TSLP regulates intestinal immunity and inflammation in mouse models of helminth infection and colitis

TSLP acts on regulatory T cells to maintain their identity and limit allergic inflammation

Thymic stromal lymphopoietin (TSLP) is a type I cytokine that promotes allergic responses and mediates type 2 immunity. A balance between effector T cells (Teffs), which drive the immune response, and regulatory T cells (Tregs), which suppress the response, is required for proper immune homeostasis. Here, we report that TSLP differentially acts on Teffs versus Tregs to balance type 2 immunity. As expected, deletion of TSLP receptor (TSLPR) on all T cells (Cd4CreCrlf2fl/fl mice) resulted in lower numbers of T helper 2 (TH2) cells and diminished ovalbumin-induced airway inflammation, but selective deletion of TSLPR on Tregs (Foxp3YFP-Cre/YCrlf2fl/fl mice) resulted in increased interleukin-5 (IL-5)- and IL-13-secreting TH2 cells and lung eosinophilia. Moreover, TSLP augmented the expression of factors that stabilize Tregs. During type 2 immune responses, TSLPR-deficient Tregs acquired TH2-like properties, with augmented GATA3 expression and secretion of IL-13. TSLP not only is a driver of TH2 effector cells but also acts in a negative feedback loop, thus promoting the ability of Tregs to limit allergic inflammation.

Helminths in alternative therapeutics of inflammatory bowel disease

Inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis, is a nonspecific chronic inflammation of the gastrointestinal tract. Despite recent advances in therapeutics and newer management strategies, IBD largely remains untreatable. Helminth therapy is a promising alternative therapeutic for IBD that has gained some attention in the last two decades. Helminths have immunomodulatory effects and can alter the gut microbiota. The immunomodulatory effects include a strong Th2 immune response, T-regulatory cell response, and the production of regulatory cytokines. Although concrete evidence regarding the efficacy of helminth therapy in IBD is lacking, clinical studies and studies done in animal models have shown some promise. Most clinical studies have shown that helminth therapy is safe and easily tolerable. Extensive work has been done on the whipworm Trichuris, but other helminths, including Schistosoma, Trichinella, Heligmosomoides, and Ancylostoma, have also been explored for pre-clinical and animal studies. This review article summarizes the potential of helminth therapy as an alternative therapeutic or an adjuvant to the existing therapeutic procedures for IBD treatment.

From the bench to the clinic: basophils and type 2 epithelial cytokines of thymic stromal lymphopoietin and IL-33

Type 2 epithelial cytokines, including thymic stromal lymphopoietin and IL-33, play central roles in modulation of type 2 immune cells, such as basophils. Basophils are a small subset of granulocytes within the leukocyte population that predominantly exist in the blood. They have non-redundant roles in allergic inflammation in peripheral tissues such as the lung, skin and gut, where they increase and accumulate at inflammatory lesions and exclusively produce large amounts of IL-4, a type 2 cytokine. These inflammatory reactions are known to be, to some extent, phenocopies of infectious diseases of ticks and helminths. Recently, biologics related to both type 2 epithelial cytokines and basophils have been approved by the US Food and Drug Administration for treatment of allergic diseases. We summarised the roles of Type 2 epithelial cytokines and basophils in basic science to translational medicine, including recent findings.

Telocytes link epithelial nutrient sensing with amplification of the ILC2-tuft cell circuit

Group 2 innate lymphocytes (ILC2s) are prevalent in small intestine but engagement of type 2 immunity during basal processes are incompletely described. Thymic stromal lymphopoietin (TSLP), a cytokine implicated in ILC2 activation, was constitutively expressed in villus telocytes and crypt-associated trophocytes, specialized fibroblasts that sustain epithelial identity. Feeding increased TSLP and induced ILC2 type 2 cytokines that were attenuated by deletion of TSLP in PDGFRα + stromal cells or TSLP receptor on ILC2s. Mouse and human telocytes expressed receptors for glucagon-like peptide-2 (GLP-2), which is released by enteroendocrine cells (EECs) after eating. GLP-2 induced intestinal TSLP, TSLP-dependent ILC2 cytokine production, and tuft cell hyperplasia. The telocyte-alarmin relay couples EEC nutrient detection with amplification of a tuft cell chemosensory circuit that diversifies surveillance of ingested cargo.

One-Sentence Summary

Intestinal telocyte TSLP relays signals from enteroendocrine cells to ILC2s to amplify the tuft cell circuit in response to feeding.

Effect of maternal prebiotic supplementation on human milk immunological composition: Insights from the SYMBA study

BACKGROUND

Immunomodulatory proteins in human milk (HM) can shape infant immune development. However, strategies to modulate their levels are currently unknown. This study investigated whether maternal prebiotic supplementation alters the levels of immunomodulatory proteins in HM.

METHODS

The study was nested within the SYMBA double-blind randomized controlled trial (ACTRN12615001075572), which investigated the effects of maternal prebiotic (short-chain galacto-oligosaccharides/long-chain fructo-oligosaccharides) supplementation from <21 weeks gestation during pregnancy until 6 months postnatal during lactation on child allergic disease risk. Mother-child dyads receiving prebiotics (n = 46) or placebo (n = 54) were included in this study. We measured the levels of 24 immunomodulatory proteins in HM collected at 2, 4, and 6 months.

RESULTS

Cluster analysis showed that the overall immunomodulatory protein composition of milk samples from both groups was similar. At 2 months, HM of prebiotic-supplemented women had decreased levels of TGF-β1 and TSLP (95% CI: -17.4 [-29.68, -2.28] and -57.32 [-94.22, -4.7] respectively) and increased levels of sCD14 (95% CI: 1.81 [0.17, 3.71]), when compared to the placebo group. At 4 months, IgG1 was lower in the prebiotic group (95% CI: -1.55 [-3.55, -0.12]) compared to placebo group.

CONCLUSION

This exploratory study shows that prebiotic consumption by lactating mothers selectively alters specific immunomodulatory proteins in HM. This finding is crucial for understanding how prebiotic dietary recommendations for pregnant and lactating women can modify the immune properties of HM and potentially influence infant health outcomes through immune support from breastfeeding.

The interplay of co-infections in shaping COVID-19 severity: Expanding the scope beyond SARS-CoV-2

High mortality has been reported in severe cases of COVID-19. Emerging reports suggested that the severity is not only due to SARS-CoV-2 infection, but also due to coinfections by other pathogens exhibiting symptoms like COVID-19. During the COVID-19 pandemic, simultaneous respiratory coinfections with various viral (Retroviridae, Flaviviridae, Orthomyxoviridae, and Picoviridae) and bacterial (Mycobacteriaceae, Mycoplasmataceae, Enterobacteriaceae and Helicobacteraceae) families have been observed. These pathogens intensify disease severity by potentially augmenting SARSCoV-2 replication, inflammation, and modulation of signaling pathways. Coinfection emerges as a critical determinant of COVID-19 severity, principally instigated by heightened pro-inflammatory cytokine levels, as cytokine storm. Thereby, in co-infection scenario, the severity is also driven by the modulation of inflammatory signaling pathways by both pathogens possibly associated with interleukin, interferon, and cell death exacerbating the severity. In the current review, we attempt to understand the role of co- infections by other pathogens and their involvement in the severity of COVID-19.

