Unaltered negative selection and Treg development of self‐reactive thymocytes in TCR transgenic Fyn‐deficient mice

The tyrosine kinase Fyn has been implicated as playing an important role in the generation of both stimulatory and inhibitory signaling events induced by TCR engagement. To assess the role of Fyn for antigen‐driven negative selection and Treg development, which are both dependent on the strength and nature of TCR signaling, we generated mice that co‐express the transgenes for OVA and the OT‐II TCR, which recognizes a peptide from OVA. In mice expressing both transgenes, negative selection, Treg development in the thymus, and the number of Treg in the periphery were each unaffected by ablation of Fyn. Moreover, fyn^?/? Treg were functional, as assessed in vitro. We further tested the role of Fyn for the adaptor function of c‐Cbl, using mice containing a point mutation in c‐Cbl that abolishes its E3 ubiquitin ligase function but maintains its adaptor function. The functional and signaling properties of this mutant c‐Cbl were unaltered in fyn^?/? thymocytes. Combined, these data indicate that Fyn was not required for the induction of central tolerance by negative selection, the adaptor protein role of c‐Cbl, or the normal development and function of Treg.     

T cell receptor targeting to thymic cortical epithelial cells in vivo induces survival,activation and differentiation of immature thymocytes

We report that targeting of T cell receptors (TcR) to non-major histocompatibility complex (MHC) molecules on thymic cortical epithelial cells by hybrid antibodies in vivo and in fetal thymic organ cultures results in phenotypic and functional differentiation of thymocytes. A single pulse with hybrid antibodies rescues immature, CD4/8 double-positive thymocytes from their programmed death in vivo, induces expression of the early activation antigen CD69 followed by TcR up-regulation, concomitant down-regulation of CD8 or CD4 and their conversion to functional mature T cells by day 3. This temporal sequence of maturation only affects small thymocytes without co-induction of blastogenesis. TcR targeting to MHC class II-positive epithelial cells predominantly induces CD4-positive T cells. This generation of CD4 single-positive T cells occurs also in MHC class II-deficient mice and thus is independent of CD4-MHC class II interactions. Moreover, in the presence of a specific deleting antigen (Mls 1^a),TcR targeting results in transient activation of immature thymocytes, however, not in subsequent TcR (Vβ6) up-regulation and development of single-positive T cells. Our findings imply that TcR cross-linking to cortical epithelial cells is sufficient to confer a differentiation signal to immature thymocytes. Futhermore, this approach distinguishes two independent TcR-mediated intrathymic events: activation and subsequent deletion of the same thymocyte subset.     

Indirect presentation in the thymus limits naive and regulatory T‐cell differentiation by promoting deletion of self‐reactive thymocytes

Acquisition of T‐cell central tolerance involves distinct pathways of self‐antigen presentation to thymocytes. One pathway termed indirect presentation requires a self‐antigen transfer step from thymic epithelial cells (TECs) to bone marrow‐derived cells before the self‐antigen is presented to thymocytes. The role of indirect presentation in central tolerance is context‐dependent, potentially due to variation in self‐antigen expression, processing and presentation in the thymus. Here, we report experiments in mice in which TECs expressed a membrane‐bound transgenic self‐antigen, hen egg lysozyme (HEL), from either the insulin (insHEL) or thyroglobulin (thyroHEL) promoter. Intrathymic HEL expression was less abundant and more confined to the medulla in insHEL mice compared with thyroHEL mice. When indirect presentation was impaired by generating mice lacking MHC class II expression in bone marrow‐derived antigen‐presenting cells, insHEL‐mediated thymocyte deletion was abolished, whereas thyroHEL‐mediated deletion occurred at a later stage of thymocyte development and Foxp3⁺ regulatory T‐cell differentiation increased. Indirect presentation increased the strength of T‐cell receptor signalling that both self‐antigens induced in thymocytes, as assessed by Helios expression. Hence, indirect presentation limits the differentiation of naive and regulatory T cells by promoting deletion of self‐reactive thymocytes.     

