Distinct T cell signatures are associated with Staphylococcus aureus skin infection in pediatric atopic dermatitis.

Atopic dermatitis (AD) is an inflammatory skin condition with a childhood prevalence of up to 25%. Microbial dysbiosis is characteristic of AD, with Staphylococcus aureus the most frequent pathogen associated with disease flares and increasingly implicated in disease pathogenesis. Therapeutics to mitigate the effects of S. aureus have had limited efficacy and S. aureus-associated temporal disease flares are synonymous with AD. An alternative approach is an anti-S. aureus vaccine, tailored to AD. Experimental vaccines have highlighted the importance of T cells in conferring protective anti-S. aureus responses; however, correlates of T cell immunity against S. aureus in AD have not been identified. We identify a systemic and cutaneous immunological signature associated with S. aureus skin infection (ADS.aureus) in a pediatric AD cohort, using a combined Bayesian multinomial analysis. ADS.aureus was most highly associated with elevated cutaneous chemokines IP10 and TARC, which preferentially direct Th1 and Th2 cells to skin. Systemic CD4+ and CD8+ T cells, except for Th2 cells, were suppressed in ADS.aureus, particularly circulating Th1, memory IL-10+ T cells, and skin-homing memory Th17 cells. Systemic γδ T cell expansion in ADS.aureus was also observed. This study suggests that augmentation of protective T cell subsets is a potential therapeutic strategy in the management of S. aureus in AD.

Key players of immunosuppression in epithelial malignancies: Tumor-infiltrating myeloid cells and γδ T cells.

BACKGROUND: The tumor microenvironment of solid tumors governs the differentiation of otherwise non-immunosuppressive macrophages and gamma delta (γδ) T cells into strong immunosuppressors while promoting suppressive abilities of known immunosuppressors such as myeloid-derived suppressor cells (MDSCs) upon infiltration into the tumor beds. RECENT FINDINGS: In epithelial malignancies, tumor-associated macrophages (TAMs), precursor monocytic MDSCs (M-MDSCs), and gamma delta (γδ) T cells often acquire strong immunosuppressive abilities that dampen spontaneous immune responses by tumor-infiltrating T cells and B lymphocytes against cancer. Both M-MDSCs and γδ T cells have been associated with worse prognosis for multiple epithelial cancers. CONCLUSION: Here we discuss recent discoveries on how tumor-associated macrophages and precursor M-MDSCs as well as tumor associated-γδ T cells acquire immunosuppressive abilities in the tumor beds, promote cancer metastasis, and perspectives on how possible novel interventions could restore the effective adaptive immune responses in epithelial cancers.

Profiles, Distribution, and Functions of Gamma Delta T Cells in Ocular Surface Homeostasis and Diseases.

The ocular surface microenvironment, containing the cornea, conjunctiva, and lacrimal gland, constitutes the mucosal frontline of the eye and houses a myriad of immune cells. As a part of unconventional T cells, gamma delta (γδ) T cells differ in the development and functions from canonical alpha beta (αß) T cells. They are predominantly situated in mucosal sites throughout the body, including ocular surface tissues. Recent research has elucidated that γδ T cells serve as the primary interleukin-17A (IL-17A) source in the conjunctiva. They play a pivotal role in preserving ocular surface homeostasis and exhibit both protective and pathogenic roles in ocular surface diseases. This review delves into the general profiles of γδ T cells, their distribution in ocular surface tissues, and consolidates current insights into their functions in different conditions including dry eye disease, infectious keratitis, corneal wound healing, anterior chamber-associated immune deviation, allergic conjunctival disease, and diabetic ocular surface disease. The aim is to provide a systemic perspective on γδ T cells in the ocular surface microenvironment and outline potential directions for future studies.

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.

Intraepithelial Lymphogram in the Diagnosis of Celiac Disease in Adult Patients: A Validation Cohort.

