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Background Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), are important causes of morbidity and mortality in critically ill patients. Gastric contents aspiration is one of the most common causes of ALI/ARDS. To date, there are still no specific and effective pharmacological treatments for ALI/ARDS. Polyvinylalcohol-carbazate (PVAC), a polymer that has the ability to bind endogenous aldehydes, neutralize oxidative stress and inhibit inflammatory factors, may be a potential treatment for ALI/ARDS. Methods A hydrochloric acid (HCl) induced mouse model were employed to assess the effect of PVAC. The changes of lung mechanics, pulmonary edema, histology and immune cells, cytokines, and lipid mediators in bronchioalveolar lavage fluid (BALF) were investigated in HCl-challenged mice. Results In the HCl model, PVAC administration alleviated airway hyperresponsiveness and improved pulmonary edema and damage. In addition, it decreased the recruitment of neutrophils to the lung, and inhibited the increase of IL-6, TNF-α and leukotriene B4. Conclusions PVAC is a potential treatment for ALI/ARDS caused by inhalation of gastric acid.

Marginal zone (MZ) B cells are innate‐like B cells that produce polyreactive antibodies with an affinity for microbial molecular patterns and carbohydrate ligands. MZ B cells have been shown to be important in mediating immunity to various bacteria including Streptococcus pneumoniae and are also implicated in inflammatory syndromes including lupus erythematosus. The intestinal microbiota is responsible for producing short‐chain fatty acids, which can regulate immune cell function by several mechanisms including ligation of the G‐protein‐coupled receptor (GPR)43. Herein, we show that MZ B cells express Gpr43 messenger RNA and that the absence of this receptor impacts on MZ B‐cell surface marker expression and antibody production. In T‐cell‐independent responses to the hapten 4‐hydroxy‐3‐nitrophenylacetic acid (NP), mice deficient in GPR43 displayed higher serum titers of NP‐specific antibodies. Moreover, in response to a pneumococcal polysaccharide vaccine, GPR43‐deficient mice developed robust serum antibody responses and had markedly increased numbers of splenic antibody‐secreting cells, compared with control mice. Finally, serum immunoglobulin M autoantibodies to double‐stranded DNA and phosphatidylcholine were increased in resting 10–15‐week‐old mice lacking GPR43. Taken together, mice lacking GPR43 have heightened antibody responses to T‐cell‐independent antigens, which may be a result of impaired regulation of MZ B cells., Marginal zone B cells express the short‐chain fatty acid receptor GPR43. Mice lacking GPR43 have heightened responses to T‐cell‐independent antigens and have elevated levels of immunoglobulin M specific for double‐stranded DNA and phosphatidylcholine. Thus, short‐chain fatty acids may regulate marginal zone B‐cell responses to several antigens.

Allergy to dogs affects around 10% of the population in developed countries. Immune therapy of allergic patients with dog allergen extracts has shown limited therapeutic benefit.We established a mouse model of dog allergy by repeatedly administering dog dander and epithelium extracts via the intranasal route. We also assessed the efficacy of a recombinant multimeric protein containing Can f 1, f 2, f 4 and f 6 in preventing inflammatory responses to dog extracts.Repeated inhalation of dog extracts induced infiltration of the airways by TDog allergen extracts induce robust T

Conventional approaches to isolate and characterize nanobodies are laborious. We combine phage display, multivariate enrichment, next-generation sequencing, and a streamlined screening strategy to identify numerous anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nanobodies. We characterize their potency and specificity using neutralization assays and hydrogen/deuterium exchange mass spectrometry (HDX-MS). The most potent nanobodies bind to the receptor binding motif of the receptor binding domain (RBD), and we identify two exceptionally potent members of this category (with monomeric half-maximal inhibitory concentrations around 13 and 16 ng/ml). Other nanobodies bind to a more conserved epitope on the side of the RBD and are able to potently neutralize the SARS-CoV-2 founder virus (42 ng/ml), the Beta variant (B.1.351/501Y.V2) (35 ng/ml), and also cross-neutralize the more distantly related SARS-CoV-1 (0.46 μg/ml). The approach presented here is well suited for the screening of phage libraries to identify functional nanobodies for various biomedical and biochemical applications.

Purpose of Review The incidence of allergic diseases such as asthma, rhinitis and atopic dermatitis has risen at an alarming rate over the last century. Thus, there is a clear need to understand the critical factors that drive such pathologic immune responses. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a nuclear receptor that has emerged as an important regulator of multiple cell types involved in the inflammatory response to allergens; from airway epithelial cells to T Helper (TH) cells. Recent Findings Initial studies suggested that agonists of PPAR-γ could be employed to temper allergic inflammation, suppressing pro-inflammatory gene expression programs in epithelial cells. Several lines of work now suggest that PPAR-γ plays an essential in promoting ‘type 2’ immune responses that are typically associated with allergic disease. PPAR-γ has been found to promote the functions of TH2 cells, type 2 innate lymphoid cells, M2 macrophages and dendritic cells, regulating lipid metabolism and directly inducing effector gene expression. Moreover, preclinical models of allergy in gene-targeted mice have increasingly implicated PPAR-γ in driving allergic inflammation. Summary Herein, we highlight the contrasting roles of PPAR-γ in allergic inflammation and hypothesize that the availability of environmental ligands for PPAR-γ may be at the heart of the rise in allergic diseases worldwide.

