Progress in the Study of Fra-2 in Respiratory Diseases

Fos-related antigen-2 (Fra-2) is a member of the activating protein-1 (AP-1) family of transcription factors. It is involved in controlling cell growth and differentiation by regulating the production of the extracellular matrix (ECM) and coordinating the balance of signals within and outside the cell. Fra-2 is not only closely related to bone development, metabolism, and immune system and eye development but also in the progression of respiratory conditions like lung tumors, asthma, pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD). The increased expression and activation of Fra-2 in various lung diseases has been shown in several studies. However, the specific molecular mechanisms through which Fra-2 affects the development of respiratory diseases are not yet understood. The purpose of this research is to summarize and delineate advancements in the study of the involvement of transcription factor Fra-2 in disorders related to the respiratory system.

Fosl2 Deficiency Predisposes Mice to Osteopetrosis, Leading to Bone Marrow Failure

Arthritis causes Fos-like 2 (Fosl2) inactivation, and various immune cells contribute to its pathogenesis. However, little is known about the role of Fosl2 in hematopoiesis and the possible pathological role of Fosl2 inactivation in the hematopoietic system in arthritis. In this study, we show that Fosl2 maintains hematopoietic stem cell (HSC) quiescence and differentiation while controlling the inflammatory response via macrophages. Fosl2-specific deletion in the hematopoietic system caused the expansion of HSCs and myeloid cell growth while affecting erythroid and B cell differentiation. Fosl2 inactivation enhanced macrophage M1 polarization and stimulated proinflammatory cytokines and myeloid growth factors, skewing HSCs toward myeloid cell differentiation, similar to hematopoietic alterations in arthritic mice. Loss of Fosl2 mediated by Vav-iCre also displays an unexpected deletion in embryonic erythro-myeloid progenitor-derived osteoclasts, leading to osteopetrosis and anemia. The reduced bone marrow cellularity in Vav-iCreFosl2f/f mice is a consequence of the reduced bone marrow space in osteopetrotic mice rather than a direct role of Fosl2 in hematopoiesis. Thus, Fosl2 is indispensable for erythro-myeloid progenitor-derived osteoclasts to maintain the medullary cavity to ensure normal hematopoiesis. These findings improve our understanding of the pathogenesis of bone-destructive diseases and provide important implications for developing therapeutic approaches for these diseases.

Unraveling the Phenotypic States of Human innate-like T Cells: Comparative Insights with Conventional T Cells and Mouse Models

The "innate-like" T cell compartment, known as Tinn, represents a diverse group of T cells that straddle the boundary between innate and adaptive immunity, having the ability to mount rapid responses following activation. In mice, this ability is acquired during thymic development. We explored the transcriptional landscape of Tinn compared to conventional T cells (Tconv) in the human thymus and blood using single cell RNA sequencing and flow cytometry. We reveal that in human blood, the majority of Tinn cells, including iNKT, MAIT, and Vδ2+Vγ9+ T cells, share an effector program characterized by the expression of unique chemokine and cytokine receptors, and cytotoxic molecules. This program is driven by specific transcription factors, distinct from those governing Tconv cells. Conversely, only a fraction of thymic Tinn cells displays an effector phenotype, while others share transcriptional features with developing Tconv cells, indicating potential divergent developmental pathways. Unlike the mouse, human Tinn cells do not differentiate into multiple effector subsets but develop a mixed type I/type III effector potential. To conduct a comprehensive cross-species analysis, we constructed a murine Tinn developmental atlas and uncovered additional species-specific distinctions, including the absence of type II Tinn cells in humans, which implies distinct immune regulatory mechanisms across species. The study provides insights into the development and functionality of Tinn cells, emphasizing their role in immune responses and their potential as targets for therapeutic interventions.