BACKGROUND: Celiac disease is a gluten-related pathology, highly prevalent and heterogeneous in its clinical presentation, which leads to delays in diagnosis and misdiagnosis. The analysis of duodenal intraepithelial lymphocytes (IELs) by flow cytometry (lymphogram) is emerging as a discriminative tool in the diagnosis of various forms of celiac disease (CD). AIMS: The aim of this study was to validate IEL lymphogram performance in the largest adult series to our knowledge, in support of its use as a diagnostic tool and as a biomarker of the dynamic celiac process. METHODS: This was a retrospective study including 768 adult patients (217 with active CD, 195 on a gluten-free diet, 15 potential CD patients, and 411 non-celiac controls). The IEL subset cut-off values were established to calculate the diagnostic accuracy of the lymphogram. RESULTS: A complete celiac lymphogram profile (≥14% increase in T cell receptor [TCR]γδ IELs and simultaneous ≤4% decrease in surface-negative CD3 [sCD3-] IELs) was strongly associated with active and potential forms in over 80% of the confirmed patients with CD, whereas the remaining patients with CD had partial lymphogram profiles (≥14% increase in TCRγδ or ≤4% decrease in sCD3- IELs), with lower diagnostic certainty. None of these patients had a non-celiac lymphogram. Quantifying the TCRγδ versus sCD3- imbalance as a ratio (≥5) is a discriminative index to discard or suspect CD at diagnosis. CONCLUSIONS: We have validated the IEL lymphogram's diagnostic efficiency (79% sensitivity, 98% specificity), with an LR+ accuracy of 36.2. As expected, the increase in TCRγδ IELs is a reliable marker for celiac enteropathy, while changes in sCD3- IEL levels throughout the dynamic CD process are useful biomarkers of mucosal lesions.

Establishment and validation of a tumor-infiltrating γδT cell related prognostic gene signature in head and neck squamous cell carcinoma.

γδT cells are unconventional T cells only accounting for 1-5 % of circulating T lymphocytes. Their potent anti-tumor capability has been evidenced by accumulating studies. However, the prognostic value of γδT cells remains not well documented in head and neck squamous cell carcinoma (HNSCC). In this study, we utilized the TCGA HNSCC database to evaluate the infiltration of γδT cells and the association between γδT cells and clinicopathological factors by related gene signature, which were then validated by a total of 100 collected tumor samples from HNSCC patient cohort. Heterogeneity and functional characteristics of distinct infiltrating γδT cell profiles in HNSCC were then investigated based on the scRNA-seq data from the GEO database. We found higher γδT cell gene signature score was significantly associated with longer survival. Cox regression models showed that γδT cell gene signature could serve as an independent prognostic indicator for HNSCC patients. A high level of γδT cell-related gene signature was positively correlated with the infiltration of tumor-infiltrating lymphocytes and immune score. Through scRNA-seq analysis, we identified that γδ+ Trm cells and γδ+ CTL cells possessed anti-tumor and immunoregulatory properties. Notably, we found a significant association between the presence of these cells and improved survival outcomes. In our cell-cell communication analyses, we identified that γδT cells have the potential to eliminate tumor cells through the secretion of interferon-gamma and granzyme. Collectively, the infiltration of γδT cells may serve as a promising prognostic tool, prompting the consideration of treatment options for patients with HNSCC.

Toll-like receptor 2 deficiency promotes the generation of alloreactive γδT17 cells after cardiac transplantation in mice.