Chronic rhinosinusitis with nasal polyps (CRSwNP) is characterized by a chronic inflammatory process often associated with comorbid asthma. In this study, we analyzed the transcriptomes of single T helper (TH) cells from nasal polyps of patients with CRSwNP and validated these findings using multiparameter flow cytometry. Polyp tissue contained suppressive T regulatory (Treg) cells, TH2 cells, type 2 innate lymphoid cells, and three transcriptionally distinct subsets of cytotoxic CD4+ T cells (CD4+ CTL). GATA3 expression was a feature of polyp Treg cells, whereas TH2 cells highly expressed TCN1, CD200R, and HPGDS and were enriched for genes involved in lipid metabolism. Only a portion of polyp TH2 cells expressed the prostaglandin D2 receptor CRTH2, whereas a subpopulation of CD109+CRTH2- TH2 cells expressed mRNA for common inhibitor receptors including LAG3 and TIM3 and produced IL-10. Together, we resolved the complexity of TH cells in patients with CRSwNP, identifying several distinct clusters of CD4+ CTL and a population of CD109+CRTH2- TH2 cells with putative regulatory potential.

CTLA-4 is required for CD4+Foxp3+ regulatory T (Treg) cell function, but its mode of action remains incompletely defined. Herein we generated Ctla-4ex2fl/flFoxp3-Cre mice with Treg cells exclusively expressing a naturally occurring, ligand-independent isoform of CTLA-4 (liCTLA-4) that cannot interact with the costimulatory molecules CD80 and CD86. The mice did not exhibit any signs of effector T cell activation early in life, however, at 6 months of age they exhibited excessive T cell activation and inflammation in lungs. In contrast, mice with Treg cells completely lacking CTLA-4 developed lymphoproliferative disease characterized by multi-organ inflammation early in life. In vitro, Treg cells exclusively expressing liCTLA-4 inhibited CD80 and CD86 expression on dendritic cells (DC). Conversely, Treg cells required the extra-cellular part of CTLA-4 to up-regulate expression of the co-inhibitory molecule PD-L2 on DCs. Transcriptomic analysis of suppressed DCs revealed that Treg cells induced a specific immunosuppressive program in DCs.

Conventional approaches to isolate and characterize nanobodies are laborious and cumbersome. Here we combine phage display, multivariate enrichment, and novel sequence analysis techniques to annotate an entire nanobody repertoire from an immunized alpaca. We combine this approach with a streamlined screening strategy to identify numerous anti-SARS-CoV-2 nanobodies, and use neutralization assays and Hydrogen/Deuterium exchange coupled to mass spectrometry (HDX-MS) epitope mapping to characterize their potency and specificity. Epitope mapping revealed that the binding site is a key determinant of neutralization potency, rather than affinity alone. The most potent nanobodies bind to the receptor binding motif of the RBD, directly preventing interaction with the host cell receptor ACE2, and we identify two exceptionally potent members of this category (with monomeric IC50s around 13 and 16 ng/ml). Other nanobodies bind to a more conserved epitope on the side of the RBD, and are able to potently neutralize the SARS-CoV-2 founder virus (42 ng/ml), the beta variant (B.1.351/501Y.V2) (35 ng/ml), and also cross-neutralize the more distantly related SARS-CoV-1 (0.46 μg/ml). The approach presented here is well suited for the screening of phage libraries to identify functional nanobodies for various biomedical and biochemical applications.

SARS-CoV-2 Variants of Concern (VOCs) with resistance to neutralizing antibodies are threatening to undermine vaccine efficacy. Vaccination and infection have led to widespread humoral immunity against the pandemic founder (Wu-Hu-1). Against this background, it is critical to assess the outcomes of subsequent immunization with variant antigens. It is not yet clear whether heterotypic boosts would be compromised by original antigenic sin, where pre-existing responses to a prior variant dampen responses to a new one, or whether the memory B cell repertoire would bridge the gap between Wu-Hu-1 and VOCs. We show, in macaques immunized with Wu-Hu-1 spike, that a single dose of adjuvanted beta variant receptor binding domain (RBD) protein broadens neutralizing antibody responses to heterologous VOCs. Passive transfer of plasma sampled after Wu-Hu-1 spike immunization only partially protects K18-hACE2 mice from lethal challenge with a beta variant isolate, whereas plasma sampled following heterotypic RBD boost protects completely against disease., Graphical Abstract, The emergence and spread of antibody-resistant SARS-CoV-2 Variants of Concern (VOCs) threatens to diminish vaccine efficacy. Sheward et al. show, in rhesus macaques and K18-hACE2 mice, that reduced vaccine protection against VOCs can be restored by broadening antibody responses with a third, heterotypic RBD booster immunization.

