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ICAP‐1 regulates β1‐integrin activation and cell adhesion. Here, we used ICAP‐1‐null mice to study ICAP‐1 potential involvement during immune cell development and function. Integrin α4β1‐dependent adhesion was comparable between ICAP‐1‐null and control thymocytes, but lack of ICAP‐1 caused a defective single‐positive (SP) CD8+ cell generation, thus, unveiling an ICAP‐1 involvement in SP thymocyte development. ICAP‐1 bears a nuclear localization signal and we found it displayed a strong nuclear distribution in thymocytes. Interestingly, there was a direct correlation between the lack of ICAP‐1 and reduced levels in SP CD8+ thymocytes of Runx3, a transcription factor required for CD8+ thymocyte generation. In the spleen, ICAP‐1 was found evenly distributed between cytoplasm and nuclear fractions, and ICAP‐1–/– spleen T and B cells displayed upregulation of α4β1‐mediated adhesion, indicating that ICAP‐1 negatively controls their attachment. Furthermore, CD3+‐ and CD19+‐selected spleen cells from ICAP‐1‐null mice showed reduced proliferation in response to T‐ and B‐cell stimuli, respectively. Finally, loss of ICAP‐1 caused a remarkable decrease in marginal zone B‐ cell frequencies and a moderate increase in follicular B cells. Together, these data unravel an ICAP‐1 involvement in the generation of SP CD8+ thymocytes and in the control of marginal zone B‐cell numbers. [ABSTRACT FROM AUTHOR]

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. Key Findings: EphB2 and EphB3 are involving in the thymus aging.The lack of both EphB receptors results in a more severe aged thymic phenotype.Thymic epithelial cells, thymocyte subsets and peripheral naive and memory T lymphocytes are particularly affected by the lack of the molecules. [ABSTRACT FROM AUTHOR]

Keywords: thymic epithelial cells; thymocyte education; Eph; ephrin; regulatory T-cells EN thymic epithelial cells thymocyte education Eph ephrin regulatory T-cells N.PAG N.PAG 3 03/12/21 20210308 NES 210308 Introduction The central tolerance to self-antigens is achieved in the thymus through a complex process in which developing thymocytes (T) sequentially interact with thymic epithelial cells (TECs) in a 3D network histologically organized in a cortex and a medulla ([1]). On the other hand, the presence of small groups of TECs properly organized from a histological view and expressing key molecules involved in the functional crosstalk between TECs and thymocytes would be sufficient to allow the thymocyte differentiation in mutant thymuses ([3], [7]). [Extracted from the article]

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 Cld3,4hiSSEA1+ 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 Vy5+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 CD40hiCD80+ and MHCIIhiUEA1+ 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The role of EphB2 and EphB3 in the organization of thymic epithelial cells has been studied in EphB-deficient fetal thymus lobes grafted under the kidney capsule of WT mice. The deficient lobes, as compared with WT ones, showed altered distribution of medullary areas, shortening of medullary epithelial cell processes and presence of K5K8 areas. EphB2 and EphB3 expressed on thymic epithelial cells play an autonomous role in their organization. The relevance of Eph/ephrinB forward and reverse signals for this process was evaluated in grafted fetal thymus lobes from mice expressing a truncated EphB2 receptor capable of activating reverse, but not forward, signaling. These deficient lobes showed important alterations of the thymic epithelial organization as compared with the grafted WT lobes, but a less severe phenotype than the grafted EphB2-deficient thymus lobes, which confirms the relevance of EphB2 forward signal for the thymic epithelial organization but, also, a role of the reverse signaling in determining the final epithelial phenotype. [ABSTRACT FROM AUTHOR]

In the current study, we extend our own previous results on the thymocyte phenotype of EphB2 and/or EphB3 deficient mice by analyzing the phenotype and the histological organization of their thymic epithelial stroma. All studied adult EphB-deficient thymi showed profound alterations with respect to the wild-type (WT) ones. Each mutant exhibited a specific phenotype, but also showed common features including occurrence of K5+K8 +MTS10+ immature medullary epithelial cells, numerous K5 -)K8-MTS20+ cells and K5+K8+ cells in the thymic cortex and cortical and medullary K5-K8- areas devoid of epithelial cell markers. In addition, comparative analysis of and EphB-deficient embryonic and newborn thymi demonstrated that the observed adult phenotype was a consequence of the gradual accumulation of early phenotypic and morphological defects, becoming more severe at the end of embryonic life and in newborn animals. Together, these results confirm a role for EphB2 and EphB3 in thymus morphogenesis. The obtained data are discussed from the point of view of the recognized role played by these two Ephs in the homeostasis of other epithelia and their possible relationships with molecules known to be involved in thymic epithelial cell development. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (EfnB1thy/thy, EfnB2thy/thy, and EfnB1thy/thyEfnB2thy/thy mice) or TECs (EfnB1tec/tec, EfnB2tec/tec, and EfnB1tec/tecEfnB2tec/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. [ABSTRACT FROM AUTHOR]