Inflammation induces dermal Vγ4+ γδT17 memory-like cells that travel to distant skin and accelerate secondary IL-17-driven responses

γδ T cells in oral diseases

OBJECTIVE

γδ T cells are a distinct subset of unconventional T cells, which link innate and adaptive immunity by secreting cytokines and interacting with other immune cells, thereby modulating immune responses. As the first line of host defense, γδ T cells are essential for mucosal homeostasis and immune surveillance. When abnormally activated or impaired, γδ T cells can contribute to pathogenic processes. Accumulating evidence has revealed substantial impacts of γδ T cells on the pathogenesis of cancers, infections, and immune-inflammatory diseases. γδ T cells exhibit dual roles in cancers, promoting or inhibiting tumor growth, depending on their phenotypes and the clinical stage of cancers. During infections, γδ T cells exert high cytotoxic activity in infectious diseases, which is essential for combating bacterial and viral infections by recognizing foreign antigens and activating other immune cells. γδ T cells are also implicated in the onset and progression of immune-inflammatory diseases. However, the specific involvement and underlying mechanisms of γδ T cells in oral diseases have not been systematically discussed.

METHODS

We conducted a systematic literature review using the PubMed/MEDLINE databases to identify and analyze relevant literature on the roles of γδ T cells in oral diseases.

RESULTS

The literature review revealed that γδ T cells play a pivotal role in maintaining oral mucosal homeostasis and are involved in the pathogenesis of oral cancers, periodontal diseases, graft-versus-host disease (GVHD), oral lichen planus (OLP), and oral candidiasis. γδ T cells mainly influence various pathophysiological processes, such as anti-tumor activity, eradication of infection, and immune response regulation.

CONCLUSION

This review focuses on the involvement of γδ T cells in oral diseases, with a particular emphasis on the main functions and underlying mechanisms by which γδ T cells influence the pathogenesis and progression of these conditions. This review underscores the potential of γδ T cells as therapeutic targets in managing oral health issues.

The mutual regulation between γδ T cells and macrophages during wound healing

Macrophages are the main cells shaping the local microenvironment during wound healing. As the prime T cells in the skin, γδ T cells participate in regulating microenvironment construction, determining their mutual regulation helps to understand the mechanisms of wound healing, and explore innovative therapeutic options for wound repair. This review introduced their respective role in wound healing firstly, and then summarized the regulatory effect of γδ T cells on macrophages, including chemotaxis, polarization, apoptosis, and pyroptosis. Last, the retrograde regulation on γδ T cells by macrophages was also discussed. The main purpose is to excavate novel interventions for treating wound and provide new thought for further research.

Inhibition of Mitochondrial Translation Ameliorates Imiquimod-Induced Psoriasis-Like Skin Inflammation by Targeting Vγ4+ γδ T Cells

Psoriasis is an inflammatory skin disorder that is characterized by keratinocyte hyperproliferation in response to immune cell infiltration and cytokine secretion in the dermis. γδ T cells expressing the Vγ4 TCR chain are among the highest contributors of IL-17A, which is a major cytokine that drives a psoriasis flare, making Vγ4+ γδ T cells a suitable target to restrict psoriasis progression. In this study, we demonstrate that mitochondrial translation inhibition within Vγ4+ γδ T cells effectively reduced erythema, scaling, and skin thickening in a murine model of psoriatic disease. The antibiotic linezolid, which blocks mitochondrial translation, inhibited the production of mitochondrial-encoded protein cytochrome c oxidase in Vγ4+ γδ T cells and systemically reduced the frequencies of IL-17A+ Vγ4+ γδ T cells, effectively resolving IL-17A-dependent inflammation. Inhibiting mitochondrial translation could be a novel metabolic approach to interrupt IL-17A signaling in Vγ4+ T cells and reduce psoriasis-like skin pathophysiology.

Interleukin-2-induced skin inflammation

Recombinant human IL-2 has been used to treat inflammatory diseases and cancer; however, side effects like skin rashes limit the use of this therapeutic. To identify key molecules and cells inducing this side effect, we characterized IL-2-induced cutaneous immune reactions and investigated the relevance of CD25 (IL-2 receptor α) in the process. We injected IL-2 intradermally into WT mice and observed increases in immune cell subsets in the skin with preferential increases in frequencies of IL-4- and IL-13-producing group 2 innate lymphoid cells and IL-17-producing dermal γδ T cells. This overall led to a shift toward type 2/type 17 immune responses. In addition, using a novel topical genetic deletion approach, we reduced CD25 on skin, specifically on all cutaneous cells, and found that IL-2-dependent effects were reduced, hinting that CD25 - at least partly - induces this skin inflammation. Reduction of CD25 specifically on skin Tregs further augmented IL-2-induced immune cell infiltration, hinting that CD25 on skin Tregs is crucial to restrain IL-2-induced inflammation. Overall, our data support that innate lymphoid immune cells are key cells inducing side effects during IL-2 therapy and underline the significance of CD25 in this process.

From Host Defense to Metabolic Signatures: Unveiling the Role of γδ T Cells in Bacterial Infections

The growth of antibiotic-resistant bacterial infections necessitates focusing on host-derived immunotherapies. γδ T cells are an unconventional T cell subset, making up a relatively small portion of healthy circulating lymphocytes but a substantially increased proportion in mucosal and epithelial tissues. γδ T cells are activated and expanded in response to bacterial infection, having the capability to produce proinflammatory cytokines to recruit neutrophils and clear infection. They also play a significant role in dampening immune response to control inflammation and protecting the host against secondary challenge, making them promising targets when developing immunotherapy. Importantly, γδ T cells have differential metabolic states influencing their cytokine profile and subsequent inflammatory capacity. Though these differential metabolic states have not been well studied or reviewed in the context of bacterial infection, they are critical in understanding the mechanistic underpinnings of the host's innate immune response. Therefore, this review will focus on the context-specific host defense conferred by γδ T cells during infection with Staphylococcus aureus, Streptococcus pneumoniae, Listeria monocytogenes, and Mycobacterium tuberculosis.

Immune cells in the epithelial immune microenvironment of psoriasis: emerging therapeutic targets

Psoriasis is a chronic autoimmune inflammatory disease characterized by erroneous metabolism of keratinocytes. The development of psoriasis is closely related to abnormal activation and disorders of the immune system. Dysregulated skin protective mechanisms can activate inflammatory pathways within the epithelial immune microenvironment (EIME), leading to the development of autoimmune-related and inflammatory skin diseases. In this review, we initially emphasized the pathogenesis of psoriasis, paying particular attention to the interactions between the abnormal activation of immune cells and the production of cytokines in psoriasis. Subsequently, we delved into the significance of the interactions between EIME and immune cells in the emergence of psoriasis. A thorough understanding of these immune processes is crucial to the development of targeted therapies for psoriasis. Finally, we discussed the potential novel targeted therapies aimed at modulating the EIME in psoriasis. This comprehensive examination sheds light on the intricate underlying immune mechanisms and provides insights into potential therapeutic avenues of immune-mediated inflammatory diseases.

PRDM16 regulates γδT17 cell differentiation via controlling type 17 program and lipid-dependent cell fitness

γδT17 cells are a subset of γδT cells producing IL-17, which is crucial for protection against bacterial and fungal infections. It has recently been shown that γδT17 cells have enriched lipid storage and lipid metabolism. However, the regulation of γδT17 cell function and differentiation with respect to lipids remains unknown. Here, we report that PRDM16 is a critical regulator of γδT17 cell differentiation, controlling type 17 immunity gene expression program and lipid-dependent cell fitness. We demonstrated that γδT17 cells have higher lipid-dependent cell fitness, which is negatively correlated with the expression of Prdm16. Loss of Prdm16 enhances the function and differentiation of γδT17 cells, and increases their fitness in lipid-rich environments. Specifically, loss of Prdm16 exacerbates development of psoriasis in the skin, a lipid-rich organ, and Prdm16 controls lipid-mediated differentiation of Vγ4+ γδT17 cells, which are the major source of IL-17 during the onset of psoriasis. Our study highlights the potential impact of PRDM16 on lipid-dependent fitness and protective immune function of γδT cells and also on the immunotherapy of psoriasis and inflammatory diseases.

