Gene-expression profiling of laser-dissected islets and studies in deficient mice reveal chemokines as differential driving force of type 1 diabetes.

Although type 1 diabetes (T1D) results from the autoimmune destruction of the insulin-producing ß-cells, its treatment is largely restricted to exogenous insulin administration. Only few therapies targeting the autoaggressive immune system have been introduced into clinical practice or are considered in clinical trials. Here, we provide a gene expression profile of the islet microenvironment obtained by laser-dissection microscopy in an inducible mouse model. Thereby, we have identified novel targets for immune intervention. Increased gene expression of most inflammatory proteins was apparent at day 10 after T1D induction and largely paralleled the observed degree of insulitis. We further focused on genes involved in leukocyte migration, including chemokines and their receptors. Besides the critical chemokine CXCL10, we found several other chemokines upregulated locally in temporary or chronic manner. Localization of the chemokine ligand/receptor pairs to the islet microenvironment has been confirmed by RNAscope. Interference with the CXCL16-CXCR6 and CX3CL1-CX3CR1 axes, but not the CCL5-CCR1/3/5 axis, resulted in reduced insulitis and lower T1D incidence. Further, we found that the receptors for the differentially expressed chemokines CXCL10, CXCL16 and CX3CL1 are distributed unevenly among islet autoantigen-specific T cells, which explains why the interference with just one chemokine axis cannot completely abrogate insulitis and T1D.

Molecular mimicry rather than identity breaks T-cell tolerance in the CYP2D6 mouse model for human autoimmune hepatitis.

In our novel mouse model for autoimmune hepatitis (AIH), wildtype FVB mice infected with an Adenovirus (Ad) expressing the major AIH autoantigen human cytochrome P450 2D6 (hCYP2D6) show persistent histological and immunological features associated with AIH, including the generation of anti-hCYP2D6 antibodies with an epitope specificity identical to LKM-1 autoantibodies in AIH-patients. Since FVB mice do not express hCYP2D6, the immune response was directed against mouse CYP (mCYP) homologues. Additional expression of hCYP2D6 in transgenic mice resulted in amelioration of the liver disease. In the present study we used the CYP2D6 model to assess why tolerance breakdown and induction of autoimmune liver disease is more efficient if the triggering antigen is similar but not identical to the target autoantigen. We found that in contrast to the specificity and magnitude of anti-hCYP2D6 antibody responses, T-cell responses differ profoundly between wildtype and transgenic mice. Detailed T-cell epitope mapping studies show a robust, antigen-specific T-cell reactivity in FVB mice largely directed against one CD4 and three CD8 epitopes, activating a total of approximately 1% CD4 and 10% CD8 T-cells, respectively, while infected hCYP2D6 mice generated almost no hCYP2D6-specific T-cells. The frequency of hCYP2D6-specific T-cells was approximately 3-fold higher in the liver compared with the spleen. Amino acid sequence comparison revealed that the immunodominant epitopes were located in hCYP2D6-segments of intermediate homology between hCYP2D6 and its mCYP homologues. Our data indicate that self/non-self molecular mimicry, rather than molecular identity, is a prerequisite for breaking T-cell tolerance in the liver.

Design, Synthesis, and Optimization of Indole Acetic Acid Derivatives as Potent and Selective CRTH2 Receptor Antagonists: Discovery of ACT-774312.

Herein we report the structure-activity relationship (SAR) studies and optimization of new highly potent and selective CRTH2 receptor antagonists as potential follow-ups of our previous reported clinical candidate setipiprant (ACT-129968) for the treatment of respiratory diseases. Structural modification of the amide part of setipiprant (ACT-129968) led to the identification of the tetrahydrocarbazole derivative (S)-B-1 (ACT-453859) ((S)-2-(3-((5-chloropyrimidin-2-yl)(methyl)amino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)acetic acid). This compound which displayed a substantial improvement in potency in the presence of plasma versus setipiprant (ACT-129968) has exhibited an excellent overall pharmacokinetic profile. Further lead optimization to overcome a safety issue as observed in non-clinical studies with (S)-B-1 (ACT-453859), led to the discovery of the 4-azaindole derivative (S)-72 (ACT-774312) ((S)-2-(8-((5-chloropyrimidin-2-yl)(methyl)amino)-2-fluoro-6,7,8,9-tetrahydro-5H-pyrido[3,2-b]indol-5-yl)acetic acid) which was selected as a potential follow-up of setipiprant (ACT-129968).