Epithelial-immune cell crosstalk for intestinal barrier homeostasis

The intestinal barrier is mainly formed by a monolayer of epithelial cells, which forms a physical barrier to protect the gut tissues from external insults and provides a microenvironment for commensal bacteria to colonize while ensuring immune tolerance. Moreover, various immune cells are known to significantly contribute to intestinal barrier function by either directly interacting with epithelial cells or by producing immune mediators. Fulfilling this function of the gut barrier for mucosal homeostasis requires not only the intrinsic regulation of intestinal epithelial cells (IECs) but also constant communication with immune cells and gut microbes. The reciprocal interactions between IECs and immune cells modulate mucosal barrier integrity. Dysregulation of barrier function could lead to dysbiosis, inflammation, and tumorigenesis. In this overview, we provide an update on the characteristics and functions of IECs, and how they integrate their functions with tissue immune cells and gut microbiota to establish gut homeostasis.

Cooperation of ILC2s and TH2 cells in the expulsion of intestinal helminth parasites

Type 2 immune responses form a critical defence against enteric worm infections. In recent years, mouse models have revealed shared and unique functions for group 2 innate lymphoid cells and T helper 2 cells in type 2 immune response to intestinal helminths. Both cell types use similar innate effector functions at the site of infection, whereas each population has distinct roles during different stages of infection. In this Perspective, we review the underlying mechanisms used by group 2 innate lymphoid cells and T helper 2 cells to cooperate with each other and suggest an overarching model of the interplay between these cell types over the course of a helminth infection.

Epithelial regulation of microbiota-immune cell dynamics

The mammalian gastrointestinal tract hosts a diverse community of trillions of microorganisms, collectively termed the microbiota, which play a fundamental role in regulating tissue physiology and immunity. Recent studies have sought to dissect the cellular and molecular mechanisms mediating communication between the microbiota and host immune system. Epithelial cells line the intestine and form an initial barrier separating the microbiota from underlying immune cells, and disruption of epithelial function has been associated with various conditions ranging from infection to inflammatory bowel diseases and cancer. From several studies, it is now clear that epithelial cells integrate signals from commensal microbes. Importantly, these non-hematopoietic cells also direct regulatory mechanisms that instruct the recruitment and function of microbiota-sensitive immune cells. In this review, we discuss the central role that has emerged for epithelial cells in orchestrating intestinal immunity and highlight epithelial pathways through which the microbiota can calibrate tissue-intrinsic immune responses.

A Trefoil factor 3-Lingo2 axis restrains proliferative expansion of type-1 T helper cells during GI nematode infection

Host defense at the mucosal interface requires collaborative interactions between diverse cell lineages. Epithelial cells damaged by microbial invaders release reparative proteins such as the Trefoil factor family (TFF) peptides that functionally restore barrier integrity. However, whether TFF peptides and their receptors also serve instructive roles for immune cell function during infection is incompletely understood. Here, we demonstrate that the intestinal trefoil factor, TFF3, restrains (T cell helper) TH1 cell proliferation and promotes host-protective type 2 immunity against the gastrointestinal parasitic nematode Trichuris muris. Accordingly, T cell-specific deletion of the TFF3 receptor, leucine-rich repeat and immunoglobulin containing nogo receptor 2 (LINGO2), impairs TH2 cell commitment, allows proliferative expansion of interferon (IFN)g+ cluster of differentiation (CD)4+ TH1 cells and blocks normal worm expulsion through an IFNg-dependent mechanism. This study indicates that TFF3, in addition to its known tissue reparative functions, drives anti-helminth immunity by controlling the balance between TH1/TH2 subsets.

The epithelium takes the stage in asthma and inflammatory bowel diseases

The epithelium is a dynamic barrier and the damage to this epithelial layer governs a variety of complex mechanisms involving not only epithelial cells but all resident tissue constituents, including immune and stroma cells. Traditionally, diseases characterized by a damaged epithelium have been considered "immunological diseases," and research efforts aimed at preventing and treating these diseases have primarily focused on immuno-centric therapeutic strategies, that often fail to halt or reverse the natural progression of the disease. In this review, we intend to focus on specific mechanisms driven by the epithelium that ensure barrier function. We will bring asthma and Inflammatory Bowel Diseases into the spotlight, as we believe that these two diseases serve as pertinent examples of epithelium derived pathologies. Finally, we will argue how targeting the epithelium is emerging as a novel therapeutic strategy that holds promise for addressing these chronic diseases.

Critical influence of cytokines and immune cells in autoimmune gastritis

Gastric cancer (GC) is a type of the most common cancers. Autoimmune gastritis (AIG) and infection with Helicobacter pylori (HP) are the risk factors of triggering GC. With the emphasis on the treatment of HP, the incidence and prevalence of HP infection in population is decreasing. However, AIG lacks accurate diagnosis and treatment methods, which occupies high cancer risk factors. AIG is controlled by the immune environment of the stomach, including immune cells, inflammatory cells, and infiltrating intercellular material. Various immune cells or cytokines play a central role in the process of regulating gastric parietal cells. Abnormal expression levels of cytokines involved in immunity are bound to face the risk of tumorigenesis. Therefore, it is particularly important for preventing or treating AIG and avoiding the risk of gastric cancer to clarify the confirmed action mode of immune cells and cytokines in the gastric system. Herein, we briefly reviewed the role of the immune environment under AIG, focussing on describing these double-edged effects between immune cells and cytokines, and pointing out potential research challenges.

Influence of Early Life Factors, including breast milk Composition, on the Microbiome of Infants Born to Mothers with and without Inflammatory Bowel Disease

BACKGROUND AND AIMS

Herein we analysed the influence of early life factors, including breast milk composition, on the development of the intestinal microbiota of infants born to mothers with and without IBD.

METHODS

The MECONIUM [Exploring MEChanisms Of disease traNsmission In Utero through the Microbiome] study is a prospective cohort study consisting of pregnant women with or without IBD and their infants. Longitudinal stool samples were collected from babies and analysed using 16s rRNA sequencing and faecal calprotectin. Breast milk proteomics was profiled using Olink inflammation panel.