Homograft rejection is the main cause of heart transplantation failure. The role of TLR2, a major member of the toll-like receptor (TLR) family, in transplantation rejection is has yet to be elucidated. In this study, we used a mouse model of acute cardiac transplantation rejection to investigate whether the TLR2 signalling pathway can regulate cardiac transplantation rejection by regulating alloreactive IL-17+γδT (γδT17) cells. We found that the expression of TLR2 on the surface of dendritic cells (DCs) and macrophages increased during acute transplantation rejection. In addition, our investigation revealed that γδT17 cells exert a significant influence on acute cardiac transplantation rejection. TLR2 gene knockout resulted in an increase in alloreactive γδT17 cells in the spleen and heart grafts of recipient mice compared with wild-type recipient mice and an increase in the mRNA expression of IL-17, IL-1ß, CCR6, and CCL20 in the heart grafts. In an in vitro experiment, a mixed lymphocyte reaction was conducted to assess the impact of TLR2 deficiency on the generation of γδT17 cells, which further substantiated a significant increase compared to that in wild-type controls. Furthermore, the mixed lymphocyte reaction showed that TLR2 regulated the production of γδT17 cells by regulating the ability of DCs to secrete IL-1ß. These results suggest that TLR2 signalling is important for regulating the generation of γδT17 cells after cardiac allograft transplantation.

The immunopathological landscape of human pre-TCRα deficiency: From rare to common variants.

We describe humans with rare biallelic loss-of-function PTCRA variants impairing pre-α T cell receptor (pre-TCRα) expression. Low circulating naive αß T cell counts at birth persisted over time, with normal memory αß and high γδ T cell counts. Their TCRα repertoire was biased, which suggests that noncanonical thymic differentiation pathways can rescue αß T cell development. Only a minority of these individuals were sick, with infection, lymphoproliferation, and/or autoimmunity. We also report that 1 in 4000 individuals from the Middle East and South Asia are homozygous for a common hypomorphic PTCRA variant. They had normal circulating naive αß T cell counts but high γδ T cell counts. Although residual pre-TCRα expression drove the differentiation of more αß T cells, autoimmune conditions were more frequent in these patients compared with the general population.

Vδ1 Effector and Vδ2 γδ T-Cell Subsets Shift in Frequency and Are Linked to Plasma Inflammatory Markers During Antiretroviral Therapy-Suppressed HIV Infection.

BACKGROUND: Chronic inflammation is prevalent with antiretroviral therapy (ART)-suppressed human immunodeficiency virus (HIV) infection and one immune cell subset putatively driving this phenomenon is TIGIT+ γδ T cells. METHODS: To elucidate γδ T-cell phenotypic diversity, spectral flow cytometry was performed on blood lymphocytes from individuals of a HIV and aging cohort and data were analyzed using bioinformatic platforms. Plasma inflammatory markers were measured and correlated with γδ T-cell subset frequencies. RESULTS: Thirty-nine distinct γδ T-cell subsets were identified (22 Vδ1+, 14 Vδ2+, and 3 Vδ1-Vδ2-Vγ9+) and TIGIT was nearly exclusively found on the Vδ1+CD45RA+CD27- effector populations. People with ART-suppressed HIV infection (PWH) exhibited high frequencies of distinct clusters of Vδ1+ effectors distinguished via CD8, CD16, and CD38 expression. Among Vδ2+ cells, most Vγ9+ (innate-like) clusters were lower in PWH; however, CD27+ subsets were similar in frequency between participants with and without HIV. Comparisons by age revealed lower 'naive' Vδ1+CD45RA+CD27+ cells in older individuals, regardless of HIV status. Plasma inflammatory markers were selectively linked to subsets of Vδ1+ and Vδ2+ cells. CONCLUSIONS: These results further elucidate γδ T-cell subset complexity and reveal distinct alterations and connections with inflammatory pathways of Vδ1+ effector and Vδ2+ innate-like subsets during ART-suppressed HIV infection.

Gut microbial fatty acid isomerization modulates intraepithelial T cells.

