Development of a unique epigenetic signature during in vivo Th17 differentiation.

Activated naive CD4(+) T cells are highly plastic cells that can differentiate into various T helper (Th) cell fates characterized by the expression of effector cytokines like IFN-γ (Th1), IL-4 (Th2) or IL-17A (Th17). Although previous studies have demonstrated that epigenetic mechanisms including DNA demethylation can stabilize effector cytokine expression, a comprehensive analysis of the changes in the DNA methylation pattern during differentiation of naive T cells into Th cell subsets is lacking. Hence, we here performed a genome-wide methylome analysis of ex vivo isolated naive CD4(+) T cells, Th1 and Th17 cells. We could demonstrate that naive CD4(+) T cells share more demethylated regions with Th17 cells when compared to Th1 cells, and that overall Th17 cells display the highest number of demethylated regions, findings which are in line with the previously reported plasticity of Th17 cells. We could identify seven regions located in Il17a, Zfp362, Ccr6, Acsbg1, Dpp4, Rora and Dclk1 showing pronounced demethylation selectively in ex vivo isolated Th17 cells when compared to other ex vivo isolated Th cell subsets and in vitro generated Th17 cells, suggesting that this unique epigenetic signature allows identifying and functionally characterizing in vivo generated Th17 cells.

Streamlining homogeneous glycoprotein production for biophysical and structural applications by targeted cell line development.

Studying the biophysical characteristics of glycosylated proteins and solving their three-dimensional structures requires homogeneous recombinant protein of high quality.We introduce here a new approach to produce glycoproteins in homogenous form with the well-established, glycosylation mutant CHO Lec3.2.8.1 cells. Using preparative cell sorting, stable, high-expressing GFP 'master' cell lines were generated that can be converted fast and reliably by targeted integration via Flp recombinase-mediated cassette exchange (RMCE) to produce any glycoprotein. Small-scale transient transfection of HEK293 cells was used to identify genetically engineered constructs suitable for constructing stable cell lines. Stable cell lines expressing 10 different proteins were established. The system was validated by expression, purification, deglycosylation and crystallization of the heavily glycosylated luminal domains of lysosome-associated membrane proteins (LAMP).

Peritoneal cavity is dominated by IFNγ-secreting CXCR3+ Th1 cells.

The chemokine receptor CXCR3, which was shown to take part in many inflammatory processes, is considered as a Th1 specific marker. Here, we show in a mouse model that CXCR3 expressing CD4(+) cells preferentially migrate to the peritoneal cavity under steady-state conditions. The peritoneal cavity milieu leads to an up-regulated expression of CXCR3. However, blocking of known ligands of this chemokine receptor did not alter the preferential migration. The peritoneal cavity environment also results in an increased percentage of memory cells producing cytokines. Up-regulation of IFNγ production occurs mostly in CXCR3(+) cells considered as Th1, whereas the up-regulation of IL-4 affects mostly in CXCR3(-) cells which are considered as Th2. We conclude that the peritoneal cavity does not change the Th-lineage of the cells, but that domination of this anatomic niche by Th1 cells rather results from preferential migration to this compartment.

Deletion of the Candida albicans histidine kinase gene CHK1 improves recognition by phagocytes through an increased exposure of cell wall beta-1,3-glucans.

The pathogenic fungus Candida albicans is able to cover its most potent proinflammatory cell wall molecules, the ß-glucans, underneath a dense mannan layer, so that the pathogen becomes partly invisible for immune cells such as phagocytes. As the C. albicans histidine kinases Chk1p, Cos1p and CaSln1p had been reported to be involved in virulence and cell wall biosynthesis, we investigated whether deletion of the respective genes influences the activity of phagocytes against C. albicans. We found that among all histidine kinase genes, CHK1 plays a prominent role in phagocyte activation. Uptake of the deletion mutant Δchk1 as well as the acidification of Δchk1-carrying phagosomes was significantly increased compared with the parental strain. These improved activities could be correlated with an enhanced accessibility of the mutant ß-1,3-glucans for immunolabelling. In addition, any inhibition of ß-1,3-glucan-mediated phagocytosis resulted in a reduced uptake of Δchk1, while ingestion of the parental strain was hardly affected. Moreover, deletion of CHK1 caused an enhanced release of interleukins 6 and 10, indicating a stronger activation of the ß-1,3-glucan receptor dectin-1. In conclusion, the Chk1p protein is likely to be involved in masking ß-1,3-glucans from immune recognition. As there are no homologues of fungal histidine kinases in mammals, Chk1p has to be considered as a promising target for new antifungal agents.