Restricted expression of transgenic HLA-DRA gene in thymic epithelial cells and its role in acquisition of T cell tolerance to self-superantigens and processed DRα-derived peptide

We have established a set of transgenic mouse lines in which the HLA-DRA gene was expressed in different cell types. In one line (DRα-24), DRαEβ^b molecules were expressed on thymic medullary and cortical epithelial cells and all lineages of bone marrow-derived antigen-presenting cells (APC) except for thymic macrophages. By contrast, expression of the molecules in another line (DRα-30) was found on thymic medullary and cortical epithelial cells but not on bone marrow-derived APC in the thymus and periphery. To evaluate the role of thymic epithelial cells in acquisition of T cell tolerance, comparative analysis of DRα-24 and DRα-30 was performed. In DRα-30, T cells expressing TcR Vβ5 and Vβ11 were eliminated to comparable levels to those in DRα-24, suggesting that expression of the DRαEβ^b molecules on thymic epithelial cells are sufficient for clonal deletion of the self-superantigen-reactive T cells. In addition, CD4⁺ T cells from DRa-30 as well as those from DRα-24 were tolerant to DRα-derived peptide/I-A^b complex expressed on spleen cells from DRα-24 even in the presence of exogenous interleukin-2. These observations suggest that expression of the DRα chain in thymic epithelial cells could induce T cell tolerance directed toward naturally processed DRα-derived peptide bound to I-A^b molecules, probably via clonal deletion of the self-reactive T cells.     

NKT cells are dispensable in the induction of oral tolerance but are indispensable in the abrogation of oral tolerance by prostaglandin E

NK1.1(+) alpha beta T cells (NKT cells) regulate the Th1/Th2 balance in response to dietary Ag, which may be involved in regulation of oral tolerance. OVA-specific IgE and IgG(1) Ab levels were significantly lower following an i.p. injection of OVA (in CFA) in C57BL/6 mice orally given a single, high dose (25 mg) of OVA than in those orally given PBS. The oral tolerance was normally induced in Jalpha281(-/-) mice which lack Valpha14(+) NKT cells, suggesting that NKT cells are dispensable for induction of oral tolerance. Treatment with PGE(1) or PGE(2 )abrogated the oral tolerance in Jalpha281(+/+) mice; this abrogation was accompanied by an OVA-specific Th2-dominant response. The abrogation of oral tolerance by PGE(1 )was not evident in Jalpha281(-/-) mice. Treatment with PGE(1) induced an early increase in IL-4 production by liver NKT cells in normal mice and neutralization of the early IL-4 by administration of anti-IL-4 mAb abolished PGE(1)-induced abrogation of oral tolerance. These results suggest that liver NKT cells producing IL-4 are responsible for the down-regulation of oral tolerance that is caused by the PGE molecules.     

Ceramide synthase 2 facilitates S1P‐dependent egress of thymocytes into the circulation in mice

Well‐defined gradients of the lipid mediator sphingosine‐1‐phosphate (S1P) direct chemotactic egress of mature thymocytes from the thymus into the circulation. Although it is known that these gradients result from low S1P levels in the thymic parenchyma and high S1P concentrations at the exit sites and in the plasma, the biochemical mechanisms that regulate these differential S1P levels remain unclear. Several studies demonstrated that ceramide synthase 2 (Cers2) regulates the levels of the S1P precursor sphingosine. We, therefore, investigated whether Cers2 is involved in the regulation of S1P gradients and S1P‐dependent egress into the circulation. By analyzing Cers2‐deficient mice, we demonstrate that Cers2 limits the levels of S1P in thymus and blood to maintain functional S1P gradients that mediate thymocyte emigration into the circulation. This function is specific for Cers2, as we also show that Cers4 is not involved in the regulation of thymic egress. Our study identified Cers2 as an important regulator of S1P‐dependent thymic egress, and thus contributes to the understanding of how S1P gradients are maintained in vivo.     

Development in vitro of human CD4+ thymocytes into functionally mature Th2 cells. Exogenous interleukin-12 is required for priming thymocytes to produce both Th1 cytokines and interleukin-10