RESULTS

We analysed gut microbiota of 1034 faecal samples from 294 infants [80 born to mothers with and 214 to mothers without IBD]. Alpha diversity was driven by maternal IBD status and time point. The major influencers of the overall composition of the microbiota were mode of delivery, feeding, and maternal IBD status. Specific taxa were associated with these exposures, and maternal IBD was associated with a reduction in Bifidobacterium. In 312 breast milk samples [91 from mothers with IBD], mothers with IBD displayed lower abundance of proteins involved in immune regulation, such as thymic stromal lymphopoietin, interleukin-12 subunit beta, tumour necrosis factor-beta, and C-C motif chemokine 20, as compared with control mothers [adjusted p = 0.0016, 0.049, 0.049, and 0.049, respectively], with negative correlations with baby´s calprotectin, and microbiome at different time points.

CONCLUSION

Maternal IBD diagnosis influences microbiota in their offspring during early life. The proteomic profile of breast milk of women with IBD differs from that of women without IBD, with distinct time-dependent associations with baby's gut microbiome and feacal calprotectin.

Helminths' therapeutic potential to treat intestinal barrier dysfunction

The intestinal barrier is a dynamic multi-layered structure which can adapt to environmental changes within the intestinal lumen. It has the complex task of allowing nutrient absorption while limiting entry of harmful microbes and microbial antigens present in the intestinal lumen. Excessive entry of microbial antigens via microbial translocation due to 'intestinal barrier dysfunction' is hypothesised to contribute to the increasing incidence of allergic, autoimmune and metabolic diseases, a concept referred to as the 'epithelial barrier theory'. Helminths reside in the intestinal tract are in intimate contact with the mucosal surfaces and induce a range of local immunological changes which affect the layers of the intestinal barrier. Helminths are proposed to prevent, or even treat, many of the diseases implicated in the epithelial barrier theory. This review will focus on the effect of helminths on intestinal barrier function and explore whether this could explain the proposed health benefits delivered by helminths.

Type III interferon exerts thymic stromal lymphopoietin in mediating adaptive antiviral immune response

Previously, it was believed that type III interferon (IFN-III) has functions similar to those of type I interferon (IFN-I). However, recently, emerging findings have increasingly indicated the non-redundant role of IFN-III in innate antiviral immune responses. Still, the regulatory activity of IFN-III in adaptive immune response has not been clearly reported yet due to the low expression of IFN-III receptors on most immune cells. In the present study, we reviewed the adjuvant, antiviral, antitumor, and disease-moderating activities of IFN-III in adaptive immunity; moreover, we further elucidated the mechanisms of IFN-III in mediating the adaptive antiviral immune response in a thymic stromal lymphopoietin (TSLP)-dependent manner, a pleiotropic cytokine involved in mucosal adaptive immunity. Research has shown that IFN-III can enhance the antiviral immunogenic response in mouse species by activating germinal center B (GC B) cell responses after stimulating TSLP production by microfold (M) cells, while in human species, TSLP exerts OX40L for regulating GC B cell immune responses, which may also depend on IFN-III. In conclusion, our review highlights the unique role of the IFN-III/TSLP axis in mediating host adaptive immunity, which is mechanically different from IFN-I. Therefore, the IFN-III/TSLP axis may provide novel insights for clinical immunotherapy.

Thymic stromal lymphopoietin participates in the host response to intra-amniotic inflammation leading to preterm labor and birth

The aim of this study was to establish the role of thymic stromal lymphopoietin (TSLP) in the intra-amniotic host response of women with spontaneous preterm labor (sPTL) and birth. Amniotic fluid and chorioamniotic membranes (CAM) were collected from women with sPTL who delivered at term (n = 30) or preterm without intra-amniotic inflammation (n = 34), with sterile intra-amniotic inflammation (SIAI, n = 27), or with intra-amniotic infection (IAI, n = 17). Amnion epithelial cells (AEC), Ureaplasma parvum, and Sneathia spp. were also utilized. The expression of TSLP, TSLPR, and IL-7Rα was evaluated in amniotic fluid or CAM by RT-qPCR and/or immunoassays. AEC co-cultured with Ureaplasma parvum or Sneathia spp. were evaluated for TSLP expression by immunofluorescence and/or RT-qPCR. Our data show that TSLP was elevated in amniotic fluid of women with SIAI or IAI and expressed by the CAM. TSLPR and IL-7Rα had detectable gene and protein expression in the CAM; yet, CRLF2 was specifically elevated with IAI. While TSLP localized to all layers of the CAM and increased with SIAI or IAI, TSLPR and IL-7Rα were minimal and became most apparent with IAI. Co-culture experiments indicated that Ureaplasma parvum and Sneathia spp. differentially upregulated TSLP expression in AEC. Together, these findings indicate that TSLP is a central component of the intra-amniotic host response during sPTL.

Basophil responses in susceptible AKR mice upon infection with the intestinal helminth parasite Trichuris muris

Intestinal helminth infection promotes a Type 2 inflammatory response in resistant C57BL/6 mice that is essential for worm clearance. The study of inbred mouse strains has revealed factors that are critical for parasite resistance and delineated the role of Type 1 versus Type 2 immune responses in worm clearance. In C57BL/6 mice, basophils are key innate immune cells that promote Type 2 inflammation and are programmed via the Notch signalling pathway during infection with the helminth Trichuris muris. However, how the host genetic background influences basophil responses and basophil expression of Notch receptors remains unclear. Here we use genetically susceptible inbred AKR/J mice that have a Type 1-skewed immune response during T. muris infection to investigate basophil responses in a susceptible host. Basophil population expansion occurred in AKR/J mice even in the absence of fulminant Type 2 inflammation during T. muris infection. However, basophils in AKR/J mice did not robustly upregulate expression of the Notch2 receptor in response to infection as occurred in C57BL/6 mice. Blockade of the Type 1 cytokine interferon-γ in infected AKR/J mice was not sufficient to elicit infection-induced basophil expression of the Notch2 receptor. These data suggest that the host genetic background, outside of the Type 1 skew, is important in regulating basophil responses during T. muris infection in susceptible AKR/J mice.

TSLP/dendritic cell axis promotes CD4+ T cell tolerance to the gut microbiome

Thymic stromal lymphopoietin (TSLP) overexpression is widely associated with atopy. However, TSLP is expressed in normal barrier organs, suggesting a homeostatic function. To determine the function of TSLP in barrier sites, we investigated the impact of endogenous TSLP signaling on the homeostatic expansion of CD4+ T cells in adult mice. Surprisingly, incoming CD4+ T cells induced lethal colitis in adult Rag1-knockout animals that lacked the TSLP receptor (Rag1KOTslprKO). Endogenous TSLP signaling was required for reduced CD4+ T cell proliferation, Treg differentiation, and homeostatic cytokine production. CD4+ T cell expansion in Rag1KOTslprKO mice was dependent on the gut microbiome. The lethal colitis was rescued by parabiosis between Rag1KOTslprKO and Rag1KO animals and wild-type dendritic cells (DCs) suppressed CD4+ T cell-induced colitis in Rag1KOTslprKO mice. A compromised T cell tolerance was noted in TslprKO adult colon, which was exacerbated by anti-PD-1 and anti-CTLA-4 therapy. These results reveal a critical peripheral tolerance axis between TSLP and DCs in the colon that blocks CD4+ T cell activation against the commensal gut microbiome.

