Guidelines for the use of flow cytometry and cell sorting in immunological studies

Mitochondria maintain controlled activation state of epithelial-resident T lymphocytes

Epithelial-resident T lymphocytes, such as intraepithelial lymphocytes (IELs) located at the intestinal barrier, can offer swift protection against invading pathogens. Lymphocyte activation is strictly regulated because of its potential harmful nature and metabolic cost, and most lymphocytes are maintained in a quiescent state. However, IELs are kept in a heightened state of activation resembling effector T cells but without cytokine production or clonal proliferation. We show that this controlled activation state correlates with alterations in the IEL mitochondrial membrane, especially the cardiolipin composition. Upon inflammation, the cardiolipin composition is altered to support IEL proliferation and effector function. Furthermore, we show that cardiolipin makeup can particularly restrict swift IEL proliferation and effector functions, reducing microbial containment capability. These findings uncover an alternative mechanism to control cellular activity, special to epithelial-resident T cells, and a novel role for mitochondria, maintaining cells in a metabolically poised state while enabling rapid progression to full functionality.

Deletion of Galectin-3 attenuates acute pancreatitis in mice by affecting activation of innate inflammatory cells

Acute pancreatitis is characterized by autodigestion of pancreatic cells followed by acute inflammation leading to pathology and death. In experimental acute pancreatitis, pancreatic acinar cells and infiltrating macrophages express Galectin-3 but its role in pathology of this disease is unknown. Therefore, we studied its role using Galectin-3 deficient mice. Deletion of Galectin-3 prolonged the survival of mice, led to attenuation of histopathology, and decreased infiltration of mononuclear cells and neutrophils that express TLR-4, in particular, pro-inflammatory N1 neutrophils. Galectin-3 and TLR-4 are also colocalized on infiltrating cells. Lack of Galectin-3 reduced expression of pro-inflammatory TNF-α and IL-1β in F4/80⁺ CD11c- and CD11c⁺ F4/80^- cells. Thus, deletion of Galectin-3 ameliorates acute pancreatitis by attenuating early influx of neutrophils and inflammatory mononuclear cells of innate immunity. These findings provide the basis to consider Galectin-3 as a therapeutic target in acute pancreatitis.

Accelerated thymopoiesis and improved T-cell responses in HLA-A2/-DR2 transgenic BRGS-based human immune system mice

Human immune system (HIS) mouse models provide a robust in vivo platform to study human immunity. Nevertheless, the signals that guide human lymphocyte differentiation in HIS mice remain poorly understood. Here, we have developed a novel Balb/c Rag2^-/- Il2rg^-/- Sirpa^NOD (BRGS) HIS mouse model expressing human HLA-A2 and -DR2 transgenes (BRGSA2DR2). When comparing BRGS and BRGSA2DR2 HIS mice engrafted with human CD34⁺ stem cells, a more rapid emergence of T cells in the circulation of hosts bearing human HLA was shown, which may reflect a more efficient human T-cell development in the mouse thymus. Development of CD4⁺ and CD8⁺ T cells was accelerated in BRGSA2DR2 HIS mice and generated more balanced B and T-cell compartments in peripheral lymphoid organs. Both B- and T-cell function appeared enhanced in the presence of human HLA transgenes with higher levels of class switched Ig, increased percentages of polyfunctional T cells and clear evidence for antigen-specific T-cell responses following immunization. Taken together, the presence of human HLA class I and II molecules can improve multiple aspects of human B- and T-cell homeostasis and function in the BRGS-based HIS mouse model.

Autoreactive B-lymphocytes in SLE and RA patients: Isolation and characterisation using extractable nuclear and citrullinated antigens bound to immunobeads

Systemic lupus erythematosus and rheumatoid arthritis are autoimmune diseases characterised by B-cell hyperactivation and production of autoantibodies (AutoAbs) against various self-antigens, including extractable nuclear antigens and citrullinated peptides. Therefore, B lymphocytes and antibody-secreting cells are considered relevant targets for therapies. However, isolation and characterisation of auto-reactive specific B lymphocytes are limited, primarily due to technical issues. In this work, we purified extractable nuclear antigen-specific and citrullinated peptide-specific auto-reactive B lymphocytes by magnetic selection with ENA- and citrullinated peptide-bound immunobeads. We obtained blood auto-reactive B lymphocytes from most patients. Their nature was primarily naïve B cells, some of them in an active status, with low levels of somatic hypermutations in the immunoglobulin heavy-chain variable regions. Their presence correlated with serum levels of autoAb. Auto-reactive B lymphocytes were able to differentiate into auto-reactive antibody-secreting cells under conditions of stimulation. In addition, based on the presence of circulating auto-reactive B cells and/or antibody-secreting cells, four different profiles were described in lupus patients. Thus, tracking auto-reactive B cells and/or antibody-secreting cells in patient blood could represent a biomarker for deciding whether to use therapies blocking either B cells, plasma cells or both, as well as a new tool for monitoring minimal residual autoimmune disease in patients.

Newly identified T cell subsets in mechanistic studies of food immunotherapy

Allergen-specific immunotherapy has shown promise for the treatment of food allergy and is currently being evaluated in clinical trials. Although immunotherapy can induce desensitization, the mechanisms underlying this process are not completely understood. Recent advances in high-throughput technologies along with concomitant advances in data analytics have enabled monitoring of cells at the single-cell level and increased the research focus on upstream cellular factors involved in the efficacy of immunotherapy, particularly the role of T cells. As our appreciation of different T cell subsets and their plasticity increases, the initial simplistic view that restoring Th1/Th2 balance by decreasing Th2 or increasing Th1 responses can ameliorate food allergy is being enhanced by a more complex model involving other T cell subsets, particularly Tregs. In this Review, we focus on the current understanding of T cell functions in food allergy, tolerance, and immunotherapy.

c-Maf-dependent Treg cell control of intestinal TH17 cells and IgA establishes host-microbiota homeostasis

Foxp3+ regulatory T cells (Treg cells) are crucial for the maintenance of immune homeostasis both in lymphoid tissues and in non-lymphoid tissues. Here we demonstrate that the ability of intestinal Treg cells to constrain microbiota-dependent interleukin (IL)-17-producing helper T cell (TH17 cell) and immunoglobulin A responses critically required expression of the transcription factor c-Maf. The terminal differentiation and function of several intestinal Treg cell populations, including RORγt+ Treg cells and follicular regulatory T cells, were c-Maf dependent. c-Maf controlled Treg cell-derived IL-10 production and prevented excessive signaling via the kinases PI(3)K (phosphatidylinositol-3-OH kinase) and Akt and the metabolic checkpoint kinase complex mTORC1 (mammalian target of rapamycin) and expression of inflammatory cytokines in intestinal Treg cells. c-Maf deficiency in Treg cells led to profound dysbiosis of the intestinal microbiota, which when transferred to germ-free mice was sufficient to induce exacerbated intestinal TH17 responses, even in a c-Maf-competent environment. Thus, c-Maf acts to preserve the identity and function of intestinal Treg cells, which is essential for the establishment of host-microbe symbiosis.

