Follicular Helper T Cells.

Although T cell help for B cells was described several decades ago, it was the identification of CXCR5 expression by B follicular helper T (Tfh) cells and the subsequent discovery of their dependence on BCL6 that led to the recognition of Tfh cells as an independent helper subset and accelerated the pace of discovery. More than 20 transcription factors, together with RNA-binding proteins and microRNAs, control the expression of chemotactic receptors and molecules important for the function and homeostasis of Tfh cells. Tfh cells prime B cells to initiate extrafollicular and germinal center antibody responses and are crucial for affinity maturation and maintenance of humoral memory. In addition to the roles that Tfh cells have in antimicrobial defense, in cancer, and as HIV reservoirs, regulation of these cells is critical to prevent autoimmunity. The realization that follicular T cells are heterogeneous, comprising helper and regulatory subsets, has raised questions regarding a possible division of labor in germinal center B cell selection and elimination.

Targeting TFH cells in human diseases and vaccination: rationale and practice.

The identification of CD4+ T cells localizing to B cell follicles has revolutionized the knowledge of how humoral immunity is generated. Follicular helper T (TFH) cells support germinal center (GC) formation and regulate clonal selection and differentiation of memory and antibody-secreting B cells, thus controlling antibody affinity maturation and memory. TFH cells are essential in sustaining protective antibody responses necessary for pathogen clearance in infection and vaccine-mediated protection. Conversely, aberrant and excessive TFH cell responses mediate and sustain pathogenic antibodies to autoantigens, alloantigens, and allergens, facilitate lymphomagenesis, and even harbor viral reservoirs. TFH cell generation and function are determined by T cell antigen receptor (TCR), costimulation, and cytokine signals, together with specific metabolic and survival mechanisms. Such regulation is crucial to understanding disease pathogenesis and informing the development of emerging therapies for disease or novel approaches to boost vaccine efficacy.

Selenium-GPX4 axis protects follicular helper T cells from ferroptosis.

Follicular helper T (TFH) cells are a specialized subset of CD4+ T cells that essentially support germinal center responses where high-affinity and long-lived humoral immunity is generated. The regulation of TFH cell survival remains unclear. Here we report that TFH cells show intensified lipid peroxidation and altered mitochondrial morphology, resembling the features of ferroptosis, a form of programmed cell death that is driven by iron-dependent accumulation of lipid peroxidation. Glutathione peroxidase 4 (GPX4) is the major lipid peroxidation scavenger and is necessary for TFH cell survival. The deletion of GPX4 in T cells selectively abrogated TFH cells and germinal center responses in immunized mice. Selenium supplementation enhanced GPX4 expression in T cells, increased TFH cell numbers and promoted antibody responses in immunized mice and young adults after influenza vaccination. Our findings reveal the central role of the selenium-GPX4-ferroptosis axis in regulating TFH homeostasis, which can be targeted to enhance TFH cell function in infection and following vaccination.

CD4+ T cell-induced inflammatory cell death controls immune-evasive tumours.

Most clinically applied cancer immunotherapies rely on the ability of CD8+ cytolytic T cells to directly recognize and kill tumour cells1-3. These strategies are limited by the emergence of major histocompatibility complex (MHC)-deficient tumour cells and the formation of an immunosuppressive tumour microenvironment4-6. The ability of CD4+ effector cells to contribute to antitumour immunity independently of CD8+ T cells is increasingly recognized, but strategies to unleash their full potential remain to be identified7-10. Here, we describe a mechanism whereby a small number of CD4+ T cells is sufficient to eradicate MHC-deficient tumours that escape direct CD8+ T cell targeting. The CD4+ effector T cells preferentially cluster at tumour invasive margins where they interact with MHC-II+CD11c+ antigen-presenting cells. We show that T helper type 1 cell-directed CD4+ T cells and innate immune stimulation reprogramme the tumour-associated myeloid cell network towards interferon-activated antigen-presenting and iNOS-expressing tumouricidal effector phenotypes. Together, CD4+ T cells and tumouricidal myeloid cells orchestrate the induction of remote inflammatory cell death that indirectly eradicates interferon-unresponsive and MHC-deficient tumours. These results warrant the clinical exploitation of this ability of CD4+ T cells and innate immune stimulators in a strategy to complement the direct cytolytic activity of CD8+ T cells and natural killer cells and advance cancer immunotherapies.

Inhaled SARS-CoV-2 vaccine for single-dose dry powder aerosol immunization.

