Transient regulatory T-cells: a state attained by all activated human T-cells

Differentiation of naive CD4+ T cells into CD4+CD25+FOXP3+ regulatory T cells by continuous antigen stimulation

Human CD4+CD25+ regulatory T (T(R)) cells express the transcription factor forkhead box p3 (FOXP3) and have potent immunosuppressive properties. While naturally occurring T(R) cells develop in the thymus, adaptive T(R) cells develop in the periphery from naive CD4+ T cells. Adaptive T(R) cells may express cyclooxygenase type 2 (COX-2) and suppress effector T cells by a PGE(2)-dependent mechanism, which is reversible with COX inhibitors. In this study we have characterized the differentiation of naive CD4+ T cells into adaptive T(R) cells in detail during 7 days of continuous antigen stimulation. After 2 days of stimulation of CD4+CD25- T cells, the cells expressed FOXP3 and COX-2 and displayed potent immunosuppressive properties. The suppressive phenotype was present at all observed time-points from Day 2, although suppression was merely present at Day 7. The adaptive T(R) cells expressed cell surface markers consistent with an activated phenotype and secreted high levels of TGF-beta, IL-10, and PGE(2). However, the suppressive phenotype was found exclusively in cells that proliferated upon activation. These data support the notion that activation of naive CD4+ T cells leads to concomitant acquisition of effector and suppressive properties.

Suppression of allergic inflammation by allergen-DNA-modified dendritic cells depends on the induction of Foxp3+ Regulatory T cells

CD4(+)CD25(+)Foxp3(+)Regulatory T cells (Tregs) play important roles in regulating allergic inflammation. To analyse if allergen-DNA-modified dendritic cells (DC) can suppress allergic responses and what roles Treg cells play in DC-based allergen-specific immunotherapy. Immature DC were transfected with retrovirus encoding Der p2 DNA, and administered to mice that sensitized and challenged with Der p2 protein. After Treg cells were depleted with anti-CD25 mAb, mice were re-challenged to observe the airway inflammation, and Treg cells in spleen CD4(+) T cells. And responses of spleen CD4(+) T cells to Der p2 were determined. Co-culture of naïve CD4(+) T cells with allergen-modified DC induced Foxp3+ Tregs. Sensitized and challenged mice developed allergic airway inflammation and Th2 responses, and decreased Foxp3(+) Tregs. Treatment with allergen-modified-DC suppressed airway inflammation and Th2 responses, and increased IL-10 and IFN-gamma production and Foxp3(+) Tregs significantly; and eliminated the responses of CD4(+) T cells to allergen. Administration of anit-CD25 mAb eliminated all the effects of modified-DC except for the increasing of IFN-gamma. Allergen-modified DC can induce immune tolerance to allergens and reverse the established Th2 responses induced by allergen, with dependence on the induction of Foxp3(+) Tregs.

GATA3-driven Th2 responses inhibit TGF-beta1-induced FOXP3 expression and the formation of regulatory T cells

Transcription factors act in concert to induce lineage commitment towards Th1, Th2, or T regulatory (T_reg) cells, and their counter-regulatory mechanisms were shown to be critical for polarization between Th1 and Th2 phenotypes. FOXP3 is an essential transcription factor for natural, thymus-derived (nT_reg) and inducible T_reg (iT_reg) commitment; however, the mechanisms regulating its expression are as yet unknown. We describe a mechanism controlling iT_reg polarization, which is overruled by the Th2 differentiation pathway. We demonstrated that interleukin 4 (IL-4) present at the time of T cell priming inhibits FOXP3. This inhibitory mechanism was also confirmed in Th2 cells and in T cells of transgenic mice overexpressing GATA-3 in T cells, which are shown to be deficient in transforming growth factor (TGF)-β–mediated FOXP3 induction. This inhibition is mediated by direct binding of GATA3 to the FOXP3 promoter, which represses its transactivation process. Therefore, this study provides a new understanding of tolerance development, controlled by a type 2 immune response. IL-4 treatment in mice reduces iT_reg cell frequency, highlighting that therapeutic approaches that target IL-4 or GATA3 might provide new preventive strategies facilitating tolerance induction particularly in Th2-mediated diseases, such as allergy.

