The liver is essential for inducing immunological tolerance toward harmless antigens to maintain immune system homeostasis. However, the precise cellular mechanisms of tolerance induction against particle-bound antigens, the role of the local hepatic microenvironment, and implications for therapeutic targets in immune-mediated diseases are currently unclear. In order to elucidate cellular mechanisms of tolerance induction in healthy and injured liver, we developed a novel in vivo system combining the systemic delivery of low-dose peptide antigens coupled to inert particles, immunological readouts, and sophisticated intravital multiphoton microscopy-based imaging of liver in mice. We show that liver resident macrophages, Kupffer cells (KCs), but not hepatic monocytederived macrophages or dendritic cells (DCs), are the central cellular scavenger for circulating particle-associated antigens in homeostasis. KC-associated antigen presentation induces CD4 T-cell arrest, expansion of naturally occurring Foxp3 1 CD25 1 interleukin-10-producing antigen-specific regulatory T cells (Tregs) and tolerogenic immunity. Particle-associated tolerance induction in the liver protected mice from kidney inflammation in T-cell-mediated glomerulonephritis, indicating therapeutic potential of targeting KC for immune-mediated extrahepatic disorders. Liver inflammation in two independent experimental models of chronic liver injury and fibrosis abrogated tolerance induction and led to an immunogenic reprogramming of antigen-specific CD4 T cells. In injured liver, infiltrating monocyte-derived macrophages largely augment the hepatic phagocyte compartment, resulting in antigen redistribution between myeloid cell populations and, simultaneously, KCs lose signature markers of their tolerogenic phenotype. Conclusions: Hepatic induction of tissue-protective immunological tolerance against particulate antigens is dependent on KCs as well as on a noninflamed liver microenvironment, thereby providing mechanistic explanations for the clinical observation of immune dysfunction and tolerance break in patients with advanced liver diseases. (HEPATOLOGY 2015;62:279-291) T he liver plays a key role in inducing immunological tolerance that is critical for maintaining homeostasis in a healthy organism. In principle, tolerance needs to be induced against self-antigens from tissues, ingested food, or commensal bacteria to prevent immune-mediated diseases. 1 On the other hand, immunological tolerance triggered by the innate immune system has been recognized as an anti-

The total number of glomeruli is a fundamental parameter of kidney function but very difficult to determine using standard methodology. Here, we counted all individual glomeruli in murine kidneys and sized the capillary tufts by combining in vivo fluorescence labeling of endothelial cells, a novel tissue-clearing technique, lightsheet microscopy, and automated registration by image analysis. Total hands-on time per organ was <1 hour, and automated counting/sizing was finished in <3 hours. We also investigated the novel use of ethyl-3-phenylprop-2-enoate (ethyl cinnamate) as a nontoxic solvent-based clearing reagent that can be handled without specific safety measures. Ethyl cinnamate rapidly cleared all tested organs, including calcified bone, but the fluorescence of proteins and immunohistochemical labels was maintained over weeks. Using ethyl cinnamate-cleared kidneys, we also quantified the average creatinine clearance rate per glomerulus. This parameter decreased in the first week of experimental nephrotoxic nephritis, whereas reduction in glomerular numbers occurred much later. Our approach delivers fundamental parameters of renal function, and because of its ease of use and speed, it is suitable for high-throughput analysis and could greatly facilitate studies of the effect of kidney diseases on whole-organ physiology.

The mechanisms by which regulatory T cells (T regs ) suppress autoantibody production are unclear. Here we have addressed this question using transgenic mice expressing model antigens in the kidney. We report that T regs were essential and sufficient to suppress autoreactive B cells in an antigen-specific manner and to prevent them from producing autoantibodies. Most of this suppression was mediated through the inhibitory cell-surface-molecule programmed death-1 (PD-1). Suppression required PD-1 expression on autoreactive B cells and expression of the two PD-1 ligands on T regs . PD-1 ligation inhibited activation of autoreactive B cells, suppressed their proliferation, and induced their apoptosis. Intermediate PD-1 + cells, such as T helper cells, were dispensable for suppression. These findings demonstrate in vivo that T regs use PD-1 ligands to directly suppress autoreactive B cells, and they identify a previously undescribed peripheral B-cell tolerance mechanism against tissue autoantigens. Regulatory T cells (T regs ) are powerful suppressors of autoreactive T cells with high therapeutic potential (1-3). T regs also suppress auto-Ab production (4, 5). We recently showed in vivo that they do so in an antigen-specific (Ag-specific) manner (6, 7). These studies used rat insulin promoter HEL/OVA (ROH) mice expressing ovalbumin (OVA) and hen egg lysozyme (HEL) in pancreatic islet β-cells. Autoreactive OVA-and HEL-specific B cells, but not B cells specific for a foreign antigen, failed to proliferate in response to in vivo autoantigen (auto-Ag) challenge and instead underwent apoptosis in a strictly T reg -dependent fashion. T regs can affect B cells indirectly by suppressing the T-helper (Th) cells required for antibody production (8, 9). This did not rule out that T regs might also suppress B cells directly. Cell culture systems have revealed that CD25 + T regs can kill cocultured B cells (10-12). A recent in vivo study showed that T regs enter germinal centers and suppress B cells in this site (13,14). The question whether this occurred directly or indirectly remained open (15). This question is difficult to address in vivo because it requires an experimental system where T regs can suppress B cells but not Th cells.Another open question concerns the molecular mechanisms by which T regs suppress. In principle, T regs may suppress other T cells by (i) secreting inhibitory mediators; (ii) deprivation of survival factors; (iii) killing target cells by granzyme/perforin; and (iv) modulation of DCs by ligating inhibitory T-cell receptors (16,17). The exact contribution of these mechanisms in relevant in vivo situations and the mechanisms by which T regs suppress are unclear.Programmed death-1 (PD-1, CD279) is an activation-induced member of the extended CD28/CTLA-4 family that suppresses T cells (18-21). It has been associated with exhausted memory T cells in chronic viral infection (22,23) and with cytotoxic T-cell cross-tolerance (24). PD-1 has two known ligands, PDL-1 (B7-H1, CD274) and PDL-2 (B7-DC, CD273) (25,...