Rhinovirus (RV) infections are associated with asthma exacerbations. MicroRNA‐146a and microRNA‐146b (miR‐146a/b) are anti‐inflammatory miRNAs that suppress signaling through the nuclear factor kappa B (NF‐κB) pathway and inhibit pro‐inflammatory chemokine production in primary human bronchial epithelial cells (HBECs). In the current study, we aimed to explore whether miR‐146a/b could regulate cellular responses to RVs in HBECs and airways during RV‐induced asthma exacerbation. We demonstrated that expression of miR‐146a/b and pro‐inflammatory chemokines was increased in HBECs and mouse airways during RV infection. However, transfection with cell‐penetrating peptide (CPP)‐miR‐146a nanocomplexes before infection with RV significantly reduced the expression of the pro‐inflammatory chemokines CCL5, IL‐8 and CXCL1, increased interferon‐λ production, and attenuated infection with the green fluorescent protein (GFP)‐expressing RV‐A16 in HBECs. Concordantly, compared to wild‐type (wt) mice, Mir146a/b−/− mice exhibited more severe airway neutrophilia and increased T helper (Th)1 and Th17 cell infiltration in response to RV‐A1b infection and a stronger Th17 response with a less prominent Th2 response in house dust mite extract (HDM)‐induced allergic airway inflammation and RV‐induced exacerbation models. Interestingly, intranasal administration of CPP‐miR‐146a nanocomplexes reduced HDM‐induced allergic airway inflammation without a significant effect on the Th2/Th1/Th17 balance in wild‐type mice. In conclusion, the overexpression of miR‐146a has a strong anti‐inflammatory effect on RV infection in HBECs and a mouse model of allergic airway inflammation, while a lack of miR‐146a/b leads to attenuated type 2 cell responses in mouse models of allergic airway inflammation and RV‐induced exacerbation of allergic airway inflammation. Furthermore, our data indicate that the application of CPP‐miR‐146a nanocomplexes has therapeutic potential for targeting airway inflammation., miR‐146a has anti‐inflammatory properties in human bronchial epithelial cells and mouse airways during rhinovirus infection and in case of allergic inflammation. Particular cell penetrating peptide(CPP)‐miR‐146a nanocomplexes have therapeutic potential for targeting of airway inflammation.

Intestinal helminth parasites can alter immune responses to vaccines, other infections, allergens and autoantigens, indicating effects on host immune responses in distal barrier tissues. We herein show that C57BL/6 mice infected with the strictly intestinal nematode Heligmosomoides polygyrus have impaired capacity to initiate skin immune responses and develop skin-resident memory cells to mycobacterial antigens, both during infection and months after deworming therapy. Surprisingly, and in contrast to a previously noted loss of T cells in peripheral lymph nodes, the skin of worm-infected mice harboured higher numbers of CD4+ T cells compared to skin of uninfected controls. H. polygyrus-specific TH2 cells accumulated during infection and remained after worm expulsion. Accumulation of TH2 cells in the skin was associated with increased expression of the skin-homing chemokine receptors CCR4 and CCR10 on CD4+ T cells in blood and mesenteric lymph nodes draining intestinal tissues, indicating gut-to-skin trafficking of cells. In conclusion, we show that infection by a strictly intestinal helminth has long-term effects on immune cell composition and local immune responses to unrelated antigens in the skin, revealing a novel mechanism for T cell colonization and worm-mediated immunosuppression in this organ.

The emergence of SARS-CoV-2 Variants of Concern (VOCs) with mutations in key neutralizing antibody epitopes threatens to undermine vaccines developed against the pandemic founder variant (Wu-Hu-1). Widespread vaccine rollout and continued transmission are creating a population that has antibody responses of varying potency to Wu-Hu-1. Against this background, it is critical to assess the outcomes of subsequent immunization with variant antigens. It is not yet known whether heterotypic vaccine boosts would be compromised by original antigenic sin, where pre-existing responses to a prior variant dampen responses to a new one, or whether the primed memory B cell repertoire would bridge the gap between Wu-Hu-1 and VOCs. Here, we show that a single adjuvanted dose of receptor binding domain (RBD) protein from VOC 501Y.V2 (B.1.351) drives an extremely potent neutralizing antibody response capable of cross-neutralizing both Wu-Hu-1 and 501Y.V2 in rhesus macaques previously immunized with Wu-Hu-1 spike protein. Passive immunization with plasma sampled following this boost protected K18-hACE2 mice from lethal challenge with a 501Y.V2 clinical isolate, whereas only partial protection was afforded by plasma sampled after two Wu-Hu-1 spike immunizations.