Fresh postnatal thymocyte cell suspensions were directly cloned under limiting dilution conditions with either phytohemagglutinin or toxic shock syndrome toxin-1 (TSST-1), a bacterial superantigen. Cultures contained allogenic irradiated feeder cells and interleukin (IL)-2, in the absence or presence of exogenous IL-4, interferon (IFN)-γ or IL-12. The resulting CD4⁺ T cell clones generated under these different experimental conditions were then analyzed for their ability to produce IL-2, IL-4, IL-5, IL-10, IFN-γ and tumor necrosis factor (TNF)-β in response to stimulation with phorbol 12-myristate 13-acetate (PMA)+anti-CD3 monoclonal antibody or PMA + ionomycin. Different from T cell clones generated from peripheral blood, virtually all CD4⁺ T cell clones generated from human thymocytes produced high concentrations of IL-2, IL-4 and IL-5, but no IFN-γ, TNF-β or IL-10. Moreover, after activation, these clones expressed on their surface membrane both CD30 and CD40 ligand, but not the product of lymphocyte activation gene (LAG)-3, and provided strong helper activity for IgE synthesis by allogeneic B cells. The Th2 cytokine pattern could not be modified by the addition of IFN-γ. However, upon addition of exogenous IL-12, the resulting CD4⁺ thymocyte clones produced TNF-β, IFN-γ, and IL-10 in addition to IL-4 and IL-5. These results suggest that CD4⁺ human thymocytes have the potential to develop into cells producing the Th2 cytokines IL-4 and IL-5, whereas the ability to produce both Th1 cytokines and IL-10 is acquired only after priming with IL-12.     

Haematopoietic antigen-presenting cells in the human thymic cortex: evidence for a role in selection and removal of apoptotic thymocytes

Only a small proportion of thymocytes survive T cell selection in the thymus and leave the thymus as mature T cells. The vast majority of thymocytes undergo cell death during selection, either due to failure to undergo positive selection on self peptide-MHC presented by thymic antigen presenting cells (APC) or due to negative selection. In the murine thymus it has been shown that most thymocytes that fail selection undergo apoptosis in the thymic cortex and are removed by cortical macrophages. However, it is unknown how apoptotic thymocytes are cleared from the cortex of the human thymus. Here we report the identification of antigen-presenting cells of haematopoietic origin (hAPCs) by expression of dendritic cell (DC) specific C-type lectin DC-SIGN (CD209) in the cortex of the human thymus, and show that these cells exhibit features of both immature DCs and macrophages. The analysis of cellular markers, in particular the expression of the molecular chaperone HLA-DM, on cortical hAPCs further suggests that these hAPCs may participate in selection of thymocytes in the cortex. Using in situ terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), we demonstrated that these cortical hAPCs are surrounded by apoptotic, TUNEL(+) thymocytes in situ. Futhermore, in situ immuno-cryo-electron microscopy suggests that cortical hAPCs take up and remove apoptotic thymocytes. Thus, DC-SIGN(+) hAPCs in the human thymic cortex appear to function in thymocyte selection and removal of apoptotic thymocytes from the thymic cortex.     

The GARP/Latent TGF‐β1 complex on Treg cells modulates the induction of peripherally derived Treg cells during oral tolerance

Treg cells can secrete latent TGF‐β1 (LTGF‐β1), but can also utilize an alternative pathway for transport and expression of LTGF‐β1 on the cell surface in which LTGF‐β1 is coupled to a distinct LTGF‐β binding protein termed glycoprotein A repetitions predominant (GARP)/LRRC32. The function of the GARP/LTGF‐β1 complex has remained elusive. Here, we examine in vivo the roles of GARP and TGF‐β1 in the induction of oral tolerance. When Foxp3^? OT‐II T cells were transferred to wild‐type recipient mice followed by OVA feeding, the conversion of Foxp3^? to Foxp3⁺ OT‐II cells was dependent on recipient Treg cells. Neutralization of IL‐2 in the recipient mice also abrogated this conversion. The GARP/LTGF‐β1 complex on recipient Treg cells, but not dendritic cell‐derived TGF‐β1, was required for efficient induction of Foxp3⁺ T cells and for the suppression of delayed hypersensitivity. Expression of the integrin αvβ8 by Treg cells (or T cells) in the recipients was dispensable for induction of Foxp3 expression. Transient depletion of the bacterial flora enhanced the development of oral tolerance by expanding Treg cells with enhanced expression of the GARP/LTGF‐β1 complex.     

NKT cell ligand alpha-galactosylceramide blocks the induction of oral tolerance by triggering dendritic cell maturation

NKT cells play contradictory roles in vivo, both regulating autoimmunity and activating immunity to intracellular pathogens and tumors. In this study, we studied the effect of NKT cell activation on the induction of systemic tolerance by oral administration of antigen. Administration of alpha-galactosylceramide (alphaGC) at the time of oral ovalbumin (OVA) feeding completely blocked the OVA-specific tolerance induced by both high- and low-dose regimens in BALB/c mice. In the mesenteric lymph nodes (MLN) of alphaGC-treated mice, the proliferation of OVA-specific T cells was greater than that seen in the MLN of vehicle-treated mice in vivo. The administration of alphaGC triggered the full maturation of mesenteric dendritic cells (DC), which were in turn responsible for the enhanced division of OVA-specific T cells in vitro. To further determine whether the costimulation provided by DC in alphaGC-treated mice was responsible for the reversal of oral tolerance in vivo, mice were given alphaGC together with anti-CD80 and anti-CD86 blocking Ab. OVA-specific systemic tolerance was restored in mice given the blocking Ab, even when they simultaneously received alphaGC. Therefore, oral tolerance can be reversed via costimulation by DC that have been triggered to fully mature by the administration of alphaGC.     

