Regulatory T-cell stability and plasticity in mucosal and systemic immune systems

CD4+ Foxp3+ Regulatory T-cells in Modulating Inflammatory Microenvironment in Chronic Rhinosinusitis with Nasal Polyps: Progress and Future Prospect

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a subtype of chronic rhinosinusitis (CRS) characterized by the presence of nasal polyps (NP) in the paranasal mucosa. Despite the complex etiology, NP is believed to result from chronic inflammation. The long-term aftermath of the type 2 response is responsible for symptoms seen in NP patients, i.e. rhinorrhea, hyposmia, and nasal obstruction. Immune cellular tolerogenic mechanisms, particularly CD4 + Foxp3 + regulatory T cells (Tregs), are crucial to curtail inflammatory responses. Current evidence suggests impaired Treg activity is the main reason underlying the compromise of self-tolerance, contributing to the onset of CRSwNP. There is compelling evidence that tumor necrosis factor 2 (TNFR2) is preferentially expressed by Tregs, and TNFR2 is able to identify the most potent suppressive subset of Tregs. Tumor necrosis factor (TNF)-TNFR2 interaction plays a decisive role in the activation and expansion of Tregs. This review summarizes current understanding of Tregs biology, focusing on the discussion of the recent advances in the study of TNF-TNFR2 axis in the upregulation of Treg function as a negative feedback mechanism in the control of chronic inflammation. The role of dysregulation of Tregs in the immunopathogenesis of CRSwNP will be analyzed. The future perspective on the harnessing Tregs-mediated self-tolerant mechanism in the management of CRSwNP will be introduced.

Beyond Immune Balance: The Pivotal Role of Decidual Regulatory T Cells in Unexplained Recurrent Spontaneous Abortion

Recurrent spontaneous abortion (RSA) is defined as two or more consecutive pregnancy failures, which brings tremendous stress to women of childbearing age and seriously affects family well-being. However, the reason in about 50% of cases remains unknown and is defined as unexplained recurrent spontaneous abortion (URSA). The immunological perspective in URSA has attracted widespread attention in recent years. The embryo is regarded as a semi-allogeneic graft to the mother. A successful pregnancy requires transition to an immune environment conducive to embryo survival at the maternal-fetal interface. As an important member of regulatory immunity, regulatory T (Treg) cells play a key role in regulating immune tolerance at the maternal-fetal interface. This review will focus on the phenotypic plasticity and lineage stability of Treg cells to illustrate its relationship with URSA.

Intricacies of TGF-β signaling in Treg and Th17 cell biology

Balanced immunity is pivotal for health and homeostasis. CD4+ helper T (Th) cells are central to the balance between immune tolerance and immune rejection. Th cells adopt distinct functions to maintain tolerance and clear pathogens. Dysregulation of Th cell function often leads to maladies, including autoimmunity, inflammatory disease, cancer, and infection. Regulatory T (Treg) and Th17 cells are critical Th cell types involved in immune tolerance, homeostasis, pathogenicity, and pathogen clearance. It is therefore critical to understand how Treg and Th17 cells are regulated in health and disease. Cytokines are instrumental in directing Treg and Th17 cell function. The evolutionarily conserved TGF-β (transforming growth factor-β) cytokine superfamily is of particular interest because it is central to the biology of both Treg cells that are predominantly immunosuppressive and Th17 cells that can be proinflammatory, pathogenic, and immune regulatory. How TGF-β superfamily members and their intricate signaling pathways regulate Treg and Th17 cell function is a question that has been intensely investigated for two decades. Here, we introduce the fundamental biology of TGF-β superfamily signaling, Treg cells, and Th17 cells and discuss in detail how the TGF-β superfamily contributes to Treg and Th17 cell biology through complex yet ordered and cooperative signaling networks.

Opposing Roles of DCs and iNKT Cells in the Induction of Foxp3 Expression by MLN CD25+CD4+ T Cells during IFNγ-Driven Colitis

We have previously shown that a deficiency of CD1d-restricted invariant natural killer T (iNKT) cells exacerbates dextran sulfate sodium (DSS)-induced colitis in Yeti mice that exhibit IFNγ-mediated hyper-inflammation. Although iNKT cell-deficiency resulted in reduced Foxp3 expression by mesenteric lymph node (MLN) CD4⁺ T cells in DSS-treated Yeti mice, the cellular mechanisms that regulate Foxp3 expression by CD25⁺CD4⁺ T cells during intestinal inflammation remain unclear. We found that Foxp3^-CD25⁺CD4⁺ T cells expressing Th1 and Th17 phenotypic hallmarks preferentially expanded in the MLNs of DSS-treated Yeti/CD1d knockout (KO) mice. Moreover, adoptive transfer of Yeti iNKT cells into iNKT cell-deficient Jα18 KO mice effectively suppressed the expansion of MLN Foxp3^-CD25⁺CD4⁺ T cells during DSS-induced colitis. Interestingly, MLN dendritic cells (DCs) purified from DSS-treated Yeti/CD1d KO mice promoted the differentiation of naive CD4⁺ T cells into Foxp3^-CD25⁺CD4⁺ T cells rather than regulatory T (Treg) cells, indicating that MLN DCs might mediate Foxp3⁺CD25⁺CD4⁺ T cell expansion in iNKT cell-sufficient Yeti mice. Furthermore, we showed that Foxp3^-CD25⁺CD4⁺ T cells were pathogenic in DSS-treated Yeti/CD1d KO mice. Our result suggests that pro-inflammatory DCs and CD1d-restricted iNKT cells play opposing roles in Foxp3 expression by MLN CD25⁺CD4⁺ T cells during IFNγ-mediated intestinal inflammation, with potential therapeutic implications.

Therapeutic targeting of regulatory T cells in cancer

The success of immunotherapy in oncology underscores the vital role of the immune system in cancer development. Regulatory T cells (Tregs) maintain a fine balance between autoimmunity and immune suppression. They have multiple roles in the tumor microenvironment (TME) but act particularly in suppressing T cell activation. This review focuses on the detrimental and sometimes beneficial roles of Tregs in tumors, our current understanding of recruitment and stabilization of Tregs within the TME, and current Treg-targeted therapeutics. Research identifying subpopulations of Tregs and their respective functions and interactions within the complex networks of the TME will be crucial to develop the next generation of immunotherapies. Through these advances, Treg-targeted immunotherapy could have important implications for the future of oncology.

Regulatory T cells in inflammation and resolution of acute lung injury

Introduction

Acute respiratory distress syndrome (ARDS) is characterized by hypoxemia and increased lung permeability and would result in acute respiratory failure and with high mortality. In patients who survive from acute lung injury (ALI)/ARDS, it is an active process of the transition from injury to resolution depending on the coordinated immune system. The roles of regulatory CD4⁺T cells (Tregs) are now gradually being clarified during inflammation and resolution of ARDS. However, clear conclusions about roles of Tregs in ALI/ARDS are only a few.

Objective

This review provides an overview of phenotype, differentiation, and suppressive mechanisms of Tregs and focuses on keys of biology of Tregs in alveolar space during the inflammatory response and resolution of ALI/ARDS.

Data Source

Literature search of Web of Science, PubMed, and EMBASE was made to find relative articles about Tregs in ALI/ARDS. We used the following search terms: Tregs, ALI, ARDS, inflammation, and resolution.