The COVID-19 pandemic has fostered major advances in vaccination technologies1-4; however, there are urgent needs for vaccines that induce mucosal immune responses and for single-dose, non-invasive administration4-6. Here we develop an inhalable, single-dose, dry powder aerosol SARS-CoV-2 vaccine that induces potent systemic and mucosal immune responses. The vaccine encapsulates assembled nanoparticles comprising proteinaceous cholera toxin B subunits displaying the SARS-CoV-2 RBD antigen within microcapsules of optimal aerodynamic size, and this unique nano-micro coupled structure supports efficient alveoli delivery, sustained antigen release and antigen-presenting cell uptake, which are favourable features for the induction of immune responses. Moreover, this vaccine induces strong production of IgG and IgA, as well as a local T cell response, collectively conferring effective protection against SARS-CoV-2 in mice, hamsters and nonhuman primates. Finally, we also demonstrate a mosaic iteration of the vaccine that co-displays ancestral and Omicron antigens, extending the breadth of antibody response against co-circulating strains and transmission of the Omicron variant. These findings support the use of this inhaled vaccine as a promising multivalent platform for fighting COVID-19 and other respiratory infectious diseases.

CXCR5(+) follicular cytotoxic T cells control viral infection in B cell follicles.

During unresolved infections, some viruses escape immunological control and establish a persistant reservoir in certain cell types, such as human immunodeficiency virus (HIV), which persists in follicular helper T cells (TFH cells), and Epstein-Barr virus (EBV), which persists in B cells. Here we identified a specialized group of cytotoxic T cells (TC cells) that expressed the chemokine receptor CXCR5, selectively entered B cell follicles and eradicated infected TFH cells and B cells. The differentiation of these cells, which we have called 'follicular cytotoxic T cells' (TFC cells), required the transcription factors Bcl6, E2A and TCF-1 but was inhibited by the transcriptional regulators Blimp1, Id2 and Id3. Blimp1 and E2A directly regulated Cxcr5 expression and, together with Bcl6 and TCF-1, formed a transcriptional circuit that guided TFC cell development. The identification of TFC cells has far-reaching implications for the development of strategies to control infections that target B cells and TFH cells and to treat B cell-derived malignancies.

A Galectin-9-Driven CD11chigh Decidual Macrophage Subset Suppresses Uterine Vascular Remodeling in Preeclampsia.

BACKGROUND: Preeclampsia is a serious disease of pregnancy that lacks early diagnosis methods or effective treatment, except delivery. Dysregulated uterine immune cells and spiral arteries are implicated in preeclampsia, but the mechanistic link remains unclear. METHODS: Single-cell RNA sequencing and spatial transcriptomics were used to identify immune cell subsets associated with preeclampsia. Cell-based studies and animal models including conditional knockout mice and a new preeclampsia mouse model induced by recombinant mouse galectin-9 were applied to validate the pathogenic role of a CD11chigh subpopulation of decidual macrophages (dMφ) and to determine its underlying regulatory mechanisms in preeclampsia. A retrospective preeclampsia cohort study was performed to determine the value of circulating galectin-9 in predicting preeclampsia. RESULTS: We discovered a distinct CD11chigh dMφ subset that inhibits spiral artery remodeling in preeclampsia. The proinflammatory CD11chigh dMφ exhibits perivascular enrichment in the decidua from patients with preeclampsia. We also showed that trophoblast-derived galectin-9 activates CD11chigh dMφ by means of CD44 binding to suppress spiral artery remodeling. In 3 independent preeclampsia mouse models, placental and plasma galectin-9 levels were elevated. Galectin-9 administration in mice induces preeclampsia-like phenotypes with increased CD11chigh dMφ and defective spiral arteries, whereas galectin-9 blockade or macrophage-specific CD44 deletion prevents such phenotypes. In pregnant women, increased circulating galectin-9 levels in the first trimester and at 16 to 20 gestational weeks can predict subsequent preeclampsia onset. CONCLUSIONS: These findings highlight a key role of a distinct perivascular inflammatory CD11chigh dMφ subpopulation in the pathogenesis of preeclampsia. CD11chigh dMφ activated by increased galectin-9 from trophoblasts suppresses uterine spiral artery remodeling, contributing to preeclampsia. Increased circulating galectin-9 may be a biomarker for preeclampsia prediction and intervention.

Context-dependent regulation of follicular helper T cell survival.