FGF21 Depletion Attenuates Colitis through Intestinal Epithelial IL-22-STAT3 Activation in Mice

Fibroblast growth factor 21 (FGF21) is a glucose and lipid metabolic regulator. Recent research revealed that FGF21 was also induced by inflammatory stimuli. Its role in inflammatory bowel disease (IBD) has not been investigated. In this study, an experimental IBD model was established in FGF21 knockout (KO) and wild-type (WT) mice by adding 2.5% (wt/vol) dextran sodium sulfate (DSS) to their drinking water for 7 days. The severity of the colitis and the inflammation of the mouse colon tissues were analyzed. In WT mice, acute DSS treatment induced an elevation in plasma FGF21 and a significant loss of body weight in a time-dependent manner. Surprisingly, the loss of body weight and the severity of the colitis induced by DSS treatment in WT mice were significantly attenuated in FGF21 KO mice. Colon and circulating pro-inflammatory factors were significantly lower in the FGF21 KO mice compared to the WT mice. As shown by BrdU staining, the FGF21 KO mice demonstrated increased colonic epithelial cell proliferation. DSS treatment reduced intestinal Paneth cell and goblet cell numbers in the WT mice, and this effect was attenuated in the FGF21 KO mice. Mechanistically, FGF21 deficiency significantly increased the signal transducer and activator of transcription (STAT)-3 activation in intestinal epithelial cells and increased the expression of IL-22. Further study showed that the expression of suppressor of cytokine signaling-2/3 (SOCS 2/3), a known feedback inhibitor of STAT3, was significantly inhibited in the DSS-treated FGF2 KO mice compared to the WT mice. We conclude that FGF21 deficiency attenuated the severity of DSS-induced acute colitis, which is likely mediated by enhancing the activation of the IL-22-STAT3 signaling pathway in intestinal epithelial cells.

Screening inflammatory protein biomarkers on premature infants with necrotizing enterocolitis

OBJECTIVE

This study aimed to explore potential inflammatory biomarkers for early prediction of necrotizing enterocolitis (NEC) in premature infants.

METHODS

Plasma samples were collected from premature infants with NEC (n = 30), sepsis (n = 29), and controls without infection (n = 29). The 92 inflammatory-related proteins were assessed via high-throughput OLINK proteomics platform.

RESULTS

There were 11 inflammatory proteins that significate differences (p < 0.05) among NEC, sepsis and control preterm infants, which include IL-8, TRAIL, IL-24, MMP-10, CCL20, CXCL1, OPG, TSLP, MCP-4, TNFSF14 and LIF. A combination of these 11 proteins could serve as differential diagnosis between NEC and control infants (AUC = 0.972), or between NEC and sepsis infants (AUC = 0.881). Furthermore, the combination of IL-8, OPG, MCP-4, IL-24, LIF and CCL20 could distinguish Stage II and III of NEC (AUC = 0.977). Further analysis showed the combination of IL-8, IL-24 and CCL20 have the best prediction value for NEC and control (AUC = 0.947), NEC and sepsis (AUC = 0.838) and different severity of NEC (AUC = 0.842).

CONCLUSION

Inflammatory proteins were different expressed in premature infants with NEC compared with controls or sepsis. Combining these proteins provide a higher diagnostic potential for preterm NEC infants.

Detection of CCL25 and the correlation between CCL25, CCL28, IL-7, and TSLP in human breast milk

In this study, CCL25, a chemokine that contributes to the immunological function of the thymus and intestines, was detected in human breast milk (HBM) for the first time. We then focused on the correlations of CCL25 with CCL28, TSLP, and IL-7, which were predicted to interact with CCL25 in HBM. We also compared their levels between primiparous and multiparous women. A total of 53 parturient women were recruited. Their HBM was collected during 0-5 days and at 1 month after parturition and the CCL25, CCL28, IL-7, and TSLP levels in the HBM were analyzed using ELISA. The results showed that CCL25 and TSLP levels were significantly higher in colostrum than in mature milk. Moreover, CCL28 and IL-7 levels in colostrum showed a positive correlation. These results indicate that CCL28 and IL-7 in colostrum might interact positively with each other when produced in the mammary glands during lactation. The findings also suggest that the level of parity has no effect on their levels in HBM. In conclusion, our results clarify that CCL25 is present in HBM and that the concentrations of CCL25 and TSLP are higher in colostrum than in mature milk. Moreover, the production of CCL28 and IL-7 might be closely correlated in human colostrum.

Development of an inhaled anti-TSLP therapy for asthma

Thymic stromal lymphopoietin (TSLP), an epithelial cell-derived cytokine, acts as a key mediator in airway inflammation and modulates the function of multiple cell types, including dendritic cells and group 2 innate lymphoid cells. TSLP plays a role in asthma pathogenesis as an upstream cytokine, and data suggest that TSLP blockade with the anti-TSLP monoclonal antibody, tezepelumab, could be efficacious in a broad asthma population. Currently approved asthma biologic therapies target allergic or eosinophilic disease and require phenotyping; therefore, an unmet need exists for a therapy that can address Type 2 (T2)-high and T2-low inflammation in asthma. All currently approved biologic treatments are delivered intravenously or subcutaneously; an inhaled therapy route that allows direct targeting of the lung with reduced systemic impact may offer advantages. Currently in development, ecleralimab (CSJ117) represents the first inhaled anti-TSLP antibody fragment that binds soluble TSLP and prevents TSLP receptor activation, thereby inhibiting further inflammatory signalling cascades. This anti-TSLP antibody fragment is being developed for patients with severe uncontrolled asthma despite standard of care inhaled therapy. A Phase IIa proof of concept study, using allergen bronchoprovocation as a model for asthma exacerbations, found that ecleralimab was well-tolerated and reduced allergen-induced bronchoconstriction in adult patients with mild asthma. These results suggest ecleralimab may be a promising, new therapeutic class for asthma treatment.

Role of thymic stromal lymphopoietin in allergy and beyond

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine that acts on multiple cell lineages, including dendritic cells, T cells, B cells, neutrophils, mast cells, eosinophils and innate lymphoid cells, affecting their maturation, survival and recruitment. It is best known for its role in promoting type 2 immune responses such as in allergic diseases and, in 2021, a monoclonal antibody targeting TSLP was approved for the treatment of severe asthma. However, it is now clear that TSLP has many other important roles in a variety of settings. Indeed, several genetic variants for TSLP are linked to disease severity, and chromosomal alterations in TSLP are common in certain cancers, indicating important roles of TSLP in disease. In this Review, we discuss recent advances in TSLP biology, highlighting how it regulates the tissue environment not only in allergic disease but also in infectious diseases, inflammatory diseases and cancer. Encouragingly, therapies targeting the TSLP pathway are being actively pursued for several diseases.

