SURFACTANT PROTEIN A: AN INNATE IMMUNE MODULATOR AND THERAPEUTIC IN ASTHMA.

Surfactant Protein A (SP-A) is an innate immune modulator produced by the lung with known protective effects against bacteria and viruses. Its role in asthma, an inflammatory lung disease that affects 10% of the world's population, is not entirely known. In this review, we demonstrate that SP-A confers protection against exposure to interleukin-13, a type 2 cytokine integral to eosinophilic asthma, in a mouse model of SP-A deficiency, a house dust mite model of asthma, and in human bronchial epithelial cells from participants with asthma. We also show that small peptides derived from SP-A, such as the major allele of single nucleotide polymorphism (SNP) rs1965708, which includes the carbohydrate recognition domain of SP-A2 at position 223, reduce airway hyperresponsiveness, airway eosinophils, and mucus in a mouse model of asthma. These data suggest that SP-A has beneficial effects relevant to asthma and that an SP-A peptide may have a new therapeutic use in asthma.

IL-13 and IL-17A activate ß1 integrin through an NF-kB/Rho kinase/PIP5K1γ pathway to enhance force transmission in airway smooth muscle.

Integrin activation resulting in enhanced adhesion to the extracellular matrix plays a key role in fundamental cellular processes. Although integrin activation has been extensively studied in circulating cells such as leukocytes and platelets, much less is known about the regulation and functional impact of integrin activation in adherent cells such as smooth muscle. Here, we show that two different asthmagenic cytokines, IL-13 and IL-17A, activate type I and IL-17 cytokine receptor families, respectively, to enhance adhesion of airway smooth muscle. These cytokines also induce activation of ß1 integrins detected by the conformation-specific antibody HUTS-4. Moreover, HUTS-4 binding is increased in the smooth muscle of patients with asthma compared to nonsmokers without lung disease, suggesting a disease-relevant role for integrin activation in smooth muscle. Indeed, integrin activation induced by the ß1-activating antibody TS2/16, the divalent cation manganese, or the synthetic peptide ß1-CHAMP that forces an extended-open integrin conformation dramatically enhances force transmission in smooth muscle cells and airway rings even in the absence of cytokines. We demonstrate that cytokine-induced activation of ß1 integrins is regulated by a common pathway of NF-κB-mediated induction of RhoA and its effector Rho kinase, which in turn stimulates PIP5K1γ-mediated synthesis of PIP2 at focal adhesions, resulting in ß1 integrin activation. Taken together, these data identify a pathway by which type I and IL-17 cytokine receptor family stimulation induces functionally relevant ß1 integrin activation in adherent smooth muscle and help to explain the exaggerated force transmission that characterizes chronic airway diseases such as asthma.

[Expression of prostacyclin receptor in chronic rhinosinusitis and its relationship with type 2 inflammation].

Objective:The purpose of this study is to explore the expression of prostacyclin receptor（IP） in patients with chronic rhinosinusitis（CRS） and its possible association with type 2 inflammation. Methods:HE staining was used to observe the morphological changes of nasal mucosa, qRT-PCR was used to detect the expression of IP in polyps and nasal mucosa, and IHC was used to detect the expression of IP, IL-4, IL-5 and IL-13 in polyps and nasal mucosa. Results:Compared with the control group, the nasal mucosa of patients with various types of CRS was obviously thickened, accompanied by inflammatory cell infiltration and gland hyperplasia. The statistical results of IHC showed that the expression levels of IL-4, IL-5 and IL-13 in CRS group were significantly higher than those in control group（P<0.05）, and the IP expression in control group was significantly higher than that in ECRS group and non-ECRS group（P<0.05）. The IP expression in ECRS group was negatively correlated with IL-4, IL-5 and IL-13. The results of qRT-PCR showed that the expression of IP mRNA in control group was significantly higher than that in ECRS group and non-ECRS group（P<0.05）. Conclusion:IL-4, IL-5 and IL-13 are highly expressed in the nasal mucosa of CRS patients, while IP is poorly expressed in the nasal mucosa of CRS patients, and IP is negatively correlated with IL-4, IL-5 and IL-13, suggesting that IP is related to the occurrence and development of type 2 inflammation and may be a potential therapeutic target for CRS patients.

