Macrophage scavenger receptor 1 mediates lipid-induced inflammation in non-alcoholic fatty liver disease.

BACKGROUND & AIMS: Obesity-associated inflammation is a key player in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). However, the role of macrophage scavenger receptor 1 (MSR1, CD204) remains incompletely understood. METHODS: A total of 170 NAFLD liver biopsies were processed for transcriptomic analysis and correlated with clinicopathological features. Msr1-/- and wild-type mice were subjected to a 16-week high-fat and high-cholesterol diet. Mice and ex vivo human liver slices were treated with a monoclonal antibody against MSR1. Genetic susceptibility was assessed using genome-wide association study data from 1,483 patients with NAFLD and 430,101 participants of the UK Biobank. RESULTS: MSR1 expression was associated with the occurrence of hepatic lipid-laden foamy macrophages and correlated with the degree of steatosis and steatohepatitis in patients with NAFLD. Mice lacking Msr1 were protected against diet-induced metabolic disorder, showing fewer hepatic foamy macrophages, less hepatic inflammation, improved dyslipidaemia and glucose tolerance, and altered hepatic lipid metabolism. Upon induction by saturated fatty acids, MSR1 induced a pro-inflammatory response via the JNK signalling pathway. In vitro blockade of the receptor prevented the accumulation of lipids in primary macrophages which inhibited the switch towards a pro-inflammatory phenotype and the release of cytokines such as TNF-ɑ. Targeting MSR1 using monoclonal antibody therapy in an obesity-associated NAFLD mouse model and human liver slices resulted in the prevention of foamy macrophage formation and inflammation. Moreover, we identified that rs41505344, a polymorphism in the upstream transcriptional region of MSR1, was associated with altered serum triglycerides and aspartate aminotransferase levels in a cohort of over 400,000 patients. CONCLUSIONS: Taken together, our data suggest that MSR1 plays a critical role in lipid-induced inflammation and could thus be a potential therapeutic target for the treatment of NAFLD. LAY SUMMARY: Non-alcoholic fatty liver disease (NAFLD) is a chronic disease primarily caused by excessive consumption of fat and sugar combined with a lack of exercise or a sedentary lifestyle. Herein, we show that the macrophage scavenger receptor MSR1, an innate immune receptor, mediates lipid uptake and accumulation in Kupffer cells, resulting in liver inflammation and thereby promoting the progression of NAFLD in humans and mice.

Secretory immunoglobulin A in preterm infants: determination of normal values in breast milk and stool.

BACKGROUND: IgA and its secretory form sIgA impact protection from infection and necrotising enterocolitis but little is known about quantities in preterm mums own milk (MOM) or infant stool, onset of endogenous production in the preterm gut, and what affects these. METHODS: We measured by ELISA in MOM and stool from healthy preterm infants total IgA and sIgA longitudinally and additionally in MOM fresh, refrigerated, frozen, and after traversing feeding systems. RESULTS: In 42 MOM (median gestation 26 weeks), we showed total IgA levels and sIgA were highest in colostrum, fell over 3 weeks, and were not impacted by gestation. Median IgA values matched previous term studies (700 mcg/ml). In MOM recipients stool IgA was detected in the first week, at around 30% of MOM quantities. Formula fed infants did not have detectable stool IgA until the third week. Levels of IgA and sIgA were approximately halved by handling processes. CONCLUSIONS: MOM in the 3 weeks after preterm delivery contains the highest concentrations of IgA and sIgA. Endogenous production after preterm birth occurs from the 3 week meaning preterm infants are dependent on MOM for IgA which should be optimised. Routine NICU practices halve the amount available to the infant. IMPACT: (Secretory) Immunoglobulin A (IgA) is present in colostrum of maternal milk from infants as preterm as 23-24 weeks gestational age, falling over the first 3 weeks to steady levels similar to term. Gestation at birth does not impact (secretory) IgA levels in breast milk. IgA is present in very preterm infant stools from maternal milk fed infants from the first week of life, but not in formula milk fed preterm infants until week three, suggesting endogenous production from this point. Refrigeration, freezing, and feeding via plastic tubing approximately halved the amount of IgA available.

