Detection of a novel population of fetal thymocytes characterized by preferential emigration and a TCRγδ+ T cell fate after dioxin exposure

The key player in the pathogenesis of environmental influence of systemic lupus erythematosus: Aryl hydrocarbon receptor

The aryl hydrocarbon receptor was previously known as an environmental receptor that modulates the cellular response to external environmental changes. In essence, the aryl hydrocarbon receptor is a cytoplasmic receptor and transcription factor that is activated by binding to the corresponding ligands, and they transmit relevant information by binding to DNA, thereby activating the transcription of various genes. Therefore, we can understand the development of certain diseases and discover new therapeutic targets by studying the regulation and function of AhR. Several autoimmune diseases, including systemic lupus erythematosus (SLE), have been connected to AhR in previous studies. SLE is a classic autoimmune disease characterized by multi-organ damage and disruption of immune tolerance. We discuss here the homeostatic regulation of AhR and its ligands among various types of immune cells, pathophysiological roles, in addition to the roles of various related cytokines and signaling pathways in the occurrence and development of SLE.

Environmental exposures and RNA N6-Methyladenosine modified long Non-Coding RNAs

Recent advances in the field of RNA modifications and long non-coding RNAs (lncRNAs) have provided substantial evidence on important biological functions. LncRNAs are defined as longer than 200 nucleotides which are not translated into proteins. The term "epitranscriptome" refers to all modifications in RNA types. Adenine-6 methylation (m⁶A) is the most common, dynamic and prominent modifications in coding and non-coding RNAs and has critical and previously unappreciated functional roles. Accumulation evidence indicated the association between RNA m6A modification and cancer and nonmalignant diseases. Recent studies reported that several lncRNAs including MALAT1, MEG3, XIST, GAS5, and KCNK15-AS1 are subject to m⁶A modification. It can be suggested that lncRNAs modified by m⁶A modification have substantive roles in diseases. Currently limited data are available regarding how environmental exposure affects m⁶A-modified lncRNAs. Furthermore, we do not know the interaction of environmental exposure and m⁶A-modified lncRNAs in development of adverse human health outcomes. Thus, in this systematic review, we aimed to present the data of the studies that reported a significant association between environmental exposure and expression/DNA methylation of m⁶A-modified long non-coding RNAs.

The Ancestral Environment Shapes Antiviral CD8+ T cell Responses across Generations

Recent studies have linked health fates of children to environmental exposures of their great grandparents. However, few studies have considered whether ancestral exposures influence immune function across generations. Here, we report transgenerational inheritance of altered T cell responses resulting from maternal (F0) exposure to the aryl hydrocarbon receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Since F0 exposure to TCDD has been linked to transgenerational transmission of reproductive problems, we asked whether maternal TCDD exposure also caused transgenerational changes in immune function. F0 exposure caused transgenerational effects on the CD8+ T cell response to influenza virus infection in females but not in males. Outcrosses showed changes were passed through both parental lineages. These data demonstrate that F0 exposure to an aryl hydrocarbon receptor (AHR) agonist causes durable changes to immune responses that can affect subsequent generations. This has broad implications for understanding how the environment of prior generations shapes susceptibility to pathogens and antiviral immunity in later generations.

Aryl hydrocarbon receptor is critical for homeostasis of invariant gammadelta T cells in the murine epidermis

An immunoregulatory role of aryl hydrocarbon receptor (AhR) has been shown in conventional αβ and γδ T cells, but its function in skin γδ T cells (dendritic epidermal T cells [DETC]) is unknown. In this study, we demonstrate that DETC express AhR in wild-type mice, and are specifically absent in the epidermis of AhR-deficient mice (AhR-KO). We show that DETC precursors are generated in the thymus and home to the skin. Proliferation of DETC in the skin was impaired in AhR-KO mice, resulting in a >90% loss compared with wild type. Surprisingly, DETC were not replaced by αβ T cells or conventional γδ T cells, suggesting a limited time frame for seeding this niche. We found that DETC from AhR-KO mice failed to express the receptor tyrosine kinase c-Kit, a known growth factor for γδ T cells in the gut. Moreover, we found that c-kit is a direct target of AhR, and propose that AhR-dependent c-Kit expression is potentially involved in DETC homeostasis. DETC are a major source of GM-CSF in the skin. Recently, we had shown that impaired Langerhans cell maturation in AhR-KO is related to low GM-CSF levels. Our findings suggest that the DETCs are necessary for LC maturation, and provide insights into a novel role for AhR in the maintenance of skin-specific γδ T cells, and its consequences for the skin immune network.