γδ T cells respond directly and selectively to the skin commensal yeast Malassezia for IL-17-dependent fungal control

Stable microbial colonization of the skin depends on tight control by the host immune system. The lipid-dependent yeast Malassezia typically colonizes skin as a harmless commensal and is subject to host type 17 immunosurveillance, but this fungus has also been associated with diverse skin pathologies in both humans and animals. Using a murine model of Malassezia exposure, we show that Vγ4+ dermal γδ T cells expand rapidly and are the major source of IL-17A mediating fungal control in colonized skin. A pool of memory-like Malassezia-responsive Vγ4+ T cells persisted in the skin, were enriched in draining lymph nodes even after fungal clearance, and were protective upon fungal re-exposure up to several weeks later. Induction of γδT17 immunity depended on IL-23 and IL-1 family cytokine signalling, whereas Toll-like and C-type lectin receptors were dispensable. Furthermore, Vγ4+ T cells from Malassezia-exposed hosts were able to respond directly and selectively to Malassezia-derived ligands, independently of antigen-presenting host cells. The fungal moieties detected were shared across diverse species of the Malassezia genus, but not conserved in other Basidiomycota or Ascomycota. These data provide novel mechanistic insight into the induction and maintenance of type 17 immunosurveillance of skin commensal colonization that has significant implications for cutaneous health.

Keratinocyte proline-rich protein modulates immune and epidermal response in imiquimod-induced psoriatic skin inflammation

Psoriasis is a persistent inflammatory skin disease thought to arise as a result of the infiltration of inflammatory cells and activation of keratinocytes. Recent advances in basic research and clinical experience revealed that the interleukin (IL)-23/IL-17 axis has been identified as a major immune pathway in psoriasis. However, it remains unclear how keratinocyte factors contribute to the pathology of psoriasis. Keratinocyte proline-rich protein (KPRP) is a proline-rich insoluble protein, which is present in the epidermis and is likely to be involved in the skin barrier function. Here, to investigate the potential roles of KPRP in psoriatic skin inflammation, Kprp-modified mice were applied in the imiquimod (IMQ)-induced skin inflammation model, which develops psoriasis-like epidermal hyperplasia and cutaneous inflammation features. Then, heterozygous knockout (Kprp+/- ) but not homozygous knockout (Kprp-/- ) mice displayed attenuated skin erythema compared to control wild-type mice. In addition, RNA sequencing, quantitative PCR and/or histological analysis detected changes in the expression of several molecules related to psoriatic inflammation or keratinocyte differentiation in Kprp+/- mice, but not Kprp-/- mice. Further analysis exhibited reduced IL-17-producing γδlow T cells and amplified epidermal hyperplasia in Kprp+/- mice, which were implied to be related to decreased expression of β-defensins and increased expression of LPAR1 (Lysophosphatidic acid receptor 1), respectively. Thus, our results imply that KPRP has the potential as a therapeutic target in psoriatic skin inflammation.

γδ T cells: origin and fate, subsets, diseases and immunotherapy

The intricacy of diseases, shaped by intrinsic processes like immune system exhaustion and hyperactivation, highlights the potential of immune renormalization as a promising strategy in disease treatment. In recent years, our primary focus has centered on γδ T cell-based immunotherapy, particularly pioneering the use of allogeneic Vδ2+ γδ T cells for treating late-stage solid tumors and tuberculosis patients. However, we recognize untapped potential and optimization opportunities to fully harness γδ T cell effector functions in immunotherapy. This review aims to thoroughly examine γδ T cell immunology and its role in diseases. Initially, we elucidate functional differences between γδ T cells and their αβ T cell counterparts. We also provide an overview of major milestones in γδ T cell research since their discovery in 1984. Furthermore, we delve into the intricate biological processes governing their origin, development, fate decisions, and T cell receptor (TCR) rearrangement within the thymus. By examining the mechanisms underlying the anti-tumor functions of distinct γδ T cell subtypes based on γδTCR structure or cytokine release, we emphasize the importance of accurate subtyping in understanding γδ T cell function. We also explore the microenvironment-dependent functions of γδ T cell subsets, particularly in infectious diseases, autoimmune conditions, hematological malignancies, and solid tumors. Finally, we propose future strategies for utilizing allogeneic γδ T cells in tumor immunotherapy. Through this comprehensive review, we aim to provide readers with a holistic understanding of the molecular fundamentals and translational research frontiers of γδ T cells, ultimately contributing to further advancements in harnessing the therapeutic potential of γδ T cells.

RORγt+ c-Maf+ Vγ4+ γδ T cells are generated in the adult thymus but do not reach the periphery

T cell receptor (TCR) Vγ4-expressing γδ T cells comprise interferon γ (IFNγ)- and interleukin-17 (IL-17)-producing effector subsets, with a preference for IL-17 effector fate decisions during early ontogeny. The existence of adult-thymus-derived IL-17+ T cells (γδ17) remains controversial. Here, we use a mouse model in which T cells are generated exclusively in the adult thymus and employ single-cell chromatin state analysis to study their development. We identify adult-thymus-derived Vγ4 T cells that have all the molecular programs to become IL-17 producers. However, they have reduced IL-17 production capabilities and rarely reach the periphery. Moreover, this study provides high-resolution profiles of Vγ4 T cells in the adult thymus and lymph nodes and identifies Zeb1 as a potential γδ17 cell regulator. Together, this study provides valuable insights into the developmental traits of Vγ4 T cells during adulthood and supports the idea of age-specific signals required for thymic export and/or peripheral maturation of γδ17 cells.

RNA-Seq and ATAC-Seq analyses reveal a global transcriptional and chromatin accessibility profiling of γδ T17 differentiation from mouse spleen

IL-17A-producing γδ T cells (γδ T17) are known to play important roles in various autoimmune diseases. However, the molecular mechanisms of γδ T17 differentiation and their functions have not been clarified yet. Here, we sorted IL-17A+ Vγ4, IL-17A- Vγ4, and Vγ1 subsets from mouse spleen by in vitro priming of γδ T17 cells and investigated their differentially expressed genes (DEGs) and differentially accessible regions (DARs) using RNA-seq and ATAC-seq, respectively. Our results showed that DEGs-1 (upregulated genes: 677 and downregulated genes: 821) and DEGs-2 (upregulated genes: 1188 and downregulated genes: 1252) were most closely related to the function and differentiation of peripheral γδ T17. We identified key modules and MCODEs involved in the control of IL-17A+ Vγ4, IL-17A- Vγ4, and Vγ1 subsets using the WGCNA and Metascape analysis. Furthermore, 26 key transcription factors were enriched in three subsets, which contributed to deciphering the potential molecular mechanism driving γδ T17 differentiation. Simultaneously, we conducted chromatin accessibility profiling under γδ T17 differentiation by ATAC-seq. The top six candidate genes were screened for γδ T17 differentiation and function by integrating RNA-seq and ATAC-seq analysis, and the results were further confirmed using RT-qPCR, flow cytometry, and western blot. In addition, the association analysis of candidate genes with the RNA-seq database of psoriasis was performed to elucidate the functional relationship. Our findings provided a novel insight into understanding the molecular mechanisms of γδ T17 differentiation and function and may improve to the development of therapeutic approaches or drugs targeting γδ T17 for autoimmune diseases.

Lipoxin A4 Ameliorates Imiquimod-Induced Psoriasis-Like Dermatitis via Promoting the Regression of Inflammation

Introduction

As a mediator of inflammation resolution, lipoxin A4 (LXA4) mainly plays an anti-inflammatory role and promotes inflammation resolution. LXA4 plays an inhibiting inflammatory role in a variety of diseases, tissues and cells, including keratinocytes. Psoriasis is a chronic inflammatory skin disease mediated by dysregulation of inflammation of immune cells and keratinocytes. However, the expression and role of LXA4 in psoriasis-like mouse models are still unclear.

Methods

Imiquimod (IMQ) topical treatment of dorsal skin induces psoriasis-like dermatitis in BALB/c mice, pretreated intraperitoneally with or without LXA4 prior to IMQ application. Severity of dorsal lesions is assessed by using a modified human scoring system and histopathology. The concentration of LXA4 and the expression of ALOX15 (a key gene in LXA4 metabolic synthesis) in lesional skins were detected by ELISA and Western blot. Quantitative PCR and ELISA were conducted to detect the mRNA and secretion levels of inflammatory cytokines. The proportion of IL-17A-producing γδT cells in skin and skin draining cervical lymph nodes and helper (Th) 17 cells in spleens was evaluated by flow cytometry. Western blotting was used to analyze the expressions of p-STAT3 and TRAF6.