Interleukin Profiling in Atopic Dermatitis and Chronic Nodular Prurigo.

The clinical manifestations of atopic dermatitis (AD) and chronic nodular prurigo (CNPG) include pruritus and eczema/lesions, posing significant challenges for patients. Th2 cells and ILC2, marked by cytokine production-particularly IL-4/13-are crucial therapeutic targets. Despite displaying a dose-dependent lack of pruritus induction post-injection, IL-13 acts through the IL-13Rα1 and IL-13Rα2 receptor system. Our study focused on investigating ex vivo skin biopsies in AD (n = 17), CNPG (n = 14) and healthy controls (HC; n = 10), examining the gene expression landscape of interleukins linked with pruritus (IL-13, IL-4, IL-31) and their corresponding receptors. Compared to HC, results revealed a significant upregulation of IL-4, IL-13, and IL-13RA1 in AD, whereas CNPG did not show increased IL13 expression. Notably, the decoy receptor IL-13RA2 displayed intriguing patterns, with AD showing a marked increase compared to both HC and CNPG. Positive correlations between receptor expression and itch intensity and hyperkinesis sensation underscore clinical relevance, potentially serving as biomarkers. The findings suggest a pivotal role of IL-4 and IL-13, along with IL-13RA1, in pruritus pathogenesis in both entities, while IL-13 upregulation in AD is countered by IL-13RA2. The comparable expression of IL-13RA2 to HC in CNPG suggests the absence of this regulatory mechanism, potentially worsening the disease and leading to prolonged scratching behavior. These insights illuminate the intricate interplay of interleukins and receptors in different pruritus phenotypes, laying the groundwork for understanding underlying mechanisms and offering avenues for therapeutic intervention.

Dupilumab: Mechanism of action, clinical, and translational science.

Allergic disease prevalence has increased globally with the subset of type 2 inflammatory diseases playing a substantial role. Type 2 inflammatory diseases may differ in clinical presentation, but they exhibit shared pathophysiology that is targeted by the unique pharmacology of dupilumab. Dupilumab binds to the interleukin (IL)-4 receptor alpha subunit (IL-4Rα) that blocks IL-4 and IL-13 signaling, two key drivers of type 2 inflammation. Herein, we review the mechanism of action and pharmacology of dupilumab, and the clinical evidence that led to the regulatory approvals of dupilumab for the treatment of numerous type 2 inflammatory diseases: atopic dermatitis, asthma, chronic rhinosinusitis with nasal polyposis, eosinophilic esophagitis, and prurigo nodularis.

Select amino acids recover cytokine-altered ENaC function in human bronchial epithelial cells.

The airway epithelium plays a pivotal role in regulating mucosal immunity and inflammation. Epithelial barrier function, homeostasis of luminal fluid, and mucociliary clearance are major components of mucosal defense mechanisms. The epithelial sodium channel (ENaC) is one of the key players in controlling airway fluid volume and composition, and characteristic cytokines cause ENaC and barrier dysfunctions following pulmonary infections or allergic reactions. Given the limited understanding of the requisite duration and magnitude of cytokines to affect ENaC and barrier function, available treatment options for restoring normal ENaC activity are limited. Previous studies have demonstrated that distinct amino acids can modulate epithelial ion channel activities and barrier function in intestines and airways. Here, we have investigated the time- and concentration-dependent effect of representative cytokines for Th1- (IFN-γ and TNF-α), Th2- (IL-4 and IL-13), and Treg-mediated (TGF-ß1) immune responses on ENaC activity and barrier function in human bronchial epithelial cells. When cells were exposed to Th1 and Treg cytokines, ENaC activity decreased gradually while barrier function remained largely unaffected. In contrast, Th2 cytokines had an immediate and profound inhibitory effect on ENaC activity that was subsequently followed by epithelial barrier disruption. These functional changes were associated with decreased membrane protein expression of α-, ß-, and γ-ENaC, and decreased mRNA levels of ß- and γ-ENaC. A proprietary blend of amino acids was developed based on their ability to prevent Th2 cytokine-induced ENaC dysfunction. Exposure to the select amino acids reversed the inhibitory effect of IL-13 on ENaC activity by increasing mRNA levels of ß- and γ-ENaC, and protein expression of γ-ENaC. This study indicates the beneficial effect of select amino acids on ENaC activity in an in vitro setting of Th2-mediated inflammation suggesting these amino acids as a novel therapeutic approach for correcting this condition.

