Antigen-specific CD4(+) regulatory T cells in the intestine

Mucosal surfaces, especially the gastrointestinal (GI) tract, are obligatory sites for tolerance induction against numerous exogenous antigens. Therefore, the mucosal surface seems to provide a microenvironment conductive to the induction of antigen-specific regulatory T cells. The cytokine milieu, which includes IL-10 and TGF-beta, affects effector function of local dendritic cells and induces regulatory T cells (iT(REG)). During immune homeostasis (steady state) in the GI tract, noninflammatory innate immune signals provided by innocuous or commensal bacteria seem to play important roles in the induction of regulatory cytokines that enable the establishment of tolerance, which involves iT(REG) function. In accordance with this viewpoint, utilizing physiological means such as probiotics and TLR ligands may improve the homeostatic conditions of immune-mediated diseases and inflammation. Antigen-specific iT(REG) is a great counterpart of thymus-derived CD25(+)CD4(+)Foxp3(+) T(REG) (nT(REG)), and therefore clinical applications of T(REG) should be developed that integrate the advantages of both of these cell populations. Close investigation of mucosal iT(REG) and related microenvironments not only will facilitate novel interventions of mucosal immunity but also will help to best utilize iT(REG) and iT(REG) in an integrated way.     

Curcumin inhibits suppressive capacity of naturally occurring CD4+CD25+ regulatory T cells in mice in vitro

Accumulating evidence has demonstrated that naturally occurring CD4(+)CD25(+) regulatory T cells (Tregs) are critical for maintenance of immunological tolerance and have been shown to be important in regulating the immune responses in many diseases. Curcumin, a phytochemical obtained from the rhizome of the plant Curcuma longa, has achieved the potential therapeutic interest to numerous immune-related disorders. However, the effect and mechanism of curcumin on Tregs remain largely elusive. In the present study, curcumin inhibition of the suppressive activity of CD4(+)CD25(+) regulatory T cells appears to be dependent on three categories: inhibiting cell-cell contact by down-regulation of CTLA-4, suppressing inhibitory cytokine secretion and decreasing the ability to consume IL-2 and/or suppress IL-2 production. In addition, Foxp3 expression was also reduced on Tregs after curcumin stimulation. Moreover, we found that nuclear translocation of p65 and c-Rel, which is critical for Foxp3 and CD25 expressions, was markedly decreased in Tregs with curcumin stimulation. Based on the role of curcumin in the suppressive activity of Tregs, it may be feasible to use curcumin as an immunotherapy for Treg-related diseases, such as tumors and sepsis.     

Oral FTY720 administration induces immune tolerance and inhibits early development of atherosclerosis in apolipoprotein E-deficient mice

Orally administered immunomodulatory drugs have recently demonstrated the ability to induce an oral tolerance via inhibition of effector T cells and induction of certain subsets of regulatory T cells (Tregs) which have the potential to prevent several autoimmune diseases. In the present study, we hypothesized that short-term, low-dose, oral FTY720 administration may induce latency-associated peptide (LAP) Tregs and CD4(+) Foxp3(+) Tregs in atherogenesis, potentially resulting in remission of early development of atherosclerosis in apolipoprotein E-deficient (APOE(-/-)) mice. FTY720 was orally administered to APOE(-/-) mice 4 weeks of age on a high-cholesterol diet and atherosclerosis was assessed at 8 weeks of age. Oral administration of FTY720 significantly reduced atherosclerotic lesion formation compared with control mice. We observed a significant increase in LAP(+) and Foxp3(+) cells in the CD4+T-cell population of FTY720-treated mice in association with increased production of the anti-inflammatory cytokine transforming growth factor-β (TGF-β) as well as suppressed T-helper type 1 immune responses. Our findings reveal that short-term, low-dose oral FTY720 treatment had great benefits in inhibiting early development of atherosclerosis in mice via induction of a regulatory T-cell response and inhibition of effector T responses. These findings suggest that oral immune modulation may represent an attractive therapeutic approach to atherosclerosis.     