FOSL2 promotes intertumoral infiltration of T cells and increases pathological complete response rates in locally advanced rectal cancer patients

The outcome of neoadjuvant chemoradiotherapy (nCRT) remains highly unpredictable for individuals with locally advanced rectal cancer (LARC). We set out to characterize effective biomarkers that promote a pathological complete response (pCR). We quantified the abundances of 6483 high-confidence proteins in pre-nCRT biopsies of 58 LARC patients from two hospitals with pressure cycling technology (PCT)-assisted pulse data-independent acquisition (PulseDIA) mass spectrometry. Compared with non-pCR patients, pCR patients achieved long-term disease-free survival (DFS) and had higher tumor immune infiltration, especially CD8+ T cell infiltration, before nCRT. FOSL2 was selected as the candidate biomarker for predicting pCR and was found to be significantly upregulated in pCR patients, which was verified in another 54 pre-nCRT biopsies of LARC patients by immunohistochemistry. FOSL2 expression was able to predict pCR by multiple reaction monitoring (MRM) with high efficiency (Area under curve (AUC) = 0.939, specificity = 1.000, sensitivity = 0.850), and high FOSL2 expression was associated with long-term DFS (p = 0.044). When treated with simulated nCRT, FOSL2 sufficiency resulted in more significant inhibition of cell proliferation, and more significant promotion of cell cycle arrest and cell apoptosis. Moreover, CXCL10 secretion with abnormal cytosolic dsDNA accumulation was found in FOSL2-wildtype (FOSL2-WT) tumor cells over nCRT, which might elevate CD8+ T-cell infiltration and CD8+ T-cell-mediated cytotoxicity to promote nCRT-induced antitumor immunity. Our study revealed proteomic profiles in LARC patients before nCRT and highlighted immune activation in the tumors of patients who achieved pCR. We identified FOSL2 as a promising biomarker to predict pCR and promote long-term DFS by contributing to CD8+ T-cell infiltration.

Investigation of the Underlying Mechanism of Huangqi-Dangshen for Myasthenia Gravis Treatment via Molecular Docking and Network Pharmacology

The herbal pairing of Huangqi and Dangshen (HD) is traditional Chinese herbal medicine and has been widely used in China, especially to treat myasthenia gravis (MG). However, the mechanism of HD on MG is unclear. Aim of the Study. This study aims to investigate HD's possible role in MG treatment. Materials and Methods. The TCMSP database was used to identify the active chemicals and their targets. The GeneCards, DisGeNET, and OMIM databases were used to search for MG-related targets. The STRING database was employed in order to identify the common PPI network targets. We next utilised Cytoscape 3.8.2 for target identification and the DAVID database for gene ontology (GO) function analysis as well as Encyclopaedia of Genomes (KEGG) pathway enrichment analysis on the selected targets. The AutoDock Vina software was used to test the affinity of essential components with the hub gene before concluding that the primary targets were corrected through molecular docking. Results. 41 active compounds were screened from HD, and the number of putative-identified target genes screened from HD was 112. There were 21 target genes that overlapped with the targets of MG, which were postulated to be potential treatment targets. Through further analysis, the results showed that the active compounds from HD (such as 7-methoxy-2-methylisoflavone, quercetin, luteolin, Kaempferol, and isorhamnetin) may achieve the purpose of treating MG by acting on some core targets and related pathways (such as EGFR, FOS, ESR2, MYC, ESR1, CASP3, and IL-6). Molecular docking findings demonstrated that these active molecules have a near-perfect ability to attach to the primary targets. Conclusion. Through network pharmacology, the findings in this study provide light on the coordinated action of several HD formula components, targets, and pathways. It provided a theoretical basis for further study of HD pharmacological action.