Allergic disorders are caused by a combination of hereditary and environmental factors. The hygiene hypothesis postulates that early life microbial exposures impede the development of subsequent allergic disease. However, unambiguous evidence that microbes reduce the development of allergic disorders is still lacking. Recently developed ‘wildling’ mice contain a rich and diverse commensal and encounter a repertoire of microbes typical of the wild, with pathogenic potential. Here, we probed the hygiene hypothesis by comparing the development of allergic inflammation in wildlings to that of genetically identical mice lacking diverse microbial exposure. We find that wildlings develop stronger allergic inflammation in response to house dust mites with allergic T cell responses driven not only by cognate peptide antigens, but also by innate cytokines. In all, the results suggest that high microbial content and diversity potentiates, rather than restricts, allergic immune responses.One sentence summaryStrong allergic inflammation in the face of rich and diverse microbial exposures

Intestinal helminth parasites can alter immune responses to vaccines, other infections, allergens and autoantigens, implying effects on host immune responses in distal barrier tissues. We herein show that the skin of C57BL/6 mice infected with the strictly intestinal nematode Heligmosomoides polygyrus contain higher numbers of CD4

Allergy to dogs affects around ten percent of the population in developed countries. Immune therapy of allergic patients with dog allergen extracts has shown limited therapeutic benefit. Herein, we established a mouse model of dog allergy and tested the efficacy of a recombinant protein containing Can f 1, f 2, f 4 and f 6 as a sublingual immune therapy (SLIT). Repeated inhalation of dog extracts induced infiltration of the airways by TH2 cells, eosinophils and goblet cells, reminiscent of the house dust mite (HDM) model of asthma. However, dog allergen extracts also induced robust TH17 cell responses, which was associated with a high neutrophilic infiltration of the airways and promoted airway hyperresponsiveness more potently than HDM allergens. scRNA-Seq analysis of T helper cells responding to dog allergens identified several unique clusters with TH17 cells being hallmarked by the expression of several receptors including IL-17RE. Analysis of T cell receptors also depicted a high frequency of clones that were shared between TH17, TH2 and suppressive Treg cells, indicative of the plasticity of T helper cells in this model. Importantly, prophylactic SLIT reduced airway hyperresponsiveness and type 2-mediated inflammation in this model supporting the use of recombinant allergens in immune therapy.

The outbreak and spread of SARS-CoV-2 (Severe Acute Respiratory Syndrome coronavirus 2), the cause of coronavirus disease 2019 (COVID-19), is a current global health emergency and a prophylactic vaccine is needed urgently. The spike glycoprotein of SARS-CoV-2 mediates entry into host cells, and thus is a target for neutralizing antibodies and vaccine design. Here we show that adjuvanted protein immunization with SARS-CoV-2 spike trimers, stabilized in prefusion conformation, results in potent antibody responses in mice and rhesus macaques with neutralizing antibody titers orders of magnitude greater than those typically measured in serum from SARS-CoV-2 seropositive humans. Neutralizing antibody responses were observed after a single dose, with exceptionally high titers achieved after boosting. Furthermore, neutralizing antibody titers elicited by a dose-sparing regimen in mice were similar to those obtained from a high dose regimen. Taken together, these data strongly support the development of adjuvanted SARS-CoV-2 prefusion-stabilized spike protein subunit vaccines.

Antibody responses vary widely between individuals1, complicating the correct classification of low-titer measurements using conventional assay cut-offs. We found all participants in a clinically diverse cohort of SARS-CoV-2 PCR+ individuals (n=105) – and n=33 PCR+ hospital staff – to have detectable IgG specific for pre-fusion-stabilized spike (S) glycoprotein trimers, while 98% of persons had IgG specific for the receptor-binding domain (RBD). However, anti-viral IgG levels differed by several orders of magnitude between individuals and were associated with disease severity, with critically ill patients displaying the highest anti-viral antibody titers and strongest in vitro neutralizing responses. Parallel analysis of random healthy blood donors and pregnant women (n=1,000) of unknown serostatus, further demonstrated highly variable IgG titers amongst seroconverters, although these were generally lower than in hospitalized patients and included several measurements that scored between the classical 3 and 6SD assay cut-offs. Since the correct classification of seropositivity is critical for individual- and population-level metrics, we compared different probabilistic algorithms for their ability to assign likelihood of past infection. To do this, we used tandem anti-S and -RBD IgG responses from our PCR+ individuals (n=138) and a large cohort of historical negative controls (n=595) as training data, and generated an equal-weighted learner from the output of support vector machines and linear discriminant analysis. Applied to test samples, this approach provided a more quantitative way to interpret anti-viral titers over a large continuum, scrutinizing measurements overlapping the negative control background more closely and offering a probability-based diagnosis with potential clinical utility. Especially as most SARS-CoV-2 infections result in asymptomatic or mild disease, these platform-independent approaches improve individual and epidemiological estimates of seropositivity, critical for effective management of the pandemic and monitoring the response to vaccination.

