Thymocyte/Splenocyte-Derived CD4+CD25+Treg Stimulated by Anti-CD200R2 Derived Dendritic Cells Suppress Mixed Leukocyte Cultures and Skin Graft Rejection

IL-35 promotes CD4+Foxp3+ Tregs and inhibits atherosclerosis via maintaining CCR5-amplified Treg-suppressive mechanisms

Tregs play vital roles in suppressing atherogenesis. Pathological conditions reshape Tregs and increase Treg-weakening plasticity. It remains unclear how Tregs preserve their function and how Tregs switch into alternative phenotypes in the environment of atherosclerosis. In this study, we observed a great induction of CD4⁺Foxp3⁺ Tregs in the spleen and aorta of ApoE^–/– mice, accompanied by a significant increase of plasma IL-35 levels. To determine if IL-35 devotes its role in the rise of Tregs, we generated IL-35 subunit P35–deficient (IL-35P35–deficient) mice on an ApoE^–/– background and found Treg reduction in the spleen and aorta compared with ApoE^–/– controls. In addition, our RNA sequencing data show the elevation of a set of chemokine receptor transcripts in the ApoE^–/– Tregs, and we have validated higher CCR5 expression in ApoE^–/– Tregs in the presence of IL-35 than in the absence of IL-35. Furthermore, we observed that CCR5⁺ Tregs in ApoE^–/– have lower Treg-weakening AKT-mTOR signaling, higher expression of inhibitory checkpoint receptors TIGIT and PD-1, and higher expression of IL-10 compared with WT CCR5⁺ Tregs. In conclusion, IL-35 counteracts hyperlipidemia in maintaining Treg-suppressive function by increasing 3 CCR5-amplified mechanisms, including Treg migration, inhibition of Treg weakening AKT-mTOR signaling, and promotion of TIGIT and PD-1 signaling.

Forkhead-box transcription factor 1 affects the apoptosis of natural regulatory T cells by controlling Aven expression

Background

Regulatory T (Treg) cells play important roles in autoimmune diseases, cancer, and organ transplantation. Forkhead box protein o1 (Foxo1) and IL-7Rα(CD127) are closely related to the homeostasis of Treg cells. However, the mechanism underlying Treg proliferation and activation remains unclear. Here, we evaluated how the over-expression of Foxo1 affects Treg cell proliferation via intracellular signaling. nTreg cells were transfected separately with Foxo1 and Aven small-interfering RNA (siRNA) or over-expression plasmid. The expression of signaling pathway genes and CD127 was confirmed using RT-qPCR and western blot analysis. The expression of cell surface molecules and apoptosis was confirmed by Flow Cytometry 3-(4, 5-Dimethylthiazol-2-yl) 2,5- diphenyltetrazolium bromide for cell proliferation assays.

Results

Foxo1 strengthened the proliferative ability of Treg cells by activating IL-7/CD127 signaling. In addition, Foxo1 suppressed Treg cell apoptosis by regulating Aven expression.

Conclusions

The results in this study indicated that Foxo1 is a positive regulatory factor for the proliferation and activity of Treg cells. Foxo1 might be a potential target for the activation of nTreg cells in vivo and in vitro.

Molecular Cross-Talk at the Feto-Maternal Interface

Molecular cross-talk at the feto-maternal interface occurs between many different cell types, including uterine leukocytes, extravillous trophoblast cells, and uterine spiral arteries, is essential for the establishment and maintenance of pregnancy. This review concentrates on human pregnancy and examines three main areas in which cross-talk occurs; immune tolerance, regulation of extravillous trophoblast invasion, and remodeling of the uterine spiral arteries.

Anti-CD200R2, anti-IL-9, anti-IL-35, or anti-TGF-β abolishes increased graft survival and Treg induction induced in cromolyn-treated CD200R1KO.CD200tg mice

BACKGROUND

Rejection is associated with early degranulation (≥80%) of graft-infiltrating CD200R1 receptor-positive mast cells (MCs). Survival is increased, and MC degranulation is decreased, in CD200 mice but not in CD200R1KO mice. CD200 engagement of CD200R2 (not present on MCs) alters dendritic cell differentiation and enhances induction of Foxp3 regulatory T cells (Tregs). We investigated whether attenuation of MC degranulation by sodium cromoglycate allowed CD200 to increase survival in CD200R1KO mice.

