CD4+CD25+ regulatory T cells in HIV infection

The immune system faces the difficult task of discerning between foreign, potentially pathogen-derived antigens and self-antigens. Several mechanisms, including deletion of self-reactive T cells in the thymus, have been shown to contribute to the acceptance of self-antigens and the reciprocal reactivity to foreign antigens. Over the last decade it has become increasingly clear that CD4(+)CD25(+) T(Reg) cells are crucial for maintenance of T cell tolerance to self-antigens in the periphery, and to avoid development of autoimmune disorders. Recently, evidence has also emerged that demonstrates that CD4(+)CD25(+) T(Reg) cells can also suppress T cell responses to foreign pathogens, including viruses such as HIV. In this article we review the current knowledge and potential role of CD4(+)CD25(+) T(Reg) cells in HIV infection.     

FTY720 ameliorates Th1-mediated colitis in mice by directly affecting the functional activity of CD4+CD25+ regulatory T cells

Following the present concepts, the synthetic sphingosine analog of myriocin FTY720 alters migration and homing of lymphocytes via sphingosine 1-phosphate receptors. However, several studies indicate that the immunosuppressive properties of FTY720 may alternatively be due to tolerogenic activities via modulation of dendritic cell differentiation or based on direct effects on CD4(+)CD25(+) regulatory T cells (Treg). As Treg play an important role for the cure of inflammatory colitis, we used the Th1-mediated 2,4,6-trinitrobenzene sulfonic acid (TNBS) colitis model to address the therapeutic potential of FTY720 in vivo. A rectal enema of TNBS was given to BALB/c mice. FTY720 was administered i.p. from days 0 to 3 or 3 to 5. FTY720 substantially reduced all clinical, histopathologic, macroscopic, and microscopic parameters of colitis analyzed. The therapeutic effects of FTY720 were associated with a down-regulation of IL-12p70 and subsequent Th1 cytokines. Importantly, FTY720 treatment resulted in a prominent up-regulation of FoxP3, IL-10, TGFbeta, and CTLA4. Supporting the hypothesis that FTY720 directly affects functional activity of CD4(+)CD25(+) Treg, we measured a significant increase of CD25 and FoxP3 expression in isolated lamina propria CD4(+) T cells of FTY720-treated mice. The impact of FTY720 on Treg induction was further confirmed by concomitant in vivo blockade of CTLA4 or IL-10R which significantly abrogated its therapeutic activity. In conclusion, our data provide clear evidence that in addition to its well-established effects on migration FTY720 leads to a specific down-regulation of proinflammatory signals while simultaneously inducing functional activity of CD4(+)CD25(+) Treg. Thus, FTY720 may offer a promising new therapeutic strategy for the treatment of IBD.     

CD4+CD25+ T regulatory cells suppress NK cell-mediated immunotherapy of cancer

CD4+CD25+ regulatory T cells (Treg) that suppress T cell-mediated immune responses may also regulate other arms of an effective immune response. In particular, in this study we show that Treg directly inhibit NKG2D-mediated NK cell cytotoxicity in vitro and in vivo, effectively suppressing NK cell-mediated tumor rejection. In vitro, Treg were shown to inhibit NKG2D-mediated cytolysis largely by a TGF-beta-dependent mechanism and independently of IL-10. Adoptively transferred Treg suppressed NK cell antimetastatic function in RAG-1-deficient mice. Depletion of Treg before NK cell activation via NKG2D and the activating IL-12 cytokine, dramatically enhanced NK cell-mediated suppression of tumor growth and metastases. Our data illustrate at least one mechanism by which Treg can suppress NK cell antitumor activity and highlight the effectiveness of combining Treg inhibition with subsequent NK cell activation to promote strong innate antitumor immunity.     

