IL-10-producing CD4+CD25+ regulatory T cells play a critical role in granulocyte-macrophage colony-stimulating factor-induced suppression of experimental autoimmune thyroiditis

Our earlier study showed that GM-CSF has the potential not only to prevent, but also to suppress, experimental autoimmune thyroiditis (EAT). GM-CSF-induced EAT suppression in mice was accompanied by an increase in the frequency of CD4(+)CD25(+) regulatory T cells that could suppress mouse thyroglobulin (mTg)-specific T cell responses in vitro, but the underlying mechanism of this suppression was not elucidated. In this study we show that GM-CSF can induce dendritic cells (DCs) with a semimature phenotype, an important characteristic of DCs, which are known to play a critical role in the induction and maintenance of regulatory T cells. Adoptive transfer of CD4(+)CD25(+) T cells from GM-CSF-treated and mTg-primed donors into untreated, but mTg-primed, recipients resulted in decreased mTg-specific T cell responses. Furthermore, lymphocytes obtained from these donors and recipients after adoptive transfer produced significantly higher levels of IL-10 compared with mTg-primed, untreated, control mice. Administration of anti-IL-10R Ab into GM-CSF-treated mice abrogated GM-CSF-induced suppression of EAT, as indicated by increased mTg-specific T cell responses, thyroid lymphocyte infiltration, and follicular destruction. Interestingly, in vivo blockade of IL-10R did not affect GM-CSF-induced expansion of CD4(+)CD25(+) T cells. However, IL-10-induced immunosuppression was due to its direct effects on mTg-specific effector T cells. Taken together, these results indicated that IL-10, produced by CD4(+)CD25(+) T cells that were probably induced by semimature DCs, is essential for disease suppression in GM-CSF-treated mice.     

CD8+ CD205+ splenic dendritic cells are specialized to induce Foxp3+ regulatory T cells

Foxp3(+)CD25(+)CD4(+) regulatory T cells (Treg) mediate immunological self-tolerance and suppress immune responses. A subset of dendritic cells (DCs) in the intestine is specialized to induce Treg in a TGF-beta- and retinoic acid-dependent manner to allow for oral tolerance. In this study we compare two major DC subsets from mouse spleen. We find that CD8(+) DEC-205/CD205(+) DCs, but not the major fraction of CD8(-) DC inhibitory receptor-2 (DCIR2)(+) DCs, induce functional Foxp3(+) Treg from Foxp3(-) precursors in the presence of low doses of Ag but without added TGF-beta. CD8(+)CD205(+) DCs preferentially express TGF-beta, and the induction of Treg by these DCs in vitro is blocked by neutralizing Ab to TGF-beta. In contrast, CD8(-)DCIR2(+) DCs better induce Foxp3(+) Treg when exogenous TGF-beta is supplied. In vivo, CD8(+)CD205(+) DCs likewise preferentially induce Treg from adoptively transferred, Ag-specific DO11.10 RAG(-/-) Foxp3(-)CD4(+) T cells, whereas the CD8(-)DCIR2(+) DCs better stimulate natural Foxp3(+) Treg. These results indicate that a subset of DCs in spleen, a systemic lymphoid organ, is specialized to differentiate peripheral Foxp3(+) Treg, in part through the endogenous formation of TGF-beta. Targeting of Ag to these DCs might be useful for inducing Ag-specific Foxp3(+) Treg for treatment of autoimmune diseases, transplant rejection, and allergy.     