Glycoprotein production for structure analysis with stable, glycosylation mutant CHO cell lines established by fluorescence-activated cell sorting.

Stable mammalian cell lines are excellent tools for the expression of secreted and membrane glycoproteins. However, structural analysis of these molecules is generally hampered by the complexity of N-linked carbohydrate side chains. Cell lines with mutations are available that result in shorter and more homogenous carbohydrate chains. Here, we use preparative fluorescence-activated cell sorting (FACS) and site-specific gene excision to establish high-yield glycoprotein expression for structural studies with stable clones derived from the well-established Lec3.2.8.1 glycosylation mutant of the Chinese hamster ovary (CHO) cell line. We exemplify the strategy by describing novel clones expressing single-chain hepatocyte growth factor/scatter factor (HGF/SF, a secreted glycoprotein) and a domain of lysosome-associated membrane protein 3 (LAMP3d). In both cases, stable GFP-expressing cell lines were established by transfection with a genetic construct including a GFP marker and two rounds of cell sorting after 1 and 2 weeks. The GFP marker was subsequently removed by heterologous expression of Flp recombinase. Production of HGF/SF and LAMP3d was stable over several months. 1.2 mg HGF/SF and 0.9 mg LAMP3d were purified per litre of culture, respectively. Homogenous glycoprotein preparations were amenable to enzymatic deglycosylation under native conditions. Purified and deglycosylated LAMP3d protein was readily crystallized. The combination of FACS and gene excision described here constitutes a robust and fast procedure for maximizing the yield of glycoproteins for structural analysis from glycosylation mutant cell lines.

Monocytes/macrophages and/or neutrophils are the target of IL-10 in the LPS endotoxemia model.

IL-10 is a potent regulator of the innate and adaptive immune responses. Several cell types produce IL-10 and its receptor chains and these may regulate different immune responses. Here we report that inactivation of the IL-10 receptor (IL-10R1) gene in mice leads to an increased susceptibility to chemically induced colitis as in the classical IL-10-deficient mutant. To identify the cells regulated by IL-10 in immune responses, we generated several cell type specific IL-10R1-deficient mutants. We show that, in an IL-10-dependent LPS model of endotoxemia, dampening of the immune response requires expression of IL-10R1 in monocytes/macrophages and/or neutrophils but not in T cells nor B cells. As the macrophage and/or neutrophil-specific IL-10-deficient mutants also display the same phenotype, our results suggest that an autocrine loop in monocytes/macrophages is the most probable mechanism for the regulation of an LPS-induced septic shock. In contrast, in an IL-10-regulated T-cell response to Trichuris muris infection, IL-10 acting on T cells or monocytes/macrophages/neutrophils is not critical for the control of the infection.

Intranasal immunization promotes th17 immune responses.

Th17 cells are a lineage of CD4+ T cells characterized by IL-17 secretion, which plays a crucial role in immune responses against important respiratory pathogens, such as Mycobacterium tuberculosis. In this study, we demonstrated that intranasal (i.n.) immunization leads per se to Th17-biased immune responses, regardless of the adjuvant used. The activated CD4+ T cells also showed an up-regulated expression of the chemokine receptor CCR6, which is a marker for murine Th17 cells. These results have important implications in the context of optimizing rational vaccine design, since i.n. immunization appears to be the strategy of choice for situations where the induction of a Th17 phenotype would be beneficial.

Listeria monocytogenes desensitizes immune cells to subsequent Ca2+ signaling via listeriolysin O-induced depletion of intracellular Ca2+ stores.

Listeriolysin O (LLO), the pore-forming toxin of Listeria monocytogenes, is a prototype of the cholesterol-dependent cytolysins (CDCs) secreted by several pathogenic and nonpathogenic gram-positive bacteria. In addition to mediating the escape of the bacterium into the cytosol, this toxin is generally believed to be a central player in host-pathogen interactions during L. monocytogenes infection. LLO triggers the influx of Ca(2+) into host cells as well as the release of Ca(2+) from intracellular stores. Thus, many of the cellular responses induced by LLO are related to calcium signaling. Interestingly, in this study, we report that prolonged exposure to LLO desensitizes cells to Ca(2+) mobilization upon subsequent stimulations with LLO. Cells preexposed to LLO-positive L. monocytogenes but not to the LLO-deficient Deltahly mutant were found to be highly refractory to Ca(2+) induction in response to receptor-mediated stimulation. Such cells also exhibited diminished Ca(2+) signals in response to stimulation with LLO and thapsigargin. The presented results suggest that this phenomenon is due to the depletion of intracellular Ca(2+) stores. The ability of LLO to desensitize immune cells provides a significant hint about the possible role played by CDCs in the evasion of the immune system by bacterial pathogens.