Heme oxygenase-1-mediated CD4+CD25high regulatory T cells suppress allergic airway inflammation

Heme oxygenase-1 (HO-1) has anti-inflammatory effects in asthma. CD4+CD25(high) regulatory T cells (Treg) are a potent immunoregulator that suppresses the immune response. We studied the effects of HO-1-mediated CD4+CD25(high) Treg on suppression of allergic airway inflammation by comparing mice treated with hemin, OVA, Sn-protoporphyrin (SnPP), and hemin plus SnPP. Airway responsiveness, airway eosinophil infiltration, the level of OVA-specific IgE, and the numbers of cells in general and eosinophils in particular in bronchial alveolar lavage fluid were lower in the hemin group than in the OVA, SnPP, and hemin plus SnPP groups. The expressions of HO-1 mRNA and protein in the lung were increased by repeated administrations of hemin and SnPP. However, the activity of HO-1 was highest in hemin mice. The percentage and suppressive function of CD4+CD25(high) Treg and the expression of Foxp3 mRNA were obviously enhanced after treatment with hemin. This increase was diminished by the administration of SnPP. The concentration of serum IL-10 was higher in the hemin group than in the other groups, whereas the level of serum TGF-beta did not significantly differ across groups. Furthermore, the ratio of IFN-gamma/IL-4 mRNA in the lung was higher in hemin-treated mice than in OVA and SnPP mice. The suppressive capacity of CD4+CD25(high) Treg was not enhanced in the IL-10-deficient mice treated with hemin. In conclusion, our experiments in the animal model demonstrated that HO-1 has anti-inflammatory effects, probably via enhancement of the secretion of IL-10 and promotion of the percentage of CD4+CD25(high) Treg.     

Cutting edge: cure of colitis by CD4+CD25+ regulatory T cells

CD4(+)CD25(+) regulatory T cells have been shown to prevent T cell-mediated immune pathology; however, their ability to ameliorate established inflammation has not been tested. Using the CD4(+)CD45RB(high) T cell transfer model of inflammatory bowel disease, we show that CD4(+)CD25(+) but not CD4(+)CD25(-)CD45RB(low) T cells are able to cure intestinal inflammation. Transfer of CD4(+)CD25(+) T cells into mice with colitis led to resolution of the lamina propria infiltrate in the intestine and reappearance of normal intestinal architecture. CD4(+)CD25(+) T cells were found to proliferate in the mesenteric lymph nodes and inflamed colon. They were located between clusters of CD11c(+) cells and pathogenic T cells and found to be in contact with both cell types. These studies suggest that manipulation of CD4(+)CD25(+) T cells may be beneficial in the treatment of chronic inflammatory diseases.     

Differential regulatory function of resting and preactivated allergen-specific CD4+ CD25+ regulatory T cells in Th2-type airway inflammation

Although CD4(+)CD25(+) regulatory T (Treg) cells are known to suppress Th1 cell-mediated immune responses, their effect on Th2-type immune responses remains unclear. In this study we examined the role of Treg cells in Th2-type airway inflammation in mice. Depletion and reconstitution experiments demonstrated that the Treg cells of naive mice effectively suppressed the initiation and development of Th2-driven airway inflammation. Despite effective suppression of Th2-type airway inflammation in naive mice, adoptively transferred, allergen-specific Treg cells were unable to suppress airway inflammation in allergen-presensitized mice. Preactivated allergen-specific Treg cells, however, could suppress airway inflammation even in allergen-presensitized mice by accumulating in the lung, where they reduced the accumulation and proliferation of Th2 cells. Upon activation, allergen-specific Treg cells up-regulated CCR4, exhibited enhanced chemotactic responses to CCR4 ligands, and suppressed the proliferation of and cytokine production by polarized Th2 cells. Collectively, these results demonstrated that Treg cells are capable of suppressing Th2-driven airway inflammation even in allergen-presensitized mice in a manner dependent on their efficient migration into the inflammatory site and their regulation of Th2 cell activation and proliferation.     

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.     

