Alterations in the thymocyte phenotype of EphB-deficient mice largely affect the double negative cell compartment

EPHB2 Knockdown Mitigated Myocardial Infarction by Inhibiting MAPK Signaling

Myocardial infarction (MI) is a common type of cardiovascular disease. The incidence of ventricular remodeling dysplasia and heart failure increases significantly after MI. The objective of this study is to investigate whether erythropoietin hepatocellular receptor B2 (EPHB2) can regulate myocardial injury after MI and explore its regulatory pathways. EPHB2 is significantly overexpressed in the heart tissues of MI mice. The downregulation of EPHB2 alleviates the cardiac function damage after MI. Knockdown EPHB2 alleviates MI-induced myocardial tissue inflammation and apoptosis, and myocardial fibrosis in mice. EPHB2 knockdown significantly inhibits the activation of mitogen activated kinase-like protein (MAPK) pathway in MI mice. Moreover, EPHB2 overexpression significantly promotes the phosphorylation of MAPK pathway-related protein, which can be reversed by MAPK-IN-1 (an MAPK inhibitor) treatment. In conclusion, silencing EPHB2 can mitigate MI-induced myocardial injury by inhibiting MAPK signaling in mice, suggesting that targeting EPHB2 can be a promising therapeutic target for MI-induced myocardial injury.

Peripheral T-cell responses of EphB2- and EphB3-deficient mice in a model of collagen-induced arthritis

Both EphB2- and EphB3-deficient mice exhibit profound histological alterations in the thymic epithelial network but few changes in T-cell differentiation, suggesting that this organization would be sufficient to produce functional T lymphocytes. Also, other antigen-presenting cells involved in immunological education could substitute the thymic epithelium. Accordingly, we found an increased frequency of plasmacytoid dendritic cells but not of conventional dendritic cells, medullary fibroblasts or intrathymic B lymphocytes. In addition, there are no lymphoid infiltrates in the organs of mutant mice nor do they contain circulating autoantibodies. Furthermore, attempts to induce arthritic lesions after chicken type II collagen administration fail totally in EphB2-deficient mice whereas all WT and half of the immunized EphB3-/- mice develop a typical collagen-induced arthritis. Our results point out that Th17 cells, IL4-producing Th2 cells and regulatory T cells are key for the induction of disease, but mutant mice appear to have deficits in T cell activation or cell migration properties. EphB2-/- T cells show reduced in vitro proliferative responses to anti-CD3/anti-CD28 antibodies, produce low levels of anti-type II collagen antibodies, and exhibit low proportions of T follicular helper cells. On the contrary, EphB3-/- lymph node cells respond accurately to the different immune stimuli although in lower levels than WT cells but show a significantly reduced migration in in vitro transwell assays, suggesting that no sufficient type II collagen-dependent activated lymphoid cells reached the joints, resulting in reduced arthritic lesions.

Altered thymocyte development observed in EphA4-deficient mice courses with changes in both thymic epithelial and extracellular matrix organization

Eph receptors and their ligands, Ephrins, are involved in the thymocyte-thymic epithelial cell (TEC) interactions, key for the functional maturation of both thymocytes and thymic epithelium. Several years ago, we reported that the lack of EphA4, a Eph of the subfamily A, coursed with reduced proportions of double positive (DP) thymocytes apparently due to an altered thymic epithelial stroma [Munoz et al. in J Immunol 177:804–813, 2006]. In the present study, we reevaluate the lymphoid, epithelial, and extracellular matrix (ECM) phenotype of EphA4^−/− mice grouped into three categories with respect to their proportions of DP thymocytes. Our results demonstrate a profound hypocellularity, specific alterations of T cell differentiation that affected not only DP thymocytes, but also double negative and single positive T cell subsets, as well as the proportions of positively and negatively selected thymocytes. In correlation, thymic histological organization changed markedly, especially in the cortex, as well as the proportions of both Ly51⁺UEA-1⁻ cortical TECs and Ly51⁻UEA-1⁺ medullary TECs. The alterations observed in the expression of ECM components (Fibronectin, Laminin, Collagen IV), integrin receptors (VLA-4, VLA-6), chemokines (CXCL12, CCL25, CCL21) and their receptors (CXCR4, CCR7, CCR9) and in vitro transwell assays on the capacity of migration of WT and mutant thymocytes suggest that the lack of EphA4 alters T-cell differentiation by presumably affecting cell adhesion between TECs and T-TEC interactions rather than by thymocyte migration.

