小鼠沙眼衣原体肺感染过程中Treg细胞与Th17反应关系

[目的]对沙眼衣原体在BALB/c小鼠肺部感染过程中CD4+ CD25+Foxp3+调节性T细胞(regulatory T cells,Treg)与Th17反应关系进行初步探讨.[方法]取6-8周龄的BALB/c小鼠,鼻腔吸入25 μL含5×103 IFU的沙眼衣原体鼠肺炎菌株(Chlamydia muridarum,Cm),建立沙眼衣原体小鼠肺感染模型.监测感染后不同时期小鼠体重变化;检测肺组织衣原体包涵体形成单位( IFU)及肺组织病理改变;利用流式细胞术检测Cm感染后小鼠体内Treg细胞百分率;ELISA检测肺组织上清液IL-6、TGF-β、IL-17、IL-2细胞因子的的表达;qRT-PCR检测KC( keratinocyte derived chemokine) mRNA和MIP-2( macrophage inflammatory protein-2)mRNA的表达差异.[结果]用5xl03 IFU Cm经鼻腔吸人感染后小鼠发生沙眼衣原体肺炎,表现为体重下降、肺组织大量炎症细胞浸润并可检测到衣原体繁殖.Cm感染后第3天,小鼠体内Treg细胞占CD4 +T细胞的百分比明显降,随后开始恢复,第7天恢复原来水平,一直持续到衣原体清除.TGF-β、IL-2的表达与Treg细胞动态变化一致.与Th17相关细胞因子IL-6、IL-17和Th17相关趋化因子KC、MIP-2的表达于第3天开始升高,至第7天达到最高水平,随后逐渐减少.[结论]在衣原体感染BALB/c小鼠过程中,Treg可能通过提供TGF-β并在IL-6帮助下促进Th17应答产生.     

Effects of natalizumab treatment on Foxp3+ T regulatory cells

Background

Natalizumab, a monoclonal humanized antibody targeting the alpha-4 chain of very late activation antigen 4 (VLA-4) exerts impressive therapeutic effects in patients with relapsing-remitting multiple sclerosis. Our objective was to study impacts of Natalizumab therapy on Foxp3+ T regulatory cells (Tregs) in multiple sclerosis (MS) patients.

Methodology

A combined approach of in vitro and ex vivo experiments using T cells isolated from the peripheral blood of healthy donors and Natalizumab treated MS patients was chosen. We determined binding of Natalizumab and its effects on the frequency, transmigratory behaviour and suppressive function of Tregs.

Principal Findings

Binding of Natalizumab and expression of CD49d (alpha-4 chain of VLA-4) differed between non-regulatory and regulatory cells. Albeit Foxp3+ Tregs had lower levels of CD49d, Natalizumab blocked the transmigration of Foxp3+ Tregs similar to non-regulatory T cells. The frequency of peripheral blood Tregs was unaffected by Natalizumab treatment. Natalizumab does not alter the suppressive capacity of CD4+CD25^highCD127^lowFoxp3+ Tregs under in vitro conditions. Furthermore, the impaired function of Tregs in MS patients is not restored by Natalizumab treatment.

Conclusions

We provide a first detailed analysis of Natalizumab effects on the regulatory T cell population. Our prospective study shows that Foxp3+ Tregs express lower levels of VLA-4 and bind less Natalizumab. We further the understanding of the mechanisms of action of Natalizumab by demonstrating that unlike other immunomodulatory drugs the beneficial therapeutic effects of the monoclonal antibody are largely independent of alterations in Treg frequency or function.     

Inflammation-driven reprogramming of CD4+ Foxp3+ regulatory T cells into pathogenic Th1/Th17 T effectors is abrogated by mTOR inhibition in vivo

