Selective reduction of post-selection CD8 thymocyte proliferation in IL-15Rα deficient mice

Peripheral CD8(+) T cells are defective in both IL-15 and IL-15Rα knock-out (KO) mice; however, whether IL-15/IL-15Rα deficiency has a similar effect on CD8 single-positive (SP) thymocytes remains unclear. In this study, we investigated whether the absence of IL-15 transpresentation in IL-15Rα KO mice results in a defect in thymic CD8 single positive (SP) TCR(hi) thymocytes. Comparison of CD8SP TCR(hi) thymocytes from IL-15Rα KO mice with their wild type (WT) counterparts by flow cytometry showed a significant reduction in the percentage of CD69(-) CD8SP TCR(hi) thymocytes, which represent thymic premigrants. In addition, analysis of in vivo 5-bromo-2-deoxyuridine (BrdU) incorporation demonstrated that premigrant expansion of CD8SP TCR(hi) thymocytes was reduced in IL-15Rα KO mice. The presence of IL-15 transpresentation-dependent expansion in CD8SP TCR(hi) thymocytes was assessed by culturing total thymocytes in IL-15Rα-Fc fusion protein-pre-bound plates that were pre-incubated with IL-15 to mimic IL-15 transpresentation in vitro. The results demonstrated that CD8SP thymocytes selectively outgrew other thymic subsets. The contribution of the newly divided CD8SP thymocytes to the peripheral CD8(+) T cell pool was examined using double labeling with intrathymically injected FITC and intravenously injected BrdU. A marked decrease in FITC(+) BrdU(+) CD8(+) T cells was observed in the IL-15Rα KO lymph nodes. Through these experiments, we identified an IL-15 transpresentation-dependent proliferation process selective for the mature CD8SP premigrant subpopulation. Importantly, this process may contribute to the maintenance of the normal peripheral CD8(+) T cell pool.     

Characterization and Favorable in Vivo Properties of Heterodimeric Soluble IL-15·IL-15Rα Cytokine Compared to IL-15 Monomer

Interleukin-15 (IL-15), a 114-amino acid cytokine related to IL-2, regulates immune homeostasis and the fate of many lymphocyte subsets. We reported that, in the blood of mice and humans, IL-15 is present as a heterodimer associated with soluble IL-15 receptor α (sIL-15Rα). Here, we show efficient production of this noncovalently linked but stable heterodimer in clonal human HEK293 cells and release of the processed IL-15·sIL-15Rα heterodimer in the medium. Purification of the IL-15 and sIL-15Rα polypeptides allowed identification of the proteolytic cleavage site of IL-15Rα and characterization of multiple glycosylation sites. Administration of the IL-15·sIL-15Rα heterodimer reconstituted from purified subunits resulted in sustained plasma IL-15 levels and in robust expansion of NK and T cells in mice, demonstrating pharmacokinetics and in vivo bioactivity superior to single chain IL-15. These identified properties of heterodimeric IL-15 provide a strong rationale for the evaluation of this molecule for clinical applications.     

Effect of cytokines (IL-2, IL-7, and IL-15) having common γ-chain of receptors on differentiation and maturation of CD4+/CD8+ T-cells in a CD45RA T-lymphocyte population in vitro

The effect of cytokines (IL-2, IL-7, and IL-15) having a common γ-chain of receptors on the maturation and differentiation of CD3⁺CD45RA⁺CD4⁺/CD8⁺ lymphocytes in homeostatic cultivation model in vitro was analyzed. It was found that the maximum IL-2 concentration in the helper CD45RA⁺-T-cell population mediates an increase in the number of CD45RA⁺CD4⁺ T lymphocytes with the phenotype of mature and immature terminally differentiated TEMRA T cells. IL-15 leads to the production of lymphocytes with CD27^–CD62L⁺ phenotype (presumably, TEMRA, in which the CD62L expression persists). In the CD45RA⁺CD8⁺ T lymphocyte populations, the studied cytokines (IL-2, IL-7, and IL-15) initiate the production of mature TEMRA (E) T lymphocytes and memory T cells with the CD45RA^?CD27⁺CD62L⁺ central phenotype (TCM).     

