Littérature scientifique sur le sujet « Dentric, NKT cells, regulatory T cells, tolerance »

Abstract Administration of subtoxic doses of mercuric chloride to genetically susceptible mice induces an autoimmune syndrome with anti-nucleolar antibody production, polyclonal B cell activation and nephritis. We investigated the role of natural killer T (NKT) cells in the modulation of this autoimmune model. Activation of NKT cells by synthetic variants of α-galactosyl ceramide worsened manifestations of mercury-induced disease. Exposure to heat killed Sphingomonas capsulata which contains NKT cell ligands in its cell wall also worsened disease manifestations. We used this model to further elucidate the interplay between NKT cells and other immune cell types. Mice can be tolerized to mercuric chloride by administration of a very low dose of the chemical. Tolerance establishment requires antigen presentation in the steady state by dendritic cells to elicit CD4+ CD25+ regulatory T cells. Activation of NKT cells by a synthetic ligand was able to completely prevent induction, but was by itself unable to break already established tolerance. Dual stimuli (NKT cell activation and TLR 9 ligation) were required to break established tolerance. This study demonstrates that NKT cell activation worsens chemically- induced autoimmunity and also shows a synergy between NKT and TLR ligands in potentiating disease manifestations. Supported by a NIH grant.

Abstract Regulatory T cells can be dramatically boosted in vivo by stimulation with a complex of IL-2 and an IL-2 mAb (JES6-1). The swift 15-fold expansion creates a tolerogenic environment that significantly perturbs autoimmunity and allograft rejection. We recently observed that IL-2/mAb treatment also expands Natural Killer T (NKT) cells, a glycolipid-specific, CD1d-restricted T cell lineage implicated in both regulatory and immunogenic responses. Interestingly, the phenotype of the IL-2/mAb-expanded NKT cells differed from those expanded with the prototypic NKT ligand, alpha-galactosylceramide (α−GalCer). The IL-2/mAb-expanded NKT cells were relatively stable and contracted slowly. They were hyper-functional, with the capacity to rapidly produce cytokines for several days after stimulation. In comparison, α−GalCer stimulated NKT cells characteristically produce a quick burst of Th1 and Th2 cytokines, an ability that then dramatically declines along with their number in the following days. Interestingly, the range of cytokines produced by IL-2/mAb-NKT cells was broad and included not only IFNγ and IL-4, but also significantly high amounts of IL-10 and IL-13. IL-17, however, was notably reduced. These variations in cytokine production appeared to alter the phenotype of dendritic cells in their vicinity. These data suggest an alternate approach to the expansion of NKT cells, specifically within the context of a regulatory milieu that may be appropriate for tolerance induction.

Every year individuals receive hematopoietic stem cell transplantation (HSCT) to eradicate malignant and nonmalignant disease. The immunobiology of allotransplantation is an area of ongoing discovery, from the recipient's conditioning treatment prior to the transplant to the donor cell populations responsible for engraftment, graft-versus-host disease, and graft-versus-tumor effect. In this review, we focus on donor-type immunoregulatory T cells, namely, natural killer T cells (NKT) and regulatory T cells (Treg), and their current and potential roles in tolerance induction after allogeneic HSCT.

Abstract NKT cells are mainly located in the liver in mice. The role of liver inherent NKT cells are still unclear. Method In this study, we employed mouse orthotopic liver transplantation and heterotopic heart transplantation models to critical examine the role of liver NKT cells in liver and peripheral tolerance induction. Results NKT cells were increased in the tolerated liver grafts which expressed higher levels of CD95L and PD-L1, while the CD4+CD25+Foxp3+ regulatory T cells (Treg) were markedly increased in the both liver and spleen at day 7 post transplantation. The heart allograft survival were prolonged significantly in the recipient which accepted donor spleen cells by portal vein (p.v.) injection in contract to the recipient which received the donor spleen cells by tail vein (i.v.) injection. In vitro immunological assay revealed that the number of NKT cells in the liver was increased and Treg were increased in both liver and spleen from the p.v. treated mice significantly. The IL-2 expression was decreased, IL-4 and IL-10 were increased. Further, significantly increased IL-4, IL-10, and IFN-γ production was detected from liver NPCs under aGalCer stimulation. Conclusion NKT cells are important to liver transplant tolerance induction, appear to play a key role in down regulation of peripheral immune responses and facilitate CD4+CD25+Foxp3+ Treg induction.