Interleukin-9 expression by T helper cells marks allergic individuals who develop asthma (see the related Research Article by Seumois et al . ).

Upon activation, naïve CD4+ T cells differentiate into a number of specialized T helper (Th) cell subsets. Th2 cells are central players in immunity to helminths and are implicated in mediating the inflammatory pathology associated with allergies. The differentiation of Th2 cells is dependent on transcription factors such as GATA3 and STAT6, which prime Th2 cells for the secretion of interleukin- (IL-) 4, IL-5, and IL-13. Several lines of work now suggest that differentiating Th2 cells in the lymph node are potent IL-4 cytokine producers, but do not become competent IL-5- and IL-13-producing cells until after receiving cues from non-lymphoid tissue. It is evident that Th2 cells that enter tissues undergo considerable changes in chromatin architecture and gene expression, and that over this time, the metabolic requirements of these cells change considerably. Herein, we discuss the metabolic requirements of Th2 cells during their early and late differentiation, focusing on the impact of glucose and lipid metabolism, mTOR activation, the nuclear receptor PPAR-γ and several metabolites.

MeDALL (Mechanisms of the Development of ALLergy; EU FP7-CP-IP; Project No: 261357; 2010-2015) has proposed an innovative approach to develop early indicators for the prediction, diagnosis, prevention and targets for therapy. MeDALL has linked epidemiological, clinical and basic research using a stepwise, large-scale and integrative approach: MeDALL data of precisely phenotyped children followed in 14 birth cohorts spread across Europe were combined with systems biology (omics, IgE measurement using microarrays) and environmental data. Multimorbidity in the same child is more common than expected by chance alone, suggesting that these diseases share causal mechanisms irrespective of IgE sensitization. IgE sensitization should be considered differently in monosensitized and polysensitized individuals. Allergic multimorbidities and IgE polysensitization are often associated with the persistence or severity of allergic diseases. Environmental exposures are relevant for the development of allergy-related diseases. To complement the population-based studies in children, MeDALL included mechanistic experimental animal studies and in vitro studies in humans. The integration of multimorbidities and polysensitization has resulted in a new classification framework of allergic diseases that could help to improve the understanding of genetic and epigenetic mechanisms of allergy as well as to better manage allergic diseases. Ethics and gender were considered. MeDALL has deployed translational activities within the EU agenda.

Drennan et al. use a new mouse to show that A20-deficient NKT cells are hyperresponsive to TCR-dependent stimuli and have severely impaired NKT cell development., Natural killer T (NKT) cells are innate lymphocytes that differentiate into NKT1, NKT2, and NKT17 sublineages during development. However, the signaling events that control NKT sublineage specification and differentiation remain poorly understood. Here, we demonstrate that the ubiquitin-modifying enzyme TNFAIP3/A20, an upstream regulator of T cell receptor (TCR) signaling in T cells, is an essential cell-intrinsic regulator of NKT differentiation. A20 is differentially expressed during NKT cell development, regulates NKT cell maturation, and specifically controls the differentiation and survival of NKT1 and NKT2, but not NKT17, sublineages. Remaining A20-deficient NKT1 and NKT2 thymocytes are hyperactivated in vivo and secrete elevated levels of Th1 and Th2 cytokines after TCR ligation in vitro. Defective NKT development was restored by compound deficiency of MALT1, a key downstream component of TCR signaling in T cells. These findings therefore show that negative regulation of TCR signaling during NKT development controls the differentiation and survival of NKT1 and NKT2 cells.

CTLA-4 is required for CD4

Objective— Dyslipidemia is a component of the metabolic syndrome, an established risk factor for atherosclerotic cardiovascular disease, and is also observed in various autoimmune and chronic inflammatory conditions. However, there are limited opportunities to study the impact of acquired dyslipidemia on cardiovascular and immune pathology. Approach and Results— We designed a model system that allows for the conversion to a state of acute hyperlipidemia in adult life, so that the consequences of such a transition could be observed, through conditionally deleting APOE (apolipoprotein E) in the adult mouse. The transition to hypercholesterolemia was accompanied by adaptive immune responses, including the expansion of T lymphocyte helper cell 1, T follicular helper cell, and T regulatory subsets and the formation of germinal centers. Unlike steady-state Apoe −/− mice, abrupt loss of APOE induced rapid production of antibodies recognizing rheumatoid disease autoantigens. Genetic ablation of the germinal center reduced both autoimmunity and atherosclerosis, indicating that the immune response that follows loss of APOE is independent of atherosclerosis but nevertheless promotes plaque development. Conclusions— Our findings suggest that immune activation in response to hyperlipidemia could contribute to a wide range of inflammatory autoimmune diseases, including atherosclerosis.