Specific immune responses against foreign or autologous antigens are driven by specialized epitope-specific T cells, whose numbers expand upon recognition of antigen found on professional antigen-presenting cells. The subsequent maturation process involves the differentiation of certain T cell phenotypes such as pro-inflammatory cells (Th1, Th2, Th17) or regulatory T (T_reg) cells, which serve to keep the immune response in check. The current study focuses on the role of two key transcription factors—FOXP3 and GATA3—in controlling the commitment of these cells. We demonstrate that the Th2 cytokine IL-4 inhibits the induction of FOXP3 and thus inhibits the generation of inducible T_reg cells. We show that IL-4–induced GATA3 mediates FOXP3 inhibition by directly binding to a GATA element in the FOXP3 promoter. We hypothesize that therapeutic agents aimed at neutralizing IL-4 could be a novel strategy to facilitate inducible T_reg cell generation and thus promotion of tolerance in allergies and other Th2-dominated diseases.

It is shown that Th2 responses prevent the generation of inducible T_regs. This is mediated by IL-4 induction of GATA3, which binds directly to and represses the FOXP3 promoter. This mechanism is likely to be relevant in the induction of immunotolerance, particularly in allergic diseases.

MicroRNAs and immunity: novel players in the regulation of normal immune function and inflammation

The discovery of microRNAs (miRNAs) is one of the major scientific breakthroughs in recent years and has revolutionized the way we look at gene regulation. Although we are still at a very early stage in understanding their impact on immunity, miRNAs are changing the way we think about the development of the immune system and regulation of immune functions. MiRNAs are implicated in establishing and maintaining the cell fate of immune cells (e.g. miR-181a and miR-223), and they are involved in innate immunity by regulating Toll-like receptor signaling and ensuing cytokine response (e.g. miR-146). Moreover, miRNAs regulate central elements of the adaptive immune response such as antigen presentation (e.g. miR-155) and T cell receptor signaling (miR-181a). Recent evidence showing altered miRNA expression in chronic inflammatory diseases (e.g. miR-203 and miR-146) suggests their involvement in immune-mediated diseases. Furthermore, miRNAs have been implicated in viral immune escape and anti-viral defense (e.g. miR-196). In this review, we will summarize the latest findings about the role of miRNAs in the development of the immune system and regulation of immune functions and inflammation.

T-cell regulation by CD4 regulatory T cells during hepatitis B and C virus infections: facts and controversies

In the past few years, we have witnessed extraordinary advances in the understanding of the functions of regulatory T (Treg) cells in immunity against pathogens. However, controversy exists over the part that these cells play in determining the outcome of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, the two main causes of chronic liver inflammation worldwide. Treg-cell responses may be either beneficial or detrimental to those infected with HBV and HCV, by either limiting liver immunopathology or suppressing protective T-cell responses. We review the latest research on CD4 Treg cells, dissect much of the Treg-related HBV and HCV literature, and discuss how new insights in Treg immunobiology apply to human and primate models of HBV and HCV infections. Moreover, we discuss the limitations of the conclusions drawn from current studies on Treg cells, and suggest experimental approaches that can resolve current conflicts and improve our understanding of the roles of Treg-cell subsets in HBV and HCV infections.

Localisation pattern of Foxp3+ regulatory T cells is associated with clinical behaviour in gastric cancer

It has been reported that the population of regulatory T cells (T regs) is increased in tumour-infiltrating lymphocytes in cancer-bearing hosts. Recently, forkhead/winged helix transcription factor p3, Foxp3, is thought to be the most reliable marker of T regs. In the present study, we investigated the prevalence and localisation pattern of Foxp3⁺ cells in gastric cancer (n=80) by immunohistochemistry, in relation to the clinical outcome of gastric cancer patients. Immunohistochemical staining was performed with anti-Foxp3 mAb, and Foxp3⁺ cells were semiquantified. We divided all cases into two groups: Foxp3⁺-high (n=40) and Foxp3⁺-low (n=40) groups, by the median size of the population of Foxp3⁺ cells. Furthermore, in terms of the localisation pattern of accumulating Foxp3⁺ cells in tumours, we classified all cases into three groups: a peri-tumour group (n=30), a diffuse group (n=40), and a follicular group (n=10). As a result, although the populations of Foxp3⁺ cells in stage IV were significantly larger than those in stage I (P<0.05), there was no significant difference in survival between the patients with high and low population levels of Foxp3⁺ cells. However, survival in patients with a diffuse pattern of Foxp3⁺ cells was significantly poorer than in those with a peri-tumoral pattern. In conclusion, the localisation pattern, but not the population size, of Foxp3⁺ cells was significantly related to patient survival.