While natural CD4(+)Foxp3(+) regulatory T (nT(REG)) cells have long been viewed as a stable and distinct lineage that is committed to suppressive functions in vivo, recent evidence supporting this notion remains highly controversial. We sought to determine whether Foxp3 expression and the nT(REG) cell phenotype are stable in vivo and modulated by the inflammatory microenvironment. Here, we show that Foxp3(+) nT(REG) cells from thymic or peripheral lymphoid organs reveal extensive functional plasticity in vivo. We show that nT(REG) cells readily lose Foxp3 expression, destabilizing their phenotype, in turn, enabling them to reprogram into Th1 and Th17 effector cells. nT(REG) cell reprogramming is a characteristic of the entire Foxp3(+) nT(REG) population and the stable Foxp3(NEG) T(REG) cell phenotype is associated with a methylated foxp3 promoter. The extent of nT(REG) cell reprogramming is modulated by the presence of effector T cell-mediated signals, and occurs independently of variation in IL-2 production in vivo. Moreover, the gut microenvironment or parasitic infection favours the reprogramming of Foxp3(+) T(REG) cells into effector T cells and promotes host immunity. IL-17 is predominantly produced by reprogrammed Foxp3(+) nT(REG) cells, and precedes Foxp3 down-regulation, a process accentuated in mesenteric sites. Lastly, mTOR inhibition with the immunosuppressive drug, rapamycin, stabilizes Foxp3 expression in T(REG) cells and strongly inhibits IL-17 but not RORγt expression in reprogrammed Foxp3(-) T(REG) cells. Overall, inflammatory signals modulate mTOR signalling and influence the stability of the Foxp3(+) nT(REG) cell phenotype.     

Foxp3+ regulatory T cells impede the priming of protective CD8+ T cells

T cell activation is controlled by incompletely defined opposing stimulation and suppression signals that together sustain the balance between optimal host defense against infection and peripheral tolerance. In this article, we explore the impacts of Foxp3(+) regulatory T cell (Treg) suppression in priming Ag-specific T cell activation under conditions of noninfection and infection. We find the transient ablation of Foxp3(+) Tregs unleashes the robust expansion and activation of peptide-stimulated CD8(+) T cells that provide protection against Listeria monocytogenes infection in an Ag-specific fashion. By contrast, Treg ablation had nonsignificant impacts on the CD8(+) T cell response primed by infection with recombinant L. monocytogenes. Similarly, nonrecombinant L. monocytogenes administered with peptide stimulated the expansion and activation of CD8(+) T cells that paralleled the response primed by Treg ablation. Interestingly, these adjuvant properties of L. monocytogenes did not require CD8(+) T cell stimulation by IL-12 produced in response to infection, but instead were associated with sharp reductions in Foxp3(+) Treg suppressive potency. Therefore, Foxp3(+) Tregs impose critical barriers that, when overcome naturally during infection or artificially with ablation, allow the priming of protective Ag-specific CD8(+) T cells.     

Inducible CD4+LAP+Foxp3- regulatory T cells suppress allergic inflammation

Regulatory T cells (Tregs) play a critical role in the maintenance of airway tolerance. We report that inhaled soluble Ag induces adaptive Foxp3(+) Tregs, as well as a regulatory population of CD4(+) T cells in the lungs and lung-draining lymph nodes that express latency-associated peptide (LAP) on their cell surface but do not express Foxp3. Blocking the cytokine IL-10 or TGF-β prevented the generation of LAP(+) Tregs and Foxp3(+) Tregs in vivo, and the LAP(+) Tregs could also be generated concomitantly with Foxp3(+) Tregs in vitro by culturing naive CD4(+) T cells with Ag and exogenous TGF-β. The LAP(+) Tregs strongly suppressed naive CD4(+) T cell proliferation, and transfer of sorted OVA-specific LAP(+) Tregs in vivo inhibited allergic eosinophilia and Th2 cytokine expression in the lung, either when present at the time of Th2 sensitization or when injected after Th2 cells were formed. Furthermore, inflammatory innate stimuli from house dust mite extract, nucleotide-binding oligomerization domain containing 2 ligand, and LPS, which are sufficient for blocking airway tolerance, strongly decreased the induction of LAP(+) Tregs. Taken together, we concluded that inducible Ag-specific LAP(+) Tregs can suppress asthmatic lung inflammation and constitute a mediator of airway tolerance together with Foxp3(+) Tregs.     