Intestinal nematodes suppress immune responses in the context of allergy, gut inflammation, secondary infection and vaccination. Several mechanisms have been proposed for this suppression including alterations in Th2 cell differentiation and increased Treg cell suppressive function. In this study, we show that chronic nematode infection leads to reduced peripheral responses to vaccination because of a generalized reduction in the available responsive lymphocyte pool. We found that superficial skin-draining lymph nodes (LNs) in mice that are chronically infected with the intestinal nematode Heligmosomides polygyrus, do not reach the same cellularity as worm-free mice upon subsequent BCG infection in the skin. B cells and T cells, all declined in skin-draining LN of H. polygyrus-infected mice, resulting in LNs atrophy and altered lymphocyte composition. Importantly, anti-helminthic treatment improved lymphocyte numbers in skin-draining LN, indicating that time after de-worming is critical to regain full-scale LN cellularity. De-worming, and time for the skin LN to recover cellularity, also mended responses to Bacille Calmette-Guerin (BCG) in the LN draining the footpad injection site. Thus, our findings show that chronic nematode infection leads to a paucity of lymphocytes in peripheral lymph nodes, which acts to reduce the efficacy of immune responses at these sites., Author summary Infections with intestinal nematodes may be one explanation to why BCG vaccination is less effective in areas of high worm burden. In support of this, we recently showed that chronic intestinal nematode infection resulted in reduced immune responses and higher mycobacterial burden at distal sites. How a gut-dwelling nematode modulate immune responses in skin-draining lymph nodes (LN) was not clear. We found a reduced expansion of LN draining the BCG injected footpad in worm-infected animals, but no evidence for a spread of regulatory cells or cytokines to the BCG-draining LN. Interestingly, we found that mice chronically infected with intestinal worms had significantly smaller skin-draining LN. We propose that the expansion of mesenteric lymph nodes (mLN) occur at the cost of other LN, leading to atrophy of skin-draining LN. Expansion of the lymphocyte pool by IL-7, allowed worm-infected animals to maintain larger skin-draining LN while the mLN did not further expand. De-worming treatment of mice eventually restored the cellularity of skin-draining LN. This, however, took time indicating that effect of worms persisted long after the infection cleared. By de-worming and allowing time for the LN to recover, the cellular responses to BCG injection in the footpad were restored in the draining popliteal LN. Thus, paucity of lymphocytes at peripheral sites can explain impaired peripheral immune responses in worm-infected animals.

Summary Naive CD4+ T cells differentiate into functionally diverse T helper (Th) cell subsets. Th2 cells play a pathogenic role in asthma, yet a clear picture of their transcriptional profile is lacking. We performed single-cell RNA sequencing (scRNA-seq) of T helper cells from lymph node, lung, and airways in the house dust mite (HDM) model of allergic airway disease. scRNA-seq resolved transcriptional profiles of naive CD4+ T, Th1, Th2, regulatory T (Treg) cells, and a CD4+ T cell population responsive to type I interferons. Th2 cells in the airways were enriched for transcription of many genes, including Cd200r1, Il6, Plac8, and Igfbp7, and their mRNA profile was supported by analysis of chromatin accessibility and flow cytometry. Pathways associated with lipid metabolism were enriched in Th2 cells, and experiments with inhibitors of key metabolic pathways supported roles for glucose and lipid metabolism. These findings provide insight into the differentiation of pathogenic Th2 cells in the context of allergy.

CD4+Foxp3+ regulatory T cells (Treg cells) are largely autoreactive yet escape clonal deletion in the thymus. We demonstrate here that CD27–CD70 co-stimulation in the thymus rescues developing Treg cells from apoptosis and thereby promotes Treg cell generation. Genetic ablation of CD27 or its ligand CD70 reduced Treg cell numbers in the thymus and peripheral lymphoid organs, whereas it did not alter conventional CD4+Foxp3− T cell numbers. The CD27–CD70 pathway was not required for pre-Treg cell generation, Foxp3 induction, or mature Treg cell function. Rather, CD27 signaling enhanced positive selection of Treg cells within the thymus in a cell-intrinsic manner. CD27 signals promoted the survival of thymic Treg cells by inhibiting the mitochondrial apoptosis pathway. CD70 was expressed on Aire− and Aire+ medullary thymic epithelial cells (mTECs) and on dendritic cells (DCs) in the thymic medulla. CD70 on both mTECs and DCs contributed to Treg cell development as shown in BM chimera experiments with CD70-deficient mice. In vitro experiments indicated that CD70 on the CD8α+ subset of thymic DCs promoted Treg cell development. Our data suggest that mTECs and DCs form dedicated niches in the thymic medulla, in which CD27–CD70 co-stimulation rescues developing Treg cells from apoptosis, subsequent to Foxp3 induction by TCR and CD28 signals.

