An endogenous aryl hydrocarbon receptor ligand enhances de novo generation of regulatory T cells in humans

The modern human aryl hydrocarbon receptor is more active when ancestralized by genome editing

The aryl hydrocarbon receptor (AHR) is a transcription factor that has many functions in mammals. Its best known function is that it binds aromatic hydrocarbons and induces the expression of cytochrome P450 genes, which encode enzymes that metabolize aromatic hydrocarbons and other substrates. All present-day humans carry an amino acid substitution at position 381 in the AHR that occurred after the divergence of modern humans from Neandertals and Denisovans. Previous studies that have expressed the ancestral and modern versions of AHR from expression vectors have yielded conflicting results with regard to their activities. Here, we use genome editing to modify the endogenous AHR gene so that it encodes to the ancestral, Neandertal-like AHR protein in human cells. In the absence of exogenous ligands, the expression of AHR target genes is higher in cells expressing the ancestral AHR than in cells expressing the modern AHR, and similar to the expression in chimpanzee cells. Furthermore, the modern human AHR needs higher doses of three ligands than the ancestral AHR to induce the expression of target genes. Thus, the ability of AHR to induce the expression of many of its target genes is reduced in modern humans.

Transcriptional regulation of innate lymphoid cells and T cells by aryl hydrocarbon receptor

The aryl hydrocarbon receptor (Ahr) is a ligand-dependent transcription factor and facilitates immune cell environmental sensing through its activation by cellular, dietary, and microbial metabolites, as well as environmental toxins. Although expressed in various cell types, Ahr in innate lymphoid cells (ILCs) and their adaptive T cell counterparts regulates essential aspects of their development and function. As opposed to T cells, ILCs exclusively rely on germ-line encoded receptors for activation, but often share expression of core transcription factors and produce shared effector molecules with their T cell counterparts. As such, core modules of transcriptional regulation are both shared and diverge between ILCs and T cells. In this review, we highlight the most recent findings regarding Ahr’s transcriptional regulation of both ILCs and T cells. Furthermore, we focus on insights elucidating the shared and distinct mechanisms by which Ahr regulates both innate and adaptive lymphocytes.

From Nucleus to Organs: Insights of Aryl Hydrocarbon Receptor Molecular Mechanisms

The aryl hydrocarbon receptor (AHR) is a markedly established regulator of a plethora of cellular and molecular processes. Its initial role in the detoxification of xenobiotic compounds has been partially overshadowed by its involvement in homeostatic and organ physiology processes. In fact, the discovery of its ability to bind specific target regulatory sequences has allowed for the understanding of how AHR modulates such processes. Thereby, AHR presents functions in transcriptional regulation, chromatin architecture modifications and participation in different key signaling pathways. Interestingly, such fields of influence end up affecting organ and tissue homeostasis, including regenerative response both to endogenous and exogenous stimuli. Therefore, from classical spheres such as canonical transcriptional regulation in embryonic development, cell migration, differentiation or tumor progression to modern approaches in epigenetics, senescence, immune system or microbiome, this review covers all aspects derived from the balance between regulation/deregulation of AHR and its physio-pathological consequences.

Targeting AhR as a Novel Therapeutic Modality against Inflammatory Diseases

For decades, activation of Aryl Hydrocarbon Receptor (AhR) was excluded from consideration as a therapeutic approach due to the potential toxic effects of AhR ligands and the induction of the cytochrome P450 enzyme, Cyp1a1, following AhR activation. However, it is now understood that AhR activation not only serves as an environmental sensor that regulates the effects of environmental toxins, but also as a key immunomodulator where ligands induce a variety of cellular and epigenetic mechanisms to attenuate inflammation. Thus, the emergence of further in-depth research into diverse groups of compounds capable of activating this receptor has prompted reconsideration of its use therapeutically. The aim of this review is to summarize the body of research surrounding AhR and its role in regulating inflammation. Specifically, evidence supporting the potential of targeting this receptor to modulate the immune response in inflammatory and autoimmune diseases will be highlighted. Additionally, the opportunities and challenges of developing AhR-based therapies to suppress inflammation will be discussed.

Dysfunctions, Molecular Mechanisms, and Therapeutic Strategies of Regulatory T Cells in Rheumatoid Arthritis

Regulatory T cells (Tregs) represent a distinct subpopulation of CD4⁺ T lymphocytes that promote immune tolerance and maintain immune system homeostasis. The dysfunction of Tregs is tightly associated with rheumatoid arthritis (RA). Although the complex pathogenic processes of RA remain unclear, studies on Tregs in RA have achieved substantial progress not only in fundamental research but also in clinical application. This review discusses the current knowledge of the characterizations, functions, and molecular mechanisms of Tregs in the pathogenesis of RA, and potential therapies for these disorders are also involved.

