Regulatory T cells (TReg) control immune responses to self and nonself Ags. The relationship between Ag-driven IL-10-secreting TReg (IL-10-TReg) and naturally occurring CD4+CD25+ TReg is as yet unclear. We show that mouse IL-10-TReg obtained using either in vitro or in vivo regimens of antigenic stimulation did not express the CD4+CD25+ TReg-associated transcription factor Foxp3. However, despite the absence of Foxp3 expression, homogeneous populations of IL-10-TReg inhibited the in vitro proliferation of CD4+CD25− T cells with a similar efficiency to that of CD4+CD25+ TReg. This inhibition of T cell proliferation by IL-10-TReg was achieved through an IL-10-independent mechanism as seen for CD4+CD25+ TReg and was overcome by exogenous IL-2. Both IL-10-TReg and CD4+CD25+ TReg were similar in that they produced little to no IL-2. These data show that Foxp3 expression is not a prerequisite for IL-10-TReg activity in vitro or in vivo, and suggest that IL-10-TReg and naturally occurring CD4+CD25+ TReg may have distinct origins.

Th17 cell differentiation is dependent on interleukin (IL)-6 and transforming growth factor (TGF)-␤ , and it is modulated by activation of the aryl hydrocarbon receptor (AhR). In this study, we show that differentiation of Th17 cells, but not Th1 or induced regulatory T (iT reg) cells, is increased by endogenous AhR agonists present in culture medium. Th17 development from wild-type mice is suboptimal in the presence of the AhR antagonist CH-223191, similar to the situation in AhR-defi cient mice, which show attenuated IL-17 production and no IL-22 production. The presence of natural AhR agonists in culture medium is also revealed by the induction of CYP1A1, a downstream target of AhR activation. However, the most commonly used medium, RPMI, supports very low levels of Th17 polarization, whereas Iscove ' s modifi ed Dulbecco ' s medium, a medium richer in aromatic amino acids, which give rise to AhR agonists, consistently results in higher Th17 expansion in both mouse and human cells. The relative paucity of AhR agonists in RPMI medium, coupled with the presence of factors conducive to IL-2 activation and enhanced Stat5 phosphorylation, conspire against optimal Th17 differentiation. Our data emphasize that AhR activation plays an essential part in the development of Th17 cells and provide a rational explanation for the poor in vitro polarization of Th17 cells that is reported in the majority of publications for both mouse and human cells.

SummaryCD4+ T cells producing interleukin-10 (IL-10) and interferon-γ (IFN-γ) are reported in chronic infections. However, the signals that direct the development of IL-10-producing T helper 1 (Th1) cells are undefined. We showed that development of IL-10-producing Th1 cells required high T cell receptor (TCR) ligation, sustained ERK1 and ERK2 MAP kinases phosphorylation, and IL-12-induced STAT4 transcription factor activation. Repeated TCR triggering led to enhanced IL-10 production by Th1 cells, and continued IL-12 action and high-dose TCR signaling were required for the development and maintenance of IL-10-producing Th1 cells. Although Th1, Th2, and Th17 cells require the activation of distinct STATs for their differentiation, activation of ERK1 and ERK2 was a common requirement for production of IL-10 by all Th cell subsets. IL-10 expression also correlated with c-maf expression. Despite having distinct functions in protection against pathogens, all Th cells share the important task of controlling overexuberant immune responses by means of IL-10 production.

1α,25-Dihydroxyvitamin D3 (1α25VitD3) has potent immunomodulatory properties. We have previously demonstrated that 1α25VitD3 promotes human and murine IL-10-secreting CD4 + T cells. Because of the clinical relevance of this observation, we characterized these cells further and investigated their relationship with Foxp3 + regulatory T (Treg) cells. 1α25VitD3 increased the frequency of both Foxp3 + and IL-10 + CD4 + T cells in vitro. However, Foxp3 was increased at high concentrations of 1α25VitD3 and IL-10 at more moderate levels, with little coexpression of these molecules. The Foxp3 + and IL-10 + T-cell populations showed comparable suppressive activity. We demonstrate that the enhancement of Foxp3 expression by 1α25VitD3 is impaired by IL-10. 1α25VitD3 enables the selective expansion of Foxp3 + Treg cells over their Foxp3 − T-cell counterparts. Equally, 1α25VitD3 maintains Foxp3 + expression by sorted populations of human and murine Treg cells upon in vitro culture. A positive in vivo correlation between vitamin D status and CD4 + Foxp3 + T cells in the airways was observed in a severe pediatric asthma cohort, supporting the in vitro observations. In summary, we provide evidence that 1α25VitD3 enhances the frequency of both IL-10 + and Foxp3 + Treg cells. In a translational setting, these data suggest that 1α25VitD3, over a broad concentration range, will be effective in enhancing the frequency of Treg cells.Keywords: 1α,25-Dihydroxyvitamin D3 r Asthma r Immune regulation r Regulatory T cells Supporting Information available online IntroductionConsiderable interest exists in the therapeutic potential of regulatory T (Treg) cells to treat a range of immune-mediated patholoCorrespondence: Dr. Catherine M. Hawrylowicz e-mail: catherine.hawrylowicz@kcl.ac.uk gies in humans. This is partly based on evidence obtained from animal models of human disease demonstrating the capacity of Treg cells to control transplant rejection, and to successfully treat autoimmune and allergic disease [1]. Two broad therapeutic * These authors contributed equally to this work. [11]. These studies demonstrate a correlation between therapeutic efficacy and increased frequency or quantities of CD4 + CD25 + T cells, IL-10, TGF-β, and CTLA-4.Our earlier studies have highlighted the capacity of 1α25VitD3 to promote human CD4 + IL-10 secreting Treg cells (IL-10-Treg) in culture both alone [12] and in concert with glucocorticoids such as dexamethasone [13,14]. Furthermore, treatment of severe steroid refractory asthma patients with 1α25VitD3 in vivo directly increased IL-10 gene expression in CD3 + CD4 + T cells [12], and restored the impaired steroid-induced IL-10 response in CD4 + cells in vitro [14,15].The present study was designed to further investigate the mechanisms underlying the therapeutic potential of 1α25VitD3 in the context of asthmatic disease, and to determine effects on the induction of both IL-10 + and Foxp3 + T cells. Specifically, we have examined the effects of 1α25VitD3 on total, unfractionated CD4 + T-cell populations, r...