Conclusion

More and more studies have indicated Tregs involved in the processes of inflammation and resolution of ALI/ARDS. A deep understanding of the roles of Tregs may indicate new treatments for patients of ARDS. Therapies aimed at expansion or adaptive transfer of Tregs could be an effective therapy to ARDS patients.

Effect of Intervention of Probiotics in Advance on Treg/Th17 in Premature Mice

To preliminarily understand the differentiation characteristics of regulatory T cells (Tregs) and Th17 at a different time in preterm mice, the impacts of probiotics on immune function progression, as well as the correlation of probiotics with Tregs and Th17. On embryonic day 18 of gestation, a mouse model of preterm birth was built using mifepristone (RU486). Following IPI of RU486, newborn mice were randomized to probiotics or NS gavage administration. Full-term newborn mice were given the same dose of NS gavage administration. Phenotypic analysis of peripheral immune cell frequency was performed using flow cytometry. Cytokine measurements were phenotyped by enzyme-linked immunosorbent assays. On the 14th and 21st days after birth, the highest and lowest expressions of Foxp3, the Treg transcription factor, were observed in full-term mice and premature mice by NS gavage administration, respectively, while the opposite trend was found in the Th17 transcription factor IL-17.IL-2, IL-6, and TGF-β rose with age but showed different trends among the three groups. IL-2 is the highest in full-term mice and the lowest in premature mice. IL-6 and TGF-β is the lowest in full-term mice and the highest in premature mice. Probiotics are beneficial to the development and maturation of the immune system, which may play a role in regulating the ratio of Treg/Th17. Probiotic preintervention can effectively promote the differentiation of Treg and inhibit the differentiation of Th17 in premature mice. Its mechanism of action may play a biological role by regulating cytokine (IL-2, IL-6, and TGF-β) secretions.

FVB/N mouse strain regulatory T cells differ in phenotype and function from the C57BL/6 and BALB/C strains

Regulatory T cells (Treg) are vital to the maintenance of immune homeostasis. The genetic background of an inbred mouse strain can have a profound effect on the immune response in the animal, including Treg responses. Most Treg studies focus on animals created on the C57BL/6 or BALB/c background. Recent studies have demonstrated a difference in the phenotype and behavior of C57BL/6 and BALB/c Tregs. In this study, we have investigated the function of FVB/N Tregs compared to C57BL/6 and BALB/c. We observed that while FVB/N Tregs appear to suppress normally in a cell contact‐dependent system, FVB/N Tregs are less capable of suppressing when regulation depends on the secretion of a soluble factor. FVB/N Tregs produce IL‐10; however, TGF‐β was not detected in any culture from C57BL/6 or FVB/N. C57BL/6 Foxp3⁺ Tregs expressed more of the TGF‐β‐related proteins glycoprotein‐A repetitions predominant (GARP) and latency‐associated peptide (LAP) on the cell surface than both FVB/N and BALB/c, but C57BL/6 Tregs expressed significantly less Ctse (Cathepsin E) mRNA. Each strain displayed different abilities of thymic Tregs (tTreg) to maintain Foxp3 expression and had a varying generation of induced Tregs (iTregs). In vitro generated FVB/N iTregs expressed significantly less GARP and LAP. These results suggest Tregs of different strains have varying phenotypes and dominant mechanisms of action for the suppression of an immune response. This information should be taken into consideration when Tregs are examined in future studies, particularly for therapeutic purposes in a genetically diverse population.

Immune determinants of endometrial receptivity: a biological perspective

Immune cells are essential for endometrial receptivity to embryo implantation and early placental development. They exert tissue-remodeling and immune regulatory roles-acting to promote epithelial attachment competence, regulate the differentiation of decidual cells, remodel the uterine vasculature, control and resolve inflammatory activation, and suppress destructive immunity to paternally inherited alloantigens. From a biological perspective, the endometrial immune response exerts a form of "quality control"-it promotes implantation success when conditions are favorable but constrains receptivity when physiological circumstances are not ideal. Women with recurrent implantation failure and recurrent miscarriage may exhibit altered numbers or disturbed function of certain uterine immune cell populations-most notably uterine natural killer cells and regulatory T cells. Preclinical and animal studies indicate that deficiencies or aberrant activation states in these cells can be causal in the pathophysiological mechanisms of infertility. Immune cells are, therefore, targets for diagnostic evaluation and therapeutic intervention. However, current diagnostic tests are overly simplistic and have limited clinical utility. To be more informative, they need to account for the full complexity and reflect the range of perturbations that can occur in uterine immune cell phenotypes and networks. Moreover, safe and effective interventions to modulate these cells are in their infancy, and personalized approaches matched to specific diagnostic criteria will be needed. Here we summarize current biological understanding and identify knowledge gaps to be resolved before the promise of therapies to target the uterine immune response can be fully realized.

The immunomodulatory effects of long-term supplementation with Lactobacillus casei Shirota depend on ovalbumin presentation in BALB/c mice

Immunomodulation is an ability of several particular probiotics. However, it still remains unclear whether the immunomodulatory effects of specific probiotics vary for different antigen presentation models with the same antigen. To investigate this matter, six groups of BALB/c mice (n = 10) were exposed to one of two antigen presentation models: ovalbumin (OVA) by injection alone, or injection plus intranasal administration. Moreover, the mice were fed distilled water or Lactobacillus casei Shirota fermented beverage (LcSFB) at low (2.5 × 109 CFU/kg body weight) or high doses (5 × 109 CFU/kg body weight) by gavage for 8 weeks. LcSFB enhanced the proliferation of splenocytes, production of OVA-specific immunoglobulin (Ig)-G and IgA, and the ratio of T-helper (Th)-2/Th1 cytokines in mice injected with OVA. Conversely, in the mice treated with OVA by injection plus intranasal administration, LcSFB attenuated the immune responses against OVA by reducing the proliferation of splenocytes, levels of OVA-specific IgE, IgG, and IgM, and ratio of Th2/Th1 cytokines. Moreover, LcSFB increased the percentage of regulatory T cells in the injection plus intranasal administration group. Taken together, this work indicates the immunoregulatory effects of LcSFB depend on how the antigen is presented. Therefore, the use of probiotics to boost the immune system must be carefully considered.

ACLY ubiquitination by CUL3-KLHL25 induces the reprogramming of fatty acid metabolism to facilitate iTreg differentiation

Inducible regulatory T (iTreg) cells play a central role in immune suppression. As iTreg cells are differentiated from activated T (Th0) cells, cell metabolism undergoes dramatic changes, including a shift from fatty acid synthesis (FAS) to fatty acid oxidation (FAO). Although the reprogramming in fatty acid metabolism is critical, the mechanism regulating this process during iTreg differentiation is still unclear. Here we have revealed that the enzymatic activity of ATP-citrate lyase (ACLY) declined significantly during iTreg differentiation upon transforming growth factor β1 (TGFβ1) stimulation. This reduction was due to CUL3-KLHL25-mediated ACLY ubiquitination and degradation. As a consequence, malonyl-CoA, a metabolic intermediate in FAS that is capable of inhibiting the rate-limiting enzyme in FAO, carnitine palmitoyltransferase 1 (CPT1), was decreased. Therefore, ACLY ubiquitination and degradation facilitate FAO and thereby iTreg differentiation. Together, we suggest TGFβ1-CUL3-KLHL25-ACLY axis as an important means regulating iTreg differentiation and bring insights into the maintenance of immune homeostasis for the prevention of immune diseases.