CD4 T cells are required for maintenance of CD8 TRM cells and virus control in the brain of MCMV-infected newborn mice

Cytomegalovirus (CMV) infection is a significant public health problem. Congenital CMV infection is a leading infectious cause of long-term neurodevelopmental sequelae, including mental retardation and sensorineural hearing loss. Immune protection against mouse cytomegalovirus (MCMV) is primarily mediated by NK cells and CD8⁺ T cells, while CD4⁺ T cells are not needed for control of MCMV in majority of organs in immunocompetent adult mice. Here, we set out to determine the role of CD4⁺ T cells upon MCMV infection of newborn mice. We provide evidence that CD4⁺ T cells are essential for clearance of MCMV infection in brain of neonatal mice and for prevention of recurrence of latent MCMV. In addition, we provide evidence that CD4⁺ T cells are required for induction and maintenance of tissue-resident memory CD8⁺ T cells in the brain of mice perinatally infected with MCMV.

Expression of IL-7Rα and KLRG1 defines functionally distinct CD8+ T-cell populations in humans

During acute viral infections in mice, IL‐7Rα and KLRG1 together are used to distinguish the short‐lived effector cells (SLEC; IL‐7Rα^loKLRG^hi) from the precursors of persisting memory cells (MPEC; IL‐7Rα^hiKLRG1^lo). We here show that these markers can be used to define distinct subsets in the circulation and lymph nodes during the acute phase and in “steady state” in humans. In contrast to the T cells in the circulation, T cells derived from lymph nodes hardly contain any KLRG1‐expressing cells. The four populations defined by IL‐7Rα and KLRG1 differ markedly in transcription factor, granzyme and chemokine receptor expression. When studying renal transplant recipients experiencing a primary hCMV and EBV infection, we also found that after viral control, during latency, Ki‐67‐negative SLEC can be found in the peripheral blood in considerable numbers. Thus, combined analyses of IL‐7Rα and KLRG1 expression on human herpes virus‐specific CD8⁺ T cells can be used to separate functionally distinct subsets in humans. As a noncycling IL‐7Rα^loKLRG1^hi population is abundant in healthy humans, we conclude that this combination of markers not only defines short‐lived effector cells during the acute response but also stable effector cells that are formed and remain present during latent herpes infections.

CD1b presents self and Borrelia burgdorferi diacylglycerols to human T cells

Lyme disease is a common multisystem disease caused by infection with a tick‐transmitted spirochete, Borrelia burgdorferi and related Borrelia species. The monoglycosylated diacylglycerol known as B. burgdorferi glycolipid II (BbGL‐II) is a major target of antibodies in sera from infected individuals. Here, we show that CD1b presents BbGL‐II to human T cells and that the TCR mediates the recognition. However, we did not detect increased frequency of CD1b‐BbGL‐II binding T cells in the peripheral blood of Lyme disease patients compared to controls. Unexpectedly, mapping the T cell specificity for BbGL‐II‐like molecules using tetramers and activation assays revealed a concomitant response to CD1b‐expressing APCs in absence of BbGL‐II. Further, among all major classes of self‐lipid tested, BbGL‐II responsive TCRs show strong cross‐reactivity to diacylglycerol, a self‐lipid antigen with structural similarities to BbGL‐II. Extending prior work on MHC and CD1b, CD1c, and CD1d proteins, this study provides evidence for cross‐reactive CD1b‐restricted T cell responses to bacterial and self‐antigens, and identifies chemically defined targets for future discovery of self and foreign antigen cross‐reactive T cells.

Epithelium-specific MyD88 signaling, but not DCs or macrophages, control acute intestinal infection with Clostridium difficile

Infection with Clostridium difficile is one of the major causes of health care acquired diarrhea and colitis. Signaling though MyD88 downstream of TLRs is critical for initiating the early protective host response in mouse models of C. difficile infection (CDI). In the intestine, MyD88 is expressed in various tissues and cell types, such as the intestinal epithelium and mononuclear phagocytes (MNP), including DC or macrophages. Using a genetic gain-of-function system, we demonstrate here that restricting functional MyD88 signaling to the intestinal epithelium, but also to MNPs is sufficient to protect mice during acute CDI by upregulation of the intestinal barrier function and recruitment of neutrophils. Nevertheless, we also show that mice depleted for CD11c-expressing MNPs in the intestine display no major defects in mounting an effective inflammatory response, indicating that the absence of these cells is irrelevant for inducing host protection during acute infection. Together, our results highlight the importance of epithelial-specific MyD88 signaling and demonstrate that although functional MyD88 signaling in DC and macrophages alone is sufficient to correct the phenotype of MyD88-deficiency, these cells do not seem to be essential for host protection in MyD88-sufficient animals during acute infection with C. difficile.

Cerebral adrenoleukodystrophy is associated with loss of tolerance to profilin

Childhood cerebral adrenoleukodystrophy (cALD) is a devastating manifestation of ALD accompanied by demyelination, inflammation, and blood brain barrier (BBB) disruption with shared characteristics of an auto-immune disease. We utilized plasma samples pre- and postdevelopment of cALD to determine the presence of specific auto-antibodies. Mass spectrometry of protein specifically bound with post-cALD plasma antibody identified Profilin1 (PFN1) as the target. In a screen of 94 boys with cALD 48 (51%) had anti-PFN1 antibodies, whereas only 2/29 boys with ALD but without cerebral disease, and 0/30 healthy controls showed anti-PFN1 immunoreactivity. Cerebral spinal fluid from those with cALD showed higher levels of PFN1 protein compared with non-cALD samples (324 ± 634 versus 42 ± 23 pg/mL, p = 0.04). Boys that were anti-PFN positive had a significant increase in the amount of gadolinium signal observed on MRI when compared to boys that were anti-PFN1 negative (p = 0.04) possibly indicating increased BBB disruption. Anti-PFN1 positivity was also associated with elevated levels of very long chain fatty acids (C26 of 1.12 ± 0.41 versus 0.97 ± 0.30 mg/dL, p = 0.03) and increased plasma BAFF (973 ± 277 versus 733 ± 269 pg/mL, p = 0.03). In conclusion, anti-PFN may be a novel biomarker associated with the development of cALD in boys with ALD.