Abstract The liver has been demonstrated in many models to favor the induction of peripheral tolerance. The mechanisms mediating this phenomenon remain undefined. In this study, we delivered the C3H spleen cells (SCs) into the B6 liver through the portal vein (p.v.) in contrast to tail vein (i.v.) injection to characterize the liver leukocytes by flow cytometry and their function by MLR, ELISPOT, and immunohistochemistry assays. Heterotopic heart transplantation was performed from C3H donors to B6 recipients at day 7 post-treatment. The TCRαβ +NK1.1+ cells (NKT) were significantly increased in the liver, and CD4+CD25+Foxp3+ regulatory T cells (Treg) were markedly increased in the both liver and spleen after p.v. but not i.v. injection of C3H SCs. The proliferative activity of T cells from the p.v. treated mice was significantly suppressed and IL-2 was decreased, IL-4 and IL-10 were increased in vitro, suggesting that the role of the Treg may contribute to these responses. Further, significantly increased IL-4, IL-10, and IFN-γ production was detected from liver nonparenchymal cells under αGalCer stimulation, suggesting the role of liver NKT cells. Heart allograft survival was significantly prolonged in the C3H SCs p.v. treated recipients than in the i.v. treated recipients. Therefore, the liver can serve as a site of systemic tolerance induction. Both NKT cells and CD4+CD25+Foxp3+ Treg appear to be involved in the regulation of peripheral immune responses after antigen immunization of the liver.

Abstract Graft-versus-host disease (GVHD) is a significant complication in hematopoietic stem cell transplantation (SCT). On the other hand, graft-versus-tumor (GVT) effect has been known to be concerned with the prevention of relapses in various hematological or non-hematological malignant disorders. The regulation of GVHD without suppressing GVT effect is a pivotal role in the success of hematopoietic SCT. Recently CD4+CD25+regulatory T cells have been recognized to regulate the maintenance of self-tolerance, and associate with several autoimmune diseases. In transplant immunity, CD4+CD25+regulatory T cells have been reported to regulate GVHD without suppressing GVT effect in several animal studies. Natural killer T (NKT) like cells also have been recognized to associated with the maintenance of self-tolerance by inducing CD4+CD25+regulatory T cells through the production of IL-2. In this study, we examined the roles of CD4+CD25+regulatory T cells and NKT like cells in cases underwent hematopoietic SCT. Blood samples from patients underwent SCT in our institution during past 3 years (7 months through 26 years of age, n =19) were obtained every two weeks until day 90 after SCT. Primary disorders of patients were non-malignant hematological disease such as aplastic anemia (n=3), chronic granulomatous disease (n=8) and malignant disease such as leukemia (n=5), and solid tumors (n=3). Pre-conditioning regimens used in this study were myeloablative regimens in 10 cases and reduced intensity regimens in 9 cases, respectively. The frequencies of CD4+CD25+regulatory T cells were assessed by the expression of CD4 and CD25, and those of NKT like cells were assessed by the expression of CD3, CD16, and CD56 using flow cytometry. The mRNA expression of FOXP3 in purified CD4+CD25+regulatory T cells were determined by quantitative real-time PCR method. In 13 patients who had none or Grade 1 acute GVHD, the frequency of CD4+CD25+regulatory T cells in CD4+ T cells was increased up to 25–90% at early period after SCT and normalized below 20% after day 45 post SCT. On the other hand, four of 6 patients who had acute GVHD (more than Grade 2) showed that the frequency of CD4+CD25+regulatory T cells in CD4+ T cells persisted below 20%. In other one patient, the development of acute GVHD (Grade 2) was associated with decreasing the frequency of CD4+CD25+regulatory T cells (30 to 10%) and the recovery of GVHD was found with increasing CD4+CD25+regulatory T cells (10 to 30%). The mean frequency of CD4+CD25+regulatory T cells in CD4+ T cells on day 15 after SCT was 44% in patients without GVHD and 21% in patients with GVHD (p=0.07). No difference in the expressions of FOXP3 mRNA in purified CD4+CD25+regulatory T cells was noted between patients with GVHD and those without GVHD. The reconstitution pattern of CD3+CD16+CD56+ NKT like cells after SCT was not associated with the development of GVHD. These results suggest that the development of acute GVHD may be strongly associated with the reconstitution of donor derived CD4+CD25+regulatory T cells in CD4+ T cells. The measurement of CD4+CD25+regulatory T cells in CD4+ T cells might lead to the early diagnosis and the prevention of acute GVHD. (Future studies will be needed to examine the association between the frequency of regulatory T cells and GVT effect.)