A hallmark of immunity to worm infections and many allergies is a strong type 2 immune response. This is characterized by the production of cytokines interleukin-5 (IL-5) and IL-13 by adaptive T helper 2 (TH2) cells and/or type 2 innate lymphoid cells. Peroxisome proliferator activated receptor-γ (PPAR-γ) is typically regarded as an anti-inflammatory factor. We report that TH2 cells express high levels of PPAR-γ in response to the allergen house dust mite and after infection with the parasite Heligmosomoides polygyrus Mice lacking PPAR-γ in T cells failed to effectively differentiate into IL-5- and IL-13-secreting cells and, hence, did not develop TH2 cell-associated pathologies, including goblet cell metaplasia and eosinophilia, in response to allergen challenge. Furthermore, these mice could not mount protective immune responses to nematode infection. In addition, mice lacking PPAR-γ in T cells had greatly reduced frequencies of TH2 cells in visceral adipose tissue. Mechanistically, PPAR-γ appeared to promote the expression of the IL-33 receptor on the surface of TH2 cells. These results pinpoint PPAR-γ as a factor that drives type 2 responses in allergy, worm infection, and visceral adipose tissue.

IL-21 has antitumor activity through actions on NK cells and CD8+ T cells, and is currently in clinical development for the treatment of cancer. However, no studies have addressed the role of endogenous IL-21 in tumor immunity. In this study, we have studied both primary and secondary immune responses in IL-21−/− and IL-21R−/− mice against several experimental tumors. We found intact immune surveillance toward methylcholanthrene-induced sarcomas in IL-21−/− and IL-21R−/− mice compared with wild-type mice and B16 melanomas showed equal growth kinetics and development of lung metastases. IL-21R−/− mice showed competent NK cell-mediated rejection of NKG2D ligand (Rae1β) expressing H-2b− RMAS lymphomas and sustained transition to CD8+ T cell-dependent memory against H-2b+ RMA lymphomas. α-Galactosylceramide stimulation showed equal expansion and activation of NKT and NK cells and mounted a powerful antitumor response in the absence of IL-21 signaling, despite reduced expression of granzyme B in NKT, NK, and CD8+ T cells. Surprisingly, host IL-21 significantly restricted the expansion of Ag-specific CD8+ T cells and inhibited primary CD8+ T cell immunity against OVA-expressing EG7 lymphomas, as well as the secondary expansion of memory CD8+ T cells. However, host IL-21 did not alter the growth of less immunogenic MC38 colon carcinomas with dim OVA expression. Overall, our results show that endogenous IL-21/IL-21R is not required for NK, NKT, and CD8+ T cell-mediated tumor immunity, but restricts Ag-specific CD8+ T cell expansion and rejection of immunogenic tumors, indicating novel immunosuppressive actions of this cytokine.

NKT cell subsets can be divided based on CD4 and NK1.1 expression and tissue of origin, but the developmental and functional relationships between the different subsets still are poorly understood. A comprehensive study of 19 cytokines across different NKT cell subsets revealed that no two NKT subpopulations exhibited the same cytokine profile, and, remarkably, the amounts of each cytokine produced varied by up to 100-fold or more among subsets. This study also revealed the existence of a population of CD4 − NK1.1 − NKT cells that produce high levels of the proinflammatory cytokine IL-17 within 2–3 h of activation. On intrathymic transfer these cells develop into mature CD4 − NK1.1 + but not into CD4 + NK1.1 + NKT cells, indicating that CD4 − NK1.1 − NKT cells include an IL-17–producing subpopulation, and also mark the elusive branch point for CD4 + and CD4 − NKT cell sublineages.

Recent studies have suggested that IL-21 is a key factor in the development of IL-17-producing CD4 T cells (Th17) and that the induction of experimental autoimmune encephalomyelitis, which depends on mounting an efficient Th17 response, is reportedly impaired in the absence of IL-21 signaling. In this study, we provide supportive in vitro evidence that IL-21 can drive Th17 responses in conjunction with TGF-β. However, more importantly we also demonstrate, using IL-21- and IL-21R-deficient mice, that IL-21 is not essential for the differentiation of Th17 cells in vitro and in vivo. Moreover, we show that IL-21- and IL-21R-deficient mice are highly susceptible to experimental autoimmune encephalomyelitis with disease scores that were comparable, or even higher at the peak of disease, to those of control mice. Thus, our results challenge the notion that IL-21 is a key factor in driving Th17 immunity and disease.