Early production of IL-22 but not IL-17 by peripheral blood mononuclear cells exposed to live Borrelia burgdorferi: the role of monocytes and interleukin-1.

If insufficiently treated, Lyme borreliosis can evolve into an inflammatory disorder affecting skin, joints, and the CNS. Early innate immunity may determine host responses targeting infection. Thus, we sought to characterize the immediate cytokine storm associated with exposure of PBMC to moderate levels of live Borrelia burgdorferi. Since Th17 cytokines are connected to host defense against extracellular bacteria, we focused on interleukin (IL)-17 and IL-22. Here, we report that, despite induction of inflammatory cytokines including IL-23, IL-17 remained barely detectable in response to B. burgdorferi. In contrast, T cell-dependent expression of IL-22 became evident within 10 h of exposure to the spirochetes. This dichotomy was unrelated to interferon-γ but to a large part dependent on caspase-1 and IL-1 bioactivity derived from monocytes. In fact, IL-1ß as a single stimulus induced IL-22 but not IL-17. Neutrophils display antibacterial activity against B. burgdorferi, particularly when opsonized by antibodies. Since neutrophilic inflammation, indicative of IL-17 bioactivity, is scarcely observed in Erythema migrans, a manifestation of skin inflammation after infection, protective and antibacterial properties of IL-22 may close this gap and serve essential functions in the initial phase of spirochete infection.

Impaired antibody response causes persistence of prototypic T cell-contained virus.

CD8 T cells are recognized key players in control of persistent virus infections, but increasing evidence suggests that assistance from other immune mediators is also needed. Here, we investigated whether specific antibody responses contribute to control of lymphocytic choriomeningitis virus (LCMV), a prototypic mouse model of systemic persistent infection. Mice expressing transgenic B cell receptors of LCMV-unrelated specificity, and mice unable to produce soluble immunoglobulin M (IgM) exhibited protracted viremia or failed to resolve LCMV. Virus control depended on immunoglobulin class switch, but neither on complement cascades nor on Fc receptor gamma chain or Fc gamma receptor IIB. Cessation of viremia concurred with the emergence of viral envelope-specific antibodies, rather than with neutralizing serum activity, and even early nonneutralizing IgM impeded viral persistence. This important role for virus-specific antibodies may be similarly underappreciated in other primarily T cell-controlled infections such as HIV and hepatitis C virus, and we suggest this contribution of antibodies be given consideration in future strategies for vaccination and immunotherapy.

Epitope spreading of the anti-CYP2D6 antibody response in patients with autoimmune hepatitis and in the CYP2D6 mouse model.

Autoimmune hepatitis (AIH) is a serious chronic inflammatory disease of the liver with yet unknown etiology and largely uncertain immunopathology. The hallmark of type 2 AIH is the generation of liver kidney microsomal-1 (LKM-1) autoantibodies, which predominantly react to cytochrome P450 2D6 (CYP2D6). The identification of disease initiating factors has been hampered in the past, since antibody epitope mapping was mostly performed using serum samples collected late during disease resulting in the identification of immunodominant epitopes not necessarily representing those involved in disease initiation. In order to identify possible environmental triggers for AIH, we analyzed for the first time the spreading of the anti-CYP2D6 antibody response over a prolonged period of time in AIH patients and in the CYP2D6 mouse model, in which mice infected with Adenovirus-human CYP2D6 (Ad-h2D6) develop antibodies with a similar specificity than AIH patients. Epitope spreading was analyzed in six AIH-2-patients and in the CYP2D6 mouse model using SPOTs membranes containing peptides covering the entire CYP2D6 protein. Despite of a considerable variation, both mice and AIH patients largely focus their humoral immune response on an immunodominant epitope early after infection (mice) or diagnosis (patients). The CYP2D6 mouse model revealed that epitope spreading is initiated at the immunodominant epitope and later expands to neighboring and remote regions. Sequence homologies to human pathogens have been detected for all identified epitopes. Our study demonstrates that epitope spreading does indeed occur during the pathogenesis of AIH and supports the concept of molecular mimicry as a possible initiating mechanism for AIH.

