Target Of Autoantibodies Research Articles

Novel autoantibody targets identified in patients with autoimmune hepatitis (AIH) by PhIP-Seq reveals pathogenic insights.

Autoimmune hepatitis (AIH) is a severe disease characterized by elevated immunoglobin levels. However, the role of autoantibodies in the pathophysiology of AIH remains uncertain. Phage Immunoprecipitation-Sequencing (PhIP-seq) was employed to identify autoantibodies in the serum of patients with AIH (n = 115), compared to patients with other liver diseases (metabolic associated steatotic liver disease (MASH) n = 178, primary biliary cholangitis (PBC), n = 26, or healthy controls, n = 94). Logistic regression using PhIP-seq enriched peptides as inputs yielded a classification AUC of 0.81, indicating the presence of a predictive humoral immune signature for AIH. Embedded within this signature were disease relevant targets, including SLA/LP, the target of a well-recognized autoantibody in AIH, disco interacting protein 2 homolog A (DIP2A), and the relaxin family peptide receptor 1 (RXFP1). The autoreactive fragment of DIP2A was a 9-amino acid stretch nearly identical to the U27 protein of human herpes virus 6 (HHV-6). Fine mapping of this epitope suggests the HHV-6 U27 sequence is preferentially enriched relative to the corresponding DIP2A sequence. Antibodies against RXFP1, a receptor involved in anti-fibrotic signaling, were also highly specific to AIH. The enriched peptides are within a motif adjacent to the receptor binding domain, required for signaling and serum from AIH patients positive for anti-RFXP1 antibody was able to significantly inhibit relaxin-2 singling. Depletion of IgG from anti-RXFP1 positive serum abrogated this effect. These data provide evidence for a novel serological profile in AIH, including a possible functional role for anti-RXFP1, and antibodies that cross react with HHV6 U27 protein.

Identification of DAGLA as an autoantibody target in cerebellar ataxia

BackgroundWe aimed to investigate the clinical, imaging and fluid biomarker characteristics in patients with antidiacylglycerol lipase alpha (DAGLA)-autoantibody-associated cerebellitis.MethodsSerum and cerebrospinal fliud (CSF) samples from four index patients were subjected...

Autoantibodies Targeting Proteasome Subunit Alpha Type 1 in Autoimmune Podocytopathies.

The antibody against proteasome subunit alpha type 1 (PSMA1) is a podocyte autoantibody in idiopathic nephrotic syndrome (INS) children identified in our previous study. The aim of this study was to explore the characteristics of INS in children and the mechanism underlying its involvement in the development of INS. The levels of serum anti-PSMA1 autoantibodies in children were detected via protein microarray and compared among different disease groups. The recombinant PSMA1 protein was injected subcutaneously and intraperitoneally into mice to observe glomerular morphology and function. The PSMA1-knockdown and PSMA1-overexpressing cell lines were constructed from mouse podocytes, and their cytoskeleton and function were analyzed. Homozygous zebrafish with psma1 knockout were observed. The levels of serum anti-PSMA1 autoantibodies were higher in INS children and varied with urinary protein. In mice immunized with PSMA1, the presence of serum anti-PSMA1 autoantibody caused albuminuria and damage to the glomerular filtration membrane. Deficiency of PSMA1 impaired the podocyte cytoskeleton and physiological function. Complete deletion of psma1 caused edema, abnormal glomerular morphology and effacement of foot processes in zebrafish. PSMA1 played an important role in the maintenance of podocyte morphology and function.

B-104 Correlation of Anti-Centromere Antibodies (ACA) Detection by Indirect Immunofluorescence (IFA) on HEp-2 Cells and by ELISA Demonstrates High Concordance but Highlights Advantage of IFA