CD226 Attenuates Treg Proliferation via Akt and Erk Signaling in an EAE Model

Cluster of differentiation 226 (CD226) molecules play a crucial role in the activation of effector CD4⁺ T cells during the immune response process, but a cell-intrinsic function of CD226 in CD4⁺ T subsets is not clear. In this study, we showed that Cd226^−/− mice were resistant to myelin oligodendrocyte glycoprotein peptide 35-55 (MOG₃₅₋₅₅)-induced experimental autoimmune encephalomyelitis (EAE) with highly expressed IL-10⁺CD4⁺ T cells and downregulated IL-17A⁺CD4⁺ T cells when compared with wild-type (WT) mice. Th17 cell infiltration into the central nervous system (CNS) was largely decreased in the absence of CD226 during EAE. CD226 deficiency facilitated the proliferation of regulatory T cells (Tregs), with increased numbers of Tregs observed in EAE mice, and supported the elevated induced regulatory T cell (iTregs) proliferation in vitro. The Akt and Erk signaling pathways were shown to be involved in Cd226^−/− Treg proliferation and function in vivo and in vitro. These findings collectively indicate that CD226 is a key molecule regulating the Treg-mediated suppression of autoimmune responses by inhibiting Treg proliferation. Thus, the results of this study identify additional mechanisms by which CD226 regulates Treg functions in EAE and supports the potential therapeutic effects of anti-CD226 molecules on autoimmune diseases.

Increased number of regulatory T cells in esophageal tissue of patients with eosinophilic esophagitis in comparison to gastro esophageal reflux disease and control groups

BACKGROUND

Eosinophilic esophagitis (EoE) is a primarily polygenic allergic disorder. Although most patients have IgE sensitization, it seems that non-IgE mediated responses mainly contribute to the pathogenesis of EoE. Regulatory T cells (Tregs) may have an important role in allergies. There are limited data on the association of Tregs and EoE. In this study, we enumerated and compared T lymphocytes and Tregs in esophageal tissue of patients with EoE, gastroesophageal reflux disease (GERD) and normal controls.

METHODS

Ten patients with EoE, ten patients with GERD and eight normal controls were included. Immunohistochemistry staining was used to enumerate T lymphocytes and Tregs. CD3+ cells were considered as T cells and FOXP3+, CD3+ cells were considered as Tregs. T cells and Tregs were counted in 10 high power fields (HPF) (×400) for each patient and the average of 10 HPFs was recorded.

RESULTS

The mean±SEM of Tregs in esophageal tissue of patients with EoE (10.90±2.14cells/HPF) was significantly higher than the GERD (2.77±0.66cells/HPF) and control groups (0.37±0.08cells/HPF) (P<0.001). Additionally, the mean±SEM of T lymphocytes in esophageal tissue of patients with EoE (24.39±3.86cells/HPF) were increased in comparison to the GERD (10.07±2.65cells/HPF) and control groups (3.17±0.93cells/HPF) (P<0.001).

CONCLUSION

There is an increase in the number of esophageal T lymphocytes and regulatory T cells in patients with EoE compared to the GERD and control groups.

Therapeutic Potential of Regulatory T Cells in Preeclampsia-Opportunities and Challenges

Inflammation is a central feature and is implicated as a causal factor in preeclampsia and other hypertensive disorders of pregnancy. Inflammatory mediators and leukocytes, which are elevated in peripheral blood and gestational tissues, contribute to the uterine vascular anomalies and compromised placental function that characterize particularly the severe, early onset form of disease. Regulatory T (Treg) cells are central mediators of pregnancy tolerance and direct other immune cells to counteract inflammation and promote robust placentation. Treg cells are commonly perturbed in preeclampsia, and there is evidence Treg cell insufficiency predates onset of symptoms. A causal role is implied by mouse studies showing sufficient numbers of functionally competent Treg cells must be present in the uterus from conception, to support maternal vascular adaptation and prevent later placental inflammatory pathology. Treg cells may therefore provide a tractable target for both preventative strategies and treatment interventions in preeclampsia. Steps to boost Treg cell activity require investigation and could be incorporated into pregnancy planning and preconception care. Pharmacological interventions developed to target Treg cells in autoimmune conditions warrant consideration for evaluation, utilizing rigorous clinical trial methodology, and ensuring safety is paramount. Emerging cell therapy tools involving in vitro Treg cell generation and/or expansion may in time become relevant. The success of preventative and therapeutic approaches will depend on resolving several challenges including developing informative diagnostic tests for Treg cell activity applicable before conception or during early pregnancy, selection of relevant patient subgroups, and identification of appropriate windows of gestation for intervention.

CD69 enhances immunosuppressive function of regulatory T-cells and attenuates colitis by prompting IL-10 production

Foxp3⁺ regulatory T cells (Tregs) can inhibit immune responses and maintain immune tolerance by secreting immunosuppressive TGF-β1 and IL-10. However, the efficiency of Tregs become the major obstacle to their use for immunotherapy. In this study, we investigated the relevance of the C-type lectin receptor CD69 to the suppressive function. Compared to CD4⁺Foxp3⁺CD69⁻ Tregs (CD69⁻ Tregs), CD4⁺Foxp3⁺CD69⁺ Tregs (CD69⁺ Tregs) displayed stronger ability to maintain immune tolerance. CD69⁺ Tregs expressed higher levels of suppression-associated markers such as CTLA-4, ICOS, CD38 and GITR, and secreted higher levels of IL-10 but not TGF-β1. CD69⁺ Tregs from Il10^+/+ rather than Il10^−/− mice significantly inhibit the proliferation of CD4⁺ T cells. CD69 over-expression stimulated higher levels of IL-10 and c-Maf expression, which was compromised by silencing of STAT3 or STAT5. In addition, the direct interaction of STAT3 with the c-Maf promoter was detected in cells with CD69 over-expression. Moreover, adoptive transfer of CD69⁺ Tregs but not CD69⁻Tregs or CD69⁺ Tregs deficient in IL-10 dramatically prevented the development of inflammatory bowel disease (IBD) in mice. Taken together, CD69 is important to the suppressive function of Tregs by promoting IL-10 production. CD69⁺ Tregs have the potential to develop new therapeutic approach for autoimmune diseases like IBD.

Development and maintenance of intestinal regulatory T cells

Gut-resident forkhead box P3 (FOXP3)(+)CD4(+) regulatory T cells (Treg cells) are distinct from those in other organs and have gut-specific phenotypes and functions. Whereas Treg cells in other organs have T cell receptors (TCRs) specific for self antigens, intestinal Treg cells have a distinct set of TCRs that are specific for intestinal antigens, and these cells have pivotal roles in the suppression of immune responses against harmless dietary antigens and commensal microorganisms. The differentiation, migration and maintenance of intestinal Treg cells are controlled by specific signals from the local environment. In particular, certain members of the microbiota continuously provide antigens and immunoregulatory small molecules that modulate intestinal Treg cells. Understanding the development and the maintenance of intestinal Treg cells provides important insights into disease-relevant host-microorganism interactions.

