Podoplanin is an inflammatory protein upregulated in Th17 cells in SKG arthritic joints

Lack of inflammation or immune response in cyst tissue of patients with symptomatic non-hydrocephalic pineal cysts

Pineal cysts are frequently encountered as incidental findings in magnetic resonance imaging, usually devoid of symptoms, yet some patients exhibit symptomatic manifestations possibly associated with the cyst, even in the absence of hydrocephalus. The etiology of these symptoms remains contentious. This study aims to investigate the presence of lymphatic endothelial cell (LEC) markers and indications of inflammation or immune response within the pineal cysts of patients experiencing symptomatic non-hydrocephalic presentations. Eight patients who underwent surgical excision of their cysts were included in the study. Immunohistochemistry was utilized to assess the expression of LYVE-1, PDPN, and VEGFR3 as LEC markers, alongside IL-6 and CD3 for indications of inflammation or immune activity. Our analysis revealed an absence of inflammatory markers or immune response. However, a distinct expression of VEGFR3 was observed, likely localized to neurons within the pineal cyst tissue. We propose that these VEGFR3+ neurons within the pineal cyst may contribute to the headache symptoms reported by these patients. Further investigations are warranted to substantiate this hypothesis.

The role of blood podoplanin in patients with viral myocarditis

Podoplanin (PDPN), a small mucin-like glycoprotein, was recently found to promote the generation of cardiac ectopic lymphoid follicles and anti-heart autoantibodies (AHA) in viral myocarditis (VMC) mice. Herein, we investigated the blood PDPN expression and its potential clinical value in VMC patients. Overall, 40 VMC patients were enrolled among 112 hospitalized patients with suspected myocarditis. Their serum PDPN levels were higher than those in controlled acute myocardial infarction (AMI) patients (n = 40) and healthy individuals (n = 30) (both p < 0.01) and positively correlated with CRP, IL-17, and IL-4 (all p < 0.01). Elevation of serum PDPN discriminated VMC from AMI (OR = 4.061, p < 0.01) and PDPN addition to the basic model (age, CRP, and peak cTNI) increased AUC values (from 0.822 to 0.933, p = 0.04). Additionally, the serum levels of PDPN ligand CCL-21 were also increased and correlated with PDPN (R = 0.59, p < 0.01) in VMC patients, accompanied by AHA production. Moreover, the anti-MHC antibody was closely related to PDPN levels (R = 0.53, p < 0.01), and anti-MHC-positive patients with VMC displayed higher percentages of CD4+IL-17A+PDPN+T cells and CD19+CCR7+B cells (both p < 0.05). Noticeably, VMC patients complicated by ventricular arrhythmias (27.50%) presented with AHA production and higher PDPN levels (p < 0.05). Finally, we screened out and verified that miR-182-5p directly targeted PDPN and negatively regulated its expression (all p < 0.01). These data suggested that blood PDPN might be a novel inflammation-associated biomarker for the early diagnosis of VMC and may contribute to AHA production by binding CCL-21 to recruit Th17 and B cells, which were regulated by miR-182-5p.

Podoplanin: Its roles and functions in neurological diseases and brain cancers

Podoplanin is a small mucin-like glycoprotein involved in several physiological and pathological processes in the brain including development, angiogenesis, tumors, ischemic stroke and other neurological disorders. Podoplanin expression is upregulated in different cell types including choroid plexus epithelial cells, glial cells, as well as periphery infiltrated immune cells during brain development and neurological disorders. As a transmembrane protein, podoplanin interacts with other molecules in the same or neighboring cells. In the past, a lot of studies reported a pleiotropic role of podoplanin in the modulation of thrombosis, inflammation, lymphangiogenesis, angiogenesis, immune surveillance, epithelial mesenchymal transition, as well as extracellular matrix remodeling in periphery, which have been well summarized and discussed. Recently, mounting evidence demonstrates the distribution and function of this molecule in brain development and neurological disorders. In this review, we summarize the research progresses in understanding the roles and mechanisms of podoplanin in the development and disorders of the nervous system. The challenges of podoplanin-targeted approaches for disease prognosis and preventions are also discussed.

The Role of Podoplanin in the Immune System and Inflammation

Podoplanin is a small cell-surface mucin-like glycoprotein that participates in multiple physiological and pathological processes. Podoplanin exerts an important function in the immune response and is upregulated in fibroblasts, macrophages, T helper cells, and epithelial cells during inflammation. Herein, we summarize the latest knowledge on the functional expression of podoplanin in the immune system and review the contribution of podoplanin to several inflammatory diseases. Furthermore, we discuss podoplanin as a novel therapeutic target for various inflammatory diseases.