Abstract Background Anti-centromere antibodies (ACA), a type of anti-nuclear antibody (ANA) first identified as a discrete speckled pattern on indirect immunofluorescence assay (IFA), are a hallmark of systemic sclerosis (SSc), especially in its limited cutaneous form (lcSSc) or CREST (calcinosis, Raynaud’s, esophageal dysmotility, sclerodactyly and telangiectasia). These mitosis-related autoantibodies mainly recognize three centromere proteins (CENP), CENP-A, CENP-B, and CENP-C, that comprise the kinetochore important to chromosome segregation, but more recently, at least three other CENP antigens have been identified (CENP-D, CENP-E and CENP-F). Anti-CENP-B is considered the main autoantibody, and many, if not most, ELISA utilize recombinant CENP-B such that antibodies to CENP antigens other than CENP-B are not detected. Here, an ELISA using both CENP-B and CENP-A is compared to the reference method, HEp-2 cell IFA, highlighting its high, but still less than 100%, sensitivity due to multiple centromere subcomponents. Methods Anti-centromere antibodies are determined in patient serum using the reference method, IFA on the HEp-2 cell substrate (Sprinter XL/EUROpattern®, Euroimmun, NJ) which is also the current method for standalone ACA testing as well as screening by selected ANA profiles designed for the rheumatology specialist. Here ACA IFA- positive and negative serum samples were further analyzed by enzyme immunosorbent assay (ELISA) utilizing recombinant CENP-A and CENP-B (QuantaLyzer® 3000, Werfen, CA). Results When compared, samples between ACA pattern by HEp-2 cell IFA and anti- centromere antibodies by ELISA yielded an agreement of 93.2%. McNemar’s Test Chi Square of p>0.999, with a relative sensitivity of 89.7% and a specificity of 100.0%. Conclusions This study demonstrated very high concordance between ELISA and accurate ACA pattern identification on HEp-2 IFA. The ELISA studied here identifies autoantibodies to both CENP-A and CENP-B where many other ELISA identify only anti-CENP-B. Although ACA are relatively specific for SSc, they have also been reported in systemic lupus erythematosus (SLE), primary biliary cholangitis (PBC), rheumatoid arthritis (RA), Sjogren Syndrome, Raynaud's phenomenon and in cancer in individuals with or without evidence of systemic autoimmune rheumatic disease (SARD). Of note, many other commercially available ELISA for anti-centromere antibodies identify only anti-CENP-B, but there at least four other known CENP antigen targets for autoantibodies causing centromere pattern on IFA. Furthermore, almost all laboratories use the ELISA for ACA on ANA panel (or other connective tissue disease) screening. Hence, it should be duly noted that these testing strategies will not detect autoantibodies to all anti-centromere antibodies. Only specialized ANA profiles designed for the difficult-to-diagnose autoimmune patient begin screening using the IFA method for anti-centromere and therefore, are capable of detecting autoantibodies to all CENP antigens. Laboratorians should advise clinicians of these diagnostic limitations especially as our knowledge about centromere subcomponents and their clinical associations increases.

Perlecan Is a Novel Target of Autoantibodies in Anti-glomerular Basement Membrane Disease

Perlecan Is a Novel Target of Autoantibodies in Anti-glomerular Basement Membrane Disease

Autoantibodies to ADAMTS13 in human immunodeficiency virus-associated thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a potentially fatal thrombotic microangiopathic disorder that can result from human immunodeficiency virus (HIV) infection. The pathogenesis involves a deficiency of the von Willebrand factor (vWF) cleaving protease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin motifs member 13) and the presence of anti-ADAMTS13 autoantibodies. However, there is insufficient information regarding the epitope specificity and reactivity of these autoantibodies. This study aimed to perform epitope-mapping analysis to provide novel insights into the specific epitopes on ADAMTS13 domains affected by autoantibodies. The study analysed 59 frozen citrate plasma samples from HIV-associated TTP patients in South Africa, measuring ADAMTS13 activity using Technozyme® ADAMTS13 activity test, total immunoglobulin (Ig) M and IgA antibodies levels using ELISA kit and purifying IgG antibodies using NAb™ Protein G spin columns. A synthetic ADAMTS13 peptide library was used for epitope mapping. Overall, 90% of samples showed anti-ADAMTS13 IgG autoantibodies, with 64% of these antibodies being inhibitory, as revealed by mixing studies. Samples with ADAMTS13 antigen levels below 5% showed high anti-ADAMTS13 IgG autoantibody titres (≥50 IU/mL), whereas those with 5%-10% levels had low autoantibody titres (<50 IU/mL).The metalloprotease, cysteine-rich and spacer domains were 100% involved in binding anti-ADAMTS13 IgG antibodies, with 58% of samples containing antibodies binding to the C-terminal part of the ADAMTS13 disintegrin-like domain, indicating different pathogenic mechanisms. The metalloprotease, cysteine-rich and spacer domains are the primary targets for anti-ADAMTS13 IgG autoantibodies in patients with HIV-associated TTP. These findings suggest potential effects on the proteolytic activity of ADAMTS13, highlighting the complex nature of the pathogenic mechanisms involved.