Fra-2 Is a Dominant Negative Regulator of Natural Killer Cell Development

Natural killer (NK) cells play an important role in recognizing and killing pathogen-infected or malignant cells. Changes in their numbers or activation can contribute to several diseases and pathologies including systemic sclerosis (SSc), an autoimmune disease characterized by inflammation and tissue remodeling. In these patients, increased expression of the AP-1 transcription factor, Fra-2 was reported. In mice ectopic overexpression of Fra-2 (TG) leads to SSc with strong pulmonary fibrosis, pulmonary hypertension, and inflammation. Analysis of the underlying immune cell profile in the lungs of young TG mice, which do not yet show any signs of lung disease, revealed increased numbers of eosinophils and T cells but strongly reduced NK numbers. Therefore, we aimed to identify the cause of the absence of NK cells in the lungs of these mice and to determine the potential role of Fra-2 in NK development. Examination of inflammatory cell distribution in TG mice revealed similar NK deficiencies in the spleen, blood, and bone marrow. Deeper analysis of the WT and TG bone marrow revealed a potential NK cell developmental defect beginning at the preNKP stage. To determine whether this defect was cell-intrinsic or extrinsic, mixed bone marrow chimera and in vitro differentiation experiments were performed. Both experiments showed that the defect caused by Fra-2 was primarily cell-intrinsic and minimally dependent on the environment. Closer examination of surface markers and transcription factors required for NK development, revealed the expected receptor distribution but changes in transcription factor expression. We found a significant reduction in Nfil3, which is essential for the transition of common lymphoid cells to NK committed precursor cells and an AP-1 binding site in the promotor of this gene. In Summary, our data demonstrates that regulation of Fra-2 is essential for NK development and maturation, and suggests that the early NK dysfunction plays an important role in the pathogenesis of systemic sclerosis.

Mechanism of TCONS_00147848 regulating apoptosis of nasal mucosa cells and alleviating allergic rhinitis through FOSL2-mediated JAK/STAT3 signaling pathway

This study was conducted to explore the roles and related mechanisms of lncRNA-TCONS_00147848 (TCONS_00147848) in nasal mucosa cell apoptosis and allergic rhinitis (AR). AR mice were sensitized with ovalbumin (OVA), with the TCONS_00147848 interference lentiviral vector (TCONS_00147848 shRNA) and FOSL2 overexpressing lentiviral vectors (pCDH-FOSL2) constructed respectively. NC shRNA, TCONS_00147848 shRNA and TCONS_00147848 shRNA + pCDH-FOSL2 were transfected into AR mice and mice with TNF-α induced nasal mucosa cells. The allergic reaction symptoms were evaluated by scoring. And in this study, we used Hematoxylin–Eosin (HE) staining and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) to detect the histological changes of nasal mucosa and apoptosis of nasal mucosa epithelial cells in mice, cell counting kit-8 (CCK-8) assay, Transwell and annexin V/PI to detect proliferation, migration and apoptosis of nasal mucosa cells of mice, respectively, enzyme-linked immunosorbent assay (ELISA) to detect the expression of inflammatory factors, qRT-PCR to detect TCONS_00147848 expression, Western blot assay to detect the expressions of FOSL2, JAK-2, STAT3, p-STAT3, BAX and BCL-2, RNA-binding protein immunoprecipitation (RIP) assay, RNA pull down assay and Co-immunoprecipitation (CoIP) assay to identify TCONS_00147848 targeting FOSL2. All these findings above reveal that knocking down TCONS_00147848 can reduce the allergic reaction symptom score of AR mice and the inflammatory reaction. The expression of IgE, IL-4, IL-5, IL-10, IL-9, IFN-γ and TNF-α in serum decreased. The expression of FOSL2, JAK-2, p-STAT3 and BAX in nasal mucosa and nasal mucosa cells of mice decreased as well, but BCL-2 expression increased. In addition, koncking down TCONS_00147848 can also inhibit the apoptosis of TNF-α induced nasal mucosa cells in mice and promote cell proliferation and migration. However, FOSL2 overexpression neutralized the effect of TCONS_00147848 shRNA. In nasal mucosa cells of mice, TCONS_00147848 can target FOSL2, interacting with STAT3. Inhibition of TCONS_00147848 can regulate JAK/STAT3 signaling pathway and reduce inflammatory response in AR mice.

