Identification of two major autoantigens negatively regulating endothelial activation in Takayasu arteritis.

The presence of antiendothelial cell antibodies (AECAs) has been documented in Takayasu arteritis (TAK), a chronic granulomatous vasculitis. Here, we identify cell-surface autoantigens using an expression cloning system. A cDNA library of endothelial cells is retrovirally transfected into a rat myeloma cell line from which AECA-positive clones are sorted with flow cytometry. Four distinct AECA-positive clones are isolated, and endothelial protein C receptor (EPCR) and scavenger receptor class B type 1 (SR-BI) are identified as endothelial autoantigens. Autoantibodies against EPCR and SR-BI are detected in 34.6% and 36.5% of cases, respectively, with minimal overlap (3.8%). Autoantibodies against EPCR are also detected in ulcerative colitis, the frequent comorbidity of TAK. In mechanistic studies, EPCR and SR-BI function as negative regulators of endothelial activation. EPCR has also an effect on human T cells and impair Th17 differentiation. Autoantibodies against EPCR and SR-BI block the functions of their targets, thereby promoting pro-inflammatory phenotype.

Liquid-liquid phase separation of the Golgi matrix protein GM130.

Golgins are an abundant class of peripheral membrane proteins of the Golgi. These very long (50-400 nm) rod-like proteins initially capture cognate transport vesicles, thus enabling subsequent SNARE-mediated membrane fusion. Here, we explore the hypothesis that in addition to serving as vesicle tethers, Golgins may also possess the capacity to phase separate and, thereby, contribute to the internal organization of the Golgi. GM130 is the most abundant Golgin at the cis Golgi. Remarkably, overexpressed GM130 forms liquid droplets in cells analogous to those described for numerous intrinsically disordered proteins with low complexity sequences, even though GM130 is neither low in complexity nor intrinsically disordered. Virtually pure recombinant GM130 also phase-separates into dynamic, liquid-like droplets in close to physiological buffers and at concentrations similar to its estimated local concentration at the cis Golgi.

A repertoire of 124 potential autoantigens for autoimmune kidney diseases identified by dermatan sulfate affinity enrichment of kidney tissue proteins.

Autoantigens are the molecular targets in autoimmune diseases. They are a cohort of seemingly unrelated self-molecules present in different parts of the body, yet they can trigger a similar chain of autoimmune responses such as autoantibody production. We previously reported that dermatan sulfate (DS) can bind self-molecules of dying cells to stimulate autoreactive CD5+ B cells to produce autoantibodies. The formation of autoantigen-DS complexes converts the normally non-antigenic self-molecules to none-self antigens, and thus DS-affinity represents a common underlying biochemical property for autoantigens. This study sought to apply this property to identify potential autoantigens in the kidney. Total proteins were extracted from mouse kidney tissues and loaded onto DS-Sepharose resins. Proteins without affinity were washed off the resins, whereas those with increasing DS-affinity were eluted with step gradients of increasing salt strength. Fractions with strong and moderate DS-affinity were sequenced by mass spectrometry and yielded 25 and 99 proteins, respectively. An extensive literature search was conducted to validate whether these had been previously reported as autoantigens. Of the 124 proteins, 79 were reported autoantigens, and 19 out of 25 of the strong-DS-binding ones were well-known autoantigens. Moreover, these proteins largely fell into the two most common autoantibody categories in autoimmune kidney diseases, including 40 ANA (anti-nuclear autoantibodies) and 25 GBM (glomerular basement membrane) autoantigens. In summary, this study compiles a large repertoire of potential autoantigens for autoimmune kidney diseases. This autoantigen-ome sheds light on the molecular etiology of autoimmunity and further supports our hypothesis DS-autoantigen complexes as a unifying principle of autoantigenicity.

A comprehensive autoantigen-ome of autoimmune liver diseases identified from dermatan sulfate affinity enrichment of liver tissue proteins.

