor NKp44. NKp44 triggering in RORγt+ ILCs selectively activated a coordinated proinflammatory program, including tumor necrosis factor (TNF), whereas cytokine stimulation preferentially induced IL-22 expression. However, combined engagement of NKp44 and cytokine receptors resulted in a strong synergistic effect. These data support the concept that NKp44+ RORγt+ ILCs can be activated without cytokines and are able to switch between IL-22 or TNF production, depending on the triggering stimulus.