Prediction of prognosis, immunogenicity and efficacy of immunotherapy based on glutamine metabolism in lung adenocarcinoma

BACKGROUND

Glutamine (Gln) metabolism has been reported to play an essential role in cancer. However, a comprehensive analysis of its role in lung adenocarcinoma is still unavailable. This study established a novel system of quantification of Gln metabolism to predict the prognosis and immunotherapy efficacy in lung cancer. Further, the Gln metabolism in tumor microenvironment (TME) was characterized and the Gln metabolism-related genes were identified for targeted therapy.

METHODS

We comprehensively evaluated the patterns of Gln metabolism in 513 patients diagnosed with lung adenocarcinoma (LUAD) based on 73 Gln metabolism-related genes. Based on differentially expressed genes (DEGs), a risk model was constructed using Cox regression and Lasso regression analysis. The prognostic efficacy of the model was validated using an individual LUAD cohort form Shandong Provincial Hospital, an integrated LUAD cohort from GEO and pan-cancer cohorts from TCGA databases. Five independent immunotherapy cohorts were used to validate the model performance in predicting immunotherapy efficacy. Next, a series of single-cell sequencing analyses were used to characterize Gln metabolism in TME. Finally, single-cell sequencing analysis, transcriptome sequencing, and a series of in vitro experiments were used to explore the role of EPHB2 in LUAD.

RESULTS

Patients with LUAD were eventually divided into low- and high-risk groups. Patients in low-risk group were characterized by low levels of Gln metabolism, survival advantage, "hot" immune phenotype and benefit from immunotherapy. Compared with other cells, tumor cells in TME exhibited the most active Gln metabolism. Among immune cells, tumor-infiltrating T cells exhibited the most active levels of Gln metabolism, especially CD8 T cell exhaustion and Treg suppression. EPHB2, a key gene in the model, was shown to promote LUAD cell proliferation, invasion and migration, and regulated the Gln metabolic pathway. Finally, we found that EPHB2 was highly expressed in macrophages, especially M2 macrophages. It may be involved in the M2 polarization of macrophages and mediate the negative regulation of M2 macrophages in NK cells.

CONCLUSION

This study revealed that the Gln metabolism-based model played a significant role in predicting prognosis and immunotherapy efficacy in lung cancer. We further characterized the Gln metabolism of TME and investigated the Gln metabolism-related gene EPHB2 to provide a theoretical framework for anti-tumor strategy targeting Gln metabolism.

The Roles of EphB2 in Cancer

The erythropoietin-producing hepatocellular carcinoma (Eph) receptors and their Eph receptor-interacting (ephrin) ligands together constitute a vital cell communication system with diverse roles. Experimental evidence revealed Eph receptor bidirectional signaling with both tumor-promoting and tumor-suppressing activities in different cancer types and surrounding environment. Eph receptor B2 (EphB2), an important member of the Eph receptor family, has been proved to be aberrantly expressed in many cancer types, such as colorectal cancer, gastric cancer and hepatocellular carcinoma, resulting in tumor occurrence and progression. However, there are no reviews focusing on the dual roles of EphB2 in cancer. Thus, in this paper we systematically summarize and discuss the roles of EphB2 in cancer. Firstly, we review the main biological features and the related signaling regulatory mechanisms of EphB2, and then we summarize the roles of EphB2 in cancer through current studies. Finally, we put forward our viewpoint on the future prospects of cancer research focusing on EphB2, especially with regard to the effects of EphB2 on tumor immunity.

Ephrin Receptors (Ephs) Expression in Thymic Epithelial Tumors: Prognostic Implications and Future Therapeutic Approaches

Ephrin receptors (Ephs) are receptor tyrosine kinases (RTKs) implicated in tissue development and homeostasis, and they are aberrantly expressed in tumors. Here, immunohistochemical Eph type-A and -B expression in thymic epithelial tumors (TETs) was assessed and correlated with clinicopathological parameters. Tissue microarrays from 98 TETs were stained for EphA1, -A2, -A4 -A6, -B1, -B2, -B4 and -B6. The relationship between neoplastic and lymphoid cell immunoreactivity score (H-score), histopathological parameters (Pearson’s test) and survival of 35 patients (Mantel-Cox model) was explored. Epithelial-rich subtypes showed higher EphA6 cytoplasmic H-score (B2/B3, carcinoma) (p < 0.001) and stronger EphA4 H-score (B3, carcinoma) (p = 0.011). The immature T-cells, especially in subtypes AB/B1, had higher EphB6 H-score than carcinoma-associated mature lymphocytes (p < 0.001); carcinomas had higher lymphocytic EphB1 H-score (p = 0.026). Higher lymphocytic and lower epithelial EphB6 H-score correlated with Masaoka stage ≤II (p = 0.043, p = 0.010, respectively). All cases showed variable epithelial and lymphocytic EphA2 expression, but clinicopathological associations were not reached. Our study confirmed that Eph type-A and -B expression in TETs is associated with established prognostic parameters, i.e., tumor subtype and Masaoka stage, although correlation with patient survival was not reached. Such findings suggest involvement of these RTKs in thymic neoplasia, as well as their potential utility as treatment targets.