BACKGROUND: Autoimmune diseases result from aberrant immune attacks by the body itself. It is mysterious how autoantigens, a large cohort of seemingly unconnected molecules expressed in different parts of the body, can induce similar autoimmune responses. We have previously found that dermatan sulfate (DS) can form complexes with molecules of apoptotic cells and stimulate autoreactive CD5+ B cells to produce autoantibodies. Hence, autoantigenic molecules share a unique biochemical property in their affinity to DS. This study sought to further test this uniform principle of autoantigenicity. RESULTS: Proteomes were extracted from freshly collected mouse livers. They were loaded onto columns packed with DS-Sepharose resins. Proteins were eluted with step gradients of increasing salt strength. Proteins that bound to DS with weak, moderate, or strong affinity were eluted with 0.4, 0.6, and 1.0 M NaCl, respectively. After desalting, trypsin digestion, and gel electrophoresis, proteins were sequenced by mass spectrometry. To validate whether these proteins have been previously identified as autoantigens, an extensive literature search was conducted using the protein name or its alternative names as keywords. Of the 41 proteins identified from the strong DS-affinity fraction, 33 (80%) were verified autoantigens. Of the 46 proteins with moderate DS-affinity, 27 (59%) were verified autoantigens. Of the 125 proteins with weak DS-affinity, 44 (35%) were known autoantigens. Strikingly, these autoantigens fell into the classical autoantibody categories of autoimmune liver diseases: ANA (anti-nuclear autoantibodies), SMA (anti-smooth muscle autoantibodies), AMA (anti-mitochondrial autoantibodies), and LKM (liver-kidney microsomal autoantigens). CONCLUSIONS: This study of DS-affinity enrichment of liver proteins establishes a comprehensive autoantigen-ome for autoimmune liver diseases, yielding 104 verified and 108 potential autoantigens. The liver autoantigen-ome sheds light on the molecular origins of autoimmune liver diseases and further supports the notion of a unifying biochemical principle of autoantigenicity.

Antigen Extraction and B Cell Activation Enable Identification of Rare Membrane Antigen Specific Human B Cells.

Determining antigen specificity is vital for understanding B cell biology and for producing human monoclonal antibodies. We describe here a powerful method for identifying B cells that recognize membrane antigens expressed on cells. The technique depends on two characteristics of the interaction between a B cell and an antigen-expressing cell: antigen-receptor-mediated extraction of antigen from the membrane of the target cell, and B cell activation. We developed the method using influenza hemagglutinin as a model viral membrane antigen, and tested it using acetylcholine receptor (AChR) as a model membrane autoantigen. The technique involves co-culturing B cells with adherent, bioorthogonally labeled cells expressing GFP-tagged antigen, and sorting GFP-capturing, newly activated B cells. Hemagglutinin-specific B cells isolated this way from vaccinated human donors expressed elevated CD20, CD27, CD71, and CD11c, and reduced CD21, and their secreted antibodies blocked hemagglutination and neutralized viral infection. Antibodies cloned from AChR-capturing B cells derived from patients with myasthenia gravis bound specifically to the receptor on cell membrane. The approach is sensitive enough to detect antigen-specific B cells at steady state, and can be adapted for any membrane antigen.

Molecular determinants regulating selective binding of autophagy adapters and receptors to ATG8 proteins.

Autophagy is an essential recycling and quality control pathway. Mammalian ATG8 proteins drive autophagosome formation and selective removal of protein aggregates and organelles by recruiting autophagy receptors and adaptors that contain a LC3-interacting region (LIR) motif. LIR motifs can be highly selective for ATG8 subfamily proteins (LC3s/GABARAPs), however the molecular determinants regulating these selective interactions remain elusive. Here we show that residues within the core LIR motif and adjacent C-terminal region as well as ATG8 subfamily-specific residues in the LIR docking site are critical for binding of receptors and adaptors to GABARAPs. Moreover, rendering GABARAP more LC3B-like impairs autophagy receptor degradation. Modulating LIR binding specificity of the centriolar satellite protein PCM1, implicated in autophagy and centrosomal function, alters its dynamics in cells. Our data provides new mechanistic insight into how selective binding of LIR motifs to GABARAPs is achieved, and elucidate the overlapping and distinct functions of ATG8 subfamily proteins.

Identification of galectin-3 as an autoantigen in patients with IgG4-related disease.