TSLP, IL-33, and IL-25: Not just for allergy and helminth infection

The release of cytokines from epithelial and stromal cells is critical for the initiation and maintenance of tissue immunity. Three such cytokines, thymic stromal lymphopoietin, IL-33, and IL-25, are important regulators of type 2 immune responses triggered by parasitic worms and allergens. In particular, these cytokines activate group 2 innate lymphoid cells, TH2 cells, and myeloid cells, which drive hallmarks of type 2 immunity. However, emerging data indicate that these tissue-associated cytokines are not only involved in canonical type 2 responses but are also important in the context of viral infections, cancer, and even homeostasis. Here, we provide a brief review of the roles of thymic stromal lymphopoietin, IL-33, and IL-25 in diverse immune contexts, while highlighting their relative contributions in tissue-specific responses. We also emphasize a biologically motivated framework for thinking about the integration of multiple immune signals, including the 3 featured in this review.

Early-Life Mebendazole Exposure Increases the Risk of Adult-Onset Ulcerative Colitis: A Population-Based Cohort Study

INTRODUCTION

According to the hygiene hypothesis, exposure to parasites may protect against inflammatory bowel disease (IBD). Our aim was to examine the risk of IBD with childhood exposure to mebendazole, a broad-spectrum antihelminthic agent.

METHODS

We conducted a population-based cohort study using prospectively collected historical data of all individuals born in Denmark between 1995 and 2018. We identified mebendazole exposure at age younger than 18 years and during early life (younger than 5 years). We performed adjusted Cox proportional hazards regression analysis to determine the risk of IBD, ulcerative colitis (UC), and Crohn's disease with mebendazole exposure after adjusting for potential confounders.

RESULTS

Of 1,520,290 individuals in the cohort, 615,794 had childhood or adolescence mebendazole exposure. One thousand five hundred fifty-five and 1,499 individuals were subsequently diagnosed with pediatric-onset and adult-onset IBD, respectively. On multivariable analysis, mebendazole exposure at age younger than 18 years did not affect pediatric-onset or adult-onset IBD risk (adjusted hazard ratio [aHR] 0.97, 95% confidence interval [CI] 0.87, 1.07, and 1.08, 95% CI 0.97, 1.19, respectively). On limiting mebendazole exposure to age younger than 5 years while there was no association with pediatric-onset IBD (aHR 0.98, 95% CI 0.87, 1.11), adult-onset IBD risk was increased (aHR 1.17, 95% CI 1.04, 1.31). This increase in risk was driven by UC (aHR 1.32, 95% CI 1.12, 1.55), but not Crohn's disease (1.03, 95% CI 0.87, 1.22).

DISCUSSION

Early-life mebendazole exposure is associated with an increase in the risk of adult-onset UC. These findings suggest the importance of early-life exposures in shaping the risk of IBD later in life.

Roseburia intestinalis stimulates TLR5-dependent intestinal immunity against Crohn's disease

Background

Methods

Findings

Interpretation

Funding

Crosstalk between epithelium, myeloid and innate lymphoid cells during gut homeostasis and disease

The gut epithelium not only provides a physical barrier to separate a noxious outside from a sterile inside but also allows for highly regulated interactions between bacteria and their products, and components of the immune system. Homeostatic maintenance of an intact epithelial barrier is paramount to health, requiring an intricately regulated and highly adaptive response of various cells of the immune system. Prolonged homeostatic imbalance can result in chronic inflammation, tumorigenesis and inefficient antitumor immune control. Here we provide an update on the role of innate lymphoid cells, macrophages and dendritic cells, which collectively play a critical role in epithelial barrier maintenance and provide an important linkage between the classical innate and adaptive arm of the immune system. These interactions modify the capacity of the gut epithelium to undergo continuous renewal, safeguard against tumor formation and provide feedback to the gut microbiome, which acts as a seminal contributor to cellular homeostasis of the gut.

Effects of physical distancing by COVID-19 pandemic on diet quality, neurological and immunological markers, and fecal microbiota of Brazilian older women

Physical distancing was used to prevent transmission of COVID-19, however there are concerns that this may promote harmful impacts on health, such as reduced levels of physical practice and changes in food intake and gut microbiota composition. This study evaluated the impacts of 6 months physical distancing on Brazilian older women upon body mass index (BMI), strength, physical activity level (IPAQ), eating habits, neurological markers (brain-derived neurotrophic factor-BDNF and cortisol), cytokines (IL-2, IL-5, IL-6, IL-10, interferon-IFN-γ, tumor necrosis factor-TNF-α), aging-associated markers (vascular endothelial growth factor-VEGF, insulin-like growth factor-IGF-1, klotho and thymic stromal lymphopoietin-TSLP), besides specific groups of fecal microbiota. Fifteen women, over 60 years old, residents of São Paulo state (Brazil), were evaluated in March and in September 2020. The older adult women, with a mean age 66 ± 6.2 years presented significantly increased BMI and high effect size for non-protective foods consumption, reduced light physical activity and strength 6 months following the physical distancing. Furthermore, the serum concentration of IFN-γ, IGF-1, and IFN-γ/IL-5 were significantly higher, while lower concentration of IL-2 and IL-5 were observed 6 months after the physical distancing. Significant increase was noted only to Blautia spp. abundance after 6 months of physical distancing. Several correlations were observed at both before and after physical distancing, however, interestingly, many of them were lost or inverted 6 months following, while new ones emerged. Taken together, these results showed that lifestyle changes and stress conditions addressed by physical distancing from the COVID-19 pandemic impacted the health of older women included in the present study. Therefore, future follow-up studies are essential to propose interventions in order to restore the health conditions observed before the pandemic period, and thus to maintain the quality of life of older adults in different socioeconomic contexts.

"Every cell is an immune cell; contributions of non-hematopoietic cells to anti-helminth immunity"

Helminths are remarkably successful parasites that can invade various mammalian hosts and establish chronic infections that can go unnoticed for years despite causing severe tissue damage. To complete their life cycles, helminths migrate through multiple barrier sites that are densely populated by a complex array of hematopoietic and non-hematopoietic cells. While it is clear that type 2 cytokine responses elicited by immune cells promote worm clearance and tissue healing, the actions of non-hematopoietic cells are increasingly recognized as initiators, effectors and regulators of anti-helminth immunity. This review will highlight the collective actions of specialized epithelial cells, stromal niches, stem, muscle and neuroendocrine cells as well as peripheral neurons in the detection and elimination of helminths at mucosal sites. Studies dissecting the interactions between immune and non-hematopoietic cells will truly provide a better understanding of the mechanisms that ensure homeostasis in the context of helminth infections.