Follicular helper T (TFH) cells are a specialized subset of CD4+ T cells that support germinal centers in producing high-affinity antibody-secreting and memory B cells in mammals and birds. Therefore, mechanisms have evolved to control the life and death of TFH cells for balanced humoral immunity. Recent studies have collectively revealed at least two programmed cell death pathways, ferroptosis and pyroptosis, which govern TFH cell survival under diverse physiopathological conditions including immunization, infection, gut homeostasis, and autoimmunity. We review major recent advances in our understanding of the context-dependent regulation of TFH cell survival via cell death pathways that are closely connected with cellular metabolism. Such knowledge might be applied to inform new strategies aimed at modulating humoral immunity, potentially including enhancement of vaccine efficacies.

Acanthopanax senticosus cultures fermented by Lactobacillus rhamnosus enhanced immune response through improvement of antioxidant activity and inflammation in crucian carp (Carassius auratus).

Lactic acid bacteria (LAB) have been recognized as safe microorganism that improve micro-flora disturbances and enhance immune response. A well-know traditional herbal medicine, Acanthopanax senticosus (As) was extensively utilized in aquaculture to improve growth performance and disease resistance. Particularly, the septicemia, skin wound and gastroenteritis caused by Aeromonas hydrophila threaten the health of aquatic animals and human. However, the effects of probiotic fermented with A. senticosus product on the immune regulation and pathogen prevention in fish remain unclear. Here, the aim of the present study was to elucidate whether the A. senticosus fermentation by Lactobacillus rhamnosus improve immune barrier function. The crucian carp were fed with basal diet supplemented with L. rhamnosus fermented A. senticosus cultures at 2 %, 4 %, 6 % and 8 % bacterial inoculum for 8 weeks. After trials, the weight gain rate (WGR), specific growth rate (SGR) were significantly increased, especially in LGG-6 group. The results confirmed that the level of the CAT, GSH-PX, SOD, lysozyme, and MDA was enhanced in fish received with probiotic fermented product. Moreover, the L. rhamnosus fermented A. senticosus cultures could trigger innate and adaptive immunity, including the up-regulation of the C3, C4, and IgM concentration. The results of qRT-PCR revealed that stronger mRNA transcription of IL-1ß, IL-10, IFN-γ, TNF-α, and MyD88 genes in the liver, spleen, kidney, intestine and gills tissues of fish treated with probiotic fermented with A. senticosus product. After infected with A. hydrophila, the survival rate of the LGG-2 (40 %), LGG-4 (50 %), LGG-6 (60 %), LGG-8 (50 %) groups was higher than the control group. Meanwhile, the pathological damage of the liver, spleen, head-kidney, and intestine tissues of probiotic fermentation-fed fish could be alleviated after pathogen infection. Therefore, the present work indicated that L. rhamnosus fermented A. senticosus could be regard as a potential intestine-target therapy strategy to protecting fish from pathogenic bacteria infection.

Systemic immunometabolism and responses to vaccines: insights from T and B cell perspectives.

Vaccination stands as the cornerstone in the battle against infectious diseases, and its efficacy hinges on several host-related factors like genetics, age, and metabolic status. Vulnerable populations, such as malnourished individuals, the obese, and the elderly, commonly exhibit diminished vaccine responses and efficacy. While the specific factors contributing to this impairment may vary, these individuals typically display a degree of metabolic dysregulation, thereby underscoring its potential significance as a fundamental determinant of suboptimal vaccine responses. The emerging field of immunometabolism aims to unravel the intricate interplay between immune regulation and metabolic pathways, and recent research has revealed diverse metabolic signatures linked to various vaccine responses and outcomes. In this review, we summarize the major metabolic pathways utilized by B and T cells during vaccine responses, their complex and varied metabolic requirements, and the impact of micronutrients and metabolic hormones on vaccine outcomes. Furthermore, we examine how systemic metabolism influences vaccine responses and the evidence suggesting that metabolic dysregulation in vulnerable populations can lead to impaired vaccine responses. Lastly, we reflect on the challenge of proving causality with respect to the contribution of metabolic dysregulation to poor vaccine outcomes, and highlight the need for a systems biology approach that combines multimodal profiling and mathematical modelling to reveal the underlying mechanisms of such complex interactions.

A novel strategy of tannery sludge disposal - converting into biochar and reusing for Cr(VI) removal from tannery wastewater.