The AP1 Transcription Factor Fosl2 Promotes Systemic Autoimmunity and Inflammation by Repressing Treg Development

Regulatory T cells (Tregs) represent a major population in the control of immune homeostasis and autoimmunity. Here we show that Fos-like 2 (Fosl2), a TCR-induced AP1 transcription factor, represses Treg development and controls autoimmunity. Mice overexpressing Fosl2 (Fosl2^tg) indeed show a systemic inflammatory phenotype, with immune infiltrates in multiple organs. This phenotype is absent in Fosl2^tg × Rag2^-/- mice lacking T and B cells, and Fosl2 induces T cell-intrinsic reduction of Treg development that is responsible for the inflammatory phenotype. Fosl2^tg T cells can transfer inflammation, which is suppressed by the co-delivery of Tregs, while Fosl2 deficiency in T cells reduces the severity of autoimmunity in the EAE model. We find that Fosl2 could affect expression of FoxP3 and other Treg development genes. Our data highlight the importance of AP1 transcription factors, in particular Fosl2, during T cell development to determine Treg differentiation and control autoimmunity.

Development of a Bioinformatics Framework for Identification and Validation of Genomic Biomarkers and Key Immunopathology Processes and Controllers in Infectious and Non-infectious Severe Inflammatory Response Syndrome

Sepsis is defined as dysregulated host response caused by systemic infection, leading to organ failure. It is a life-threatening condition, often requiring admission to an intensive care unit (ICU). The causative agents and processes involved are multifactorial but are characterized by an overarching inflammatory response, sharing elements in common with severe inflammatory response syndrome (SIRS) of non-infectious origin. Sepsis presents with a range of pathophysiological and genetic features which make clinical differentiation from SIRS very challenging. This may reflect a poor understanding of the key gene inter-activities and/or pathway associations underlying these disease processes. Improved understanding is critical for early differential recognition of sepsis and SIRS and to improve patient management and clinical outcomes. Judicious selection of gene biomarkers suitable for development of diagnostic tests/testing could make differentiation of sepsis and SIRS feasible. Here we describe a methodologic framework for the identification and validation of biomarkers in SIRS, sepsis and septic shock patients, using a 2-tier gene screening, artificial neural network (ANN) data mining technique, using previously published gene expression datasets. Eight key hub markers have been identified which may delineate distinct, core disease processes and which show potential for informing underlying immunological and pathological processes and thus patient stratification and treatment. These do not show sufficient fold change differences between the different disease states to be useful as primary diagnostic biomarkers, but are instrumental in identifying candidate pathways and other associated biomarkers for further exploration.

Transcription factor Fra-2 and its emerging role in matrix deposition, proliferation and inflammation in chronic lung diseases

Fos-related antigen-2 (Fra-2) belongs to the activator protein 1 (AP-1) family of transcription factors and is involved in a broad variety of cellular processes, such as proliferation or differentiation. Aberrant expression of Fra-2 or regulation can lead to severe growth defects or diverse pathologies. Elevated Fra-2 expression has been described in several chronic lung diseases, such as pulmonary fibrosis, chronic obstructive pulmonary disease and asthma. However, the pathomechanisms behind the Fra-2-induced pulmonary remodelling are still not fully elucidated. Fra-2 overexpressing mice were initially described as a model of systemic sclerosis associated organ fibrosis, with predominant alterations in the lung. High levels of Fra-2 expression give rise to profound inflammation with severe remodelling of the parenchyma and the vasculature, resulting in fibrosis and pulmonary hypertension, respectively, but also alters bronchial function. In this review we discuss the central role of Fra-2 connecting inflammation, cellular proliferation and extracellular matrix deposition underlying chronic lung diseases and what we can learn for future therapeutic options.