Interleukin 27 Signaling in Rheumatoid Arthritis Patients: Good or Evil?

The occurrence and development of rheumatoid arthritis (RA) is regulated by numerous cytokines. Interleukin 27 (IL-27) is a soluble cytokine that exerts biological effects by regulating the Janus tyrosine kinase (JAK)/signal transducer and activator of the transcription (STAT) signaling pathway via the IL-27 receptor. IL-27 is known for its pleiotropic roles in modulating inflammatory responses. Previous studies found that IL-27 levels are elevated in RA blood, synovial fluid, and rheumatoid nodules. Cellular and animal experiments indicated that IL-27 exerts multiple regulatory functions in RA patients via different mechanisms. IL-27 inhibits ectopic-like structure (ELS) formation and CD4⁺ T helper type 2 (Th2) cell, CD4⁺ T helper type 17 (Th17) cell, and osteoclast differentiation in RA, contributing to alleviating RA. However, IL-27 promotes Th1 cell differentiation, which may exacerbate RA synovitis. Moreover, IL-27 also acts on RA synovial fibroblasts (RA-FLSs) and regulatory T cells (Tregs), but some of its functions are unclear. There is currently insufficient evidence to determine whether IL-27 promotes or relieves RA. Targeting IL-27 signaling in RA treatment should be deliberate based on current knowledge.

Cholesterol 25-hydroxylase is a metabolic switch to constrain T cell-mediated inflammation in the skin

Interleukin-27 (IL-27) is an immunoregulatory cytokine whose essential function is to limit immune responses. We found that the gene encoding cholesterol 25-hydroxylase (Ch25h) was induced in CD4+ T cells by IL-27, enhanced by transforming growth factor–β (TGF-β), and antagonized by T-bet. Ch25h catalyzes cholesterol to generate 25-hydroxycholesterol (25OHC), which was subsequently released to the cellular milieu, functioning as a modulator of T cell response. Extracellular 25OHC suppressed cholesterol biosynthesis in T cells, inhibited cell growth, and induced nutrient deprivation cell death without releasing high-mobility group box 1 (HMGB1). This growth inhibitory effect was specific to actively proliferating cells with high cholesterol demand and was reversed when extracellular cholesterol was replenished. Ch25h-expressing CD4+ T cells that received IL-27 and TGF-β signals became refractory to 25OHC-mediated growth inhibition in vitro. Nonetheless, IL-27–treated T cells negatively affected viability of bystander cells in a paracrine manner, but only if the bystander cells were in the early phases of activation. In mouse models of skin inflammation due to autoreactive T cells or chemically induced hypersensitivity, genetic deletion of Ch25h or Il27ra led to worse outcomes. Thus, Ch25h is an immunoregulatory metabolic switch induced by IL-27 and dampens excess bystander T effector expansion in tissues through its metabolite derivative, 25OHC. This study reveals regulation of cholesterol metabolism as a modality for controlling tissue inflammation and thus represents a mechanism underlying T cell immunoregulatory functions.

Comparison of allergenicity among cow, goat, and horse milks using a murine model of atopy

Due to the prevalence and severity of cow milk (CM) allergy (CMA), an ideal substitute is urgently needed to develop hypoallergenic infant formula for infants who experience anaphylaxis to typical whey-based CM formula. Goat milk (GM) and horse milk (HM) are considered appropriate substitutes; however, whether GM and HM are less allergenic than CM is unclear. In the present study, the difference in allergenicity among CM, GM, and HM was investigated using the Balb/c mouse model. The number of mice with severe respiratory symptoms was significantly lower in the GM- and HM-sensitised groups than in the CM-sensitised group. Furthermore, histologic examination of intestinal and lung tissues revealed a thinner lamina propria of the small intestine and obvious inflammation and congestion in lungs in the CM-sensitised group than in the GM- and HM-sensitised groups. CM-specific immunoglobulin (Ig) E, serum IgG1, and plasma histamine levels were also higher in CM-sensitised mice than in GM- or HM-sensitised mice. In addition, higher interleukin (IL) 4 and IL-17A levels and lower interferon-γ (IFN-γ) and IL-10 levels were observed in CM-sensitised mice compared with GM- and HM-sensitised mice, according to qPCR, indicating Th1/Th2 and Treg/Th17 imbalances. The CM-sensitised group had a higher proportion of IL-4- and IL-17A-producing CD3+ T cells but a lower proportion of IFN-γ- and IL-10-producing CD3+ T cells compared with the GM- and HM-sensitised groups, confirming the Th1/Th2 and Treg/Th17 imbalances. In conclusion, GM and HM were less allergenic than CM in mice as a result of a shift in the Th1/Th2 and Treg/Th17 imbalances; however, HM was less allergenic than GM and can be used as an alternative milk to develop infant formulas for children with CMA.