A transgenic mouse model of inducible macrophage depletion: effects of diphtheria toxin-driven lysozyme M-specific cell lineage ablation on wound inflammatory, angiogenic, and contractive processes.

Whether the wound macrophage is a key regulatory inflammatory cell type in skin repair has been a matter of debate. A transgenic mouse model mediating inducible macrophage depletion during skin repair has not been used to date to address this question. Here, we specifically rendered the monocyte/macrophage leukocyte lineage sensitive to diphtheria toxin by expressing the lysozyme M promoter-driven, Cre-mediated excision of a transcriptional STOP cassette from the simian DT receptor gene in mice (lysM-Cre/DTR). Application of diphtheria toxin to lysM-Cre/DTR mice led to a rapid reduction in both skin tissue and wound macrophage numbers at sites of injury. Macrophage-depleted mice revealed a severely impaired wound morphology and delayed healing. In the absence of macrophages, wounds were re-populated by large numbers of neutrophils. Accordingly, macrophage-reduced wound tissues exhibited the increased and prolonged persistence of macrophage inflammatory protein-2, macrophage chemoattractant protein-1, interleukin-1beta, and cyclooxygenase-2, paralleled by unaltered levels of bioactive transforming growth factor-beta1. Altered expression patterns of vascular endothelial growth factor on macrophage reduction were associated with a disturbed neo-vascularization at the wound site. Impaired wounds revealed a loss of myofibroblast differentiation and wound contraction. Our data in the use of lysM-Cre/DTR mice emphasize the pivotal function of wound macrophages in the integration of inflammation and cellular movements at the wound site to enable efficient skin repair.

Viral triggers for autoimmunity: is the 'glass of molecular mimicry' half full or half empty?

In this review we want to consider some of the requirements for autoimmune disease to develop and how this may be reproduced in animal models. Besides a genetic predisposition, environmental triggering factors seem to play a central role in the etiology of many autoimmune diseases. In theory, a structural similarity or identity between the host and an invading pathogen might cause the immune system of the host to react not only to the pathogen but also to self-components. However, in order for such a process of molecular mimicry to induce autoimmunity the mechanisms of maintaining tolerance or ignorance to the self-components need to be circumvented. Subsequently, in order to advance autoimmunity to overt autoimmune disease the frequency and avidity of autoaggressive lymphocytes has to be of sufficient magnitude. Intuitively, one would assume that tolerance might be stronger to identical structures than to structures that just share a certain degree of similarity. Self-reactive lymphocytes with high-avidity are more likely to be deleted or functionally silenced by central and/or peripheral tolerance mechanisms. Thus, perfect mimicry between identical structures might fail in inducing autoimmunity because of efficient tolerance mechanisms. In contrast, imperfect mimicry between similar but not identical structures might on one hand circumvent tolerance but on the other hand result in the generation of lymphocytes with only low- to intermediate avidity. Here we examine animal models that use the concept of molecular mimicry as a potential mechanism for inducing or accelerating autoimmunity. We focus on the RIP-LCMV model for type 1 diabetes and the novel cytochrome P450 2D6 (CYP2D6) model for autoimmune hepatitis, which use either identical or similar triggering and target antigens.

Cytochrome P450 2D6 as a model antigen.

Cytochrome P450 2D6 (CYP2D6) has been identified as the major autoantigen in type 2 autoimmune hepatitis (AIH). However, because of a lack of appropriate animal models, the etiology of AIH is still poorly understood. We generated a mouse model for AIH using the human CYP2D6 as a triggering molecule for autoimmunity. We infected wild-type FVB mice with an adenovirus expressing human CYP2D6 (Ad-2D6) to break self-tolerance to the mouse CYP2D6 homologues. Ad-2D6-infected mice showed persistent features of liver damage including hepatic fibrosis, cellular infiltrations, focal-to-confluent necrosis and generation of anti-CYP2D6 antibodies, which predominantly recognized the identical immunodominant epitope recognized by LKM-1 antibodies from AIH patients. Interestingly, Ad-2D6 infection of transgenic mice expressing the human CYP2D6 (CYP2D6 mice) resulted in delayed kinetics and reduced severity of liver damage. However, the quantity and quality of anti-CYP2D6 antibodies was only moderately reduced in CYP2D6 mice. In contrast, the frequency of CYP2D6-specific CD4 and CD8 T cells was dramatically decreased in CYP2D6 mice, indicating the presence of a strong T cell tolerance to human CYP2D6 established in CYP2D6 mice, but not in wild-type mice. CYP2D6-specific T cells reacted to human CYP2D6 peptides with intermediate homology to the mouse homologues, but not to those with high homology, indicating that molecular mimicry rather than molecular identity breaks tolerance and subsequently causes severe persistent autoimmune liver damage. The CYP2D6 model provides a platform to investigate mechanisms involved in the immunopathogenesis of autoimmune-mediated chronic hepatic injury and evaluate possible ways of therapeutic interference.