T cells with a CD4+CD25+ regulatory phenotype suppress in vitro proliferation of virus-specific CD8+ T cells during chronic hepatitis C virus infection

Chronic hepatitis C virus (HCV) infection is associated with impaired proliferative, cytokine, and cytotoxic effector functions of HCV-specific CD8(+) T cells that probably contribute significantly to viral persistence. Here, we investigated the potential role of T cells with a CD4(+)CD25(+) regulatory phenotype in suppressing virus-specific CD8(+) T-cell proliferation during chronic HCV infection. In vitro depletion studies and coculture experiments revealed that peptide specific proliferation as well as gamma interferon production of HCV-specific CD8(+) T cells were inhibited by CD4(+)CD25(+) T cells. This inhibition was dose dependent, required direct cell-cell contact, and was independent of interleukin-10 and transforming growth factor beta. Interestingly, the T-cell-mediated suppression in chronically HCV-infected patients was not restricted to HCV-specific CD8(+) T cells but also to influenza virus-specific CD8(+) T cells. Importantly, CD4(+)CD25(+) T cells from persons recovered from HCV infection and from healthy blood donors exhibited significantly less suppressor activity. Thus, the inhibition of virus-specific CD8(+) T-cell proliferation was enhanced in chronically HCV-infected patients. This was associated with a higher frequency of circulating CD4(+)CD25(+) cells observed in this patient group. Taken together, our results suggest that chronic HCV infection leads to the expansion of CD4(+)CD25(+) T cells that are able to suppress CD8(+) T-cell responses to different viral antigens. Our results further suggest that CD4(+)CD25(+) T cells may contribute to viral persistence in chronically HCV-infected patients and may be a target for immunotherapy of chronic hepatitis C.     

Follicular lymphoma intratumoral CD4+CD25+GITR+ regulatory T cells potently suppress CD3/CD28-costimulated autologous and allogeneic CD8+CD25- and CD4+CD25- T cells

Regulatory T cells (T(R)) play a critical role in the inhibition of self-reactive immune responses and as such have been implicated in the suppression of tumor-reactive effector T cells. In this study, we demonstrate that follicular lymphoma (FL)-infiltrating CD8+ and CD4+ T cells are hyporesponsive to CD3/CD28 costimulation. We further identify a population of FL-infiltrating CD4+CD25+GITR+ T(R) that are significantly overrepresented within FL nodes (FLN) compared with that seen in normal (nonmalignant, nonlymphoid hyperplastic) or reactive (nonmalignant, lymphoid hyperplastic) nodes. These T(R) actively suppress both the proliferation of autologous nodal CD8+CD25- and CD4+CD25- T cells, as well as cytokine production (IFN-gamma, TNF-alpha and IL-2), after CD3/CD28 costimulation. Removal of these cells in vitro by CD25+ magnetic bead depletion restores both the proliferation and cytokine production of the remaining T cells, demonstrating that FLN T cell hyporesponsiveness is reversible. In addition to suppressing autologous nodal T cells, these T(R) are also capable of suppressing the proliferation of allogeneic CD8+CD25- and CD4+CD25- T cells from normal lymph nodes as well as normal donor PBL, regardless of very robust stimulation of the target cells with plate-bound anti-CD3 and anti-CD28 Abs. The allogeneic suppression is not reciprocal, as equivalent numbers of CD25+FOXP3+ cells derived from either normal lymph nodes or PBL are not capable of suppressing allogeneic CD8+CD25- and CD4+CD25- T cells, suggesting that FLN T(R) are more suppressive than those derived from nonmalignant sources. Lastly, we demonstrate that inhibition of TGF-beta signaling partially restores FLN T cell proliferation suggesting a mechanistic role for TGF-beta in FLN T(R)-mediated suppression.     