Maternal breastmilk, infant gut microbiome and the impact on preterm infant health.

AIM: This narrative review summarises the benefits of maternal breastmilk to both the infant and the mother, specifically the benefits that relate to modification of the infant microbiome, and how this might vary in the preterm infant. METHODS: We used PubMed to primarily identify papers, reviews, case series and editorials published in English until May 2020. Based on this, we report on the components of breastmilk, their associated hypothesised benefits and the implications for clinical practice. RESULTS: Breastmilk is recommended as the exclusive diet for newborn infants because it has numerous nutritional and immunological benefits. Additionally, exposure to the maternal breastmilk microbiome may confer a lasting effect on gut health. In the preterm infant, breastmilk is associated with a significant reduction in necrotising enterocolitis, an inflammatory gastrointestinal disease and reduction in other key morbidities, together with improved neurodevelopmental outcomes. CONCLUSION: These impacts have long-term benefits for the child (and the mother) even after weaning. This benefit is likely due, in part, to modification of the infant gut microbiome by breastmilk microbes and bioactive components, and provide potential areas for research and novel therapies in preterm and other high-risk infants.

Identification of a xenobiotic as a potential environmental trigger in primary biliary cholangitis.

BACKGROUND & AIMS: Primary biliary cholangitis (PBC) is an autoimmune-associated chronic liver disease triggered by environmental factors, such as exposure to xenobiotics, which leads to a loss of tolerance to the lipoic acid-conjugated regions of the mitochondrial pyruvate dehydrogenase complex, typically to the E2 component. We aimed to identify xenobiotics that might be involved in the environmental triggering of PBC. METHODS: Urban landfill and control soil samples from a region with high PBC incidence were screened for xenobiotic activities using analytical, cell-based xenobiotic receptor activation assays and toxicity screens. RESULTS: A variety of potential xenobiotic classes were ubiquitously present, as identified by their interaction with xenobiotic receptors - aryl hydrocarbon receptor, androgen receptor and peroxisome proliferator activated receptor alpha - in cell-based screens. In contrast, xenoestrogens were present at higher levels in soil extracts from around an urban landfill. Furthermore, two landfill sampling sites contained a chemical(s) that inhibited mitochondrial oxidative phosphorylation and induced the apoptosis of a hepatic progenitor cell. The mitochondrial effect was also demonstrated in human liver cholangiocytes from three separate donors. The chemical was identified as the ionic liquid [3-methyl-1-octyl-1H-imidazol-3-ium]+ (M8OI) and the toxic effects were recapitulated using authentic pure chemical. A carboxylate-containing human hepatocyte metabolite of M8OI, bearing structural similarity to lipoic acid, was also enzymatically incorporated into the E2 component of the pyruvate dehydrogenase complex via the exogenous lipoylation pathway in vitro. CONCLUSIONS: These results identify, for the first time, a xenobiotic in the environment that may be related to and/or be a component of an environmental trigger for PBC. Therefore, further study in experimental animal models is warranted, to determine the risk of exposure to these ionic liquids. LAY SUMMARY: Primary biliary cholangitis is a liver disease in which most patients have antibodies to mitochondrial proteins containing lipoic acid binding site(s). This paper identified a man-made chemical present in soils around a waste site. It was then shown that this chemical was metabolized into a product with structural similarity to lipoic acid, which was capable of replacing lipoic acid in mitochondrial proteins.

Impaired hepatic lipid synthesis from polyunsaturated fatty acids in TM6SF2 E167K variant carriers with NAFLD.