Generation of potent and stable human CD4+ T regulatory cells by activation-independent expression of FOXP3

Therapies based on enhancing the numbers and/or function of T regulatory cells (Tregs) represent one of the most promising approaches to restoring tolerance in many immune-mediated diseases. Several groups have investigated whether human Tregs suitable for cellular therapy can be obtained by in vitro expansion, in vitro conversion of conventional T cells into Tregs, or gene transfer of the FOXP3 transcription factor. To date, however, none of these approaches has resulted in a homogeneous and stable population of cells that is as potently suppressive as ex vivo Tregs. We developed a lentivirus-based strategy to ectopically express high levels of FOXP3 that do not fluctuate with the state of T-cell activation. This method consistently results in the development of suppressive cells that are as potent as Tregs and can be propagated as a homogeneous population. Moreover, using this system, both naïve and memory CD4(+) T cells can be efficiently converted into Tregs. To date, this is the most efficient and reliable protocol for generating large numbers of suppressive CD4(+) Tregs, which can be used for further biological study and developed for antigen-specific cellular therapy applications.

Administration of a CD25-directed immunotoxin, LMB-2, to patients with metastatic melanoma induces a selective partial reduction in regulatory T cells in vivo

CD25+ CD4+ T regulatory (Treg) cells regulate peripheral self tolerance and possess the ability to suppress antitumor responses, which may in part explain the poor clinical response of cancer patients undergoing active immunization protocols. We have previously shown that in vitro incubation of human PBMC with LMB-2, a CD25-directed immunotoxin, significantly reduced CD25+ FOXP3+ CD4+ Treg cells without impairing the function of the remaining lymphocytes. In the current study, eight patients with metastatic melanoma were treated with LMB-2 followed by MART-1 and gp100-specific peptide vaccination. LMB-2 administration resulted in a preferential, transient reduction in mean circulating CD25+ CD4+ T cell number, from 83 +/- 16 cells/microl to a nadir of 17 +/- 5 cells/microl, a 79.1% reduction. FOXP3 analysis revealed a less robust depletion with mean FOXP3+ CD4+ Treg cell number decreasing from 74 +/- 15 cells/microl to 36 +/- 8 cells/microl, a 51.4% reduction. FOXP3+ CD4+ Treg cells that survived LMB-2-mediated cytotoxicity expressed little or no CD25. Similar to the peripheral blood, immunohistochemical analysis showed a 68.9% mean reduction in FOXP3+ CD4+ Treg cell frequency in evaluable lesions. Despite inducing a reduction in Treg cell numbers in vivo, LMB-2 therapy did not augment the immune response to cancer vaccination and no patient experienced an objective response or autoimmunity. These data demonstrate the capacity of a CD25-directed immunotoxin to selectively mediate a transient partial reduction in circulating and tumor-infiltrating Treg cells in vivo, and suggest that more comprehensive Treg cell elimination may be required to bolster antitumor responses in patients with metastatic melanoma.

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked: forkhead box protein 3 mutations and lack of regulatory T cells

The rare X-linked disorder immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) and its murine counterpart scurfy have provided important new insights into the essential role of regulatory T cells (Treg) in maintaining tolerance to self-antigens. Mutations of the FOXP3 gene, identified in patients with IPEX, have helped pinpoint key structural domains of the protein that are essential for its function as a transcriptional regulator. Ongoing work using these and associated models has begun to elucidate factors important for the development, function, and competitive fitness of Treg. This improved understanding is beginning to lead to the identification of other defects that may be present in patients who have the clinical phenotype of IPEX but only wild-type FOXP3. It has also led to improved treatment options for IPEX including immunosuppressive drugs and bone marrow transplantation. We are hopeful that the knowledge gained about mechanisms that regulate FOXP3 expression and Treg function will have a major effect on how other autoimmune and allergic disorders are approached.

Relationship between early intestinal colonization, mucosal immunoglobulin A production and systemic immune development

BACKGROUND

Variations in early intestinal colonization patterns have been implicated in the predispostion to allergic disease through effects on mucosal and systemic immune function.

METHODS

Colonization patterns and mucosal IgA production at 6 months of age were examined in relation to early exposures, systemic immune development and early allergic outcomes. This was performed in a cohort (n=189) who had received either Lactobacillus acidophilus or a placebo since birth.