BACKGROUND: The antigenic trigger that drives expansion of circulating plasmablasts and CD4+ cytotoxic T cells in patients with IgG4-related disease (IgG4-RD) is presently unknown. OBJECTIVE: We sought to sequence immunoglobulin genes from single-cell clones of dominantly expanded plasmablasts and generate recombinant human mAbs to identify relevant antigens in patients with IgG4-RD by using mass spectrometry. METHODS: Paired heavy and light chain cDNAs from dominant plasmablast clones were expressed as mAbs and used to purify antigens by using immunoaffinity chromatography. Affinity-purified antigens were identified by using mass spectrometry and validated by means of ELISA. Plasma levels of the antigen of interest were also determined by using ELISA. RESULTS: mAbs expressed from the 2 dominant plasmablast clones of a patient with multiorgan IgG4-RD stained human pancreatic tissue sections. Galectin-3 was identified as the antigen specifically recognized by both mAbs. Anti-galectin-3 autoantibody responses were predominantly of the IgG4 isotype (28% of the IgG4-RD cohort, P = .0001) and IgE isotype (11% of the IgG4-RD cohort, P = .009). No significant responses were seen from the IgG1, IgG2, or IgG3 isotypes. IgG4 anti-galectin-3 autoantibodies correlated with increased plasma galectin-3 levels (P = .001), lymphadenopathy (P = .04), total IgG level increase (P = .05), and IgG4 level increase (P = .03). CONCLUSION: Affinity chromatography using patient-derived mAbs identifies relevant autoantigens in patients with IgG4-RD. IgG4 galectin-3 autoantibodies are present in a subset of patients with IgG4-RD and correlate with galectin-3 plasma levels. The marked increases in levels of circulating IgG4 and IgE observed clinically are, at least in part, caused by the development of IgG4- and IgE-specific autoantibody responses.

The identification of autoantigens in mucous membrane pemphigoid using immortalized oral mucosal keratinocytes.

BACKGROUND: Mucous membrane pemphigoid (MMP) is a rare chronic autoimmune subepithelial blistering disorder, targeting multiple basement membrane zone (BMZ) proteins including collagen XVII (COL17). Circulating autoantibodies of MMP are often undetected due to their lower titers. The oral mucosa is a valuable substrate for the detection of autoantibodies in MMP patients. However, obtaining normal human oral mucosa is more difficult than obtaining normal human skin. We established immortalized normal human oral mucosal keratinocytes (OMKs) and performed immunoblotting using immortalized OMK lysate for detecting autoantigens in MMP. METHODS: Immortalized OMKs were generated from primary OMKs using E6/E7 proteins of HPV. We compared the protein expression levels of major BMZ proteins between primary OMKs and immortalized OMKs. We performed immunoblotting to detect autoantigens using cell lysates from immortalized OMKs in 30 MMP patients. RESULTS: There were no significant differences between primary OMKs and immortalized OMKs in terms of protein expression levels of the BMZ proteins, including COL17, laminin 332, integrin α6/ß4, collagen VII, and collagen IV. Cell lysates of immortalized OMKs effectively identified MMP autoantigens in 60% (18/30) of MMP sera. We found an interesting case of MMP whose autoantibodies preferentially reacted to the 120-kD protein that is an ectodomain of COL17. CONCLUSION: We demonstrated that a cell lysate of immortalized OMKs is a reliable substrate for the detection of MMP autoantigens. This newly developed immunoblotting analysis method promises to contribute to the diagnosis of MMP.

IC-Tagging methodology applied to the expression of viral glycoproteins and the difficult-to-express membrane-bound IGRP autoantigen.

We have previously developed a methodology to produce protein microspheres (MS) that can be loaded with proteins of interest in living cells through their C or N-terminal tagging with the so-called IC-Tag. The IC-Tagging method has many applications ranging from the production of immobilized enzymes for industrial use to the production of subunit vaccines due to its intrinsic adjuvancy. Here we show the adaptation of the IC-Tagging to work inside the endoplasmic reticulum and bacteria, allowing us to produce properly modified viral glycoproteins. Additionally, we were able to express the Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP), whose expression remained elusive to date possibly due to its toxicity when over-expressed. IGRP is an antigen of enormous pharmaceutical interest as it is specifically targeted during the autoimmune response taking place in both the Non-Obese Diabetic (NOD) mice and type 1 diabetes (T1D) patients leading to the destruction of insulin-producing beta cells.