CD4+CD25+Foxp3+调节性T细胞与慢性乙型肝炎病毒感染的关系

目的 探讨调节性T细胞（Treg）在慢性乙型肝炎病毒感染中的免疫调节作用。方法 采用流式细胞术检测慢性活动性肝炎患者、乙型肝炎病毒携带者、乙型肝炎恢复者及健康对照者外周血CIN^＋T细胞中的CIN^＋CD25^＋Foxp3^＋调节性T细胞的比例。采用免疫组织化学法检测肝组织中Foxp3的表达。统计分析外周血中CIN^＋CD25^＋Foxp3^＋调节性T细胞的比例数与血清HBeAg和HBVDNA含量的关系。结果 外周血CIN^＋T细胞中CIN^＋CD25^＋Foxp3^＋调节性T细胞的比例数在慢性活动型肝炎组和乙型肝炎病毒携带组均高于健康对照组（P〈0．05），乙型肝炎病毒携带者组高于乙型肝炎恢复组（P〈0．05）。Foxp3在慢性活动型肝炎组肝组织中的阳性率和阳性细胞数均高于乙型肝炎病毒携带者组（P〈0．05）。外周血HBeAg（＋）患者Treg的比例数高于血清HBeAg（-）患者Treg的比例数（t=1．67．P〈0．05）。患者外周血CIN^＋CD25^＋Foxp3^＋Treg的比例数与血清HBV DNA含量呈正相关（r=0．56，P〈0．01）。结论 CIN^＋CD25^＋Foxp3^＋调节性T细胞可能与乙型肝炎病毒感染慢性化及乙型肝炎病毒的清除有关。     

Unexpected modulation of recall B and T cell responses after immunization with rotavirus-like particles in the presence of LT-R192G

LT-R192G, a mutant of the thermolabile enterotoxin of E. coli, is a potent adjuvant of immunization. Immune responses are generally analyzed at the end of protocols including at least 2 administrations, but rarely after a prime. To investigate this point, we compared B and T cell responses in mice after one and two intrarectal immunizations with 2/6 rotavirus-like particles (2/6-VLP) and LT-R192G. After a boost, we found, an unexpected lower B cell expansion measured by flow cytometry, despite a secondary antibody response. We then analyzed CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) and CD4(+)CD25(+)Foxp3(-) helper T cells after in vitro (re)stimulation of mesenteric lymph node cells with the antigen (2/6-VLP), the adjuvant (LT-R192G) or both. 2/6-VLP did not activate CD4(+)CD25(+)Foxp3(-) nor Foxp3(+) T cells from non-immunized and 2/6-VLP immunized mice, whereas they did activate both subsets from mice immunized with 2/6-VLP in the presence of adjuvant. LT-R192G dramatically decreased CD4(+)CD25(+)Foxp3(+) T cells from non-immunized and 2/6-VLP immunized mice but not from mice immunized with 2/6-VLP and adjuvant. Moreover, in this case, LT-R192G increased Foxp3 expression on CD4(+)CD25(+)Foxp3(+) cells, suggesting specific Treg activation during the recall. Finally, when both 2/6-VLP and LT-R192G were used for restimulation, LT-R192G clearly suppressed both 2/6-VLP-specific CD4(+)CD25(+)Foxp3(-) and Foxp3(+) T cells. All together, these results suggest that LT-R192G exerts different effects on CD4(+)CD25(+)Foxp3(+) T cells, depending on a first or a second contact. The unexpected immunomodulation observed during the recall should be considered in designing vaccination protocols.     

In-vitro generation and characterisation of murine CD4+CD25+ regulatory T cells with indirect allospecificity