The Detection of Plasma Soluble Podoplanin of Patients with Breast Cancer and Its Clinical Signification

Background

Podoplanin (PDPN) is a type-1 membrane sialoglycoprotein that is expressed in many cancer tumors including breast cancer; nonetheless, its roles in tumor occurrence, development, and metastasis are unclear. In this study, we aimed to investigate the clinical significance of plasma soluble PDPN (sPDPN) levels in patients with breast cancer and its significance in the diagnosis and metastasis.

Materials and Methods

Blood samples from healthy controls (CTL), patients with fibroadenomas of breast (FOB), and breast cancer (pathological type: invasive ductal carcinoma, IDC) were collected. sPDPN levels in the plasma of CTL and patients with FOB and IDC were measured by the ELISA.

Results

The plasma sPDPN levels in IDC patients (159 cases, 22.59±3.70 ng/mL) were higher than those in FOB patients (50 cases, 8.29±1.09 ng/mL; P<0.05) and CTL (100 cases, 1.21±0.12 ng/mL; P<0.0001). The sPDPN levels in patients at stage III and stage IV (30.08±4.66 ng/mL) were higher than in patients at stage I and stage II (11.84±1.12 ng/mL; P=0.005). The sPDPN levels in patients with high-moderate and moderate differentiation (17.50±3.02 ng/mL) were lower than those in patients with moderately low and low differentiation (35.73±4.26 ng/mL; P=0.026). The sPDPN levels in patients with metastasis (30.60±4.27 ng/mL) were much higher than those in patients without metastasis (13.02±1.30 ng/mL; P=0.017).

Conclusion

Plasma sPDPN may be used as a new marker for the determination of the clinical stage, differentiation degree, and metastasis status of breast cancer.

Stromal Cells in the Pathogenesis of Inflammatory Bowel Disease

Up till now, research on inflammatory bowel disease [IBD] has mainly been focused on the immune cells present in the gastrointestinal tract. However, recent insights indicate that stromal cells also play an important and significant role in IBD pathogenesis. Stromal cells in the intestines regulate both intestinal epithelial and immune cell homeostasis. Different subsets of stromal cells have been found to play a role in other inflammatory diseases [e.g. rheumatoid arthritis], and these various stromal subsets now appear to carry out also specific functions in the inflamed gut in IBD. Novel potential therapies for IBD utilize, as well as target, these pathogenic stromal cells. Injection of mesenchymal stromal cells [MSCs] into fistula tracts of Crohn's disease patients is already approved and used in clinical settings. In this review we discuss the current knowledge of the role of stromal cells in IBD pathogenesis. We further outline recent attempts to modify the stromal compartment in IBD with agents that target or replace the pathogenic stroma.

New Therapeutic Strategies for Osteoarthritis by Targeting Sialic Acid Receptors

Osteoarthritis (OA) is the most common degenerative joint disease characterized by articular cartilage degradation and joint degeneration. The articular cartilage is mainly formed by chondrocytes and a collagen-proteoglycan extracellular matrix that contains high levels of glycosylated proteins. It was reported that the shift from glycoproteins containing α-2,6-linked sialic acids to those that contain α-2,3 was associated with the onset of common types of arthritis. However, the pathophysiology of α-2,3-sialylation in cartilage has not been yet elucidated. We show that cartilage from osteoarthritic patients expresses high levels of the α-2,3-sialylated transmembrane mucin receptor, known as podoplanin (PDPN). Additionally, the Maackia amurensis seed lectin (MASL), that can be utilized to target PDPN, attenuates the inflammatory response mediated by NF-kB activation in primary chondrocytes and protects human cartilage breakdown ex vivo and in an animal model of arthritis. These findings reveal that specific lectins targeting α-2,3-sialylated receptors on chondrocytes might effectively inhibit cartilage breakdown. We also present a computational 3D molecular model for this interaction. These findings provide mechanistic information on how a specific lectin could be used as a novel therapy to treat degenerative joint diseases such as osteoarthritis.