H2A- and H2E-derived CD4+CD25+ regulatory T cells: a potential role in reciprocal inhibition by class II genes in autoimmune thyroiditis

We recently described a novel H2E class II-transgenic model (A(-)E(+)) of experimental autoimmune thyroiditis (EAT) that permits disease induction with heterologous thyroglobulin (Tg), but unlike conventional susceptible strains, precludes self-reactivity to autologous mouse Tg. In transgenic E(+)B10 (A(+)E(+)) mice, the presence of endogenous H2A genes is protective against H2E-mediated thyroiditis, inhibiting EAT development. The suppressive effect of H2A genes on H2E-mediated thyroiditis mirrors previous reports of H2E suppression on H2A-mediated autoimmune diseases, including EAT. The mechanism of the reciprocal-suppressive effect between class II genes is unclear, although the involvement of regulatory T cells has been proposed. We have recently reported that CD4(+)CD25(+) regulatory T cells mediate peripheral tolerance induced with mouse Tg in CBA mice. To determine whether these cells play a role in our E(+)-transgenic model, we first confirmed the existence of CD4(+)CD25(+) T cells regulating thyroiditis in E(+)B10.Ab(0) (A(-)E(+)) and B10 (A(+)E(-)) mice by i.v. administration of CD25 mAb before EAT induction. The depletion of CD4(+)CD25(+) T cells enhanced thyroiditis induction in the context of either H2E or H2A. Moreover, reconstitution of CD4(+)CD25(+) T cells from naive B10 mice restored resistance to EAT. E(+)B10 (A(+)E(+)) mice were also depleted of CD4(+)CD25(+) T cells before the challenge to determine their role in thyroiditis in the presence of both H2A and H2E genes. Depletion of CD4(+)CD25(+) regulatory T cells offset the suppression of H2E-mediated thyroiditis by H2A. Thus, these regulatory T cells may be involved in the reciprocal-suppressive effect between class II genes.     

Impairment of regulatory capacity of CD4+CD25+ regulatory T cells mediated by dendritic cell polarization and hyperthyroidism in Graves' disease

Graves' disease (GD) is one of the most common autoimmune diseases. The immune dysfunction in GD involves the generation of thyroid-stimulating hormone receptor (TSHR) autoantibodies that presumably arise consequent to interactions among dendritic cells (DCs), T cells, and regulatory T (Treg) cells. However, the immunological mechanisms of interactions between them that lead to the induction and regulation of this autoimmune disease are poorly defined. In this study, we investigated whether DCs are the main cause of the defective activity of Treg cells in GD patients. We found a significant decrease in the percentage of circulating CD4(+)CD25(+)FOXP3(+) Treg cells in untreated GD patients (uGD), which was negatively correlated with the concentration of TSHR autoantibodies. uGD-derived DCs were polarized to increase the number of plasmacytoid DCs (pDCs) and conferred the ability to abrogate the suppressive function of Treg cells through inducing apoptosis of CD4(+)CD25(+) Treg cells in an IFN-α-dependent manner, and elevated thyroid hormones further exacerbated the effect. The nucleotide UDP, which inhibits IFN-α secretion of pDCs through P2Y6 receptor signaling, restored the suppressive function of CD4(+)CD25(+) Treg cells. Collectively, uGD-derived DCs through pDC polarization and elevated thyroid hormones act in concert to impair the regulatory capacity of Treg cells, facilitating the production of TSHR autoantibodies in the pathogenesis of GD.     

Cutting edge: IL-4-induced protection of CD4+CD25- Th cells from CD4+CD25+ regulatory T cell-mediated suppression

CD4(+)CD25(+) T regulatory (Treg) cells are a CD4(+) T cell subset involved in the control of the immune response. In vitro, murine CD4(+)CD25(+) Treg cells inhibit CD4(+)CD25(-) Th cell proliferation induced by anti-CD3 mAb in the presence of APCs. The addition of IL-4 to cocultured cells inhibits CD4(+)CD25(+) Treg cell-mediated suppression. Since all cell types used in the coculture express the IL-4Ralpha chain, we used different combinations of CD4(+)CD25(-) Th cells, CD4(+)CD25(+) Treg cells, and APCs from wild-type IL-4Ralpha(+/+) or knockout IL-4Ralpha(-/-) mice. Results show that the engagement of the IL-4Ralpha chain on CD4(+)CD25(-) Th cells renders these cells resistant to suppression. Moreover, the addition of IL-4 promotes proliferation of IL-4Ralpha(+/+)CD4(+)CD25(+) Treg cells, which preserve full suppressive competence. These findings support an essential role of IL-4 signaling for CD4(+)CD25(-) Th cell activation and indicate that IL-4-induced proliferation of CD4(+)CD25(+) Treg cells is compatible with their suppressive activity.     