Optimized upstream and downstream process conditions for the improved production of recombinant human asparaginase (rhASP) from Escherichia coli and its characterization.

The present work elucidates the production of recombinant human asparaginase (rhASP) under optimized fermentation and downstream processes in Escherichia coli. The maximum biomass yield of 6.7 g/L was achieved with fed-batch fermentation. The highest rhASP inclusion bodies recovery yield (91%) was achieved with the optimized lysis conditions. The 8.0 M urea at pH 8.5 has shown efficient solubilization (94%) of rhASP inclusion bodies. The refolding efficiency of rhASP increased at pH 8.5 (84%) and temperature 25°C (86%). The diluted rhASP solution was concentrated and partially purified (92%) using cross flow filtration. A single step ion exchange chromatography is successfully achieved the maximum purity of ≥ 97%. The molecular mass of purified rhASP is confirmed as 34.1 kDa by mass spectrometry. The secondary structure of rhASP is characterized by FT-IR spectroscopy based on the structural elements. Finally, cell proliferative assay of purified rhASP is signifies the similar biological activity over the standard.

Identification of hnRNP C1/C2 as an Autoantigen in Patients with Behcet's Disease.

BACKGROUND: Ribonucleoproteins particles that form the spliceosomes are among the most frequently targeted molecules of the autoimmune response. In the last few years, autoantibodies against all A/B hnRNP proteins have been found in the sera of patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), mixed connective tissue disease (MCTD), and serve as diagnostic markers for several rheumatic diseases. However, the functional role of hnRNP C1/C2 in autoimmune diseases is still not clearly understood. OBJECTIVE: To identify hnRNP C1/C2 as an autoantigen in patients with Behcet's Disease (BD). METHODS: First, HaCaT and EA.hy926 cells were cultured and RNA was extracted. Second, amplification of the corresponding gene by RT-PCR, cloning, and purification techniques was applied to acquire the recombinant protein hnRNP C1/C2. Third, the target protein band was excised from gel electrophoresis, digested with trypsin, and analyzed by (MALDI-TOF/). Finally, Western blotting and ELISA were performed to verify the immunoreactivity of BD serum with recombinant hnRNPC1/C2. RESULTS: Results demonstrated that the reactivity of BD serum against recombinant hnRNP C1/C2 protein was significantly higher as compared to healthy control (P<0.001). CONCLUSION: hnRNP C1/C2 can be considered as a self antigen which might be involved in BD pathology in Hans Chinese population.

Routinely used immunoassays do not detect circulating anti-GBM antibodies against native NC1 hexamer and EA epitope of the α3 chain of type IV collagen.

Detection of circulating anti-GBM antibodies has a key role for the diagnosis of Goodpasture syndrome but immunoassays using purified or recombinant alpha3(IV)NC1 as antigen do not recognize all anti-GBM antibodies. We show that anti-GBM antibodies directed against epitopes in their native conformation or cryptic epitopes are detected by indirect immunofluorescence.

Effect and mechanism of the aß2­GP I/rhß2­GP I complex on JEG­3 cell proliferation, migration and invasion.

