Dendritic cells (DCs) are well-established as major players in the regulation of immune responses. They either induce inflammatory or tolerogenic responses, depending on the DC-subtype and stimuli they receive from the local environment. This dual capacity of DCs has raised therapeutic interest for their use to modify immune-activation via the generation of tolerogenic DCs (tolDCs). Several compounds such as vitamin D3, retinoic acid, dexamethasone, or IL-10 and TGF-β have shown potency in the induction of tolDCs. However, an increasing interest exists in defining tolerance inducing receptors on DCs for new targeting strategies aimed to develop tolerance inducing immunotherapies, on which we focus particular in this review. Ligation of specific cell surface molecules on DCs can result in antigen presentation to T cells in the presence of inhibitory costimulatory molecules and tolerogenic cytokines, giving rise to regulatory T cells. The combination of factors such as antigen structure and conformation, delivery method, and receptor specificity is of paramount importance. During the last decades, research provided many tools that can specifically target various receptors on DCs to induce a tolerogenic phenotype. Based on advances in the knowledge of pathogen recognition receptor expression profiles in human DC subsets, the most promising cell surface receptors that are currently being explored as possible targets for the induction of tolerance in DCs will be discussed. We also review the different strategies that are being tested to target DC receptors such as antigen-carbohydrate conjugates, antibody-antigen fusion proteins and antigen-adjuvant conjugates.

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are contributed equally to this work.Abbreviations: Abcc6, ATP binding cassette subfamily c member 6; BB-FCF, brilliant blue-FCF; Cx30, connexin30; Cx30.3, connexin30.3; Cx37, connexin37; Entpd2, ectonucleoside triphosphate diphosphohydrolase 2; Entpd3, ectonucleoside triphosphate diphosphohydrolase 3; FBS, fetal bovine serum; FSS, fluid shear stress; Gapdh, glyceraldehyde 3-phosphate dehydrogenase; MO, translation blocking morpholino; Nt5e, ecto-5′-nucleotidase; Panx1, pannexin-1; PC1, polycystin-1; PC2, polycystin-2; PKD, polycystic kidney disease; Pkd1, polycystic kidney disease 1; Pkd2, polycystic kidney disease 2; Ptgs2, prostaglandin-endoperoxide synthase 2. AbstractTubular ATP release is regulated by mechanosensation of fluid shear stress (FSS).Polycystin-1/polycystin-2 (PC1/PC2) functions as a mechanosensory complex in the kidney. Extracellular ATP is implicated in polycystic kidney disease (PKD), where PC1/PC2 is dysfunctional. This study aims to provide new insights into the ATP signaling under physiological conditions and PKD. Microfluidics, pharmacologic inhibition, and loss-of-function approaches were combined to assess the ATP release in mouse distal convoluted tubule 15 (mDCT15) cells. Kidney-specific Pkd1 knockout mice (iKsp-Pkd1 −/− ) and zebrafish pkd2 morphants (pkd2-MO) were as models for PKD. FSS-exposed mDCT15 cells displayed increased ATP release. Pannexin-1 inhibition and knockout decreased FSS-modulated ATP release. In iKsp-Pkd1 −/− mice, elevated renal pannexin-1 mRNA expression and urinary ATP were observed. In Pkd1 −/− mDCT15 cells, elevated ATP release was observed upon the FSS mechanosensation. In these cells, increased pannexin-1 mRNA expression was observed.Importantly, pannexin-1 inhibition in pkd2-MO decreased the renal cyst growth. Our results demonstrate that pannexin-1 channels mediate ATP release into the tubular lumen due to pro-urinary flow. We present pannexin-1 as novel therapeutic target to prevent the renal cyst growth in PKD. K E Y W O R D SATP, fluid shear stress, pannexin-1, polycystin-1, purinergic signaling | 6383 VERSCHUREN Et al.

Polycomb Group (PcG) genes are transcriptional repressors that are described to be important during development and differentiation. There is significant interest in PcGs proteins because of their role in stem cell biology and tumorigenesis. In this study we characterize the expression of a selection of PcG genes in the adult germline of zebrafish and during embryogenesis. In adults, expression of selected PcG genes is found to be enriched in germ line over somatic tissues. Therefore, the germ line of adult zebrafish was analyzed for the expression pattern of a selection of PcG genes by whole mount in situ hybridization. We detected presence of the tested PcG gene transcripts at early stages of both oogenesis and spermatogenesis. This enriched expression for early stages of gametogenesis is also observed in developing gonads at 4 and 5 weeks post fertilization. Additionally, zebrafish embryos were used to study the spatio-temporal expression patterns of a selection of PcG genes during development. The PcG genes that we tested are maternally loaded and ubiquitously expressed at early developmental stages, except of ezh1. The expression of the PcG genes that were assessed becomes enriched anteriorly and is more defined during tissue specification. The data shown here is an important resource for functional PcG gene studies in vivo.