Interferon signature in patients with STAT1 gain-of-function mutation is epigenetically determined

STAT1 gain-of-function (GOF) variants lead to defective Th17 cell development and chronic mucocutaneous candidiasis (CMC), but frequently also to autoimmunity. Stimulation of cells with STAT1 inducing cytokines like interferons (IFN) result in hyperphosphorylation and delayed dephosphorylation of GOF STAT1. However, the mechanism how the delayed dephosphorylation exactly causes the increased expression of STAT1-dependent genes, and how the intracellular signal transduction from cytokine receptors is affected, remains unknown. In this study we show that the circulating levels of IFN-α were not persistently elevated in STAT1 GOF patients. Nevertheless, the expression of interferon signature genes was evident even in the patient with low or undetectable serum IFN-α levels. Chromatin immunoprecipitation (ChIP) experiments revealed that the active chromatin mark trimethylation of lysine 4 of histone 3 (H3K4me3), was significantly enriched in areas associated with interferon-stimulated genes in STAT1 GOF cells in comparison to cells from healthy donors. This suggests that the chromatin binding of GOF STAT1 variant promotes epigenetic changes compatible with higher gene expression and elevated reactivity to type I interferons, and possibly predisposes for interferon-related autoimmunity. The results also suggest that epigenetic rewiring may be responsible for treatment failure of Janus kinase 1/2 (JAK1/2) inhibitors in certain patients.

The thioredoxin-1 and glutathione/glutaredoxin-1 systems redundantly fuel murine B-cell development and responses

Antioxidant systems maintain cellular redox homeostasis. The thioredoxin-1 (Trx1) and the glutathione (GSH)/glutaredoxin-1 (Grx1) systems are key players in preserving cytosolic redox balance. In fact, T lymphocytes critically rely on reducing equivalents from the Trx1 system for DNA biosynthesis during metabolic reprogramming upon activation. We here show that the Trx1 system is also indispensable for development and functionality of marginal zone (MZ) B cells and B1 cells in mice. In contrast, development of conventional B cells, follicular B-cell homeostasis, germinal center reactions, and antibody responses are redundantly sustained by both antioxidant pathways. Proliferating B2 cells lacking Txnrd1 have increased glutathione (GSH) levels and upregulated cytosolic Grx1, which is barely detectable in expanding thymocytes. These results suggest that the redox capacity driving proliferation is more robust and flexible in B cells than in T cells, which may have profound implications for the therapy of B and T-cell neoplasms.

IL-4 promotes stromal cell expansion and is critical for development of a type-2, but not a type 1 immune response

IL-4 is critical for differentiation of Th2 cells and antibody isotype switching, but our work demonstrated that it is produced in the peripheral LN under both Type 2, and Type 1 conditions, raising the possibility of other functions. We found that IL-4 is vital for proper positioning of hematopoietic and stromal cells in steady state, and the lack of IL-4 or IL-4Rα correlates with disarrangement of both follicular dendritic cells and CD31+ endothelial cells. We observed a marked disorganization of B cells in these mice, suggesting that the lymphocyte-stromal cell axis is maintained by the IL-4 signaling pathway. This study showed that absence of IL-4 correlates with significant downregulation of Lymphotoxin alpha (LTα) and Lymphotoxin beta (LTβ), critical lymphokines for the development and maintenance of lymphoid organs. Moreover, immunization of IL-4 deficient mice with Type 2 antigens failed to induce lymphotoxin production, LN reorganization, or germinal center formation, while this process is IL-4 independent following Type 1 immunization. Additionally, we found that Type 1 antigen mediated LN reorganization is dependent on IFN-γ in the absence of IL-4. Our findings reveal a role of IL-4 in the maintenance of peripheral lymphoid organ microenvironments during homeostasis and antigenic challenge.

Enhancing immunity prevents virus-induced T-cell-mediated immunopathology in B cell-deficient mice

Hyper-activated or deviated immune responses can result in immunopathological diseases. Paradoxically, immunodeficiency represents a frequent cause of such immune-mediated pathologies. Immunopathological manifestations are commonly treated by immunosuppression, but in situations in which immunodeficiency is the basis of disease development, enhancing immunity may represent an alternative treatment option. Here, we tested this counterintuitive concept in a preclinical model using infection of mice with lymphocytic choriomeningitis virus (LCMV). Firstly, we demonstrate that infection of B-cell-deficient (B^-/- ) but not of wild-type (WT) mice with the LCMV strain Docile induced a rapid and fatal CD8⁺ T-cell-mediated immunopathological disease. Similar to WT mice, LCMV-infected B^-/- mice generated a potent, functional LCMV-specific CD8⁺ T-cell response but exhibited prolonged viral antigen presentation and increased vascular leakage in liver and lungs. Secondly, we were able to prevent this virus-induced immunopathology in B^-/- mice by active or passive T-cell immunizations or by treatment with LCMV-specific virus neutralizing or non-neutralizing monoclonal antibodies (mAb). Thus, boosting antiviral immunity did not aggravate immunopathology in this model, but prevented it by decreasing the formation of target structures for damage-causing CD8⁺ T cells.

Optimization of single-cell plate sorting for high throughput sequencing applications

Single cell sequencing has recently been applied to many immunological studies. Flow cytometric index sorting isolates cells for single cell sequencing with protein level data linked to sequences. However, successful sequencing of index sorted samples requires careful optimization of several sort parameters, including nozzle size, flow rate, threshold rate, and yield calculations. In this study, considerations and optimization data for each of these variables are presented. Our analysis focused on index sorting, but the findings can be applied to any plate sorting protocol. Minimization of flow rates and use of the 70 μm nozzle improved cell yields. Improvements in total read counts after sequencing were obtained by decreasing the threshold rate, or the number of cells processed per second. In addition, this technique provided linked protein and gene expression analysis of the cytokine interferon (IFN)γ, demonstrating that on a single cell basis IFNγ+ cells tend to express IFNG mRNA, and IFNγ- cells do not. Through rigorous optimization and quality control, we have identified parameters important to plate sorting and recommend the use of the 70 μm nozzle and low flow and threshold rates for analysis of rare populations of human lymphocytes.