Pemphigus vulgaris autoantibodies induce an ER stress response.

Desmosomes are intercellular junctions that mediate cell-cell adhesion and are essential for maintaining tissue integrity. Pemphigus vulgaris (PV) is an autoimmune epidermal blistering disease caused by autoantibodies (IgG) targeting desmoglein 3 (Dsg3), a desmosomal cadherin. PV autoantibodies cause desmosome disassembly and loss of cell-cell adhesion, but the molecular signaling pathways that regulate these processes are not fully understood. Using high-resolution time-lapse imaging of live keratinocytes, we found that ER tubules make frequent and persistent contacts with internalizing Dsg3 puncta in keratinocytes treated with PV patient IgG. Biochemical experiments demonstrated that PV IgG activated ER stress signaling pathways, including both IRE1⍺ and PERK pathways, in cultured keratinocytes. Further, ER stress transcripts were upregulated in PV patient skin. Pharmacological inhibition of ER stress protected against PV IgG-induced desmosome disruption and loss of keratinocyte cell-cell adhesion, suggesting that ER stress may be an important pathomechanism and therapeutically targetable pathway for PV treatment. These data support a model in which desmosome adhesion is integrated with ER function to serve as a cell adhesion stress sensor that is activated in blistering skin disease.

Roles of TRIM21/Ro52 in connective tissue disease-associated interstitial lung diseases.

Multiple factors contribute to the development of connective tissue diseases (CTD), often alongside a range of interstitial lung diseases (ILD), including Sjögren's syndrome-associated ILD, systemic sclerosis-associated ILD, systemic lupus erythematosus-associated ILD, idiopathic inflammatory myositis-associated ILD. TRIM21(or Ro52), an E3 ubiquitin ligase, plays a vital role in managing innate and adaptive immunity, and maintaining cellular homeostasis, and is a focal target for autoantibodies in various rheumatic autoimmune diseases. However, the effectiveness of anti-TRIM21 antibodies in diagnosing CTD remains a matter of debate because of their non-specific nature. Recent studies indicate that TRIM21 and its autoantibody are involved in the pathogenesis of CTD-ILD and play an important role in diagnosis and prognosis. In this review, we focus on the contribution of TRIM21 in the pathogenesis of CTD-ILD, as well as the potential diagnostic value of its autoantibodies in different types of CTD-ILD for disease progression and potential as a novel therapeutic target.

Abstract We110: Novel allosteric ligand designed to prevent Autoantibody targeting the Angiotensin Type 1 Receptor (AT1R) in cardiovascular diseases (CVD)

Background: The clinical data suggest an association of autoantibodies (AAb) targeting angiotensin II type1 receptor (AT1R) and outcomes in heart failure (HF) and preeclampsia. Notably, patient’s risk increases 2 to 4-fold for heart diseases and hypertension. Although AT1R blockers (ARBs) have emerged as a key component in the therapeutic arsenal against CVD, we believe that rather than completely blocking AT1R signaling, maintaining a balanced signaling is crucial for cardiovascular homeostasis. Therefore, we posit that reducing AT1R overactivation and blocking AAb-mediated activation could benefit cardiac health and attenuate the progression of CVD. In our previous study (PMID:36440576), we identified small molecules capable of inhibiting AAb-induced AT1R signaling. Leveraging these observations, we have developed a novel AT1R allosteric ligand that inhibits autoantibody binding to AT1R while still retaining normal AT1R signaling. Methods: Using computational and medicinal chemistry approaches, we designed a series of novel AT1R ligands and obtained compounds with &gt;98% purity through chemical synthesis. Monoclonal antibodies mimicking AT1R-AAb have been generated. Serum samples from dilated cardiomyopathy (DCM) and preeclampsia (PE) patient cohorts were collected and presence of AT1R-AAb was determined using ELISA and epitope-peptide competition studies. Pharmacological characterization of compounds was performed using calcium mobilization, 125I -AngII binding, ex vivo vasoconstriction, and ELISA assays. Results: We identified an AT1R allosteric compound that reduced AngII-mediated calcium signaling with a 5-fold shift in EC 50 . The IC 50 was determined to be 18 µM. It reduces the AngII-mediated vasoconstriction while blocking both monoclonal and patient-derived autoantibody binding with an IC 50 of 5 µM. Conclusion: We have identified a novel AT1R allosteric ligand with negative allosteric modulator (NAM) properties, which has the potential to block autoantibodies and could serve as a new generation of ARBs. Uniquely, it retains beneficial AT1R signaling without competing with AngII, and its allosteric ligand property can be tailored to achieve optimal AT1R signaling.