Antiphospholipid antibody (aPL)­mediated antiphospholipid syndrome (APS) is an autoimmune disease. Upon binding to aPL, the primary antigen of aPL, ß2­glycoprotein I (ß2­GP I), induces abnormal immune function, which further activates downstream signaling pathways in the cell and eventually leads to APS. The present study aimed to determine whether ß2­GP I antigen and anti­ß2­glycoprotein I antibody (aß2­GP I), which belong to the aPL class of antibodies, may affect human chorionic epithelium cell (JEG­3) proliferation, migration and invasion. Recombinant human (rh)ß2­GP I protein was expressed using a prokaryotic expression system and aß2­GP I antibody was purified from the blood serum of 10 patients with recurrent pregnancy loss. JEG­3 cells were stimulated with rhß2­GP I and aß2­GP I separately or simultaneously, and serum immunoglobulin G of normal pregnant women was used as negative control. Using cell counting kit­8, cell cycle and transwell assays in addition to EdU staining, it was determined that aß2­GP I/rhß2­GP I complex markedly increased JEG­3 cell proliferation, migration and invasion. The results revealed that mRNA levels of inhibitor of nuclear factor (NF)­κB kinase subunit (IKKß), myeloid differentiation primary response protein MyD88 (MyD88), NF­κB and NF­κB inhibitor α (IκBα), as well as the protein levels of MyD88, IκBα and phospho(p)­IκBα in JEG­3 cells increased following incubation with the aß2­GP I/rhß2­GP I complex. The observed upregulation of p­IκBα protein suggested that IκBα­mediated inhibition of NF­κB was weakened. Furthermore, JEG­3 cells were transfected with PGMLV­NF­κB­Lu vector. Luciferase activity in JEG­3­NFκB­Luc1 and JEG­3­NFκB­Luc2 cells was enhanced following treatment with aß2­GP I/rhß2­GP I complex. The present study demonstrated that aß2­GP I/rhß2­GP I complex activates NF­κB through MyD88 signal transduction pathway, which further enhances JEG­3 cell proliferation, migration and invasion.

Purification of recombinant human thyroid peroxidase (hTPO) from AD293 mammalian cells.

Human thyroid peroxidase (hTPO) has been secretory expressed in AD293 mammalian cells. cDNA sequence of 'Gluc' (Gaussia luciferase) protein from Gaussia princeps was incorporated at the amino terminal of hTPO gene for secretion of targeted protein outside the mammalian cells. Augmentation of TPO clone in serum free mediums was investigated and a simplified purification procedure of hTPO has been reported here. Purified hTPO was further analyzed by SDS-PAGE and immunoblotting (western blotting). The relative molecular mass of hTPO was found to be 105kDa. This is the first report with respect to cost effective and simplified purification approach to get highest yield and purity of recombinant hTPO.

Identification of carbamylated alpha 1 anti-trypsin (A1AT) as an antigenic target of anti-CarP antibodies in patients with rheumatoid arthritis.

In 2011 a novel autoantibody system, anti-carbamylated protein (anti-CarP) antibodies, was described in rheumatoid arthritis (RA) patients. Anti-CarP antibody positivity associates with a more severe disease course, is observed years before disease onset, and may predict the development of RA in arthralgia patients. Although many clinical observations have been carried out, information on the antigenic targets of anti-CarP antibodies is limited. Most studies on anti-CarP antibodies utilize an ELISA-based assay with carbamylated fetal calf serum (Ca-FCS) as antigen, a complex mixture of proteins. Therefore, we analysed the molecular identity of proteins within Ca-FCS that are recognized by anti-CarP antibodies. Ca-FCS was fractionated using ion exchange chromatography, selecting one of the fractions for further investigation. Using mass-spectrometry, carbamylated alpha-1-antitrypsin (Ca-A1AT) was identified as a potential antigenic target of anti-CarP antibodies in RA patients. A1AT contains several lysines on the protein surface that can readily be carbamylated. A large proportion of the RA patients harbour antibodies that bind human Ca-A1AT in ELISA, indicating that Ca-A1AT is indeed an autoantigen for anti-CarP antibodies. Next to the Ca-A1AT protein, several homocitrulline-containing peptides of A1AT were recognized by RA sera. Moreover, we identified a carbamylated peptide of A1AT in the synovial fluid of an RA patient using mass spectrometry. We conclude that Ca-A1AT is not only a target of anti-CarP antibodies but is also present in the synovial compartment, suggesting that Ca-A1AT recognized by anti-CarP antibodies in the joint may contribute to synovial inflammation in anti-CarP-positive RA.

Splicing factor proline/glutamine-rich is a novel autoantigen of dermatomyositis and associated with anti-melanoma differentiation-associated gene 5 antibody.