Persistence of Candida albicans in the Oral Mucosa Induces a Curbed Inflammatory Host Response That Is Independent of Immunosuppression

Controlled immune activation in response to commensal microbes is critical for the maintenance of stable colonization and prevention of microbial overgrowth on epithelial surfaces. Our understanding of the host mechanisms that regulate bacterial commensalism has increased substantially, however, much less data exist regarding host responses to members of the fungal microbiota on colonized surfaces. Using a murine model of oropharyngeal candidiasis, we have recently shown that differences in immune activation in response to diverse natural isolates of Candida albicans are associated with different outcomes of the host-fungal interaction. Here we applied a genome-wide transcriptomic approach to show that rapid induction of a strong inflammatory response characterized by neutrophil-associated genes upon C. albicans colonization inversely correlated with the ability of the fungus to persist in the oral mucosa. Surprisingly, persistent fungal isolates showed no signs of a compensatory regulatory immune response. By combining RNA-seq data, genetic mouse models, and co-infection experiments, we show that attenuation of the inflammatory response at the onset of infection with a persistent isolate is not a consequence of enhanced immunosuppression. Importantly, depletion of regulatory T cells or deletion of the immunoregulatory cytokine IL-10 did not alter host-protective type 17 immunity nor did it impair fungal survival in the oral mucosa, indicating that persistence of C. albicans in the oral mucosa is not a consequence of suppressed antifungal immunity.

CCL21-expression and accumulation of CCR7+ NK cells in livers of patients with primary sclerosing cholangitis

The pathogenesis of primary sclerosing cholangitis (PSC), an autoimmune liver disease, remains unknown. The aim of this study was to characterize peripheral blood and intrahepatic NK cells from patients with PSC. Peripheral blood samples from patients with PSC, other autoimmune liver diseases, and from healthy control individuals were used, as well as liver tissues from PSC patients undergoing liver transplantation. Multiparameter flow cytometry showed that peripheral blood NK cells from PSC patients were significantly enriched for CCR7⁺ and CXCR3⁺ cells, and CCR7⁺ but not CXCR3⁺ cells were also significantly increased within intrahepatic NK cells. PSC patients undergoing liver transplantation furthermore had significantly higher plasma levels of the CCR7-ligand CCL21, and the CXCR3-ligands CXCL10 and CXCL11, and significantly higher levels of CCL21, but not CXCL10, were detected in liver tissues. CCR7⁺ and CXCR3⁺ NK cells from PSC patients exhibited significantly higher functional capacity in peripheral blood, but not liver tissues, consistent with chronic activation of these NK cells in the inflamed liver. These data show that PSC is characterized by intrahepatic CCL21 expression and accumulation of CCR7⁺ NK cells in the inflamed liver tissue.

CXCR4, but not CXCR3, drives CD8+ T-cell entry into and migration through the murine bone marrow

The BM serves as a blood-forming organ, but also supports the maintenance and immune surveillance function of many T cells. Yet, in contrast to other organs, little is known about the molecular mechanisms that drive T-cell migration to and localization inside the BM. As BM accumulates many CXCR3-expressing memory CD8⁺ T cells, we tested the involvement of this chemokine receptor, but found that CXCR3 is not required for BM entry. In contrast, we could demonstrate that CXCR4, which is highly expressed on both naive and memory CD8⁺ T cells in BM, is critically important for homing of all CD8⁺ T-cell subsets to the BM in mice. Upon entry into the BM parenchyma, both naïve and memory CD8⁺ T cells locate close to sinusoidal vessels. Intravital imaging experiments revealed that CD8 T cells are surprisingly immobile and we found that they interact with ICAM-1+VCAM-1+BP-1+ perivascular stromal cells. These cells are the major source of CXCL12, but also express key survival factors and maintenance cytokines IL-7 and IL-15. We therefore conclude that CXCR4 is not only crucial for entry of CD8⁺ T cells into the BM, but also controls their subsequent localization toward BM niches that support their survival.

Styk1 is specifically expressed in NK1.1+ lymphocytes including NK, γδ T, and iNKT cells in mice, but is dispensable for their ontogeny and function

Innate T cells, NK cells, and innate-like lymphocytes (ILCs) share transcriptional signatures that translate into overlapping developmental and functional programs. A prominent example for genes that are highly expressed in NK cells but not in ILCs is serine-threonine-tyrosine kinase 1 (Styk1 encoded by Styk1). We found Styk1 to be specifically expressed in lymphocytes positive for Killer cell lectin-like receptor subfamily B, member 1, also known as CD161 or NK1.1, i.e. in NK cell, αβ iNKT, and γδ NKT cell lineages. To investigate the role of Styk1 in the development and function of NK1.1⁺ innate T-cell subsets, we generated and analyzed a novel Styk1^null mutant mouse line. Furthermore, we validated Styk1 expression in γδ NKT cells and in thymic, but not in peripheral invariant αβ iNKT cells through ex vivo analysis of a concomitantly generated transgenic Styk1 reporter mouse line. Despite the very specific expression of Styk1 in NK cells, γδ NKT cells, and thymic αβ iNKT, its absence did not alter homeostasis and function of these lineages. Thus, Styk1 expression is specific for NK cells and selected NK-like innate T-cell subsets, but dispensable for their development and function.

Lipopolysaccharide impacts murine CD103+ DC differentiation, altering the lung DC population balance

Conventional DCs are a heterogeneous population that bridge the innate and adaptive immune systems. The lung DC population comprises CD103⁺ XCR1⁺ DC1s and CD11b⁺ DC2s; their various combined functions cover the whole spectrum of immune responses needed to maintain homeostasis. Here, we report that in vivo exposure to LPS leads to profound alterations in the proportions of CD103⁺ XCR1⁺ DCs in the lung. Using ex vivo LPS and TNF stimulations of murine lung and spleen-isolated DCs, we show that this is partly due to a direct downregulation of the GM-CSF-induced DC CD103 expression. Furthermore, we demonstrate that LPS-induced systemic inflammation alters the transcriptional signature of DC precursors toward a lower capacity to differentiate into XCR1⁺ DCs. Also, we report that TNF prevents the capacity of pre-DCs to express CD103 upon maturation. Overall, our results indicate that exposure to LPS directly impacts the capacity of pre-DCs to differentiate into XCR1⁺ DCs, in addition to lowering their capacity to express CD103. This leads to decreased proportions of CD103⁺ XCR1⁺ DCs in the lung, favoring CD11b⁺ DCs, which likely plays a role in the break in homeostasis following LPS exposure, and in determining the nature of the immune response to LPS.