Results

The concentration of LXA4 and the expression of ALOX15 were decreased in IMQ-induced lesional skin. LXA4 significantly relieved psoriasis-like lesions in IMQ-induced mouse models. Furthermore, LXA4 decreased IMQ-induced systemic inflammation, including reduced the proportion of IL-17A-producing gdT cells in skin and skin draining cervical lymph nodes and Th17 cells in spleens, the secretion and expression of CCL20, IL-17A, IL-1β, and TNF-α in skin and serum. LXA4 markedly inhibited IMQ-induced expression of TRAF6 and p-STAT3.

Conclusion

LXA4 significantly ameliorates IMQ-induced psoriasis-like inflammation, and LXA4 can be used as a target for psoriasis treatment.

Reversal of the detrimental effects of social isolation on ischemic cerebral injury and stroke-associated pneumonia by inhibiting small intestinal T-cell migration into the brain and lung

Social isolation (ISO) is associated with an increased risk and poor outcomes of ischemic stroke. However, the roles and mechanisms of ISO in stroke-associated pneumonia (SAP) remain unclear. Adult male mice were single- or pair-housed with an ovariectomized female mouse and then subjected to transient middle cerebral artery occlusion. Isolated mice were treated with the natriuretic peptide receptor A antagonist A71915 or anti-gamma-delta (γδ) TCR monoclonal antibody, whereas pair-housed mice were treated with recombinant human atrial natriuretic peptide (rhANP). Subdiaphragmatic vagotomy (SDV) was performed 14 days before single- or pair-housed conditions. We found that ISO significantly worsened brain and lung injuries relative to pair housing, which was partially mediated by elevated interleukin (IL)-17A levels and the migration of small intestine-derived inflammatory γδ T-cells into the brain and lung. However, rhANP treatment or SDV could ameliorate ISO-exacerbated post-stroke brain and lung damage by reducing IL-17A levels and inhibiting the migration of inflammatory γδ T-cells into the brain and lung. Our results suggest that rhANP mitigated ISO-induced exacerbation of SAP and ischemic cerebral injury by inhibiting small intestine-derived γδ T-cell migration into the lung and brain, which could be mediated by the subdiaphragmatic vagus nerve.

IL-17 Signaling in Keratinocytes Orchestrates the Defense against Staphylococcus aureus Skin Infection

Keratinocytes (KCs) form the outer epithelial barrier of the body, protecting against invading pathogens. Mice lacking the IL-17RA or both IL-17A and IL-17F develop spontaneous Staphylococcusaureus skin infections. We found a marked expansion of T17 cells, comprised of RORγt-expressing γδ T cells and T helper 17 cells in the skin-draining lymph nodes of these mice. Contradictory to previous suggestions, this expansion was not a result of a direct negative feedback loop because we found no expansion of T17 cells in mice lacking IL-17 signaling specifically in T cells. Instead, we found that the T17 expansion depended on the microbiota and was observed only when KCs were deficient for IL-17RA signaling. Indeed, mice that lack IL-17RA only in KCs showed an increased susceptibility to experimental epicutaneous infection with S. aureus together with an accumulation of IL-17A-producing γδ T cells. We conclude that deficiency of IL-17RA on KCs leads to microbiota dysbiosis in the skin, which triggers the expansion of IL-17A-producing T cells. Our data show that KCs are the primary target cells of IL-17A and IL-17F, coordinating the defense against microbial invaders in the skin.

Protein Kinase CK2 Promotes Proliferation, Abnormal Differentiation, and Proinflammatory Cytokine Production of Keratinocytes via Regulation of STAT3 and Akt Pathways in Psoriasis

Protein kinase CK2 is a constitutively active and ubiquitously expressed serine/threonine kinase that is closely associated with various types of cancers, autoimmune disorders, and inflammation. However, the role of CK2 in psoriasis remains unknown. Herein, the study indicated elevated expression of CK2 in skin lesions from patients with psoriasis and from psoriasis-like mice. In the psoriasis-like mouse model, the CK2-specific inhibitor CX-4945 ameliorated imiquimod-induced psoriasis symptoms with reduced proliferation, abnormal differentiation, inflammatory cytokine production (especially IL-17A) of keratinocytes, and infiltration of γδ T cells. In in vitro studies, exogenous CK2 promoted hyperproliferation and abnormal differentiation of human keratinocytes, which were reversed by the suppression of CK2 with CX-4945 or siRNA. Furthermore, knockdown of CK2 reduced IL-17A expression and abolished IL-17A-induced proliferation and inflammatory cytokine expression in keratinocytes. Interestingly, IL-17A increased the expression of CK2 in keratinocytes, thereby establishing a positive feedback loop. In addition, suppression of CK2 inhibited the activation of STAT3 and Akt signaling pathways in human keratinocytes and imiquimod-induced psoriatic lesions of mice. These findings indicate that a highly expressed CK2 level in the skin lesions is required in the development of psoriasis by promoting epidermal hyperplasia, abnormal differentiation, and inflammatory response via regulation of the STAT3 and Akt signaling pathways. CK2 may be a target for the treatment of psoriasis.

Pathogenic sphingosine 1-phosphate pathway in psoriasis: a critical review of its pathogenic significance and potential as a therapeutic target

Sphingosine-1-phosphate (S1P) is a sphingolipid mediator that exerts a variety of biological functions, including immune, cardiovascular, and neurological regulation as well as tumor promotion, through high-affinity G protein-coupled receptors (S1P_1-5). It has been reported that circulating S1P levels remain higher in patients with psoriasis than in healthy individuals and that circulating S1P levels do not decrease after anti-TNF-α treatment in those patients. The S1P-S1PR signaling system plays an important role in inhibiting keratinocyte proliferation, regulating lymphocyte migration, and promoting angiogenesis, thus contributing to the regulation of psoriasis pathogenesis. Here, we review the mechanisms by which S1P-S1PR signaling affects the development of psoriasis and the available clinical/preclinical evidence for targeting S1P-S1PR in psoriasis. S1P-S1PR signaling mechanisms may partially explain the link between psoriasis and its comorbidities. Although the detailed mechanisms remain to be elucidated, S1P may be a new target for future psoriasis remission.

Comparative studies on mannan and imiquimod induced experimental plaque psoriasis inflammation in inbred mice

Psoriasis is a genetically determined, environmentally triggered, immune system-mediated autoimmune disease. Different animal models are needed to investigate the complex pathological mechanisms underlying this disease. Therefore, we established mannan-induced psoriasis model and compared with the most commonly used imiquimod-induced psoriasis in terms of disease, induction of innate immune cells, expression of cytokines, and the effect of dexamethasone treatment. Mannan significantly induced more severe psoriasis with better disease relapsing feature than imiquimod (IMQ). As determined by immunohistochemistry, IMQ induced significantly more infiltration of CD11c+ and F4/80+ cells than mannan in the skin. However, cytometric analysis showed a significant increase in the percentage of Gr-1+ neutrophils in the spleen and lymph nodes as well as F4/80+ macrophages in the spleen after mannan exposure. Variation in the percentage of significantly increased Vγ4 T cells was also found to be dependent on the lymphoid organs tested. However, there is a clear difference between these models in terms of expression of certain cytokine genes: IL-22, IL-23, IL-17E, and IL-17F were expressed more predominantly in mannan-induced inflammation, while IL-6 and IL-17A expressions were significantly higher in IMQ model. Interestingly, dexamethasone treatment strongly reduced epidermal thickness and histological scores induced by mannan than IMQ. Despite inducing psoriasis-like inflammation, certain differences and similarities were observed in the immune responses induced by mannan and IMQ. However, mannan-induced psoriasis model is relatively more simple, economical and less harmful to mice with an increased possibility to develop a chronic psoriasis model by exposing mice to mannan.

Modified Gegen Qinlian decoction ameliorates DSS-induced chronic colitis in mice by restoring the intestinal mucus barrier and inhibiting the activation of γδT17 cells

BACKGROUND

Current therapeutics for ulcerative colitis (UC) have limitations. Classical Formula Gegen Qinlian decoction (GQD) is derived from Shang Han Lun and has a long history of treating gastrointestinal diseases such as diarrhea and UC. Nevertheless, the exact mechanism of it needs to be further clarified.

PURPOSE

We aimed to investigate the treatment effects of modified GQD (MGQD) on dextran sodium sulfate (DSS)-induced chronic colitis in mice and conduct further exploration of its underlying mechanisms.