Single-cell transcriptomics analysis of bullous pemphigoid unveils immune-stromal crosstalk in type 2 inflammatory disease.

Bullous pemphigoid (BP) is a type 2 inflammation- and immunity-driven skin disease, yet a comprehensive understanding of the immune landscape, particularly immune-stromal crosstalk in BP, remains elusive. Herein, using single-cell RNA sequencing (scRNA-seq) and in vitro functional analyzes, we pinpoint Th2 cells, dendritic cells (DCs), and fibroblasts as crucial cell populations. The IL13-IL13RA1 ligand-receptor pair is identified as the most significant mediator of immune-stromal crosstalk in BP. Notably, fibroblasts and DCs expressing IL13RA1 respond to IL13-secreting Th2 cells, thereby amplifying Th2 cell-mediated cascade responses, which occurs through the specific upregulation of PLA2G2A in fibroblasts and CCL17 in myeloid cells, creating a positive feedback loop integral to immune-stromal crosstalk. Furthermore, PLA2G2A and CCL17 contribute to an increased titer of pathogenic anti-BP180-NC16A autoantibodies in BP patients. Our work provides a comprehensive insight into BP pathogenesis and shows a mechanism governing immune-stromal interactions, providing potential avenues for future therapeutic research.

Unveiling the value of C-reactive protein as a severity biomarker and the IL4/IL13 pathway as a therapeutic target in recessive dystrophic epidermolysis bullosa: A multiparametric cross-sectional study.

Patients with recessive dystrophic epidermolysis bullosa (RDEB) experience numerous complications, which are exacerbated by inflammatory dysregulation and infection. Understanding the immunological mechanisms is crucial for selecting medications that balance inflammation control and immunocompetence. In this cross-sectional study, aiming to identify potential immunotherapeutic targets and inflammatory biomarkers, we delved into the interrelationship between clinical severity and systemic inflammatory parameters in a representative RDEB cohort. Encompassing 84 patients aged 1-67 and spanning all three Epidermolysis Bullosa Disease Activity and Scarring Index (EBDASI) severity categories, we analysed the interrelationship of infection history, standard inflammatory markers, systemic cytokines and Ig levels to elucidate their roles in RDEB pathophysiology. Our findings identify C-reactive protein as an excellent biomarker for disease severity in RDEB. A type 2 inflammatory profile prevails among moderate and severe RDEB patients, correlating with dysregulated circulating IgA and IgG. These results underscore the IL4/IL13 pathways as potential evidence-based therapeutic targets. Moreover, the complete inflammatory scenario aligns with Staphylococcus aureus virulence mechanisms. Concurrently, abnormalities in IgG, IgE and IgM levels suggest an immunodeficiency state in a substantial number of the cohort's patients. Our results provide new insights into the interplay of infection and immunological factors in the pathogenesis of RDEB.

Effect of 2 weeks rest-pause on oxidative stress and inflammation in female basketball players.