BACKGROUND: Carriers of the transmembrane 6 superfamily member 2 E167K gene variant (TM6SF2EK/KK) have decreased expression of the TM6SF2 gene and increased risk of NAFLD and NASH. Unlike common 'obese/metabolic' NAFLD, these subjects lack hypertriglyceridemia and have lower risk of cardiovascular disease. In animals, phosphatidylcholine (PC) deficiency results in a similar phenotype. PCs surround the core of VLDL consisting of triglycerides (TGs) and cholesteryl-esters (CEs). We determined the effect of the TM6SF2 E167K on these lipids in the human liver and serum and on hepatic gene expression and studied the effect of TM6SF2 knockdown on hepatocyte handling of these lipids. METHODS: Liver biopsies were taken from subjects characterized with respect to the TM6SF2 genotype, serum and liver lipidome, gene expression and histology. In vitro, after TM6SF2 knockdown in HuH-7 cells, we compared incorporation of different fatty acids into TGs, CEs, and PCs. RESULTS: The TM6SF2EK/KK and TM6SF2EE groups had similar age, gender, BMI and HOMA-IR. Liver TGs and CEs were higher and liver PCs lower in the TM6SF2EK/KK than the TM6SF2EE group (p<0.05). Polyunsaturated fatty acids (PUFA) were deficient in liver and serum TGs and liver PCs but hepatic free fatty acids were relatively enriched in PUFA (p<0.05). Incorporation of PUFA into TGs and PCs in TM6SF2 knockdown hepatocytes was decreased (p<0.05). Hepatic expression of TM6SF2 was decreased in variant carriers, and was co-expressed with genes regulated by PUFAs. CONCLUSIONS: Hepatic lipid synthesis from PUFAs is impaired and could contribute to deficiency in PCs and increased intrahepatic TG in TM6SF2 E167K variant carriers.

An extended mini-complement factor H molecule ameliorates experimental C3 glomerulopathy.

Abnormal regulation of the complement alternative pathway is associated with C3 glomerulopathy. Complement factor H is the main plasma regulator of the alternative pathway and consists of 20 short consensus repeat (SCR) domains. Although recombinant full-length factor H represents a logical treatment for C3 glomerulopathy, its production has proved challenging. We and others have designed recombinant mini-factor H proteins in which 'non-essential' SCR domains have been removed. Here, we report the in vitro and in vivo effects of a mini-complement factor H protein, FH1-5^18-20, using the unique factor H-deficient (Cfh-/-) mouse model of C3 glomerulopathy. FH1-5^18-20 is comprised of the key complement regulatory domains (SCRs 1-5) linked to the surface recognition domains (SCRs 18-20). Intraperitoneal injection of FH1-5^18-20 in Cfh-/- mice reduced abnormal glomerular C3 deposition, similar to full-length factor H. Systemic effects on plasma alternative pathway control were comparatively modest, in association with a short half-life. Thus, FH1-5^18-20 is a potential therapeutic agent for C3 glomerulopathy and other renal conditions with alternative pathway-mediated tissue injury.

Chemokine receptor CXCR3 agonist prevents human T-cell migration in a humanized model of arthritic inflammation.

The recruitment of T lymphocytes during diseases such as rheumatoid arthritis is regulated by stimulation of the chemokine receptors expressed by these cells. This study was designed to assess the potential of a CXCR3-specific small-molecule agonist to inhibit the migration of activated human T cells toward multiple chemokines. Further experiments defined the molecular mechanism for this anti-inflammatory activity. Analysis in vitro demonstrated agonist induced internalization of both CXCR3 and other chemokine receptors coexpressed by CXCR3(+) T cells. Unlike chemokine receptor-specific antagonists, the CXCR3 agonist inhibited migration of activated T cells toward the chemokine mixture in synovial fluid from patients with active rheumatoid arthritis. A humanized mouse air-pouch model showed that intravenous treatment with the CXCR3 agonist prevented inflammatory migration of activated human T cells toward this synovial fluid. A potential mechanism for this action was defined by demonstration that the CXCR3 agonist induces receptor cross-phosphorylation within CXCR3-CCR5 heterodimers on the surface of activated T cells. This study shows that generalized chemokine receptor desensitization can be induced by specific stimulation of a single chemokine receptor on the surface of activated human T cells. A humanized mouse model was used to demonstrate that this receptor desensitization inhibits the inflammatory response that is normally produced by the chemokines present in synovial fluid from patients with active rheumatoid arthritis.

The methylimidazolium ionic liquid M8OI is detectable in human sera and is subject to biliary excretion in perfused human liver.