Super-Treg: Toward a New Era of Adoptive Treg Therapy Enabled by Genetic Modifications

Regulatory Tcells (Treg) are essential components of peripheral immune homeostasis. Adoptive Treg cell therapy has shown efficacy in a variety of immune-mediated diseases in preclinical studies and is now moving from phase I/IIa to larger phase II studies aiming to demonstrate efficacy. However, hurdles such as in vivo stability and efficacy remain to be addressed. Nevertheless, preclinical models have shown that Treg function and specificity can be increased by pharmacological substances or gene modifications, and even that conventional T cells can be converted to Treg potentially providing new sources of Treg and facilitating Treg cell therapy. The exponential growth in genetic engineering techniques and their application to T cells coupled to a large body of knowledge on Treg open numerous opportunities to generate Treg with "superpowers". This review summarizes the genetic engineering techniques available and their applications for the next-generation of Super-Treg with increased function, stability, redirected specificity and survival.

An Insight into the Roles of Dietary Tryptophan and Its Metabolites in Intestinal Inflammation and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is complex, chronic, and relapsing gastrointestinal inflammatory disorders, which includes mainly two conditions, namely ulcerative colitis (UC) and Crohn's disease (CD). Development of IBD in any individual is closely related to his/her autoimmune regulation, gene-microbiota interactions, and dietary factors. Dietary tryptophan (Trp) is an essential amino acid for intestinal mucosal cells, and it is associated with the intestinal inflammation, epithelial barrier, and energy homeostasis of the host. According to recent studies, Trp and its three major metabolic pathways, namely kynurenine (KYN) pathway, indole pathway, and 5-hydroxytryptamine (5-HT) pathway, have vital roles in the regulation of intestinal inflammation by acting directly or indirectly on the pro/anti-inflammatory cytokines, functions of various immune cells, as well as the intestinal microbial composition and homeostasis. In this review, recent advances in Trp- and its metabolites-associated intestinal inflammation are summarized. It further discusses the complex mechanisms and interrelationships of the three major metabolic pathways of Trp in regulating inflammation, which could elucidate the value of dietary Trp to be used as a nutrient for IBD patients.

Particulate matter of 2.5 μm or less in diameter disturbs the balance of TH17/regulatory T cells by targeting glutamate oxaloacetate transaminase 1 and hypoxia-inducible factor 1α in an asthma model

BACKGROUND

Epidemiologic evidence suggests that exposure to particulate matter of 2.5 μm or less in diameter (PM2.5) aggravates asthma.

OBJECTIVE

We sought to investigate the underlying mechanisms between PM2.5 exposure and asthma severity.

METHODS

The relationship between PM2.5 exposure and asthma severity was investigated in an asthma model with CD4⁺ T cell-specific aryl hydrocarbon receptor (AhR)-null mice. Effects of PM2.5 and polycyclic aromatic hydrocarbons (PAHs) on differentiation of T_H17/regulatory T (Treg) cells were investigated by using flow cytometry and quantitative RT-PCR. Mechanisms were investigated by using mRNA sequencing, chromatin immunoprecipitation, bisulfite sequencing, and glycolysis rates.

RESULTS

PM2.5 impaired differentiation of Treg cells, promoted differentiation of T_H17 cells, and aggravated asthma in an AhR-dependent manner. PM2.5 and one of its prominent PAHs, indeno[1,2,3-cd]pyrene (IP), promoted differentiation of T_H17 cells by upregulating hypoxia-inducible factor 1α expression and enhancing glycolysis through AhRs. Exposure to PM2.5 and IP enhanced glutamate oxaloacetate transaminase 1 (Got1) expression through AhRs and accumulation of 2-hydroxyglutarate, which inhibited ten-eleven translocation methylcytosine dioxygenase 2 activity, resulting in hypermethylation in the forkhead box P3 locus and impaired differentiation of Treg cells. A GOT1 inhibitor, (aminooxy)acetic acid, ameliorated asthma by shifting differentiation of T_H17 cells to Treg cells. Similar regulatory effects of exposure to PM2.5 or IP on T_H17/Treg cell imbalance were noted in human T cells, and in a case-control design PAH exposure appeared to be a potential risk factor for asthma.

CONCLUSIONS

The AhR-hypoxia-inducible factor 1α and AhR-GOT1 molecular pathways mediate pulmonary responses on exposure to PM2.5 through their ability to disturb the balance of T_H17/Treg cells.

Progress and history of the 10th Federation of African Immunological Societies Congress

The 10th Federation of African Immunological Societies (FAIS) Congress, held in Tunisia in November 2017, marked a significant scientific milestone. It enabled scientists from across the continent to promote immunology research and to showcase major achievements made by immunologists throughout Africa. This issue of the Journal of Leukocyte Biology (JLB) features manuscripts from the FAIS Congress. As noted in these papers, research in infectious diseases remains the focus of the African immunology community; however, increasingly noncommunicable diseases-such as autoimmunity, allergy, primary immunodeficiency, cancer and transplantation immunology-are also an emerging priority. This overview gives a brief history of the FAIS meeting, which also commemorated the 25th anniversary of the FAIS. It describes the current activities of the organization, as well as its history and the future opportunities for this Federation.