Th17 responses and natural IgM antibodies are related to gut microbiota composition in systemic lupus erythematosus patients

Intestinal dysbiosis, characterized by a reduced Firmicutes/Bacteroidetes ratio, has been reported in systemic lupus erythematosus (SLE) patients. In this study, in vitro cultures revealed that microbiota isolated from SLE patient stool samples (SLE-M) promoted lymphocyte activation and Th17 differentiation from naïve CD4⁺ lymphocytes to a greater extent than healthy control-microbiota. Enrichment of SLE-M with Treg-inducing bacteria showed that a mixture of two Clostridia strains significantly reduced the Th17/Th1 balance, whereas Bifidobacterium bifidum supplementation prevented CD4⁺ lymphocyte over-activation, thus supporting a possible therapeutic benefit of probiotics containing Treg-inducer strains in order to restore the Treg/Th17/Th1 imbalance present in SLE. In fact, ex vivo analyses of patient samples showed enlarged Th17 and Foxp3⁺ IL-17⁺ populations, suggesting a possible Treg-Th17 trans-differentiation. Moreover, analyses of fecal microbiota revealed a negative correlation between IL-17⁺ populations and Firmicutes in healthy controls, whereas in SLE this phylum correlated directly with serum levels of IFNγ, a Th1 cytokine slightly reduced in patients. Finally, the frequency of Synergistetes, positively correlated with the Firmicutes/Bacteroidetes ratio in healthy controls, tended to be reduced in patients when anti-dsDNA titers were increased and showed a strong negative correlation with IL-6 serum levels and correlated positively with protective natural IgM antibodies against phosphorylcholine.

Regulatory T Cells and Their Role in Animal Disease

In humans and mouse models, Foxp3(+) regulatory T cells are known to control all aspects of immune responses. However, only limited information exists on these cells' role in diseases of other animals. In this review, we cover the most important features and different types of regulatory T cells, which include those that are thymus-derived and peripherally induced, the mechanisms by which they control immune responses by targeting effector T cells and antigen-presenting cells, and most important, their role in animal health and diseases including cancer, infections, and other conditions such as hypersensitivities and autoimmunity. Although the literature regarding regulatory T cells in domestic animal species is still limited, multiple articles have recently emerged and are discussed. Moreover, we also discuss the evidence suggesting that regulatory T cells might limit the magnitude of effector responses, which can have either a positive or negative result, depending on the context of animal and human disease. In addition, the issue of plasticity is discussed because plasticity in regulatory T cells can result in the loss of their protective function in some microenvironments during disease. Lastly, the manipulation of regulatory T cells is discussed in assessing the possibility of their use as a treatment in the future.

Suppression of CD4+ Effector Responses by Naturally Occurring CD4+ CD25+ Foxp3+ Regulatory T Cells Contributes to Experimental Cerebral Malaria

The role of naturally occurring CD4(+) CD25(+) Foxp3(+) regulatory T cells (nTreg) in the pathogenesis of cerebral malaria (CM), which involves both pathogenic T cell responses and parasite sequestration in the brain, is still unclear. To assess the contribution and dynamics of nTreg during the neuropathogenesis, we unbalanced the ratio between nTreg and naive CD4(+) T cells in an attenuated model of Plasmodium berghei ANKA-induced experimental CM (ECM) by using a selective cell enrichment strategy. We found that nTreg adoptive transfer accelerated the onset and increased the severity of CM in syngeneic C57BL/6 (B6) P. berghei ANKA-infected mice without affecting the level of parasitemia. In contrast, naive CD4(+) T cell enrichment prevented CM and promoted parasite clearance. Furthermore, early during the infection nTreg expanded in the spleen but did not efficiently migrate to the site of neuroinflammation, suggesting that nTreg exert their pathogenic action early in the spleen by suppressing the protective naive CD4(+) T cell response to P. berghei ANKA infection in vivo in both CM-susceptible (B6) and CM-resistant (B6-CD4(-/-)) mice. However, their sole transfer was not sufficient to restore CM susceptibility in two CM-resistant congenic strains tested. Altogether, these results demonstrate that nTreg are activated and functional during P. berghei ANKA infection and that they contribute to the pathogenesis of CM. They further suggest that nTreg may represent an early target for the modulation of the immune response to malaria.

Epigenetic control of Foxp3 by SMYD3 H3K4 histone methyltransferase controls iTreg development and regulates pathogenic T-cell responses during pulmonary viral infection

The generation of regulatory T (Treg) cells is driven by Foxp3 and is responsible for dampening inflammation and reducing autoimmunity. In this study, the epigenetic regulation of inducible Treg (iTreg) cells was examined and an H3K4 histone methyltransferase, SMYD3 (SET and MYND Domain 3), which regulates the expression of Foxp3 by a TGFβ1/Smad3 (transforming growth factor-β1/Smad3)-dependent mechanism, was identified. Using chromatin immunoprecipitation assays, SMYD3 depletion led to a reduction in H3K4me3 in the promoter region and CNS1 (conserved noncoding DNA sequence) of the foxp3 locus. SMYD3 abrogation affected iTreg cell formation while allowing dysregulated interleukin-17 production. In a mouse model of respiratory syncytial virus (RSV) infection, a model in which iTreg cells have a critical role in regulating lung pathogenesis, SMYD3(-/-) mice demonstrated exacerbation of RSV-induced disease related to enhanced proinflammatory responses and worsened pathogenesis within the lung. Our data highlight a novel activation role for the TGFβ-inducible SMYD3 in regulating iTreg cell formation leading to increased severity of virus-related disease.

Continuum model of T-cell avidity: Understanding autoreactive and regulatory T-cell responses in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease that results from the destruction of insulin-secreting pancreatic β cells, leading to abolition of insulin secretion and onset of diabetes. Cytotoxic CD4(+) and CD8(+) T cells, activated by antigen presenting cells (APCs), are both implicated in disease onset and progression. Regulatory T cells (Tregs), on the other hand, play a leading role in regulating immunological tolerance and resistant homoeostasis in T1D by suppressing effector T cells (Teffs). Recent data indicates that after activation, conventional Teffs transiently produce interleukin IL-2, a cytokine that acts as a growth factor for both Teffs and Tregs. Tregs suppress Teffs through IL-2 deprivation, competition and Teff conversion into inducible Tregs (iTregs). To investigate the interactions of these components during T1D progression, a mathematical model of T-cell dynamics is developed as a predictor of β-cell loss, with the underlying hypothesis that avidity of Teffs and Tregs, i.e., the binding affinity of T-cell receptors to peptide-major histocompatibility complexes on host cells, is continuum. The model is used to infer a set of criteria that determines susceptibility to T1D in high risk subjects. Our findings show that diabetes onset is guided by the absence of Treg-to-Teff dominance at specific high avidities, rather than over the whole range of avidity, and that the lack of overall dominance of Teffs-to-Tregs over time is the underlying cause of the "honeymoon period", the remission phase observed in some T1D patients. The model also suggests that competition between Teffs and Tregs is more effective than Teff-induction into iTregs in suppressing Teffs, and that a prolonged full width at half maximum of IL-2 release is a necessary condition for curbing disease onset. Finally, the model provides a rationale for observing rapid and slow progressors of T1D based on modest heterogeneity in the kinetic parameters.