RESULTS

Children who developed sensitization to one or more allergens by 12 months of age had significantly higher total (but not secretory) IgA levels at 6 months (P=0.024), but this was independent of probiotic treatment. There were no relationships between colonization patterns and IgA (total or secretory IgA) levels or allergic outcomes (sensitization, atopic dermatitis or food allergies). Breastfeeding, and the use of yoghurt or probiotic supplements were independently associated with significantly higher proportions of 'favourable' lactobacilli and bifidobacteria species. Caesarean delivery and the use of antibiotics during the first 6 months were not associated with significant variations in colonization. Higher proportions of 'favourable' bacteria (notably bifidobacteria) were associated with reduced production of most cytokine response to allergens, but increased expression of regulatory cell markers (P=0.009) and transforming growth factor-beta (P=0.016).

CONCLUSION

'Favourable' colonization, particularly with bifidobacteria, was associated with effects on cellular immune function, but this was not associated with mucosal immunity (secretory IgA) or reduced risk of allergic disease.

DNA demethylation in the human FOXP3 locus discriminates regulatory T cells from activated FOXP3(+) conventional T cells

The transcription factor FOXP3 is critical for development and function of regulatory T cells (Treg). Their number and functioning appears to be crucial in the prevention of autoimmunity and allergy, but also to be a negative prognostic marker for various solid tumors. Although expression of the transcription factor FOXP3 currently constitutes the best-known marker for Treg, in humans, transient expression is also observed in activated non-Treg. Extending our recent findings for the murine foxp3 locus, we observed epigenetic modification of several regions in the human FOXP3 locus exclusively occurring in Treg. Importantly, activated conventional CD4(+) T cells and TGF-beta-treated cells displayed no FOXP3 DNA demethylation despite expression of FOXP3, whereas subsets of Treg stable even upon extended in vitro expansion remained demethylated. To investigate whether a whole set of genes might be epigenetically imprinted in the Treg lineage, we conducted a genome-wide differential methylation hybridization analysis. Several genes were found displaying differential methylation between Treg and conventional T cells, but none beside FOXP3 turned out to be entirely specific to Treg when tested on a broad panel of cells and tissues. We conclude that FOXP3 DNA demethylation constitutes the most reliable criterion for natural Treg available at present.

Induction of FOXP3 expression in naive human CD4+FOXP3 T cells by T-cell receptor stimulation is transforming growth factor-beta dependent but does not confer a regulatory phenotype

Thymic-derived natural T-regulatory cells (nTregs) are important for the induction of self-tolerance and the control of autoimmunity. Murine CD4+CD25(-)Foxp3(-) cells can be induced to express Foxp3 after T-cell receptor (TCR) activation in the presence of transforming growth factor beta (TGFbeta) and are phenotypically similar to nTregs. Some studies have suggested that TCR stimulation of human CD4+CD25(-) cells results in the induction of transient expression of FOXP3, but that the induced cells lack a regulatory phenotype. We demonstrate here that TCR stimulation alone was insufficient to induce FOXP3 expression in the absence of TGFbeta, whereas high levels of FOXP3 expression could be induced in the presence of TGFbeta. Although FOXP3 expression was stable, the TGFbeta-induced FOXP3+ T cells were neither anergic nor suppressive and produced high levels of effector cytokines. These results suggest that even high levels of FOXP3 expression are insufficient to define a human CD4+ T cell as a T-regulatory cell.

Histone deacetylase inhibitors and transplantation

Simply detecting the presence or absence of Foxp3, a transcription factor characteristic of naturally occurring CD4+ CD25+ regulatory T cells (Tregs), now appears of minimal value in predicting the outcome of immunologic responses, since dividing human CD4+ effector T cells can induce Foxp3 without attaining repressive functions, and additional molecular interactions, as well epigenetic events, affect Foxp3-dependent Treg functions in humans and mice. Experimentally, in vivo and in vitro studies show histone deacetylase inhibitors (HDACi) can enhance the numbers and suppressive function of regulatory T cells (Tregs) by promoting Foxp3+ cell production, enhancing chromatin remodeling within Tregs, and inducing acetylation of Foxp3 protein itself. Human studies consistent with a role for HDACi in controlling Fox3-dependent Treg functions are also available. We review these molecular interactions and how they may be exploited therapeutically to enhance Treg-dependent functions, including post-transplantation.