The human gut microbiome constantly converts natural products derived from the host and diet into numerous bioactive metabolites1-3. Dietary fats are essential micronutrients that undergo lipolysis to release free fatty acids (FAs) for absorption in the small intestine4. Gut commensal bacteria modify some unsaturated FAs-for example, linoleic acid (LA)-into various intestinal FA isomers that regulate host metabolism and have anticarcinogenic properties5. However, little is known about how this diet-microorganism FA isomerization network affects the mucosal immune system of the host. Here we report that both dietary factors and microbial factors influence the level of gut LA isomers (conjugated LAs (CLAs)) and that CLAs in turn modulate a distinct population of CD4+ intraepithelial lymphocytes (IELs) that express CD8αα in the small intestine. Genetic abolition of FA isomerization pathways in individual gut symbionts significantly decreases the number of CD4+CD8αα+ IELs in gnotobiotic mice. Restoration of CLAs increases CD4+CD8αα+ IEL levels in the presence of the transcription factor hepatocyte nuclear factor 4γ (HNF4γ). Mechanistically, HNF4γ facilitates CD4+CD8αα+ IEL development by modulating interleukin-18 signalling. In mice, specific deletion of HNF4γ in T cells leads to early mortality from infection by intestinal pathogens. Our data reveal a new role for bacterial FA metabolic pathways in the control of host intraepithelial immunological homeostasis by modulating the relative number of CD4+ T cells that were CD4+CD8αα+.

γδ T cells in autoimmune uveitis pathogenesis: A promising therapeutic target.

Autoimmune uveitis is a non-infectious, inflammatory intraocular disease that affects the uveal and adjacent tissues. It frequently causes varying degrees of visual loss. Evidence for the strong association between activated γδ T cells and the development of autoimmune uveitis is growing. The innate and adaptive immune response are connected in the early phases by the γδ T cells that contain the γ and δ chains. γδ T cells can identify antigens in a manner that is not constrained by the MHC. When activated by various pathways, γδ T cells can not only secrete pro-inflammatory factors early on (such as IL-17), but they can also promote Th17 cells responses, which ultimately exacerbates autoimmune uveitis. Therefore, we review the mechanisms by which γδ T cells affect autoimmune uveitis in different activation and disease states. Moreover, we also prospect for immunotherapies targeting different γδ T cell-related action pathways, providing a reference for exploring new drug for the treatment of autoimmune uveitis.

Single-cell RNA-seq and chromatin accessibility profiling decipher the heterogeneity of mouse γδ T cells.

The distinct characteristics of γδ T cells determine their vital roles in the formation of local immune responses and contribute to tissue homeostasis. However, the heterogeneity of γδ T cells across tissues remains unclear. By combining transcriptional and chromatin analyses with a truly unbiased fashion, we constructed a single-cell transcriptome and chromatin accessibility landscape of mouse γδ T cells in the lymph, spleen, and thymus. We also revealed the heterogeneity of γδ T1 and γδ T17 cells across these tissues and inferred their potential regulatory mechanisms. In the thymus, we reconstructed the developmental trajectory and gained further insights into the signature genes from the mature stage, intermediate stage, and immature stage of γδ T cells on the basis of single-cell RNA sequencing and single-cell assay for transposase-accessible chromatin sequencing data. Notably, a novel Gzma+ γδ T cell subset was identified with immature properties and only localized to the thymus. Finally, NR1D1, a circadian transcription factor (TF), was validated as a key and negative regulator of γδ T17 cell differentiation by performing a combined analysis of TF motif enrichment, regulon enrichment, and Nr1d1 knockout mice. In summary, our data represent a comprehensive mapping on the transcriptome and chromatin accessibility dynamics of mouse γδ T cells, providing a valuable resource and reference for future studies on γδ T cells.

The γδ IEL effector API5 masks genetic susceptibility to Paneth cell death.