Abstract We have previously shown that the liver plays an important role in oral tolerance induction. The liver can transfer tolerance to OVA from OVA fed mice to naïve mice. In this study we employed an oral tolerance model by OVA feeding to further explore the mechanisms underlying the role of the liver in oral tolerance induction. OVA feeding, either high dose or low dose, expanded NKT cells in the liver which expressed higher levels of CD95L and PD-L1, a moderate level of PD-1 on the surface, peaked at the 2nd dose feeding in the high dose group and at the 3rd dose feeding in the low dose group. The Foxp3+CD4+CD25+ T regulatory cells (Treg) showed a slight increase in the livers and spleens in the low-fed group, but increased only in the livers in the high-fed group. OVA feeding inhibited NKT cell linked T cell proliferation in both low and high dose fed livers and spleens. Elispot assay revealed an increase in IL-4 and IFN-γ production in the low-fed mice, but increased IL-10 in the high-fed mice. Moreover, the DTH responses to OVA stimulation were increased markedly in the NKT−/− mice with high dose feeding, but showed no significant change in the PD-L1−/− mice compared to that in WT mice. Our results indicate that the liver NKT cells are important in OVA-induced oral tolerance, particularly in high dose feeding. The function of NKT cell appears to depend on CD95L and CD4+CD25+Treg, but not on the PD-1/PD-L1 pathway. IL-10 appears dominant in high dose feeding, while IL-4 and IFN-γ show importance in low dose feeding.

Abstract Regulatory T (Treg) cells, a distinct lineage of T cells, are required to maintain immunological tolerance. However, the molecular mechanism(s) by which Treg cells modulate tumor growth and clearance needs further investigation. Thus, the goal of this study is to analyze the absolute number and role of Treg cells during tumorigenesis. To achieve this goal, tumor induction studies were performed on C57/B6 mice using transgenic adenocarcinoma mouse prostate (TRAMP) cell lines C1, C2 and C3. Interestingly, TRAMP C1 and C2 are tumorigenic while TRAMP C3 fail to form tumor. C57/B6 mice treated with different tumorigenic concentrations of TRAMP (C1, C2, and C3) cells. The experimental design also included appropriate controls. Developing tumors, spleen and draining lymph nodes were dissected out and single cell suspensions were prepared. Cells were stained with the specific antibodies such as NK cells, NKT cells, CD4, CD8, macrophages, B cells and Treg cells and analyzed using a 13-color flowcytometer. Preliminary data revealed that development of tumors by TRAMP C1 and TRAMP C2 cells and non-tumorigenesis by TRAMP C3 cells was dependent on number of Treg cells in tumor microenvironment. Therefore, the data suggest that the number of Treg cells present in tumor microenvironment may have a direct impact on tumor progression and clearance. Thus, modulating the number of Treg cells in tumor microenvironment may be a successful therapeutic strategy to control tumor progression

