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Epithelial cells control a variety of immune cells by secreting cytokines to maintain tissue homeostasis on mucosal surfaces. Regulatory T (Treg) cells are essential for immune homeostasis and for preventing tissue inflammation; however, the precise molecular mechanisms by which epithelial cell-derived cytokines function on Treg cells in the epithelial tissues are not well understood. Here, we show that peripheral Treg cells preferentially respond to thymic stromal lymphoprotein (TSLP). Although TSLP does not affect thymic Treg differentiation, TSLP receptor-deficient induced Treg cells derived from naïve CD4+ T cells are less activated in an adoptive transfer model of colitis. Mechanistically, TSLP activates induced Treg cells partially through mTORC1 activation and fatty acid uptake. Thus, TSLP modulates the activation status of induced Treg through the enhanced uptake of fatty acids to maintain homeostasis in the large intestine. [ABSTRACT FROM AUTHOR]

Common alphacoronaviruses and human rhinoviruses (HRV) induce type I and III interferon (IFN) responses important to limiting viral replication in the airway epithelium. In contrast, highly pathogenic betacoronaviruses including SARS-CoV-2 may evade or antagonize RNA-induced IFN I/III responses. In airway epithelial cells (AECs) from children and older adults we compared IFN I/III responses to SARS-CoV-2 and HRV-16, and assessed whether pre-infection with HRV-16, or pretreatment with recombinant IFN-β or IFN-λ, modified SARS-CoV-2 replication. Bronchial AECs from children (ages 6–18 years) and older adults (ages 60–75 years) were differentiated ex vivo to generate organotypic cultures. In a biosafety level 3 (BSL-3) facility, cultures were infected with SARS-CoV-2 or HRV-16, and RNA and protein was harvested from cell lysates 96 h. following infection and supernatant was collected 48 and 96 h. following infection. In additional experiments cultures were pre-infected with HRV-16, or pre-treated with recombinant IFN-β1 or IFN-λ2 before SARS-CoV-2 infection. In a subset of experiments a range of infectious concentrations of HRV-16, SARS-CoV-2 WA-01, SARS-CoV-2 Delta variant, and SARS-CoV-2 Omicron variant were studied. Despite significant between-donor heterogeneity SARS-CoV-2 replicated 100 times more efficiently than HRV-16. IFNB1, INFL2, and CXCL10 gene expression and protein production following HRV-16 infection was significantly greater than following SARS-CoV-2. IFN gene expression and protein production were inversely correlated with SARS-CoV-2 replication. Treatment of cultures with recombinant IFNβ1 or IFNλ2, or pre-infection of cultures with HRV-16, markedly reduced SARS-CoV-2 replication. In addition to marked between-donor heterogeneity in IFN responses and viral replication, SARS-CoV-2 (WA-01, Delta, and Omicron variants) elicits a less robust IFN response in primary AEC cultures than does rhinovirus, and heterologous rhinovirus infection, or treatment with recombinant IFN-β1 or IFN-λ2, reduces SARS-CoV-2 replication, although to a lesser degree for the Delta and Omicron variants. [ABSTRACT FROM AUTHOR]

Medullary thymic epithelial cells (mTECs) are critical in establishing and maintaining the appropriate microenvironment for negative selection and maturation of immunocompetent T cells with a self-tolerant T cell antigen receptor repertoire. Cues that direct proliferation and maturation of mTECs are provided by members of the tumor necrosis factor (TNF) superfamily expressed on developing thymocytes. Here we demonstrate a negative role of the morphogen TGF-β in tempering these signals under physiological conditions, limiting both growth and function of the thymic medulla. Eliminating TGF-β signaling specifically in TECs or by pharmacological means increased the size of the mTEC compartment, enhanced negative selection and functional maturation of medullary thymocytes as well as the production of regulatory T cells, thus reducing the autoreactive potential of peripheral T cells. [ABSTRACT FROM AUTHOR]