Effects of helminths on the human immune response and the microbiome

Helminths have evolved sophisticated immune regulating mechanisms to prevent rejection by their mammalian host. Our understanding of how the human immune system responds to these parasites remains poor compared to mouse models of infection and this limits our ability to develop vaccines as well as harness their unique properties as therapeutic strategies against inflammatory disorders. Here, we review how recent studies on human challenge infections, self-infected individuals, travelers, and endemic populations have improved our understanding of human type 2 immunity and its effects on the microbiome. The heterogeneity of responses between individuals and the limited access to tissue samples beyond the peripheral blood are challenges that limit human studies on helminths, but also provide opportunities to transform our understanding of human immunology. Organoids and single-cell sequencing are exciting new tools for immunological analysis that may aid this pursuit. Learning about the genetic and immunological basis of resistance, tolerance, and pathogenesis to helminth infections may thus uncover mechanisms that can be utilized for therapeutic purposes.

Emerging role for thymic stromal lymphopoietin-responsive regulatory T cells in colorectal cancer progression in humans and mice

Recruitment of regulatory T cells (T_regs) to tumors is a hallmark of cancer progression. Tumor-derived factors, such as the cytokine thymic stromal lymphopoietin (TSLP), can influence T_reg function in tumors. In our study, we identified a subset of T_regs expressing the receptor for TSLP (TSLPR⁺ T_regs) that were increased in colorectal tumors in humans and mice and largely absent in adjacent normal colon. This T_reg subset was also found in the peripheral blood of patients with colon cancer but not in the peripheral blood of healthy control subjects. Mechanistically, we found that this T_reg subset coexpressed the interleukin-33 (IL-33) receptor [suppressor of tumorigenicity 2 (ST2)] and had high programmed cell death 1 (PD-1) and cytotoxic lymphocyte-associated antigen 4 (CTLA-4) expression, regulated in part by the transcription factor Mef2c. T_reg-specific deletion of TSLPR, but not ST2, was associated with a reduction in tumor number and size with concomitant increase in T_H1 cells in tumors in chemically induced mouse models of colorectal cancer. Therapeutic blockade of TSLP using TSLP-specific monoclonal antibodies effectively inhibited the progression of colorectal tumors in this mouse model. Collectively, these data suggest that TSLP controls the progression of colorectal cancer through regulation of tumor-specific T_reg function and represents a potential therapeutic target that requires further investigation.

Defining the early stages of intestinal colonisation by whipworms

Whipworms are large metazoan parasites that inhabit multi-intracellular epithelial tunnels in the large intestine of their hosts, causing chronic disease in humans and other mammals. How first-stage larvae invade host epithelia and establish infection remains unclear. Here we investigate early infection events using both Trichuris muris infections of mice and murine caecaloids, the first in-vitro system for whipworm infection and organoid model for live helminths. We show that larvae degrade mucus layers to access epithelial cells. In early syncytial tunnels, larvae are completely intracellular, woven through multiple live dividing cells. Using single-cell RNA sequencing of infected mouse caecum, we reveal that progression of infection results in cell damage and an expansion of enterocytes expressing of Isg15, potentially instigating the host immune response to the whipworm and tissue repair. Our results unravel intestinal epithelium invasion by whipworms and reveal specific host-parasite interactions that allow the whipworm to establish its multi-intracellular niche.

Inhalant Mammal-Derived Lipocalin Allergens and the Innate Immunity

A major part of important mammalian respiratory allergens belongs to the lipocalin family of proteins. By this time, 19 respiratory mammalian lipocalin allergens have been registered in the WHO/IUIS Allergen Nomenclature Database. Originally, lipocalins, small extracellular proteins (molecular mass ca. 20 kDa), were characterized as transport proteins but they are currently known to exert a variety of biological functions. The three-dimensional structure of lipocalins is well-preserved, and lipocalin allergens can exhibit high amino acid identities, in several cases more than 50%. Lipocalins contain an internal ligand-binding site where they can harbor small principally hydrophobic molecules. Another characteristic feature is their capacity to bind to specific cell-surface receptors. In all, the physicochemical properties of lipocalin allergens do not offer any straightforward explanations for their allergenicity. Allergic sensitization begins at epithelial barriers where diverse insults through pattern recognition receptors awaken innate immunity. This front-line response is manifested by epithelial barrier-associated cytokines which together with other components of immunity can initiate the sensitization process. In the following, the crucial factor in allergic sensitization is interleukin (IL)-4 which is needed for stabilizing and promoting the type 2 immune response. The source for IL-4 has been searched widely. Candidates for it may be non-professional antigen-presenting cells, such as basophils or mast cells, as well as CD4+ T cells. The synthesis of IL-4 by CD4+ T cells requires T cell receptor engagement, i.e., the recognition of allergen peptides, which also provides the specificity for sensitization. Lipocalin and innate immunity-associated cell-surface receptors are implicated in facilitating the access of lipocalin allergens into the immune system. However, the significance of this for allergic sensitization is unclear, as the recognition by these receptors has been found to produce conflicting results. As to potential adjuvants associated with mammalian lipocalin allergens, the hydrophobic ligands transported by lipocalins have not been reported to enhance sensitization while it is justified to suppose that lipopolysaccharide plays a role in it. Taken together, type 2 immunity to lipocalin allergens appears to be a harmful immune response resulting from a combination of signals involving both the innate and adaptive immunities.

Food for thought - ILC metabolism in the context of helminth infections

Helminths are multicellular ancient organisms residing as parasites at mucosal surfaces of their host. Through adaptation and co-evolution with their hosts, helminths have been able to develop tolerance mechanisms to limit inflammation and avoid expulsion. The study of helminth infections as an integral part of tissue immunology allowed us to understand fundamental aspects of mucosal and barrier immunology, which led to the discovery of a new group of tissue-resident immune cells, innate lymphoid cells (ILC), over a decade ago. Here, we review the intricate interplay between helminth infections and type 2 ILC (ILC2) biology, discuss the host metabolic adaptation to helminth infections and the metabolic pathways fueling ILC2 responses. We hypothesize that nutrient competition between host and helminths may have prevented chronic inflammation in the past and argue that a detailed understanding of the metabolic restraints imposed by helminth infections may offer new therapeutic avenues in the future.

Oxytocin suppresses epithelial cell-derived cytokines production and alleviates intestinal inflammation in food allergy

Food allergy is a growing healthcare problem worldwide, but prophylactic options and regulatory therapies are limited. Oxytocin (OXT), conventionally acknowledged as a hormone, was recently proven to have potent anti-inflammatory and immunomodulatory activities in certain diseases. Here, we reported the novel function and its underlying mechanisms of OXT on food allergy in vivo and in vitro. We showed that the levels of OXT were elevated in ovalbumin (OVA)-allergic mice and patients with food allergy. In HT-29 cells, OXT inhibited the production of the epithelial cell-derived cytokines thymic stromal lymphopoietin (TSLP), interleukin (IL)-25 and IL-33 by suppressing NF-κB signaling, in which β-arrestin2 participated. These functions of OXT were abolished by oxytocin receptor (OXTR) depletion. Treating OVA-induced BALB/c mice with OXT suppressed TSLP, IL-25 and IL-33 production and attenuated systemic anaphylaxis and intestinal inflammation. OXTR-/- mice showed extreme increases in TSLP, IL-25 and IL-33 levels as well as severe systemic anaphylaxis and intestinal inflammation. In conclusion, through OXTRs, OXT has a promising antiallergic effect on experimental food allergy by suppressing epithelial TSLP, IL-25 and IL-33 production via inhibiting NF-κB signaling and upregulating β-arrestin2 expression. Our study provides a new therapeutic perspective for food allergy in humans.