Il-23/Th17 cell pathway: A promising target to alleviate thymic inflammation maintenance in myasthenia gravis

IL-23/Th17 pathway has been identified to sustain inflammatory condition in several autoimmune diseases and therefore being targeted in various therapeutic and effective approaches. Patients affected with autoimmune myasthenia gravis exhibit a disease effector tissue, the thymus, that harbors ectopic germinal centers that sustain production of auto-antibodies, targeting proteins located in the neuromuscular junction, cause of the organ-specific chronic autoimmune disease. The present study aims to investigate the IL-23/Th17 cell pathway in the thymic inflammatory and pathogenic events. We found that thymuses of MG patients displayed overexpression of Interleukin-17, signature cytokine of activated Th17 cells. This activation was sustained by a higher secretion of Interleukin-23 by TEC, in addition to the increased expression of cytokines involved in Th17 cell development. The overexpression of Interleukin-23 was due to a dysregulation of interferon type I pathway. Besides, Interleukin-17 secreted, and Th17 cells were localized around thymic ectopic germinal centers. These cells expressed podoplanin, a protein involved in B-cell maturation and antibody secretion. Finally, production of Interleukin-23 was also promoted by Interleukin-17 secreted itself by Th17 cells, highlighting a chronic loop of inflammation sustained by thymic cell interaction. Activation of the IL-23/Th17 pathway in the thymus of autoimmune myasthenia gravis patients creates an unstoppable loop of inflammation that may participate in ectopic germinal center maintenance. To alleviate the physio-pathological events in myasthenia gravis patients, this pathway may be considered as a new therapeutic target.

Podoplanin in Inflammation and Cancer

Podoplanin is a small cell-surface mucin-like glycoprotein that plays a crucial role in the development of the alveoli, heart, and lymphatic vascular system. Emerging evidence indicates that it is also involved in the control of mammary stem-cell activity and biogenesis of platelets in the bone marrow, and exerts an important function in the immune response. Podoplanin expression is upregulated in different cell types, including fibroblasts, macrophages, T helper cells, and epithelial cells, during inflammation and cancer, where it plays important roles. Podoplanin is implicated in chronic inflammatory diseases, such as psoriasis, multiple sclerosis, and rheumatoid arthritis, promotes inflammation-driven and cancer-associated thrombosis, and stimulates cancer cell invasion and metastasis through a variety of strategies. To accomplish its biological functions, podoplanin must interact with other proteins located in the same cell or in neighbor cells. The binding of podoplanin to its ligands leads to modulation of signaling pathways that regulate proliferation, contractility, migration, epithelial⁻mesenchymal transition, and remodeling of the extracellular matrix. In this review, we describe the diverse roles of podoplanin in inflammation and cancer, depict the protein ligands of podoplanin identified so far, and discuss the mechanistic basis for the involvement of podoplanin in all these processes.

Functional significance of the platelet immune receptors GPVI and CLEC-2

Although platelets are best known for their role in hemostasis, they are also crucial in development, host defense, inflammation, and tissue repair. Many of these roles are regulated by the immune-like receptors glycoprotein VI (GPVI) and C-type lectin receptor 2 (CLEC-2), which signal through an immunoreceptor tyrosine-based activation motif (ITAM). GPVI is activated by collagen in the subendothelial matrix, by fibrin and fibrinogen in the thrombus, and by a remarkable number of other ligands. CLEC-2 is activated by the transmembrane protein podoplanin, which is found outside of the vasculature and is upregulated in development, inflammation, and cancer, but there is also evidence for additional ligands. In this Review, we discuss the physiological and pathological roles of CLEC-2 and GPVI and their potential as targets in thrombosis and thrombo-inflammatory disorders (i.e., disorders in which inflammation plays a critical role in the ensuing thrombosis) relative to current antiplatelet drugs.

Levels of tight junction protein CLDND1 are regulated by microRNA-124 in the cerebellum of stroke-prone spontaneously hypertensive rats

