Cytosolic alterations of calcium ion concentrations are an integral part of signal transduction. Similar functions have been hypothesized for other metal ions, in particular zinc (Zn2+), but this still awaits experimental verification. Zn2+ is important for multiple cellular functions, especially in the immune system. Among other effects, it influences formation and secretion of pro-inflammatory cytokines, including TNF-α. Here we demonstrate that these effects are due to a physiological signaling system involving intracellular Zn2+ signals. An increase of the intracellular zinc ion concentration occurs upon stimulation of human leukocytes with Escherichia coli, LPS, Pam3CSK4, TNF-α, or insulin, predominantly in monocytes. Chelating this zinc signal with the membrane permeable zinc-specific chelator TPEN (N,N,N′,N′-tetrakis-(2-pyridyl-methyl)ethylenediamine) completely blocks activation of LPS-induced signaling pathways involving p38 MAPK, ERK1/2, and NF-κB, and abrogates the release of proinflammatory cytokines, including TNF-α. This function of Zn2+ is not limited to monocytes or even the immune system, but seems to be another generalized signaling system based on intracellular fluctuations of metal ion concentrations, acting parallel to Ca2+.

human steady-state skin. Interestingly, although during lo-@@@@@@@@@@@@@@@@@ not required for monocyte recruitment or differentiation-tolerogenic functions, and maintained a tolerogenic nucle-@@@@@@@@@@@@@@@@@@@ @@@@@@@@@@@@@@@@@@-@@@@@@@@@@@@@@@@-lograft damage due to either innate-mediated ischemia-@@@@@@@@@@@@@@@@ Dr. Kupiec-Weglinski is director of the Dumont-UCLA Transplantation Gomez de Agüero M, Vocanson M, Hacini-Rachinel F, Taillardet M, Sparwasser T, Kissenpfennig A, et al. Langerhans cells protect from allergic contact dermatitis in mice by tolerizing CD8(+) T cells and activating Foxp3(+) regulatory T cells. J Clin Invest 2012; 122: 1700-1711. Greter M, Lelios I, Pelczar P, Hoeffel G, Price J, Leboeuf M, et al. Stroma-derived interleukin-34 controls the development and maintenance of langerhans cells and the maintenance of microglia. Immunity 2012; 37: 1050-1060. Seneschal J, Clark RA, Gehad A, Baecher-Allan CM, Kupper TS. Human epidermal Langerhans cells maintain immune homeostasis in skin by activating skin resident regulatory T cells. Immunity 2012; 36: 873-884.

Psoriasis is an autoinflammatory skin disease of unknown etiology. Topical application of Aldara cream containing the Toll-like receptor (TLR)7 agonist Imiquimod (IMQ) onto patients induces flares of psoriasis. Likewise, in mice IMQ triggers pathological changes closely resembling psoriatic plaque formation. Key cytokines like IL-23 and type-I IFN (IFN-I), both being produced mainly by dendritic cells (DCs), have been implicated in psoriasis. Although plasmacytoid DCs (pDCs) are the main source of IFNα and thought to initiate disease, conventional DCs (cDCs) appear to maintain the psoriatic lesions. Any role of cDCs during lesion formation remains elusive. Here, we report that selective activation of TLR7 signaling specifically in CD11c + DCs was sufficient to induce psoriasiform skin disease in mice. Intriguingly, both pDCs and the IFN-I pathway were dispensable for the development of local skin inflammation. Selective TLR7 triggering of Langerin + DCs resulted in attenuated disease, whereas their depletion did not alter the severity of skin lesions. Moreover, after IMQ-painting, IL-23 was exclusively produced by Langerin neg DCs in vivo. In conclusion, TLR7-activated Langerin neg cDCs trigger psoriatic plaque formation via IL-23-mediated activation of innate IL-17/IL-22-producing lymphocytes, independently of pDCs or IFN-I. These results suggest therapeutic targeting of IL-23 production by cDCs to refine current treatment strategies for psoriasis.

Zinc signals, i.e. a change of the intracellular concentration of free zinc ions in response to receptor stimulation, are involved in signal transduction in several immune cells. Here, the role of zinc signals in T-cell activation by IL-2 was investigated in the murine cytotoxic T-cell line CTLL-2 and in primary human T cells. Measurements with the fluorescent dyes FluoZin-3 and Zinquin showed that zinc is released from lysosomes into the cytosol in response to stimulation of the IL-2-receptor. Activation of the ERK-pathway was blocked by chelation of free zinc with N,N,N 0 ,N 0 -tetrakis-2(pyridyl-methyl)ethylenediamine, whereas zinc was not required for STAT5 phosphorylation. In addition, the key signaling molecules MEK and ERK were activated in response to elevated free intracellular zinc, induced by incubation with zinc and the ionophore pyrithione. Downstream of ERK activation, ERK-specific gene expression of c-fos and IL-2-induced proliferation was found to depend on zinc. Further experiments indicated that inhibition of MEK and ERK-dephosphorylating protein phosphatases is the molecular mechanism for the influence of zinc on this pathway. In conclusion, an increase of cytoplasmic free zinc is required for IL-2-induced ERK signaling and proliferation of T cells. Key words: IL-2 . T cells . Zinc Supporting Information available online IntroductionZinc signals have been observed in different cell types of the immune system, including monocytes, dendritic cells, and mast cells [1]. T-cell function is particularly susceptible to zinc deprivation, and zinc signals were suggested to activate protein kinase C in T cells [1,2]. Furthermore, zinc is involved in the activation of the Src-family kinase Lck by the TCR. Here, zinc ions are required for interactions at two protein/protein interface sites. First, they stabilize the interaction between Lck and CD4 or CD8, recruiting the kinase to the TCR signaling complex [3]. Second, zinc ions stabilize homodimerization of Lck, which promotes activating transphosphorylation between two Lck molecules [4]. Cellular zinc homeostasis is mediated by ten members of the ZnT family and 14 members of the Zrt-, Irt-like protein (ZIP) family of zinc transporters [5]. Intracellular localization for most of these transporters remains to be determined. So far, no nuclear zinc transporters were identified, even though there is evidence that nuclear and cytoplasmic zinc are differentially regulated [6]. In general, ZIP transport zinc into the cytoplasm, whereas ZnT transport zinc out of the cell or into cellular compartments, SHORT COMMUNICATION 1496including different vesicular structures [7]. Importantly, zinc accumulates in a lysosomal compartment of T cells, from which it is released by ZIP8 in response to TCR-mediated activation by antibodies against CD2, CD3, and CD28 [8].Previously, zinc was also shown to be required for T-cell activation by IL-2, a growth-factor that stimulates proliferation of T cells [9]. These data point to IL-2 signaling as another target for zinc in T cell...