Intrathymic Selection and Defects in the Thymic Epithelial Cell Development

Intimate interactions between thymic epithelial cells (TECs) and thymocytes (T) have been repeatedly reported as essential for performing intrathymic T-cell education. Nevertheless, it has been described that animals exhibiting defects in these interactions were capable of a proper positive and negative T-cell selection. In the current review, we first examined distinct types of TECs and their possible role in the immune surveillance. However, EphB-deficient thymi that exhibit profound thymic epithelial (TE) alterations do not exhibit important immunological defects. Eph and their ligands, the ephrins, are implicated in cell attachment/detachment and govern, therefore, TEC–T interactions. On this basis, we hypothesized that a few normal TE areas could be enough for a proper phenotypical and functional maturation of T lymphocytes. Then, we evaluated in vivo how many TECs would be necessary for supporting a normal T-cell differentiation, concluding that a significantly low number of TEC are still capable of supporting normal T lymphocyte maturation, whereas with fewer numbers, T-cell maturation is not possible.

Thymus aging in mice deficient in either EphB2 or EphB3, two master regulators of thymic epithelium development

BACKGROUND

The epithelial microenvironment is involved in thymus aging, but the possible role of EphB receptors that govern the thymic epithelium development has not been investigated. Herein, we study the changes undergone by the thymus of EphB-deficient mice throughout their life.

RESULTS

Immune alterations occurring throughout life were more severe in mutant than in wild-type (WT) mice. Mutant thymuses exhibit lower cellularity than WT ones, as well as lower proportions of early thymic progenitors cells and double-positive (CD4⁺ CD8⁺ ) thymocytes, but higher of double-negative (CD4^- CD8^- ) and single-positive (CD4⁺ CD8^- , CD4^- CD8⁺ ) cells. Throughout life, CD4⁺ naïve cells decreased particularly in mutant mice. In correlation, memory T cells, largely CD8⁺ cells, increased. Aged thymic epithelium undergoes changes including appearance of big epithelial free areas, decrease of K8⁺ K5^- areas, which, however, contain higher proportions of Ly51⁺ UEA1^- cortical epithelial cells, in correlation with reduced Aire⁺ medullary epithelial cells. Also, aged thymuses particularly those derived from mutant mice exhibited increased collagen IV, fat-storing cells, and connective cells.

CONCLUSIONS

The absence of EphB accelerates the alterations undergone throughout life by both thymic epithelium and thymocytes, and the proportions of peripheral naïve and memory T cells, all of which are hallmarks of immune aging.

Semaphorin-3A-Related Reduction of Thymocyte Migration in Chemically Induced Diabetic Mice

BACKGROUND

Previous work revealed the existence of a severe thymic atrophy with massive loss of immature CD4+CD8+ thymocytes in animals developing insulin-dependent diabetes, chemically induced by alloxan. Furthermore, the intrathymic expression of chemokines, such as CXCL12, is changed in these animals, suggesting that cell migration-related patterns may be altered. One molecular interaction involved in normal thymocyte migration is that mediated by soluble semaphorin-3A and its cognate receptor neuropilin-1.

OBJECTIVES

We investigated herein the expression and role of semaphorin-3A in the migratory responses of thymocytes from alloxan-induced diabetic mice. We characterized semaphorin-3A and its receptor, neuropilin-1, in thymuses from control and diabetic mice as well as semaphorin-3A-dependent migration of developing thymocytes in both control and diabetic animals.

METHODS

Diabetes was chemically induced after a single injection of alloxan in young adult BALB/c mice. Thymocytes were excised from control and diabetic individuals and subjected to cytofluorometry for simultaneous detection of semaphorin-3A or neuropilin-1 in CD4/CD8-defined subsets. Cell migration in response to semaphorin-3A was performed using cell migration transwell chambers.