It has been 65 years since the scurfy mutation arose spontaneously in mice at the Oak Ridge National Laboratory in the United States, and it is 13 years since the molecular cloning of the forkhead box P3 (FOXP3) gene was reported. In this Timeline article, we review the events that have occurred during and since this time. This is not meant as an exhaustive review of the biology of FOXP3 or of regulatory T cells, rather it is an attempt to highlight the landmark events that have demonstrated the importance of FOXP3 in immune function. These events have driven, and continue to drive, the extensive research effort to fully understand the role of regulatory T cells in the immune system. [ABSTRACT FROM AUTHOR]

Dendritic cells (DCs) are critical in immune responses, linking innate and adaptive immunity. We found here that DC-specific deletion of the transcription factor STAT5 was not critical for development but was required for T helper type 2 (TH2), but not TH1, allergic responses in both the skin and lungs. Loss of STAT5 in DCs led to the inability to respond to thymic stromal lymphopoietin (TSLP). STAT5 was required for TSLP-dependent DC activation, including upregulation of the expression of costimulatory molecules and chemokine production. Furthermore, TH2 responses in mice with DC-specific loss of STAT5 resembled those seen in mice deficient in the receptor for TSLP. Our results show that the TSLP-STAT5 axis in DCs is a critical component for the promotion of type 2 immunity at barrier surfaces. [ABSTRACT FROM AUTHOR]

CD4+ T-helper type 2 (TH2) cells, characterized by their expression of interleukin (IL)-4, IL-5, IL-9 and IL-13, are required for immunity to helminth parasites and promote the pathological inflammation associated with asthma and allergic diseases. Polymorphisms in the gene encoding the cytokine thymic stromal lymphopoietin (TSLP) are associated with the development of multiple allergic disorders in humans, indicating that TSLP is a critical regulator of TH2 cytokine-associated inflammatory diseases. In support of genetic analyses, exaggerated TSLP production is associated with asthma, atopic dermatitis and food allergies in patients, and studies in murine systems demonstrated that TSLP promotes TH2 cytokine-mediated immunity and inflammation. However, the mechanisms through which TSLP induces TH2 cytokine responses remain poorly defined. Here we demonstrate that TSLP promotes systemic basophilia, that disruption of TSLP-TSLPR interactions results in defective basophil responses, and that TSLPR-sufficient basophils can restore TH2-cell-dependent immunity in vivo. TSLP acted directly on bone-marrow-resident progenitors to promote basophil responses selectively. Critically, TSLP could elicit basophil responses in both IL-3-IL-3R-sufficient and -deficient environments, and genome-wide transcriptional profiling and functional analyses identified heterogeneity between TSLP-elicited versus IL-3-elicited basophils. Furthermore, activated human basophils expressed TSLPR, and basophils isolated from eosinophilic oesophagitis patients were distinct from classical basophils. Collectively, these studies identify previously unrecognized heterogeneity within the basophil cell lineage and indicate that expression of TSLP may influence susceptibility to multiple allergic diseases by regulating basophil haematopoiesis and eliciting a population of functionally distinct basophils that promote TH2 cytokine-mediated inflammation. [ABSTRACT FROM AUTHOR]

Thymic stromal lymphopoietin (TSLP) is an interleukin 7 (IL-7)-like cytokine originally characterized by its ability to promote the activation of B cells and dendritic cells (DCs). Subsequent studies have shown that TSLP promotes T helper type 2 (TH2) cell responses associated with immunity to some helminth parasites and the pathogenesis of many inflammatory diseases, including atopic dermatitis and asthma. This review will focus on recent findings indicating that in addition to influencing B cell and DC function, TSLP can promote TH2 cytokine–associated inflammation by directly promoting the effector functions of CD4+ TH2 cells, basophils and other granulocyte populations while simultaneously limiting the expression of DC-derived proinflammatory cytokines and promoting regulatory T cell responses in peripheral tissues. [ABSTRACT FROM AUTHOR]