Galectin‐1 is essential for the induction of MOG35–55‐based intravenous tolerance in experimental autoimmune encephalomyelitis

In experimental autoimmune encephalomyelitis (EAE), intravenous (i.v.) injection of the antigen, myelin oligodendrocyte glycoprotein‐derived peptide, MOG_35–55, suppresses disease development, a phenomenon called i.v. tolerance. Galectin‐1, an endogenous glycan‐binding protein, is upregulated during autoimmune neuroinflammation and plays immunoregulatory roles by inducing tolerogenic dendritic cells (DCs) and IL‐10 producing regulatory type 1 T (Tr1) cells. To examine the role of galectin‐1 in i.v. tolerance, we administered MOG_35–55‐i.v. to wild‐type (WT) and galectin‐1 deficient (Lgals1^?/?) mice with ongoing EAE. MOG_35–55 suppressed disease in the WT, but not in the Lgals1^?/? mice. The numbers of Tr1 cells and Treg cells were increased in the CNS and periphery of tolerized WT mice. In contrast, Lgals1^?/? MOG‐i.v. mice had reduced numbers of Tr1 cells and Treg cells in the CNS and periphery, and reduced IL‐27, IL‐10, and TGF‐β1 expression in DCs in the periphery. DCs derived from i.v.‐tolerized WT mice suppressed disease when adoptively transferred into mice with ongoing EAE, whereas DCs from Lgals1^?/? MOG‐i.v. mice were not suppressive. These findings demonstrate that galectin‐1 is required for i.v. tolerance induction, likely via induction of tolerogenic DCs leading to enhanced development of Tr1 cells, Treg cells, and downregulation of proinflammatory responses.     

Identification and cellular distribution of the rat interleukin-2 receptor β chain: induction of the IL-2Rα−β+ phenotype by major histocompatibility complex class I recognition during T cell development in vivo and by T cell receptor stimulation of CD4+8+ immature thymocytes in vitro

A mouse monoclonal antibody (mAb) to the rat interleukin-2 receptor β (IL-2Rβ) chain was generated using IL-2Rβ cDNA-transfected mouse L929 cells for immunization and differential screening. This antibody, called L316, detects a cell surface protein with an apparent molecular mass of about 80 kDa. In peripheral lymphoid organs of young adult rats, IL-2Rβ expression is restricted to T and natural killer (NK) cells, and less than 10% of IL-2Rβ⁺ cells co-express the IL-2Rα chain. IL-2Rβ was detected on all NKRP-1^hi (NK⁻) and NKRP-1^lo cells (T-lineage cells of unknown function), most peripheral γδ T cells and on 30–40% of CD8 and 10% of CD4 αβ T cells. In the adult rat thymus, mAb L316 detects a small subset (about 1%) of predominantly IL-2Rα⁻ cells which express cell surface markers characteristic of mature T lymphocytes and contain a high proportion of CD4⁻8⁻ and CD4⁻8⁺ αβ T cell receptor (TCR)⁺ thymocytes. TCR-V usage suggests that major histocompatibility complex (MHC) class I plays a more important role than MHC class II in the selection of these cells. On immature CD4⁺8⁺ rat thymocytes, IL-2Rβ cell surface expression is readily induced by TCR stimulation in vitro, supporting the idea that in vivo, the IL-2Rβ⁺ phenotype is the result of TCR engagement during thymic selection.     