RESULTS

Confirming previous data, we observed a severe decrease in the total numbers of thymocytes in diabetic mice, which comprised alterations in both immature (double-negative subpopulations) and mature CD4/CD8-defined thymocyte subsets. These were accompanied by a decrease in the absolute numbers of semaphorin-3A-bearing thymocytes, comprising CD4-CD8-, CD4+CD8+, and CD4-CD8+ cells. Additionally, immature CD4-CD8- and CD4+CD8+ developing T cells exhibited a decrease in the membrane density of semaphorin-3A. The relative and absolute numbers of neuropilin-1-positive thymocytes were also decreased in diabetic mouse thymocytes compared to controls, as seen in CD4-CD8-, CD4+CD8+, and CD4-CD8+ cell subpopulations. Functionally, we observed a decrease in the chemorepulsive role of semaphorin-3A, as revealed by transwell migration chambers. Such an effect was seen in all immature and mature thymocyte subsets.

CONCLUSIONS

Taken together, our data clearly unravel a disruption in the normal cell migration pattern of developing thymocytes following chemically induced insulin-dependent diabetes, as ascertained by the altered migratory response to sempahorin-3A. In conceptual terms, it is plausible to think that such disturbances in the migration pattern of thymocytes from these diabetic animals may exert an impact in the cell-mediated immune response of these mice.

Emerging Roles for Eph Receptors and Ephrin Ligands in Immunity

Eph receptors are the largest family of receptor tyrosine kinases and mediate a myriad of essential processes in humans from embryonic development to adult tissue homeostasis through interactions with membrane-bound ephrin ligands. The ubiquitous expression of Eph receptors and ephrin ligands among the cellular players of the immune system underscores the importance of these molecules in orchestrating an optimal immune response. This review provides an overview of the various roles of Eph receptors and ephrin ligands in immune cell development, activation, and migration. We also discuss the role of Eph receptors in disease pathogenesis as well as the implications of Eph receptors as future immunotherapy targets. Given the diverse and critical roles of Eph receptors and ephrin ligands throughout the immune system during both resting and activated states, this review aims to highlight the critical yet underappreciated roles of this family of signaling molecules in the immune system.

EphB receptors, mainly EphB3, contribute to the proper development of cortical thymic epithelial cells

EphB and their ligands ephrin-B are an important family of protein tyrosine kinase receptors involved in thymocyte-thymic epithelial cell interactions known to be key for the maturation of both thymic cell components. In the present study, we have analyzed the maturation of cortical thymic epithelium in EphB-deficient thymuses evaluating the relative relevance of EphB2 and EphB3 in the process. Results support a relationship between the epithelial hypocellularity of mutant thymuses and altered development of thymocytes, lower proportions of cycling thymic epithelial cells and increased epithelial cell apoptosis. Together, these factors induce delayed development of mutant cortical TECs, defined by the expression of different cell markers, i.e. Ly51, CD205, MHCII, CD40 and β5t. Furthermore, although both EphB2 and EphB3 are necessary for cortical thymic epithelial maturation, the relevance of EphB3 is greater since EphB3-/- thymic cortex exhibits a more severe phenotype than that of EphB2-deficient thymuses.

Altered Maturation of Medullary TEC in EphB-Deficient Thymi Is Recovered by RANK Signaling Stimulation

In the present study, the relevance of EphB2 and EphB3 tyrosine kinase receptors for the maturation of medullary thymic epithelial cells (TECs) is analyzed. The absence of both molecules, but particularly that of EphB2, courses with altered maturation of medullary Cld3,4^hiSSEA1⁺ epithelial progenitor cells, mature medulla epithelial cells, defined by the expression of specific cell markers, including UEA1, MHCII, CD40, CD80, and AIRE, and reduced expansion of medullary islets. In vivo assays demonstrate that these changes are a consequence of the absence of EphBs in both TECs and thymocytes. On the other hand, the changes, that remains in the adult thymus, correlated well with reduced proportions of E15.5 Vγ5⁺RANKL⁺ cells in EphB-deficient thymi that could result in decreased stimulation of RANK⁺ medullary TECs to mature, a fact that was confirmed by recovering of proportions of both CD40^hiCD80⁺ and MHCII^hiUEA1⁺ mature medullary TECs of mutant E14.5 alymphoid thymic lobes by agonist anti-RANK antibody treatment. Accordingly, the effects of EphB deficiency on medullary TECs maturation are recovered by RANK stimulation.