T helper cells that produce IL-17 (TH17 cells) promote autoimmunity in mice and have been implicated in the pathogenesis of human inflammatory diseases. At mucosal surfaces, TH17 cells are thought to protect the host from infection, whereas regulatory T (Treg) cells control immune responses and inflammation triggered by the resident microflora. Differentiation of both cell types requires transforming growth factor-β (TGF-β), but depends on distinct transcription factors: RORγt (encoded by Rorc(γt)) for TH17 cells and Foxp3 for Treg cells. How TGF-β regulates the differentiation of T cells with opposing activities has been perplexing. Here we demonstrate that, together with pro-inflammatory cytokines, TGF-β orchestrates TH17 cell differentiation in a concentration-dependent manner. At low concentrations, TGF-β synergizes with interleukin (IL)-6 and IL-21 (refs 9–11) to promote IL-23 receptor (Il23r) expression, favouring TH17 cell differentiation. High concentrations of TGF-β repress IL23r expression and favour Foxp3+ Treg cells. RORγt and Foxp3 are co-expressed in naive CD4+ T cells exposed to TGF-β and in a subset of T cells in the small intestinal lamina propria of the mouse. In vitro, TGF-β-induced Foxp3 inhibits RORγt function, at least in part through their interaction. Accordingly, lamina propria T cells that co-express both transcription factors produce less IL-17 (also known as IL-17a) than those that express RORγt alone. IL-6, IL-21 and IL-23 relieve Foxp3-mediated inhibition of RORγt, thereby promoting TH17 cell differentiation. Therefore, the decision of antigen-stimulated cells to differentiate into either TH17 or Treg cells depends on the cytokine-regulated balance of RORγt and Foxp3. [ABSTRACT FROM AUTHOR]

The cytokine thymic stromal lymphopoietin (TSLP) drives immature B cell development in vitro and may regulate T helper type 2 responses. Here we analyzed the involvement of TSLP in B cell development in vivo with a doxycycline-inducible, keratin 5–driven transgene encoding TSLP (K5-TSLP). K5-TSLP-transgenic mice given doxycycline showed an influx of immature B cells into the periphery, with population expansion of follicular mature B cells, near-complete loss of marginal zone and marginal zone precursor B cells, and 'preferential' population expansion of peritoneal B-1b B cells. These changes promoted cryoglobulin production and immune complex–mediated renal disease. Identical events occurred in mice without T cells, in alternative TSLP-transgenic models and in K5-TSLP-transgenic mice with undetectable systemic TSLP. These observations suggest that signals mediating localized TSLP expression may modulate systemic B cell development and promote humoral autoimmunity. [ABSTRACT FROM AUTHOR]

In the periphery, tolerance to self antigens is mainly mediated by the CD4+CD25+FOXP3+ subset of regulatory T cells, which can suppress the activity of autoreactive T cells that have escaped deletion in the thymus. The essential role of the transcription factor FOXP3 (forkhead box P3) in the development and function of these regulatory T cells has been well documented. It is also clear that regulatory T cells and effector T cells respond differently to T-cell receptor stimulation. In this Opinion article, we propose that these differences in responses are mediated by FOXP3, and are manifested by alterations in biochemical signalling pathways, patterns of gene expression and the appearance of cell-surface homing receptors. [ABSTRACT FROM AUTHOR]

The article presents the uses of thymic stromal lymphopoietin (TSLP) in pathogenic and normal T cell function and development. The TSLP is a potent activator of several cell types, specifically myeloid dendritic cells, and is expressed by barrier epithelial cells. It has an effect on the outcome of interactions between dendritic cells and T cells, like the regulation of the positive selection of T cells.