Preterm cord blood CD4⁺ T cells exhibit increased IL-6 production in chorioamnionitis and decreased CD4⁺ T cells in bronchopulmonary dysplasia

BACKGROUND

Chorioamnionitis (CA) is associated with premature delivery and bronchopulmonary dysplasia (BPD). We hypothesize that preterm infants exposed to CA have reduced suppressive regulatory T cells (Treg) and increased non-regulatory T cell pro-inflammatory cytokines, increasing risk for BPD.

OBJECTIVE

To evaluate cord blood CD4(+) T cell regulatory phenotype and pro-inflammatory cytokine production in CA and BPD groups.

STUDY DESIGN

Cord blood mononuclear cells from infants (GA ⩽32 weeks), with or without placental histological evidence of CA (hChorio), were analyzed by flow cytometry. Clinical information was collected by retrospective chart review. Numbers of putative Treg (CD4(+)FoxP3(+)CD25(+)CD127Dim), CD4(+) non-Tregs, and CD4(+) T cell intracellular cytokine content following in vitro stimulation were compared with CA status and oxygen requirement at 36weeks postmenstrual age.

RESULT

Absolute Treg numbers were not different in CA and non-CA exposed samples. However, the infants who developed BPD had a significant decrease in Treg and non-regulatory T cell numbers. Greater IL-6 production was observed in hCA group.

CONCLUSION

A pro-inflammatory CD4(+) T cell status is noted in CA and BPD but the later disease is also associated with decrease in Tregs, suggesting that the development of BPD is marked by distinct inflammatory changes from those of CA exposed infants.

SOCS1 and regulation of regulatory T cells plasticity

Several reports have suggested that natural regulatory T cells (Tregs) lose Forkhead box P3 (Foxp3) expression and suppression activity under certain inflammatory conditions. Treg plasticity has been studied because it may be associated with the pathogenesis of autoimmunity. Some studies showed that a minor uncommitted Foxp3⁺ T cell population, which lacks hypomethylation at Treg-specific demethylation regions (TSDRs), may convert to effector/helper T cells. Suppressor of cytokine signaling 1 (SOCS1), a negative regulator of cytokine signaling, has been reported to play an important role in Treg cell integrity and function by protecting the cells from excessive inflammatory cytokines. In this review, we discuss Treg plasticity and maintenance of suppression functions in both physiological and pathological settings. In addition, we discuss molecular mechanisms of maintaining Treg plasticity by SOCS1 and other molecules. Such information will be useful for therapy of autoimmune diseases and reinforcement of antitumor immunity.

Current status of interleukin-10 and regulatory T-cells in cancer

PURPOSE OF REVIEW

Tumor growth elicits antigen-specific cytotoxic as well as immune suppressive responses. Interleukin-10 (IL-10) is a key immune-suppressive cytokine produced by regulatory T-cells and by helper T-cells. Here, we review pleiotropic functions of IL-10 that impact the immune pathology of cancer.

RECENT FINDINGS

The role of IL-10 in cancer has become less certain with the knowledge of its immune stimulatory functions. IL-10 is needed for T-helper cell functions, T-cell immune surveillance, and suppression of cancer-associated inflammation. By promoting tumor-specific immune surveillance and hindering pathogenic inflammation, IL-10 is emerging as a key cytokine in the battle of the host against cancer.

SUMMARY

IL-10 functions at the cross-roads of immune stimulation and immune suppression in cancer. Immunological mechanisms of action of IL-10 can be ultimately exploited to develop novel and effective cancer therapies.

Role of regulatory T cells during virus infection

The host response to viruses includes multiple cell types that have regulatory function. Most information focuses on CD4(+) regulatory T cells that express the transcription factor Foxp3(+) (Tregs), which are the topic of this review. We explain how viruses through specific and non-specific means can trigger the response of thymus-derived natural Tregs as well as induce Tregs. The latter derive under appropriate stimulation conditions either from uncommitted precursors or from differentiated cells that convert to become Tregs. We describe instances where Tregs appear to limit the efficacy of antiviral protective immunity and other, perhaps more common, immune-mediated inflammatory conditions, where the Tregs function to limit the extent of tissue damage that occurs during a virus infection. We discuss the controversial roles that Tregs may play in the pathogenesis of human immunodeficiency and hepatitis C virus infections. The issue of plasticity is discussed, as this may result in Tregs losing their protective function when present in inflammatory environments. Finally, we mention approaches used to manipulate Treg numbers and function and assess their current value and likely future success to manage the outcome of virus infection, especially those that are responsible for chronic tissue damage.

Immunology of pediatric HIV infection

Most infants born to human immunodeficiency virus (HIV)-infected women escape HIV infection. Infants evade infection despite an immature immune system and, in the case of breastfeeding, prolonged repetitive exposure. If infants become infected, the course of their infection and response to treatment differs dramatically depending upon the timing (in utero, intrapartum, or during breastfeeding) and potentially the route of their infection. Perinatally acquired HIV infection occurs during a critical window of immune development. HIV's perturbation of this dynamic process may account for the striking age-dependent differences in HIV disease progression. HIV infection also profoundly disrupts the maternal immune system upon which infants rely for protection and immune instruction. Therefore, it is not surprising that infants who escape HIV infection still suffer adverse effects. In this review, we highlight the unique aspects of pediatric HIV transmission and pathogenesis with a focus on mechanisms by which HIV infection during immune ontogeny may allow discovery of key elements for protection and control from HIV.

Regulation of regulatory T cells: epigenetics and plasticity

Regulatory T (Treg) cells, as central mediators of immune suppression, play crucial roles in many aspects of immune system's physiology and pathophysiology. The transcription factor Foxp3 has been characterized as a master gene of Tregs. Yet Treg cells possess a distinct pattern of gene expression, including upregulation of immune-suppressive genes and silencing of inflammatory cytokine genes. Recent studies have revealed the molecular mechanisms that establish and maintain such gene regulation in Treg cells. This review discusses recent progress in our understanding of molecular features of Treg cells, with particular attention to Treg-cell lineage commitment and stability.

TRAF6 is essential for maintenance of regulatory T cells that suppress Th2 type autoimmunity

Regulatory T cells (Tregs) maintain immune homeostasis by limiting inflammatory responses. TRAF6 plays a key role in the regulation of innate and adaptive immunity by mediating signals from various receptors including the T-cell receptor (TCR). T cell-specific deletion of TRAF6 has been shown to induce multiorgan inflammatory disease, but the role of TRAF6 in Tregs remains to be investigated. Here, we generated Treg-specific TRAF6-deficient mice using Foxp3-Cre and TRAF6-flox mice. Treg-specific TRAF6-deficient (cKO) mice developed allergic skin diseases, arthritis, lymphadenopathy and hyper IgE phenotypes. Although TRAF6-deficient Tregs possess similar in vitro suppression activity compared to wild-type Tregs, TRAF6-deficient Tregs did not suppress colitis in lymphopenic mice very efficiently due to reduced number of Foxp3-positive cells. In addition, the fraction of TRAF6-deficient Tregs was reduced compared with wild-type Tregs in female cKO mice without inflammation. Moreover, adoptive transfer of Foxp3 ⁺ Tregs into Rag2^-/- mice revealed that TRAF6-deficient Tregs converted into Foxp3^- cells more rapidly than WT Tregs under lymphopenic conditions. Fate-mapping analysis also revealed that conversion of Tregs from Foxp3⁺ to Foxp3^- (exFoxp3 cells) was accelerated in TRAF6-deficient Tregs. These data indicate that TRAF6 in Tregs plays important roles in the maintenance of Foxp3 in Tregs and in the suppression of pathogenic Th2 type conversion of Tregs.