The claudin family shows organ- and tissue-specific expression of individual members. Deficiency or aberrant expression of distinct claudins has been reported to be associated with severe pathophysiological consequences. Claudin domain-containing 1 (CLDND1), also known as claudin-25, shows homology to this family of proteins. Furthermore, serum CLDND1-derived peptide antibody levels are elevated in patients with cerebral infarction, as compared with healthy controls. We previously reported that, in the adult murine brain, CLDND1 is abundantly expressed in the cerebellum in common sites of intracerebral hemorrhage, and CLDND1 levels are transiently decreased after hemorrhagic insult. However, regulation of CLDND1 expression levels in cerebrovascular disease is poorly studied, and most regulatory microRNAs remain to be defined. We assessed its expression level, according to the presence of early signs of cerebrovascular disease, in the brain of stroke-prone spontaneously hypertensive rats (SHRSPs) and investigated the microRNA regulation of Cldnd1 mRNA. We investigated the post-transcriptional regulation of Cldnd1 by examining the subcellular distribution of its mRNA and evaluating its translational regulation by microRNA in human brain endothelial cells (HBECs) and in the brain of SHRSPs. Using bioinformatics, we identified a conserved microRNA-124 (miR-124)-binding site in the 3'-untranslated region of Cldnd1 and demonstrated that miR-124 regulates the translation of Cldnd1 mRNA reporters in a sequence-specific manner in luciferase assays. HBECs transfected with an miR-124 mimic showed decreased levels of CLDND1 mRNA in reverse transcription quantitative PCR. miR-124 levels were markedly lower in SHRSP than in Wister Kyoto rat brains, whereas Cldnd1 mRNA and protein levels were significantly higher. In SHRSP brains, Cldnd1 mRNA levels increased with a decrease in miR-124. Therefore, by interacting with Cldnd1 mRNA, miR-124 influences CLDNL1 levels in the brain, thus playing a role in the development of cerebrovascular disease in SHRSPs.

Podoplanin emerges as a functionally relevant oral cancer biomarker and therapeutic target

Oral cancer has become one of the most aggressive types of cancer, killing 140,000 people worldwide every year. Current treatments for oral cancer include surgery and radiation therapies. These procedures can be very effective; however, they can also drastically decrease the quality of life for survivors. New chemotherapeutic treatments are needed to more effectively combat oral cancer. The transmembrane receptor podoplanin (PDPN) has emerged as a functionally relevant oral cancer biomarker and chemotherapeutic target. PDPN expression promotes tumor cell migration leading to oral cancer invasion and metastasis. Here, we describe the role of PDPN in oral squamous cell carcinoma progression, and how it may be exploited to prevent and treat oral cancer.

Podoplanin is a negative regulator of Th17 inflammation

Recent data indicate that there are different subpopulations of Th17 cells that can express a regulatory as opposed to an inflammatory gene signature. The transmembrane glycoprotein PDPN is critical in the development of multiple organs including the lymphatic system and has been described on T cells in mouse models of autoimmune Th17 inflammation. Here, we demonstrate that unlike in mice, PDPN+ T cells induced under classic Th17-polarizing conditions express transcription factors associated with Th17 cells but do not produce IL-17. Moreover, these cells express a transcriptional profile enriched for immunosuppressive and regulatory pathways and express a distinct cytokine profile compared with potentially pathogenic PDPN- Th17 cells. Ligation of PDPN by its ligand CLEC-2 ameliorates the Th17 inflammatory response. IL-17 secretion is restored with shRNA gene silencing of PDPN. Furthermore, PDPN expression is reduced via an Sgk1-mediated pathway under proinflammatory, high sodium chloride conditions. Finally, CD3+PDPN+ T cells are devoid of IL-17 in skin biopsies from patients with candidiasis, a prototypical Th17-driven skin disease. Thus, our data support the hypothesis that PDPN may serve as a marker of a nonpathogenic Th17 cell subset and may also functionally regulate pathogenic Th17 inflammation.

Rheumatoid arthritis onset in postmenopausal women: Does the ACPA seropositive subset result from genetic effects, estrogen deficiency, skewed profile of CD4(+) T-cells, and their interactions?

Rheumatoid arthritis (RA) incidence displays a differentiated age-dependent female-to-male ratio in which women outnumber men. Evidence that the peak incidence of RA in women coincides with menopause age, suggests a potential estrogenic role to disease etiology. Estrogens exert physiologically both stimulatory and inhibitory effects on the immune system. Epidemiologic and animal model studies with estrogen deprivation or supplementation suggested estrogens as to play, mainly, a protective role in RA immunopathology. In this review, we propose that some yet unidentified disturbances associated with estrogen circulating levels, differentiated by the menopausal status, play a major role in women's RA susceptibility. We focus on the interaction between estrogen deprivation and genetic risk alleles for anti-citrullinated protein antibodies (ACPA) seropositive RA, as a major driving force for increased immune reactivity and RA susceptibility, in postmenopausal women. This opens up new fields for research concerning the association among different irregular estrogenic conditions, the cytokine milieu, and age/menopausal status bias in RA.