Chronic antigen stimulation in vivo induces a distinct population of antigen-specific Foxp3 CD25 regulatory T cells.

The concept of immune regulation/suppression has been well-established and, besides thymus-derived CD4+CD25+ regulatory T (TR) cells, it became clear that a variety of additional peripherally induced TR cells play vital roles in protection from many harmful immune responses including intestinal inflammation. In the present study, we have analyzed in vivo-induced Ag-specific CD4+ TR cells with respect to their molecular and functional phenotype. By comparative genomics we could show that these Ag-specific TR cells induced by chronic Ag stimulation in vivo clearly differ in their genetic program from naturally occurring thymus-derived CD4+CD25+ TR cells. This distinct population of induced TR cells express neither CD25 nor the TR-associated transcription factor Foxp3. Strikingly, CD25 is not even up-regulated upon stimulation. Despite the lack in Foxp3 expression, these in vivo-induced CD25- TR cells are able to interfere with an Ag-specific CD8+ T cell-mediated intestinal inflammation without significant increase in CD25 and Foxp3 expression. Thus, our results demonstrate that in vivo-induced Ag-specific TR cells represent a distinct population of Foxp3-CD25- TR cells with regulatory capacity both in vitro and in vivo.

The multiple mechanisms of Ca2+ signalling by listeriolysin O, the cholesterol-dependent cytolysin of Listeria monocytogenes.

Cholesterol-dependent cytolysins (CDCs) represent a large family of conserved pore-forming toxins produced by several Gram-positive bacteria such as Listeria monocytogenes, Streptococcus pyrogenes and Bacillus anthracis. These toxins trigger a broad range of cellular responses that greatly influence pathogenesis. Using mast cells, we demonstrate that listeriolysin O (LLO), a prototype of CDCs produced by L. monocytogenes, triggers cellular responses such as degranulation and cytokine synthesis in a Ca(2+)-dependent manner. Ca(2+) signalling by LLO is due to Ca(2+) influx from extracellular milieu and release of from intracellular stores. We show that LLO-induced release of Ca(2+) from intracellular stores occurs via at least two mechanisms: (i) activation of intracellular Ca(2+) channels and (ii) a Ca(2+) channels independent mechanism. The former involves PLC-IP(3)R operated Ca(2+) channels activated via G-proteins and protein tyrosine kinases. For the latter, we propose a novel mechanism of intracellular Ca(2+) release involving injury of intracellular Ca(2+) stores such as the endoplasmic reticulum. In addition to Ca(2+) signalling, the discovery that LLO causes damage to an intracellular organelle provides a new perspective in our understanding of how CDCs affect target cells during infection by the respective bacterial pathogens.

UBD, a downstream element of FOXP3, allows the identification of LGALS3, a new marker of human regulatory T cells.

Here, we report the identification of the ubiquitin-like gene UBD as a downstream element of FOXP3 in human activated regulatory CD4(+)CD25(hi) T cells (T(reg)). Retroviral transduction of UBD in human allo-reactive effector CD4(+) T helper (T(h)) cells upregulates CD25 and mediates downregulation of IL4 and IL5 expression similar to overexpression of FOXP3. Moreover, UBD impairs T(h) cell proliferation without upregulation of FOXP3 and impairs calcium mobilization. In the presence of ionomycin, overexpression of UBD in T(h) cells leads to the induction of IL1R2 that resemble FOXP3-transduced T(h) cells and naturally derived T(reg) cells. A comparison of the transcriptome of FOXP3- and UBD-transduced T(h) cells with T(reg) cells allowed the identification of the gene LGALS3. However, high levels of LGALS3 protein expression were observed only in human CD4(+)CD25(hi) derived T(reg) cells and FOXP3-transduced T(h) cells, whereas little was induced in UBD-transduced T(h) cells. Thus, UBD contributes to the anergic phenotype of human regulatory T cells and acts downstream in FOXP3 induced regulatory signaling pathways, including regulation of LGALS3 expression. High levels of LGALS3 expression represent a FOXP3-signature of human antigen-stimulated CD4(+)CD25(hi) derived regulatory T cells.