Brain-targeting autoantibodies in patients with dementia.

Autoantibodies against proteins in the brain are increasingly considered as a potential cause of cognitive decline, not only in subacute autoimmune encephalopathies but also in slowly progressing impairment of memory in patients with classical neurodegenerative dementias. In this retrospective cohort study of 161 well-characterized patients with different forms of dementia and 34 controls, we determined the prevalence of immunoglobulin (Ig) G and IgA autoantibodies to brain proteins using unbiased immunofluorescence staining of unfixed murine brain sections. Autoantibodies were detected in 21.1% of dementia patients and in 2.9% of gender-matched controls, with higher frequencies in vascular dementia (42%), Alzheimer's disease (30%), dementia of unknown cause (25%), and subjective cognitive impairment (16.7%). Underlying antigens involved glial fibrillary acidic protein (GFAP), glycine receptor, and Rho GTPase activating protein 26 (ARHGAP26), but also a range of yet undetermined epitopes on neurons, myelinated fiber tracts, choroid plexus, glial cells, and blood vessels. Antibody-positive patients were younger than antibody-negative patients but did not differ in the extent of cognitive impairment, epidemiological and clinical factors, or comorbidities. Further research is needed to understand the potential contribution to disease progression and symptomatology, and to determine the antigenic targets of dementia-associated autoantibodies.

Reactivity against the BP180 ectodomain in patients with bullous pemphigoid, mucous membrane pemphigoid, multiple sclerosis and Parkinson disease

AbstractThe 16th non‐collagenous domain (NC16A) of BP180 is the main antigenic target of autoantibodies in bullous pemphigoid (BP) and mucous membrane pemphigoid (MMP). Commercially available assays detect serum autoantibodies against NC16A in the majority of BP (80%–90%) and in approximately 50% of MMP patients. However, a standardized test system for detecting antibodies against other regions of BP180 is still lacking. Moreover, anti‐BP180 autoantibodies have been found in neurological conditions such as multiple sclerosis and Parkinson disease. This study aimed at identifying primary epitopes recognized by BP autoantibodies on the BP180 ectodomain. Serum samples of 51 BP and 30 MMP patients both without anti‐NC16A reactivity were included along with 44 multiple sclerosis and 75 Parkinson disease sera. Four overlapping His‐tagged proteins covering the entire BP180 ectodomain (BP180(ec)1–4) were cloned, expressed, purified and tested for reactivity by immunoblot. IgG antibodies to BP180(ec)3 were detected in 98% of BP, 77% of MMP and 2% of normal human sera. Only weak reactivity was detected for neurological diseases against BP180(ec)1, BP180(ec)2 and BP180(ec)4, in 3%, 11% and 7% of tested multiple sclerosis sera, respectively. 8% of Parkinson disease sera reacted with BP180(ec)2 and 9% with BP180(ec)4. In conclusion, this study successfully identified epitopes recognized by BP autoantibodies outside the NC16A domain in pemphigoid diseases. These findings contribute to a better understanding of the immune response in BP and MMP with potential implications for a future diagnostic assay for NC16A‐negative pemphigoid patients.

Inflammatory Bowel Disease: A Comprehensive Analysis of Molecular Bases, Predictive Biomarkers, Diagnostic Methods, and Therapeutic Options.