Mechanisms underlying immune effects of dietary oligosaccharides

The WHO refers to human milk as the nutritional gold standard for term infants. Human milk contains many immunomodulatory compounds, including oligosaccharides. Human-milk oligosaccharides can serve as prebiotics because the nondigestible oligosaccharides present in human milk show a clear bifidogenic effect on the gut microbiota. Dietary oligosaccharide structures that have prebiotic effects similar to human-milk oligosaccharides include galacto-oligosaccharides, fructo-oligosaccharides, and pectin-derived acidic oligosaccharides. Both animal studies and human clinical trials showed that dietary intervention with these dietary oligosaccharides in early life could lead to the prevention of atopic dermatitis, food allergy, and allergic asthma. The immune-modulating effects of these oligosaccharides are likely assisted via alteration of the intestinal microbiota or in a microbiota-independent manner by direct interaction on immune cells or both. In this review, an overview of the prebiotic role of dietary oligosaccharides on the microbiota and the microbiota-independent immune modulation by these prebiotics is provided. In addition, recent publications that report on the pathways by which the oligosaccharides might exert their direct immunomodulatory effect are summarized.

Altered gut microbiota promotes colitis-associated cancer in IL-1 receptor-associated kinase M-deficient mice

BACKGROUND

Microbial sensing by Toll-like receptors (TLR) and its negative regulation have an important role in the pathogenesis of inflammation-related cancer. In this study, we investigated the role of negative regulation of Toll-like receptors signaling and gut microbiota in the development of colitis-associated cancer in mouse model.

METHODS

Colitis-associated cancer was induced by azoxymethane and dextran sodium sulfate in wild-type and in interleukin-1 receptor-associated kinase M (IRAK-M)-deficient mice with or without antibiotic (ATB) treatment. Local cytokine production was analyzed by multiplex cytokine assay or enzyme-linked immunosorbent assay, and regulatory T cells were analyzed by flow cytometry. Changes in microbiota composition during tumorigenesis were analyzed by pyrosequencing, and β-glucuronidase activity was measured in intestinal content by fluorescence assay.

RESULTS

ATB treatment of wild-type mice reduced the incidence and severity of tumors. Compared with nontreated mice, ATB-treated mice had significantly lower numbers of regulatory T cells in colon, altered gut microbiota composition, and decreased β-glucuronidase activity. However, the β-glucuronidase activity was not as low as in germ-free mice. IRAK-M-deficient mice not only developed invasive tumors, but ATB-induced decrease in β-glucuronidase activity did not rescue them from severe carcinogenesis phenotype. Furthermore, IRAK-M-deficient mice had significantly increased levels of proinflammatory cytokines in the tumor tissue.

CONCLUSIONS

We conclude that gut microbiota promotes tumorigenesis by increasing the exposure of gut epithelium to carcinogens and that IRAK-M-negative regulation is essential for colon cancer resistance even in conditions of altered microbiota. Therefore, gut microbiota and its metabolic activity could be potential targets for colitis-associated cancer therapy.

Altered generation of induced regulatory T cells in the FVB.mdr1a-/- mouse model of colitis

The FVB.mdr1a(-/-) mouse, lacking the small molecule pump P-glycoprotein (P-gp), is a commonly used model for the study of spontaneous T cell-mediated colitis. In addition, MDR1 polymorphisms and P-gp deficiency in humans have been linked to the development of ulcerative colitis. We now demonstrate that mice with P-gp deficiency have decreased levels of Foxp3(+) regulatory T cells (Tregs) in the intestinal lamina propria. This decrease is not due to either increased Treg apoptosis, altered Treg trafficking, or enhanced Treg plasticity to become Foxp3(+)IL-17(+) cells. Instead, P-gp deficiency appears to restrict the development of induced Treg cells (iTregs), as fewer Foxp3(+) iTregs developed from naive FVB.mdr1a(-/-) T cells both upon transforming growth factor-β (TGF-β) treatment in vitro and after adoptive transfer into FVB.rag2(-/-) recipients. Rather, in vitro TGF-β treatment results in a IL-17(+)CD4(+) T cell. This failure of iTregs to develop explains the decrease in Foxp3(+) Tregs in the FVB.mdr1a(-/-) intestine, representing a need to investigate this novel disease mechanism in human inflammatory bowel disease patients with MDR1 polymorphisms.

Enhanced generation of suppressor T cells in patients with asthma taking oral contraceptives

Introduction. A dysregulation of regulatory T cells (Tregs) could play a major role in the pathogenesis of bronchial asthma. Sex-dependent differences as well as the impact of hormonal changes in the incidence and severity of asthma are widely recognized. Emerging evidence suggests that asthma symptoms are alleviated in female patients taking hormone oral contraceptives (OCs). The impact of OCs on the generation of induced Tregs (iTregs) was assessed in a cohort of female patients with asthma. Methods. Thirteen patients were included in this pilot study. During three distinct phases of their menstrual cycles, we measured exhaled nitric oxide (eNO) levels, forced expiratory volume at 1 second (FEV1s), asthma control test (ACT) score, sex steroid hormone levels in serum, natural Tregs in peripheral blood, and the ability of CD4(+) T cells to generate iTregs ex vivo. Results. The luteal serum levels of estradiol and progesterone negatively correlated with the proportion of iTregs generated ex vivo in patients not taking OCs. In addition, physiological doses of estradiol and progesterone prevented the acquisition of a suppressor T cell phenotype in vitro. Interestingly, patients taking OCs had reduced serum sex hormone levels associated with higher iTreg induction, a better ACT score, and a tendency toward lower eNO levels. Conclusions. Our results identify an impact of sex hormones on the capacity of T cells to polarize towards a regulatory phenotype and suggest the regulation of peripheral T cell lineage plasticity as a potential mechanism underlying the beneficial effects of OCs in women with asthma.

Functional tumor infiltrating TH1 and TH2 effectors in large early-stage cervical cancer are suppressed by regulatory T cells

OBJECTIVE

Analysis of tumor-infiltrating lymphocytes (TILs) is one of the cornerstones for the understanding of immune responses prevailing in the tumor microenvironment. We studied TILs from squamous cell carcinoma of the cervix ex vivo without proliferating them in vitro before analysis.

METHODS

Whereas TILs were magnetic activated cell separation enriched and flow sorted into CD4 CD25 (regulatory T cells [Tregs]), CD4 CD25 (effector T cells [Teffs]) were directly purified by flow cytometry, and both these subsets were characterized phenotypically and functionally. Tissue sections were probed for interleukin 4 (IL-4) and interferon γ.

RESULTS

Effector T cells constitutively expressed both interferon γ and IL-4 prototypical cytokines of TH1 and TH2, respectively, and were able to proliferate and secrete higher quantities of both cytokines in response to anti-CD3/anti-CD28 and autologous tumor lysates. Only 53% of cervical cancer Tregs were FOXP3, elaborated transforming growth factor β1, and IL-10 and were able to inhibit both T helper subsets.