Naturally arising CD4(+)CD25(+) regulatory T cells play a pivotal role in the prevention of autoimmunity and in the induction of donor-specific transplantation tolerance. Harnessing regulatory cells for potential adoptive cell therapy is hampered by their lack of antigen-specificity and their limited numbers. Here we describe the generation and expansion of murine CD4(+)CD25(+) T cells with antigen-specificity for an K(d) peptide as potential reagents for adoptive cell therapy in promoting donor-specific transplantation tolerance. Using bone marrow-derived autologous dendritic cells pulsed with the K(d) peptide, we generated T cell lines from purified CD4(+)CD25(+) T cells from C56BL/6 mice. The T cell lines expressed high level of CD25 and low level of CD45RB and CD69. They maintained the expression of CD62L, GITR, CTLA-4 and more importantly FoxP3. The CD4(+)CD25(+) T cell lines were anergic after TCR stimulation and produced little cytokine such as IL-2 and IFN-gamma. Importantly, they were more potent than freshly isolated CD4(+)CD25(+) T cells in suppressing proliferation and cytokine secretion by effector CD4(+) T cells. Furthermore, the CD4(+)CD25(+) T cell lines could be expanded to large cell numbers and maintained in culture up to 1 year. The K(d)-specific CD4(+)CD25(+) T cell lines will be invaluable in devising a strategy for the induction of cardiac transplantation tolerance in wild-type B6 mice carrying a full mismatch BALB/c heart.     

Indoleamine 2,3-dioxygenase, Tregs and cancer

The IDO pathway is implicated in a number of settings which lead to acquired peripheral tolerance. One such setting may be the functional tolerance displayed by tumor-bearing hosts toward tumor-associated antigens. Foxp3(+) Tregs are now recognized as a major contributor to tumor-induced immune suppression and functional tolerance. Emerging evidence links the IDO pathway with Treg biology at several points. The first is the ability of IDO-expressing DCs to drive the differentiation of naive CD4(+) T cells toward a Foxp3+ (inducible Treg) phenotype. The second link is the ability of IDO-expressing DCs to directly activate mature, pre-existing Tregs for markedly enhanced suppression of target cells. And the third link is the ability of IDO to prevent the inflammation-induced conversion ("reprogramming") of Tregs into pro-inflammatory T-helper-like cells in vivo. Taken together, these findings suggest that IDO may represent an important regulatory checkpoint influencing Treg activity: both by stabilizing and augmenting the suppressive phenotype, and by preventing Treg reprogramming into non-suppressive helper-like cells.     

CD8 blockade promotes the expansion of antigen-specific CD4+ FOXP3+ regulatory T cells in vivo

Treatment with a cocktail of CD4 and CD8-specific monoclonal antibodies (mAb) induces long-term transplantation tolerance and regulatory CD4(+) T cells that induce tolerance in non-tolerant T cells. In contrast, treatment with a CD4-specific mAb alone fails to induce long-term tolerance. The current study was designed to test the hypothesis that CD8 blockade plays a role in promoting the development of CD4(+) regulatory T cells. Using the DO11.10 CD4(+) TCR transgenic mouse model we show that treatment with a CD4/CD8-specific mAb cocktail induces antigen-specific tolerance to OVA, measured by a significant decrease in OVA-specific IgG, on challenge with antigen. Although treatment with OVA and the CD4-specific mAb alone also induces a significant decrease in OVA-specific antibody, the number of DO11.10 cells is significantly greater in mice treated with the CD4/CD8-specific mAb cocktail, and this is associated with a significant increase in proliferation of DO11.10 cells in response to specific antigen. DO11.10 cells sorted from mice made tolerant to OVA with the CD4/CD8-specific mAb cocktail promote an OVA-specific IgG1 (Th2-type) response but not an OVA-specific IgG3 (Th1-type) response on transfer into new syngeneic recipients, suggesting their ability to regulate the type of antigen-specific immune response that ensues after priming with antigen. In addition, DO11.10 cells from tolerant mice express markers that are characteristic of CD4(+) regulatory cells, including FOXP3, GITR and CTLA4, but not CD25. Taken as a whole, these data suggest that CD8 blockade promotes CD4(+) FOXP3(+) regulatory CD4(+) T cells by promoting their proliferation in tolerant mice.     