Can a Proper T-Cell Development Occur in an Altered Thymic Epithelium? Lessons From EphB-Deficient Thymi

For a long time, the effects of distinct Eph tyrosine kinase receptors and their ligands, ephrins on the structure, immunophenotype, and development of thymus and their main cell components, thymocytes (T) and thymic epithelial cells (TECs), have been studied. In recent years, the thymic phenotype of mutant mice deficient in several Ephs and ephrins B has been determined. Remarkably, thymic stroma in these animals exhibits important defects that appear early in ontogeny but little alterations in the proportions of distinct lymphoid cell populations. In the present manuscript, we summarize and extend these results discussing possible mechanisms governing phenotypical and functional thymocyte maturation in an absence of the critical T-TEC interactions, concluding that some signaling mediated by key molecules, such as MHCII, CD80, β5t, Aire, etc. could be sufficient to enable a proper maturation of thymocytes, independently of morphological alterations affecting thymic epithelium.

Ephrin B1-mediated repulsion and signaling control germinal center T cell territoriality and function

Follicular T helper (T_FH) cells orchestrate the germinal center (GC) reaction locally. Local mechanisms regulating their dynamics and helper functions are not well defined. Here we found that GC-expressed ephrin B1 (EFNB1) repulsively inhibited T cell to B cell adhesion and GC T_FH retention by signaling through T_FH-expressed EPHB6 receptor. At the same time, EFNB1 promoted interleukin-21 production from GC T_FH cells by signaling predominantly through EPHB4. Consequently, EFNB1-null GCs were associated with defective production of plasma cells despite harboring excessive T_FH cells. In a competitive GC reaction, EFNB1-deficient B cells more efficiently interacted with T_FH cells and produced more bone-marrow plasma cells, likely as a result of gaining more contact-dependent help. Our results reveal a contact-dependent repulsive guidance system that controls GC T_FH dynamics and effector functions locally.

Eph/ephrin-B-mediated cell-to-cell interactions govern MTS20(+) thymic epithelial cell development

Thymus development is a complex process in which cell-to-cell interactions between thymocytes and thymic epithelial cells (TECs) are essential to allow a proper maturation of both thymic cell components. Although signals that control thymocyte development are well known, mechanisms governing TEC maturation are poorly understood, especially those that regulate the maturation of immature TEC populations during early fetal thymus development. In this study, we show that EphB2-deficient, EphB2LacZ and EphB3-deficient fetal thymuses present a lower number of cells and delayed maturation of DN cell subsets compared to WT values. Moreover, deficits in the production of chemokines, known to be involved in the lymphoid seeding into the thymus, contribute in decreased proportions of intrathymic T cell progenitors (PIRA/B(+)) in the mutant thymuses from early stages of development. These features correlate with increased proportions of MTS20(+) cells but fewer MTS20(-) cells from E13.5 onward in the deficient thymuses, suggesting a delayed development of the first epithelial cells. In addition, in vitro the lack of thymocytes or the blockade of Eph/ephrin-B-mediated cell-to-cell interactions between either thymocytes-TECs or TECs-TECs in E13.5 fetal thymic lobes coursed with increased proportions of MTS20(+) TECs. This confirms, for the first time, that the presence of CD45(+) cells, corresponding at these stages to DN1 and DN2 cells, and Eph/ephrin-B-mediated heterotypic or homotypic cell interactions between thymocytes and TECs, or between TECs and themselves, contribute to the early maturation of MTS20(+) TECs.

Regulation of cell differentiation by Eph receptor and ephrin signaling

There is increasing evidence that in addition to having major roles in morphogenesis, in some tissues Eph receptor and ephrin signaling regulates the differentiation of cells. In one mode of deployment, cell contact dependent Eph-ephrin activation induces a distinct fate of cells at the interface of their expression domains, for example in early ascidian embryos and in the vertebrate hindbrain. In another mode, overlapping Eph receptor and ephrin expression underlies activation within a cell population, which promotes or inhibits cell differentiation in bone remodelling, neural progenitors and keratinocytes. Eph-ephrin activation also contributes to formation of the appropriate number of progenitor cells by increasing or decreasing cell proliferation. These multiple roles of Eph receptor and ephrin signaling may enable a coupling between morphogenesis and the differentiation and proliferation of cells.