Lymphocyte innateness defined by transcriptional states reflects a balance between proliferation and effector functions

How innate T cells (ITC), including invariant natural killer T (iNKT) cells, mucosal-associated invariant T (MAIT) cells, and γδ T cells, maintain a poised effector state has been unclear. Here we address this question using low-input and single-cell RNA-seq of human lymphocyte populations. Unbiased transcriptomic analyses uncover a continuous ‘innateness gradient’, with adaptive T cells at one end, followed by MAIT, iNKT, γδ T and natural killer cells at the other end. Single-cell RNA-seq reveals four broad states of innateness, and heterogeneity within canonical innate and adaptive populations. Transcriptional and functional data show that innateness is characterized by pre-formed mRNA encoding effector functions, but impaired proliferation marked by decreased baseline expression of ribosomal genes. Together, our data shed new light on the poised state of ITC, in which innateness is defined by a transcriptionally-orchestrated trade-off between rapid cell growth and rapid effector function.

Innate T cells (ITC) contain many subsets and are poised to promptly respond to antigens and pathogens, but how this poised state is maintained is still unclear. Here the authors perform single-cell RNA-seq to align the various ITC subsets along an ‘innateness gradient’ that is associated with changes in proliferation and effector functions.

The ins and outs of type I iNKT cell development

Natural killer T (NKT) cells are innate-like lymphocytes that bridge the gap between the innate and adaptive immune responses. Like innate immune cells, they have a mature, effector phenotype that allows them to rapidly respond to threats, compared to adaptive cells. NKT cells express T cell receptors (TCRs) like conventional T cells, but instead of responding to peptide antigen presented by MHC class I or II, NKT cell TCRs recognize glycolipid antigen in the context of CD1d. NKT cells are subdivided into classes based on their TCR and antigen reactivity. This review will focus on type I iNKT cells that express a semi invariant Vα14Jα18 TCR and respond to the canonical glycolipid antigen, α-galactosylceramide. The innate-like effector functions of these cells combined with their T cell identity make their developmental path quite unique. In addition to the extrinsic factors that affect iNKT cell development such as lipid:CD1d complexes, co-stimulation, and cytokines, this review will provide a comprehensive delineation of the cell intrinsic factors that impact iNKT cell development, differentiation, and effector functions - including TCR rearrangement, survival and metabolism signaling, transcription factor expression, and gene regulation.

Regulation of the terminal maturation of iNKT cells by mediator complex subunit 23

Invariant natural killer T cells (iNKT cells) are a specific subset of T cells that recognize glycolipid antigens and upon activation rapidly exert effector functions. This unique function is established during iNKT cell development; the detailed mechanisms of this process, however, remain to be elucidated. Here the authors show that deletion of the mediator subunit Med23 in CD4⁺CD8⁺ double positive (DP) thymocytes completely blocks iNKT cell development at stage 2. This dysregulation is accompanied by a bias in the expression of genes related to the regulation of transcription and metabolism, and functional impairment of the cells including the loss of NK cell characteristics, reduced ability to secrete cytokines and attenuated recruitment capacity upon activation. Moreover, Med23-deficient iNKT cells exhibit impaired anti-tumor activity. Our study identifies Med23 as an essential transcriptional regulator that controls iNKT cell differentiation and terminal maturation.

Invariant Natural Killer T cells (iNKT) rapidly exert effector functions upon activation, but the mechanisms of their functional maturation remain to be determined. Here, Xu and colleagues show that the mediator subunit Med23 is a transcriptional regulator controlling iNKT cell terminal maturation.

Fra-2 regulates B cell development by enhancing IRF4 and Foxo1 transcription

The role of AP-1 transcription factors in early B cell development and function is still incompletely characterized. Ubieta at al. describe the function of the Fra-2/AP-1 transcription factor as a regulator of Foxo1 and Irf4 expression in B cells. Fra-2 affects B cell proliferation and maintains their number in bone marrow.