A methylimidizolium ionic liquid (M8OI) was recently found to be contaminating the environment and to be related to and/or potentially a component of an environmental trigger for the autoimmune liver disease primary biliary cholangitis (PBC). The aims of this study were to investigate human exposure to M8OI, hepatic metabolism and excretion. PBC patient and control sera were screened for the presence of M8OI. Human livers were perfused with 50µM M8OI in a closed circuit and its hepatic disposition examined. Metabolism was examined in cultured human hepatocytes and differentiated HepaRG cells by the addition of M8OI and metabolites in the range 10-100 µM. M8OI was detected in the sera from 5/20 PBC patients and 1/10 controls. In perfused livers, M8OI was cleared from the plasma with its appearance - primarily in the form of its hydroxylated (HO8IM) and carboxylated (COOH7IM) products - in the bile. Metabolism was reflected in cultured hepatocytes with HO8IM production inhibited by the cytochrome P450 inhibitor ketoconazole. Further oxidation of HO8IM to COOH7IM was sequentially inhibited by the alcohol and acetaldehyde dehydrogenase inhibitors 4-methyl pyrazole and disulfiram respectively. Hepatocytes from 1 donor failed to metabolise M8OI to COOH7IM over a 24 h period. These results demonstrate exposure to M8OI in the human population, monooxygenation by cytochromes P450 followed by alcohol and acetaldehyde dehydrogenase oxidation to a carboxylic acid that are excreted, in part, via the bile in human liver.

The toxicity of the methylimidazolium ionic liquids, with a focus on M8OI and hepatic effects.

Ionic liquids are a diverse range of charged chemicals with low volatility and often liquids at ambient temperatures. This characteristic has in part lead to them being considered environmentally-friendly replacements for existing volatile solvents. However, methylimidazolium ionic liquids are slow to break down in the environment and a recent study at Newcastle detected 1 octyl 3 methylimidazolium (M8OI) - an 8 carbon variant methylimidazolium ionic liquid - in soils in close proximity to a landfill site. The current M8OI toxicity database in cultured mammalian cells, in experimental animal studies and in model indicators of environmental impact are reviewed. Selected analytical data from the Newcastle study suggest the soils in close proximity to the landfill site, an urban soil lacking overt contamination, had variable levels of M8OI. The potential for M8OI - or a structurally related ionic liquid - to trigger primary biliary cholangitis (PBC), an autoimmune liver disease thought to be triggered by an unknown agent(s) in the environment, is reviewed.

Xenobiotic incorporation into pyruvate dehydrogenase complex can occur via the exogenous lipoylation pathway.

UNLABELLED: Lipoylated enzymes such as the E2 component of pyruvate dehydrogenase complex (PDC-E2) are targets for autoreactive immune responses in primary biliary cirrhosis, with lipoic acid itself forming a component of the dominant auto-epitopes. A candidate mechanism for the initiation of tolerance breakdown in this disease is immune recognition of neo-antigens formed by xenobiotic substitution of normal proteins. Importantly, sensitization with proteins artificially substituted with the lipoic acid analogue xenobiotic 6-bromohexanoic acid (6BH) can induce an immune response that cross-reacts with PDC-E2. This study investigated the potential of recombinant lipoylation enzymes lipoate activating enzyme and lipoyl-AMP(GMP):N-lysine lipoyl transferase to aberrantly incorporate xenobiotics into PDC-E2. It was found that these enzymes could incorporate lipoic acid analogues including octanoic and hexanoic acids and the xenobiotic 6BH into PDC-E2. The efficiency of incorporation of these analogues showed a variable dependence on activation by adenosine triphosphate (ATP) or guanosine triphosphate (GTP), with ATP favoring the incorporation of hexanoic acid and 6BH whereas GTP enhanced substitution by octanoic acid. Importantly, competition studies showed that the relative incorporation of both 6BH and lipoic acid could be regulated by the balance between ATP and GTP, with the formation of 6BH-substituted PDC-E2 predominating in an ATP-rich environment. CONCLUSION: Using a well-defined system in vitro we have shown that an important xenobiotic can be incorporated into PDC in place of lipoic acid by the exogenous lipoylation system; the relative levels of lipoic acid and xenobiotic incorporation may be determined by the balance between ATP and GTP. These observations suggest a clear mechanism for the generation of an auto-immunogenic neo-antigen of relevance for the pathogenesis of primary biliary cirrhosis.