In inflammatory bowel diseases (IBDs), such as Crohn's disease (CD) and ulcerative colitis (UC), the immune system relentlessly attacks intestinal cells, causing recurrent tissue damage over the lifetime of patients. The etiology of IBD is complex and multifactorial, involving environmental, microbiota, genetic, and immunological factors that alter the molecular basis of the organism. Among these, the microbiota and immune cells play pivotal roles; the microbiota generates antigens recognized by immune cells and antibodies, while autoantibodies target and attack the intestinal membrane, exacerbating inflammation and tissue damage. Given the altered molecular framework, the analysis of multiple molecular biomarkers in patients proves exceedingly valuable for diagnosing and prognosing IBD, including markers like C reactive protein and fecal calprotectin. Upon detection and classification of patients, specific treatments are administered, ranging from conventional drugs to new biological therapies, such as antibodies to neutralize inflammatory molecules like tumor necrosis factor (TNF) and integrin. This review delves into the molecular basis and targets, biomarkers, treatment options, monitoring techniques, and, ultimately, current challenges in IBD management.

The role of antibodies in small fiber neuropathy: a review of currently available evidence.

Small fiber neuropathy (SFN) is a peripheral nerve condition affecting thin myelinated Aδ and unmyelinated C-fibers, characterized by severe neuropathic pain and other sensory and autonomic symptoms. A variety of medical disorders can cause SFN; however, more than 50% of cases are idiopathic (iSFN). Some investigations suggest an autoimmune etiology, backed by evidence of the efficacy of IVIG and plasma exchange. Several studies suggest that autoantibodies directed against nervous system antigens may play a role in the development of neuropathic pain. For instance, patients with CASPR2 and LGI1 antibodies often complain of pain, and invitro and invivo studies support their pathogenicity. Other antibodies have been associated with SFN, including those against TS-HDS, FGFR3, and Plexin-D1, and new potential targets have been proposed. Finally, a few studies reported the onset of SFN after COVID-19 infection and vaccination, investigating the presence of potential antibody targets. Despite these overall findings, the pathogenic role has been demonstrated only for some autoantibodies, and the association with specific clinical phenotypes or response to immunotherapy remains to be clarified. The purpose of this review is to summarise known autoantibody targets involved in neuropathic pain, putative attractive autoantibody targets in iSFN patients, their potential as biomarkers of response to immunotherapy and their role in the development of iSFN.

Autoantibodies Targeting Nephrin in Podocytopathies

BackgroundMinimal change disease and primary focal segmental glomerulosclerosis in adults, along with idiopathic nephrotic syndrome in children, are immune-mediated podocytopathies that lead to nephrotic syndrome. Autoantibodies targeting nephrin have been found in patients with minimal change disease, but their clinical and pathophysiological roles are unclear.MethodsWe conducted a multicenter study to analyze antinephrin autoantibodies in adults with glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, antineutrophil cytoplasmic antibody–associated glomerulonephritis, and lupus nephritis, as well as in children with idiopathic nephrotic syndrome and in controls. We also created an experimental mouse model through active immunization with recombinant murine nephrin.ResultsThe study included 539 patients (357 adults and 182 children) and 117 controls. Among the adults, antinephrin autoantibodies were found in 46 of the 105 patients (44%) with minimal change disease, 7 of 74 (9%) with primary focal segmental glomerulosclerosis, and only in rare cases among the patients with other conditions. Of the 182 children with idiopathic nephrotic syndrome, 94 (52%) had detectable antinephrin autoantibodies. In the subgroup of patients with active minimal change disease or idiopathic nephrotic syndrome who were not receiving immunosuppressive treatment, the prevalence of antinephrin autoantibodies was as high as 69% and 90%, respectively. At study inclusion and during follow-up, antinephrin autoantibody levels were correlated with disease activity. Experimental immunization induced a nephrotic syndrome, a minimal change disease–like phenotype, IgG localization to the podocyte slit diaphragm, nephrin phosphorylation, and severe cytoskeletal changes in mice.ConclusionsIn this study, circulating antinephrin autoantibodies were common in patients with minimal change disease or idiopathic nephrotic syndrome and appeared to be markers of disease activity. Their binding at the slit diaphragm induced podocyte dysfunction and nephrotic syndrome, which highlights their pathophysiological significance. (Funded by Deutsche Forschungsgemeinschaft and others.)