Eph/Ephrins-Mediated Thymocyte-Thymic Epithelial Cell Interactions Control Numerous Processes of Thymus Biology

Numerous studies emphasize the relevance of thymocyte-thymic epithelial cell (TECs) interactions for the functional maturation of intrathymic T lymphocytes. The tyrosine kinase receptors, Ephs (erythropoietin-producing hepatocyte kinases) and their ligands, ephrins (Eph receptor interaction proteins), are molecules known to be involved in the regulation of numerous biological systems in which cell-to-cell interactions are particularly relevant. In the last years, we and other authors have demonstrated the importance of these molecules in the thymic functions and the T-cell development. In the present report, we review data on the effects of Ephs and ephrins in the functional maturation of both thymic epithelial microenvironment and thymocyte maturation as well as on their role in the lymphoid progenitor recruitment into the thymus.

Developing stratified epithelia: lessons from the epidermis and thymus

Stratified squamous epithelial cells are found in a number of organs, including the skin epidermis and the thymus. The progenitor cells of the developing epidermis form a multi-layered epithelium and appendages, like the hair follicle, to generate an essential barrier to protect against water loss and invasion of foreign pathogens. In contrast, the thymic epithelium forms a three-dimensional mesh of keratinocytes that are essential for positive and negative selection of self-restricted T cells. While these distinct stratified epithelial tissues derive from distinct embryonic germ layers, both tissues instruct immunity, and the epithelial differentiation programs and molecular mechanisms that control their development are remarkably similar. In this review, we aim to highlight some of the similarities between the thymus and the skin epidermis and its appendages during developmental specification.

EphB2 contributes to human naive B-cell activation and is regulated by miR-185

EphB2 is an important member of the receptor tyrosine kinases. Recently, EphB2 was shown to facilitate T-cell migration and monocyte activation. However, the effects of EphB2 on B cells remain unknown. In this study, the expression of EphB2 on B cells was tested by Western blot, and the roles of EphB2 in B-cell proliferation, cytokine secretion, and immunoglobulin (Ig) production were evaluated using EphB2 siRNA interference in human B cells from healthy volunteers. Our study revealed that EphB2 was distributed on naive B cells and was up-regulated on activated B cells. Moreover, B-cell proliferation (decreased by 22%, P<0.05), TNF-α secretion (decreased by 40%, P<0.01) and IgG production (decreased by 26%, P < 0.05) were depressed concordantly with the down-regulated EphB2 expression. Subsequently, we screened microRNAs that could regulate EphB2 expression in B cells, and discovered that miR-185 directly targeted to EphB2 mRNA and suppressed its expression. Furthermore, miR-185 overexpression inhibited B-cell activation, and the inhibitor of miR-185 enhanced B-cell activation. Moreover, abatement of EphB2 through miR-185 mimics or EphB2 siRNA attenuated the activation of Src-p65 and Notch1 signaling pathways in human B cells. Our study first suggested that EphB2 was involved in human naive B cell activation through Src-p65 and Notch1 signaling pathways and could be regulated by miR-185.

EphB and Ephrin-B interactions mediate human mesenchymal stem cell suppression of activated T-cells

Mesenchymal stromal/stem cells (MSC) express the contact-dependent erythropoietin-producing hepatocellular (Eph) receptor tyrosine kinase family and their cognate ephrin ligands, which are known to regulate thymocyte maturation and selection, T-cell transendothelial migration, activation, co-stimulation, and proliferation. However, the contribution of Eph/ephrin molecules in mediating human MSC suppression of activated T-cells remains to be determined. In the present study, we showed that EphB2 and ephrin-B2 are expressed by ex vivo expanded MSC, while the corresponding ligands, ephrin-B1 and EphB4, respectively, are highly expressed by T-cells. Initial studies demonstrated that EphB2-Fc and ephrin-B2-Fc molecules suppressed T-cell proliferation in allogeneic mixed lymphocyte reaction (MLR) assays compared with human IgG-treated controls. While the addition of a third-party MSC population demonstrated dramatic suppression of T-cell proliferation responses in the MLR, blocking the function of EphB2 or EphB4 receptors using inhibitor binding peptides significantly increased T-cell proliferation. Consistent with these observations, shRNA EphB2 or ephrin-B2 knockdown expression in MSC reduced their ability to inhibit T-cell proliferation. Importantly, the expression of immunosuppressive factors, indoleamine 2, 3-dioxygenase, transforming growth factor-β1, and inducible nitric oxide synthase expressed by MSC, was up-regulated after stimulation with EphB4 and ephrin-B1 in the presence of interferon (IFN)-γ, compared with untreated controls. Conversely, key factors involved in T-cell activation and proliferation, such as interleukin (IL)-2, IFN-γ, tumor necrosis factor-α, and IL-17, were down-regulated by T-cells treated with EphB2 or ephrin-B2 compared with untreated controls. Studies utilizing signaling inhibitors revealed that inhibition of T-cell proliferation is partly mediated through EphB2-induced ephrin-B1 reverse signaling or ephrin-B2-mediated EphB4 forward signaling by activating Src, PI3Kinase, Abl, and JNK kinase pathways, activated by tyrosine phosphorylation. Taken together, these observations suggest that EphB/ephrin-B interactions play an important role in mediating human MSC inhibition of activated T cells.