Directly recruited GATA6 + peritoneal cavity macrophages contribute to the repair of intestinal serosal injury

Recruitment of bone marrow derived monocytes via bloodstream and their subsequent conversion to CX3CR1⁺ macrophages in response to intestinal injury is dependent on CCR2, Nr4a1, and the microbiome. This process is critical for proper tissue repair; however, GATA6⁺ peritoneal cavity macrophages might represent an alternative, more readily available source of mature and functional myeloid cells at the damaged intestinal locations. Here we show, using spinning-disk confocal microscopy, that large F4/80^hiGATA6⁺ peritoneal cavity macrophages promptly accumulate at damaged intestinal sites upon intestinal thermal injury and upon dextran sodium sulfate induced colitis in mice via a direct route from the peritoneal cavity. In contrast to bloodstream derived monocytes/macrophages, cavity macrophages do not depend on CCR2, Nr4a1 or the microbiome for recruitment, but rather on the ATP-release and exposed hyaluronan at the site of injury. They participate in the removal of necrotic cells, revascularization and collagen deposition and thus resolution of tissue damage. In summary, peritoneal cavity macrophages represent a rapid alternative route of intestinal tissue repair to traditional monocyte-derived macrophages.

Upon intestinal injury, bone marrow derived monocytes are recruited to the damaged site through the bloodstream. Authors here show that peritoneal cavity macrophages directly migrate to the damaged intestine in an ATP and hyaluronan dependent manner, and participate in the restoration of tissue integrity.

Type 2 immunity in intestinal homeostasis and inflammatory bowel disease

Type 2 immune responses commonly emerge during allergic reactions or infections with helminth parasites. Most of the cytokines associated with type 2 immune responses are IL-4, IL-5, and IL13, which are mainly produced by T helper 2 cells (T_H2), eosinophils, basophils, mast cells, and group 2 innate lymphoid cells (ILC2s). Over the course of evolution, humans have developed type 2 immune responses to fight infections and to protect tissues from the potential collateral damage caused by inflammation. For example, worm parasites induce potent type 2 immune responses, which are needed to simultaneously clear the pathogen and to promote tissue repair following injury. Due to the strong type 2 immune responses induced by helminths, which can promote tissue repair in the damaged epithelium, their use has been suggested as a possible treatment for inflammatory bowel disease (IBD); however, the role of type 2 immune responses in the initiation and progression of IBD is not fully understood. In this review, we discuss the molecular and cellular mechanisms that regulate type 2 immune responses during intestinal homeostasis, and we briefly discuss the scarce evidence linking type 2 immune responses with the aetiology of IBD.

Pilot Study of Anti-Th2 Immunotherapy for the Treatment of Breast Cancer-Related Upper Extremity Lymphedema

Recent studies suggest that Th2 cells play a key role in the pathology of secondary lymphedema by elaborating cytokines such as IL4 and IL13. The aim of this study was to test the efficacy of QBX258, a monoclonal IL4/IL13 neutralizing antibody, in women with breast cancer-related lymphedema (BCRL). We enrolled nine women with unilateral stage I/II BCRL and treated them once monthly with intravenous infusions of QBX258 for 4 months. We measured limb volumes, bioimpedance, and skin tonometry, and analyzed the quality of life (QOL) using a validated lymphedema questionnaire (Upper Limb Lymphedema 27, ULL-27) before treatment, immediately after treatment, and 4 months following treatment withdrawal. We also obtained 5 mm skin biopsies from the normal and lymphedematous limbs before and after treatment. Treatment was well-tolerated; however, one patient with a history of cellulitis developed cellulitis during the trial and was excluded from further analysis. We found no differences in limb volumes or bioimpedance measurements after drug treatment. However, QBX258 treatment improved skin stiffness (p < 0.001) and improved QOL measurements (Physical p < 0.05, Social p = 0.01). These improvements returned to baseline after treatment withdrawal. Histologically, treatment decreased epidermal thickness, the number of proliferating keratinocytes, type III collagen deposition, infiltration of mast cells, and the expression of Th2-inducing cytokines in the lymphedematous skin. Our limited study suggests that immunotherapy against Th2 cytokines may improve skin changes and QOL of women with BCRL. This treatment appears to be less effective for decreasing limb volumes; however, additional studies are needed.

Trichuris muris Model: Role in Understanding Intestinal Immune Response, Inflammation and Host Defense

Several parasites have evolved to survive in the human intestinal tract and over 1 billion people around the world, specifically in developing countries, are infected with enteric helminths. Trichuris trichiura is one of the world’s most common intestinal parasites that causes human parasitic infections. Trichuris muris, as an immunologically well-defined mouse model of T. trichiura, is extensively used to study different aspects of the innate and adaptive components of the immune system. Studies on T. muris model offer insights into understanding host immunity, since this parasite generates two distinct immune responses in resistant and susceptible strains of mouse. Apart from the immune cells, T. muris infection also influences various components of the intestinal tract, especially the gut microbiota, mucus layer, epithelial cells and smooth muscle cells. Here, we reviewed the different immune responses generated by innate and adaptive immune components during acute and chronic T. muris infections. Furthermore, we discussed the importance of studying T. muris model in understanding host–parasite interaction in the context of alteration in the host’s microbiota, intestinal barrier, inflammation, and host defense, and in parasite infection-mediated modulation of other immune and inflammatory diseases.

Acceleration of Trichinella spiralis worm expulsion by leukotriene B4 receptor binding inhibition

AIMS

Helminth infection typically induces a Th2 inflammatory response that is characterized by eosinophilia, high levels of IgE and mast cells. LTB4 is generated from innate immune cells, such as neutrophils, macrophages and mast cells, in response to a range of stimuli. It mainly acts on myeloid leukocytes, inducing the activation of integrins, adhesion to endothelium walls, and chemotaxis.

METHODS AND RESULTS

The objective of the present study was to determine the role of the LTB4 receptor in Trichinella spiralis expulsion. We treated mice with the LTB4 receptor antagonist before infection with T. spiralis. We observed that the number of mast cells and worm infection decreased following treatment with the BLT antagonist during the intestinal phase. We also demonstrated that blocking the LTB4 receptor inhibited neutrophil and eosinophil infiltration.

CONCLUSIONS

Further studies are required to investigate the specific mechanism of mast cell number decrease and worm infection and the in vitro interactions between LTB4 and worm expulsion.