A tolerogenic semimature dendritic cells induce effector T-cell hyporesponsiveness by activation of antigen-specific CD4+CD25+ T regulatory cells that promotes skin allograft survival in mice

Semimature dendritic cells (smDCs) can induce autoimmune tolerance by activation of host antigen-specific CD4⁺CD25⁺ regulatory T (Treg) cells. We hypothesized that donor smDCs injected into recipients would induce effector T-cell hyporesponsiveness by activating CD4⁺CD25⁺Treg cells, and promote skin allograft survival. Myeloid smDCs were derived from C57BL/6J mice (donors) in vitro. BALB/c mice (recipients) were injected with smDCs to generate antigen-specific CD4⁺CD25⁺Treg cells in vivo. Allograft survival was prolonged when BALB/c recipients received either C57BL/6J smDCs prior to grafting or C57BL/6J smDC-derived CD4⁺CD25⁺Treg cells post-grafting, and skin flaps from these grafts showed the highest IL-10 production regardless of rapamycin treatments. Our findings confirm that smDCs constitute an independent subgroup of DCs that play a key role for inducing CD4⁺CD25⁺Treg cells to express high IL-10 levels, which induce hyporesponsiveness of effector T cells. Pre-treating recipients with donor smDCs may have potential for transplant tolerance induction.     

A novel costimulation pathway via the 4C8 antigen for the induction of CD4+ regulatory T cells

CD4(+)CD25(+) regulatory T (Treg) cells naturally occur in mice and humans, and similar Treg cells can be induced in vivo and in vitro. However, the molecular mechanisms that mediate the generation of these Treg cell populations remain unknown. We previously described anti-4C8 mAbs that inhibit the postadhesive transendothelial migration of T cells through human endothelial cell monolayers. We demonstrate in this work that Treg cells are induced by costimulation of CD4(+) T cells with anti-CD3 plus anti-4C8. The costimulation induced full activation of CD4(+) T cells with high levels of IL-2 production and cellular expansion that were comparable to those obtained on costimulation by CD28. However, upon restimulation, 4C8-costimulated cells produced high levels of IL-10 but no IL-2 or IL-4, and maintained high expression levels of CD25 and intracellular CD152, as compared to CD28-costimulated cells. The former cells showed hyporesponsiveness to anti-CD3 stimulation and suppressed the activation of bystander T cells depending on cell contact but not IL-10 or TGF-beta. The suppressor cells developed from CD4(+)CD25(-)CD45RO(+) cells. The results suggest that 4C8 costimulation induces the generation of Treg cells that share phenotypic and functional features with CD4(+)CD25(+) T cells, and that CD25(-) memory T cells may differentiate into certain Treg cell subsets in the periphery.     

Selective induction of dendritic cells using granulocyte macrophage-colony stimulating factor,but not fms-like tyrosine kinase receptor 3-ligand,activates thyroglobulin-specific CD4+/CD25+ T cells and suppresses experimental autoimmune thyroiditis

