Regulatory T cells use "Itch" to control asthma

Deciphering the developmental trajectory of tissue-resident Foxp3+ regulatory T cells

Foxp3+ TREG cells have been at the focus of intense investigation for their recognized roles in preventing autoimmunity, facilitating tissue recuperation following injury, and orchestrating a tolerance to innocuous non-self-antigens. To perform these critical tasks, TREG cells undergo deep epigenetic, transcriptional, and post-transcriptional changes that allow them to adapt to conditions found in tissues both at steady-state and during inflammation. The path leading TREG cells to express these tissue-specialized phenotypes begins during thymic development, and is further driven by epigenetic and transcriptional modifications following TCR engagement and polarizing signals in the periphery. However, this process is highly regulated and requires TREG cells to adopt strategies to avoid losing their regulatory program altogether. Here, we review the origins of tissue-resident TREG cells, from their thymic and peripheral development to the transcriptional regulators involved in their tissue residency program. In addition, we discuss the distinct signalling pathways that engage the inflammatory adaptation of tissue-resident TREG cells, and how they relate to their ability to recognize tissue and pathogen-derived danger signals.

Epigenetics in T-cell driven inflammation and cancer

For decades, scientists have been investigating how processes such as gene expression, stem cell plasticity, and cell differentiation can be modulated. The discovery of epigenetics helped unravel these processes and enabled the identification of major underlying mechanisms that, for example, are central for T cell maturation. T cells go through various stages in their development evolving from progenitor cells into double positive CD4/CD8 T cells that finally leave the thymus as naïve T cells. One major mechanism driving T cell maturation is the modulation of gene activity by temporally sequenced transcription of spatially exposed gene loci. DNA methylation, demethylation, and acetylation are key processes that enable a sequenced gene expression required for T cell differentiation. In vivo, differentiated T cells are subjected to enormous pressures originating from the microenvironment. Signals from this environment, particularly from an inflammatory or a tumor microenvironment, can push T cells to differentiate into specific effector and memory T cells, and even prompt T cells to adopt a state of dysfunctional exhaustion, en route of an epigenetically controlled mechanism. Fundamentals of these processes will be discussed in this review highlighting potential therapeutic interventions, in particular those beneficial to revive exhausted T cells.

The functional adaptation of effector Foxp3+ regulatory T cells to pulmonary inflammation

During infections, the timings of effector differentiation of pulmonary immune responses are of paramount importance, as pathogen persistence and unsuppressed inflammation can rapidly lead to a loss of function, increased frailty, and death. Thus, both an efficient clearance of the danger and a rapid resolution of inflammation are critical to host survival. We now know that tissue-localized FoxP3+ regulatory T cells, a subset of CD4+ T cells, are highly attuned to the type of immune response, acquiring unique phenotypic characteristics that allow them to adapt their suppressive functions with the nature of inflammatory cells. To achieve this, activated effector TREG cells acquire specialized TH 1, TH 2, and TH 17-like characteristics that allow them to migrate, survive, and time their function(s) through refined mechanisms. Herein, we describe how this process requires a unique developmental path that includes the acquisition of master transcription factors and the expression of receptors adapted to sense local danger signals that are found during pulmonary inflammation. In turn, we offer an overview of how these characteristics promote the capacity of local effector TREG cells to proliferate, survive, and display suppressive strategies to resolve lung injury.

Astragaloside IV Ameliorates Airway Inflammation in an Established Murine Model of Asthma by Inhibiting the mTORC1 Signaling Pathway

Astragaloside IV (AS-IV), a main active constituent of Astragalus membranaceus, has been confirmed to have antiasthmatic effects. However, it remained unclear whether the beneficial effects of AS-IV on asthma were attributed to the mTOR inhibition; this issue was the focus of the present work. BALB/c mice were sensitized and challenged with ovalbumin followed with 3 weeks of rest/recovery and then reexposure to ovalbumin. AS-IV was administrated during the time of rest and reexposure. The characteristic features of allergic asthma, including airway hyperreactivity, histopathology, cytokines (IL-4, IL-5, IL-13, IL-17, and INF-γ), and CD4⁺CD25⁺Foxp3⁺Treg cells in bronchoalveolar lavage fluid (BALF), and downstream proteins of mTORC1/2 signaling were examined. AS-IV markedly suppressed airway hyperresponsiveness and reduced IL-4, IL-5, and IL-17 levels and increased INF-γ levels in the BALF. Histological studies showed that AS-IV markedly decreased inflammatory infiltration in the lung tissues. Notably, AS-IV inhibited mTORC1 activity, whereas it had limited effects on mTORC2, as assessed by phosphorylation of mTORC1 and mTORC2 substrates S6 ribosomal protein, p70 S6 Kinase, and Akt, respectively. CD4⁺CD25⁺Foxp3⁺Treg cells in BALF were not significantly changed by AS-IV. Together, these results suggest that the antiasthmatic effects of AS-IV were at least partially from inhibiting the mTORC1 signaling pathway.

Overexpression and varied clinical significance of Th9 versus Th17 cells in distinct subtypes of oral lichen planus

OBJECTIVE

Oral lichen planus (OLP) presents with large numbers of T lymphocytes accumulating beneath the epithelium of the oral mucosa; however, its aetiology remains obscure. A potential role for an emerging novel T cell subset, Th9, in OLP has recently been suggested but remains to be clarified. The current aim was to investigate the expression and potential clinical significance of Th9 cells in distinct subtypes of OLP.