Animal models for autoimmune hepatitis.

The liver is the target of adverse immune reactions in three putative autoimmune diseases: autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). These three diseases can be distinguished by clinical, histological, and immunological features. However, especially on the level of specific antibody formation an overlap can occur, which sometimes complicates diagnosis. In this review, we will concentrate on autoimmune hepatitis and the current state of animal models for this severe disease. AIH is characterized by the presence of interface hepatitis and portal plasma cell infiltration, hypergammaglobulinemia, and autoantibodies. The hallmark of type 2 AIH is the generation of autoantibodies of the LKM-1 type. The major target of these antibodies is the cytochrome P450 isoform 2D6 (CYP2D6). In the past several attempts have been made to develop a reliable animal model that reflects the persistent hepatic destruction that occurs in human AIH. However, most models were only successful in causing a transient form of hepatic damage and often used rather complex ways of disease induction.

Blockade but not overexpression of the junctional adhesion molecule C influences virus-induced type 1 diabetes in mice.

Type 1 diabetes (T1D) results from the autoimmune destruction of insulin-producing beta-cells in the pancreas. Recruitment of inflammatory cells is prerequisite to beta-cell-injury. The junctional adhesion molecule (JAM) family proteins JAM-B and JAM-C are involved in polarized leukocyte transendothelial migration and are expressed by vascular endothelial cells of peripheral tissue and high endothelial venules in lympoid organs. Blocking of JAM-C efficiently attenuated cerulean-induced pancreatitis, rheumatoid arthritis or inflammation induced by ischemia and reperfusion in mice. In order to investigate the influence of JAM-C on trafficking and transmigration of antigen-specific, autoaggressive T-cells, we used transgenic mice that express a protein of the lymphocytic choriomeningitis virus (LCMV) as a target autoantigen in the ß-cells of the islets of Langerhans under the rat insulin promoter (RIP). Such RIP-LCMV mice turn diabetic after infection with LCMV. We found that upon LCMV-infection JAM-C protein was upregulated around the islets in RIP-LCMV mice. JAM-C expression correlated with islet infiltration and functional beta-cell impairment. Blockade with a neutralizing anti-JAM-C antibody reduced the T1D incidence. However, JAM-C overexpression on endothelial cells did not accelerate diabetes in the RIP-LCMV model. In summary, our data suggest that JAM-C might be involved in the final steps of trafficking and transmigration of antigen-specific autoaggressive T-cells to the islets of Langerhans.

Rapamycin induces the TGFbeta1/Smad signaling cascade in renal mesangial cells upstream of mTOR.

The mTOR kinase inhibitor rapamycin (sirolimus) is a drug with potent immunosuppressive and antiproliferative properties. We found that rapamycin induces the TGFbeta/Smad signaling cascade in rat mesangial cells (MC) as depicted by the nuclear translocation of phospho-Smads 2, -3 and Smad-4, respectively. Concomitantly, rapamycin increases the nuclear DNA binding of receptor (R)- and co-Smad proteins to a cognate Smad-binding element (SBE) which in turn causes an increase in profibrotic gene expression as exemplified by the connective tissue growth factor (CTGF) and plasminogen activator inhibitor 1 (PAI-1). Using small interfering (si)RNA we demonstrate that Smad 2/3 activation by rapamycin depends on its endogenous receptor FK binding protein 12 (FKBP12). Mechanistically, Smad induction by rapamycin is initiated by an increase in active TGFbeta(1) as shown by ELISA and by the inhibitory effects of a neutralizing TGFbeta antibody. Using an activin receptor-like kinase (ALK)-5 inhibitor and by siRNA against the TGFbeta type II receptor (TGFbeta-RII) we furthermore demonstrate a functional involvement of both types of TGFbeta receptors. However, rapamycin did not compete with TGFbeta for TGFbeta-receptor binding as found in radioligand-binding assay. Besides SB203580, a specific inhibitor of the p38 MAPK, the reactive oxygen species (ROS) scavenger N-acetyl-cysteine (NAC) and a cell-permeable superoxide dismutase (SOD) mimetic strongly abrogated the stimulatory effects of rapamycin on Smad 2 and 3 phosphorylation. Furthermore, the rapid increase in dichlorofluorescein (DCF) formation implies that rapamycin mainly acts through ROS. In conclusion, activation of the profibrotic TGFbeta/Smad signaling cascade accompanies the immunosuppressive and antiproliferative actions of rapamycin.