Fms-like tyrosine kinase receptor 3-ligand (Flt3-L) and GM-CSF cause expansion of different subsets of dendritic cells and skew the immune response toward predominantly Th1 and Th2 type, respectively. In the present study, we investigated their effects on experimental autoimmune thyroiditis in CBA/J mice. Relative to mouse thyroglobulin (mTg) immunized controls, mTg-immunized mice treated with Flt3-L showed more severe thyroiditis characterized by enhanced lymphocytic infiltration of the thyroid, and IFN-gamma and IL-2 production. In contrast, mice treated with GM-CSF, either before or after immunization with mTg, showed suppressed T cell response to mTg and failed to develop thyroiditis. Lymphocytes from these mice, upon activation with mTg in vitro, produced higher levels of IL-4 and IL-10. Additionally, GM-CSF-treated mice showed an increase in the frequency of CD4(+)/CD25(+) T cells, which suppressed the mTg-specific T cell response. Neutralization of IL-10, but not IL-4, or depletion of CD4(+)/CD25(+) cells resulted in increased mTg-specific in vitro T cell proliferation suggesting that IL-10 produced by the Ag-specific CD4(+)/CD25(+) regulatory T cells might be critical for disease suppression. These results indicate that skewing immune response toward Th2, through selective activation of dendritic cells using GM-CSF, may have therapeutic potential in Th1 dominant autoimmune diseases including Hashimoto's thyroiditis.     

Human CD4+CD25high regulatory T cells modulate myeloid but not plasmacytoid dendritic cells activation

Human CD4(+)CD25(+) regulatory T cells (Treg) play an essential role in the prevention of autoimmune diseases. However, the mechanisms of immune suppression and the spectrum of cells they target in vivo remain incompletely defined. In particular, although Treg directly suppress conventional T cells in vitro, they have been shown to inhibit the Ag-presenting functions of macrophage- and monocyte-derived dendritic cells (DC). We have now studied the maturation of human blood-derived myeloid DC and plasmacytoid DC activated with TLR ligands in the presence of Treg. Preactivated Treg suppressed strongly TLR-triggered myeloid DC maturation, as judged by the blocking of costimulatory molecule up-regulation and the inhibition of proinflammatory cytokines secretion that resulted in poor Ag presentation capacity. Although IL-10 played a prominent role in inhibiting cytokines secretion, suppression of phenotypic maturation required cell-cell contact and was independent of TGF-beta and CTLA-4. In contrast, the acquisition of maturation markers and production of cytokines by plasmacytoid DC triggered with TLR ligands were insensitive to regulatory T cells. Therefore, human Treg may enlist myeloid, but not plasmacytoid DC for the initiation and the amplification of tolerance in vivo by restraining their maturation after TLR stimulation.     

IL-4 modulation of CD4+CD25+ T regulatory cell-mediated suppression

Murine CD4(+)CD25(+) T regulatory (Treg) cells were cocultured with CD4(+)CD25(-) Th cells and APCs or purified B cells and stimulated by anti-CD3 mAb. Replacement of APCs by B cells did not significantly affect the suppression of CD4(+)CD25(-) Th cells. When IL-4 was added to separate cell populations, this cytokine promoted CD4(+)CD25(-) Th and CD4(+)CD25(+) Treg cell proliferation, whereas the suppressive competence of CD4(+)CD25(+) Treg cells was preserved. Conversely, IL-4 added to coculture of APCs, CD4(+)CD25(-) Th cells, and CD4(+)CD25(+) Treg cells inhibited the suppression of CD4(+)CD25(-) Th cells by favoring their survival through the induction of Bcl-2 expression. At variance, suppression was not affected by addition of IL-13, although this cytokine shares with IL-4 a receptor chain. When naive CD4(+)CD25(-) Th cells were replaced by Th1 and Th2 cells, cell proliferation of both subsets was equally suppressed, but suppression was less pronounced compared with that of CD4(+)CD25(-) Th cells. IL-4 production by Th2 cells was also inhibited. These results indicate that although CD4(+)CD25(+) Treg cells inhibit IL-4 production, the addition of IL-4 counteracts CD4(+)CD25(+) Treg cell-mediated suppression by promoting CD4(+)CD25(-) Th cell survival and proliferation.     