Role of podoplanin in the high interleukin-17A secretion resulting from interactions between activated lymphocytes and psoriatic skin-derived mesenchymal cells

In the context of psoriasis, T helper type 17 (Th17) cells infiltrate the inflammatory site and interact with local mesenchymal cells, including skin fibroblasts. The aim of this work was to study the interactions of skin-derived fibroblasts with peripheral blood mononuclear cells (PBMC) with a focus on the Th17 pathway and to identify a mechanism which leads to a high interleukin (IL)-17 secretion. A co-culture system between PBMC and skin fibroblasts was developed. Healthy and patient PBMC were added to non-lesional or lesional skin fibroblasts at a 5:1 ratio for 48 h in the presence or not of activation with phytohaemagglutinin (PHA). Monocytes were removed or not by adherence before the co-culture. An anti-podoplanin antibody was also used during the co-culture. Cytokine production (IL-8, IL-6, IL-1β and IL-17) was measured by enzyme-linked immunosorbent assay (ELISA) and cell staining (CD3, CD4, IL-17 and podoplanin) by flow cytometry. Without T cell receptor (TCR) activation, IL-8, IL-6 and IL-1β production increased in PBMC-fibroblast co-culture compared to PBMC alone. No additional effect was observed with TCR activation, with no difference in the Th17 cell percentage in activated-PBMC alone or co-cultured. Conversely, IL-17 production was increased highly only in co-cultures between control and patient activated-PBMC and skin fibroblasts. Removal of monocytes decreased cytokine production, notably that of IL-17. Addition of an anti-podoplanin antibody decreased IL-17 secretion by 60%. Interactions between resting PBMC and fibroblasts induce the IL-8, IL-6 and IL-1β production. PBMC activation and cell interactions are critical for a high IL-17 secretion. Podoplanin contributes largely to this massive IL-17 secretion.

PDGF upregulates CLEC-2 to induce T regulatory cells

The effect of platelet derived growth factor (PDGF) on immune cells is not elucidated. Here, we demonstrate PDGF inhibited the maturation of human DCs and induced IL-10 secretion. Culture of PDGF-DCs with T cells induced the polarization of T cells towards FoxP3 expressing T regulatory cells that secreted IL-10. Gene expression studies revealed that PDGF induced the expression of C-type lectin like receptor member 2, (CLEC-2) receptor on DCs. Furthermore, DCs transfected with CLEC-2 induced T regulatory cells in DC-T cell co-culture. CLEC-2 is naturally expressed on platelets. Therefore, to confirm whether CLEC-2 is responsible for inducing the T regulatory cells, T cells were cultured with either CLEC-2 expressing platelets or soluble CLEC-2. Both conditions resulted in the induction of regulatory T cells. The generation of T regulatory cells was probably due to the binding of CLEC-2 with its ligand podoplanin on T cells, since crosslinking of podoplanin on the T cells also resulted in the induction of T regulatory cells. These data demonstrate that PDGF upregulates the expression of CLEC-2 on cells to induce T regulatory cells.

Interaction among activated lymphocytes and mesenchymal cells through podoplanin is critical for a high IL-17 secretion

Background

During chronic inflammation, immune cells, notably Th17 cells, infiltrate the inflammatory site and interact with local mesenchymal cells. Applied to rheumatoid arthritis (RA), the aim is to study the interactions between synoviocytes and peripheral blood mononuclear cells (PBMC) with a focus on the Th17 pathway and to identify a mechanism which leads to high IL-17 secretion with an interest on podoplanin.

Methods

PBMC from healthy donors and RA patients were co-cultured with RA synoviocytes during 48 h, in the presence or not of phytohemagglutinin. An antibody against podoplanin was used in co-culture. Cytokine production (IL-6, IL-1β and IL-17) was measured by ELISA and cell staining (CD3, CD4, IL-17 and podoplanin) by flow cytometry.

Results

In control conditions, IL-6 and IL-1β production was increased in PBMC-synoviocyte co-culture compared to PBMC alone (p = 0.02). No additional effect was observed with PBMC activation. Flow cytometry analysis showed no difference in the percentage of Th17 cells in activated PBMC alone or with synoviocytes (p = 0.4), indicating that Th17 differentiation requires only T cell activation. Conversely, IL-17 production was highly increased in co-cultures with activated PBMC vs. activated PBMC alone (p = 0.002). Transwell experiments confirm that cell-cell contact was critical for IL-17 secretion. The incubation of either PBMC or synoviocytes with an anti-podoplanin antibody decreased IL-17 secretion by 60 % (p = 0.008).

Conclusions

Interactions between resting PBMC and synoviocytes are sufficient to induce IL-6 and IL-1β production. Both PBMC activation and cell interactions are needed to induce a high IL-17 secretion. Podoplanin contributes at the level of both lymphocytes and synoviocytes.