The role of AP-1 transcription factors in early B cell development and function is still incompletely characterized. Here we address the role of Fra-2 in B cell differentiation. Deletion of Fra-2 leads to impaired B cell proliferation in the bone marrow. In addition, IL-7–stimulated pro–B cell cultures revealed a reduced differentiation from large pre–B cells to small B cells and immature B cells. Gene profiling and chromatin immunoprecipitation sequencing analyses unraveled a transcriptional reduction of the transcription factors Foxo1, Irf4, Ikaros, and Aiolos in Fra-2–deficient B cells. Moreover, expression of IL7Rα and Rag 1/2, downstream targets of Irf4 and Foxo1, were also reduced in the absence of Fra-2. Pro–B cell proliferation and small pre–B cell differentiation were fully rescued by expression of Foxo1 and Irf4 in Fra-2–deficient pro–B cells. Hence, Fra-2 is a key upstream regulator of Foxo1 and Irf4 expression and influences proliferation and differentiation of B cells at multiple stages.

The histone demethylase UTX regulates the lineage-specific epigenetic program of invariant natural killer T cells

Invariant natural killer T cells (iNKT cells) are innate-like lymphocytes that protect against infection, autoimmune disease and cancer. However, little is known about the epigenetic regulation of iNKT cell development. Here we found that the H3K27me3 histone demethylase UTX was an essential cell-intrinsic factor that controlled an iNKT-cell lineage-specific gene-expression program and epigenetic landscape in a demethylase-activity-dependent manner. UTX-deficient iNKT cells exhibited impaired expression of iNKT cell signature genes due to a decrease in activation-associated H3K4me3 marks and an increase in repressive H3K27me3 marks within the promoters occupied by UTX. We found that JunB regulated iNKT cell development and that the expression of genes that were targets of both JunB and the iNKT cell master transcription factor PLZF was UTX dependent. We identified iNKT cell super-enhancers and demonstrated that UTX-mediated regulation of super-enhancer accessibility was a key mechanism for commitment to the iNKT cell lineage. Our findings reveal how UTX regulates the development of iNKT cells through multiple epigenetic mechanisms.

Coupling of T cell receptor specificity to natural killer T cell development by bivalent histone H3 methylation

The fidelity of T cell immunity depends greatly on coupling T cell receptor signaling with specific T cell effector functions. Here, we describe a chromatin-based mechanism that enables integration of TCR specificity into definite T cell lineage commitment. Using natural killer T cells (iNKT cell) as a model of a T cell subset that differentiates in response to specific TCR signaling, we identified a key role of histone H3 lysine 27 trimethylation (H3K27me3) in coupling iNKT cell TCR specificity with the generation of iNKT cells. We found that the Zbtb16/PLZF gene promoter that drives iNKT cell differentiation possesses a bivalent chromatin state characterized by the simultaneous presence of negative and positive H3K27me3 and H3K4me3 modifications. Depletion of H3K27me3 at the Zbtb16/PLZF promoter leads to uncoupling of iNKT cell development from TCR specificity and is associated with accumulation of iNKT-like CD4(+) cells that express a non-iNKT cell specific T cell repertoire. In turn, stabilization of H3K27me3 leads to a drastic reduction of the iNKT cell population. Our data suggest that H3K27me3 levels at the bivalent Zbtb16/PLZF gene define a threshold enabling precise coupling of TCR specificity to lineage commitment.

Transcriptional control of the development and function of Vα14i NKT cells

The majority of T lymphocytes, sometimes referred to as as mainstream or conventional T cells, are characterized by a diverse T cell antigen receptor (TCR) repertoire. They require antigen priming in order to become memory cells capable of mounting a rapid effector response. It has become established, however, that there are several distinct T cell lineages that exhibit a memory phenotype in the absence of antigen priming, even as they differentiate in the thymus. These lymphocytes typically express a markedly restricted TCR repertoire and their rapid response kinetics has led to their being described as innate-like T cells. In addition, several of these subsets typically express surface markers commonly found on natural killer cells, which has led to the moniker natural killer T cells (NKT cells). This review will describe our current understanding of the unique ways whereby transcription factors control the development and function of an abundant and widely studied lineage of NKT cells that recognizes glycolipid antigens.