Tannery sludge with high chromium content has been identified as hazardous solid waste due to its potential toxic effects. The safety disposal and valorization of the tannery sludge remains a challenge. In this study, the chromium stabilization mechanism was systematically investigated during chromium-rich tannery sludge was converted to biochar and the removal performance of the sludge biochar (SBC) for Cr(VI) from tannery wastewater was also investigated. The results showed that increase in pyrolysis temperature was conductive to the stabilization of Cr and significant reduction of the proportion of Cr(VI) in SBC. It was confirmed that the stabilization of chromium mainly was attributed to the embedding of chromium in the C matrix and the transformation of the chromium-containing substances from the amorphous Cr(OH)3 to the crystalline state, such as (FeMg)Cr2O5. The biochar presented high adsorption capacity of Cr(VI) at low pH and the maximal theoretical adsorption capacity of SBC produced at 800°C can reach 352 mg Cr(VI)/g, the process of which can be well expressed by Langmuir adsorption isotherm and pseudo second order model. The electrostatic effect and reduction reaction were dominantly responsible for the Cr(VI) adsorption by SBC800. Overall, this study provided a novel strategy for the harmless disposal and resource utilization for the solid waste containing chromium in leather industry.

Attenuation of renal injury by depleting cDC1 and by repurposing Flt3 inhibitor in anti-GBM disease.

Previous studies found cDC1s to be protective in early stage anti-GBM disease through Tregs, but pathogenic in late stage Adriamycin nephropathy through CD8+ T cells. Flt3 ligand is a growth factor essential for cDC1 development and Flt3 inhibitors are currently used for cancer treatment. We conducted this study to clarify the role and mechanisms of effects of cDC1s at different time points in anti-GBM disease. In addition, we aimed to utilize drug repurposing of Flt3 inhibitors to target cDC1s as a treatment of anti-GBM disease. We found that in human anti-GBM disease, the number of cDC1s increased significantly, proportionally more than cDC2s. The number of CD8+ T cells also increased significantly and their number correlated with cDC1 number. In XCR1-DTR mice, late (day 12-21) but not early (day 3-12) depletion of cDC1s attenuated kidney injury in mice with anti-GBM disease. cDC1s separated from kidneys of anti-GBM disease mice were found to have a pro-inflammatory phenotype (i.e. express high level of IL-6, IL-12 and IL-23) in late but not early stage. In the late depletion model, the number of CD8+ T cells was also reduced, but not Tregs. CD8+ T cells separated from kidneys of anti-GBM disease mice expressed high levels of cytotoxic molecules (granzyme B and perforin) and inflammatory cytokines (TNF-α and IFN-γ), and their expression reduced significantly after cDC1 depletion with diphtheria toxin. These findings were reproduced using a Flt3 inhibitor in wild type mice. Therefore, cDC1s are pathogenic in anti-GBM disease through activation of CD8+ T cells. Flt3 inhibition successfully attenuated kidney injury through depletion of cDC1s. Repurposing Flt3 inhibitors has potential as a novel therapeutic strategy for anti-GBM disease.

Low-dose IL-2 therapy invigorates CD8+ T cells for viral control in systemic lupus erythematosus.

Autoimmune diseases are often treated by glucocorticoids and immunosuppressive drugs that could increase the risk for infection, which in turn deteriorate disease and cause mortality. Low-dose IL-2 (Ld-IL2) therapy emerges as a new treatment for a wide range of autoimmune diseases. To examine its influence on infection, we retrospectively studied 665 patients with systemic lupus erythematosus (SLE) including about one third receiving Ld-IL2 therapy, where Ld-IL2 therapy was found beneficial in reducing the incidence of infections. In line with this clinical observation, IL-2 treatment accelerated viral clearance in mice infected with influenza A virus or lymphocytic choriomeningitis virus (LCMV). Noticeably, despite enhancing anti-viral immunity in LCMV infection, IL-2 treatment exacerbated CD8+ T cell-mediated immunopathology. In summary, Ld-IL2 therapy reduced the risk of infections in SLE patients and enhanced the control of viral infection, but caution should be taken to avoid potential CD8+ T cell-mediated immunopathology.

Bifidobacterium longum subsp. infantis as widespread bacteriocin gene clusters carrier stands out among the Bifidobacterium.