2,3,7,8-Tetrachlorodibenzo-p-dioxin impairs stable establishment of oral tolerance in mice

The toxic environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent immunomodulatory chemical. TCDD activates the aryl hydrocarbon receptor (AhR) and suppresses peripheral humoral and cellular adaptive immune responses. Though the major route of uptake is via food, little is known until now on the immunotoxic effects of TCDD on the gut-associated lymphoid tissue. We show here that AhR is strongly expressed along the small intestine, especially in intestinal epithelial cells (IEC). The AhR marker gene cyp1a1 is induced in IEC by oral TCDD exposure. We asked how TCDD affects oral tolerance, a unique function of mucosal immunity. C57BL/6 mice were injected with 10 μg/kg body weight TCDD and fed with ovalbumin (OVA) in a high-dose tolerization protocol. Mice were immunized and boosted with OVA on days 12, 23, and 55 after tolerization. Five of 14, 6 of 15, and 13 of 14 TCDD-treated mice generated OVA-specific immunoglobulin (Ig)G1 antibodies after the first, second, and third immunization with OVA, respectively. Only one mouse harbored anti-OVA IgG1 antibodies in the control group even after the third immunization with OVA. OVA-specific IgA in fecal samples of tolerized and TCDD-exposed mice could be detected at the levels of nontolerized mice, whereas completely absent in tolerant control mice. Correlated to this, we found in TCDD-treated mice an increase in interleukin-6 producing CD103+ dendritic cells (DC) present in the gut-draining mesenteric lymph nodes (MLN) and a small increase in the frequency of Th17 cells. Neither the frequencies nor the absolute numbers of immune cells in the lamina propria (LP) or in intraepithelial lymphocytes were changed by TCDD treatment. Our data not only have implications for food allergies in settings of environmental exposure but also raise concerns regarding the harmlessness of overdosing potential AhR agonist in food, which needs to be studied further.

Microarray analysis of the AHR system: Tissue-specific flexibility in signal and target genes

Data mining published microarray experiments require that expression profiles are directly comparable. We performed linear global normalization on the data of 1967 Affymetrix U74av2 microarrays, i.e. the transcriptomes of >100 murine tissues or cell types. The mathematical transformation effectively nullifies inter-experimental or inter-laboratory differences between microarrays. The correctness of expression values was validated by quantitative RT-PCR. Using the database we analyze components of the aryl hydrocarbon receptor (AHR) signaling pathway in various tissues. We identified lineage and differentiation specific variant expression of AHR, ARNT, and HIF1alpha in the T-cell lineage and high expression of CYP1A1 in immature B cells and dendritic cells. Performing co-expression analysis we found unorthodox expression of the AHR in the absence of ARNT, particularly in stem cell populations, and can reject the hypothesis that ARNT2 takes over and is highly expressed when ARNT expression is low or absent. Furthermore the AHR shows no co-expression with any other transcript present on the chip. Analysis of differential gene expression under 308 conditions revealed 53 conditions under which the AHR is regulated, numerous conditions under which an intrinsic AHR action is modified as well as conditions activating the AHR even in the absence of known AHR ligands. Thus meta-analysis of published expression profiles is a powerful tool to gain novel insights into known and unknown systems.

Transcriptional signatures of immune cells in aryl hydrocarbon receptor (AHR)-proficient and AHR-deficient mice

The ligand-activated aryl hydrocarbon receptor (AHR) is known to modulate many genes in a highly cell-specific manner, either directly or indirectly via secondary effects. In contrast, little is known about the effects of AHR deficiency on gene expression balance. We compared the transcriptome of CD4 T cells from AHR-/- mice and wild-type mice; 390 genes, many of them immunotypic, were deregulated in AHR-deficient CD4 cells. TCDD-induced transcriptome changes correlated with the AHR expression level in immune cells. However, there was little overlap in AHR-dependent transcripts found in T lineage cells or dendritic cells. Our results demonstrate flexible gene accessibility for the AHR in immune cells. The idea of a universal battery of AHR-responsive genes is not tenable.