Long-term maternal imprinting of the specific B cell repertoire by maternal antibodies.

Maternal antibodies protect newborns whilst they are immunologically immature. This study shows that maternal antibodies can also shape the B cell repertoire of the offspring long after the maternal antibodies themselves become undetectable. V(H)DJ(H) gene-targeted (VI10) mice expressing a heavy chain specific for vesicular stomatitis virus (VSV) produce a 20-fold increased spontaneous titer of VSV-neutralizing antibodies. When transferred from mother to offspring, these antibodies prevented accumulation of Ag-specific transitional type 2 and marginal zone B cells with an activated phenotype and favored selection to the B cell follicles. This effect was B cell-intrinsic and lasted up to adulthood. The pups nursed by mothers producing specific antibodies developed higher endogenous antibody titers of this specificity which perpetuated the effects of specific B cell selection into the mature follicular compartment, presumably by blocking auto-Ag-dependent development of transitional type 2 B cells in the spleen. This repertoire change was functional, as following infection of adult mice with VSV, those pups that had received specific maternal antibodies as neonates had increased pre-immune titers and mounted strong early IgG neutralizing antibodies.

Breaking tolerance to the natural human liver autoantigen cytochrome P450 2D6 by virus infection.

Autoimmune liver diseases, such as autoimmune hepatitis (AIH) and primary biliary cirrhosis, often have severe consequences for the patient. Because of a lack of appropriate animal models, not much is known about their potential viral etiology. Infection by liver-tropic viruses is one possibility for the breakdown of self-tolerance. Therefore, we infected mice with adenovirus Ad5 expressing human cytochrome P450 2D6 (Ad-2D6). Ad-2D6-infected mice developed persistent autoimmune liver disease, apparent by cellular infiltration, hepatic fibrosis, "fused" liver lobules, and necrosis. Similar to type 2 AIH patients, Ad-2D6-infected mice generated type 1 liver kidney microsomal-like antibodies recognizing the immunodominant epitope WDPAQPPRD of cytochrome P450 2D6 (CYP2D6). Interestingly, Ad-2D6-infected wild-type FVB/N mice displayed exacerbated liver damage when compared with transgenic mice expressing the identical human CYP2D6 protein in the liver, indicating the presence of a stronger immunological tolerance in CYP2D6 mice. We demonstrate for the first time that infection with a virus expressing a natural human autoantigen breaks tolerance, resulting in a chronic form of severe, autoimmune liver damage. Our novel model system should be instrumental for studying mechanisms involved in the initiation, propagation, and precipitation of virus-induced autoimmune liver diseases.

Early type I interferon-mediated signals on B cells specifically enhance antiviral humoral responses.

Type I interferons (IFN-I) limit viral spread by inducing antiviral genes in infected target cells and by shaping the adaptive response through induction of additional cytokines. Vesicular stomatitis virus (VSV) efficiently triggers the production of IFN-I in mice, and it is suggested that IFN-alpha is induced after binding of VSV to TLR7 in infected cells. Our study with virus-specific B cell receptor-transgenic mice demonstrates here that IFN-I directly fuel early humoral immune responses in vivo. VSV-specific B cells that lacked IFN-alpha/beta receptors were considerably impaired in plasma cell formation and in generating antiviral IgM. At low viral titers, production of IFN-alpha following VSV infection was independent of TLR7-mediated signals. Interestingly, however, TLR7 ligation in B cells increased the formation of early antiviral IgM. These findings indicate that IFN-alpha-mediated augmentation of specific B cell responses is a partially TLR7- and virus dose-dependent mechanism.