MHC class I and TCR avidity control the CD8 T cell response to IL-15/IL-15Rα complex

IL-15 operates via a unique mechanism termed transpresentation. In this system, IL-15 produced by one cell type is bound to IL-15Rα expressed by the same cell and is presented to apposing cells expressing the IL-15Rβ/γC complex. We have shown that administering soluble IL-15Rα complexed with IL-15 can greatly enhance IL-15 activity. We now show that the naive CD8 T cell response to exogenous IL-15/IL-15Rα complex is MHC class I dependent. In the absence of β2 microglobulin, naive CD8 T cells scarcely proliferated in response to IL-15/IL-15Rα complex, whereas memory cells proliferated, although to a lesser extent, compared with levels in control mice. The loss of β2m or FcRn slightly reduced the extended half-life of IL-15/IL-15Rα complex, whereas FcRn deficiency only partially reduced the naive CD8 T cell proliferative response to IL-15/IL-15Rα complex. In addition, we demonstrated a link between TCR avidity and the ability of a T cell to respond to IL-15/IL-15Rα complex. Thus, T cells expressing low-avidity TCR responded poorly to IL-15/IL-15Rα complex, which correlated with a poor homeostatic proliferative response to lymphopenia. The inclusion of cognate peptide along with complex resulted in enhanced proliferation, even when TCR avidity was low. IL-15/IL-15Rα complex treatment, along with peptide immunization, also enhanced activation and the migratory ability of responding T cells. These data suggest that IL-15/IL-15Rα complex has selective effects on Ag-activated CD8 T cells. Our findings have important implications for directing IL-15/IL-15Rα complex-based therapy to specific Ag targets and illustrate the possible adjuvant uses of IL-15/IL-15Rα complex.     

CD40／CD40L介导信号的免疫调节作用

Ｂ细胞的ＣＤ４０分子与活化Ｔ细胞的ＣＤ４０配体（ＣＤ４０Ｌ）结合可调节Ｂ细胞生长分化、克隆转换、Ｉｇ分泌、阻断Ｂ细胞凋亡和导Ｆａｓ表面分隔表达等,直接参与调节体液免疫。ＣＤ４０与ＣＤ４０Ｌ结合也影响细胞免疫功能,诱导Ｔｈ１和Ｔｈ２细胞因子产生《ＣＤ４０和ＣＤ４０Ｌ连接ＴＲＡＦ蛋白多聚化,从而调节基因的转录。ＣＤ４０介导的信号传导过程与蛋白酷氨酸酶、蛋白酪氨酸磷酸化有等有关。     

CD40 ligation converts TGF-β-secreting tolerogenic CD48 dendritic cells into IL-12-secreting immunogenic ones

CD40L, the ligand for CD40 on dendritic cells (DCs), plays an important role in maturation and activation of DCs leading to induction of immune responses. Our previous studies showed that the mouse splenic CD4⁻8⁻ DCs are tolerogenic and capable of stimulating suppressive type 1 CD4⁺ regulatory T (Tr1) cell responses via TGF-β secretion. In this study, we investigated whether CD40 ligation is able to convert tolerogenic CD4⁻8⁻ DCs into immunogenic ones by in vitro treatment of DCs with anti-CD40 antibody. Our data showed that in vitro CD40 ligation with anti-CD40 antibody converted TGF-β-secreting tolerogenic CD4⁻8⁻ DCs into IL-12-secreting immunogenic ones capable of stimulating type 1 CD4⁺ helper T (Th1) and CD8⁺ cytotoxic T lymphocyte (CTL) responses leading to induction of antitumor immunity. In addition, in vivo CD40 ligation by intratumoral injection of adenoviral vector AdVCD40L expressing CD40 ligand also induced tumor growth inhibition and regression of established P815 tumors with infiltration of tolerogenic CD4⁻8⁻ DCs. Therefore, our data provide new information for and may thus have useful impacts in CD40 ligation-based immunotherapy of cancer.     