Pilot study of peripheral muscle function in primary biliary cirrhosis: potential implications for fatigue pathogenesis.

BACKGROUND & AIMS: Primary biliary cirrhosis (PBC) is characterized in 95% of patients by autoantibody responses directed against the mitochondrial antigen pyruvate dehydrogenase complex (PDC). Although anti-PDC inhibits PDC function in vitro, mitochondrial function in vivo in PBC has not been examined. METHODS: (31)P magnetic resonance spectroscopy was performed in PBC patients (n = 15) and fatigued (chronic fatigue syndrome/myalgic encephalomyelitis, n = 8), cholestatic (primary sclerosing cholangitis [PSC], n = 4), and normal (n = 8) controls to define mitochondrial function and pH regulation in peripheral muscle during exercise at 25% and 35% of maximum voluntary contraction. RESULTS: Normal, chronic fatigue syndrome/myalgic encephalomyelitis, and PSC subjects all showed close correlation between kinetics of adenosine diphosphate (ADP) and phosphocreatine (PCr) recovery after low-impact exercise, reflecting the normal tight regulation of PCr "response" by mitochondria to ADP "drive." This relationship was lost in PBC patients, indicating mitochondrial dysfunction (normal r(2) = 0.78, P < .005; PBC r(2) = 0.007, P = ns). Ratio between PCr and ADP recovery half-times (constant in controls, indicating normal mitochondrial responsivity) was significantly elevated in PBC patients (but not PSC) and was associated with anti-PDC levels. At higher levels of exercise PBC (but not PSC) patients showed excess muscle acidosis, with pH correlating with elevation of PCr/ADP recovery ratio, indicating a link to mitochondrial dysfunction. PBC patients alone also showed significant prolongation of muscle pH recovery time after exercise (unrelated to mitochondrial function), which correlated with clinical fatigue. CONCLUSIONS: PBC patients exhibit a variable degree of muscle mitochondrial dysfunction that manifests as excess acidosis after exercise. The extent to which patients can recover rapidly from acidosis appears to determine whether they are clinically fatigued.

Potential role of indoleamine 2,3-dioxygenase in primary biliary cirrhosis.

Indoleamine 2,3-dioxygenase (IDO)-induced immunosuppression can be clinically beneficial for autoimmune diseases. Primary biliary cirrhosis (PBC) is characterized by autoimmune lesions of intrahepatic bile duct epithelial cells that may lead to irreversible cirrhosis or hepatocellular carcinoma. The present study assessed the expression and function of IDO in a cell culture model and in PBC patients. IDO expression was monitored in a human immortalized but non-malignant biliary epithelial cell (iBEC) line. Increased expression of IDO1/2 was observed in the iBECs following stimulation with interferon-γ (IFN-γ). The induction of IDO was IFN-γ-dependent, but was independent of the transforming growth factor-ß (TGF-ß) pathway. IDO enzymatic activity was observed in the supernatant of iBECs following stimulation with IFN-γ using colorimetric assays. A total of 47 serum samples from PBC patients were used to examine IDO activity by high-performance liquid chromatography, with samples from 24 healthy volunteers used as controls. Patients with PBC exhibited an increased rate of tryptophan to kynurenine conversion (P>0.01). Liver sections from patients with PBC (n=5) and those of healthy controls (n=5) were used for immunohistochemical studies. IDO expression was observed in biliary epithelial cells and in hepatocytes of PBC patients. Finally, the effect of tryptophan metabolites on human cluster of differentiation (CD) 4+ T cells in inducing polarization towards a regulatory T cell phenotype was examined. 3-Hydroxykynurenine significantly upregulated the fraction of CD4+ cells expressing forkhead box p3 (Foxp3). The results of the present study suggest a therapeutic opportunity for the management of PBC and indicate that tryptophan catabolism could serve as a potential biomarker to monitor disease progression.