METHODS

C57BL/6 control, CD200R1KO, CD200, or CD200R1KO.CD200 mice received BALB/c grafts with or without treatment with cromoglycate. Survival was monitored daily from day 10, with mixed lymphocyte culture responses measured on day 14 or 21 and graft immunohistology performed on day 14.

RESULTS

Decreased MC degranulation and increased graft Foxp3 Treg infiltration/survival occurred in CD200 mice and in CD200-treated control mice or CD200R1KO.CD200 mice receiving cromoglycate. Neutralizing anti-CD200 or anti-CD200R1/R2 monoclonal antibody caused graft rejection, as did anti-interleukin (IL)-9, anti-IL-35, or anti-transforming growth factor-β antibodies, with the latter also decreasing graft-infiltrating Tregs.

CONCLUSION

These data imply a coordinated effect of MCs and Tregs on increased graft survival induced by CD200, with a critical role for IL-9, IL-35, and transforming growth factor-β in the development/function of Tregs.

Persistence of gene expression profile in CD200 transgenic skin allografts is associated with graft survival on retransplantation to normal recipients

BACKGROUND

Expression of CD200 increases allograft survival by suppressing inflammation and acquired immunity. Increased allograft survival in transgenic mice overexpressing CD200 (CD200) occurs in association with increased intragraft expression of messenger RNAs (mRNAs) for genes associated with altered T-cell differentiation.

METHODS

We investigated whether donor CD200 BL/6 skin grafts taken from primary control or CD200 recipient BALB/c mice persisted after retransplantation at 14 days to control (nontransgenic) secondary BALB/c recipients, with or without transfer of splenocytes from autologous primary recipients. Splenocytes from primary and secondary recipients were analyzed 14 days after grafting, using in vitro mixed leukocyte cultures (MLCs) incubated with irradiated BL/6 (or third-party C3H/HeJ) stimulator cells and assayed for antigen-specific cytotoxic T lymphocyte. Cytotoxic T lymphocyte responses were correlated with changes in the mRNA gene expression profile observed in the skin tissue harvested from primary or secondary recipients on day 14 after grafting, using real-time polymerase chain reaction to compare quantitative mRNA expression in the graft tissue of primary/secondary recipients.

RESULTS AND CONCLUSIONS

Adoptive transfer of tolerance in MLC to BL/6 grafts was most evident when both skin and splenocytes were transferred from primary BALB/c recipients, although there was an attenuation of MLC responses after graft transfer alone. Adoptive transfer of tolerance occurred concomitant with persistent overexpression of genes encoding Foxp3, transforming growth factor β, interleukin 10, and PD-1 (and PD-L1/PD-L2) in tolerant skin grafts and increased expression of mRNAs for indoleamine 2,3-dioxygenase and the subunits encoding interleukin 35. Infusion of anti-CD4 or anti-transforming growth factor β to secondary recipients on retransplantation abolished increased graft survival, suggesting the importance of each to the final outcome.

Aberrant CD200/CD200R1 expression and function in systemic lupus erythematosus contributes to abnormal T-cell responsiveness and dendritic cell activity

INTRODUCTION

CD200 is a type I transmembrane glycoprotein that can regulate the activation threshold of inflammatory immune responses, polarize cytokine production, and maintain immune homeostasis. We therefore evaluated the functional status of CD200/CD200 receptor 1 (CD200R1) interactions in subjects with systemic lupus erythematosus (SLE).

METHODS

Serum CD200 level was detected by ELISA. The expression of CD200/CD200R1 by CD4+ T cells and dendritic cells (DCs) was examined by flow cytometry, and then compared between SLE patients and healthy controls. Peripheral blood mononuclear cells were stained with carboxyfluorescein diacetate succinimidyl ester and annexin V/propidium iodide for evaluation of the effect of CD200 on cell proliferation and apoptosis. In addition, the effect of CD200 on DC function was determined by transwell migration assay as well as by measurement of binding and phagocytosis of apoptotic cells.

RESULTS

In SLE patients, the number of CD200+ cells and the level of soluble CD200 were significantly higher than in healthy controls, whereas the expression of CD200R1 by CD4+ T cells and DCs was decreased. Furthermore, the increased CD200 expression by early apoptotic cells contributed to their diminished binding and phagocytosis by DCs in SLE. Importantly, the engagement of CD200 receptor on CD4+ T cells with CD200-Fc fusion protein in vitro reduced the differentiation of T-helper type 17 cells and reversed the defective induction of CD4+CD25highFoxP3+ T cells by transforming growth factor beta in SLE patients. Conversely, blockade of CD200-CD200R1 interaction with anti-CD200R1 antibody promoted CD4+ T-cell proliferation.