Expression and regulation of IL-22 in the IL-17-producing CD4＋ T lymphocytes

IL-22 is a novel cytokine in the IL-10 family that functions to promote innate immunity of tissues against infection. Although CD4＋ helper T lymphocytes （TH） were found as a source of IL-22, the regulation of this cytokine has been poorly understood. Here, we show that IL-22 is expressed at both mRNA and protein levels by a novel subset of TH cells that also makes IL-17. IL-22 and IL-17 were found to be coordinately regulated by TGFI3 and IL-6 during TH differentiation by real-time PCR as well as ELISA analysis. However, IL-22 does not regulate TH differentiation; exogenous IL-22 or an IL-22 antagonist had no effect on TH differentiation. These data demonstrate a novel cytokine expressed by IL-17-producing T cells, and suggest interaction and synergy of IL-22 and IL-l 7 signaling pathways in tissue inflammation and autoimmune diseases.     

CD40/CD40L信号系统与子痫前期的关系

子痫前期是病理产科中常见的疾病,是导致孕产妇和围生儿死亡的主要原因,其具体病因目前尚未完全阐明,大多数学者认为主要与氧化应激导致的血管内皮细胞损伤,胎盘浅着床,免疫平衡的破坏等因素有关,其中内皮细胞损伤导致的内皮细胞生理功能失衡是其病因学研究的热点.CD40/CD40L是一对互补的肿瘤坏死因子和肿瘤坏子因子受体超家族跨膜糖蛋白,相互作用可以促进内皮细胞、平滑肌细胞表达和释放细胞因子、组织因子、金属蛋白酶、粘附分子,这些物质间接或直接的参与了炎症反应和免疫调节,导致内皮细胞损伤.因此,CD40/CD40L相互作用在炎症反应和免疫失调中亦起着关键作用,可能是子痫前期的病因之一,以CD40/CD40L为靶点为子痫前期的诊断和治疗提供了新的思路和方向.本文拟对CD40/CD40L信号系统与子痫前期的关系做一综述.     

Involvement of nuclear factor κB in platelet CD40 signaling

CD40 ligand (CD40L) is a thrombo-inflammatory molecule that predicts cardiovascular events. Platelets constitute the major source of soluble CD40L (sCD40L), which has been shown to potentiate platelet activation and aggregation, in a CD40-dependent manner, via p38 mitogen activated protein kinase (MAPK) and Rac1 signaling. In many cells, the CD40L/CD40 dyad also induces activation of nuclear factor kappa B (NF-κB). Given that platelets contain NF-κB, we hypothesized that it may be involved in platelet CD40 signaling and function. In human platelets, sCD40L induces association of CD40 with its adaptor protein the tumor necrosis factor receptor associated factor 2 and triggers phosphorylation of IκBα, which are abolished by CD40L blockade. Inhibition of IκBα phosphorylation reverses sCD40L-induced IκBα phosphorylation without affecting p38 MAPK phosphorylation. On the other hand, inhibition of p38 MAPK phosphorylation has no effect on IκBα phosphorylation, indicating a divergence in the signaling pathway originating from CD40 upon its ligation. In functional studies, inhibition of IκBα phosphorylation reverses sCD40L-induced platelet activation and potentiation of platelet aggregation in response to a sub-threshold concentration of collagen. This study demonstrates that the sCD40L/CD40 axis triggers NF-κB activation in platelets. This signaling pathway plays a critical role in platelet activation and aggregation upon sCD40L stimulation and may represent an important target against thrombo-inflammatory disorders.     

TGF-β Sensitivity Restrains CD8+ T Cell Homeostatic Proliferation by Enforcing Sensitivity to IL-7 and IL-15

The pleiotropic cytokine TGF-β has been implicated in the regulation of numerous aspects of the immune response, including naïve T cell homeostasis. Previous studies found that impairing TGF-β responsiveness (through expression of a dominant-negative TGF-β RII [DNRII] transgene) leads to accumulation of memory phenotype CD8 T cells, and it was proposed that this resulted from enhanced IL-15 sensitivity. Here we show naïve DNRII CD8 T cells exhibit enhanced lymphopenia-driven proliferation and generation of “homeostatic” memory cells. However, this enhanced response occurred in the absence of IL-15 and, unexpectedly, even in the combined absence of IL-7 and IL-15, which were thought essential for CD8 T cell homeostatic expansion. DNRII transgenic CD8 T cells still require access to self Class I MHC for homeostatic proliferation, arguing against generalized dysregulation of homeostatic cues. These findings suggest TGF-β responsiveness is critical for enforcing sensitivity to homeostatic cytokines that limit maintenance and composition of the CD8 T cell pool. (154 words).     