Progenitor-derived hepatocyte-like (B-13/H) cells metabolise 1'-hydroxyestragole to a genotoxic species via a SULT2B1-dependent mechanism.

Rat B-13 progenitor cells are readily converted into functional hepatocyte-like B-13/H cells capable of phase I cytochrome P450-dependent activation of pro-carcinogens and induction of DNA damage. The aim of the present study was to investigate whether the cells are also capable of Phase II sulphotransferase (SULT)-dependent activation of a pro-carcinogen to an ultimate carcinogen. To this end we therefore examined the bioactivation of the model hepatic (hepato- and cholangio-) carcinogen estragole and its proximate SULT1A1-activated genotoxic metabolite 1'-hydroxyestragole. Exposing B-13 or B-13/H cells to estragole (at concentrations up to 1mM) resulted in the production of low levels of 1'-hydroxyestragole, but did not result in detectable DNA damage. Exposing B-13/H cells - but not B-13 cells - to 1'-hydroxyestragole resulted in a dose-dependent increase in DNA damage in comet assays, confirmed by detection of N(2)-(trans-isoestragol-3'-yl)-2'-deoxyguanosine adducts. Genotoxicity was inhibited by general SULT inhibitors, supporting a role for SULTS in the activation of 1-hydroxyestragole in B-13/H cells. However, B-13 and B-13/H cells did not express biologically significant levels of SULT1A1 as determined by qRT-PCR, Western blotting and its associated 7-hydroxycoumarin sulphation activity. B-13 and B-13/H cells expressed - relative to intact rat liver - high levels of SULT2B1 (primarily the b isoform) and SULT4A1 mRNAs and proteins. B-13 and B-13/H cells also expressed the 3'-phosphoadenosine 5'-phosphosulphate synthase 1 required for the generation of activated sulphate cofactor 3'-phosphoadenosine 5'-phosphosulphate. However, only B-13/H cells expressed functional SULT activities towards SULT2B1 substrates DHEA, pregnenolone and 4 methylumbelliferone. Since liver progenitor cells are bi-potential and also form cholangiocytes, we therefore hypothesised that B-13 cells express a cholangiocyte-like SULT profile. To test this hypothesis, the expression of SULTs was examined in liver by RT-PCR and immunohistochemistry. SULT2B1 - but not SULT1A1 - was determined to be expressed in both rat and human cholangiocytes. Since 1'-hydroxyestragole exposure readily produced DNA injury in B-13/H cells, these data suggest that cholangiocarcinomas generated in rats fed estragole may be dependent, in part, on SULT2B1 activation of the 1'-hydroxyestragole metabolite.

Rapid site-directed mutagenesis of chemokines and their purification from a bacterial expression system.

Chemokines are a family of small chemoattractant cytokines implicated in the recruitment and migration of leukocytes from the blood into tissues during disease and routine immune homeostasis. Although there are many similarities in the structure and function of certain chemokines, the importance of many residues in the function of these proteins is yet to be determined, and studies from related chemokines have shown that similar sequences may play different roles in each protein. The migration-inducing capacity of many chemokines is thought to involve the cell surface glycosaminoglycan (GAG), heparan sulphate (HS), which may assist in the formation of an immobilised chemokine gradient within inflamed tissues. To examine the heparan sulphate binding ability of the CC chemokine monocyte chemoattractant protein (MCP)-3 and its importance in chemotactic migration, we have identified and mutated conserved basic residues within the mature MCP-3 protein to the neutral amino acid alanine using a novel inverse polymerase chain reaction (I-PCR) method that rapidly generates essentially 100% mutational efficiency due to decreased requirements for template DNA and an alkaline denaturation step; this increased mutational efficiency reduces both screening time and sequencing costs. We also describe an optimised method for the expression of soluble, correctly folded MCP-3 in a bacterial system using nickel affinity columns and reverse-phase fast protein liquid chromatography (RP-FPLC), and achieve purified yields of up to 0.4 mg/l of initial culture medium after 5 h of induction. These optimised methods could work equally well for any small circular plasmid (< or =4.5 kb) incorporating a polyhistidine tag.