CONCLUSION

CD200 and CD200R1 expression and function are abnormal in SLE and may contribute to the immunologic abnormalities in SLE.

Gene expression analysis of dendritic cells that prevent diabetes in NOD mice: analysis of chemokines and costimulatory molecules

We have demonstrated previously that BM-derived DCs can prevent diabetes development and halt progression of insulitis in NOD mice, the mouse model of type 1 diabetes. The DC population that was most effective in this therapy had a mature phenotype, expressed high levels of costimulatory molecules, and secreted low levels of IL-12p70. The protective DC therapy induced Treg and Th2 cells in vitro and in vivo. Microarray analysis of therapeutic and nontherapeutic DC populations revealed differences in the expression of OX40L, CD200, Ym-1, CCL2, and CCL5, which could play important roles in the observed DC-mediated therapy. The unique pattern of costimulatory molecules and chemokines expressed by the therapeutic DCs was confirmed by flow cytometry and ELISA. Using a novel cell-labeling and (19)F NMR, we observed that the chemokines secreted by the therapeutic DCs altered the migration of diabetogenic Th1 cells in vivo and attracted Th2 cells. These results suggest that the therapeutic function of DCs is mediated by a combination of costimulatory and chemokine properties that results in the attraction of diabetogenic Th1 and the induction of Th2 and/or Treg differentiation.

Role of CD200 expression in regulation of metastasis of EMT6 tumor cells in mice

Previous studies have confirmed that levels of CD200 expression on the cells of the transplantable EMT6 mouse breast cancer line are increased markedly during growth in immunocompetent mice, unlike the persistent low levels of expression observed in NOD-SCID.IL-2(γr-/-) mice or mice with generalized over-expression of a CD200 transgene (CD200(tg) mice). Faster tumor growth occurs in both of these latter mice, with decreased evidence for a host immune reaction in lymph nodes draining the tumor (DLN). We now report evidence for a role for CD200 expression (by the host and/or tumor cells) in increased seeding of tumor cells to DLN in immunocompromised (CD200(tg) or NOD-SCID.IL-2(γr-/-)) vs immunocompetent mice, by limiting dilution cloning of tumor cells from DLN (vs contralateral lymph nodes, CLN), using control and GFP-tagged EMT6 cells. Neutralization of expressed CD200 by anti-CD200mAbs decreased the tumor metastasis at the same time as increasing detection of cytotoxic anti-tumor immune cells in DLN. Infusion of either anti-CD4 to deplete T-effector cells, or anti-TGFβ antibody, increased metastasis to DLN, as did indeed the infusion of EMT6 cells selected for the loss of TGFβRII expression. It is concluded that the increased CD200 expression by breast cancer cells (and/or host tissue) may be an important variable involved in determining the risk of metastasis.

Potent immunosuppression by a bivalent molecule binding to CD200R and TGF-betaR

BACKGROUND

The novel immunosuppressive molecule, CD200, has been reported to induce immunoregulation after interaction with its receptor(s), CD200R(s), in part at least through augmented induction of regulatory T-cell populations. Independent studies have also described increased expression of indoleamine-2,3-dioxygenase after CD200R triggering, whereas others have provided evidence that TGF-beta is important for the induction or function of many populations of regulatory T cells. We have asked whether a hybrid molecule in which a soluble fusion protein containing CD200, CD200Fc, was linked to TGF-beta through a glycine linker (Gly6) functions as a superior immunosuppressant molecule when compared with CD200Fc or TGF-beta alone, or in combination.

METHODS

The hybrid molecule CD200FcGly6TGF-beta was expressed by transient transfection in CHO cells and purified over a protein A column. Functional activity of this and recombinant CD200Fc or TGF-beta alone were assessed in mixed leukocyte cultures (MLCs) and in skin graft rejection in vivo.

RESULTS

Immunosuppression mediated by CD200FcGly6TGF-beta is dependent on both functional CD200 and TGF-beta moieties, as indicated by inhibition of suppression using anti-CD200 or anti-TGF-beta antibodies. Using as responder cells, using antigen-presenting cell from mice with a deletion of the CD200R gene and responder T cells from mice with siRNA-mediated suppression of expression of the TGF-betaII receptor, we show that suppression follows binding to TGF-betaRII on T cells, and CD200R1 on antigen-presenting cells. Indoleamine-2,3-dioxygenase inhibitors did not attenuate suppression by CD200FcGly6TGF-beta.