CONCLUSIONS

Intratumoral Teffs represented functionally active subsets of both TH1 and TH2 that were not anergic but were suppressed by multiple Treg subsets, which comprised FOXP3 + Tregs and Tregs secreting transforming growth factor β1 and IL-10. These results imply that the microenvironment of cervical carcinomas harbored both TH1 and TH2 subsets of CD4 Teffs that were functionally active but were perhaps unable to perform because of the overpowering effect of Tregs.

Plasticity within the αβ⁺CD4⁺ T-cell lineage: when, how and what for?

Following thymic output, αβ⁺CD4⁺ T cells become activated in the periphery when they encounter peptide-major histocompatibility complex. A combination of cytokine and co-stimulatory signals instructs the differentiation of T cells into various lineages and subsequent expansion and contraction during an appropriate and protective immune response. Our understanding of the events leading to T-cell lineage commitment has been dominated by a single fate model describing the commitment of T cells to one of several helper (T(H)), follicular helper (T(FH)) or regulatory (T(REG)) phenotypes. Although a single lineage-committed and dedicated T cell may best execute a single function, the view of a single fate for T cells has recently been challenged. A relatively new paradigm in αβ⁺CD4⁺ T-cell biology indicates that T cells are much more flexible than previously appreciated, with the ability to change between helper phenotypes, between helper and follicular helper, or, most extremely, between helper and regulatory functions. In this review, we comprehensively summarize the recent literature identifying when T(H) or T(REG) cell plasticity occurs, provide potential mechanisms of plasticity and ask if T-cell plasticity is beneficial or detrimental to immunity.

TNFRp55 controls regulatory T cell responses in Yersinia-induced reactive arthritis

In addition to its well-known pro-inflammatory effects, tumor necrosis factor (TNF) displays anti-inflammatory activities through mechanisms poorly understood. Previously, we reported the development of severe chronic Yersinia enterocolitica-induced reactive arthritis (ReA) in mice lacking the TNF receptor (TNFR)p55. As regulatory T (T(reg)) cells limit chronic inflammation, here we aim to investigate the expansion and function of CD4(+)CD25(+)FoxP3(+) T(reg) cells in the ReA animal model. The number of T(reg) cells as well as the FoxP3 mRNA expression and interleukin (IL)-10 levels were significantly decreased in joint regional lymph nodes (RLNs) of TNFRp55(-/-) mice vs wild-type (WT) mice at the arthritis onset. However, at chronic phase of arthritis, the number of T(reg) cell in TNFRp55(-/-) was similar to WT mice. To explore the in vivo function of T(reg) cells at this chronic phase in WT and TNFRp55-deficient mice, we adoptively transferred CD4(+) T cells from TNFRp55-deficient mice of day 21, into naïve WT or TNFRp55(-/-) mice. When knockout mice were used as recipients we observed higher delayed-type hypersensitivity (DTH) responses and joint inflammation after heat-killed Yersinia (HKY) stimulation. Accordingly, we found higher levels of IL-17, interferon (IFN)-γ, IL-6, transforming growth factor (TGF)-β1 and IL-12/23p40 and lower IL-10 levels in RLN of paws challenged with HKY in TNFRp55(-/-) recipient mice. In addition, we found that CD4(+) T cells from TNFRp55(-/-) mice controlled antigen-specific IL-12/23(p40) production in recipient WT mice. Our results show that TNFRp55 controls the induction and function of T(reg) cells through differential regulation of cytokine production, suggesting a novel molecular target for immune intervention in ReA.

Immunity to the model intestinal helminth parasite Heligmosomoides polygyrus

Heligmosomoides polygyrus is a natural intestinal parasite of mice, which offers an excellent model of the immunology of gastrointestinal helminth infections of humans and livestock. It is able to establish long-term chronic infections in many strains of mice, exerting potent immunomodulatory effects that dampen both protective immunity and bystander reactions to allergens and autoantigens. Immunity to the parasite develops naturally in some mouse strains and can be induced in others through immunization; while the mechanisms of protective immunity are not yet fully defined, both antibodies and a host cellular component are required, with strongest evidence for a role of alternatively activated macrophages. We discuss the balance between resistance and susceptibility in this model system and highlight new themes in innate and adaptive immunity, immunomodulation, and regulation of responsiveness in helminth infection.

Inflammatory and regulatory T cells contribute to a unique immune microenvironment in tumor tissue of colorectal cancer patients

Colorectal cancer is one of the five leading causes of cancer mortality worldwide. The mechanisms of pathogen clearance, inflammation and regulation by T cells in the healthy bowel are also important in controlling tumor growth. The majority of studies analyzing T cells and their relationship to colorectal tumor growth have focused on individual T cell markers or gene clusters and thus the complexity of the T cell response contributing to the growth of the tumor is not clear. We have studied the T cells in colorectal cancer patients and have defined a unique T cell signature for colorectal tumor tissue. Using a novel analytical flow cytometric approach in concert with confocal microscopy, we have shown that the tumor has a lower frequency of effector T cells (CD69+), but a higher frequency of both regulatory (CD25hi Foxp3+) and inflammatory T cells (IL-17+) compared with associated nontransformed bowel tissue. We have also identified minor populations of T cells expressing conventional markers of both inflammatory and regulatory T cells (CD4+IL-17+Foxp3+) in the tumor tissue. These cells may represent intermediate populations or they may dictate an inflammatory versus regulatory function in surrounding T cells. Together, these data describe an immune microenvironment in colorectal cancer unique to the tumor tissue and distinct from the surrounding healthy bowel tissue, and this distinct environment is reflected by a gradient of T cells expressing markers of multiple T cell populations. These findings may be used to improve diagnosis and prognosis of colorectal cancer patients.

Context and location dependence of adaptive Foxp3(+) regulatory T cell formation during immunopathological conditions

Circulating Foxp3(+) regulatory T cells (Treg) may arise in the thymus (natural Treg, nTreg) or through the adaptive upregulation of Foxp3 after T cell activation (induced Treg, iTreg). In this brief review, we explore evidence for the formation and function of iTreg during pathologic conditions. Determining the ontogeny and function of Treg populations has relied on the use of manipulated systems in which either iTreg or nTreg are absent, or lineage tracing of T cell clones through repertoire analyses. iTreg appear particularly important at mucosal interfaces. iTreg can also ameliorate tissue-specific autoimmunity and are a prominent source of tumor-infiltrating Treg in some models. However, under many conditions, including in CNS autoimmunity, diabetes, and some tumor systems, iTreg formation appears limited. The immunological contribution of iTreg is thus highly context dependent. Deciphering immune parameters responsible for iTreg formation and their role in modulating pathologic immune responses will be important.

IgA plasma cells express the negative regulatory co-stimulatory molecule programmed cell death 1 ligand and have a potential tolerogenic role in the intestine

To maintain immune homeostasis in the intestine, the intestinal immune system has evolved several tolerogenic mechanisms toward intestinal microflora and food antigens. Although programmed cell death-1 (PD-1) protein has been implicated in immunological tolerance in the intestine and gut-associated lymphoid tissues (GALTs), distribution of its ligands PD-L1 and PD-L2 in the small intestine lamina propria (LP) are unknown. We investigated PD-L1 expression in intestinal LP and found that IgA plasma cells (PCs) were major PD-L1 expressing cells. PD-L1 expression levels on IgA PCs were higher than that on IgG PCs in peripheral lymphoid tissues. IgA PCs expressed antigen-presenting molecule MHC class II and co-stimulatory molecules CD80, CD86, and PD-L2. IgA PCs isolated from intestinal LP exhibited antigen presentation activity, and in the presence of TGF-β induced FoxP3(+) regulatory T cells, but not IFN-γ(+) Th1 cells, from naïve T cells. Thus, IgA PCs in the intestine may be involved in an immune regulatory role in the intestinal immune system.