Intense exercise leads to increased production of free radicals, resulting in an inflammatory response in athletes. For this reason, it was decided to investigate whether a single intensive exercise until exhaustion applied after a 2-week rest period would result in a violation of the pro-oxidant-antioxidant balance. Twenty-seven trained female basketball players (age: 16.55 ± 0.96 years, body mass: 66.40 ± 13.68 kg, height: 173.45 ± 5.14 cm) were enrolled to the study following the application of inclusion and exclusion criteria. Study was conducted at the end of the competitive training phase. Participants underwent incremental treadmill exercise, with blood samples collected before the test, immediately post-exercise, and after a 3-h restitution period. Total antioxidant capacity (TAC) levels increased significantly after exercise and remained unchanged after 3 h. Concentration of interleukin-10 (IL-10) and creatine kinase (CK) significantly increased after exercise and then decreased. Concentration of interleukin-2 (IL-2) was significantly reduced immediately and 3 h after exercise, while interleukin-13 (IL-13), interleukin-1α (IL-1α), and tryptophan (TRP) decreased 3 h after exercise. No significant changes were observed in other biochemical parameters. Obtained results show an increased antioxidant capacity which reduced oxidative stress and inflammation in response to intense exercise indicating that rested athletes have a high adaptation and elevated tolerance to effort.

IL-4 and IL-13 are not involved in IL-31-induced itch-associated scratching behaviour in mice.

Itchy skin or pruritus is a common cutaneous symptom that causes an urge to scratch, and the role of interleukins (IL) in itchy skin has been widely studied. IL-4 and IL-13 are known to induce chronic itch. Similarly, the direct role of IL-31 in inducing itch has been demonstrated in clinical situations such as atopic dermatitis and prurigo nodularis. Moreover, IL-4 receptor α antibodies (dupilumab) and IL-31 receptor A antibodies (nemolizumab) inhibit pruritus. However, the interplay between these ILs in pruritus remains unclear. Therefore, we investigated the reciprocal effects of these cytokines on pruritus in mice. The intradermal administration of IL-31 induced itch-associated scratching behaviour in a dose-dependent manner. Interestingly, the amount of IL-31 and IL-4/IL-13, co-administration or 30 min pre-administration of IL-4/IL-13 and intradermal or intravenous pre-administration of IL-4 did not affect IL-31-induced itch-associated scratching behaviour when it was observed for 30 min, 2 h, 24 h or 48 h. Pre-administration of neutralising antibodies against IL-4 and IL-13 also did not affect IL-31-induced itch-associated scratching behaviour. These results suggest that IL-31 can induce itching independently of IL-4 and IL-13 in vivo.

SLAM-family receptors promote resolution of ILC2-mediated inflammation.

Type 2 innate lymphoid cells (ILC2) initiate early allergic inflammation in the lung, but the factors that promote subsequent resolution of type 2 inflammation and prevent prolonged ILC2 activation are not fully known. Here we show that SLAM-family receptors (SFR) play essential roles in this process. We demonstrate dynamic expression of several SFRs on ILC2s during papain-induced type 2 immunity in mice. SFR deficiency exacerbates ILC2-driven eosinophil infiltration in the lung, and results in a significant increase in IL-13 production by ILC2s exclusively in mediastinal lymph nodes (MLN), leading to increased dendritic cell (DC) and TH2 cell numbers. In MLNs, we observe more frequent interaction between ILC2s and bystander T cells, with T cell-expressed SFRs (especially SLAMF3 and SLAMF5) acting as self-ligands to suppress IL-13 production by ILC2s. Mechanistically, homotypic engagement of SFRs at the interface between ILC2s and T cells delivers inhibitory signaling primarily mediated by SHIP-1. This prevents activation of NF-κB, driven by IL-7 and IL-33, two major drivers of ILC2-mediated type 2 immunity. Thus, our study shows that an ILC2-DC-TH2 regulatory axis may promote the resolution of pulmonary type 2 immune responses, and highlights SLAMF3/SLAMF5 as potential therapeutic targets for ameliorating type 2 immunity.