Maintenance of homeostasis in the immune system involves competition for resources between T lymphocytes, which avoids the development of immune pathology seen in lymphopenic mice. CD25+ CD4+ T cells are important for homeostasis, but there is as yet no consensus on their mechanisms of action. Although CD25+ CD4+ T cells cause substantial down-regulation of IL-2 mRNA in responder T cells in an in vitro co-culture system, the presence of IL-protein can be demonstrated by intracellular staining. As a consequence of competition for IL-2, CD25+ CD4+ T cells further up-regulate the IL-2R alpha chain (CD25), a process that is strictly dependent on IL-2, whereas responder T cells fail to up-regulate CD25. Similarly, adoptive transfer into lymphopenic mice showed that CD25+ CD4+ T cells interfere with CD25 up-regulation on co-transferred naive T cells, while increasing their own CD25 levels. IL-2 sequestration by CD25+ CD4+ T cells is not a passive phenomenon but instead initiates--in conjunction with signals through the TCR--their differentiation to IL-10 production. Although IL-10 is not required for in vitro suppression, it is vital for the in vivo function of regulatory T cells. Our data provide a link explaining the apparent difference in regulatory mechanisms in vitro and in vivo.

The molecular mechanisms that regulate expression of the immunosuppressive cytokine IL-10 remain poorly understood. In this study, by measuring sensitivity to DNase I digestion, we show that production of IL-10 by primary mouse bone marrow-derived macrophages stimulated through pattern recognition receptors was associated with chromatin remodeling of the IL-10 locus. We also demonstrate that the IL-10 locus is remodeled in primary Th2 cells and IL-10-producing regulatory T cells that have been differentiated in vitro. Strikingly, a novel DNase I-hypersensitive site (HSS-4.5) was identified in stimulated macrophages, but not in T cells. We show that hyperacetylated histones were recruited to this site in stimulated macrophages. Furthermore, HSS-4.5 is highly conserved and contains a putative NF-κB binding site. In support of a function for this site, NF-κB p65/RelA was recruited to HSS-4.5 in vivo and its activation was required for optimal IL-10 gene expression in LPS-stimulated macrophages.

Foxp3-expressing Tregs play a non-redundant role in protecting against immune pathologies.

Influenza A virus causes worldwide epidemics and pandemics and the investigation of memory T helper (Th) cells that help maintain serological memory following infection is important for vaccine design. In this study we investigated CD94 and NKG2 gene expression in memory CD4 T-cell clones established from the spleens of C57BL/10 (H-2(b)) and BALB/c (H-2(d)) mice infected with influenza A virus (H3N2). CD94 and NKG2A/C/E proteins form heterodimeric membrane receptors that are involved in virus recognition. CD94 and NKG2 expression have been well characterized in natural killer (NK) and cytotoxic T cells. Despite CD94 being potentially an important marker for Th1 cells involved in virus infection, however, there has been little investigation of its expression or function in the CD4 T-cell lineage and no studies have looked at in-vivo-generated Th cells or memory cells. We show in this study that in-vivo-generated CD4 Th1 cells, but not Th2 cells, exhibited full-length CD94 and NKG2A gene expression following activation with viral peptide. For NKG2A, a novel 'short' (possibly redundant) truncated isoform was detectable in a Th2 cell clone. Another member of the NK receptor family, NKG2D, but not NKG2C or E, was also differentially expressed in Th1 cells. We show here that CD94 and NKG2A may exist as multiple isoforms with the potential to distinguish helper T-cell subsets.