Loss of Paneth cells and their antimicrobial granules compromises the intestinal epithelial barrier and is associated with Crohn's disease, a major type of inflammatory bowel disease1-7. Non-classical lymphoid cells, broadly referred to as intraepithelial lymphocytes (IELs), intercalate the intestinal epithelium8,9. This anatomical position has implicated them as first-line defenders in resistance to infections, but their role in inflammatory disease pathogenesis requires clarification. The identification of mediators that coordinate crosstalk between specific IEL and epithelial subsets could provide insight into intestinal barrier mechanisms in health and disease. Here we show that the subset of IELs that express γ and δ T cell receptor subunits (γδ IELs) promotes the viability of Paneth cells deficient in the Crohn's disease susceptibility gene ATG16L1. Using an ex vivo lymphocyte-epithelium co-culture system, we identified apoptosis inhibitor 5 (API5) as a Paneth cell-protective factor secreted by γδ IELs. In the Atg16l1-mutant mouse model, viral infection induced a loss of Paneth cells and enhanced susceptibility to intestinal injury by inhibiting the secretion of API5 from γδ IELs. Therapeutic administration of recombinant API5 protected Paneth cells in vivo in mice and ex vivo in human organoids with the ATG16L1 risk allele. Thus, we identify API5 as a protective γδ IEL effector that masks genetic susceptibility to Paneth cell death.

RNA m6A demethylase ALKBH5 regulates the development of γδ T cells.

γδ T cells are an abundant T cell population at the mucosa and are important in providing immune surveillance as well as maintaining tissue homeostasis. However, despite γδ T cells' origin in the thymus, detailed mechanisms regulating γδ T cell development remain poorly understood. N6-methyladenosine (m6A) represents one of the most common posttranscriptional modifications of messenger RNA (mRNA) in mammalian cells, but whether it plays a role in γδ T cell biology is still unclear. Here, we show that depletion of the m6A demethylase ALKBH5 in lymphocytes specifically induces an expansion of γδ T cells, which confers enhanced protection against gastrointestinal Salmonella typhimurium infection. Mechanistically, loss of ALKBH5 favors the development of γδ T cell precursors by increasing the abundance of m6A RNA modification in thymocytes, which further reduces the expression of several target genes including Notch signaling components Jagged1 and Notch2. As a result, impairment of Jagged1/Notch2 signaling contributes to enhanced proliferation and differentiation of γδ T cell precursors, leading to an expanded mature γδ T cell repertoire. Taken together, our results indicate a checkpoint role of ALKBH5 and m6A modification in the regulation of γδ T cell early development.

TCR-Vγδ usage distinguishes protumor from antitumor intestinal γδ T cell subsets.

γδ T cells represent a substantial fraction of intestinal lymphocytes at homeostasis, but they also constitute a major lymphocyte population infiltrating colorectal cancers (CRCs); however, their temporal contribution to CRC development or progression remains unclear. Using human CRC samples and murine CRC models, we found that most γδ T cells in premalignant or nontumor colons exhibit cytotoxic markers, whereas tumor-infiltrating γδ T cells express a protumorigenic profile. These contrasting T cell profiles were associated with distinct T cell receptor (TCR)-Vγδ gene usage in both humans and mice. Longitudinal intersectional genetics and antibody-dependent strategies targeting murine γδ T cells enriched in the epithelium at steady state led to heightened tumor development, whereas targeting γδ subsets that accumulate during CRC resulted in reduced tumor growth. Our results uncover temporal pro- and antitumor roles for γδ T cell subsets.

Vaccine-induced systemic and mucosal T cell immunity to SARS-CoV-2 viral variants.

The first-generation COVID-19 vaccines have been effective in mitigating severe illness and hospitalization, but recurring waves of infections are associated with the emergence of SARS-CoV-2 variants that display progressive abilities to evade antibodies, leading to diminished vaccine effectiveness. The lack of clarity on the extent to which vaccine-elicited mucosal or systemic memory T cells protect against such antibody-evasive SARS-CoV-2 variants remains a critical knowledge gap in our quest for broadly protective vaccines. Using adjuvanted spike protein­based vaccines that elicit potent T cell responses, we assessed whether systemic or lung-resident CD4 and CD8 T cells protected against SARS-CoV-2 variants in the presence or absence of virus-neutralizing antibodies. We found that 1) mucosal or parenteral immunization led to effective viral control and protected against lung pathology with or without neutralizing antibodies, 2) protection afforded by mucosal memory CD8 T cells was largely redundant in the presence of antibodies that effectively neutralized the challenge virus, and 3) "unhelped" mucosal memory CD8 T cells provided no protection against the homologous SARS-CoV-2 without CD4 T cells and neutralizing antibodies. Significantly, however, in the absence of detectable virus-neutralizing antibodies, systemic or lung-resident memory CD4 and "helped" CD8 T cells provided effective protection against the relatively antibody-resistant B1.351 (ß) variant, without lung immunopathology. Thus, induction of systemic and mucosal memory T cells directed against conserved epitopes might be an effective strategy to protect against SARS-CoV-2 variants that evade neutralizing antibodies. Mechanistic insights from this work have significant implications in the development of T cell­targeted immunomodulation or broadly protective SARS-CoV-2 vaccines.