Genetics and Epigenetics in Acquired Hemophilia A: From Bench to Bedside.

Acquired hemophilia A (AHA) is a bleeding disorder characterized by the immunological inhibition of factor VIII (FVIII) of the hemostatic pathway leading to hemorrhagic events. Different domains of FVIII are the target of autoantibodies (mainly immunoglobulin (Ig) G) leading to the deficiency of FVIII. Several factors have been associated with the activation of the auto-immunity towards FVIII. Emerging evidence implicates CD4+ T cell activation in mediating this autoimmune response, with their involvement like that observed in congenital hemophilia A. Several genes such as HLA II DRB*16, DQB1*0502, and CTLA-4 + 49 are responsible for the pathogenesis of AHA. Epigenetic modifications and mainly long-coding RNAS (lncRNAs) are potentially contributing to the pathogenesis of AHA. The treatment approach of AHA includes the management of acute bleeding events and the administration of immunosuppressive medications. This review aimed to summarize the published data on the genetics and epigenetics of AHA. The severity and the mortality of this disease are creating an emerging need for further research in the field of the genetics and epigenetics of acquired hemorrhagic disorder.

#2553 Circulating anti-slit diaphragm NEPHRIN and KIRREL-2 antibodies associate with nephrotic syndrome

Abstract Background and Aims Pathogenesis of Idiopathic Nephrotic Syndrome (INS) is still largely unknown. Recently, circulating anti-NEPHRIN antibodies have been proposed as responsible of disarrangement of the slit diaphragm architecture upon glomerular deposition. However, previous experience referred to limited cases and controls with different ELISA assays for antibodies detection. We compared the performance of three different ELISA assays quantifying circulating anti-NEPHRIN antibodies and we developed ELISA assays to quantify circulating antibodies against two proteins homologous of NEPHRIN, the KIRREL.1 and KIRREL-2. Method We compared the performance of three different ELISA assays, two against the extracellular (aa 1-1055NEPHRIN-A and aa 23-1029 NEPHRIN-B) and one against the intracytoplasmic (aa 1160-1241 NEPHRIN-C) domain of NEPHRIN. We tested a large cohort of 166 patients (396 serum samples) with INS, 32 focal segmental glomerulosclerosis kidney transplant recipients, 143 healthy controls and 40 lupus nephritis and membranous nephropathy, respectively. Furthermore, to investigate sensitivity and specificity of circulating anti-NEPHRIN antibodies, we developed ELISA assays to quantify circulating antibodies against two proteins homologous of NEPHRIN, the KIRREL-1 and KIRREL-2. We tested NEPHRIN and KIRREL-2 gene expression among glomeruli in kidney biopsies from 4 FSGS patient and 4 controls. Results Serum levels of anti-NEPHRIN antibodies against the two extracellular domains were highly correlated, but differed significantly to the levels detected using the intracytoplasmic domain of NEPHRIN. Neither the circulating anti-NEPHRIN targeting the extracellular nor the intracellular domains of the protein could differentiate INS patients overall from healthy controls (Fig. 1A). However, after age stratification, we found that circulating anti-NEPHRIN antibodies against the extracellular domain were significatively higher in INS than in healthy controls &amp;gt;6 years old (Fig. 1B).Circulating anti-NEPHRIN antibodies against extracellular domain appeared more specific for INS than anti-NEPHRIN antibodies against cytoplasmic domain. Circulating anti-NEPHRIN antibodies did not correlate with disease activity nor FSGS recurrence after kidney transplant (Fig. 1C). Of note, circulating anti-KIRREL-2 antibodies could differentiate INS and healthy controls more effectively than anti-NEPHRIN antibodies (Fig. 1D). We than confirmed that KIRREL-2 is transcript in glomeruli (Fig. 1E) and, in line with circulating anti-KIRREL-2 antibodies, spatial transcriptomic analyses showed that KIRREL-2 is increased in FSGS than in controls. Conclusion In a large cohort of patients, we showed that circulating anti-NEPHRIN antibodies are positive in a subset of INS and FSGS recurrence. However, they are not associated with disease activity and the circulating levels appeared as age related. Circulating anti-KIRREL-2 antibodies are more strongly associated with INS. Therefore, based on our findings, several podocyte antigens may be supposed target for specific autoantibodies in INS.