Blockade of CD80/CD86-CD28 co-stimulation augments the inhibitory function of peptide antigen-specific regulatory T cells.

Mixed lymphocyte culture under the blockade of CD80/CD86-CD28 co-stimulation induces anergic (completely hyporesponsive) T cells with immune suppressive function (inducible suppressing T cells: iTS cells). Previously, iTS cell therapy has demonstrated outstanding benefits in clinical trials for organ transplantation. Here, we examined whether peptide antigen-specific iTS cells are inducible. DO 11.10 iTS cells were obtained from splenocytes of BALB/c DO 11.10 mice by stimulation with OVA peptide and antagonistic anti-CD80/CD86 mAbs. When DO 11.10 iTS or Foxp3- DO 11.10 iTS cells were stimulated with OVA, these cells produced IL-13, but not IL-4. DO 11.10 iTS cells decreased IL-4 and increased IL-13 production from OVA-stimulated naïve DO 11.10 splenocytes. When Foxp3+ DO 11.10 iTS cells were prepared, these cells significantly inhibited the production of IL-4 and IL-13 compared with freshly isolated Foxp3+ DO 11.10 T cells. Moreover, an increase in the population expressing OX40, ICOS, and 4-1BB suggested activation of Foxp3+ DO 11.10 iTS cells. Thus, blockade of CD80/CD86-CD28 co-stimulation during peptide antigen stimulation augments the inhibitory function of Foxp3+ regulatory T cells, and does not induce anergic Foxp3- conventional T cells. Peptide-specific Foxp3+ regulatory iTS cells could be useful for the treatment of allergic and autoimmune diseases without adverse effects.

Evaluation of the maternal systemic immune system during frozen euploid embryo transfer according to cycle outcome.

Infertility affects 15 % of couples in the US, and many turn to assisted reproductive technologies, including in vitro fertilization and subsequent frozen embryo transfer (FET) to become pregnant. This study aimed to perform a broad assessment of the maternal immune system to determine if there are systemic differences on the day of FET in cycles that result in a live birth compared to those that do not. Women undergoing FET of euploid embryos were recruited and blood was collected on the day of FET as well as at early timepoints in pregnancy. Sixty immune and angiogenic proteins were measured in plasma, and gene expression of 92 immune-response related genes were evaluated in peripheral blood mononuclear cells (PBMCs). We found plasma concentrations of interleukin-13 (IL-13) and macrophage derived chemokine (MDC) were significantly lower on the day of FET in cycles that resulted in a live birth. We also found genes encoding C-C chemokine receptor type 5 (CCR5), CD8 subunit alpha (CD8A) and SMAD family member 3 (SMAD3) were upregulated in PBMCs on the day of FET in cycles that resulted in live birth. Measurements of immune mediators from maternal blood could serve as prognostic markers during FET to guide clinical decision making and further our understanding of implantation failure.

Ectoine Enhances Mucin Production Via Restoring IL-13/IFN-γ Balance in a Murine Dry Eye Model.