Ephrin-B-dependent thymic epithelial cell-thymocyte interactions are necessary for correct T cell differentiation and thymus histology organization: relevance for thymic cortex development

Previous analysis on the thymus of erythropoietin-producing hepatocyte kinases (Eph) B knockout mice and chimeras revealed that Eph-Eph receptor-interacting proteins (ephrins) are expressed both on T cells and thymic epithelial cells (TECs) and play a role in defining the thymus microenvironments. In the current study, we have used the Cre-LoxP system to selectively delete ephrin-B1 and/or ephrin-B2 in either thymocytes (EfnB1(thy/thy), EfnB2(thy/thy), and EfnB1(thy/thy)EfnB2(thy/thy) mice) or TECs (EfnB1(tec/tec), EfnB2(tec/tec), and EfnB1(tec/tec)EfnB2(tec/tec) mice) and determine the relevance of these Eph ligands in T cell differentiation and thymus histology. Our results indicate that ephrin-B1 and ephrin-B2 expressed on thymocytes play an autonomous role in T cell development and, expressed on TECs, their nonautonomous roles are partially overlapping. The effects of the lack of ephrin-B1 and/or ephrin-B2 on either thymocytes or TECs are more severe and specific on thymic epithelium, contribute to the cell intermingling necessary for thymus organization, and affect cortical TEC subpopulation phenotype and location. Moreover, ephrin-B1 and ephrin-B2 seem to be involved in the temporal appearance of distinct cortical TECs subsets defined by different Ly51 levels of expression on the ontogeny.

Eph/ephrinB signalling is involved in the survival of thymic epithelial cells

The signals that determine the survival/death of the thymic epithelial cells (TECs) component during embryonic development of the thymus are largely unknown. In this study, we combine different in vivo and in vitro experimental approaches to define the role played by the tyrosine kinase receptors EphB2 and EphB3 and their ligands, ephrinsB, in the survival of embryonic and newborn (NB) TECs. Our results conclude that EphB2 and EphB3 are involved in the control of TEC survival and that the absence of these molecules causes increased apoptotic TEC proportions that result in decreased numbers of thymic cells and a smaller-sized gland. Furthermore, in vitro studies using either EphB2-Fc or ephrinB1-Fc fusion proteins demonstrate that the blockade of Eph/ephrinB signalling increases TEC apoptosis, whereas its activation rescues TECs from cell death. In these assays, both heterotypic thymocyte-TEC and homotypic TEC-TEC interactions are important for Eph/ephrinB-mediated TEC survival.

Developing T-cell migration: role of semaphorins and ephrins

Cell migration is a crucial event for normal T-cell development, and various ligand/receptor pairs have been implicated. Most of them, including chemokines and extracellular matrix proteins, have attractant properties on thymocytes. We discuss herein two further groups of ligand/receptor pairs, semaphorins/neuropilins and ephs/ephrins, which are constitutively expressed by thymocytes and thymic microenvironmental cells. Evidence shows that the corresponding interactions are relevant for developing T-cell migration, including the entry of bone marrow progenitor cells, migration of CD4/CD8-defined thymocyte subpopulations triggered by chemokines and/or extracellular matrix proteins, and thymocyte export. Conceptually, the data summarized here show that thymocyte migration results from a complex network of molecular interactions, which generate not only attraction, but also repulsion of migrating T-cell precursors.