Keratinocyte growth factor induces expansion of murine peripheral CD4+Foxp3+ regulatory T cells and increases their thymic output

Keratinocyte growth factor (KGF) has been shown to reduce the incidence and severity of graft-versus-host disease by prevention of epithelial damage and by modulating alloreactivity. Since regulatory T cells (Treg) play a crucial role in immune modulation, we evaluated the effects of exogenous KGF on peripheral CD4(+)Foxp3(+) Treg and the generation of Treg in the thymus of normal mice. A 3-day course of KGF induced a rapid selective increase in the number of highly suppressive CD4(+)Foxp3(+) Treg. Blood Treg numbers remained elevated for >2 mo, but the frequency normalized after 2 wk due to a concomitant increase in CD4(+)Foxp3(-) T cells. Analysis of single joint TCR excision circles frequency and Ki-67 expression in peripheral blood Treg showed that the early selective increase of Treg was predominantly accounted for by peripheral expansion. Thymectomy before KGF administration did not affect the early selective increase of Treg but abrogated the late increase in CD4(+) T cell numbers, thereby showing its dependence on thymic output. Collectively, these results show that KGF induces an increase in blood CD4(+)Foxp3(+) Treg numbers via two independent mechanisms. First by selective peripheral expansion of Treg and thereafter by enhanced thymic output of newly developed Treg.     

Nitric oxide modulates TGF-beta-directive signals to suppress Foxp3+ regulatory T cell differentiation and potentiate Th1 development

TGF-β can induce Foxp3(+) inducible regulatory T cells (Treg) and also synergize with IL-6 and IL-4 to induce Th17 and Th9 cells. We now report that NO modulates TGF-β activity away from Treg but toward the Th1 lineage. NO potentiated Th1 differentiation in the presence of TGF-β in both IL-12-independent and -dependent fashions by augmenting IFN-γ-activated STAT-1 and T-bet. Differentiation into Treg, Th1, and Th17 lineages could be modulated by NO competing with other cofactors, such as IL-6 and retinoic acid. NO antagonized IL-6 to block TGF-β-directed Th17 differentiation, and together with IL-6, NO suppressed Treg development induced by TGF-β and retinoic acid. Furthermore, we show that physiologically produced NO from TNF and inducible NO synthase-producing dendritic cells can contribute to Th1 development predominating over Treg development through a synergistic activity induced when these cells cocluster with conventional dendritic cells presenting Ag to naive Th cells. This illustrates that NO is another cofactor allowing TGF-β to participate in development of multiple Th lineages and suggests a new mechanism by which NO, which is associated with protection against intracellular pathogens, might maintain effective Th1 immunity.     

Function of the IL-2R for thymic and peripheral CD4+CD25+ Foxp3+ T regulatory cells

IL-2 contributes to the production, function, and homeostasis of CD4+CD25+ T(reg) cells. However, it remains uncertain whether IL-2 is essential for the development of T(reg) cells in the thymus, their homeostasis in the periphery, or both. The present study was undertaken to investigate the contribution of IL-2 during thymic T(reg) cell development and its maintenance in peripheral immune tissue. Relying on genetic mouse models where IL-2R signaling was either completely blocked or selectively inhibited in peripheral CD4+CD25+ T(reg) cells, we show that the IL-2/IL-2R interaction is active in the thymus at the earliest stage of the development of T(reg) cells to promote their expansion and to up-regulate Foxp3 and CD25 to normal levels. Furthermore, CD4+CD25+Foxp3+ T(reg) cells with impaired IL-2-induced signaling persist in the periphery and control autoimmunity without constant thymic output. These peripheral T(reg) cells with poor responsiveness to IL-2 exhibited slower growth and extended survival in vivo, somewhat lower suppressive activity, and poor IL-2-dependent survival in vitro. Mixed thymic and bone marrow chimeric mice showed that wild-type-derived T(reg) cells were substantially more effective in populating peripheral immune tissue than T(reg) cells with impaired IL-2 signaling. Collectively, these data support the notion that normally IL-2 is a dominant mechanism controlling the number of thymic and peripheral T(reg) cells.     