IL-6 produced by dendritic cells from lupus-prone mice inhibits CD4+CD25+ T cell regulatory functions

The B6.Sle1.Sle2.Sle3 triple congenic mouse (B6.TC) is a model of lupus coexpressing the three major NZM2410-derived susceptibility loci on a C57BL/6 background. B6.TC mice produce high titers of antinuclear nephrogenic autoantibodies and a highly penetrant glomerulonephritis. Previous studies have shown the Sle1 locus is associated with a reduced number of regulatory T cells (Treg) and that Sle3 results in intrinsic defects of myeloid cells that hyperactivate T cells. In this report, we show that B6.TC dendritic cells (DCs) accumulate in lymphoid organs and present a defective maturation process, in which bone marrow-derived, plasmacytoid, and myeloid DCs express a significantly lower level of CD80, CD86, and MHC class II. B6.TC DCs also induce a higher level of proliferation in CD4(+) T cells than B6 DCs, and B6.TC DCs block the suppressive activity of Treg. B6.TC DCs overproduce IL-6, which is necessary for the blockade of Treg activity, as shown by the effect of anti-IL-6 neutralizing Ab in the suppression assays. The overproduction of IL-6 by DCs and the blockade of Treg activity maps to Sle1, which therefore not only confers a reduced number of Treg but also blocks their ability to regulate autoreactive T cells. Taken together, these results provide a genetic and mechanistic evidence for systemic autoimmunity resulting from an impaired regulatory T cell compartment in both number and function and for Sle1-expressing DCs playing a major role in the latter defect though their production of IL-6.     

The early IL-4 response to Leishmania major and the resulting Th2 cell maturation steering progressive disease in BALB/c mice are subject to the control of regulatory CD4+CD25+ T cells

Susceptibility and development of Th2 cells in BALB/c mice infected with Leishmania major result from early IL-4 production by Vbeta4Valpha8 CD4+ T cells in response to the Leishmania homolog of mammalian RACK1 Ag. A role for CD4+CD25+ regulatory T cells in the control of this early IL-4 production was investigated by depleting in vivo this regulatory T cell population. Depletion induced an increase in the early burst of IL-4 mRNA in the draining lymph nodes of BALB/c mice, and exacerbated the course of disease with higher levels of IL-4 mRNA and protein in their lymph nodes. We further showed that transfer of 10(7) BALB/c spleen cells that were depleted of CD4+CD25+ regulatory T cells rendered SCID mice susceptible to infection and allowed Th2 differentiation while SCID mice reconstituted with 10(7) control BALB/c spleen cells were resistant to infection with L. major and developed a Th1 response. Treatment with a mAb against IL-4 upon infection with L. major in SCID mice reconstituted with CD25-depleted spleen cells prevented the development of Th2 polarization and rendered them resistant to infection. These results demonstrate that CD4+CD25+ regulatory T cells play a role in regulating the early IL-4 mRNA and the subsequent development of a Th2 response in this model of infection.     

Naturally arising CD4+CD25+ regulatory T cells suppress the expansion of colitogenic CD4+CD44highCD62L- effector memory T cells

Naturally arising CD4+CD25+ regulatory T (T(R)) cells have been shown to prevent and cure murine T cell-mediated colitis. However, their exact mechanism of controlling colitogenic memory CD4+ T cells in in vivo systems excluding the initial process of naive T cell activation and differentiation has not been examined to date. Using the colitogenic effector memory (T(EM)) CD4+ cell-mediated colitis model induced by adoptive transfer of colitogenic CD4+CD44(high)CD62L(-) lamina propria (LP) T cells obtained from colitic CD4+CD45RB(high) T cell-transferred mice, we have shown in the present study that CD4+CD25+ T(R) cells are able not only to suppress the development of colitis, Th1 cytokine production, and the expansion of colitogenic LP CD4+ T(EM) cells but also to expand these cells by themselves extensively in vivo. An in vitro coculture assay revealed that CD4+CD25+ T(R) cells proliferated in the presence of IL-2-producing colitogenic LP CD4+ T(EM) cells at the early time point (48 h after culture), followed by the acquisition of suppressive activity at the late time point (96 h after culture). Collectively, these data suggest the distinct timing of the IL-2-dependent expansion of CD4+CD25+ T(R) cells and the their suppressive activity on colitogenic LP CD4+ T(EM) cells.     