Abstract A more nuanced analysis of the changes in the balance of immune cell subsets is needed to understand the impact of radiation on immune function. We show the balance of T cell subsets changes after increasing single doses of total body irradiation(TBI) or after fractionated irradiation of the lymphoid tissues(TLI) of mice. These changes are due to differences in radioresistance and Bcl-2 expression of the NKT, CD4+CD25+ Treg and conventional T cell subsets to favor CD4+Bcl-2hi NKT and CD4+CD25+Bcl-2hi Treg cells. Reduction of the Bcl-2lo mature T cell subsets was at least 100 fold greater than that of the Bcl-2hi subsets. CD4+ NKT cells upregulated Bcl-2 and developed a Th2 bias after irradiation, while conventional T cells failed to do so. GVHD was more severe after bone marrow transplantation in NKT cell deficient than in wild type hosts and the residual NKT cells were 10 fold more abundant in the wild type spleen after the TLI versus TBI. Although the changes in the balance of T cell subsets and increase in Bcl-2hi cells occurred in irradiated wild type mice, these changes did not occur in p53-/- mice. In conclusion, differences in the level of Bcl-2 and associated differences in resistance of T cell subsets to radiation induced p53 dependent apoptosis results in a marked alteration in the balance of T cell subsets favoring NKT cells and CD4+CD25+ T cells that promote transplantation tolerance.

Regulatory T cells (Treg) are key players in the maintenance of peripheral tolerance, preventing autoimmune diseases and restraining chronic inflammatory diseases. Evidence suggests Treg cells and NK cells have important roles in feline immunodeficiency virus (FIV) pathogenesis; however, in vivo studies investigating the interplay between these two cell populations are lacking. We previously described innate immune defects in FIV-infected cats characterized by cytokine deficits and impaired natural killer cell (NK) and NK T cell (NKT) functions. In this study, we investigated whether in vivo Treg depletion by treatment with an anti-feline CD25 monoclonal antibody would improve the innate immune response against subcutaneous challenge with Listeria monocytogenes (Lm). Treg depletion resulted in an increased overall number of cells in Lm-draining lymph nodes and increased proliferation of NK and NKT cells in FIV-infected cats. Treg depletion did not normalize expression of perforin or granzyme A by NK and NKT cells, nor did Treg depletion result in improved clearance of Lm. Thus, despite the quantitative improvements in the NK and NKT cell responses to Lm, there was no functional improvement in the early control of Lm. CD1a+ dendritic cell percentages in the lymph nodes of FIV-infected cats were lower than in specific-pathogen-free control cats and failed to upregulate CD80 even when Treg were depleted. Taken together, Treg depletion failed to improve the innate immune response of FIV-infected cats against Lm and this may be due to dendritic cell dysfunction.

Invariant Natural Killer (iNK)T cells play opposite immune functions. They participate in the innate immune response to promote anti-microbial and anti-tumor immunity and they are crucial to maintain T cell tolerance and prevent autoimmune diseases. While it is well known that the adjuvant function of iNKT cells is mediated through maturation of dendritic cells (DC), the mechanism underlying the tolerogenic function of iNKT cells remains unclear. We performed co-culture experiments with immature myeloid DC and purified regulatory iNKT cells and found that under steady-state conditions, i.e. in the absence of any other maturation signal, iNKT cells triggered a unique pathway of DC maturation. iNKT cell-modulated DC (nkt-DC) showed the phenotype of tolerogenic mature DC with intermediate levels of expression of MHC class II and co-stimulatory molecules and a predominant secretion of the modulatory cytokine IL-10 with minimal release of pro-inflammatory cytokines (IL-12 and IL-6). Our experiments in transwells, with blocking anti-cytokine mAbs and with knockout DC lacking key molecules involved in the DC-(iNK)T cell interaction (CD1d, ICAM-1, CD40) showed that the iNKT cell-modulation of DC required cell-cell contact while cytokine were dispensable. Together with the phenotypical markers of tolerogenic DC, nkt-DC showed important tolerogenic function both in vitro and in vivo. Specifically, they were able to induce antigen-specific regulatory T cells from naïve diabetogenic BDC2.5 CD4 T cells (characterized by an anergic state, strong immunosuppressive capacity and secretion of immunomodulatory cytokines like IL-10) both in vitro and in vivo and to protect toward the development of an autoimmune disease (like T1D in NOD mouse). On the contrary, in the presence of pathogens (such as LPS) NKT cells exert an adjuvant effect and sustain the proinflammatory DC maturation (up-regulation of the maturation markers and increased IL12p70 production) favoring, in this way, the clearance of the pathogens. Our data suggest that, depending on the environment in which the two cells populations are present, NKT cells might exert a tolerogenic or an immunogenic role by affecting directly DCs maturation.