TLR signals license CD8 T cells to destroy oligodendrocytes expressing an antigen shared with a Listeria pathogen

Increasing evidence suggests a role of CD8 T cells in autoimmune demyelinating CNS disease, which, however, is still controversially discussed. Mice, which express ovalbumin (OVA) as cytosolic self-antigen in oligodendrocytes (ODC-OVA mice), respond to CNS infection induced by OVA-expressing attenuated Listeria with CD8 T cell-mediated inflammatory demyelination. This model is suitable to decipher the contribution of CD8 T cells and the pathogen in autoimmune CNS disease. Here, we show that both antigen and pathogen are required in the CNS for disease induction, though not in a physically linked fashion. Intracerebral challenge with combined toll like receptor (TLR) TLR2 and TLR9 as well as TLR7 and TLR9 agonists substituted for the bacterial stimulus, but not with individual TLR agonists (TLR2, TLR3,TLR5,TLR7, TLR9). Furthermore, MyD88 inactivation rendered ODC-OVA mice resistant to disease induction. Collectively, CD8 T cell-mediated destruction of oligodendrocytes is activated if (i) an antigen shared with an infectious agent is provided in the CNS microenvironment and (ii) innate immune signals inform the CNS microenvironment that pathogen removal warrants an immune attack by CD8 T cells, even at the expense of locally restricted demyelination.

The contribution of active and passive mechanisms of 5mC and 5hmC removal in human T lymphocytes is differentiation- and activation-dependent

In mammals, the 5'-methylcytosine (5mC) modification in the genomic DNA contributes to the dynamic control of gene expression. 5mC erasure is required for the activation of developmental programs and occurs either by passive dilution through DNA replication, or by enzymatic oxidation of the methyl mark to 5-hydroxymethylcytosine (5hmC), which can persist as such or undergo further oxidation and enzymatic removal. The relative contribution of each mechanism to epigenetic control in dynamic biological systems still remains a compelling question. To explore this critical issue, we used primary human T lymphocytes, in which two cellular states can be clearly identified, namely quiescent naïve T cells, which are slowly or rarely proliferating, and rapidly proliferating activated T cells. We found that active mechanisms of methylation removal were selectively at work in naïve T cells, while memory T lymphocytes entirely relied on passive, replication-dependent dilution, suggesting that proliferative capacity influences the choice of the preferential demethylation mechanism. Active processes of demethylation appear to be critical in quiescent naïve T lymphocytes for the maintenance of regulatory regions poised for rapid responses to physiological stimuli.

Soluble CD93 is an apoptotic cell opsonin recognized by αx β2

Efferocytosis is essential for homeostasis and prevention of the inflammatory and autoimmune diseases resulting from apoptotic cell lysis. CD93 is a transmembrane glycoprotein previously implicated in efferocytosis, with mutations in CD93 predisposing patients to efferocytosis-associated diseases. CD93 is a cell surface protein, which is proteolytically shed under inflammatory conditions, but it is unknown how CD93 mediates efferocytosis or whether its efferocytic activity is mediated by the soluble or membrane-bound form. Herein, using cell lines and human monocytes and macrophages, we demonstrate that soluble CD93 (sCD93) potently opsonizes apoptotic cells but not a broad range of microorganisms, whereas membrane-bound CD93 has no phagocytic, efferocytic, or tethering activity. Using mass spectrometry, we identified α_x β₂ as the receptor that recognizes sCD93, and via deletion mutagenesis determined that sCD93 binds to apoptotic cells via its C-type lectin-like domain and to α_x β₂ by its EGF-like repeats. The bridging of apoptotic cells to α_x β₂ markedly enhanced efferocytosis by macrophages and was abrogated by α_x β₂ knockdown. Combined, these data elucidate the mechanism by which CD93 regulates efferocytosis and identifies a previously unreported opsonin-receptor system utilized by phagocytes for the efferocytic clearance of apoptotic cells.

Prevention of allergy by virus-like nanoparticles (VNP) delivering shielded versions of major allergens in a humanized murine allergy model

Background

In high‐risk populations, allergen‐specific prophylaxis could protect from sensitization and subsequent development of allergic disease. However, such treatment might itself induce sensitization and allergies, thus requiring hypoallergenic vaccine formulations. We here characterized the preventive potential of virus‐like nanoparticles (VNP) expressing surface‐exposed or shielded allergens.

Methods

Full‐length major mugwort pollen allergen Art v 1 was selectively targeted either to the surface or to the inner side of the lipid bilayer envelope of VNP. Upon biochemical and immunological analysis, their preventive potential was determined in a humanized mouse model of mugwort pollen allergy.

Results

Virus‐like nanoparticles expressing shielded version of Art v 1, in contrast to those expressing surface‐exposed Art v 1, were hypoallergenic as they hardly induced degranulation of rat basophil leukemia cells sensitized with Art v 1‐specific mouse or human IgE. Both VNP versions induced proliferation and cytokine production of allergen‐specific T cells in vitro. Upon intranasal application in mice, VNP expressing surface‐exposed but not shielded allergen induced allergen‐specific antibodies, including IgE. Notably, preventive treatment with VNP expressing shielded allergen‐protected mice from subsequent sensitization with mugwort pollen extract. Protection was associated with a Th1/Treg‐dominated cytokine response, increased Foxp3⁺ Treg numbers in lungs, and reduced lung resistance when compared to mice treated with empty particles.

Conclusion

Virus‐like nanoparticles represent a novel and versatile platform for the in vivo delivery of allergens to selectively target T cells and prevent allergies without inducing allergic reactions or allergic sensitization.

Impaired antigen-specific lymphocyte priming in mice after Toll-like receptor 4 activation via induction of monocytic myeloid-derived suppressor cells

In sepsis, the pathology involves a shift from a proinflammatory state toward an immunosuppressive phase. We previously showed that an agonistic anti-TLR4 antibody induced long-term endotoxin tolerance and suppressed antigen-specific secondary IgG production when primed prior to immunization with antigen. These findings led us to speculate that TLR4-induced innate tolerance due to primary infection causes an immunosuppressive pathology in sepsis. Therefore, the mechanism underlying impaired antigen-specific humoral immunity by the TLR4 antibody was investigated. We showed, in a mouse model, that primary antigen-specific IgG responses were impaired in TLR4 antibody-induced tolerized mice, which was the result of reduced numbers of antigen-specific GC B cells and plasma cells. Ovalbumin-specific CD4 and CD8 T-cell responses were impaired in TLR4 antibody-injected OT-I and -II transgenic mice ex vivo. Adoptive transfer studies demonstrated suppression of OVA-specific CD4 and CD8 T-cell responses by the TLR4 antibody in vivo. The TLR4 antibody induced Gr1⁺ CD11b⁺ myeloid-derived suppressor cell (MDSC) expansion with suppression of T-cell activation. Monocytic MDSCs were more suppressive and exhibited higher expression of PD-L1 and inducible nitric oxidase compared with granulocytic MDSCs. In conclusion, immune tolerance conferred by TLR4 activation induces the expansion of monocytic MDSCs, which impairs antigen-specific T-cell priming and IgG production.