We showed previously that NKT cell–deficient TCR Jα18−/− mice are more susceptible to methylcholanthrene (MCA)-induced sarcomas, and that normal tumor surveillance can be restored by adoptive transfer of WT liver-derived NKT cells. Liver-derived NKT cells were used in these studies because of their relative abundance in this organ, and it was assumed that they were representative of NKT cells from other sites. We compared NKT cells from liver, thymus, and spleen for their ability to mediate rejection of the sarcoma cell line (MCA-1) in vivo, and found that this was a specialized function of liver-derived NKT cells. Furthermore, when CD4+ and CD4− liver-derived NKT cells were administered separately, MCA-1 rejection was mediated primarily by the CD4− fraction. Very similar results were achieved using the B16F10 melanoma metastasis model, which requires NKT cell stimulation with α-galactosylceramide. The impaired ability of thymus-derived NKT cells was due, in part, to their production of IL-4, because tumor immunity was clearly enhanced after transfer of IL-4–deficient thymus-derived NKT cells. This is the first study to demonstrate the existence of functionally distinct NKT cell subsets in vivo and may shed light on the long-appreciated paradox that NKT cells function as immunosuppressive cells in some disease models, whereas they promote cell-mediated immunity in others.

NKT cells are typically defined as CD1d-dependent T cells that carry an invariant TCR α-chain and produce high levels of cytokines. Traditionally, these cells were defined as NK1.1+ T cells, although only a few mouse strains express the NK1.1 molecule. A popular alternative marker for NKT cells has been DX5, an Ab that detects the CD49b integrin, expressed by most NK cells and a subset of T cells that resemble NKT cells. Interpretation of studies using DX5 as an NKT cell marker depends on how well DX5 defines NKT cells. Using a range of DX5 and other anti-CD49b Abs, we reveal major differences in reactivity depending on which Ab and which fluorochrome are used. The brightest, PE-conjugated reagents revealed that while most CD1d-dependent NKT cells expressed CD49b, they represented only a minority of CD49b+ T cells. Furthermore, CD49b+ T cell numbers were near normal in CD1d−/− mice that are completely deficient for NKT cells. CD1d tetramer− CD49b+ T cells differ from NKT cells by their activation and memory marker expression, tissue distribution, and CD4/CD8 coreceptor profile. Interestingly, both NKT cells and CD1d tetramer− CD49b+ T cells produce cytokines, but the latter are clearly biased toward Th1-type cytokines, in contrast to NKT cells that produce both Th1 and Th2 cytokines. Finally, we demonstrate that expression of CD49b by NKT cells does not dramatically alter with age, contrasting with earlier reports proposing DX5 as a maturation marker for NKT cells. In summary, our data demonstrate that DX5/CD49b is a poor marker for identifying CD1d-dependent NKT cells.

Upon their activation, CD4 T cells can differentiate into distinct T helper cell subsets with specialised functions. Different T helper cell subsets produce specific cytokines that mediate beneficial and sometimes detrimental effects, depending on the infection or disease setting. CD4 T-cell priming relies on signals delivered by the T-cell antigen receptor, co-stimulatory receptors and cytokine receptors on the CD4 T-cell surface. Cytokine receptors are well known to deliver instructive signals that direct T helper cell differentiation. However, it is less appreciated that co-stimulatory receptors also exert potent modulatory effects on this process. In this review, we outline the contribution of co-stimulatory and co-inhibitory receptors to the process of T helper cell differentiation, focusing on those pathways for which the underlying mechanisms are best known. Herein, we depict the physiological context of T-cell priming and emphasise the impact of cell-cell communication on directing T helper cell differentiation.

Asthma is a T helper 2 (Th2)-cell-mediated disease; however, recent findings implicate Th17 and innate lymphoid cells also in regulating airway inflammation. Herein, we have demonstrated profound interleukin-21 (IL-21) production after house dust mite (HDM)-driven asthma by using T cell receptor (TCR) transgenic mice reactive to Dermatophagoides pteronyssinus 1 and an IL-21GFP reporter mouse. IL-21-producing cells in the mediastinal lymph node (mLN) bore characteristics of T follicular helper (Tfh) cells, whereas IL-21(+) cells in the lung did not express CXCR5 (a chemokine receptor expressed by Tfh cells) and were distinct from effector Th2 or Th17 cells. Il21r(-/-) mice developed reduced type 2 responses and the IL-21 receptor (IL-21R) enhanced Th2 cell function in a cell-intrinsic manner. Finally, administration of recombinant IL-21 and IL-25 synergistically promoted airway eosinophilia primarily via effects on CD4(+) lymphocytes. This highlights an important Th2-cell-amplifying function of IL-21-producing CD4(+) T cells in allergic airway inflammation.