Role of Palatine Tonsil and Epipharyngeal Lymphoid Tissue in the Development of Glomerular Active Lesions (Glomerular vasculitis) in Immunoglobulin A Nephropathy.

Hematuria is an essential symptom of immunoglobulin A nephropathy (IgAN). Although the etiology of hematuria in IgAN has not been fully elucidated, it is thought that the rupture of the glomerular basement membranes caused by intra-capillary leukocyte influx, so-called glomerular vasculitis, is the pathological condition responsible for severe hematuria. Glomerular vasculitis are active lesions that exist in the glomeruli of acute phase IgAN and it is important because it is suspected to make the transition to segmental glomerular sclerosis (SGS) as a repair scar lesion in the chronic phase, and the progression of SGS would eventually lead to glomerular obsolescence. Worsening of hematuria concomitant with acute pharyngitis is common in patients with IgAN; therefore, elucidating the relationship between the immune system of Waldeyer's ring, including the palatine tonsil and epipharyngeal lymphoid tissue, and the glomerular vasculitis may lead to understanding the nature of IgAN. The epipharynx is an immunologically activated site even under normal conditions, and enhanced activation of innate immunity is likely to occur in response to airborne infection. Hyperactivation of innate immunity via upregulation of Toll-like receptors in the interfollicular area of the palatine tonsil and epipharyngeal lymphoid tissue, followed by enhanced fractalkine/CX3CR1 interactions, appears to play an important role in the development of glomerular vasculitis in IgAN. As latent but significant epipharyngitis is present in most patients with IgAN, it is plausible that acute upper respiratory infection may contribute as a trigger for the innate epipharyngeal immune system, which is already upregulated in a chronically inflamed environment. Given that epipharyngitis and its effects on IgAN are not fully understood, we propose that the so-called "epipharynx-kidney axis" may provide an important focus for future research.

Title IgA Nephropathy and Oral Bacterial Species Related to Dental Caries and Periodontitis.

A relationship between IgA nephropathy (IgAN) and bacterial infection has been suspected. As IgAN is a chronic disease, bacteria that could cause chronic infection in oral areas might be pathogenetic bacteria candidates. Oral bacterial species related to dental caries and periodontitis should be candidates because these bacteria are well known to be pathogenic in chronic dental disease. Recently, several reports have indicated that collagen-binding protein (cnm)-(+) Streptococcs mutans is relate to the incidence of IgAN and the progression of IgAN. Among periodontal bacteria, Treponema denticola, Porphyromonas gingivalis and Campylobacte rectus were found to be related to the incidence of IgAN. These bacteria can cause IgAN-like histological findings in animal models. While the connection between oral bacterial infection, such as infection with S. mutans and periodontal bacteria, and the incidence of IgAN remains unclear, these bacterial infections might cause aberrantly glycosylated IgA1 in nasopharynx-associated lymphoid tissue, which has been reported to cause IgA deposition in mesangial areas in glomeruli, probably through the alteration of microRNAs related to the expression of glycosylation enzymes. The roles of other factors related to the incidence and progression of IgA, such as genes and cigarette smoking, can also be explained from the perspective of the relationship between these factors and oral bacteria. This review summarizes the relationship between IgAN and oral bacteria, such as cnm-(+) S. mutans and periodontal bacteria.