The characteristics, importance, and molecular requirements for interactions between mast cells (MCs) and CD8(+) T cells have not been elucidated. Here, we demonstrated that MCs induced antigen-specific CD8(+) T cell activation and proliferation. This process required direct cell contact and MHC class I-dependent antigen cross-presentation by MCs and induced the secretion of interleukin-2, interferon-gamma, and macrophage inflammatory protein-1alpha by CD8(+) T cells. MCs regulated antigen-specific CD8(+) T cell cytotoxicity by increasing granzyme B expression and by promoting CD8(+) T cell degranulation. Because MCs also upregulated their expression of costimulatory molecules (4-1BB) and released osteopontin upon direct T cell contact, MC-T cell interactions probably are bidirectional. In vivo, adoptive transfer of antigen-pulsed MCs induced MHC class I-dependent, antigen-specific CD8(+) T cell proliferation, and MCs regulated CD8(+) T cell-specific priming in experimental autoimmune encephalomyelitis. Thus, MCs are important players in antigen-specific regulation of CD8(+) T cells.

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Very little is known about the role of the innate immune system in the course of human type 1 diabetes. Here we investigated neutrophil numbers along with other leukocyte populations in patients at diagnosis of type 1 diabetes and during prediabetes. Complete and differential blood counts were analyzed from 107 adult patients with newly diagnosed type 1 diabetes, 21 children with persistent islet autoantibodies and a family history of type 1 diabetes, and 1 238 age and gender matched control subjects, all individuals without any signs of acute infection.Adult patients with newly diagnosed type 1 diabetes had significantly lower total WBC (p<1×10⁻⁶), neutrophil (p<1×10⁻⁶), basophil (p<1×10⁻⁶), monocyte (p=4×10⁻⁶) and lymphocyte (p<1×10⁻⁶) counts compared to control subjects. Erythrocyte, eosinophil and platelet counts did not differ between groups. Similarly, children with persistent islet autoantibodies had decreased WBC (p=0.001), neutrophils (p=0.003), and lymphocytes (p=0.006) in comparison to control children. Our findings demonstrate a perturbation of leukocyte homeostasis at and prior to onset of type 1 diabetes suggesting a general involvement of the innate immune system in the pathogenesis of type 1 diabetes.

Syntaxin 11 (STX11) controls vesicular trafficking and is a key player in exocytosis. SinceStx11 mutations are causally associated with a familial hemophagocytic lymphohistiocytosis, we wanted to clarify whether STX11 is functionally important for key immune cell populations. This was studied in primary cells obtained from newly generated Stx11 −/− mice. Our data revealed that STX11 is not only widely expressed in different immune cells, but also induced upon LPS or IFN-γ treatment. However, Stx11 deficiency does not affect macrophage phagocytic function and cytokine secretion, mast cell activation, or antigen presentation by DCs. Instead, STX11 selectively controls lymphocyte cytotoxicity in NK and activated CD8 + T cells and degranulation in neutrophils. Stx11 −/− NK cells and CTLs show impaired degranulation, despite a comparable activation, maturation and expression of the complex-forming partners MUNC18-2 and VTI1B. In addition, Stx11 −/− CTLs and NK cells produce abnormal levels of IFN-γ. Since functional reconstitution rescues the defective phenotype of Stx11 −/− CTLs, we suggest a direct, specific and key role of STX11 in controlling lymphocyte cytotoxicity, cytokine production and secretion. Finally, we show that these mice are a very useful tool for dissecting the role of STX11 in vesicular trafficking and secretion. Keywords: CTL r Cytokines r Exocytosis r N-ethylmaleimide-sensitive factor attachment protein receptorSee accompanying Commentary by Lopez and Voskoboinik.Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionSyntaxin 11 (STX11) belongs to the family of N-ethylmaleimidesensitive factor attachment protein receptor (SNARE) proteins Correspondence: Prof. Silvia Bulfone-Paus e-mail: sbulfone@fz-borstel.de and is involved in intracellular membrane trafficking events by interacting with other family members or by associating with membranes by palmitoylation of cysteine residues [1][2][3]. STX11 is expressed in a wide variety of cells including human monocytes/macrophages, neutrophils, B cells, NK cells and CD8 + T cells [2][3][4][5][6][7][8][9]. STX11 is enriched in immune tissues such as thymus, spleen C 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2013. 43: 194-208 Immunomodulation 195 Values represent the mean ± SEM percentage of cell subsets in the spleen (n = 8) and lymph nodes (WT n = 7; Stx11 −/− n = 6) and are the summary of three experiments performed.and lymph nodes, but lower levels of protein are detectable also in heart, kidney and liver [2]. STX11 localizes mainly in the vesicular tubular clusters, an organelle complex between the endoplasmic reticulum and the Golgi, and displays, in addition, a spotted staining pattern throughout the cell periphery [2,9]. While STX11 has been recognized to act as a negative regulator of both phagocytosis and intracellular trafficking between endosomes, lysosomes and the outer membrane in macrophages [6,9], in human NK cells and CTLs, ST...

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IL-15 regulates the development, survival, and proliferation of multiple innate and adaptive immune cells and plays a dual role, inducing both tumor cell growth and antitumor immunity. However, the role of IL-15 in inflammation-induced cancer remains unclear. To explore this, we have compared the colon carcinoma burden of Il15 ¡/¡ and Il15ra ¡/¡ mice with wild type (WT) mice after induction of colitis-associated colon carcinogenesis utilizing the AOM/DSS model. Compared to WT mice, Il15¡/¡ but not Il15ra ¡/¡ mice showed reduced survival, along with higher tumor incidence, colon weight, and tumor size. This suggests that low affinity IL-15 signaling via the shared IL-2Rb/gc decreases the risk for developing colitis-associated cancer. CD11c-Il15 mice, in which IL-15 expression is reconstituted in Il15 ¡/¡ mice under the control of the CD11c-promoter, showed that selective reconstitution of IL-15 in antigen-presenting cells restored the CD8 C T and NK cell compartments, serum levels of IFNg, G-CSF, IL-10, and CXCL1 and reduced tumor burden. After demonstrating IL-15 expression in human colorectal cancer (CRC) cells in situ, we investigated the role of this cytokine in the modulation of key colonic oncogenic pathways in the tumor. While these pathways were found to be unaltered in the absence of IL-15, tumor transcriptome analysis showed that the loss of IL-15 upregulates key inflammatory mediators associated with colon cancer progression, such as IL-1b, IL-22, IL-23, Cxcl5, and Spp1. These findings provide evidence that IL-15 suppresses colitis-associated colon carcinogenesis through regulation of antitumor cytotoxicity, and modulation of the inflammatory tumor micromilieu.

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