Transcriptome signature for dampened Th2 dominance in acellular pertussis vaccine-induced CD4(+) T cell responses through TLR4 ligation

Current acellular pertussis (aP) vaccines promote a T helper 2 (Th2)-dominated response, while Th1/Th17 cells are protective. As our previous study showed, after adding a non-toxic TLR4 ligand, LpxL1, to the aP vaccine in mice, the Bordetella pertussis-specific Th2 response is decreased and Th1/Th17 responses are increased as measured at the cytokine protein level. However, how this shift in Th response by LpxL1 addition is regulated at the gene expression level remains unclear. Transcriptomics analysis was performed on purified CD4(+) T cells of control and vaccinated mice after in vitro restimulation with aP vaccine antigens. Multiple key factors in Th differentiation, including transcription factors, cytokines, and receptors, were identified within the differentially expressed genes. Upregulation of Th2- and downregulation of follicular helper T cell-associated genes were found in the CD4(+) T cells of both aP- and aP+LpxL1-vaccinated mice. Genes exclusively upregulated in CD4(+) T cells of aP+LpxL1-vaccinated mice included Th1 and Th17 signature cytokine genes Ifng and Il17a respectively. Overall, our study indicates that after addition of LpxL1 to the aP vaccine the Th2 component is not downregulated at the gene expression level. Rather an increase in expression of Th1- and Th17-associated genes caused the shift in Th subset outcome.

Platelets and their role in cancer evolution and immune system

Platelets are anucleate fragments formed from the cytoplasm of megakaryocytes and represent the smallest circulating hematopoietic cells. Thought for almost a century to possess solely hemostatic potentials, platelets actually play a much wider role in tissue regeneration and repair and interact intimately with tumor cells. On the one hand, tumor cells induce platelet aggregation, known to act as the trigger of cancer-associated thrombosis and on the other hand, platelets recruited to the tumor microenvironment interact directly with tumor cells favoring proliferation, and indirectly through the release of angiogenic and mitogenic proteins. Furthermore, platelets are immunosuppressive cells that protect metastatic cancer cells from surveillance by killer cells, nullifying the effects of immunotherapy.

Interleukin-27 inhibits ectopic lymphoid-like structure development in early inflammatory arthritis

Decreased interleukin-27 signaling in humans and mice induces the formation of ectopic lymphoid-like structures (ELSs), which are associated with severe disease pathology and resistance to biological therapy in rheumatoid arthritis patients. Increased numbers of podoplanin-expressing Th17 cells in the absence of IL-27R signaling may be involved in driving ELS formation.

Ectopic lymphoid-like structures (ELSs) reminiscent of secondary lymphoid organs often develop at sites of chronic inflammation where they contribute to immune-mediated pathology. Through evaluation of synovial tissues from rheumatoid arthritis (RA) patients, we now show that low interleukin-27 (IL-27) expression corresponds with an increased incidence of ELS and gene signatures associated with their development and activity. The presence of synovial ELS was also noted in mice deficient in the IL-27 receptor (IL-27R) after the onset of inflammatory arthritis. Here, pathology was associated with increased synovial expression of pro-inflammatory cytokines, homeostatic chemokines, and transcriptional regulators linked with lymphoid neogenesis. In both clinical and experimental RA, synovial ELS coincided with the heightened local expression of cytokines and transcription factors of the Th17 and T follicular helper (Tfh) cell lineages, and included podoplanin-expressing T cells within lymphoid aggregates. IL-27 inhibited the differentiation of podoplanin-expressing Th17 cells, and an increased number of these cells were observed in IL-27R–deficient mice with inflammatory arthritis. Thus, IL-27 appears to negatively regulate ELS development in RA through control of effector T cells. These studies open new opportunities for patient stratification and treatment.

Methylglyoxal Induced Basophilic Spindle Cells with Podoplanin at the Surface of Peritoneum in Rat Peritoneal Dialysis Model

Peritoneal dialysis (PD) is a common treatment for patients with reduced or absent renal function. Long-term PD leads to peritoneal injury with structural changes and functional decline. At worst, peritoneal injury leads to encapsulating peritoneal sclerosis (EPS), which is a serious complication of PD. In order to carry out PD safely, it is important to define the mechanism of progression of peritoneal injury and EPS. We prepared rat models of peritoneal injury by intraperitoneal administration of glucose degradation products, such as methylglyoxal (MGO) or formaldehyde (FA), chlorhexidine gluconate (CG), and talc. In rats treated with MGO, peritoneal fibrous thickening with the appearance of basophilic spindle cells with podoplanin, cytokeratin, and α-smooth muscle actin at the surface of the peritoneum was observed. These cells may have been derived from mesothelial cells by epithelial-to-mesenchymal transition. In FA- or CG-treated rats, the peritoneum was thickened, and mesothelial cells were absent at the surface of the peritoneum. The CG- or MGO-treated rats presented with a so-called abdominal cocoon. In the talc-treated rats, extensive peritoneal adhesion and peritoneal thickening were observed. MGO-induced peritoneal injury model may reflect human histopathology and be suitable to analyze the mechanism of progression of peritoneal injury and EPS.