METHODS

The protective effect of MGQD was estimated in a DSS-induced chronic colitis mouse model. Model evaluation included body weight, disease activity index (DAI) score, colon length and histopathology. Alcian Blue/Phosphoric Acid Schiff (AB/PAS) staining, transmission electron microscopy (TEM), immunofluorescence and real time‒PCR (RT-PCR) were used to assess goblet cell function. ELISA, flow cytometry and immunofluorescence were applied to estimate the immunoinflammatory status. Western blot was performed to test the protein expression levels of relevant pathways and related receptors. All experiments were conducted in duplicate.

RESULTS

MGQD alleviated DSS‑induced chronic colitis symptoms in mice, protected goblet cell function and restored the intestinal mucus barrier. Furthermore, MGQD efficiently suppressed the abnormal immune inflammatory response and the activate of γδT17 cells and NLRP3 inflammasome.

CONCLUSION

The mechanisms by which MGQD protects against DSS-induced chronic colitis may involve restoring goblet cell function, repairing the intestinal mucus barrier, and modulating the immune inflammatory response. More importantly, MGQD inhibited NLRP3 inflammasome-associated signaling pathway activation, which consequently reduced the activation of γδT17 cells.

PD-L1 Enhanced by cis-Urocanic Acid on Langerhans Cells Inhibits Vγ4+ γδT17 Cells in Psoriatic Skin Inflammation

Psoriasis is an IL-23/IL-17-mediated inflammatory autoimmune dermatosis and ultraviolet B (UVB) may contribute to immunosuppression and ameliorate associated symptoms. One of the pathophysiology underlying UVB therapy is through the production of cis-urocanic acid (cis-UCA) from keratinocytes. However, the detailed mechanism is yet to be fully understood. In the current study, we found filaggrin expression and serum cis-UCA levels were significantly lower in psoriasis patients than in healthy controls. We also noted that cis-UCA application inhibited psoriasiform inflammation through the reduction of Vγ4⁺ γδT17 cells in murine skin and draining lymph nodes. Meanwhile, CCR6 was down-regulated on γδT17 cells, which would suppress the inflammatory reaction at a distal skin site. We revealed that 5-HT_2A receptor (HTR2A), the known cis-UCA receptor, was highly expressed on Langerhans cells (LCs) in the skin. cis-UCA also inhibited IL-23 expression and induced PD-L1 on LCs, leading to the attenuated proliferation and migration of γδT cells. Compared to the isotype control, α-PD-L1 treatment in vivo could reverse the anti-psoriatic effects of cis-UCA. PD-L1 expression on LCs was sustained through cis-UCA-induced MAPK/ERK pathway. These findings uncover the cis-UCA-induced PD-L1-mediated immunosuppression on LCs, which facilitates the resolution of inflammatory dermatoses.

PD-1 and TIM-3 differentially regulate subsets of mouse IL-17A-producing γδ T cells

IL-17A-producing γδ T cells in mice consist primarily of Vγ6+ tissue-resident cells and Vγ4+ circulating cells. How these γδ T cell subsets are regulated during homeostasis and cancer remains poorly understood. Using single-cell RNA sequencing and flow cytommetry, we show that lung Vγ4+ and Vγ6+ cells from tumor-free and tumor-bearing mice express contrasting cell surface molecules as well as distinct co-inhibitory molecules, which function to suppress their expansion. Vγ6+ cells express constitutively high levels of PD-1, whereas Vγ4+ cells upregulate TIM-3 in response to tumor-derived IL-1β and IL-23. Inhibition of either PD-1 or TIM-3 in mammary tumor-bearing mice increased Vγ6+ and Vγ4+ cell numbers, respectively. We found that genetic deletion of γδ T cells elicits responsiveness to anti-PD-1 and anti-TIM-3 immunotherapy in a mammary tumor model that is refractory to T cell checkpoint inhibitors, indicating that IL-17A-producing γδ T cells instigate resistance to immunotherapy. Together, these data demonstrate how lung IL-17A-producing γδ T cell subsets are differentially controlled by PD-1 and TIM-3 in steady-state and cancer.

CCR4+ CD8+ T cells clonally expand to differentiated effectors in murine psoriasis and in human psoriatic arthritis

Psoriasis is a chronic inflammatory skin disease with an autoimmune component and associated with joint inflammation in up to 30% of cases. To investigate autoreactive T cells, we developed an imiquimod-induced psoriasis-like inflammation model in K5-mOVA.tg C57BL/6 mice expressing ovalbumin (OVA) on the keratinocyte membrane, adoptively transferred with OT-I OVA-specific CD8⁺ T cells. We evaluated the expansion of OT-I CD8⁺ T cells and their localization in skin, blood, and spleen. scRNA-seq and TCR sequencing data from patients with psoriatic arthritis were also analyzed. In the imiquimod-treated K5-mOVA.tg mouse model, OT-I T cells were markedly expanded in the skin and blood at early time points. OT-I T cells in the skin showed mainly CXCR3⁺ effector memory phenotype, whereas in peripheral blood there was an expansion of CCR4⁺ CXCR3⁺ OT-I cells. At a later time point, expanded OVA-specific T-cell population was found in the spleen. In patients with psoriatic arthritis, scRNA-seq and TCR sequencing data showed clonal expansion of CCR4⁺ T_CM cells in the circulation and further expansion in the synovial fluid. Importantly, there was a clonotype overlap between CCR4⁺ T_CM in the peripheral blood and CD8⁺ T-cell effectors in the synovial fluid. This mechanism could play a role in the generation and spreading of autoreactive T cells to the synovioentheseal tissues in psoriasis patients at risk of developing psoriatic arthritis.

New insights into immunity to skin fungi shape our understanding of health and disease

Fungi represent an integral part of the skin microbiota. Their complex interaction network with the host shapes protective immunity during homeostasis. If host defences are breached, skin-resident fungi including Malassezia and Candida, and environmental fungi such as dermatophytes can cause cutaneous infections. In addition, fungi are associated with diverse non-infectious skin disorders. Despite their multiple roles in health and disease, fungi remain elusive and understudied, and the mechanisms underlying the emergence of pathological conditions linked to fungi are largely unclear. The identification of IL-17 as an important antifungal effector mechanism represents a milestone for understanding homeostatic antifungal immunity. At the same time, host-adverse, disease-promoting roles of IL-17 have been delineated, as in psoriasis. Fungal dysbiosis represents another feature of many pathological skin conditions with an unknown causal link of intra- and interkingdom interactions to disease pathogenesis. The emergence of new fungal pathogens such as Candida auris highlights the need for more research into fungal immunology to understand how antifungal responses shape health and diseases. Recent technological advances for genetically manipulating fungi to target immunomodulatory fungal determinants, multi-omics approaches for studying immune cells in the human skin, and novel experimental models open up a promising future for skin fungal immunity.

Pellino-1 promotes intrinsic activation of skin-resident IL-17A-producing T cells in psoriasis

BACKGROUND

Psoriasis is a chronically relapsing inflammatory skin disease primarily perpetuated by skin-resident IL-17-producing T (T17) cells. Pellino-1 (Peli1) belongs to a member of E3 ubiquitin ligase mediating immune receptor signaling cascades, including nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) pathway.

OBJECTIVE

We explored the potential role of Peli1 in psoriatic inflammation in the context of skin-resident T17 cells.

METHODS

We performed single-cell RNA sequencing of relapsing and resolved psoriatic lesions with analysis for validation data set of psoriasis. Mice with systemic and conditional depletion of Peli1 were generated to evaluate the role of Peli1 in imiquimod-induced psoriasiform dermatitis. Pharmacologic inhibition of Peli1 in human CD4⁺ T cells and ex vivo human skin cultures was also examined to evaluate its potential therapeutic implications.

RESULTS

Single-cell RNA sequencing analysis revealed distinct T-cell subsets in relapsing psoriasis exhibiting highly enriched gene signatures for (1) tissue-resident T cells, (2) T17 cells, and (3) NF-κB signaling pathway including PELI1. Peli1-deficient mice were profoundly protected from psoriasiform dermatitis, with reduced IL-17A production and NF-κB activation in γδ T17 cells. Mice with conditional depletion of Peli1 treated with FTY720 revealed that Peli1 was intrinsically required for the skin-resident T17 cell immune responses. Notably, pharmacologic inhibition of Peli1 significantly ameliorated murine psoriasiform dermatitis and IL-17A production from the stimulated human CD4⁺ T cells and ex vivo skin explants modeling psoriasis.