Oral tolerisation to pyruvate dehydrogenase complex as a potential therapy for primary biliary cirrhosis.

Primary biliary cirrhosis (PBC) is characterised by immune-mediated damage to the intra-hepatic biliary epithelial cells (BEC). Immuno-modulatory/suppressive therapy represents, therefore, alogical approach to treatment in this disease. Conventional immuno-suppressive and immuno-modulatory agents suffer from the breadth of their action and/or excessive side effects. Autoreactive responses to pyruvate dehydrogenase complex (PDC) have been extensively characterised in PBC, and implicated in target cell damage. The aim of the current study was to study the potential efficacy of an antigen specific approach (oral tolerisation with autoantigen) to modulation of anti-PDC immune responses characteristic of PBC, utilising a mouse model of PDC immuno-reactivity. Groups of SJL/J mice were orally dosed with PDC alone, dosed with carrier only (saline) but systemically sensitised with PDC in adjuvant, or orally dosed with PDC at high (5 mg) or low (0.01 mg) dose and systemically sensitised with PDC. Oral dosing with PDC in isolation had no adverse effects on the animals and did not prime anti-PDC responses at doses below 1 mg. Pre-dosing with PDC at both high and low doses was effective at skewing the phenotype of the T-cell response to PDC induced by subsequent sensitisation away from the disease associated Th-1 phenotype (IL-2 and IFN-gamma secreting) and towards a theoretically protective Th-2 phenotype (IL-4 secreting) in a majority of, but not all, animals. No augmentation of Th-1 response was seen in any animal. Although the effects on liver histology remain to established oral tolerisation with PDC holds promise as a novel, antigen specific approach to therapy in PBC.

PDC-E3BP is not a dominant T-cell autoantigen in primary biliary cirrhosis.

BACKGROUND: Autoantibody responses reactive with the E2 and E3BP components of pyruvate dehydrogenase complex (PDC), which characterise primary biliary cirrhosis (PBC) crossreact, precluding the identification, from serological studies, of the antigen to which the principal breakdown of tolerance occurs. Although autoreactive T-cell responses to PDC-E2 have been well characterised it is, at present, unclear whether T-cell tolerance breakdown also occurs to PDC-E3BP. The aims of this study were to characterise autoreactive T-cell responses to PDC-E3BP in PBC and potential factors regulating their expression. METHODS: Peripheral blood T-cell proliferative responses to purified recombinant human PDC-E2 and PDC-E3BP at a range of concentrations were characterised in PBC patients and control subjects. RESULTS: T-cell proliferative responses to both E2 and E3BP were absent from control subjects (median peak stimulation index (SI) to PDC-E2 1.2 [range 0.3-1.9], 0/10 positive (SI>2.32), median peak SI to PDC-E3BP 1.1 [0.7-2.1]], 0/10 positive). Significant responses to PDC-E2 were seen in the majority of patients (median peak SI 11.4 [0.4-24.4], 17/20 (85%) positive) but to PDC-E3BP in only a minority (median peak SI 1-9 [0.6-9.95], 8/20 (40%) positive). Where responses to PDC-E3BP were seen they were universally secondary to responses to PDC-E2. CONCLUSIONS: Despite the presence of antibodies reactive with PDC-E3BP in the majority of PBC patients this self-protein is not a dominant T-cell autoantigen in PBC.

Hip3 interacts with the HIRA proteins Hip1 and Slm9 and is required for transcriptional silencing and accurate chromosome segregation.