CCR7 deficiency causes diarrhea associated with altered ion transport in colonocytes in the absence of overt colitis

The chemokine receptor CCR7 is a central regulator in the maintenance of cellular homeostasis of mucosal tissues. CCR7⁻/⁻ mice develop autoimmune gastritis and exocrinopathy accompanied by the formation of mucosal tertiary lymphoid follicles. Here we found that CCR7-deficient mice frequently suffered from chronic diarrhea linked with increased gastrointestinal motility and the development of severe anorectal prolapse. Enhanced formation of intestinal lymphoid follicles was associated with an elevated proportion of activated colonic T cells and increased production of the cytokine interleukin (IL)-1β. To uncover the pathomechanisms of diarrhea in CCR7⁻/⁻ mice, colonic epithelial barrier and ion channel activities were analyzed in Ussing chambers. Although overt acute colitis was absent, CCR7 deficiency resulted in reduced electrogenic sodium absorption and colonic chloride secretion. As it is known that IL-1β regulates epithelial sodium channel (ENaC) activity, these data imply a causal link between CCR7 expression, IL-1β level, and Na⁺ malabsorption owing to altered ENaC expression and diarrhea.

Abating colon cancer polyposis by Lactobacillus acidophilus deficient in lipoteichoic acid

An imbalance of commensal bacteria and their gene products underlies mucosal and, in particular, gastrointestinal inflammation and a predisposition to cancer. Lactobacillus species have received considerable attention as examples of beneficial microbiota. We have reported previously that deletion of the phosphoglycerol transferase gene that is responsible for lipoteichoic acid (LTA) biosynthesis in Lactobacillus acidophilus (NCK2025) rendered this bacterium able to significantly protect mice against induced colitis when delivered orally. Here we report that oral treatment with LTA-deficient NCK2025 normalizes innate and adaptive pathogenic immune responses and causes regression of established colonic polyps. This study reveals the proinflammatory role of LTA and the ability of LTA-deficient L. acidophilus to regulate inflammation and protect against colonic polyposis in a unique mouse model.

Maintenance of small intestinal and colonic tolerance by IL-10-producing regulatory T cell subsets

The intestinal mucosa is continuously exposed to harmless exogenous antigens derived from food proteins and microbiota. Continuous surveillance by suppressive regulatory T cells prevents inflammatory responses to these antigens thereby maintaining intestinal homeostasis. The nature of the antigenic pressure varies at different locations of the intestinal tract. In agreement with this strong microenvironmental control, small intestinal and colonic regulatory T cell homeostasis varies considerably. In this review, we summarize the substantial advances that have been made in dissecting the phenotype and function of intestinal regulatory T cells, discuss how microbiota can modulate the intestinal regulatory T cell pool and review the crucial role of the immunoregulatory cytokine interleukin-10 (IL-10) in shaping and maintenance of mucosal tolerance.

Therapeutic potential of induced and natural FoxP3(+) regulatory T cells for the treatment of Graft-versus-host disease

Graft-versus-host disease (GvHD) remains a major complication after allogeneic hematopoietic stem-cell-transplantation. Present GvHD prophylaxis and treatment is still based on unspecific immunosuppressive drug therapy. Over the last decade, the potential of cell-based therapies involving the infusion of regulatory T cells has emerged as a feasible alternative approach for the treatment and prevention of GvHD. Here we review current efforts to translate data obtained in rodent models into clinical trials. Special emphasis is placed on the variety of strategies to generate sufficient numbers of alloantigen-specific regulatory T cells for adoptive cell therapy. This can be achieved either by expansion or by induction of a regulatory phenotype in naive T cells. Stability of the immunosuppressive phenotype of transferred regulatory T cells even in the highly inflammatory environment of acute GvHD will be thereby a critical parameter for actual therapeutic application.

Tpl2 ablation promotes intestinal inflammation and tumorigenesis in Apcmin mice by inhibiting IL-10 secretion and regulatory T-cell generation

To address the role of Tpl2, a MAP3K8 that regulates innate/adaptive immunity and inflammation, in intestinal tumorigenesis, we crossed a Tpl2 KO allele into the Apc(min/+) genetic background. Here, we show that Apc(min/+)/Tpl2(-/-) mice exhibit a fivefold increase in the number of intestinal adenomas. Bone marrow transplantation experiments revealed that the enhancement of polyposis was partially hematopoietic cell-driven. Consistent with this observation, Tpl2 ablation promoted intestinal inflammation. IL-10 levels and regulatory T-cell numbers were lower in the intestines of Tpl2(-/-) mice, independent of Apc and polyp status, suggesting that they were responsible for the initiation of the enhancement of tumorigenesis caused by the ablation of Tpl2. The low IL-10 levels correlated with defects in mTOR activation and Stat3 phosphorylation in Toll-like receptor-stimulated macrophages and with a defect in inducible regulatory T-cell generation and function. Both polyp numbers and inflammation increased progressively with time. The rate of increase of both, however, was more rapid in Apc(min/+)/Tpl2(-/-) mice, suggesting that the positive feedback initiated by inflammatory signals originating in developing polyps is more robust in these mice. This may be because these mice have a higher intestinal polyp burden as a result of the enhancement of tumor initiation.

Immunohistochemical investigation of Foxp3 expression in the intestine in healthy and diseased dogs

Intestinal immune regulation including development of oral tolerance is of great importance for the maintenance of intestinal homeostasis. Concerning this, regulatory T cells (Tregs) occupy a pivotal role in cell-mediated immunosuppression. Dysregulation of mucosal immunology leading to an abnormal interaction with commensal bacteria is suggested to play a key role in the pathogenesis of Inflammatory Bowel Disease (IBD) in men and dogs. The aim of this study was to characterise the expression of Foxp3 in the normal canine gut of 18 dogs (mean age: 6.03 years), in 16 dogs suffering from IBD (mean age: 5.05 years), and of 6 dogs with intestinal nematode infection (mean age: 0.87 years) using immunohistochemistry. In the duodenum, Tregs in healthy dogs declined from villi (median: 10.67/62 500 μm2) to crypts (median: 1.89/62 500 μm2). Tregs were further increased in the villi of middle-aged dogs (median: 18.92/62 500 μm2) in contrast to juvenile (median: 3.50/62 500 μm2) and old (median: 9.56/62 500 μm2) individuals. Compared to healthy controls, animals suffering from IBD revealed reduced numbers of Tregs in duodenal villi (median: 4.13/62 500 μm2). Dogs with intestinal nematode infection displayed increased numbers of Tregs (median: 21.06/62 500 μm2) compared to healthy animals.Age-related changes indicate a progressive establishment of oral tolerance and immunosenescence in the canine elderly. The results further suggest that a defect in Treg homeostasis may be involved in the pathogenesis of canine IBD. In contrast, increased numbers of Tregs in the duodenum may be due to nematode infection.