CD40-CD40L与斑块的不稳定性

随着对动脉粥样硬化性疾病研究的深入,人们发现众多的心脑血管疾病是由于粥样斑块不稳定所引起。近来研究表明CD40-CD40L不仅在免疫炎症反应中起着重要作用,同时影响斑块的稳定性。     

Different dynamics of IL-15R activation following IL-15 cis- or trans-presentation

Interleukin (IL)-15 is a cytokine critical for the homeostasis and the function of NK cells, NK-T cells, and memory CD8+ T cells. IL-15 signals are delivered through the IL-15Rβ and the common γ (γ(c)) receptor chains. The third receptor chain, IL-15Rα, confers specificity and high affinity for the cytokine. While IL-15 can activate with high affinity the trimeric receptor expressed by a target cell (cis-presentation), IL-15Rα is also known to trans-present IL-15 with high affinity to target cells expressing the IL-15Rβ/γ(c) complex. In order to compare the IL-15 cis- and trans-presentation processes, and using a T cell line expressing both IL-15Rα/β/γ(c) and IL-15Rβ/γ(c), we analyzed cell surface receptor chain down-modulation, cytokine internalization and signaling responses induced either with IL-15 (cis-presentation) or with RLI, a protein resulting from fusion between IL-15 and an extended IL-15Rα sushi domain, that mimics trans-presentation. Whereas IL-15 bound with high affinity to IL-15Rα/β/γ(c), RLI bound with a similar high affinity to IL-15Rβ/γ(c). The kinetics of cell surface IL-15R down-modulation were slower following RLI treatment than after IL-15 treatment, as were the kinetics of RLI internalization, which was slower than that of IL-15. IL-15 and RLI dose-dependently induced the activation of similar signaling pathways. However, the kinetics and duration of these activations were markedly different, RLI-induced signaling, being slower, but more prolonged than that induced by IL-15, although the final proliferative responses at 48?h were similar. These findings collectively indicate that IL-15 cis- and trans-presentation mechanisms lead to different dynamics of receptor activation and signal transduction, with cis-presentation inducing fast and transient responses, and trans-presentation inducing slower, more persistent ones. They provide clues for a better understanding of how IL-15 action is controlled, and how it plays a key role in the coordination between innate and adaptative immunity.     

Paracrine and Transpresentation Functions of IL-15 Are Mediated by Diverse Splice Versions of IL-15Rα in Human Monocytes and Dendritic Cells

Species-specific differences of post-translational modifications suggested the existence of human IL-15Rα isoforms. We identified eight new isoforms that are predicted to modify the intracellular C termini of IL-15Rα, and another N-terminal exon “Ex2A” that was consistently present in all but one of the C-terminal isoforms. Ex2A encodes a 49-amino acid domain that allowed the transfer of IL-15/IL-15Rα complex to the cell surface but prevented its cleavage from cell membranes and its secretion thus facilitating the transpresentation of IL-15 as part of the immunological synapse. The Ex2A domain also affected the O-glycosylation of IL-15Rα that explained the species-specific differences. The Ex2A domain appeared to be removed from major IL-15Rα species during protein maturation, but both Ex2A and IL-15Rα appeared on the surface of monocytic cells upon activation. The membrane-associated form of the only C-terminal isoform that lacked Ex2A (IC3) was retained inside the cell, but soluble IL-15/IL-15Rα complexes were readily released from cells that expressed IL-15/IL-15Rα-IC3 thus limiting this IL-15/IL-15Rα isoform to act as a secreted molecule. These data suggest that splice versions of IL-15Rα determine the range of IL-15 activities.     