The fission yeast HIRA proteins Hip1 and Slm9 are members of an evolutionarily conserved family of histone chaperones that are implicated in nucleosome assembly. Here we have used single-step affinity purification and mass spectrometry to identify factors that interact with both Hip1 and Slm9. This analysis identified Hip3, a previously uncharacterized 187-kDa protein, with similarity to S. cerevisiae Hir3. Consistent with this, cells disrupted for hip3+ exhibit a range of growth defects that are similar to those associated with loss of Hip1 and Slm9. These include temperature sensitivity, a cell cycle delay, and synthetic lethality with cdc25-22. Furthermore, genetic analysis also indicates that disruption of hip3+ is epistatic with mutation of hip1+ and slm9+. Mutation of hip3+ alleviates transcriptional silencing at several heterochromatic loci, including in the outer (otr) centromeric repeats, indicating that Hip3 is required for the integrity of pericentric heterochromatin. As a result, loss of Hip3 function leads to high levels of minichromosome loss and an increased frequency of lagging chromosomes during mitosis. Importantly, the function of Hip1, Slm9, and Hip3 is not restricted to constitutive heterochromatic loci, since these proteins also repress the expression of a number of genes, including the Tf2 retrotransposons.

A key role for autoreactive B cells in the breakdown of T-cell tolerance to pyruvate dehydrogenase complex in the mouse.

The key immunological event in the pathogenesis of the autoimmune liver disease primary biliary cirrhosis is breakdown of T-cell self-tolerance to pyruvate dehydrogenase complex (PDC). The mechanism resulting in this breakdown of tolerance remains unclear. Mice exposed to self-PDC mount no immune response; however, animals coexposed to self-PDC and PDC of foreign origin (which in isolation induces a cross-reactive antibody but not an autoreactive T-cell response) show breakdown of T-cell as well as B-cell tolerance. This observation raises the possibility that a cross-reactive antibody response to self-PDC can promote breakdown of T-cell tolerance. The aim of this study was to address the hypothesis that breakdown of T-cell tolerance to PDC can be driven by the presence of B cells and/or antibodies cross-reactive with this self-antigen. Naive female SJL/J mice were exposed to self-PDC alone and in the presence of purified splenic B cells from animals primed with foreign PDC (or controls) or purified immunoglobulin (Ig) G from the same animals. Breakdown of T-cell tolerance was assessed by splenic T-cell proliferative response to antigen at 5 weeks. CD4(+) T-cell proliferative responses indicative of breakdown of T-cell tolerance to self-PDC were seen in the majority (7 of 9, 78%) of animals receiving self-PDC together with purified PDC-reactive B cells. Tolerance breakdown was not seen in animals receiving self-PDC with purified anti-PDC IgG or with B cells from animals sensitized with an irrelevant antigen. In conclusion, breakdown of T-cell tolerance to the highly conserved self-antigen PDC may be mediated by high-level presentation of self-derived epitopes by activated cross-reactive B cells.

Covalent modification as a mechanism for the breakdown of immune tolerance to pyruvate dehydrogenase complex in the mouse.

The autoimmune liver disease primary biliary cirrhosis (PBC) is characterized by the breakdown of normal immune self tolerance to pyruvate dehydrogenase complex (PDC). How tolerance is broken to such a central and highly conserved self antigen in the initiation of autoimmunity remains unclear. One postulated mechanism is that reactivity arises to an altered form of self antigen with subsequent cross-reactivity to native self. In this murine study, we set out to examine whether sensitization with a covalently modified form of self PDC can give rise to the pattern of breakdown of B-cell and T-cell tolerance to self PDC seen in PBC patients. The notion that altered self can lead to tolerance breakdown was studied by sensitizing SJL/J mice with a covalently modified (biotinylated) preparation of self murine PDC (mP/O-B). Subsequently, antibody and T-cell reactivities to unmodified self mP/O were studied. Sensitization with mP/O-B elicited high-titre, high-affinity antibody responses reactive with both the mP/O-B immunogen and, importantly, native mP/O. In addition, significant MHC class II restricted splenic T-cell responses to native mP/O (i.e., true autoimmune responses) were seen in mP/O-B sensitized animals. The breakdown of T-cell self tolerance to mP/O was not seen in animals sensitized with irrelevant biotinylated antigens. In conclusion, this study provides evidence to support the concept that exposure to covalently modified self PDC can, in the correct proimmune environment, replicate the full breakdown of B-cell and T-cell immune tolerance to PDC seen in PBC. One potential etiological pathway in PBC therefore could be the breakdown of tolerance to self PDC occurring after exposure to self antigen covalently modified in the metabolically active environment of the liver.