CLEC-2 expression is maintained on activated platelets and on platelet microparticles

The C-type lectin-like receptor CLEC-2 mediates platelet activation through a hem-immunoreceptor tyrosine-based activation motif (hemITAM). CLEC-2 initiates a Src- and Syk-dependent signaling cascade that is closely related to that of the 2 platelet ITAM receptors: glycoprotein (GP)VI and FcγRIIa. Activation of either of the ITAM receptors induces shedding of GPVI and proteolysis of the ITAM domain in FcγRIIa. In the present study, we generated monoclonal antibodies against human CLEC-2 and used these to measure CLEC-2 expression on resting and stimulated platelets and on other hematopoietic cells. We show that CLEC-2 is restricted to platelets with an average copy number of ∼2000 per cell and that activation of CLEC-2 induces proteolytic cleavage of GPVI and FcγRIIa but not of itself. We further show that CLEC-2 and GPVI are expressed on CD41+ microparticles in megakaryocyte cultures and in platelet-rich plasma, which are predominantly derived from megakaryocytes in healthy donors, whereas microparticles derived from activated platelets only express CLEC-2. Patients with rheumatoid arthritis, an inflammatory disease associated with increased microparticle production, had raised plasma levels of microparticles that expressed CLEC-2 but not GPVI. Thus, CLEC-2, unlike platelet ITAM receptors, is not regulated by proteolysis and can be used to monitor platelet-derived microparticles.

Fungal β-glucan, a Dectin-1 ligand, promotes protection from type 1 diabetes by inducing regulatory innate immune response

β-Glucans are naturally occurring polysaccharides in cereal grains, mushrooms, algae, or microbes, including bacteria, fungi, and yeast. Immune cells recognize these β-glucans through a cell surface pathogen recognition receptor called Dectin-1. Studies using β-glucans and other Dectin-1 binding components have demonstrated the potential of these agents in activating the immune cells for cancer treatment and controlling infections. In this study, we show that the β-glucan from Saccharomyces cerevisiae induces the expression of immune regulatory cytokines (IL-10, TGF-β1, and IL-2) and a tolerogenic enzyme (IDO) in bone marrow-derived dendritic cells as well as spleen cells. These properties can be exploited to modulate autoimmunity in the NOD mouse model of type 1 diabetes (T1D). Treatment of prediabetic NOD mice with low-dose β-glucan resulted in a profound delay in hyperglycemia, and this protection was associated with increase in the frequencies of Foxp3(+), LAP(+), and GARP(+) T cells. Upon Ag presentation, β-glucan-exposed dendritic cells induced a significant increase in Foxp3(+) and LAP(+) T cells in in vitro cultures. Furthermore, systemic coadministration of β-glucan plus pancreatic β cell Ag resulted in an enhanced protection of NOD mice from T1D as compared with treatment with β-glucan alone. These observations demonstrate that the innate immune response induced by low-dose β-glucan is regulatory in nature and can be exploited to modulate T cell response to β cell Ag for inducing an effective protection from T1D.

The physiological and pathophysiological roles of platelet CLEC-2

CLEC-2 is a C-type lectin receptor which is highly expressed on platelets but also found at low levels on different immune cells. CLEC-2 elicits powerful platelet activation upon engagement by its endogenous ligand, the mucin-type glycoprotein podoplanin. Podoplanin is expressed in a variety of tissues, including lymphatic endothelial cells, kidney podocytes, type I lung epithelial cells, lymph node stromal cells and the choroid plexus epithelium. Animal models have shown that the correct separation of the lymphatic and blood vasculatures during embryonic development is dependent on CLEC-2-mediated platelet activation. Additionally, podoplanin-deficient mice show abnormalities in heart, lungs, and lymphoid tissues, whereas absence of CLEC-2 affects brain development. This review summarises the current understanding of the molecular pathways regulating CLEC-2 and podoplanin function and suggests other physiological and pathological processes where this molecular interaction might exert crucial roles.