CD4+CD25+ T regulatory cells and TGF-beta in mucosal immune system: the good and the bad

Three major mucosal systems exist in the body, the oral-gastrointestinal, the respiratory and the genitourinary systems. In particular, the gastrointestinal (GI) tract contains the largest mucosal surface in the body and is the major port of entry for foreign antigens. Therefore, the gut immune system has to differentiate to tolerate dietary antigens and expel infectious and harmful pathogens. During the complex but well-orchestrated immune responses in the mucosal system, T cells play a pivotal role in both immunity and tolerance. Of many T cell subpopulations, CD4(+)CD25(+) T regulatory cells (Tregs) are instrumental in regulation of immune responses in mucosea. Among the multitude of cytokines and factors that are produced in the gut, Transforming Growth Factor-beta (TGF-beta) is probably the most important one in influencing mucosal T cell responses. The interaction and mutual regulation between TGF-beta and CD4(+)CD25(+) Tregs may be the key in maintaining the balance between T cell immunity and tolerance in mucosal system. In this article, we attempt to discuss both beneficial and detrimental effects of TGF-beta and Tregs on oral tolerance, mucosal inflammation and autoimmunity, colon cancer and HIV infection in the gut.     

T cell tolerance in transplantation: possibilities for therapeutic intervention

It is now possible to induce donor-specific transplantation tolerance in adult rodents using a number of therapeutic strategies. These include the use of non-depleting monoclonal antibodies against T cell co-receptor and costimulation molecules, and immunisation with tolerogenic antigen-presenting cells. It is a common finding to all of these models of peripheral tolerance, as well as to various mouse models of autoimmune disease, that regulatory CD4(+) T cells are the principle mediators. There are currently no specific markers for regulatory T cells and their activity has been associated with different T cell subsets defined by the expression of activation markers, such as CD25 and cytotoxic T lymphocyte antigen-4 (CTLA-4), or anti-inflammatory cytokines, such as IL-10 and TGF-beta. Differential gene expression analyses have been used to identify potential new markers for regulatory T cells and to find novel targets for therapeutic manipulation of the immune system. The challenge now is to understand the biological principles that allow such immune reprogramming so that they can be safely applied to clinical situations.     

Oral tolerance and TGF-beta-producing cells

Multiple mechanisms have been proposed to explain the immune hyporesponsiveness to fed antigens, a phenomenon named oral tolerance. Low doses of orally administered antigen are reported to favor active suppression with the generation of regulatory cells, whereas high doses would favor clonal anergy/deletion. A major conceptual advance in oral tolerance has been the demonstration that TGF-beta plays a central role in oral tolerance as a mediator secreted by Th3 cells. In addition, recent pieces of evidence suggest that TGF-beta may be a primary link between distinct populations of regulatory T cells that are induced by feeding. Conversion of CD4+CD25- into CD4+CD25+ T cells by the expression of FoxP3 involves TGF-beta. A membrane-bound form of TGF-beta (containing latency-associated peptide - LAP) has also been described and LAP+ CD4+ T cells mediate suppression in the gut by a TGF-beta-dependent mechanism. Most of these regulatory T cells are anergic cells indicating that anergy may be also related to Treg induction. Moreover, deletional events taking place in the gut mucosa induce TGF-beta production by either macrophages that phagocyte apoptotic cells or by the dying T cells. Thus, it appears that TGF-beta-producing cells are not only crucial for oral tolerance, but they may be master regulators of most of the mechanisms triggered by antigen feeding.     

溃疡性结肠炎患者肠黏膜CD4＋CD25＋调节性T细胞及Foxp3表达水平的研究

目的通过分析溃疡性结肠炎（UC）患者肠黏膜中CD4＋CD2＋5调节性T细胞及其特异性标志物Foxp3的表达特点,探讨CD4＋CD2＋5调节性T细胞和Foxp3在UC发病机制中的作用。方法 18例UC活动期患者和12例健康体检者作为正常对照组,分别经电子肠镜活检肠黏膜组织,以流式细胞术检测肠固有层单个核细胞（LPMC）中CD4＋CD2＋5T细胞和CD4＋T细胞比例,应用免疫组化方法检测肠黏膜中Foxp3的表达。结果 UC患者肠黏膜CD4＋CD2＋5T细胞占CD4＋T细胞比例和Foxp3＋T细胞表达明显高于正常对照组（P〈0.05）,两组LPMC中CD4＋T细胞比例无明显差异（P〉0.05）。结论 CD4＋CD2＋5调节性T细胞在UC的发病机制中起重要作用,参与肠黏膜炎症的发生、发展,Foxp3是CD4＋CD2＋5调节性T细胞的特异性表达因子,外周血调节性T细胞数量减少可能是疾病发生的重要因素。