OBJECTIVE: Anti-MDA5 antibody positive dermatomyositis (DM) and clinically amyopathic DM (CADM) often develop into rapidly progressive interstitial lung disease, but their pathogenesis remains unclear. We observed that sera from DM/CADM patients immunoprecipitated a common 110 kDa polypeptide. We investigated this autoantigen and its clinical significance. METHODS: Autoantibodies were screened in 333 patients with various connective tissue diseases (CTDs) and 20 healthy controls (HCs) by immunoprecipitation with [35S]methionine-labeled HeLa cells. Immunoabsorbent column chromatography was used to purify the reactive autoantigen which was subsequently analyzed by peptide mass fingerprinting. RESULTS: Anti-110 kDa antibody was detected in sera from 27 DM/CADM patients, but not in sera from other CTD patients or HCs. All patients with anti-110 kDa antibody had anti-MDA5 antibody. The maximum KL-6 levels in anti-110 kDa antibody-positive patients were higher than in anti-110 kDa antibody-negative patients, and all anti-MDA5-antibody-positive patients who showed the recurrence of DM/CADM were anti-110 kDa antibody-positive. The corresponding autoantigen was identified as splicing factor proline/glutamine-rich protein (SFPQ). In some cases, anti-SFPQ antibody was detected at diagnosis (early-detected group), but in other cases, it appeared during the disease course (delayed-detected group). The diagnosis timing of DM/CADM showed seasonal patterns according to the timing of anti-SFPQ antibody appearance. Specifically, 77% (10/13) of patients were diagnosed between August and October in the early-detected group, while 57% (8/14) of patients were diagnosed between January and March in the delayed-detected group. CONCLUSIONS: Some anti-MDA5 antibody-positive patients had an antibody to SFPQ, which is known to play a role in innate immune responses. Anti-SFPQ antibody may be involved in the chronic disease course of DM/CADM. The diagnosis timing of DM/CADM in anti-MDA5 antibody-positive patients showed seasonal patterns according to the timing of anti-SFPQ antibody appearance. These findings may provide new insights into the pathogenesis of DM/CADM.

The progress and potential of proteomic biomarkers for type 1 diabetes in children.

INTRODUCTION: Although it is possible to identify the genetic risk for type 1 diabetes (T1D), it is not possible to predict who will develop the disease. New biomarkers are needed that would help understand the mechanisms of disease onset and when to administer targeted therapies and interventions. Areas covered: An overview is presented of international study efforts towards understanding the cause of T1D, including the collection of several extensive temporal sample series that follow the development of T1D in at risk children. The results of the proteomics analysis of these materials are presented, which have included bodily fluids, such as serum or plasma and urine, as well as tissue samples from the pancreas. Expert commentary: Promising recent reports have indicated detection of early proteomic changes in the serum of patients prior to diagnosis, potentially providing new measures for risk assessment. Similarly, there has been evidence that post-translational modification (PTM) may result in the recognition of islet cell proteins as autoantigens; modified proteins could thus be used as targets for immunomodulation to overcome the threat of the autoimmune response.

Immunoblotting Using Radiolabeled Reagents for Detection.

Development of immunoblots is commonly performed using enzyme-labeled antibodies which convert soluble substrates into insoluble colored products. A simple, rapid, and sensitive alternative method which produces low background and allows a rapid quantitative evaluation is the use of radiolabeled antibodies or protein A conjugates. Here we describe the use of iodinated secondary antibodies for immunodetection of an autoantigen during HPLC purification.

Strip immunoblotting of multiple antigenic peptides.

Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis can be employed to efficiently separate multiple antigenic peptides (MAPs). Moreover, the electrophoresed MAPs are amenable for transfer to nitrocellulose membrane for immunoblotting. MAPs involve a hepta lysine core with end groups for anchoring multiple copies of the same synthetic peptide. MAPs are amenable to staining with Coomassie and silver on SDS polyacrylamide gels as well as by Fast Green on a blotted nitrocellulose membrane. They lend themselves to analysis on an immunoblot as they behave like low molecular weight proteins. Affinity immunoblotting for analysis of antibody clonotype distribution has also been carried out using these peptides.