CD72 is an inhibitory pattern recognition receptor that recognizes ribosomes and suppresses production of anti-ribosome autoantibody

B cell responses to nucleic acid-containing self-antigens that involve intracellular nucleic acid sensors play a crucial role in autoantibody production in SLE. CD72 is an inhibitory B cell co-receptor that down-regulates BCR signaling, and prevents the development of SLE. We previously showed that CD72 recognizes the RNA-containing self-antigen Sm/RNP, a target of SLE-specific autoantibodies, and induces B cell tolerance to Sm/RNP by specifically inhibiting B cell response to this self-antigen. Here, we address whether CD72 inhibits B cell response to ribosomes because the ribosome is an RNA-containing self-antigen and is a target of SLE-specific autoantibodies as well as Sm/RNP. We demonstrate that CD72 recognizes ribosomes as a ligand, and specifically inhibits BCR signaling induced by ribosomes. Although conventional protein antigens by themselves do not induce proliferation of specific B cells, ribosomes induce proliferation of B cells reactive to ribosomes in a manner dependent on RNA. This proliferative response is down-regulated by CD72. These results suggest that ribosomes activate B cells by inducing dual signaling through BCR and intracellular RNA sensors and that CD72 inhibits B cell response to ribosomes. Moreover, CD72−/− but not CD72+/+ mice spontaneously produce anti-ribosome autoantibodies. Taken together, CD72 induces B cell self-tolerance to ribosomes by recognizing ribosomes and inhibiting RNA-dependent B cell response to this self-antigen. CD72 appears to prevent development of SLE by inhibiting autoimmune B cell responses to multiple RNA-containing self-antigens. Because these self-antigens but not protein self-antigens induce RNA-dependent B cell activation, self-tolerance to RNA-containing self-antigens may require a distinct tolerance mechanism mediated by CD72.

The common variable immunodeficiency IgM repertoire narrowly recognizes erythrocyte and platelet glycans

BackgroundAutoantibody-mediated cytopenias (AICs) regularly occur in profoundly IgG-deficient common variable immunodeficiency (CVID) patients. The isotypes, antigenic targets, and origin(s) of their disease-causing autoantibodies are unclear. ObjectiveTo determine reactivity, clonality and provenance of AIC-associated IgM autoantibodies in CVID patients. MethodsWe utilized glycan arrays, patient erythrocytes, and platelets to determine targets of CVID IgM autoantibodies. Glycan binding profiles were used to identify auto-reactive clones across B cell subsets, specifically circulating marginal zone-like (MZ) B cells, for sorting and IGH sequencing. The locations, transcriptomes and responses of tonsillar MZ B cells to different T helper cell subsets were determined by confocal microscopy, RNA-sequencing, and co-cultures, respectively. ResultsAutoreactive IgM coated erythrocytes and platelets from many CVID patients with AICs (CVID+AIC). On glycan arrays, CVID+AIC plasma IgM narrowly recognized erythrocytic i antigens and platelet i-related antigens and failed to bind hundreds of pathogen- and tumor-associated carbohydrates. Polyclonal i antigen-recognizing B-cell receptors were highly enriched among CVID+AIC circulating marginal zone (MZ) B cells. Within tonsillar tissues, MZ B cells secreted copious IgM when activated by the combination of IL-10 and IL-21 or when cultured with IL10/IL-21 secreting FOXP3-CD25hiTfh cells. In lymph nodes from immunocompetent controls, MZ B cells, plentiful FOXP3+ regulatory T cells, and rare FOXP3-CD25+ cells that represented likely CD25hiTfh cells, all localized outside of GCs. In CVID+AIC lymph nodes, cellular positions were similar but CD25hiTfh cells greatly outnumbered regulatory cells. ConclusionsOur findings indicate glycan-reactive IgM autoantibodies produced outside of GCs may contribute to the autoimmune pathogenesis of CVID.

Expression of Collagen XIII in Tissues of the Thyroid and Orbit With Relevance to Thyroid-Associated Ophthalmopathy.