Interleukin-22 protects intestinal stem cells against genotoxic stress

Environmental genotoxic factors pose a challenge to the genomic integrity of epithelial cells at barrier surfaces that separate host organisms from the environment. They can induce mutations that, if they occur in epithelial stem cells, contribute to malignant transformation and cancer development1-3. Genome integrity in epithelial stem cells is maintained by an evolutionarily conserved cellular response pathway, the DNA damage response (DDR). The DDR culminates in either transient cell-cycle arrest and DNA repair or elimination of damaged cells by apoptosis4,5. Here we show that the cytokine interleukin-22 (IL-22), produced by group 3 innate lymphoid cells (ILC3) and γδ T cells, is an important regulator of the DDR machinery in intestinal epithelial stem cells. Using a new mouse model that enables sporadic inactivation of the IL-22 receptor in colon epithelial stem cells, we demonstrate that IL-22 is required for effective initiation of the DDR following DNA damage. Stem cells deprived of IL-22 signals and exposed to carcinogens escaped DDR-controlled apoptosis, contained more mutations and were more likely to give rise to colon cancer. We identified metabolites of glucosinolates, a group of phytochemicals contained in cruciferous vegetables, to be a widespread source of genotoxic stress in intestinal epithelial cells. These metabolites are ligands of the aryl hydrocarbon receptor (AhR)6, and AhR-mediated signalling in ILC3 and γδ T cells controlled their production of IL-22. Mice fed with diets depleted of glucosinolates produced only very low levels of IL-22 and, consequently, the DDR in epithelial cells of mice on a glucosinolate-free diet was impaired. This work identifies a homeostatic network protecting stem cells against challenge to their genome integrity by AhR-mediated 'sensing' of genotoxic compounds from the diet. AhR signalling, in turn, ensures on-demand production of IL-22 by innate lymphocytes directly regulating components of the DDR in epithelial stem cells.

CD69+ memory T lymphocytes of the bone marrow and spleen express the signature transcripts of tissue-resident memory T lymphocytes

It is a matter of current debate whether the bone marrow is a hub for circulating memory T lymphocytes and/or the home of resident memory T lymphocytes. Here we demonstrate for CD69⁺ murine CD8⁺ , and CD69⁺ murine and human CD4⁺ memory T lymphocytes of the bone marrow, making up between 30 and 60% of bone marrow memory T lymphocytes, that they express the gene expression signature of tissue-resident memory T lymphocytes. This suggests that a substantial proportion of bone marrow memory T lymphocytes are resident. It adds to previous evidence that bone marrow memory T cells are resting in terms of mobility and proliferation, and maintain exclusive long-term memory to distinct, systemic antigens.

Transformation of mature mouse B cells into malignant plasma cells in vitro via introduction of defined genetic elements

An experimental system where defined alterations in gene function or gene expression levels in primary B cells would result in the development of transformed plasma cells in vitro would be useful in order to facilitate studies of the underlying molecular mechanisms of plasma cell malignancies. Here, such a system is described in which primary murine B cells rapidly become transformed into surface CD138⁺ , IgM^-/low , CD19^- IgM-secreting plasma cells as a result of expression of the transcription factors IRF4 and MYC together with simultaneous expression of BMI1, mutated p53 or silencing of p19^Arf , and suppression of intrinsic apoptosis through expression of BCLXL. Analysis of gene expression patterns revealed that this combination of transforming genes resulted in expression of a number of genes previously associated with terminally differentiated B cells (plasma cells) and myeloma cells, whereas many genes associated with mature B cells and B-cell lymphomas were not expressed. Upon transplantation, the transformed cells preferentially localized to the bone marrow, presenting features of a plasma cell malignancy of the IgM isotype. The present findings may also be applicable in the development of novel methods for production of monoclonal antibodies.

The mannose 6-phosphate/insulin-like growth factor 2 receptor mediates plasminogen-induced efferocytosis

The plasminogen system is harnessed in a wide variety of physiological processes, such as fibrinolysis, cell migration, or efferocytosis; and accordingly, it is essential upon inflammation, tissue remodeling, wound healing, and for homeostatic maintenance in general. Previously, we identified a plasminogen receptor in the mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R, CD222). Here, we demonstrate by means of genetic knockdown, knockout, and rescue approaches combined with functional studies that M6P/IGF2R is up-regulated on the surface of macrophages, recognizes plasminogen exposed on the surface of apoptotic cells, and mediates plasminogen-induced efferocytosis. The level of uptake of plasminogen-coated apoptotic cells inversely correlates with the TNF-α production by phagocytes indicating tissue clearance without inflammation by this mechanism. Our results reveal an up-to-now undetermined function of M6P/IGF2R in clearance of apoptotic cells, which is crucial for tissue homeostasis.

Antigen-specific CD8 T cells in cell cycle circulate in the blood after vaccination

Although clonal expansion is a hallmark of adaptive immunity, the location(s) where antigen‐responding T cells enter cell cycle and complete it have been poorly explored. This lack of knowledge stems partially from the limited experimental approaches available. By using Ki67 plus DNA staining and a novel strategy for flow cytometry analysis, we distinguished antigen‐specific CD8 T cells in G₀, in G₁ and in S‐G₂/M phases of cell cycle after intramuscular vaccination of BALB/c mice with antigen‐expressing viral vectors. Antigen‐specific cells in S‐G₂/M were present at early times after vaccination in lymph nodes (LNs), spleen and, surprisingly, also in the blood, which is an unexpected site for cycling of normal non‐leukaemic cells. Most proliferating cells had high scatter profile and were undetected by current criteria of analysis, which under‐estimated up to 6 times antigen‐specific cell frequency in LNs. Our discovery of cycling antigen‐specific CD8 T cells in the blood opens promising translational perspectives.

High-dimensional single-cell proteomics analysis identifies immune checkpoint signatures and therapeutic targets in ulcerative colitis

Immune checkpoints are regulators of immune cells and play key roles in the modulation of immune responses. The role of checkpoints in autoimmune disease is poorly understood but likely to be central since checkpoint inhibition during cancer treatment can cause autoimmunity. We generated a high-dimensional single-cell proteomics data set from PBMCs of healthy individuals and patients with ulcerative colitis (UC) by mass cytometry, enabling systems-wide analyses of immune cell frequencies and cell type-specific expression patterns of 12 immune checkpoints. Subtle but significant changes in immune cell frequencies and checkpoint expression were observed between UC patients on different treatment regimens and between patients and healthy controls. Most strikingly, UC patients showed a reduced number of peripheral NK-cells and those cells showed an altered phenotype including increased TIGIT expression. Based on these results, we modulated NK-cell function ex vivo through targeting of TIGIT pathway members. In summary, we describe a pattern of changes in immune cell abundance and checkpoint expression as a basis for UC patient stratification and we show modulation of a corresponding immune cell subset through checkpoint targeting. Our approach can be used for the identification of pathogenic immune cell subsets and guide target selection in autoimmunity and chronic inflammation.