Bifidobacterium is the dominant genus, particularly in the intestinal tract niche of healthy breast-fed infants, and many of these strains have been proven to elicit positive effects on infant development. In addition to its effective antimicrobial activity against detrimental microorganisms, it helps to improve the intestinal microbiota balance. The isolation and identification of bacteriocins from Bifidobacterium have been limited since the mid-1980s, leading to an underestimation of its ability for bacteriocin production. Here, we employed a silicon-based search strategy to mine 354 putative bacteriocin gene clusters (BGCs), most of which have never been reported, from the genomes of 759 Bifidobacterium strains distributed across 9 species. Consistent with previous reports, most Bifidobacterium strains did not carry or carry only a single BGC; however, Bifidobacterium longum subsp. infantis, in contrast to other Bifidobacterium species, carried numerous BGCs, including lanthipeptides, lasso peptides, thiopeptides, and class IId bacteriocins. The antimicrobial activity of the crude bacteriocins and transcription analysis confirmed its potential for bacteriocin biosynthesis. Additionally, we investigated the association of bacteriocins with the phylogenetic positions of their homologs from other genera and niches. In conclusion, this study re-examines a few Bifidobacterium species traditionally regarded as a poor source of bacteriocins. These bacteriocin genes impart a competitive advantage to Bifidobacterium in colonizing the infant intestinal tract. IMPORTANCE Development of the human gut microbiota commences from birth, with bifidobacteria being among the first colonizers of the newborn intestinal tract and dominating it for a considerable period. To date, the genetic basis for the successful adaptation of bifidobacteria to this particular niche remains unclear since studies have mainly focused on glycoside hydrolase and adhesion-related genes. Bacteriocins are competitive factors that help producers maintain colonization advantages without destroying the niche balance; however, they have rarely been reported in Bifidobacterium. The advancement in sequencing methods and bacteriocin databases enables the use of a silicon-based search strategy for the comprehensive and rapid re-evaluation of the bacteriocin distribution of Bifidobacterium. Our study revealed that B. infantis carries abundant bacteriocin biosynthetic gene clusters for the first time, presenting new evidence regarding the competitive interactions of Bifidobacterium in the infant intestinal tract.

Mesenchymal stem cells suppressed skin and lung inflammation and fibrosis in topoisomerase I-induced systemic sclerosis associated with lung disease mouse model.

Systemic sclerosis associated with lung interstitial lung disease (SSc-ILD) is the most common cause of death among patients with SSc. Mesenchymal stem cell (MSCs) transplantations had been treated by SSc patients that showed in the previous case report. The therapeutic mechanisms and effects of MSCs on SSc-ILD are still obscure. In this study, we investigated the therapeutic effects and mechanisms of treatment of BM-MSC derived from C57BL/6 on the topoisomerase I (TOPO I) induced SSc-ILD-like mice model. The mice were immunized with a mixture of recombinant human TOPO I in PBS solution (500 U/mL) and completed Freund's adjuvant [CFA; 1:1 (volume/volume)] twice per week for 9 weeks. On week 10, the mice were sacrificed to analyze the related pathological parameters. Lung and skin pathologies were analyzed using histochemical staining. CD4 T-helper (TH) cell differentiation in lung and skin-draining lymph nodes was detected using flow cytometry. Our results revealed that allogeneic and syngeneic MSCs exhibited similar repressive effects on TOPO I-induced IgG1 and IgG2a in the SSc group. After intravascular (IV) treatment with syngeneic or allogeneic MSCs, the dermal thickness and fibrosis dramatically condensed and significantly reduced airway hyperresponsiveness. These findings showed that both allogeneic and syngeneic MSCs have therapeutic potential for SSc-ILD.

Variants in genes related to development of the urinary system are associated with Mayer-Rokitansky-Küster-Hauser syndrome.

Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, also known as Müllerian agenesis, is characterized by uterovaginal aplasia in an otherwise phenotypically normal female with a normal 46,XX karyotype. Previous studies have associated sequence variants of PAX8, TBX6, GEN1, WNT4, WNT9B, BMP4, BMP7, HOXA10, EMX2, LHX1, GREB1L, LAMC1, and other genes with MRKH syndrome. The purpose of this study was to identify the novel genetic causes of MRKH syndrome. Ten patients with MRKH syndrome were recruited at Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, China. Whole-exome sequencing was performed for each patient. Sanger sequencing confirmed the potential causative genetic variants in each patient. In silico analysis and American College of Medical Genetics and Genomics (ACMG) guidelines helped to classify the pathogenicity of each variant. The Robetta online protein structure prediction tool determined whether the variants affected protein structures. Eleven variants were identified in 90% (9/10) of the patients and were considered a molecular genetic diagnosis of MRKH syndrome. These 11 variants were related to nine genes: TBC1D1, KMT2D, HOXD3, DLG5, GLI3, HIRA, GATA3, LIFR, and CLIP1. Sequence variants of TBC1D1 were found in two unrelated patients. All variants were heterozygous. These changes included one frameshift variant, one stop-codon variant, and nine missense variants. All identified variants were absent or rare in gnomAD East Asian populations. Two of the 11 variants (18.2%) were classified as pathogenic according to the ACMG guidelines, and the remaining nine (81.8%) were classified as variants of uncertain significance. Robetta online protein structure prediction analysis suggested that missense variants in TBC1D1 (p.E357Q), HOXD3 (p.P192R), and GLI3 (p.L299V) proteins caused significant structural changes compared to those in wild-type proteins, which in turn may lead to changes in protein function. This study identified many novel genes, especially TBC1D1, related to the pathogenesis of MRKH syndrome. The identification of these variants provides new insights into the etiology of MRKH syndrome and a new molecular genetic reference for the development of the reproductive tract.

MicroRNAs in Tfh cells: micromanaging inflammaging.

MicroRNA (miR)-146a-deficient mice develop low-grade, chronic, and systemic inflammation, similar to inflammaging. Hu et al. (2014) demonstrate that the lack of miR-155 prevents the accumulation of Tfh cells and inflammaging in miR-146a-deficient mice. They identify Fosl2 as a functionally important target of miR-155 in Tfh cells.

A fine-tuned yeast surface-display/secretion platform enables the rapid discovery of neutralizing antibodies against Clostridioides difficile toxins.

BACKGROUND: Neutralizing antibody plays a key role in protecting hosts from invasive pathogens and their virulent components. Current high-throughput assays for antibody screening are based on binding activities. However, those antibodies with high affinity may not have neutralizing activities. Subsequent functionality assays are necessary to identify neutralizing antibodies from binders with high affinity to their target antigens, which is laborious and time-consuming. Therefore, a versatile platform that can rapidly identify antibodies with both high binding affinity and neutralizing activity is desired to curb future pandemics like COVID-19. RESULTS: In this proof-of-concept study, we adapted Saccharomyces cerevisiae to either display human antibodies on the yeast surface or secrete soluble antibodies into the cultivation supernatant under a controllable 'switch' through different carbon source induced promoters. Initially, an engineered chimeric-bispecific Fab antibody, derived from humanized nanobodies against both Clostridioides difficile toxin A and B (TcdA and TcdB), was successfully expressed either on the yeast cell surface or in the culture medium with intact bioactivity, suggesting the applicability of our system in antibody display and secretion. Next, a combinatorial Fab library was constructed from B cells isolated from a convalescent patient with a high serological neutralizing titer against TcdB. Following three rounds of magnetic bead enrichment and one round of flow cytometry sorting, antibodies against TcdB were enriched efficiently. We then sorted out single binders with high binding affinity and induced them to express soluble antibodies in culture medium. The neutralizing activity of culture supernatant was analyzed using cell-based assay immediately. This way, we rapidly identified two unique neutralizers (out of seven binders) that can neutralize the cytotoxicity of TcdB. CONCLUSION: The antibody screening platform described here simplifies the neutralizing antibody discovery procedure and will be an attractive alternative for screening functional antibodies against infectious diseases.

pH and Proton Sensor GPR65 Determine Susceptibility to Atopic Dermatitis.

pH sensing by GPR65 regulates various inflammatory conditions, but its role in skin remains unknown. In this study, we performed a phenome-wide association study and report that the T allele of GPR65-intronic single-nucleotide polymorphism rs8005161, which reduces GPR65 signaling, showed a significant association with atopic dermatitis, in addition to inflammatory bowel diseases and asthma, as previously reported. Consistent with this genetic association in humans, we show that deficiency of GPR65 in mice resulted in markedly exacerbated disease in the MC903 experimental model of atopic dermatitis. Deficiency of GPR65 also increased neutrophil migration in vitro. Moreover, GPR65 deficiency in mice resulted in higher expression of the inflammatory cytokine TNF-α by T cells. In humans, CD4+ T cells from rs8005161 heterozygous individuals expressed higher levels of TNF-α after PMA/ionomycin stimulation, particularly under pH 6 conditions. pH sensing by GPR65 appears to be important for regulating the pathogenesis of atopic dermatitis.