Intrarenal crystal formation activates the Nlrp3 inflammasome in myeloid cells and triggers a profound inflammatory response. Here, we studied whether a specific inhibitor of the Nlrp3 inflammasome, CP-456,773, can prevent kidney fibrosis in a murine model of crystal nephropathy induced by diets rich in oxalate or adenine. Inflammasome activation in renal dendritic cells and the resulting interleukin (IL)-1β and IL-18 production were markedly reduced by CP-456,773 treatment both ex vivo and in vivo. We directly visualized intrarenal inflammasome activation and its inhibition by CP-456,773 in vivo by adoptive transfer of bone marrow cells transduced with interleukin-1β-Gaussia luciferase, a proteolytic luciferase-based reporter for inflammasome activation, into irradiated mice. CP-456,773 treatment strongly attenuated kidney fibrosis when given early in the genesis of crystal nephropathy, but was unable to reverse established crystal-induced fibrosis. The urinary IL-18 concentration appeared to be a useful noninvasive biomarker for renal inflammasome activation. Finally, NLRP3 inhibition did not compromise adaptive immune responses as previously reported for the global inhibition of IL-1 signaling. Thus, early NLRP3 inhibition by CP-456,773 may be an effective treatment for crystal nephropathy. Use of iGLuc transfected cells introduces a novel imaging technique for inflammasome activation in mice.

Foxp3(+) T-regulatory cells (Tregs) may suppress pathogenic inflammation; however, although transferred Tregs lessen glomerulonephritis in mice, the role of endogenous foxp3(+) cells is not known. To study this, we characterized endogenous foxp3(+) cells in accelerated anti-glomerular basement membrane (GBM) nephritis by using foxp3(GFP) reporter mice to track their responses in early and established disease. Further, diphtheria toxin was used to ablate foxp3(+) Tregs in foxp3(DTR) mice after establishing an immune response. In this model, mice were immunized with sheep globulin in adjuvant, and sheep anti-mouse GBM globulin was injected after 4 days to initiate progressive histological and functional injury. Intrarenal leukocytic infiltrates were increased by day 3 but intrarenal foxp3(+) Tregs, present in interstitial and periglomerular areas, were only increased at day 7. Ablation of foxp3(+) Tregs after injection of anti-GBM globulin increased renal injury and systemic T-cell responses, including increased interferon-γ and interleukin-17A (IL-17A) production, but no change in antibody titers. Compared with foxp3(+) Tregs isolated from naive mice, those from immunized mice produced more IL-10 and more effectively regulated CD4(+)foxp3(-) responder T cells. Thus, endogenous foxp3(+) Tregs infiltrate the kidney in glomerulonephritis, and deleting foxp3(+) cells after the induction of immune responses upregulated T-cell reactions and enhanced disease. Hence, endogenous foxp3(+) cells have increased suppressive capacity after immune stimuli.

Cutaneous dendritic cells (DC) are pivotal for the elicitation of antigen-specific immune responses following gene gun-mediated biolistic transfection of the skin. We transcriptionally targeted transgene expression to DC using vectors containing the murine fascin promoter (pFascin) to control antigen production and compared the immune response elicited with conventional DNA immunization using plasmid constructs with the ubiquitously active CMV promoter (pCMV). Biolistic transfection with pFascin initiated a marked type 1 immune response characterized by the occurrence of a large population of IFN-gamma-producing T helper (Th) cells in spleen and draining lymph nodes. Consistently, immunoglobulin production was dominated by IgG2a antibodies. In contrast, the humoral response after repeated administration of pCMV was strongly enhanced and characterized by a type 2-like isotype pattern (IgG1 > IgG2a). Cytokine production analysis in vitro indicated compartmentalization of the immune response, revealing large numbers of IL-4-producing Th cells in the lymph nodes and dominant presence of IFN-gamma-producing Th cells in the spleen. Biolistic transfection with pFascin, like immunization with pCMV, led to potent induction of cytotoxic T cells as was assessed by JAM test. Thus gene gun immunization with plasmids that focus transgene expression and antigen production specifically to DC propagates type 1-biased cellular immune responses.