Thymic stromal lymphopoietin contributes to protection of mice from Strongyloides venezuelensis infection by CD4+ T cell-dependent and -independent pathways

When animals are infected with helminthic parasites, resistant hosts mount type II helper T (Th2) immune responses to expel worms. Recent studies have clearly shown that epithelial cell-derived cytokines contribute to the induction of Th2 immune responses. Here we demonstrate the role of endogenous thymic stromal lymphopoietin (TSLP) for protection against Strongyloides venezuelensis (S. venezuelensis) infection, utilizing TSLP receptor-deficient Crlf2-/- mice. The number of eggs per gram of feces (EPG) and worm burden were significantly higher in Crlf2-/- mice than in wild type (WT) mice. S. venezuelensis infection induced Tslp mRNA expression in the skin, lung, and intestine and also facilitated the accumulation of mast cells in the intestine in a TSLP-dependent manner. Furthermore, CD4+ T cells from S. venezuelensis-infected Crlf2-/- mice showed diminished capacity to produce Th2 cytokines in the early stage of infection. Finally, CD4+ cell-depleted Crlf2-/- mice still showed higher EPG counts and worm burden than CD4+ cell-depleted WT mice, indicating that TSLP contributes to protecting mice against S. venezuelensis infection in both CD4+ T cell-dependent and -independent manners.

Dual function of Langerhans cells in skin TSLP-promoted TFH differentiation in mouse atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is among the most common chronic inflammatory skin diseases, usually occurring early in life, and often preceding other atopic diseases such as asthma. TH2 has been believed to play a crucial role in cellular and humoral response in AD, but accumulating evidence has shown that follicular helper T cell (TFH), a critical player in humoral immunity, is associated with disease severity and plays an important role in AD pathogenesis.

OBJECTIVES

This study aimed at investigating how TFHs are generated during the pathogenesis of AD, particularly what is the role of keratinocyte-derived cytokine TSLP and Langerhans cells (LCs).

METHODS

Two experimental AD mouse models were employed: (1) triggered by the overproduction of TSLP through topical application of MC903, and (2) induced by epicutaneous allergen ovalbumin (OVA) sensitization.

RESULTS

This study demonstrated that the development of TFHs and germinal center (GC) response were crucially dependent on TSLP in both the MC903 model and the OVA sensitization model. Moreover, we found that LCs promoted TFH differentiation and GC response in the MC903 model, and the depletion of Langerin+ dendritic cells (DCs) or selective depletion of LCs diminished the TFH/GC response. By contrast, in the model with OVA sensitization, LCs inhibited TFH/GC response and suppressed TH2 skin inflammation and the subsequent asthma. Transcriptomic analysis of Langerin+ and Langerin- migratory DCs revealed that Langerin+ DCs became activated in the MC903 model, whereas these cells remained inactivated in OVA sensitization model.

CONCLUSIONS

Together, these studies revealed a dual functionality of LCs in TSLP-promoted TFH and TH2 differentiation in AD pathogenesis.

The Fate of Activated Group 2 Innate Lymphoid Cells

Group 2 innate lymphoid cells (ILC2s) reside in both mucosal and non-mucosal tissues and play critical roles in the first line of defense against parasites and irritants such as allergens. Upon activation by cytokines released from epithelial and stromal cells during tissue damage or stimulation, ILC2s produce copious amounts of IL-5 and IL-13, leading to type 2 inflammation. Over the past 10 years, ILC2 involvement in a variety of human diseases has been unveiled. However, questions remain as to the fate of ILC2s after activation and how that might impact their role in chronic inflammatory diseases such as asthma and fibrosis. Here, we review studies that have revealed novel properties of post-activation ILC2s including the generation of immunological memory, exhausted-like phenotype, transdifferentiation and activation-induced migration.

Thymic stromal lymphopoietin limits primary and recall CD8+ T-cell anti-viral responses

Thymic stromal lymphopoietin (TSLP) is a cytokine that acts directly on CD4+ T cells and dendritic cells to promote progression of asthma, atopic dermatitis, and allergic inflammation. However, a direct role for TSLP in CD8+ T-cell primary responses remains controversial and its role in memory CD8+ T cell responses to secondary viral infection is unknown. Here, we investigate the role of TSLP in both primary and recall responses in mice using two different viral systems. Interestingly, TSLP limited the primary CD8+ T-cell response to influenza but did not affect T cell function nor significantly alter the number of memory CD8+ T cells generated after influenza infection. However, TSLP inhibited memory CD8+ T-cell responses to secondary viral infection with influenza or acute systemic LCMV infection. These data reveal a previously unappreciated role for TSLP on recall CD8+ T-cell responses in response to viral infection, findings with potential translational implications.

IL-17A both initiates, via IFNγ suppression, and limits the pulmonary type-2 immune response to nematode infection

Nippostrongylus brasiliensis is a well-defined model of type-2 immunity but the early lung-migrating phase is dominated by innate IL-17A production. In this study, we confirm previous observations that Il17a-KO mice infected with N. brasiliensis exhibit an impaired type-2 immune response. Transcriptional profiling of the lung on day 2 of N. brasiliensis infection revealed an increased Ifng signature in Il17a-KO mice confirmed by enhanced IFNγ protein production in lung lymphocyte populations. Depletion of early IFNγ rescued type-2 immune responses in the Il17a-KO mice demonstrating that IL-17A-mediated suppression of IFNγ promotes type-2 immunity. Notably, later in infection, once the type-2 response was established, IL-17A limited the magnitude of the type-2 response. IL-17A regulation of type-2 immunity was lung-specific and infection with Trichuris muris revealed that IL-17A promotes a type-2 immune response in the lung even when infection is restricted to the intestine. Together our data reveal IL-17A as a major regulator of pulmonary type-2 immunity such that IL-17A supports early development of a protective type-2 response by suppression of IFNγ but subsequently limits excessive type-2 responses. A failure of this feedback loop may contribute to conditions such as severe asthma, characterised by combined elevation of IL-17 and type-2 cytokines.

Heterogeneity in the initiation, development and function of type 2 immunity

Type 2 immune responses operate under varying conditions in distinct tissue environments and are crucial for protection against helminth infections and for the maintenance of tissue homeostasis. Here we explore how different layers of heterogeneity influence type 2 immunity. Distinct insults, such as allergens or infections, can induce type 2 immune responses through diverse mechanisms, and this can have heterogeneous consequences, ranging from acute or chronic inflammation to deficits in immune regulation and tissue repair. Technological advances have provided new insights into the molecular heterogeneity of different developmental lineages of type 2 immune cells. Genetic and environmental heterogeneity also contributes to the varying magnitude and quality of the type 2 immune response during infection, which is an important determinant of the balance between pathology and disease resolution. Hence, understanding the mechanisms underlying the heterogeneity of type 2 immune responses between individuals and between different tissues will be crucial for treating diseases in which type 2 immunity is an important component.