European Journal of Immunology update, may 9
Written by admin on May 20th, 2008 | Filed under: immunology UPDATE
Circumvention of regulatory CD4+ T cell activity during cross-priming strongly enhances T cell-mediated immunity
Immunization with purified antigens is a safe and practical vaccination strategy but is generally unable to induce sustained CD8+ T cell-mediated protection against intracellular pathogens. Most efforts to improve the CD8+ T cell immunogenicity of these vaccines have focused on co-administration of adjuvant to support cross-presentation and dendritic cell maturation. In addition, it has been shown that CD4+ T cell help during the priming phase contributes to the generation of protective CD8+ memory T cells. In this report we demonstrate that the depletion of CD4+ T cells paradoxically enhances long-lasting CD8-mediated protective immunity upon protein vaccination. Functional and genetic in vivo inactivation experiments attribute this enhancement primarily to MHC class II-restricted CD4+ regulatory T cells (Treg), which appear to physiologically suppress the differentiation process towards long-living effector memory T cells. Since, in functional terms, this suppression by Treg largely exceeds the positive effects of conventional CD4+ T cell help, even the absence of all CD4+ T cells or lack of MHC class II-mediated interactions on priming dendritic cells result in enhanced CD8+ T cell immunogenicity. These findings have important implications for the improvement of vaccines against intracellular pathogens or tumors, especially in patients with highly active Treg.Supporting Information for this article is available at www.wiley-vch.de/contents/jc_2040/2008/37966_s.pdf
Immunological mechanisms and clinical implications of regulatory T cell deficiency in a systemic autoimmune disorder: Roles of IL-2 versus IL-15
Regulatory T cell deficiency is evident in patients with lupus, but the casual relationship and underlying mechanism leading to Treg deficiency are unclear. We analyzed the Treg profile, induction and functions of Treg in a lupus mouse model. A characteristic age-dependent biphasic change of Treg frequency was observed in the MRL/lpr mice, which developed a spontaneous lupus-like disease. After an early increase, Treg frequency in the peripheral lymphoid organs rapidly declined with age. Functionally, Treg from both young and old MRL/lpr mice were fully competent in suppressing the wild-type MRL/+ T effector cell (Teff) responses. Adoptive transfer of MRL/+ Treg markedly suppressed clinical disease in the MRL/lpr mice. We demonstrated that the reduced Treg frequency was a result of insufficient peripheral Treg expansion due to defective MRL/lpr Teff in IL-2 production, and the associated defects in dendritic cells, which could be fully restored by exogenous IL-2. In the absence of IL-2, MRL/lpr Teff but not MRL/lpr Treg were highly responsive to IL-15 and could expand rapidly due to enhanced IL-15R expression and IL-15 synthesis. These findings thus provide a clear causal relationship and immunological mechanism underlying Treg deficiency and systemic autoimmunity.Supporting Information for this article is available at www.wiley-vch.de/contents/jc_2040/2008/38190_s.pdf
Modulation of murine dendritic cell function by adenine nucleotides and adenosine: Involvement of the A2B receptor
Adenosine triphosphate has previously been shown to induce semi-mature human monocyte-derived dendritic cells (DC). These are characterized by the up-regulation of co-stimulatory molecules, the inhibition of IL-12 and the up-regulation of some genes involved in immune tolerance, such as thrombospondin-1 and indoleamine 2,3-dioxygenase. The actions of adenosine triphosphate are mediated by the P2Y11 receptor; since there is no functional P2Y11 gene in the murine genome, we investigated the action of adenine nucleotides on murine DC. Adenosine 5[prime]-(3-thiotriphosphate) and adenosine inhibited the production of IL-12p70 by bone marrow-derived DC (BMDC). These inhibitions were relieved by 8-p-sulfophenyltheophylline, an adenosine receptor antagonist. The use of selective ligands and A2B-/- BMDC indicated the involvement of the A2B receptor. A microarray experiment, confirmed by quantitative PCR, showed that, in presence of LPS, 5[prime]-(N-ethylcarboxamido) adenosine (NECA, the most potent A2B receptor agonist) regulated the expression of several genes: arginase I and II, thrombospondin-1 and vascular endothelial growth factor were up-regulated whereas CCL2 and CCL12 were down-regulated. We further showed that NECA, in combination with LPS, increased the arginase I enzymatic activity. In conclusion, the described actions of adenine nucleotides on BMDC are mediated by their degradation product, adenosine, acting on the A2B receptor, and will possibly lead to an impairment of Th1 response or tolerance.