Purpose: This study aimed to explore protective effects and potential mechanism of ectoine, a natural osmoprotectant, on ocular surface mucin production in dry eye disease. Methods: A dry eye model was established in C57BL/6 mice exposed to desiccating stress (DS) with untreated (UT) mice as controls. DS mice were topically treated with 2.0% ectoine or PBS vehicle. Corneal epithelial defects were assessed by Oregon Green Dextran (OGD) fluorescent staining. Conjunctival goblet cells, ocular mucins, and T help (Th) cytokines were evaluated by immunofluorescent staining or ELISA, and RT-qPCR. Results: Compared with UT mice, corneal epithelial defects were detected as strong punctate OGD fluorescent staining in DS mice with vehicle, whereas ectoine treatment largely reduced OGD staining to near-normal levels. Conjunctival goblet cell density and cell size decreased markedly in DS mice, but was significantly recovered by ectoine treatment. The protein production and mRNA expression of two gel-forming secreted MUC5AC and MUC2, and 4 transmembrane mucins, MUC1, MUC4, MUC16, and MUC15, largely decreased in DS mice, but was restored by ectoine. Furthermore, Th2 cytokine IL-13 was inhibited, whereas Th1 cytokine IFN-γ was stimulated at protein and mRNA levels in conjunctiva and draining cervical lymph nodes (CLNs) of DS mice, leading to decreased IL-13/IFN-γ ratio. Interestingly, 2.0% ectoine reversed their alternations and restored IL-13/IFN-γ balance. Conclusions: Our findings demonstrate that topical ectoine significantly reduces corneal damage, and enhances goblet cell density and mucin production through restoring imbalanced IL-13/IFN-γ signaling in murine dry eye model. This suggests therapeutic potential of natural osmoprotectant ectoine for dry eye disease.

The stimulation of TH2 cells results in increased IL-5 and IL-13 production via the H4 receptor.

BACKGROUND: Atopic dermatitis (AD) is a chronic inflammatory skin disease resulting in decreased quality of life. Histamine and specifically the H4 receptor play a key role in the inflammatory process in AD and serve as targets for novel therapeutic approaches. OBJECTIVE: In the present study we aimed to elucidate the immunopathological mechanisms with which the H4 receptor impacts TH2 cells and contributes to AD pathophysiology. METHODS: Total CD4+ T cells obtained from healthy or AD individuals and in vitro differentiated TH2 cells were cultured under different conditions and the mRNA expression or protein production of target molecules were determined using quantitative real-time PCR and ELISA. RESULTS: H4 receptor mRNA expression was upregulated concentration dependent upon IL-4 stimulation in in vitro differentiated TH2 cells progressively during the differentiation. Transcriptomic analysis of in vitro differentiated TH2 versus TH1 cells revealed that the H4 receptor among other genes represents one of the highly upregulated genes in TH2 cells. Most importantly, increased amounts of IL-5 and IL-13 mRNA expression were detected in in vitro differentiated TH2 cells as well as protein secretion in the presence of histamine or of the H4 receptor-selective-agonist when compared to the untreated control. CONCLUSION: We show for the first time an H4 receptor dependent upregulation of the pro-inflammatory cytokines IL-5 and IL-13 in human TH2 cells by histamine. This suggests that the blockade of the H4 receptor may lead to downregulation of these cytokines and amelioration of AD symptoms as reported in first clinical studies.

Peroxidase-mediated mucin cross-linking drives pathologic mucus gel formation in IL-13-stimulated airway epithelial cells.

Mucus plugs occlude airways to obstruct airflow in asthma. Studies in patients and in mouse models show that mucus plugs occur in the context of type 2 inflammation, and studies in human airway epithelial cells (HAECs) show that IL-13-activated cells generate pathologic mucus independently of immune cells. To determine how HAECs autonomously generate pathologic mucus, we used a magnetic microwire rheometer to characterize the viscoelastic properties of mucus secreted under varying conditions. We found that normal HAEC mucus exhibited viscoelastic liquid behavior and that mucus secreted by IL-13-activated HAECs exhibited solid-like behavior caused by mucin cross-linking. In addition, IL-13-activated HAECs shows increased peroxidase activity in apical secretions, and an overlaid thiolated polymer (thiomer) solution shows an increase in solid behavior that was prevented by peroxidase inhibition. Furthermore, gene expression for thyroid peroxidase (TPO), but not lactoperoxidase (LPO), was increased in IL-13-activated HAECs and both TPO and LPO catalyze the formation of oxidant acids that cross-link thiomer solutions. Finally, gene expression for TPO in airway epithelial brushings was increased in patients with asthma with high airway mucus plug scores. Together, our results show that IL-13-activated HAECs autonomously generated pathologic mucus via peroxidase-mediated cross-linking of mucin polymers.