Aberrant CD40-Induced NF-κB Activation in Human Lupus B Lymphocytes

Auto-reactive B lymphocytes and its abnormal CD40 signaling play important roles in the pathogenesis of systemic lupus erythematosus (SLE). In this study, we analyzed CD40 expression and CD40/CD154 induced activation of NF-κB signaling pathway in B cells from SLE patients. B cells from healthy volunteers and tonsilar B cells from chronic tonsillitis were used as negative and positive controls. Results showed CD40-induced NF-κB signaling was constitutively activated in B cells from active lupus patients, including decreased CD40 in raft portion, increased phosphorylation and degradation of IκBα, phosphorylation of P65, as well as increased nuclear translocation of P65, P50, c-Rel, which could be blocked by anti-CD154. CD154 stimulation could induce further phosphorylation and degradation of IκBα, as well as phosphorylation of P65 and nuclear translocation of P65. In addition, CD40-induced kinase activities in B cells from lupus patients mimicked that of tonsil B cells, in that IKKα/β were more activated compared to normal B cells. CD40-induced NF-κB activity was blocked by both IκB phosphorylation and proteosome degradation inhibitors in both lupus and normal B cells. All together, our findings revealed that canonical NF-κB signaling is constitutively activated in active lupus and is mediated by CD154/CD40. CD40 induced NF-κB activation is different in human lupus B lymphocytes compared with normal B cells.     

NK Cell Activation in Human Hantavirus Infection Explained by Virus-Induced IL-15/IL15Rα Expression

Clinical infection with hantaviruses cause two severe acute diseases, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). These diseases are characterized by strong immune activation, increased vascular permeability, and up to 50% case-fatality rates. One prominent feature observed in clinical hantavirus infection is rapid expansion of natural killer (NK) cells in peripheral blood of affected individuals. We here describe an unusually high state of activation of such expanding NK cells in the acute phase of clinical Puumala hantavirus infection. Expanding NK cells expressed markedly increased levels of activating NK cell receptors and cytotoxic effector molecules. In search for possible mechanisms behind this NK cell activation, we observed virus-induced IL-15 and IL-15Rα on infected endothelial and epithelial cells. Hantavirus-infected cells were shown to strongly activate NK cells in a cell-cell contact-dependent way, and this response was blocked with anti-IL-15 antibodies. Surprisingly, the strength of the IL-15-dependent NK cell response was such that it led to killing of uninfected endothelial cells despite expression of normal levels of HLA class I. In contrast, hantavirus-infected cells were resistant to NK cell lysis, due to a combination of virus-induced increase in HLA class I expression levels and hantavirus-mediated inhibition of apoptosis induction. In summary, we here describe a possible mechanism explaining the massive NK cell activation and proliferation observed in HFRS patients caused by Puumala hantavirus infection. The results add further insights into mechanisms behind the immunopathogenesis of hantavirus infections in humans and identify new possible targets for intervention.     

CD40-CD40L功能与疾病的研究进展

CD40与CD40L的相互作用不仅在细胞免疫和 体液免疫中起作用,而且在疾病的发病机制和临床治疗中起重要作用。     

CD4 T cells play important roles in maintaining IL-17-producing γδ T-cell subsets in naive animals

A proportional balance between αβ and γδ T-cell subsets in the periphery is exceedingly well maintained by a homeostatic mechanism. However, a cellular mechanism underlying the regulation remains undefined. We recently reported that a subset of developing γδ T cells spontaneously acquires interleukin (IL)-17-producing capacity even within naive animals through a transforming growth factor (TGF)β1-dependent mechanism, thus considered 'innate' IL-17-producing cells. Here, we report that γδ T cells generated within αβ T cell (or CD4 T cell)-deficient environments displayed altered cytokine profiles; particularly, 'innate' IL-17 expression was significantly impaired compared with those in wild-type mice. Impaired IL-17 production in γδ T cells was directly related to CD4 T-cell deficiency, because depletion of CD4 T cells in wild-type mice diminished and adoptive CD4 T-cell transfer into T-cell receptor β-/- mice restored IL-17 expression in γδ T cells. CD4 T cell-mediated IL-17 expression required TGFβ1. Moreover, Th17 but not Th1 or Th2 effector CD4 T cells were highly efficient in enhancing γδ T-cell IL-17 expression. Taken together, our results highlight a novel CD4 T cell-dependent mechanism that shapes the generation of IL-17+ γδ T cells in naive settings.     