CONCLUSION

Targeting Peli1 would be a promising therapeutic strategy for psoriasis by limiting skin-resident T17 cell immune responses.

Up-regulation of BTN3A1 on CD14 + cells promotes Vγ9Vδ2 T cell activation in psoriasis

Vγ9Vδ2 T cells play an important role in the development and progression of psoriasis vulgaris (PV), but how they promote skin inflammation and the molecular mechanisms underlying Vγ9Vδ2 T cell dysfunction are poorly understood. Here, we show that circulating Vγ9Vδ2 T cells are decreased and exhibit enhanced proliferation and increased production of IFN-γ and TNF-α in PV patients. Monocytes from PV patients express higher levels of the phosphoantigen sensor butyrophilin 3A1 (BTN3A1) than monocytes from healthy controls. Blockade of BTN3A1 suppresses Vγ9Vδ2 T cell activation and abolishes the difference in Vγ9Vδ2 T cell activation between PV patients and healthy controls. The CD14 + cells in PV skin lesions highly express BTN3A1 and juxtapose to Vδ2 T cells. In addition, IFN-γ induces the up-regulation of BTN3A1 on monocytes. Collectively, our results demonstrate a crucial role of BTN3A1 on monocytes in regulating Vγ9Vδ2 T cell activation and highlight BTN3A1 as a potential therapeutic target for psoriasis.

CD96 Blockade Ameliorates Imiquimod-Induced Psoriasis-like Dermatitis via Suppression of IL-17A Production by Dermal γδ T Cells

Psoriasis is a chronic inflammatory skin disease. IL-23 plays a critical role in its pathogenesis by inducing production of IL-17A from pathological Th17 cells and IL-17A-producing γδ T cells. However, the mechanisms regulating the IL-23/IL-17 axis in psoriasis are incompletely understood. In this study, we show that, in comparison with wild-type mice, those deficient in the CD96 immunoreceptor had lower production of IL-17A in their dermal γδ T cells and milder psoriasis-like dermatitis after topical application of imiquimod (IMQ). Moreover, transfer of CD96-deficient dermal γδ T cells into the skin of Rag1-deficient mice resulted in them developing milder IMQ-induced dermatitis compared with Rag1-deficient mice transferred with wild-type dermal γδ T cells. In γδ T cells in vitro, CD96 provides a costimulatory signal for the production of IL-23-induced IL-17A. In mice given an anti-CD96 neutralizing Ab, IL-17A production from dermal γδ T cells decreased and IMQ-induced dermatitis was milder compared with mice given a control Ab. These results suggest that CD96 is a potential molecular target for the treatment of psoriasis.

A Distinctive γδ T Cell Repertoire in NOD Mice Weakens Immune Regulation and Favors Diabetic Disease

Previous studies in mice and humans suggesting that γδ T cells play a role in the development of type 1 diabetes have been inconsistent and contradictory. We attempted to resolve this for the type 1 diabetes-prone NOD mice by characterizing their γδ T cell populations, and by investigating the functional contributions of particular γδ T cells subsets, using Vγ-gene targeted NOD mice. We found evidence that NOD Vγ4+ γδ T cells inhibit the development of diabetes, and that the process by which they do so involves IL-17 production and/or promotion of regulatory CD4+ αβ T cells (Tregs) in the pancreatic lymph nodes. In contrast, the NOD Vγ1+ cells promote diabetes development. Enhanced Vγ1+ cell numbers in NOD mice, in particular those biased to produce IFNγ, appear to favor diabetic disease. Within NOD mice deficient in particular γδ T cell subsets, we noted that changes in the abundance of non-targeted T cell types also occurred, which varied depending upon the γδ T cells that were missing. Our results indicate that while certain γδ T cell subsets inhibit the development of spontaneous type 1 diabetes, others exacerbate it, and they may do so via mechanisms that include altering the levels of other T cells.

Dynamic trafficking patterns of IL-17-producing γδ T cells are linked to the recurrence of skin inflammation in psoriasis-like dermatitis

BACKGROUND

Psoriasis recurrence is a clinically challenging issue. However, the underlying mechanisms haven't been fully understood.

METHODS

RNAseq analysis from affected skin of psoriatic patients treated with topical glucocorticoid (GC) with different outcomes was performed. In addition, imiquimod (IMQ)-induced mouse psoriasis-like model was used to mimic GC treatment in human psoriasis patients. Skin tissues and draining and distant lymph nodes (LNs) were harvested for flow cytometry and histology analyses.

FINDINGS

RNAseq analysis revealed that chemokine and chemokine receptor gene expression was decreased in post-treated skin compared to pre-treated samples but was subsequently increased in the recurred skin. In IMQ-induced mouse psoriasis-like model, we found that γδT17 cells were decreased in the skin upon topical GC treatment but surprisingly increased in the draining and distant LNs. This redistribution pattern lasted even two weeks post GC withdrawal. Upon IMQ re-challenge on the same site, mice previously treated with GC developed more severe skin inflammation. There were γδT17 cells migrated from LNs to the skin. This dynamic trafficking was dependent on CCR6 as this phenomenon was completely abrogated in CCR6-deficient mice. In addition, inhibition of lymphocyte egress prevented this heightened skin inflammation induced by IMQ rechallenge.

INTERPRETATION

Redistribution of pathogenic γδT17 cells may be vital to prevent disease recurrence and this model of psoriasis-like dermatitis.

FUNDING

This work was supported by National Natural Science Foundation of China 81830095/H1103, 81761128008/H10 (J.Z.) and the NIH R01AI128818 and the National Psoriasis Foundation (J.Y.).

Sphingosine 1-Phosphate Signaling at the Skin Barrier Interface

Sphingosine 1-phosphate (S1P) is a product of membrane sphingolipid metabolism. S1P is secreted and acts via G-protein-coupled receptors, S1PR1-5, and is involved in diverse cellular functions, including cell proliferation, immune suppression, and cardiovascular functions. Recent studies have shown that the effects of S1P signaling are extended further by coupling the different S1P receptors and their respective downstream signaling pathways. Our group has recently reported that S1P inhibits cell proliferation and induces differentiation in human keratinocytes. There is a growing understanding of the connection between S1P signaling, skin barrier function, and skin diseases. For example, the activation of S1PR1 and S1PR2 during bacterial invasion regulates the synthesis of inflammatory cytokines in human keratinocytes. Moreover, S1P-S1PR2 signaling is involved in the production of inflammatory cytokines and can be triggered by epidermal mechanical stress and bacterial invasion. This review highlights how S1P affects human keratinocyte proliferation, differentiation, immunoreaction, and mast cell immune response, in addition to its effects on the skin barrier interface. Finally, studies targeting S1P-S1PR signaling involved in inflammatory skin diseases are also presented.

The accumulation of Vγ4 T cells with aging is associated with an increased adaptive Vγ4 T cell response after foodborne Listeria monocytogenes infection of mice

BACKGROUND

It is generally accepted that aging has detrimental effects on conventional T cell responses to systemic infections. However, most pathogens naturally invade the body through mucosal barriers. Although mucosal sites are highly enriched in unconventional immune sentinels like γδ T cells, little is currently known about the impact of aging on unconventional mucosal T cell responses. We previously established that foodborne infection with a mouse-adapted internalin A mutant Listeria monocytogenes (Lm) generates an adaptive intestinal memory CD44^hi CD27^neg Vγ4 T cells capable of co-producing IL-17A and IFNγ. Therefore, we used this model to evaluate the impact of aging on adaptive Vγ4 T cell responses elicited by foodborne infection.

RESULTS

Foodborne Lm infection of female Balb/c and C57BL/6 mice led to an increased adaptive CD44^hi CD27^neg Vγ4 T cell response associated with aging. Moreover, Lm-elicited CD44^hi CD27^neg Vγ4 T cells maintained diverse functional subsets despite some alterations favoring IL-17A production as mice aged. In contrast to the documented susceptibility of aged mice to intravenous Lm infection, mice contained bacteria after foodborne Lm infection suggesting that elevated bacterial burden was not a major factor driving the increased adaptive CD44^hi CD27^neg Vγ4 T cell response associated with mouse age. However, CD44^hi CD27^neg Vγ4 T cells accumulated in naïve mice as they aged suggesting that an increased precursor frequency contributes to the robust Lm-elicited mucosal response observed. Body mass did not appear to have a strong positive association with CD44^hi CD27^neg Vγ4 T cells within age groups. Although an increased adaptive CD44^hi CD27^neg Vγ4 T cell response may contribute to foodborne Lm resistance of C57BL/6 mice aged 19 or more months, neither anti-TCRδ or anti-IL-17A treatment impacted Lm colonization after primary infection. These results suggest that γδTCR signaling and IL-17A are dispensable for protection after primary foodborne Lm infection consistent with the role of conventional T cells during the early innate immune response to Lm.