CD103+CD11b+ dendritic cells (DCs) are unique to the intestine, but the factors governing their differentiation are unclear. Here we show that transforming growth factor receptor 1 (TGFβR1) has an indispensable, cell intrinsic role in the development of these cells. Deletion of Tgfbr1 results in markedly fewer intestinal CD103+CD11b+ DCs and a reciprocal increase in the CD103−CD11b+ dendritic cell subset. Transcriptional profiling identifies markers that define the CD103+CD11b+ DC lineage, including CD101, TREM1 and Siglec-F, and shows that the absence of CD103+CD11b+ DCs in CD11c-Cre.Tgfbr1 fl/fl mice reflects defective differentiation from CD103−CD11b+ intermediaries, rather than an isolated loss of CD103 expression. The defect in CD103+CD11b+ DCs is accompanied by reduced generation of antigen-specific, inducible FoxP3+ regulatory T cells in vitro and in vivo, and by reduced numbers of endogenous Th17 cells in the intestinal mucosa. Thus, TGFβR1-mediated signalling may explain the tissue-specific development of these unique DCs.

Recent studies have demonstrated that β-catenin in DCs serves as a key mediator in promoting both CD4+ and CD8+ T-cell tolerance, although how β-catenin exerts its functions remains incompletely understood. Here we report that activation of β-catenin in DCs inhibits cross-priming of CD8+ T cells by up-regulating mTOR-dependent IL-10, suggesting blocking β-catenin/mTOR/IL-10 signaling as a viable approach to augment CD8+ T-cell immunity. However, vaccination of DC–β-catenin−/− (CD11c-specific deletion of β-catenin) mice surprisingly failed to protect them against tumor challenge. Further studies revealed that DC–β-catenin−/− mice were deficient in generating CD8+ T-cell immunity despite normal clonal expansion, likely due to impaired IL-10 production by β-catenin−/− DCs. Deletion of β-catenin in DCs or blocking IL-10 after clonal expansion similarly led to reduced CD8+ T cells, suggesting that β-catenin in DCs plays a positive role in CD8+ T-cell maintenance postclonal expansion through IL-10. Thus, our study has not only identified mTOR/IL-10 as a previously unidentified mechanism for β-catenin–dependent inhibition of cross-priming, but also uncovered an unexpected positive role that β-catenin plays in maintenance of CD8+ T cells. Despite β-catenin’s opposite functions in regulating CD8+ T-cell responses, selectively blocking β-catenin with a pharmacological inhibitor during priming phase augmented DC vaccine-induced CD8+ T-cell immunity and improved antitumor efficacy, suggesting manipulating β-catenin signaling as a feasible therapeutic strategy to improve DC vaccine efficacy.

Whereas CD8⁺ T cells are essential for anti-tumor immunity, tumors often evade CD8⁺ T cell surveillance by immunosuppression. As the initiators of antigen-specific immune responses, DCs are likely to play a central role in regulating the balance between immunity and tolerance to tumor antigens and are specialized in their ability to cross-present exogenous tumor antigens on MHC class I molecules to initiate CD8⁺ T cell immunity. However, it remains unclear whether and how tumors modulate DC functions to suppress CD8⁺ T cell responses. We have shown previously that β-catenin signaling in DCs promotes DC-mediated CD8⁺ T cell tolerance. Here, we tested the hypothesis that β-catenin in DCs mediates tumor-induced suppression of CD8⁺ T cell immunity by inhibiting the ability of DCs in cross-priming. β-Catenin was activated in DCs by multiple tumors in vivo and in vitro. B16 melanoma-bearing mice, when vaccinated with DC-targeting anti-DEC-205 mAb fused with tumor antigens, exhibited dampened CD8⁺ immunity, similar to DC-β-catenin(active) mice. DCs from DC-β-catenin(active) and tumor-bearing mice were deficient in cross-priming, and antigen-specific CD8⁺ T cells primed in these mice resulted in dampened CD8⁺ memory responses. Importantly, DC-β-catenin⁻/⁻ mice completely abrogate tumor-mediated inhibition of cross-priming, suggesting that tumor-induced inhibition of cross-priming is dependent on β-catenin. Finally, enhancing cross-priming at the priming or recall phase rescued β-catenin-suppressed CD8⁺ immunity in DC-β-catenin(active) and tumor-bearing mice. Thus, β-catenin-mediated inhibition of cross-priming represents a new and potentially general mechanism that tumors employ to achieve immunosuppression.

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