The cytokine thymic stromal lymphopoietin (TSLP) has been linked to human allergic inflammatory diseases. We show here that TSLP expression was increased in the lungs of mice with antigen-induced asthma, whereas TSLP receptor–deficient mice had considerably attenuated disease. Lung-specific expression of a Tslp transgene induced airway inflammation and hyperreactivity characterized by T helper type 2 cytokines and increased immunoglobulin E. The lungs of Tslp-transgenic mice showed massive infiltration of leukocytes, goblet cell hyperplasia and subepithelial fibrosis. TSLP was capable of activating bone marrow–derived dendritic cells to upregulate costimulatory molecules and produce the T helper type 2 cell–attracting chemokine CCL17. These findings suggest that TSLP is an important factor necessary and sufficient for the initiation of allergic airway inflammation. [ABSTRACT FROM AUTHOR]

Scurfy (sf) is an X-linked recessive mouse mutant resulting in lethality in hemizygous males 16?25 days after birth, and is characterized by overproliferation of CD4+CD8? T lymphocytes, extensive multiorgan infiltration and elevation of numerous cytokines. Similar to animals that lack expression of either Ctla-4 (refs. 5,6) or Tgf-β (refs. 7,8), the pathology observed in sf mice seems to result from an inability to properly regulate CD4+CD8? T-cell activity. Here we identify the gene defective in sf mice by combining high-resolution genetic and physical mapping with large-scale sequence analysis. The protein encoded by this gene (designated Foxp3) is a new member of the forkhead/winged-helix family of transcriptional regulators and is highly conserved in humans. In sf mice, a frameshift mutation results in a product lacking the forkhead domain. Genetic complementation demonstrates that the protein product of Foxp3, scurfin, is essential for normal immune homeostasis. [ABSTRACT FROM AUTHOR]

Signaling by type I cytokines involves the formation of receptor homodimers, heterodimers or higher order receptor oligomers. Here we report the cloning of a type I cytokine receptor subunit that is most closely related to the common cytokine receptor γ chain (γc). Binding and crosslinking experiments demonstrate that this protein is the receptor for a recently described interleukin 7 (IL-7)-like factor, thymic stromal lymphopoietin (TSLP). Binding of TSLP to the thymic stromal lymphopoietin receptor (TSLPR) is increased markedly in the presence of the IL-7 receptor α chain (IL-7Rα). IL-7Rα?expressing but not parental 32D cells proliferate in the presence of exogenous TSLP. Moreover, a combination of IL-7Rα and TSLPR is required for TSLP-dependent activation of a STAT5-dependent reporter construct. Thus it is shown that IL-7Rα is a component of both the IL-7 and TSLP receptors, which helps to explain why deletion of the gene that encodes IL-7Rα affects the lymphoid system more severely than deletion of the gene encoding IL-7 does. Cloning of TSLPR should facilitate an understanding of TSLP function and its signaling mechanism. [ABSTRACT FROM AUTHOR]

Severe combined immunodeficiency (SCID) is caused by multiple genetic defects. The most common form of SCID, X-linked SCID (XSCID), results from mutations in IL2RG (ref. 4), which encodes the common cytokine receptor γ chain (γc) that is shared by the IL-2, IL-4, IL-7, IL-9 and IL-15 receptors. In XSCID and SCID resulting from mutations in JAK3, which encodes a Janus family tyrosine kinase that couples to γc (Refs 9,12) and is required for γc-dependent signalling, T- and natural killer (NK)-cells are decreased but B-cell numbers are normal (T-B+NK- SCID). Some SCID patients lack T cells but retain NK cells. Given diminished T-cell development in Il7- or Il7r-deficient mice and that Il7r-deficient mice have NK cells, we hypothesized that T?B+NK+ SCID might result from defective IL-7 signalling, although apparent differences in the role of the IL-7/IL-7R pathway in humans and mice in T-cell and B-cell development have been suggested. We now demonstrate that defective IL7R expression causes T?B+NK+ SCID, indicating that the T-cell, but not the NK-cell, defect in XSCID results from inactivation of IL-7Rα signalling. [ABSTRACT FROM AUTHOR]