CONCLUSIONS

Lm-elicited adaptive Vγ4 T cells appear resistant to immunosenescence and memory Vγ4 T cells could be utilized to provide protective immune functions during enteric infection of aged hosts. As such, oral immunization might offer an efficient therapeutic approach to generate unconventional memory T cells in the elderly.

Topical Application of Tetrandrine Nanoemulsion Promotes the Expansion of CD4+Foxp3+ Regulatory T Cells and Alleviates Imiquimod-Induced Psoriasis in Mice

There is compelling evidence that CD4⁺Foxp3⁺ regulatory T cells (Tregs) are indispensable in the inhibition of autoimmune inflammatory responses, including psoriasis. Recently, we showed that systemically treatment with tetrandrine (TET), a two-pore channel inhibitor identified from the Chinese herb Stephania tetrandra S. Moor, could promote the proliferative expansion of Tregs in mice through stimulation of TNF-TNFR2 interaction. We thus hypothesized that topical administration of TET might also expand Tregs and consequently inhibit psoriasis. To this end, we developed a TET nanoemulsion and examined its effect on the expansion of Tregs after topical administration on mouse psoriasis induced by imiquimod. The result of our experiment showed that topical treatment with TET nanoemulsion markedly increased the proportion and number of Tregs in the spleen, as well as TNFR2 and Ki-67 expression by Tregs, in WT and TNFR1 KO mice, but not in TNFR2 KO mice. Consequently, TET nanoemulsion potently inhibited IL-17-expressing cells in the spleen and lymph nodes of imiquimod-treated WT mice, accompanied by decreased serum levels of IL-17A, INF-γ, and TNF and their mRNA levels in the flamed lesion. Importantly, TET nanoemulsion treatment markedly inhibited the development of psoriasis-like disease in WT and TNFR1 KO mice but not in TNFR2 KO mice. Therefore, our study indicates that the topical administration of TET could also stimulate the expansion of Tregs through the TNF-TNFR2 pathway. This effect of TET and its analogs may be useful in the treatment of inflammatory skin diseases such as psoriasis.

Mutation of the Polyproline Sequence in CD3ε Evidences TCR Signaling Requirements for Differentiation and Function of Pro-Inflammatory Tγδ17 Cells

Tγδ17 cells have emerged as a key population in the development of inflammatory and autoimmune conditions such as psoriasis. Thus, the therapeutic intervention of Tγδ17 cells can exert protective effects in this type of pathologies. Tγδ cells commit to IL-17 production during thymus development, and upon immune challenge, additional extrathymic signals induce the differentiation of uncommitted Tγδ cells into Tγδ17 effector cells. Despite the interest in Tγδ17 cells during the past 20 years, the role of TCR signaling in the generation and function of Tγδ17 cells has not been completely elucidated. While some studies point to the notion that Tγδ17 differentiation requires weak or no TCR signaling, other works suggest that Tγδ17 require the participation of specific kinases and adaptor molecules downstream of the TCR. Here we have examined the differentiation and pathogenic function of Tγδ17 cells in “knockin” mice bearing conservative mutations in the CD3ε polyproline rich sequence (KI-PRS) with attenuated TCR signaling due to lack of binding of the essential adaptor Nck. KI-PRS mice presented decreased frequency and numbers of Tγδ17 cells in adult thymus and lymph nodes. In the Imiquimod model of skin inflammation, KI-PRS presented attenuated skin inflammation parameters compared to wild-type littermates. Moreover, the generation, expansion and effector function Tγδ17 cells were impaired in KI-PRS mice upon Imiquimod challenge. Thus, we conclude that an intact CD3ε-PRS sequence is required for optimal differentiation and pathogenic function of Tγδ17 cells. These data open new opportunities for therapeutic targeting of specific TCR downstream effectors for treatment of Tγδ17-mediated diseases.

Skin γδ T Cells and Their Function in Wound Healing

For the skin immune system, γδ T cells are important components, which help in defensing against damage and infection of skin. Compared to the conventional αβ T cells, γδ T cells have their own differentiation, development and activation characteristics. In adult mice, dendritic epidermal T cells (DETCs), Vγ4 and Vγ6 γδ T cells are the main subsets of skin, the coordination and interaction among them play a crucial role in wound repair. To get a clear overview of γδ T cells, this review synopsizes their derivation, development, colonization and activation, and focuses their function in acute and chronic wound healing, as well as the underlining mechanism. The aim of this paper is to provide cues for the study of human epidermal γδ T cells and the potential treatment for skin rehabilitation.

The relapse of psoriasis: what’s the veil of mystery?

Over the past decades, tremendous success in the treatment of psoriasis has been achieved using biologics, such as neutralizing antibodies against TNF/TNFR, IL-23, and IL-17A/IL-17RA. Although psoriatic skin lesions appear to resolve after treatment with these biologics, lesions often recur after therapy is discontinued or during therapy. Memory T cells residing in the skin have been considered as the major driver of psoriasis relapse. However, whether structural cells in the skin such as keratinocytes and fibroblasts are involved in the relapse of psoriasis is unknown. In this review, we outline the therapeutic rationale of biologics used in the treatment of psoriasis, summarize different clinical features of psoriasis relapse on the basis of preclinical and clinical data, and specifically discuss how memory T cells and structural cells in the skin are involved in psoriasis relapse. Finally, we discuss the future challenges in the basic or clinical research on psoriasis.

D-Mannose Suppresses γδ T Cells and Alleviates Murine Psoriasis

Psoriasis is a chronic skin disorder associated with multiple sequelae, such as psoriatic arthritis and cardiovascular diseases. Increasing evidence has shown that γδ T cells, as sources of IL-17A, play critical roles in psoriatic inflammations. However, there still lack effective ways to manipulate these pathogenic γδ T cells, which are less well studied than αβ T cells. The present study aims to characterize the phenotype of γδ T cells and evaluate the impact of D-mannose (a C-2 epimer of glucose) on γδ T cell-mediated psoriasis. We found that skin-draining LN γδ T cells underwent robust proliferation and acquired an IL-17-producing phenotype during psoriasis. The transcriptomic profiles of these psoriatic γδ T cells had elevated glycolytic signatures. Importantly, D-mannose treatment suppressed the γδ T cell reaction and successfully alleviated the local and systematic inflammation induced by imiquimod. The decreased AKT/mTOR/HIF-1α signaling and glycolytic ability may contribute to the suppression of γδ T cells achieved by D-mannose. Our study increased understanding of γδ T cells in psoriasis and promoted D-mannose utilization as a potential clinical application for autoimmune diseases driven by γδ T cells.

γδ T Cells in Skin Inflammation

Gamma delta (γδ) T cells are a subset of T lymphocytes that express T cell receptor γ and 5 chains and display structural and functional heterogeneity. γδ T cells are typically of low abundance in the body and account for 1-5% of the blood lymphocytes and peripheral lymphoid tissues. As a bridge between innate and adaptive immunity, γδ T cells are uniquely poised to rapidly respond to stimulation and can regulate immune responses in peripheral tissues. The dendritic epidermal T cells in the skin epidermis can secrete growth factors to regulate skin homeostasis and re-epithelization and release inflammatory factors to mediate wound healing during skin inflammatory responses. Dermal γδ T cells can regulate the inflammatory process by producing interleukin-17 and other cytokines or chemokines. Here, we offer a review of the immune functions of γδ T cells, intending to understand their role in regulating skin barrier integrity and skin wound healing, which may be crucial for the development of novel therapeutics in skin diseases like atopic dermatitis and psoriasis.