HMGB1+ microparticles present in urine are hallmarks of nephritis in patients with systemic lupus erythematosus

Non-classical monocytes infiltrate the kidney parenchyma and participate in tissue damage in patients with lupus nephritis (LN). Circulating microparticles (MPs) seem to play critical roles in the activation of monocytes in systemic lupus erythematosus (SLE) patients. This study aims to characterize the phenotypes of MPs and monocyte subsets in LN patients and to determine their potential to discriminate between SLE patients with and without LN. Blood and urine samples from SLE patients were collected. In monocyte subsets from whole blood samples several phenotypic markers were evaluated. MPs were isolated from platelet-poor plasma and urine by centrifugation. This phenotypic marker characterization was performed using multiparametric flow cytometry. We observed that patients with active LN have lower counts of non-classical monocytes than do those without renal involvement. All monocyte subsets exhibited lower expression of CX3CR1 and ICAM-1 in LN than in patients without LN. High frequencies of MP-HMGB1⁺ and MP-HLA-DR⁺ were detected in circulation and urine of LN patients. Although MP-HMGB1⁺ , MP-HLA-DR⁺ , and MP-CX3CR1⁺ from urine were able to discriminate between patients with and without LN, only urinary MP-HMGB1⁺ were different between patients with active and inactive LN. Therefore, these vesicles may be useful as biomarkers of LN.

IL-10 signaling in dendritic cells is required for tolerance induction in a murine model of allergic airway inflammation

Allergen specific tolerance induction efficiently ameliorates subsequent allergen induced inflammatory responses. The underlying regulatory mechanisms have been attributed mainly to interleukin (IL)-10 produced by diverse hematopoietic cells, while targets of IL-10 in allergen specific tolerance induction have not yet been well defined. Here, we investigate potential cellular targets of IL-10 in allergen specific tolerance induction using mice with a cell type specific inactivation of the IL-10 receptor gene. Allergic airway inflammation was effectively prevented by tolerance induction in mice with IL-10 receptor (IL-10R) deficiency in T or B cells. Similarly, IL-10R on monocytes/macrophages and/or neutrophils was not required for tolerance induction. In contrast, tolerance induction was impaired in mice that lack IL-10R on dendritic cells: those mice developed an allergic response characterized by a pronounced neutrophilic lung infiltration, which was not ameliorated by tolerogenic treatment. In conclusion, our results show that allergen specific tolerance can be effectively induced without a direct impact of IL-10 on cells of the adaptive immune system, and highlight dendritic cells, but not macrophages nor neutrophils, as the main target of IL-10 during tolerance induction.

High-Dimensional Immunophenotyping with Fluorescence-Based Cytometry: A Practical Guidebook

Recent technological advances have greatly diversified the platforms that are available for high-dimensional single-cell immunophenotyping, including mass cytometry, single-cell RNA sequencing, and fluorescent-based flow cytometry. The latter is currently the most commonly used approach, and modern instrumentation allows for the measurement of up to 30 parameters, revealing deep insights into the complexity of the immune system.Here, we provide a practical guidebook for the successful design and execution of complex fluorescence-based immunophenotyping panels. We address common misconceptions and caveats, and also discuss challenges that are associated with the quality control and analysis of these data sets.

Isolation, Expansion, and Characterization of Natural Killer Cells and Their Precursors as a Tool to Study Cancer Immunosurveillance

This chapter will describe the current methodologies to isolate and expand NK cells from Peripheral Blood (PB) or tissues for "in vitro" studies, including NK cell antitumor immune function. In addition, methods to induce NK cell maturation, differentiation, and expansion from CD34⁺ precursors will also be described. Finally, it will also be treated the topical issue of the characterization of new functionally and phenotypically defined NK cell subsets.

Experimental Cutaneous Leishmaniasis: Mouse Models for Resolution of Inflammation Versus Chronicity of Disease

Experimental cutaneous leishmaniasis of mice is a valuable model to study the immune response to the protozoan pathogen Leishmania and to define mechanisms of parasite control and resolution of inflammation as well as of parasite evasion and chronicity of disease. In addition, over many years Leishmania-infected mice have been successfully used to analyze the function of newly discovered immune cell types, transcription factors, cytokines, and effector mechanisms in vivo. In this chapter we present detailed protocols for the culture, propagation, and inoculation of Leishmania promastigotes, the monitoring of the course of cutaneous infection, the determination of the tissue parasite burden and for the phenotyping of the ensuing immune response. The focus lies on the L. major mouse model, but an overview on other established models of murine cutaneous leishmaniasis is also provided.

USP14 promotes K63-linked RIG-I deubiquitination and suppresses antiviral immune responses

Retinoic acid-inducible gene I (RIG-I) is a critical RNA virus sensor that initiates antiviral immune response through K63-linked ubiquitination. In this study, we demonstrated USP14, a deubiquitinating enzyme, as a negative regulator in antiviral responses by directly deubiquitinating K63-linked RIG-I. USP14 knockdown significantly enhanced RIG-I-triggered type I IFN signaling and inhibited vesicular stomatitis virus (VSV) replication both in mouse peritoneal macrophages and THP1 cells. USP14 overexpression in HeLa cells attenuated RIG-I-triggered IFN-β expression and promoted VSV replication. Besides, USP14-specific inhibitor, IU1, increased RIG-I-mediated type I IFN production and antiviral responses in vitro and in vivo. In addition, USP14 could interact with RIG-I and remove RIG-I K63-linked polyubiquitination chains. This article is the first to report that USP14 acts as a negative regulator in antiviral response through deubiquitinating K63-linked RIG-I. These findings provide insights into a potential new therapy targeting USP14 for RNA virus-related diseases.