Functional and genomic analyses of FOXP3-transduced Jurkat-T cells as regulatory T (Treg)-like cells

FOXP3, a forkhead transcription factor is essential for the development and function of CD4(+)CD25(+) regulatory T cells (Tregs). In contrast to conversion of murine naive T cells to Tregs by transduction of Foxp3, it is controversial whether ectopic expression of FOXP3 in human CD4(+) T cells is sufficient for acquisition of suppressive activity. Here, we show that retroviral transduction of FOXP3 induces a Treg phenotype in human leukemic CD4(+) Jurkat-T cells, evidenced by increased expression of Treg-associated cell surface markers as well as inhibition of cytokine production. Furthermore, FOXP3-transduced Jurkat-T cells suppress the proliferation of human CD4(+)CD25(-) T cells. Additionally, DNA microarray analysis identifies Treg-related genes regulated by FOXP3. Our study demonstrates that enforced expression of FOXP3 confers Treg-like properties on Jurkat-T cells, which can be a convenient and efficient Treg-like cell model for further study to identify Treg cell surface markers and target genes regulated by FOXP3.

Human regulatory T cells: a unique, stable thymic subset or a reversible peripheral state of differentiation?

FOXP3 is probably the best marker available currently for identifying natural regulatory T cells (T(reg)s) in mice and humans. Evidence from mouse literature suggests that natural FOXP3(+) T(reg)s are formed in the thymus and expand in the periphery to contribute significantly to peripheral T(reg)s. In this review, we discuss recent reports that show that, in humans, the formation of FOXP3(+) T(reg)s is a natural consequence of T cell activation and that de novo peripheral generation of FOXP3(+) T(reg)s is a much more dominant source of circulating T(reg)s than natural thymically derived T(reg)s. We also suggest that the role of T(reg)s in human diseases must be reviewed in light of these new findings and great caution should be exercised in immunotherapeutic interventions that involve the modulation or generation of putative T(reg)s.

Effects of pollen and nasal glucocorticoid on FOXP3+, GATA-3+ and T-bet+ cells in allergic rhinitis

BACKGROUND

T-regulatory cells (Treg) affect the balance of T(H)2 and T(H)1 cells. Treg, T(H)2 and T(H)1 cells are regulated by the FOXP3, GATA-3 and T-bet transcription factors respectively. Our aim was to determine the number of FOXP3(+), GATA-3(+) and T-bet(+) cells in nasal mucosa in symptom-free allergic rhinitis (AR) patients vs healthy controls, as well as the effects of natural pollen exposure and concomitant nasal glucocorticoid treatment on these cells.

METHODS

Nasal biopsies were taken from healthy controls and patients with grass-pollen AR preseason. The AR patients were randomized to receive treatment with either fluticasone propionate (FP) or a placebo, and additional biopsies were taken during the pollen season. FOXP3(+), GATA-3(+) and T-bet(+) cells in nasal mucosa were quantified by immunohistochemistry.

RESULTS

The number of FOXP3(+) and GATA-3(+) cells, but not T-bet(+) cells, was significantly higher in AR patients vs controls preseason. The number of FOXP3(+) cells remained unchanged in the former group after the pollen season but decreased significantly in the nasal mucosa as a result of FP treatment. The pollen season substantially increased the number of GATA-3(+) cells, which was inhibited by FP. The number of T-bet(+) cells was not affected by pollen or FP.

CONCLUSION

These data suggest that nasal glucocorticoids attenuate the allergic inflammation partly by reducing the number of T(H)2 cells, but not by means of local upregulation of Treg cells. The local relationship between T(H)1 and T(H)2 cells as well as between Treg and T(H)2 is maintained by nasal glucocorticoid treatment.

Proportions of circulating T cells with a regulatory cell phenotype increase with HIV-associated immune activation and remain high on antiretroviral therapy

OBJECTIVE

To examine the relationships between blood CD4 natural regulatory T (Treg) cells, plasma HIV RNA level, CD4 T-cell count and immune activation in untreated HIV-infected patients and immunodeficient patients beginning antiretroviral therapy (ART), using a novel phenotype to define Treg cells (CD25CD127CD4). Data were compared with established Treg cell markers (FoxP3, CTLA-4 and GITR).