A blend of broadly-reactive and pathogen-selected Vγ4 Vδ1 T cell receptors confer broad bacterial reactivity of resident memory γδ T cells

Although murine γδ T cells are largely considered innate immune cells, they have recently been reported to form long-lived memory populations. Much remains unknown about the biology and specificity of memory γδ T cells. Here, we interrogated intestinal memory Vγ4 Vδ1 T cells generated after foodborne Listeria monocytogenes (Lm) infection to uncover an unanticipated complexity in the specificity of these cells. Deep TCR sequencing revealed that a subset of non-canonical Vδ1 clones are selected by Lm infection, consistent with antigen-specific clonal expansion. Ex vivo stimulations and in vivo heterologous challenge infections with diverse pathogenic bacteria revealed that Lm-elicited memory Vγ4 Vδ1 T cells are broadly reactive. The Vγ4 Vδ1 T cell recall response to Lm, Salmonella enterica serovar Typhimurium (STm) and Citrobacter rodentium was largely mediated by the γδTCR as internalizing the γδTCR prevented T cell expansion. Both broadly-reactive canonical and pathogen-selected non-canonical Vδ1 clones contributed to memory responses to Lm and STm. Interestingly, some non-canonical γδ T cell clones selected by Lm infection also responded after STm infection, suggesting some level of cross-reactivity. These findings underscore the promiscuous nature of memory γδ T cells and suggest that pathogen-elicited memory γδ T cells are potential targets for broad-spectrum anti-infective vaccines.

NF-κB1 Contributes to Imiquimod-Induced Psoriasis-Like Skin Inflammation by Inducing Vγ4+Vδ4+γδT17 Cells

Recent studies have identified NF-κB1 as a new disease susceptibility gene for psoriasis. Although accumulating evidence has shown the importance of NF-κB signaling in various cell types in the pathogenesis of psoriasis, it remains unclear how NF-κB1 contributes to the pathogenesis of psoriasis. In this study, we examined psoriasis-like skin diseases induced by topical administration of imiquimod in Nf-κb1‒deficient (Nf-κb1^-/-) mice and littermate wild-type (WT) mice. Compared with WT mice, Nf-κb1^-/- mice exhibited attenuated skin inflammation. The numbers of Vγ4⁺Vδ4⁺γδT17 cells, which cause skin inflammation in this model, were significantly reduced in the skin and draining lymph nodes in imiquimod-treated Nf-κb1^-/- mice. Nf-κb1 is preferentially phosphorylated in Vγ4⁺Vδ4⁺γδT17 cells in WT mice. In vitro proliferation of Vγ4⁺Vδ4⁺γδT17 cells but not conventional CD4⁺ T cells was significantly impaired in Nf-κb1^-/- mice compared with that in WT mice. RNA-sequencing analyses revealed that the expression of E2 factor target genes was decreased in Vγ4⁺Vδ4⁺γδT cells by the absence of NF-κB1. Consistently, the cell cycle progression of Vγ4⁺Vδ4⁺γδT cells was reduced in Nf-κb1^-/- mice compared with that in WT mice. These results suggest that Nf-κb1 plays a crucial role in the pathogenesis of imiquimod-induced psoriasis-like skin inflammation by promoting the proliferation of Vγ4⁺Vδ4⁺γδT17 cells.

Skin Barrier Dysregulation in Psoriasis

The skin barrier is broadly composed of two elements-a physical barrier mostly localised in the epidermis, and an immune barrier localised in both the dermis and epidermis. These two systems interact cooperatively to maintain skin homeostasis and overall human health. However, if dysregulated, several skin diseases may arise. Psoriasis is one of the most prevalent skin diseases associated with disrupted barrier function. It is characterised by the formation of psoriatic lesions, the aberrant differentiation and proliferation of keratinocytes, and excessive inflammation. In this review, we summarize recent discoveries in disease pathogenesis, including the contribution of keratinocytes, immune cells, genetic and environmental factors, and how they advance current and future treatments.

Kynureninase contributes to the pathogenesis of psoriasis through pro-inflammatory effect

Kynureninase (KYNU) is a key enzyme in the tryptophan metabolism pathway with elevated expression in psoriatic lesions relative to normal skin. However, whether KYNU contributes to the pathogenesis of psoriasis remains unknown. We sought to investigate the role of KYNU in psoriasis and its possible regulation mechanism. In the results, KYNU is upregulated in psoriatic skin samples from patients or animal models compared with normal skin control which was assayed in psoriatic patient samples, IMQ-induced psoriasis-like skin inflammation in BABL/c mice and M5-stimulated keratinocyte cell lines by immunohistochemistry (IHC). KYNU knockdown had a trivial impact on keratinocyte proliferation, but significantly inhibited the production of inflammatory cytokines in HaCaT, HEKα, and HEKn cells by quantitative reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and western blot analysis. The 3'-untranslated region of KYNU contains a conserved target site of a skin-specific microRNA (miRNA), miR-203a, as predicted by TargetScan software. Furthermore, miR-203a exhibited an inversed expression kinetics to KYNU during the development of IMQ-induced psoriasis-like skin inflammation in BABL/c mice. Overexpression of miR-203 subsequently leading to the inhibition of KYNU, could significantly reduce the production of M5-induced, psoriasis-related inflammatory factors in keratinocytes. Finally, KYNU inhibitors could alleviate the pathological phenotypes in IMQ-mice. Our study supported the contributive role of KYNU in the development of psoriasis and provided preliminary evidence for KYNU as a potential therapeutic target in psoriasis.

Evolved to protect, designed to destroy: IL-17-producing γδ T cells in infection, inflammation, and cancer

T cells of the gamma delta (γδ) lineage are evolutionary conserved from jawless to cartilaginous and bony fish to mammals and represent the "swiss army knife" of the immune system capable of antigen-dependent or independent responses, memory, antigen presentation, regulation of other lymphocytes, tissue homeostasis, and mucosal barrier maintenance, to list a few. Over the last 10 years, γδ T cells that produce the cytokine IL-17 (γδT17) have taken a leading position in our understanding of how our immune system battles infection, inflicts tissue damage during inflammation, and gets rewired by the tumor microenvironment. A lot of what we know about γδT17 cells stems from mouse models, however, increasing evidence implicates these cells in numerous human diseases. Herein, we aim to give an overview of the most common mouse models that have been used to study the role of γδT17 cells in infection, inflammation, and cancer, while at the same time we will evaluate evidence for their importance in humans. We hope and believe that in the next 10 years, means to take advantage of the protective and destructive properties of γδ T and in particular γδT17 cells will be part of our standard immunotherapy toolkit.

Differentiation and functional plasticity of gamma-delta (γδ) T cells under homeostatic and disease conditions

Gamma-delta (γδ) T cells are a heterogeneous population of immune cells, which constitute <5% of total T cells in mice lymphoid tissue and human peripheral blood. However, they comprise a higher proportion of T cells in the epithelial and mucosal barrier, where they perform immune functions, help in tissue repair, and maintaining homeostasis. These tissues resident γδ T cells possess properties of innate and adaptive immune cells which enables them to perform a variety of functions during homeostasis and disease. Emerging data suggest the involvement of γδ T cells during transplant rejection and survival. Interestingly, several functions of γδ T cells can be modulated through their interaction with other immune cells. This review provides an overview of development, differentiation plasticity into regulatory and effector phenotypes of γδ T cells during homeostasis and various diseases.

Fatty acid-binding protein 3 controls contact hypersensitivity through regulating skin dermal Vγ4+ γ/δ T cell in a murine model

BACKGROUND

Fatty acid-binding protein 3 (FABP3) is a cytosolic carrier protein of polyunsaturated fatty acids (PUFAs) and regulates cellular metabolism. However, the physiological functions of FABP3 in immune cells and how FABP3 regulates inflammatory responses remain unclear.

METHODS

Contact hypersensitivity (CHS) induced by 2,4-dinitrofluorobenzene (DNFB) and fluorescein isothiocyanate was applied to the skin wild-type and Fabp3-/- mice. Skin inflammation was assessed using FACS, histological, and qPCR analyses. The development of γ/δ T cells was evaluated by a co-culture system with OP9/Dll1 cells in the presence or absence of transgene of FABP3.

RESULTS

Fabp3-deficient mice exhibit a more severe phenotype of contact hypersensitivity (CHS) accompanied by infiltration of IL-17-producing Vγ4+ γ/δ T cells that critically control skin inflammation. In Fabp3-/- mice, we found a larger proportion of Vγ4+ γ/δ T cells in the skin, even though the percentage of total γ/δ T cells did not change at steady state. Similarly, juvenile Fabp3-/- mice also contained a higher amount of Vγ4+ γ/δ T cells not only in the skin but in the thymus when compared with wild-type mice. Furthermore, thymic double-negative (DN) cells expressed FABP3, and FABP3 negatively regulates the development of Vγ4+ γ/δ T cells in the thymus.