First insight into the kinome of human regulatory T cells

Regulatory T cells (Tregs) are essential for controlling peripheral tolerance by the active suppression of various immune cells including conventional T effector cells (Teffs). Downstream of the T cell receptor (TCR), more than 500 protein kinases encoded by the human genome have to be considered in signaling cascades regulating the activation of Tregs and Teffs, respectively. Following TCR engagement, Tregs posses a number of unique attributes, such as constitutive expression of Foxp3, hyporesponsiveness and poor cytokine production. Furthermore, recent studies showed that altered regulation of protein kinases is important for Treg function. These data indicate that signaling pathways in Tregs are distinctly organized and alterations at the level of protein kinases contribute to the unique Treg phenotype. However, kinase-based signaling networks in Tregs are poorly understood and necessitate further systematic characterization. In this study, we analyzed the differential expression of kinases in Tregs and Teffs by using a kinase-selective proteome strategy. In total, we revealed quantitative information on 185 kinases expressed in the human CD4(+) T cell subsets. The majority of kinases was equally abundant in both T cell subsets, but 11 kinases were differentially expressed in Tregs. Most strikingly, Tregs showed an altered expression of cell cycle kinases including CDK6. Quantitative proteomics generates first comparative insight into the kinase complements of the CD4(+) Teff and Treg subset. Treg-specific expression pattern of 11 protein kinases substantiate the current opinion that TCR-mediated signaling cascades are altered in Tregs and further suggests that Tregs exhibit significant specificities in cell-cycle control and progression.

A novel feedback mechanism by Ephrin-B1/B2 in T-cell activation involves a concentration-dependent switch from costimulation to inhibition

Bidirectional signals via Eph receptors/ephrins have been recognized as major forms of contact-dependent cell communications such as cell attraction and repulsion. T cells express EphBs, and their ligands, the ephrin-Bs, have been known as costimulatory molecules for T-cell proliferation. Recently, another remarkable feature of ephrin-As has emerged in the form of a concentration-dependent transition from promotion to inhibition in axon growth. Here we examined whether this modification plays a role in ephrin-B costimulation in murine primary T cells. Low doses of ephrin-B1 and ephrin-B2 costimulated T-cell proliferation induced by anti-CD3, but high concentrations strongly inhibited it. In contrast, ephrin-B3 showed a steadily increasing stimulatory effect. This modulation was virtually preserved in T cells from mice simultaneously lacking four genes, EphB1, EphB2, EphB3, and EphB6. High concentrations of ephrin-B1/B2, but not ephrin-B3, inhibited the anti-CD3-induced phosphorylation of Lck and its downstream signals such as Erk and Akt. Additionally, high doses of any ephrin-Bs could phosphorylate EphB4. However, only ephrin-B1/B2 but not ephrin-B3 recruited SHP1, a phosphatase to suppress the phosphorylation of Lck. These data suggest that EphB4 signaling could engage in negative feedback to TCR signals. T-cell activation may be finely adjusted by the combination and concentration of ephrin-Bs expressed in the immunological microenvironment.

Eph/Ephrin-mediated interactions in the thymus

In the present study, we review available information on the relevance of Eph and ephrins in numerous processes occurring in the thymus that regulate not only T cell differentiation but also thymic epithelial cell (TEC) development and organization. Eph/ephrins are a large family of receptors and ligands involved in organogenesis and homeostasis of adult tissues. They are extensively expressed in the thymus and seem to be involved in the colonization of lymphoid progenitor cells and their migration throughout the thymic parenchyma necessary to provide an adequate topological location of developing thymocytes in the epithelial network that ensures their correct differentiation. In addition, EphB2 and EphB3 play a cell-autonomous role in regulating the transitions of double-negative to double-positive cells and of double-positive to single-positive thymocytes and the lack of these molecules or their ligands ephrin B1 and ephrin B2 induces profound alterations of the TEC maturation and in the arrangement of epithelial network. We emphasize that these results are largely reflecting the role played by this family of molecules in controlling thymocyte-TEC interactions within the thymus.

EphB-ephrin-B2 interactions are required for thymus migration during organogenesis

Thymus organogenesis requires coordinated interactions of multiple cell types, including neural crest (NC) cells, to orchestrate the formation, separation, and subsequent migration of the developing thymus from the third pharyngeal pouch to the thoracic cavity. The molecular mechanisms driving these processes are unclear; however, NC-derived mesenchyme has been shown to play an important role. Here, we show that, in the absence of ephrin-B2 expression on thymic NC-derived mesenchyme, the thymus remains in the cervical area instead of migrating into the thoracic cavity. Analysis of individual NC-derived thymic mesenchymal cells shows that, in the absence of ephrin-B2, their motility is impaired as a result of defective EphB receptor signaling. This implies a NC-derived cell-specific role of EphB-ephrin-B2 interactions in the collective migration of the thymic rudiment during organogenesis.