MATERIALS AND METHODS

Peripheral blood samples were collected from 41 OLP patients and 18 healthy controls (HCs). Flow cytometric analysis was used to detect the CD4+ T helper subset Th9 (IL-9⁺IL-17^-CD4⁺ Th cells) and Th17 (IL-9^-IL-17⁺CD4⁺ Th cells) expression levels.

RESULTS

Flow cytometry results showed significantly elevated levels of Th9 cells in reticular and erosive OLP compared to HCs. Th9 expression in erosive OLP was less than in reticular OLP, indicating that Th9 but not Th17 cells may play a predominant role in reticular disease. However, in erosive OLP patients, we found much higher levels of Th17 cells compared to reticular OLP patients and HCs, indicating that Th17 dominates in erosive OLP. Statistical analysis showed positive correlations of Th9 cells and Th17 cells in patients with reticular or erosive OLP but none in HCs.

CONCLUSIONS

Th9 and Th17 cells may take the predominant roles in reticular and erosive OLP respectively, and their numbers were positively correlated in reticular and erosive OLP patients. Elevated circulating Th9 cells may help maintain immune balance in OLP immunopathogenesis, which requires further investigation.

Allergies - A T cells perspective in the era beyond the TH1/TH2 paradigm

Allergic diseases have emerged as a major health care burden, especially in the western hemisphere. They are defined by overshooting reactions of an aberrant immune system to harmless exogenous stimuli. The T_H1/T_H2 paradigm assumes that a dominance of T_H2 cell activation and an inadequate T_H1 cell response are responsible for the development of allergies. However, the characterization of additional T helper cell subpopulations such as T_H9, T_H17, T_H22, T_HGM-CSF and their interplay with regulatory T cells suggest further layers of complexity. This review summarizes state-of-the-art knowledge on T cell diversity and their induction, while revisiting the T_H1/T_H2 paradigm. With respect to these numerous contributors, it offers a new perspective on the pathogenesis of asthma, allergic rhinitis (AR) and atopic dermatitis (AD) incorporating recent discoveries in the field of T cell plasticity.

Regulatory T cells in cardiovascular diseases

Inflammation is essential in the initial development and progression of many cardiovascular diseases involving innate and adaptive immune responses. The role of CD4(+)CD25(+)FOXP3(+) regulatory T (TREG) cells in the modulation of inflammation and immunity has received increasing attention. Given the important role of TREG cells in the induction and maintenance of immune homeostasis and tolerance, dysregulation in the generation or function of TREG cells can trigger abnormal immune responses and lead to pathology. A wealth of evidence from experimental and clinical studies has indicated that TREG cells might have an important role in protecting against cardiovascular disease, in particular atherosclerosis and abdominal aortic aneurysm. In this Review, we provide an overview of the roles of TREG cells in the pathogenesis of a number of cardiovascular diseases, including atherosclerosis, hypertension, ischaemic stroke, abdominal aortic aneurysm, Kawasaki disease, pulmonary arterial hypertension, myocardial infarction and remodelling, postischaemic neovascularization, myocarditis and dilated cardiomyopathy, and heart failure. Although the exact molecular mechanisms underlying the cardioprotective effects of TREG cells are still to be elucidated, targeted therapies with TREG cells might provide a promising and novel future approach to the prevention and treatment of cardiovascular diseases.

Helicobacter pylori neutrophil-activating protein: a potential Treg modulator suppressing allergic asthma?

The ultimate aim of the immune system is to eliminate pathogens without being harmful to the host. But what if eliminating the pathogen in itself is discomforting for the host? One such emerging case is of Helicobacter pylori. Modern medicine, infantile vaccination, and ultra-hygienic conditions have led to progressive disappearance of H. pylori in different parts of the world. However, the adversities caused by H. pylori's absence are much larger than those caused by its presence. Asthma is rising as an epidemic in last few decades and several reports suggest an inverse-relationship between H. pylori's persistence and early-life onset asthma. Regulatory T cells play an important role in both the cases. This is further supported by experiments on mouse-models. Hence, need of the hour is to discern the relationship between H. pylori and its host and eliminating its negative impacts without disturbing our indigenous microbiota. To resolve whether H. pylori is a pathogen or an amphibiont is another important side. This review explores the biological basis of H. pylori-induced priming of immune system offering resistance to childhood-onset asthma. HP-NAP-Tregs interaction has been predicted using molecular docking and dynamic simulation.

Cutting edge: maresin-1 engages regulatory T cells to limit type 2 innate lymphoid cell activation and promote resolution of lung inflammation

Asthma is a chronic inflammatory disease that fails to resolve. Recently, a key role for type 2 innate lymphoid cells (ILC2s) was linked to asthma pathogenesis; however, mechanisms for ILC2 regulation remain to be determined. In this study, metabololipidomics of murine lungs identified temporal changes in endogenous maresin 1 (MaR1) during self-limited allergic inflammation. Exogenous MaR1 reduced lung inflammation and ILC2 expression of IL-5 and IL-13 and increased amphiregulin. MaR1 augmented de novo generation of regulatory T cells (Tregs), which interacted with ILC2s to markedly suppress cytokine production in a TGF-β-dependent manner. Ab-mediated depletion of Tregs interrupted MaR1 control of ILC2 expression of IL-13 in vivo. Together, the findings uncover Tregs as potent regulators of ILC2 activation; MaR1 targets Tregs and ILC2s to restrain allergic lung inflammation, suggesting MaR1 as the basis for a new proresolving therapeutic approach to asthma and other chronic inflammatory diseases.