CONCLUSIONS

These findings suggest that FABP3 functions as a negative regulator of skin inflammation through limiting pathogenic Vγ4+ γ/δ T-cell generation in the thymus.

Inflammatory adaptation in barrier tissues

Surface epithelia provide a critical barrier to the outside world. Upon a barrier breach, resident epithelial and immune cells coordinate efforts to control infections and heal tissue damage. Inflammation can etch lasting marks within tissues, altering features such as scope and quality of future responses. By remembering inflammatory experiences, tissues are better equipped to quickly and robustly respond to barrier breaches. Alarmingly, in disease states, memory may fuel the inflammatory fire. Here, we review the cellular communication networks in barrier tissues and the integration between tissue-resident and recruited immune cells and tissue stem cells underlying tissue adaptation to environmental stress.

Preclinical and clinical characterization of the RORγt inhibitor JNJ-61803534

The nuclear receptor retinoid-related orphan receptor gamma t (RORγt) plays a critical role in driving Th17 cell differentiation and expansion, as well as IL-17 production in innate and adaptive immune cells. The IL-23/IL-17 axis is implicated in several autoimmune and inflammatory diseases, and biologics targeting IL-23 and IL-17 have shown significant clinical efficacy in treating psoriasis and psoriatic arthritis. JNJ-61803534 is a potent RORγt inverse agonist, selectively inhibiting RORγt-driven transcription versus closely-related family members, RORα and RORβ. JNJ-61803534 inhibited IL-17A production in human CD4⁺ T cells under Th17 differentiation conditions, but did not inhibit IFNγ production under Th1 differentiation conditions, and had no impact on in vitro differentiation of regulatory T cells (Treg), nor on the suppressive activity of natural Tregs. In the mouse collagen-induced arthritis model, JNJ-61803534 dose-dependently attenuated inflammation, achieving ~ 90% maximum inhibition of clinical score. JNJ-61803534 significantly inhibited disease score in the imiquimod-induced mouse skin inflammation model, and dose-dependently inhibited the expression of RORγt-regulated genes, including IL-17A, IL-17F, IL-22 and IL-23R. Preclinical 1-month toxicity studies in rats and dogs identified doses that were well tolerated supporting progression into first-in-human studies. An oral formulation of JNJ-61803534 was studied in a phase 1 randomized double-blind study in healthy human volunteers to assess safety, pharmacokinetics, and pharmacodynamics. The compound was well tolerated in single ascending doses (SAD) up to 200 mg, and exhibited dose-dependent increases in exposure upon oral dosing, with a plasma half-life of 164 to 170 h. In addition, dose-dependent inhibition of ex vivo stimulated IL-17A production in whole blood was observed, demonstrating in vivo target engagement. In conclusion, JNJ-61803534 is a potent and selective RORγt inhibitor that exhibited acceptable preclinical safety and efficacy, as well as an acceptable safety profile in a healthy volunteer SAD study, with clear evidence of a pharmacodynamic effect in humans.

Hyperforin Ameliorates Imiquimod-Induced Psoriasis-Like Murine Skin Inflammation by Modulating IL-17A-Producing γδ T Cells

Hyperforin is a major active constituent of Hypericum perforatum L. extract, which is widely used for the treatment of depressive disorders. Recent studies have reported that hyperforin reduced inflammation in stroke and suppressed proliferation and differentiation in keratinocytes. Psoriasis is a chronic immune-mediated inflammatory skin disease in which the IL-23/IL-17 axis plays an important role. To investigate the underlying inflammatory mechanisms and response of hyperforin in psoriasis, we use imiquimod (IMQ)-induced mice model, in vitro cultured murine splenic γδ T cells, and HaCaT cells in this study. Data showed that hyperforin reduced epidermal thickness and decreased IMQ-induced pathological scores of cutaneous skin lesions in mice. Meanwhile we proved that hyperforin suppressed infiltration of CD3+ T cells and downregulated expression of Il1, Il6, Il23, Il17a, Il22, antimicrobial peptides (AMPs) in the skin lesion. Hyperforin significantly inhibited imiquimod-induced splenomegaly, reduced serum levels of TNF-α and IL-6, and IL-17A in splenocytes and draining lymph nodes. Our study also suggested that hyperforin lessened the infiltration of γδ T cell and CCR6+ γδ T cells in spleen and lymph nodes. Hyperforin also suppressed the typical psoriasis-like inflammatory responses and the infiltration of IL-17A+ cells in dermal γδ T cells of IMQ treated Tcrd-/- mice transferred with γδ T cells. In vitro studies, hyperforin reduced the expression and secretion of IL-17A in γδ T cells, and suppressed the activation of MAPK/STAT3 pathways in human keratinocyte HaCaT cells and γδ T cells. In conclusion, hyperforin alleviates IMQ-induced inflammation in psoriasis through suppressing the immune responses exerted by IL-17 A-producing γδ T cells and related cytokines by modulating MAPK/STAT3 pathways. Our study provided a novel therapeutic tragedy for psoriasis by which hyperforin attenuates psoriasis-related inflammatory responses.

Xiao-Yin-Fang Therapy Alleviates Psoriasis-like Skin Inflammation Through Suppressing γδT17 Cell Polarization

Psoriasis is an immune-mediated chronic inflammatory skin disease primarily mediated by the activation of interleukin (IL)-17-producing T cells. Traditional Chinese Medicine (TCM) represents one of the most effective complementary and alternative medicine (CAM) agents for psoriasis, which provides treasured sources for the development of anti-psoriasis medications. Xiao-Yin-Fang (XYF) is an empirically developed TCM formula that has been used to treat psoriasis patients in Shanghai Changhai Hospital for over three decades. Imiquimod (IMQ)-induced psoriasis-like dermatitis mouse model was utilized to investigate the therapeutic effects of XYF by the assessment of disease severity and skin thickness. Flow cytometric assay was performed to explore the influence of XYF on skin-related immunocytes, primarily T cells. And, RNA sequencing analysis was employed to determine the alternation in gene expression upon XYF therapy. We discovered that XYF alleviated psoriasis-like skin inflammation mainly through suppressing dermal and draining lymph-node IL-17-producing γδT (γδT17) cell polarization. Moreover, XYF therapy ameliorated the relapse of psoriasis-like dermatitis and prohibited dermal γδT cell reactivation. Transcriptional analysis suggested that XYF might regulate various inflammatory signaling pathways and metabolic processes. In conclusion, our results clarified the therapeutic efficacy and inner mechanism of XYF therapy in psoriasis, which might promote its clinical application in psoriasis patients and facilitate the development of novel anti-psoriasis drugs based on the bioactive components of XYF.

Fingolimod ameliorates imiquimod-induced psoriasiform dermatitis by sequestrating interleukin-17-producing ?d T cells in secondary lymph nodes

BACKGROUND

Psoriasis is a chronic inflammatory skin disease. Interleukin (IL)-17A plays a key role in the pathogenesis of psoriasis. Fingolimod, which is available for the treatment of multiple sclerosis, exerts anti-inflammatory effects by sequestrating inflammatory lymphocytes in secondary lymphoid tissues and the thymus. The effect of fingolimod on psoriasis has not been reported yet.

OBJECTIVE

Our objectives were to investigate the effect of fingolimod on psoriasis utilizing mice with imiquimod (IMQ)-induced psoriasiform dermatitis, and explore the possibility of fingolimod as a therapeutic agent for psoriasis.

METHODS

Psoriasiform dermatitis was induced by imiquimod application on murine shaved back skin for six days. Fingolimod prepared in phosphate-buffered saline (PBS), or PBS alone as a control, was administered intraperitoneally daily from days 0 to 5.

RESULTS

Fingolimod ameliorated IMQ-induced psoriasis dermatitis clinically and histologically. On day 6, the mRNA expression level of IL-17A was lower in the skin of fingolimod-treated mice than in that of PBS-treated mice, whereas it was higher in the inguinal lymph nodes of fingolimod-treated mice than in those of PBS-treated mice. Flow cytometric analyses revealed that fingolimod reduced IL-17A-producing ?d T cells infiltrating into the skin, whereas it increased these cells in the inguinal lymph nodes. Fingolimod inhibited egress of Langerhans cells from the skin to lymph nodes.

CONCLUSION

Our results demonstrated that fingolimod showed effectiveness for IMQ-induced psoriasiform dermatitis by hindering the emigration of IL-17A-producing ?d T cells from the lymph nodes to the skin, and suggest that fingolimod is a promising candidate for the treatment of psoriasis.