CONCLUSION

CD200FcGly6TGF-beta is a potent immunosuppressant in vivo and in vitro.

How tolerogenic dendritic cells induce regulatory T cells

Since their discovery by Steinman and Cohn in 1973, dendritic cells (DCs) have become increasingly recognized for their crucial role as regulators of innate and adaptive immunity. DCs are exquisitely adept at acquiring, processing, and presenting antigens to T cells. They also adjust the context (and hence the outcome) of antigen presentation in response to a plethora of environmental inputs that signal the occurrence of pathogens or tissue damage. Such signals generally boost DC maturation, which promotes their migration from peripheral tissues into and within secondary lymphoid organs and their capacity to induce and regulate effector T cell responses. Conversely, more recent observations indicate that DCs are also crucial to ensure immunological peace. Indeed, DCs constantly present innocuous self- and nonself-antigens in a fashion that promotes tolerance, at least in part, through the control of regulatory T cells (Tregs). Tregs are specialized T cells that exert their immunosuppressive function through a variety of mechanisms affecting both DCs and effector cells. Here, we review recent advances in our understanding of the relationship between tolerogenic DCs and Tregs.

Expression of a CD200 transgene is necessary for induction but not maintenance of tolerance to cardiac and skin allografts

CD200, a type 2 transmembrane molecule of the Ig supergene family, can induce immunosuppression in a number of biological systems, as well as promote increased graft acceptance, following binding to its receptors (CD200Rs). Skin and cardiac allograft acceptance are readily induced in transgenic mice overexpressing CD200 under control of a doxycycline-inducible promoter, both of which are associated with increased intragraft expression of mRNAs for a number of genes associated with altered T cell subset differentiation, including GATA-3, type 2 cytokines (IL-4, IL-13), GITR, and Foxp3. Interestingly, some 12-15 days after grafting, induction of transgenic CD200 expression can be stopped (by doxycycline withdrawal), without obvious significant effect on graft survival. However, neutralization of all CD200 expression (including endogenous CD200 expression) by anti-CD200 mAb caused graft loss, as did introduction of an acute inflammatory stimulus (LPS, 10 microg/mouse, delivered by i.p. injection). We conclude that even with apparently stably accepted tissue allografts, disruption of the immunoregulatory balance by an intense inflammatory stimulus can cause graft loss.

Induction of tolerogenic vs immunogenic dendritic cells (DCs) in the presence of GM-CSF is regulated by the strength of signaling from monophosphoryl lipid A (MPLA) in association with glutathione and fetal hemoglobin gamma-chain

Previous studies showed a fetal sheep liver extract (FSLE), in association with monophosphoryl lipid A, MPLA (a bioactive component of lipid A of LPS), could interact to induce the development of dendritic cells (DCs) which regulated production of Foxp3+ Treg. This interaction was associated with an altered gene expression both of distinct subsets of TLRs and of CD200Rs. Prior studies had suggested that major interacting components within FSLE were gamma-chain of fetal hemoglobin (Hgbgamma) and glutathione (GSH). We investigated whether differentiation/maturation of DCs in vitro in the presence of either GM-CSF or Flt3L to produce preferentially either immunogenic or tolerogenic DCs was itself controlled by an interaction between MPLA, GSH and Hgbgamma. At low (approximately 10 microg/ml) Hgbgamma concentrations, DCs developing in culture with GSH and MPLA produced optimal stimulation of allogeneic CTL cell responses in vitro (and enhanced skin graft rejection in vivo). At higher concentrations (>40 microg/ml Hgbgamma) and equivalent concentrations of MPLA and GSH, the DCs induce populations of Treg which can suppress the induction of allogeneic CTL and graft rejection in vivo. These different populations of DCs express different patterns of mRNAs for the CD200R family. Addition of anti-TLR or anti-MD-1 mAbs to DCs developing in this mixture (Hgbgamma+GSH+MPLA), suggests that one effect of (GSH+Hgbgamma) on MPLA stimulation may involve altered signaling through TLR4.