METHODS

Twenty-nine untreated HIV-infected patients with CD4 T-cell counts of < 300 or > 400/microl were compared in a cross-sectional study and 12 patients beginning combination ART with < 100 CD4 T cells/mul were followed for 1 year on therapy. Three- and four-colour flow cytometry was used to quantitate proportions of Treg cells.

RESULTS

In control donors and patients with high CD4 T-cell counts, 28-89% (median 60%) of CD25CD127CD4 cells were FoxP3, but < 10% expressed GITR or CTLA-4. Immunodeficient patients also had CD4-negative lymphocytes with the phenotype FoxP3CD127. Proportions of CD25CD127 cells and activated (HLA-DR) cells in the CD4 T-cell population were increased in patients with low CD4 T cell counts. The proportion of CD25CD127CD4 T cells correlated positively with plasma HIV RNA level and CD4 T-cell activation, but inversely with CD4 T-cell count. Longitudinal studies of 12 patients receiving ART in two distinct cohorts (Western Australia and Malaysia) showed that the proportion of CD25CD127CD4 cells decreased slightly over time, but remained above levels seen in non-HIV controls.

CONCLUSIONS

Proportions of circulating T cells with a regulatory cell phenotype increase with HIV-associated immune activation and remain high after 1 year on ART.

Anti-CD25 treatment and FOXP3-positive regulatory T cells in heart transplantation

The interleukin-2 receptor alpha chain (IL-2Ra, CD25) plays a major part in shaping the dynamics of T cell populations following immune activation, due to its role in T cell proliferation and survival. Strategies to blunt the effector responses in transplantation have been developed by devising pharmaceutical agents to block the IL-2 pathways. However, such strategies could adversely affect the CD25(+)FOXP3(+)T regulatory (T reg) populations which also rely on intereukin-2 signaling for survival. The present study shows that a cohort of heart allograft recipients treated with Daclizumab (a humanized anti-CD25 antibody) display FOXP3 expression patterns consistent with functional T regulatory cell populations. High levels of FOXP3 were observed to correlate with lower incidence of and recovery from acute rejection, as well as lower levels of anti-donor HLA antibody production. Therefore, T reg populations appear fully functional in patients treated with Daclizumab, even when 5 doses were administered. By comparison, patients treated with fewer doses or no Daclizumab had a higher incidence of acute rejection, antibody production and graft failure. Therefore, our data indicates that Daclizumab treatment does not interfere with the generation of regulatory T cells and has a beneficial effect on heart allograft survival.

Flow cytometry-based methods for studying signaling in human CD4+CD25+FOXP3+ T regulatory cells

T regulatory (Treg) cells have a fundamental role in the establishment and maintenance of peripheral tolerance. It is well established that Treg cells have a phenotype and function that is distinct from conventional T effector cells, although how these two T cell subsets differ in terms of molecular signaling cascades remains largely unknown. Analysis of signaling events in Treg cells using classical biochemistry has been hampered due to difficulties in isolating homogeneous populations and limited cell numbers. In order to overcome these challenges, we defined the optimal conditions for culture, in vitro expansion, and stimulation of human CD4(+)CD25(+) Treg and T effector cells to study intracellular signaling events by flow cytometry. In order to avoid the pitfalls associated with cell isolation based on CD25 expression, we developed methodology to analyze subpopulations of FOXP3 positive and negative cells from ex vivo CD4(+) T cells. In addition to examination of ex vivo cells, we optimized expansion conditions for analysis of signaling in Treg and T effector cell lines. Using these methods, we found that human FOXP3(+) Treg cells displayed a greater capacity to phosphorylate the extracellular regulated kinase (ERK) compared to T effector cells, upon TCR-mediated activation. In contrast, FOXP3(+) Treg cells showed a significantly diminished capacity to phosphorylate AKT. This methodology provides a foundation for future investigation into the molecular events that regulate the phenotype and function of Treg cells, and may ultimately lead to the identification of Treg-cell specific therapeutic targets.