Targeted CTLA-4 engagement induces CD4+CD25+CTLA-4high T regulatory cells with target (allo)antigen specificity

CTLA-4 (CD152) is actively involved in down-regulating T cell activation and maintaining lymphocyte homeostasis. Our earlier studies showed that targeted engagement of CTLA-4 can down-modulate T cell response and suppress allo- and autoimmune responses. In this study, we report that targeted CTLA-4 engagement can induce immune tolerance to a specific target through selective induction of an Ag-specific CD4(+)CD25(+)CTLA-4(high) regulatory T cell (Treg cell) population. Allogeneic cells coated with anti-CTLA-4 Ab induced immune hyporesponsiveness through suppression of proinflammatory cytokines IFN-gamma and IL-2, and up-regulation of the regulatory cytokines IL-10, TGF-beta1, and IL-4, presumably through the engagement of CTLA-4 on activated T cells. Although rechallenge with alloantigen failed to break the unresponsiveness, a transient recovery from tolerance was observed in the presence of high concentrations of exogenous IL-2, saturating concentrations of neutralizing anti-TGF-beta1 and anti-IL-10 Abs, and blocking anti-CTLA-4 Ab, and upon depletion of CD4(+)CD25(+) Treg cells. The CD4(+)CD25(+)CTLA-4(high) Treg cells from tolerant mice suppressed the effector function of CD25(-) T cells from Ag-primed mice. Adoptive transfer of these Treg cells into Ag-primed mice resulted in a significantly reduced alloantigen-specific response. Further characterization demonstrated that the Treg cells with memory phenotype (CD62L(-)) were more potent in suppressing the alloantigen-specific T cell response. These results strongly support that the targeted engagement of CTLA-4 has therapeutic potential for the prevention of transplant rejection.     

CD27/CFSE-based ex vivo selection of highly suppressive alloantigen-specific human regulatory T cells

Naturally occurring CD4(+)CD25(+) regulatory T cells (Treg) are crucial in immunoregulation and have great therapeutic potential for immunotherapy in the prevention of transplant rejection, allergy, and autoimmune diseases. The efficacy of Treg-based immunotherapy critically depends on the Ag specificity of the regulatory T cells. Moreover, the use of Ag-specific Treg as opposed to polyclonal expanded Treg will reduce the total number of Treg necessary for therapy. Hence, it is crucial to develop ex vivo selection procedures that allow selection and expansion of highly potent, Ag-specific Treg. In this study we describe an ex vivo CFSE cell sorter-based isolation method for human alloantigen-specific Treg. To this end, freshly isolated CD4(+)CD25(+) Treg were labeled with CFSE and stimulated with (target) alloantigen and IL-2 plus IL-15 in short-term cultures. The alloantigen-reactive dividing Treg were characterized by low CFSE content and could be subdivided by virtue of CD27 expression. CD27/CFSE cell sorter-based selection of CD27(+) and CD27(-) cells resulted in two highly suppressive Ag-specific Treg subsets. Each subset suppressed naive and Ag-experienced memory T cells, and importantly, CD27(+) Treg also suppressed ongoing T cell responses. Summarizing, the described procedure enables induction, expansion, and especially selection of highly suppressive, Ag-specific Treg subsets, which are crucial in Ag-specific, Treg-based immunotherapy.     

Selective survival of naturally occurring human CD4+CD25+Foxp3+ regulatory T cells cultured with rapamycin