Control of viral immunoinflammatory lesions by manipulating CD200:CD200 receptor interaction

Previous investigators have demonstrated that the CD200:Fc that engages CD200 receptors (CD200R) shows promise as an immunosuppressive and anti-inflammatory reagent. In this report, we evaluate the use of CD200:Fc to control a viral induced immunoinflammatory reactions caused by ocular infection with herpes simplex virus (HSV). Our results show that HSV infection causes invasion of the cornea by CD200R(+) cells most of which were CD11b(+) cells. Systemic administration of CD200:Fc, starting at 5 days post infection (p.i.), resulted in diminished incidence and severity of lesions compared to controls. Splenocytes isolated from treated animals showed reduced IL-12 and IFN-gamma responses when stimulated in vitro and ex vivo. Treated animals also had increased frequencies of Foxp3(+) regulatory T cells in both the cornea and draining lymph nodes perhaps contributing also to the control of the corneal immunopathology. Treatment of animals in the chronic phase was minimally effective. Our data are the first to demonstrate the use of CD200R stimulation to control lesion severity in a viral induced inflammatory disease.

Resolving the conundrum of islet transplantation by linking metabolic dysregulation, inflammation, and immune regulation

Although type 1 diabetes cannot be prevented or reversed, replacement of insulin production by transplantation of the pancreas or pancreatic islets represents a definitive solution. At present, transplantation can restore euglycemia, but this restoration is short-lived, requires islets from multiple donors, and necessitates lifelong immunosuppression. An emerging paradigm in transplantation and autoimmunity indicates that systemic inflammation contributes to tissue injury while disrupting immune tolerance. We identify multiple barriers to successful islet transplantation, each of which either contributes to the inflammatory state or is augmented by it. To optimize islet transplantation for diabetes reversal, we suggest that targeting these interacting barriers and the accompanying inflammation may represent an improved approach to achieve successful clinical islet transplantation by enhancing islet survival, regeneration or neogenesis potential, and tolerance induction. Overall, we consider the proinflammatory effects of important technical, immunological, and metabolic barriers including: 1) islet isolation and transplantation, including selection of implantation site; 2) recurrent autoimmunity, alloimmune rejection, and unique features of the autoimmune-prone immune system; and 3) the deranged metabolism of the islet transplant recipient. Consideration of these themes reveals that each is interrelated to and exacerbated by the other and that this connection is mediated by a systemic inflammatory state. This inflammatory state may form the central barrier to successful islet transplantation. Overall, there remains substantial promise in islet transplantation with several avenues of ongoing promising research. This review focuses on interactions between the technical, immunological, and metabolic barriers that must be overcome to optimize the success of this important therapeutic approach.

Mice lacking CD200R1 show absence of suppression of lipopolysaccharide-induced tumor necrosis factor-alpha and mixed leukocyte culture responses by CD200

BACKGROUND

CD200:CD200R interactions deliver immunoregulatory signals. A family of CD200Rs (CD200R1-5) has been described, and engagement of CD200R1 by its ligand CD200 suppresses LPS-induced macrophage cytokine production, decreases alloimmune responses in vivo and in vitro, and suppresses collagen-induced arthritis.

METHODS

We generated C57BL/6 mice lacking the genomic exons encoding the extracellular domains of the CD200R1 molecule using transformation of ES cells and explored cell subtypes and immune responses in these mice.

RESULTS

Myeloid cells/splenocytes from CD200R1(-/-) mice were not stained in FACS by anti-CD200R1 mAb. Stimulation of splenic tumor necrosis factor-alpha production by lipopolysaccharide was enhanced relative to control (+/+) mice and was not suppressed by addition of exogenous CD200Fc. Modulation of alloreactivity in mixed leukocyte cultures by CD200Fc depended upon CD200R1+ stimulatory cells, although maximal immunoregulation by CD200Fc occurred only when CD200R1+ T responder cells also were used. CD200Fc failed to suppress graft rejection in CD200R1(-/-) mice.

CONCLUSION

CD200:CD200R1 plays an immunoregulatory role in vivo.

Dendritic cells: key to fetal tolerance?

Pregnancy is a unique event in which a fetus, despite being genetically and immunologically different from the mother (a hemi-allograft), develops in the uterus. Successful pregnancy implies avoidance of rejection by the maternal immune system. Fetal and maternal immune cells come into direct contact at the decidua, which is a highly specialized mucous membrane that plays a key role in fetal tolerance. Uterine dendritic cells (DC) within the decidua have been implicated in pregnancy maintenance. DC serve as antigen-presenting cells with the unique ability to induce primary immune responses. Just as lymphocytes comprise different subsets, DC subsets have been identified that differentially control lymphocyte function. DC may also act to induce immunologic tolerance and regulation of T cell-mediated immunity. Current understanding of DC immunobiology within the context of mammalian fetal-maternal tolerance is reviewed and discussed herein.