腺病毒载体介导的CTLA4-Ig基因转移促进异基因小鼠皮肤移植耐受

目的　探讨CTLA4 Ig重组腺病毒 (AdCTLA4 Ig)促进“脾细胞 (spleencells ,SP) 环磷酰胺 (cyclophosphamide ,CP)”系统诱导移植耐受的作用及其机制。方法　BALB c(H 2 d)小鼠经尾静脉注射C57BL 6(H 2 b,B6)小鼠脾细胞和AdCTLA4 Ig颗粒 ,48h后腹腔注射环磷酰胺 ,并同天进行皮肤移植 ,于耐受 2 5d时对受体小鼠进行混合淋巴细胞反应 (mixedlymphocytereaction ,MLR)、迟发型超敏反应 (delayedtypehypersensitivity ,DTH)等耐受状态的检查。结果　B6小鼠的皮肤移植物在耐受的BALB c小鼠中存活期特异延长。MLR和DTH检验证明BALB c小鼠对B6小鼠的脾细胞产生特异性耐受 ,对无关第三者ICR小鼠的脾细胞仍表现出强烈免疫应答。结论　AdCTLA4 Ig颗粒可以明显促进“细胞 环磷酰胺”诱导的异基因皮肤移植耐受 ;克隆排除和克隆无能是耐受诱导的主要因素     

Acquired immunological tolerance in aged mice III. The contribution of lymphoid cells and their environments to the age related resistance to tolerance induction

Whether lymphoid cells or their environment are responsible for the decreased tolerogen sensitivity of aged mice was examined using an adoptive transfer system. Bone marrow cells from old (24 months), middle aged (12 months) and young adult mice (2 months) were equally sensitive to tolerance induction with deaggregated human immunoglobulin (DHGG) when they were transplanted into young lethally irradiated syngeneic hosts. Adoptively transferred splenocytes also showed no age related difference in tolerogen sensitivity. Thus, the age related difference seen in the intact animal is due largely to environmental factors acting on lymphoid cells in the aged animal. The role of lipopolysaccharide (LPS) as one such environmental factor affecting tolerance induction was investigated. LPS administered to aged mice produced greater polyclonal B cell activation and autoantibody formation than it did in young animals. When LPS was administered shortly after DHGG injection it converted the tolerogen to an immunogen with greater efficiency in aged animals.     

Fonsecaea pedrosoi‐induced Th17‐cell differentiation in mice is fostered by Dectin‐2 and suppressed by Mincle recognition

Chromoblastomycosis is a chronic skin infection caused by the pigmented saprophytic mould Fonsecaea pedrosoi. Chronicity of infection can be broken by a coordinated innate recognition of the spores by pattern recognition receptors. While Mincle signaling via the Syk/Card9 pathway is required for fungal recognition by host cells, it is not sufficient for host control. Exogenously applied TLR agonists are necessary to promote the induction of proinflammatory cytokines and clearance of infection in vivo. Here, we investigated whether costimulation by TLR agonists fosters the development of adaptive immune responses, by examining the development of fungus‐specific T cells. Subcutaneous infection of mice with F. pedrosoi spores induced the activation, expansion, and differentiation of Ag‐specific CD4⁺ T cells but TLR costimulation did not further augment these T‐cell responses. The Dectin‐2/FcRγ/Card9 signaling pathway promoted the differentiation of fungus‐specific CD4⁺ T cells into Th17 cells, whereas Mincle inhibited the development of this T‐helper subset in infected mice. These results indicate differential roles for Dectin‐2 and Mincle in the generation of adaptive immune responses to F. pedrosoi infection.     

Immune tolerance induction to enzyme-replacement therapy by co-administration of short-term, low-dose methotrexate in a murine Pompe disease model

Clinical investigations of recombinant human acid alpha-glucosidase for the treatment of Pompe disease often reveal the appearance of therapy-specific antibodies. These antibodies could potentially interfere with recombinant human acid alpha-glucosidase efficacy and induce immunological consequences. Several immunosuppressive agents, including methotrexate, mycophenolate mofetil and cyclosporin A with azathioprine, were evaluated for their potential to induce immune tolerance to recombinant human acid alpha-glucosidase. Methotrexate was the only agent that reduced recombinant human acid alpha-glucosidase-specific antibody responses in acid alpha-glucosidase knock-out mice. A 3-week, low-dose methotrexate regimen controlled recombinant human acid alpha-glucosidase-specific antibody levels throughout 8 months of weekly recombinant human acid alpha-glucosidase treatment. The success of this methotrexate regimen appears to require methotrexate administration within the first 24 h of recombinant human acid alpha-glucosidase treatment. In an attempt to understand the benefit of methotrexate within the first day of recombinant human acid alpha-glucosidase administration, the immune response 24 h following intravenous recombinant human acid alpha-glucosidase treatment was investigated. A consistent expansion of peritoneal B1 B cells was observed. Control over this B1 B cell response may be part of the complex mechanism of action of methotrexate-induced immune tolerance.