Anti-CD4-mediated selection of Treg in vitro - in vitro suppression does not predict in vivo capacity to prevent graft rejection
Regulatory T cells (Treg) have been shown to play a role in the prevention of autoimmune diseases and transplant rejection. Based on an established protocol known to generate alloantigen reactive Treg in vivo, we have developed a strategy for the in vitro selection of Treg. Stimulation of unfractionated CD4+ T cells from naive CBA.Ca (H2k) mice with C57BL/10 (H2b) splenocytes in the presence of an anti-CD4 antibody, YTS 177, resulted in the selection of Treg able to inhibit proliferation of naive T cells. In vivo, the cells were able to prevent rejection of 80% C57BL/10 skin grafts when co-transferred to CBA.Rag-/- mice together with naive CD45RBhighCD4+ cells. Purification of CD62L+CD25+CD4+ cells from the cultures enriched for cells with regulatory activity; as now 100% survival of C57BL/10 skin grafts was achieved. Furthermore, differentiation of Treg could be also achieved when using purified CD25-CD4+ naive T cells as a starting population. Interestingly, further in vitro expansion resulted in a partial loss of CD4+ cells expressing both CD62L and CD25 and abrogation of their regulatory activity in vivo. This study shows that alloantigen stimulation in the presence of anti-CD4 in vitro provides a simple and effective strategy to generate alloreactive Treg.
Role of Ets-1 phosphorylation in the effector function of Th cells
The transcription factor Ets-1 critically regulates differentiation and function of T helper (Th) cells. In vitro studies have demonstrated that DNA binding and transcriptional activity of Ets-1 are regulated by phosphorylation. Depending on the site of phosphorylation, Ets-1 function can either be increased or inhibited. In addition, a splice variant lacking several inhibitory phosphorylation sites has been identified, raising the possibility that this splice variant may function differently from the full-length Ets-1. However, it is unclear how the activating and inhibitory phosphorylation events of Ets-1 are coordinated during Th cell activation. Furthermore, the biological consequences of Ets-1 phosphorylation and alternative splicing in regulating the function of Th cells are unknown. We report here that both activating and inhibitory phosphorylation events of Ets-1 occur simultaneously and independently of each other during Th cell activation. We further demonstrate that the effect of Ets-1 phosphorylation is very modest and that full-length Ets-1 and its splice variant are functionally interchangeable in the regulation of cytokine production in Th cells.Supporting Information for this article is available at www.wiley-vch.de/contents/jc_2040/2008/38112_s.pdf
N-Ras or K-Ras inhibition increases the number and
enhances the function of Foxp3 regulatory T cells
Naturally occurring regulatory T cells (Treg) driven by their transcriptional controller Foxp3 are compromised in immune-mediated disorders and confer protection when adoptively transferred. We examined the Ras-inhibitory effect on functional determinants of Treg in vivo and in vitro. Ras was inhibited in Jurkat T cells by transfection with a dominant-negative form of Ras, or by shRNA for N-Ras, K-Ras, and H-Ras, or by farnesylthiosalycylic acid, a small-molecule inhibitor. Except for H-Ras transduction with shRNA, each inhibitory mode increased expression of Foxp3 and nuclear factor of activated T cell proteins, and surface expression of CD25. Ras inhibition in PBMC and spleen-derived lymphocytes reproduced these findings. The heightened Foxp3 expression reflected both increased basal cellular protein and peripheral conversion of non-Treg to Treg. Ras inhibition enhanced Treg-induced suppression; thus, when adoptively transferred to mice, Ras-inhibited Treg reduced the incidence of diabetes. Inhibition of Foxp3 by respective siRNA reversed the enhancement. Thus, inhibition of the N- or K-Ras isoform triggers an anti-inflammatory effect by up-regulating, via Foxp3 elevation, the numbers and functional suppressive properties of Treg.
Mast cell regulation of epithelial TSLP expression plays an important role in the development of allergic rhinitis
Epithelial cell-derived thymic stromal lymphopoietin (TSLP) is a master switch for asthma or atopic dermatitis by inducing a dendritic cell-mediated Th2-type allergic inflammation. Allergic rhinitis is also pathologically characterized by Th2-type allergic inflammation. This study demonstrates that mast cells regulate the epithelial TSLP expression in allergic rhinitis. TSLP expression was found to be up-regulated predominantly in the nasal epithelium in the ovalbumin (OVA)-sensitized and -nasally challenged mouse model of allergic rhinitis, which was abolished in mast cell-deficient WBB6F1-W/Wv in comparison with control WBB6F1-+/+ mice. Similarly, the epithelial TSLP expression was reduced in Fc receptor [ggr] chain (Fc[ggr]R)-deficient mice, where the high-affinity IgE receptor (Fc[egr]RI) is not expressed on mast cells, in comparison with control C57BL/6 mice. Furthermore, the administration of neutralizing TSLP antibody during the challenge phase of OVA inhibited the development of allergic rhinitis. These results suggest that the direct stimulation of epithelial cells by antigens alone may not be sufficient to induce TSLP expression in the nasal epithelium, and that mast cell regulation of epithelial TSLP expression, possibly via Fc[egr]RI, plays an important role in the development of allergic rhinitis.
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