Naturally occurring CD4(+)CD25(+) regulatory T (nTreg) cells are essential for maintaining T cell tolerance to self Ags. We show that discrimination of human Treg from effector CD4(+)CD25(+) non-nTreg cells and their selective survival and proliferation can now be achieved using rapamycin (sirolimus). Human purified CD4(+)CD25(high) T cell subsets stimulated via TCR and CD28 or by IL-2 survived and expanded up to 40-fold in the presence of 1 nM rapamycin, while CD4(+)CD25(low) or CD4(+)CD25(-) T cells did not. The expanding pure populations of CD4(+)CD25(high) T cells were resistant to rapamycin-accelerated apoptosis. In contrast, proliferation of CD4(+)CD25(-) T cells was blocked by rapamycin, which induced their apoptosis. The rapamycin-expanded CD4(+)CD25(high) T cell populations retained a broad TCR repertoire and, like CD4(+) CD25(+) T cells freshly obtained from the peripheral circulation, constitutively expressed CD25, Foxp3, CD62L, glucocorticoid-induced TNFR family related protein, CTLA-4, and CCR-7. The rapamycin-expanded T cells suppressed proliferation and effector functions of allogeneic or autologous CD4(+) and CD8(+) T cells in vitro. They equally suppressed Ag-specific and nonspecific responses. Our studies have defined ex vivo conditions for robust expansion of pure populations of human nTreg cells with potent suppressive activity. It is expected that the availability of this otherwise rare T cell subset for further studies will help define the molecular basis of Treg-mediated suppression in humans.     

CD137 signaling interferes with activation and function of CD4+CD25+ regulatory T cells in induced tolerance to experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT), a model for Hashimoto's thyroiditis, is a T cell-mediated disease inducible with mouse thyroglobulin (mTg). Pretreatment with mTg, however, can induce CD4+ T cell-mediated tolerance to EAT. We demonstrate that CD4+CD25+ regulatory cells are critical for the tolerance induction, as in vivo depletion of CD25+ cells abrogated established tolerance, and CD4+CD25+ cells from tolerized mice suppressed mTg-responsive cells in vitro. Importantly, administration of an agonistic CD137 monoclonal antibody (mAb) inhibited tolerance development, and the mediation of established tolerance. CD137 mAb also inhibited the suppression of mTg-responsive cells by CD4+CD25+ cells in vitro. Signaling through CD137 likely resulted in enhancement of the responding inflammatory T cells, as anti-CD137 did not enable CD4+CD25+ T cells to proliferate in response to mTg in vitro.     

Characterization of IL-10-secreting T cells derived from regulatory CD4+CD25+ cells by the TIRC7 surface marker

Natural CD25(+)CD4(+) regulatory T cells (Treg) are essential for self-tolerance and for the control of T cell-mediated immune pathologies. However, the identification of Tregs in an ongoing immune response or in inflamed tissues remains elusive. Our experiments indicate that TIRC7, T cell immune response cDNA 7, a novel membrane molecule involved in the regulation of T lymphocyte activation, identifies two Treg subsets (CD25(low)TIRC7(+) and CD25(high)TIRC7(-)) that are characterized by the expression of Foxp3 and a suppressive activity in vitro and in vivo. We also showed that the CD25(low)TIRC7(+) subset represents IL-10-secreting Tregs in steady state, which is accumulated intratumorally in a tumor-bearing mice model. Blockade of the effect of IL-10 reversed the suppression imposed by the CD25(low)TIRC7(+) subset. Interestingly, these IL-10-secreting cells derived from the CD25(high)TIRC7(-) subset, both in vitro and in vivo, in response to tumoral Ags. Our present results strongly support the notion that, in the pool of natural Tregs, some cells can recognize foreign Ags and that this recognition is an essential step in their expansion and suppressive activity in vivo.     

Selective expansion of foxp3-positive regulatory T cells and immunosuppression by suppressors of cytokine signaling 3-deficient dendritic cells