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.     

Human CD4+CD25low adaptive T regulatory cells suppress delayed-type hypersensitivity during transplant tolerance

Adaptive T regulatory (T(R)) cells mediate the suppression of donor-specific, delayed-type hypersensitivity (DTH) in tolerant organ transplant recipients. We hypothesized that cells belonging to the CD4(+)CD25(+) T cell subset but distinct from natural T(R) cells may fulfill this role. To test this hypothesis, PBMC and biopsy samples from two tolerant kidney transplant recipients (K1 and K2) were analyzed. When transferred with recipient APC into a SCID mouse footpad, CD4(+) T cells were hyporesponsive in DTH to donor type HLA-B Ags and derivative allopeptides. However, anti-human TGF-beta1 Ab revealed a response to immunodominant allopeptides in both patients, suggesting that CD4(+) T effector (T(E)) cells coexisted with suppressive, TGF-beta1-producing CD4(+) T(R) cells. During in vitro culture, allopeptide stimulation induced both IFN-gamma-producing and surface TGF-beta1(+) T cells. The relative strength of the latter response in patient K1 was inversely correlated with the level of systemic anti-donor DTH, which varied over a 6-year interval. Allopeptide-induced surface TGF-beta1 expression was found primarily in Forkhead box P3 (FoxP3)-negative CD4(+)CD25(low) T cells, which could adoptively transfer suppression of donor-specific DTH. Biopsy samples contained numerous surface TGF-beta1(+) mononuclear cells that costained for CD4 and, less frequently CD25, but were negative for FoxP3. The CD4(+)TGF-beta1(+) T cells were localized primarily to the tubulointerstitium, whereas TGF-beta1(-)FoxP3(+)CD25(+) cells were found mainly in lymphoid aggregates. Thus, adaptive T(R) cells suppressing T(E) cell responses to donor allopeptides in two tolerant patients appear to be functionally and phenotypically distinct from CD4(+)CD25(high)FoxP3(+) T cells.     

Downregulation of CD4＋CD25＋ regulatory T cells may underlie enhanced Th1 immunity caused by immunization with activated autologous T cells

Regulatory T cells （Treg） play important roles in immune system homeostasis, and may also be involved in tumor immunotolerance by suppressing Th1 immune response which is involved in anti-tumor immunity. We have previously reported that immunization with attenuated activated autologous T cells leads to enhanced anti-tumor immunity and upregulated Thl responses in vivo. However, the underlying molecular mechanisms are not well understood. Here we show that Treg function was significantly downregulated in mice that received immunization of attenuated activated autologous T cells. We found that Foxp3 expression decreased in CD4＋CD25＋ T cells from the immunized mice. Moreover, CD4＋CD25＋Foxp3＋ Treg obtained from immunized mice exhibited diminished immunosuppression ability compared to those from naive mice. Further analysis showed that the serum of immunized mice contains a high level ofanti-CD25 antibody （about 30 ng/ml, p〈0.01 vs controls）. Consistent with a role ofanti-CD25 response in the downregulation of Treg, adoptive transfer of serum from immunized mice to naive mice led to a significant decrease in Treg population and function in recipient mice. The triggering of anti-CD25 response in immunized mice can be explained by the fact that CD25 was induced to a high level in the ConA activated autologous T cells used for immunization. Our results demonstrate for the first time that immunization with attenuated activated autologous T cells evokes anti-CD25 antibody production, which leads to impeded CD4＋CD25＋Foxp3＋ Treg expansion and function in vivo. We suggest that dampened Treg function likely contributes to enhanced Thl response in immunized mice and is at least part of the mechanism underlying the boosted anti-tumor immunity.