FoxP3 enhances HIV-1 gene expression by modulating NFkappaB occupancy at the long terminal repeat in human T cells

FoxP3 determines the development of CD4+CD25+ regulatory T (Treg) cells and represses interleukin-2 (IL-2) expression in Treg cells. However, human immunodeficiency virus type 1 (HIV-1) infects and replicates efficiently in FoxP3+ Treg cells. We report that, while inhibiting IL-2 gene expression, FoxP3 enhances gene expression from HIV-1 long terminal repeat (LTR). This FoxP3 activity requires both the N- and C-terminal domains and is inactivated by human IPEX (immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome) mutations. FoxP3 enhances HIV-1 LTR via its specific NFkappaB binding sequences in an NFkappaB-dependent fashion in T cells but not in HEK293 cells. FoxP3 decreases level of histone acetylation at the interleukin-2 locus but not at the HIV-1 LTR. Although NFkappaB nuclear translocation is not altered, FoxP3 enhances NFkappaB-p65 binding to HIV-1 LTR. These data suggest that FoxP3 modulates gene expression in a promoter sequence-dependent fashion by modulating chromatin structure and NFkappaB activity. HIV-1 LTR has evolved to both highjack the T-cell activation pathway for expression and to resist FoxP3-mediated suppression of T-cell activation.

Immunohistochemical Analysis of Regulatory T Cell Markers FOXP3 and GITR on CD4+CD25+ T Cells in Normal Skin and Inflammatory Dermatoses

Regulatory T cells (Treg) are a subset of T lymphocytes that play a central role in immunologic tolerance and in the termination of immune responses. The identification of these cells in normal and inflammatory conditions may contribute to a better understanding of underlying pathology. We investigated the expression of FOXP3 and GITR in normal skin and in a panel of different inflammatory dermatoses. Immunohistochemical double stainings in skin tissue sections revealed that FOXP3 and GITR were almost exclusively present on T cells that express both CD4 and CD25. Further, immunohistochemical double staining, as well as fluorescence-activated cell sorter analysis, on peripheral blood T cells showed that most FOXP3+ cells expressed GITR and vice versa, whereas a minority were single-positive for these markers. The mean frequency of FOXP3+ T cells in spongiotic dermatitis, psoriasis, and lichen planus was in the same range (25-29%), but the frequency of these cells in leishmaniasis appeared to be lower (∼15%), although this was not statistically significant. The mean frequency of GITR+ T cells was fairly similar in all conditions studied (14-20%). Normal human skin also contained FOXP3+ and GITR+ cells in the same frequency range as in diseased skin, but the absolute numbers were, of course, much lower. In conclusion, frequencies of FOXP3+ and GITR+ T cells were similar in all inflammatory skin diseases studied and normal skin, despite the well-known differences among the inflammatory conditions under investigation.

Severe food allergy as a variant of IPEX syndrome caused by a deletion in a noncoding region of the FOXP3 gene

BACKGROUND & AIMS

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX; OMIM 304930) syndrome is a congenital syndrome characterized by autoimmune enteropathy, endocrinopathy, dermatitis, and other autoimmune phenomena. In the present work, we aimed to uncover the molecular basis of a distinct form of IPEX syndrome presenting at the edge of autoimmunity and severe allergy.

METHODS

The FOXP3 gene was sequenced, FOXP3 messenger RNA (mRNA) was quantified by real-time polymerase chain reaction (PCR), and protein expression in peripheral blood lymphocytes was analyzed by flow cytometry after intracellular staining. In coculture experiments (CD4(+)CD25(-) and CD4(+)CD25(+) cells), the functions of regulatory T cells were analyzed. Expression of interferon gamma and interleukin 2 and 4 mRNA within the inflamed intestinal mucosa was quantified by real-time PCR.

RESULTS

Here, we describe a distinct familial form of IPEX syndrome that combines autoimmune and allergic manifestations including severe enteropathy, food allergies, atopic dermatitis, hyper-IgE, and eosinophilia. We have identified a 1388-base pair deletion (g.del-6247_-4859) of the FOXP3 gene encompassing a portion of an upstream noncoding exon (exon -1) and the adjacent intron (intron -1). This deletion impairs mRNA splicing, resulting in accumulation of unspliced pre-mRNA and alternatively spliced mRNA. This causes low FOXP3 mRNA levels and markedly decreased protein expression in peripheral blood lymphocytes of affected patients. Numbers of CD4(+)CD25(+)FOXP3(+) regulatory T cells are extremely low, and the CD4(+)CD25(+) T cells that are present exhibit little regulatory function.

CONCLUSIONS

A new mutation within an upstream noncoding region of FOXP3 results in a variant of IPEX syndrome associating autoimmune and severe immunoallergic symptoms.