Ligation of cytotoxic T lymphocyte antigen-4 to T cell receptor inhibits T cell activation and directs differentiation into Foxp3+ regulatory T cells

Cross-linking of ligand-engaged cytotoxic T lymphocyte antigen-4 (CTLA-4) to the T cell receptor (TCR) during the early phase of T cell activation attenuates TCR signaling, leading to T cell inhibition. To promote this event, a bispecific fusion protein comprising a mutant mouse CD80 (CD80w88a) and lymphocyte activation antigen-3 was engineered to concurrently engage CTLA-4 and cross-link it to the TCR. Cross-linking is expected to be attained via ligation of CTLA-4 first to MHCII and then indirectly to the TCR, generating a CTLA-4-MHCII-TCR trimolecular complex that forms between T cells and antigen-presenting cells during T cell activation. Treating T cells with this bispecific fusion protein inhibited T cell activation. In addition, it induced the production of IL-10 and TGF-β and attenuated AKT and mTOR signaling. Intriguingly, treatment with the bispecific fusion protein also directed early T cell differentiation into Foxp3-positive regulatory T cells (Tregs). This process was dependent on the endogenous production of TGF-β. Thus, bispecific fusion proteins that engage CTLA-4 and co-ligate it to the TCR during the early phase of T cell activation can negatively regulate the T cell response. Bispecific biologics with such dual functions may therefore represent a novel class of therapeutics for immune modulation. These findings presented here also reveal a potential new role for CTLA-4 in Treg differentiation.     

Foxp3+ follicular regulatory T cells control the germinal center response

Follicular helper (T(FH)) cells provide crucial signals to germinal center B cells undergoing somatic hypermutation and selection that results in affinity maturation. Tight control of T(FH) numbers maintains self tolerance. We describe a population of Foxp3(+)Blimp-1(+)CD4(+) T cells constituting 10-25% of the CXCR5(high)PD-1(high)CD4(+) T cells found in the germinal center after immunization with protein antigens. These follicular regulatory T (T(FR)) cells share phenotypic characteristics with T(FH) and conventional Foxp3(+) regulatory T (T(reg)) cells yet are distinct from both. Similar to T(FH) cells, T(FR) cell development depends on Bcl-6, SLAM-associated protein (SAP), CD28 and B cells; however, T(FR) cells originate from thymic-derived Foxp3(+) precursors, not naive or T(FH) cells. T(FR) cells are suppressive in vitro and limit T(FH) cell and germinal center B cell numbers in vivo. In the absence of T(FR) cells, an outgrowth of non-antigen-specific B cells in germinal centers leads to fewer antigen-specific cells. Thus, the T(FH) differentiation pathway is co-opted by T(reg) cells to control the germinal center response.     

An intrinsic mechanism predisposes Foxp3-expressing regulatory T cells to Th2 conversion in vivo

Naturally occurring regulatory T (nTreg) cells express Foxp3 and were originally discovered as immune suppressors critical for self-tolerance and immune homeostasis. Through yet-to-be-defined mechanisms, nTreg cells were recently shown to convert into proinflammatory cells. Particularly, attenuation of Foxp3 expression led to Th2 conversion of nTreg cells in vivo. In this paper, we demonstrated an nTreg-specific mechanism controlling their Th2 conversion. We found that wild-type nTreg cells expressing reduced levels of Foxp3 but not those expressing no Foxp3 produced the Th2 cytokine IL-4. Intriguingly, IL-4 production by converted nTreg cells is required for Th2 differentiation of coexisting naive CD4 T cells in vivo, suggesting that Th2 conversion of nTreg cells might be critical for directing Th2 immune responses. Th2 conversion of nTreg cells was not due to their inability to become Th1 cells, because IFN-γ was produced by Foxp3-low-expressing cells when IL-4/STAT-6 signaling was abrogated. Surprisingly, however, unlike naive CD4 T cells whose IL-4 production is dependent on STAT-6, Foxp3-low-expressing cells generated IL-4 independent of STAT-6, indicating an intrinsic mechanism that favors nTreg-to-Th2 differentiation. Indeed, compared with naive CD4 T cells, nTreg expressed elevated levels of GATA-3 independent of STAT-6. And GATA-3 was required for nTreg-to-Th2 conversion. Foxp3 may account for this GATA-3 upregulation in nTreg cells, because ectopic expression of Foxp3 preferentially promoted GATA-3 but not T-bet expression. Thus, we have identified an intrinsic mechanism that imposes a Th2/Th1 imbalance and predisposes Foxp3-expressing cells to IL-4 production independent of STAT-6 signaling.     