Dendritic cells (DCs) induce immunity and immunological tolerance as APCs. It has been shown that DCs secreting IL-10 induce IL-10(+) Tr1-type regulatory T (Treg) cells, whereas Foxp3-positive Treg cells are expanded from naive CD4(+) T cells by coculturing with mature DCs. However, the regulatory mechanism of expansion of Foxp3(+) Treg cells by DCs has not been clarified. In this study, we demonstrated that suppressors of cytokine signaling (SOCS)-3-deficient DCs have a strong potential as Foxp3(+) T cell-inducing tolerogenic DCs. SOCS3(-/-) DCs expressed lower levels of class II MHC, CD40, CD86, and IL-12 than wild-type (WT)-DCs both in vitro and in vivo, and showed constitutive activation of STAT3. Foxp3(-) effector T cells were predominantly expanded by the priming with WT-DCs, whereas Foxp3(+) Treg cells were selectively expanded by SOCS3(-/-) DCs. Adoptive transfer of SOCS3(-/-) DCs reduced the severity of experimental autoimmune encephalomyelitis. Foxp3(+) T cell expansion was blocked by anti-TGF-beta Ab, and SOCS3(-/-) DCs produced higher levels of TGF-beta than WT-DCs, suggesting that TGF-beta plays an essential role in the expansion of Foxp3(+) Treg cells. These results indicate an important role of SOCS3 in determining on immunity or tolerance by DCs.     

Ex vivo expansion of CD4+CD25+FoxP3+ T regulatory cells based on synergy between IL-2 and 4-1BB signaling

Naturally occurring CD4(+)CD25(+)FoxP3(+) T regulatory (Treg) cells require three distinct signals transduced via TCR, CD28, and IL-2R for their development and maintenance. These requirements served as the basis for several recently developed ex vivo expansion protocols that relied on the use of solid support-bound Abs to CD3 and CD28 in the presence of high dose IL-2. We report in this study that Treg cells up-regulate the expression of inducible costimulatory receptor 4-1BB in response to IL-2, and stimulation using this receptor via a novel form of 4-1BB ligand (4-1BBL) fused to a modified form of core streptavidin (SA-4-1BBL) was effective in expanding these cells up to 110-fold within 3 wk. Expanded cells up-regulated CD25, 4-1BB, and membranous TGF-beta, suppressed T cell proliferation, and prevented the rejection of allogeneic islets upon adoptive transfer into graft recipients. Importantly, SA-4-1BBL rendered CD4(+)CD25(-) T effector cells refractive to suppression by Treg cells. This dual function of signaling via 4-1BB, vis-à-vis Treg cell expansion and licensing T effector cells resistant to Treg cell suppression, as well as the up-regulation of 4-1BB by IL-2 may serve as important regulatory mechanisms for immune homeostasis following antigenic challenge. Stimulation using a soluble form of SA-4-1BBL represents a novel approach to expand Treg cells with potential therapeutic applications in autoimmunity and transplantation.     

CD11c+CD11b+ dendritic cells play an important role in intravenous tolerance and the suppression of experimental autoimmune encephalomyelitis

The central role of T cells in the induction of immunological tolerance against i.v. Ags has been well documented. However, the role of dendritic cells (DCs), the most potent APCs, in this process is not clear. In the present study, we addressed this issue by examining the involvement of two different DC subsets, CD11c(+)CD11b(+) and CD11c(+)CD8(+) DCs, in the induction of i.v. tolerance. We found that mice injected i.v. with an autoantigen peptide of myelin oligodendrocyte glycoprotein (MOG) developed less severe experimental autoimmune encephalomyelitis (EAE) following immunization with MOG peptide but presented with more CD11c(+)CD11b(+) DCs in the CNS and spleen. Upon coculturing with T cells or LPS, these DCs exhibited immunoregulatory characteristics, including increased production of IL-10 and TGF-beta but reduced IL-12 and NO; they were also capable of inhibiting the proliferation of MOG-specific T cells and enhancing the generation of Th2 cells and CD4(+)CD25(+)Foxp3(+) regulatory T cells. Furthermore, these DCs significantly suppressed ongoing EAE upon adoptive transfer. These results indicate that CD11c(+)CD11b(+) DCs, which are abundant in the CNS of tolerized animals, play a crucial role in i.v. tolerance and EAE and may be a candidate cell population for immunotherapy of autoimmune diseases.