Strong cell-type-specific promoters are basic tools in gene therapy allowing for novel applications and focused strategies by transcriptionally targeting gene expression to selected cells. In immunotherapy, dendritic cells (DC) are of central importance, since they represent the principal inducers of immune responses. Here we describe isolation and use of the promoter of the murine actin-bundling protein fascin to target transcriptionally gene expression to cutaneous DC. Using the reporter gene enhanced green fluorescent protein (EGFP), we demonstrate that the fascin promoter mediates a strong antigen expression that is restricted to mature DC. DNA vaccination with antigenencoding expression vectors under control of the fascin promoter using a gene gun resulted, consistently, in limited antigen expression by few directly transfected DC. Nevertheless, nearly as many antigen-specific CD8 + T cells directed against the encoded antigens EGFP and bgalactosidase, respectively, were induced as with expression constructs under control of the ubiquitously expressed CMV promoter. This result impressively underlines the pivotal role of directly transfected DC in DNA vaccination. Immunization using the fascin promoter induced markedly lower levels of antigen-specific antibodies following single or repeated immunization. Thus, our DC-targeted DNA vaccination approach induces qualitatively distinct, predominantly cellular immune responses and provides new opportunities for immunotherapy.

To study the role of CD25؉ regulatory T cells (T regs ) in peripheral B cell tolerance, we generated transgenic rat insulin promoter RIP-OVA/HEL mice expressing the model Ags OVA and HEL in pancreatic islet ␤ cells (where RIP is rat insulin promoter and HEL is hen egg lysozyme). Adoptively transferred transgenic OVA-specific CD4؉ and CD8 ؉ T cells proliferated only in the autoantigen-draining pancreatic lymph node (PLN), demonstrating pancreas-specific Ag expression. A utoreactive B cells are controlled by several checkpoints that operate in the bone marrow by receptor editing or central deletion (1-4) and in the periphery by inducing deletion or anergy (4, 5). Anergic B cells fail to enter the long-lived mature B cell pool and are arrested in a transitional developmental stage that is characterized by low surface IgM, reduced BCR signaling, and Ab secretion (4, 6, 7). In the periphery, autoreactive B cells are deleted after continuous BCR signaling (8) or controlled by limiting T cell help (9). Recently, regulatory T cells (T regs )4 have been proposed to also suppress B cells based on the observations that T reg depletion aggravated disease in some autoantibody-mediated disease models (10 -12) and that T regs induced B cell apoptosis in vitro (13-15). Suppression of autoreactive T cells by T regs has been shown to occur in autoantigen (auto-Ag)-draining lymph nodes (LNs) by inhibiting their proliferation (16). The in vivo role of T regs in the suppression of B cells against nonlymphoid tissuerestricted auto-Ags has not yet been studied. In the present work, we addressed this question by using a novel transgenic (tg) model that allowed following the fate of naive B cells specific for a tg pancreatic auto-Ag after adoptive transfer. Materials and Methods Animals and reagentsC57/BL6, OT-I.Rag Ϫ/Ϫ , OT-II, and IgHEL (B cells expressing a tg BCR for hen egg lysozyme (HEL)) mice were bred under specific pathogen-free conditions and used at 8 -16 wk of age in accordance with German animal experimentation guidelines. To generate tg mice expressing OVA and HEL under control of the rat insulin promoter (RIP) (ROH high ), HEL cDNA amplified from the plasmid plExV3-HEL (17) was introduced into the pBlueRIP/TfrOva plasmid that had been used for generating RIP-membrane bound OVA (mOVA) mice (18,19). A 3.47-kb fragment containing RIP, the human transferrin receptor membrane domain, the genes for OVA (aa 161-407) and HEL, and an SV40 poly(A) tail was excised and injected into pronuclei of fertilized C57/BL6 oocytes. All reagents, if not specified otherwise, were from SigmaAldrich. CD25 ϩ cells were depleted by injecting 300 g of PC61.5 Ab purified from a hybridoma supernatant. Cell preparation and adoptive transferIgHEL cells were isolated from spleens of IgHEL mice, depleted of erythrocytes by buffered NH 4 Cl, and enriched by magnetic separation using a B cell separation kit (Miltenyi Biotec). OT-I and OT-II cells were isolated and labeled with CFSE as described (19). ELISPOT and Western blottingCell suspensions were incuba...