Bioactivity of nitrolinoleate: effects on adhesion molecules and CD40–CD40L system

The vascular effects of nitrolinoleate (LNO₂), an endogenous product of linoleic acid (LA) nitration by nitric oxide-derived species and a potential nitrosating agent, were investigated on rat endothelial-leukocyte interactions. Confocal microscopy analysis demonstrated that LNO₂ was capable to deliver free radical nitric oxide (^·NO) into cells, 5 min after its administration to cultured cells, with a peak of liberation at 30 min. THP-1 monocytes incubated with LNO₂ for 5 min presented nitrosation of CD40, leading to its inactivation. Other anti-inflammatory actions of LNO₂ were observed in vivo by intravital microscopy assays. LNO₂ decreased the number of adhered leukocytes in postcapillary venules of the mesentery network. In addition to this, LNO₂ reduced mRNA and protein expression of β2-integrin in circulating leukocytes, as well as VCAM-1 in endothelial cells isolated from postcapillary venules, confirming its antiadhesive effects on both cell types. Moreover, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a nitric oxide scavenger, partially abolished the inhibitory action of LNO₂ on leukocyte-endothelium interaction, suggesting that the antiadhesion effects of LNO₂ involve a dual role in leukocyte adhesion, acting as a nitric oxide donor as well as through nitric oxide-independent mechanisms. In conclusion, LNO₂ inhibited adhesion molecules expression and promoted ^·NO inactivation of the CD40–CD40L system, both important processes of the inflammatory response.     

IL-15和IL-T与IL-2共有活性与受体

两组研究人员报道发现了新的细胞因子,一个称之为IL-15,另一个称作IL-(?)。二者均有类似IL-2的活性,均通过部分IL-2受体刺激细胞,它们可能是同一种蛋白质,因而有助于澄清某些相互纠缠的观察。例如,IL-2缺陷小鼠令人惊奇地显示正常的免疫应答,这与IL2在体外起关键作用形成鲜明对照IL-2的作用是否受某些已知细胞因子组合或受一种未知因子的支持?答案可能就在IL-15/IL-1之中。 Grabstein等人培养的猿肾Ⅰ皮细胞系的上清液中分离出一种称作IL-15的因子能支持IL-2依赖细胞系的增殖,其表观分子量(SDS-PAGE)为14～15kD。N-     

A role for IL-15 in driving the onset of spontaneous autoimmune thyroiditis?

The obese strain (OS) of chickens, which suffers from spontaneous autoimmune thyroiditis, is an excellent animal model for Hashimoto's thyroiditis and provides a unique opportunity to investigate the mechanisms underlying and driving the onset of the disease. Following recent advances in cloning chicken cytokines, we can now begin to investigate the role of cytokines in driving the lymphoid infiltration of the thyroid seen in these birds from day 7 posthatch. Using real-time quantitative RT-PCR, we characterized the expression of IFN-gamma, IL-1beta, IL-2, IL-6, IL-8, IL-15, and IL-18 in thyroids from OS birds and control CB line birds, both in the embryo just before hatch (embryonic day 20) and at 3 and 5 days posthatch. All of these cytokines were up-regulated compared with levels in thyroids from CB birds, at least at some time points, with some evidence for coordination of regulation, e.g., for the proinflammatory cytokines IL-1beta and IL-8. Only IL-15 was up-regulated at all time points. IL-15 was also shown to be up-regulated in spleens of OS birds at embryonic day 20 and 5 days posthatch, suggesting that IL-15 is constitutively up-regulated in this line of birds. This could explain the general immune system hyperreactivity exhibited by OS chickens and may be a factor driving the lymphoid infiltration of the thyroid.