Tonic type 2 immunity is a critical tissue checkpoint controlling autoimmunity in the skin.

Immunoregulatory mechanisms established in the lymphoid organs are vital for preventing autoimmunity. However, the presence of similar mechanisms in non-lymphoid tissues remains unclear. Through transcriptomic and lipidomic analyses, we find a negative association between psoriasis and fatty acid metabolism, as well as Th2 signature. Homeostatic expression of liver X receptor (LXR) and peroxisome proliferator-activated receptor gamma (PPARγ) is essential for maintaining fatty acid metabolism and for conferring resistance to psoriasis in mice. Perturbation of signal transducer and activator of transcription 6 (STAT6) diminishes the homeostatic levels of LXR and PPARγ. Furthermore, mice lacking STAT6, interleukin 4 receptor alpha (IL-4Rα), or IL-13, but not IL-4, exhibit increased susceptibility to psoriasis. Under steady state, innate lymphoid cells (ILCs) are the primary producers of IL-13. In human skin, inhibiting tonic type 2 immunity exacerbates psoriasis-like inflammation and IL-17A, while activating LXR or PPARγ inhibits them. Hence, we propose that tonic type 2 immunity, driven by IL-13-producing ILCs, represents a crucial tissue checkpoint that represses autoimmunity and maintains lipid homeostasis in the skin.

Chronic skin damage induces small intestinal damage via IL-13-induced apoptosis.

The gut-skin axis has recently been widely recognized, and both the gut and skin have been found to affect each other through a bidirectional connection; however, the precise mechanisms remain to be elucidated. Therefore, we aimed to investigate the effects of chronic skin damage (CSD) on mouse intestines. Following the CSD model, 4% sodium dodecyl sulfate was applied to the back-shaved murine skin six times for 2 weeks after tape stripping. The small and large intestines were analyzed histologically and immunologically, respectively. Intestinal permeability was measured using fluorescein isothiocyanate-conjugated-dextran. The role of interleukin-13 (IL-13) in the ileum was investigated using an anti-IL-13 antibody. Apoptotic intestinal cells were analyzed using TUNEL staining. Villus atrophy was observed in the small intestine in the CSD model, along with increased permeability. Mast cells, but not T cells, eosinophils, or innate lymph cell-2, were increased in the intestinal mucosa. However, no significant changes were observed in the large intestine. mRNA expression of IL-13 was increased only in the ileum of the CSD model. Apoptotic intestinal epithelial cells were significantly increased in the ileum of the CSD model. Administration of an anti-IL-13 antibody ameliorated the intestinal damage caused by CSD, along with decreased apoptotic cells and mast cell infiltration. Skin damage causes morphological changes in the small intestine, accompanied by increased intestinal permeability, possibly through the IL-13-induced apoptosis of mast cells in the epithelium. Surfactant-mediated mechanical skin damage can cause a leaky gut.

Tuft cell acetylcholine is released into the gut lumen to promote anti-helminth immunity.

Upon parasitic helminth infection, activated intestinal tuft cells secrete interleukin-25 (IL-25), which initiates a type 2 immune response during which lamina propria type 2 innate lymphoid cells (ILC2s) produce IL-13. This causes epithelial remodeling, including tuft cell hyperplasia, the function of which is unknown. We identified a cholinergic effector function of tuft cells, which are the only epithelial cells that expressed choline acetyltransferase (ChAT). During parasite infection, mice with epithelial-specific deletion of ChAT had increased worm burden, fitness, and fecal egg counts, even though type 2 immune responses were comparable. Mechanistically, IL-13-amplified tuft cells release acetylcholine (ACh) into the gut lumen. Finally, we demonstrated a direct effect of ACh on worms, which reduced their fecundity via helminth-expressed muscarinic ACh receptors. Thus, tuft cells are sentinels in naive mice, and their amplification upon helminth infection provides an additional type 2 immune response effector function.