Antibodies against collagen XIII have previously been identified in patients with active thyroid-associated ophthalmopathy (TAO). Although collagen XIII expression has been described in extraocular muscles and orbital fat, its detailed localization in extraocular and thyroid tissues and the connection to autoimmunity for collagen XIII remain unclear. Our objective was to map the potential targets for these antibodies in the tissues of the orbit and thyroid. We evaluated the expression of collagen XIII in human patient and mouse orbital and thyroid tissues with immunostainings and RT-qPCR using Col13a1-/- mice as negative controls. COL13A1 expression in Graves' disease and goiter thyroid samples was compared with TGF-β1 and TNF, and these were also studied in human thyroid epithelial cells and fibroblasts. Collagen XIII expression was found in the neuromuscular and myotendinous junctions of extraocular muscles, blood vessels of orbital connective tissue and fat and the thyroid, and in the thyroid epithelium. Thyroid expression was also seen in germinal centers in Graves' disease and in neoplastic epithelium. The expression of COL13A1 in goiter samples correlated with levels of TGF-B1. Upregulation of COL13A1 was reproduced in thyroid epithelial cells treated with TGF-β1. We mapped the expression of collagen XIII to various locations in the orbit, demonstrated its expression in the pathologies of the Graves' disease thyroid and confirmed the relationship between collagen XIII and TGF-β1. Altogether, these data add to our understanding of the targets of anti-collagen XIII autoantibodies in TAO.

Abstract 1033: Evaluation of autoantibodies to proteins encoded by cancer driver genes as biomarkers for prostate cancer

Abstract Prostate cancer (PCa) is a complex disease driven by genomic alterations, and understanding the immune response to these alterations can provide valuable insights into its pathogenesis. This study aimed at exploring the immunogenicity of proteins encoded by PCa driver genes and identifying corresponding autoantibodies as potential PCa biomarkers. Bioinformatics analysis, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry (IHC) were conducted in this study. A comprehensive screening process involving bioinformatics analysis and published studies identified a set of PCa driver genes for further investigation. Three strategies were employed to identify candidate driver genes: (1) utilizing the IntOGen database (Martínez-Jiménez et.al, Nature Reviews Cancer 2020), nine cohorts comprising 1503 primary PCa patient samples were analyzed, resulting in the identification of 63 PCa driver genes, with the top 20 genes exhibiting high mutation rates and frequencies in these cohorts; (2) employing the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, 16 driver genes that were enriched in prostate cancer pathways were identified from the initial 63 genes; (3) referring to a published article (Dietlein et.al, Nature Genetics 2020), the top 17 driver genes that highly related to prostate cancer across 28 tumor types were selected. A final set of 15 PCa driver genes, which appeared in at least two of the screening strategies, were included in subsequent analyses. ELISA was then performed to assess the presence of autoantibodies targeting proteins encoded by these 15 PCa driver genes. Autoantibodies were evaluated using serum samples from 203 PCa patients and 93 normal controls. The results revealed that seven out of the 15 autoantibodies showed significantly elevated levels in the sera of PCa patients compared to normal controls. Notably, the autoantibody targeting SPOP (speckled-type POZ protein) exhibited the highest frequency of 42.4%, followed by the autoantibody to PTEN (phosphatase and tensin homolog) at 37.4% in the PCa group. Finally, the SPOP protein was analyzed by IHC on the prostate tissue microarray containing PCa tissues, prostate simple hyperplasia tissues, cancer adjacent prostate tissues, and normal prostate tissues further to explore the consistency of SPOP expression in antigen-antibody reactions. High expression of SPOP protein was found in the PCa tissues. These findings suggest that proteins encoded by PCa driver genes may possess immunogenic properties due to neoepitopes possibly generated by mutations, leading to the production of corresponding autoantibodies. Identifying specific autoantibodies associated with PCa driver genes could offer novel opportunities for discovering autoantibody-based biomarkers in PCa. Further validation of these autoantibodies is warranted to evaluate their diagnostic potential in PCa. Citation Format: Cuipeng Qiu, Xiao Wang, Carlos A. Casiano, Jian-Ying Zhang. Evaluation of autoantibodies to proteins encoded by cancer driver genes as biomarkers for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1033.