Physiologic control of the functional status of Foxp3+ regulatory T cells

Foxp3-lineage CD4 regulatory T cells (Tregs) were named for their ability to maintain self tolerance and suppress T cell immunity. However, resting Tregs from noninflamed tissues exhibit little suppressor activity, and must be stimulated to acquire such function. Conversely, under certain inflammatory conditions, Tregs may undergo rapid reprogramming to acquire helper/effector functions. In this Brief Review, we describe recent progress in elucidating physiologic processes that control the functional status of Foxp3-lineage Tregs. Emerging evidence suggests the surprising possibility that reprogrammed Tregs can be an indispensable source of helper activity in some physiologic settings, such as priming CD8(+) T cell responses. This suggests a novel paradigm in which Foxp3(+) Tregs intrinsically possess bifunctional potential, acting as a preformed pool of first-responder cells at sites of local inflammation that can either provide classical regulatory/suppressor activity, or rapidly reprogram to supply helper/effector activity, contingent on signals that manifest in local physiologic settings.     

Connexin 43 signaling enhances the generation of Foxp3+ regulatory T cells

Despite their importance for the functioning of the immune system, thymic development and peripheral maintenance of Foxp3(+) regulatory T (T(R)) cells are poorly understood. We have found that connexin 43 (Cx43), expressed by thymic T(R) cells progenitors, supports T(R) development. Mice with deletion of the Cx43 gene induced in T cells produce only few T(R) cells and had increased proportion of activated T cells in the lymph nodes, suggesting impaired peripheral tolerance. Reduction of the T(R) cell numbers was accompanied by increased presence of CD4(+)CD25(+)GITR(+)Foxp3(-) T cells, which did not produce inflammatory cytokines and lost suppressor function. These results strongly argue that we have discovered a novel signaling pathway, controlled by Cx43, that enhances the generation of T(R) cells. We propose that a possible mechanism of Cx43 activity is by regulating Foxp3 expression in T(R) lineage cells.     

Pertussis toxin reduces the number of splenic Foxp3+ regulatory T cells

Pertussis toxin (PTx) is a bacterial toxin used to enhance the severity of experimental autoimmune diseases such as experimental autoimmune encephalomyelitis. It is known to promote permeabilization of the blood-brain barrier, maturation of APC, activation of autoreactive lymphocytes and alteration of lymphocyte migration. In this study, we show that i.v. injection of PTx in mice induces a decrease in the number of splenic CD4(+)CD25(+) regulatory T cells (Treg cells). Furthermore, PTx not only induces a depletion of the dominant CD4(+)CD25(+)Foxp3(+) subpopulation of splenic Treg cells, but also reduces to a similar extent the CD4(+)CD25(-)Foxp3(+) subpopulation. On a per cell basis, the suppressive properties of the remaining Treg cells are not modified by PTx treatment. The reduction in splenic Treg cells is associated with preferential migration of these cells to the liver. Additionally, Treg cells exhibit a high sensitivity to PTx-mediated apoptosis in vitro. Finally, in vivo depletion of Treg cells by injection of an anti-CD25 Ab, and PTx treatment, present synergistic experimental autoimmune encephalomyelitis exacerbating effects. Therefore, we identify a new effect of PTx and provide an additional illustration of the influence of microbial components on the immune system affecting the balance between tolerance, inflammation and autoimmunity.     

Foxp3+ regulatory T cells control persistence of viral CNS infection

We earlier established a model of a persistent viral CNS infection using two week old immunologically normal (genetically unmodified) mice and recombinant measles virus (MV). Using this model infection we investigated the role of regulatory T cells (Tregs) as regulators of the immune response in the brain, and assessed whether the persistent CNS infection can be modulated by manipulation of Tregs in the periphery. CD4(+) CD25(+) Foxp3(+) Tregs were expanded or depleted during the persistent phase of the CNS infection, and the consequences for the virus-specific immune response and the extent of persistent infection were analyzed. Virus-specific CD8(+) T cells predominantly recognising the H-2D(b)-presented viral hemagglutinin epitope MV-H(22-30) (RIVINREHL) were quantified in the brain by pentamer staining. Expansion of Tregs after intraperitoneal (i.p.) application of the superagonistic anti-CD28 antibody D665 inducing transient immunosuppression caused increased virus replication and spread in the CNS. In contrast, depletion of Tregs using diphtheria toxin (DT) in DEREG (depletion of regulatory T cells)-mice induced an increase of virus-specific CD8(+) effector T cells in the brain and caused a reduction of the persistent infection. These data indicate that manipulation of Tregs in the periphery can be utilized to regulate virus persistence in the CNS.