Control of early stages in invariant natural killer T-cell development

Natural killer T (NKT) cells develop in the thymus from the same precursors as conventional CD4(+) and CD8(+) αβ T cells, CD4(+)  CD8(+) double-positive cells. In contrast to conventional αβT cells, which are selected by MHC-peptide complexes presented by thymic epithelial cells, invariant NKT cells are selected by lipid antigens presented by the non-polymorphic, MHC I-like molecule CD1d, present on the surface of other double-positive thymocytes, and require additional signals from the signalling lymphocytic-activation molecule (SLAM) family of receptors. In this review, we provide a discussion of recent findings that have modified our understanding of the NKT cell developmental programme, with an emphasis on events that affect the early stages of this process. This includes factors that control double-positive thymocyte lifespan, and therefore the ability to generate the canonical Vα rearrangements that characterize this lineage, as well as the signal transduction pathways engaged downstream of the T-cell receptor and SLAM molecules.

Transcriptional control of invariant NKT cell development

Invariant natural killer T (iNKT) cells comprise a rare lymphocyte sublineage with phenotypic and functional properties similar to T and NK cells. Akin to conventional αβ T cells, their development occurs primarily in the thymus, where they originate from CD4(+) CD8(+) double positive (DP) progenitors. However, the selection of iNKT cells is unique in that it is mediated by homotypic interactions of DP cells and recognition of glycolipid antigen-CD1d complexes. Additionally, iNKT cells acquire an activated innate-like phenotype during development that allows them to release cytokines rapidly following antigen exposure. Given their hybrid features, it is not surprising that the developmental program of iNKT cells partially overlaps with that of T and NK cells. Several recent reports have provided new and exciting insights into the developmental mechanisms that direct natural killer T (NKT) cell lineage commitment and maturation. In this review, we provide a discussion of the NKT cell developmental program with an emphasis on the signaling mechanisms and transcription factors that influence the ontogeny of this lineage. Continued investigations into the complex interplay of these transcription factors and their relationship with other extracellular and intracellular signaling molecules will undoubtedly provide important clues into the biology of this unusual T-cell lineage.

Expression of functional GPR35 in human iNKT cells

The aim of this study was to examine the expression of G protein-coupled receptor (GPR)35 in human invariant natural killer T (iNKT) cells and to determine the functional effects induced by selective activation of this receptor. RT-PCR analysis showed that both human iNKT cells and resting PBMC expressed GPR35; GPR35 protein resulted mostly localized in the plasma membrane, while it internalized in punctate intracellular structures following specific receptor activation (Western blot and immunofluorescence/confocal microscopy analysis). The specific activation of GPR35 by selective receptor agonists [l-kynurenic acid (KYNA)] or 1,4-dihydro-5-(2-propoxyphenyl)-7H-1,2,3-triazolo [4,5-d]pyrimidine-7-one (zaprinast)] functionally correlated with a significant reduction in IL-4 release from alpha-galactosylceramide (alpha-GalCer)-activated human iNKT cells, and this effect resulted mediated by pertussis toxin (PTX)-sensitive Gi/o proteins. In conclusion, our results demonstrate that human iNKT cells express GPR35 functionally active in reducing IL-4 release.

Raising the NKT cell family

Natural killer T cells (NKT cells) are CD1d-restricted, lipid antigen-reactive, immunoregulatory T lymphocytes that can promote cell-mediated immunity to tumors and infectious organisms, including bacteria and viruses, yet paradoxically they can also suppress the cell-mediated immunity associated with autoimmune disease and allograft rejection. Furthermore, in some diseases, such as atherosclerosis and allergy, NKT cell activity can be deleterious to the host. Although the precise means by which these cells carry out such contrasting functions is unclear, recent studies have highlighted the existence of many functionally distinct NKT cell subsets. Because their frequency and number vary widely between individuals, it is important to understand the mechanisms that regulate the development and maintenance of NKT cells and subsets thereof, which is the subject of this review.