Surface Barcoding of Live PBMC for Multiplexed Mass Cytometry

Sample barcoding is a powerful method for harmonizing mass cytometry data. By assigning a unique combination of barcode labels to each cell sample, a set of individual samples can be pooled and further processed and acquired as a large, single sample. For assays that require uncompromised profiling of cell-surface markers on live cells, barcoding by metal-labeled antibodies targeting cell-surface epitopes is the barcoding approach of choice. Here we provide an optimized and validated protocol for cell-surface barcoding of ten PBMC samples with palladium-labeled β2-microglobulin (B2M) antibodies used in a 5-choose-2 barcoding scheme, for subsequent immune phenotyping by mass cytometry. We further provide details on the generation of palladium-labeled antibodies utilizing amine-reactive isothiocyanobenzyl-EDTA (ITCB-EDTA) that permits the implementation of antibody-based barcoding not interfering with lanthanide channels typically used for analyte detection in mass cytometry assays.

Isolation and Phenotypic Characterization of Inflammatory Cells from Clinical Samples: Purification of Macrophages from Trypanosoma cruzi-Infected Hearts

Trypanosoma cruzi, the causal agent of chronic Chagas cardiomyopathy, exhibits an important tropism for cardiac tissue. In consequence, T. cruzi experimental infection represents a unique model to study cardiac macrophage behavior and effector functions during either acute or chronic immune response. In this chapter we describe a protocol to isolate immune cells from T. cruzi-infected murine cardiac tissue and to determine the percentage, absolute number, phenotype, and functionality of monocytes and macrophages by using flow cytometry. Moreover, we describe the parameters to discriminate between resident and infiltrating mononuclear phagocytic cells within infected hearts. The investigations in this field will provide mechanistic insights about the roles of these innate immune cells in the context of a clinically relevant target tissue.

Memory CD4+ T cells enhance B-cell responses to drifting influenza immunization

Influenza A annually infects 5-10% of the world's human population resulting in one million deaths. Influenza causes annual epidemics and reinfects previously exposed individuals because of antigenic drift in the glycoprotein hemagglutinin. Due to antigenic drift, the immune system is simultaneously exposed to novel and conserved parts of the influenza virus via vaccination and/or infection throughout life. Preexisting immunity has long been known to augment subsequent hemagglutination inhibitory antibody (hAb) responses. However, the preexisting immunological contributors that influence hAb responses are not understood. Therefore, we adapted and developed sequential infection and immunization mouse models using drifted influenza strains to show that MHC Class II haplotype and T-cell reactivity influences subsequent hAb responses. We found that CB6F1 mice infected with A/CA followed by immunization with A/PR8 have increased hAb responses to A/PR8 compared to C57BL/6 mice. Increased hAb responses in CB6F1 mice were CD4⁺  T-cell and B-cell dependent and corresponded to increased germinal center A/PR8-specific B and T-follicular helper cells. These results suggest conserved MHC Class II restricted epitopes within HA are essential for B cells to respond to drifting influenza and could be leveraged to boost hAb responses.

Human anti-NKp46 antibody for studies of NKp46-dependent NK cell function and its applications for type 1 diabetes and cancer research

Natural killer (NK) cells are innate lymphocytes that efficiently eliminate cancerous and infected cells. NKp46 is an important NK activating receptor shown to participate in recognition and activation of NK cells against pathogens, tumor cells, virally infected cells, and self-cells in autoimmune conditions, including type I and II diabetes. However, some of the NKp46 ligands are unknown and therefore investigating human NKp46 activity and its critical role in NK cell biology is problematic. We developed a unique anti-human NKp46 monocloncal antibody, denoted hNKp46.02 (02). The 02 mAb can induce receptor internalization and degradation. By binding to a unique epitope on a particular domain of NKp46, 02 lead NKp46 to lysosomal degradation. This downregulation therefore enables the investigation of all NKp46 activities. Indeed, using the 02 mAb we determined NK cell targets which are critically dependent on NKp46 activity, including certain tumor cells lines and human pancreatic beta cells. Most importantly, we showed that a toxin-conjugated 02 inhibits the growth of NKp46-positive cells; thus, exemplifying the potential of 02 in becoming an immunotherapeutic drug to treat NKp46-dependent diseases, such as, type I diabetes and NK and T cell related malignancies.

B7H6 is a functional ligand for NKp30 in rat and cattle and determines NKp30 reactivity toward human cancer cell lines

NK cells kill cancer cells and infected cells upon activation by cell surface receptors. Human NKp30 is an activating receptor expressed by all mature NK cells. The B7 family member B7H6 has been identified as one ligand for NKp30. Several alternative ligands have also been reported, and the field remains unsettled. To this end, we have identified full-length functional B7H6 orthologs in rat and cattle, demonstrated by phylogenetic analysis and transfection experiments. In cell-cell contact-dependent assays, chimeric NKp30 reporter cells responded strongly to B7H6 in rat and cattle. Likewise, rat NKp30 expressing target cells induced strong activation of B7H6 reporter cells. Together, these observations demonstrate that B7H6 is conserved as a functional ligand for NKp30 in mammalian species separated by more than 100 million years of evolution. B7H6 and NKp30 are pseudogenes in laboratory mice. The rat thus represents an attractive experimental animal model to study the NKp30-B7H6 interaction in vivo. B7H6 was widely expressed among human cancer cell lines, and the expression level correlated strongly with the activation of human NKp30 reporter cells. Furthermore, siRNA knockdown of B7H6 abolished NKp30 reporter responses, suggesting that B7H6 is the major functionally relevant expressed ligand for NKp30 on these cancer cell lines.

STAT6 inhibitory peptide reduces dendritic cell migration to the lymph nodes to control Th2 adaptive immunity in the mouse lung

Type 2 immunity in the lung is promoted through the release of innate cytokines, including TSLP, from lung structural cells. These cytokines drive Type 2 immunity in part through upregulation of OX40L on dendritic cells (DCs). DCs expressing OX40L are potent inducers of Th2 differentiation. We have shown previously that STAT6 inhibitory peptide (STAT6-IP), a cell penetrating peptide designed to inhibit the STAT6 transcription factor, reduces the induction of Th2 adaptive immunity in murine models of respiratory syncytial virus infection. Here we show that intranasal administration of STAT6-IP at the time of antigen priming with ovalbumin (OVA), in conjunction with the Nod2 agonist, MDP, reduced frequencies of CD11b⁺ lung DCs expressing OX40L. Consistent with these reductions, fewer activated DCs were localized to the lung draining lymph nodes in STAT6-IP-treated mice. Upon OVA challenge four weeks later, mice treated with STAT6-IP at the time of OVA/MDP priming did not develop airway hyperresponsiveness (AHR) and had reduced influx of eosinophils into the airways, mucus production, and serum OVA-specific IgE levels. Our findings provide evidence that the long-lasting inhibitory effects of STAT6-IP are due in part to inhibition of DC responses that drive maladaptive Th2 adaptive immunity and allergic airways disease.