RNA recognition motif (RRM) of La/SSB: the bridge for interparticle spreading of autoimmune response to U1-RNP

TLR7 activation of age-associated B cells mediates disease in a mouse model of primary Sjögren's disease

Primary Sjögren's disease (pSD) (also referred to as Sjögren's syndrome) is an autoimmune disease that primarily occurs in women. In addition to exocrine gland dysfunction, pSD patients exhibit B cell hyperactivity. B cell-intrinsic TLR7 activation is integral to the pathogenesis of systemic lupus erythematosus, a disease that shares similarities with pSD. The role of TLR7-mediated B cell activation in pSD, however, remains poorly understood. We hypothesized that age-associated B cells (ABCs) were expanded in pSD and that TLR7-stimulated ABCs exhibited pathogenic features characteristic of disease. Our data revealed that ABC expansion and TLR7 expression were enhanced in a pSD mouse model in a Myd88-dependent manner. Splenocytes from pSD mice showed enhanced sensitivity to TLR7 agonism as compared with those derived from control animals. Sort-purified marginal zone B cells and ABCs from pSD mice showed enhanced inflammatory cytokine secretion and were enriched for antinuclear autoantibodies following TLR7 agonism. Finally, IgG from pSD patient sera showed elevated antinuclear autoantibodies, many of which were secreted preferentially by TLR7-stimulated murine marginal zone B cells and ABCs. These data indicate that pSD B cells are hyperresponsive to TLR7 agonism and that TLR7-activated B cells contribute to pSD through cytokine and autoantibody production. Thus, therapeutics that target TLR7 signaling cascades in B cells may have utility in pSD patients.

CDetection.v2: One-pot assay for the detection of SARS-CoV-2

Introduction

The ongoing 2019 coronavirus disease pandemic (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and its variants, is a global public health threat. Early diagnosis and identification of SARS-CoV-2 and its variants plays a critical role in COVID-19 prevention and control. Currently, the most widely used technique to detect SARS-CoV-2 is quantitative reverse transcription real-time quantitative PCR (RT-qPCR), which takes nearly 1 hour and should be performed by experienced personnel to ensure the accuracy of results. Therefore, the development of a nucleic acid detection kit with higher sensitivity, faster detection and greater accuracy is important.

Methods

Here, we optimized the system components and reaction conditions of our previous detection approach by using RT-RAA and Cas12b.

Results

We developed a Cas12b-assisted one-pot detection platform (CDetection.v2) that allows rapid detection of SARS-CoV-2 in 30 minutes. This platform was able to detect up to 5,000 copies/ml of SARS-CoV-2 without cross-reactivity with other viruses. Moreover, the sensitivity of this CRISPR system was comparable to that of RT-qPCR when tested on 120 clinical samples.

Discussion

The CDetection.v2 provides a novel one-pot detection approach based on the integration of RT-RAA and CRISPR/Cas12b for detecting SARS-CoV-2 and screening of large-scale clinical samples, offering a more efficient strategy for detecting various types of viruses.

Systemic manifestations of primary Sjögren's syndrome in the NOD.B10Sn-H2b/J mouse model

Animal models that recapitulate human disease are crucial for the study of Sjögren's Syndrome (SS). While several SS mouse models exist, there are few primary SS (pSS) models that mimic systemic disease manifestations seen in humans. Similar to pSS patients, NOD.B10Sn-H2^b/J (NOD.B10) mice develop exocrine gland disease and anti-nuclear autoantibodies. However, the disease kinetics and spectrum of extra-glandular disease remain poorly characterized in this model. Our objective was to characterize local and systemic SS manifestations in depth in NOD.B10 female mice at early and late disease time points. To this end, sera, exocrine tissue, lung, and kidney were analyzed. NOD.B10 mice have robust lymphocytic infiltration of salivary and lacrimal tissue. In addition, they exhibit significant renal and pulmonary inflammation. We identified numerous autoantibodies, including those directed against salivary proteins. In conclusion, the NOD.B10 model recapitulates both local and systemic pSS disease and represents an excellent model for translational studies.

Impact of anti-peroxynitrite-damaged-thymidine-monophosphate antibodies on disease activity in patients with systemic lupus erythematosus

Present study probes the role of peroxynitrite (ONOO(-))-modified thymidine-5'-monophosphate (TMP) in SLE patients with different disease activity scores according to the SLE Disease Activity Index (SLEDAI). Serum analysis showed significant increased number of subjects positive for anti-ONOO(-)-TMP-protein antibodies in SLE patients with different SLEDAI scores. Interestingly, the levels of these antibodies were significantly higher among SLE patients, whose SLEDAI scores were ≥20. In addition, a significant correlation was observed between the levels of anti-ONOO(-)-TMP-protein antibodies and the SLEDAI score (r = 0.595, p < 0.0001). In short, this study shows a positive association between anti-ONOO(-)-TMP-protein antibodies and SLEDAI. The stronger response observed in patients with higher SLEDAI scores suggests that anti-ONOO(-)-TMP-protein antibodies may be useful in evaluating the progression of SLE and in elucidating the mechanisms of disease pathogenesis.

Toll-like receptor 3 stimulation promotes Ro52/TRIM21 synthesis and nuclear redistribution in salivary gland epithelial cells, partially via type I interferon pathway

Up-regulated expression of Ro52/tripartite motif-containing protein 21 (TRIM21), Ro60/TROVE domain family, member 2 (TROVE2) and lupus LA protein/Sjögren's syndrome antigen B (La/SSB) autoantigens has been described in the salivary gland epithelial cells (SGEC) of patients with Sjögren's syndrome (SS). SGECs, the key regulators of autoimmune SS responses, express high levels of surface functional Toll-like receptor (TLR)-3, whereas Ro52/TRIM21 negatively regulates TLR-3-mediated inflammation. Herein, we investigated the effect of TLR-3-signalling on the expression of Ro52/TRIM21, as well as Ro60/TROVE2 and La/SSB autoantigens, by SGECs. The effect of TLR-3 or TLR-4 stimulation on autoantigen expression was evaluated by polyI:C or lipopolysaccharide (LPS) treatment, respectively, of SGEC lines (10 from SS patients, 12 from non-SS controls) or HeLa cells, followed by analysis of mRNA and protein expression. PolyI:C, but not LPS, resulted in a two-step induction of Ro52/TRIM21 mRNA expression by SGECs, a 12-fold increment at 6 h followed by a 2.5-fold increment at 24-48 h, whereas it induced a late two-fold up-regulation of Ro60/TROVE2 and La/SSB mRNAs at 48 h. Although protein expression levels were not affected significantly, the late up-regulation of Ro52/TRIM21 mRNA was accompanied by protein redistribution, from nucleolar-like pattern to multiple coarse dots spanning throughout the nucleus. These late phenomena were mediated significantly by interferon (IFN)-β production, as attested by cognate secretion and specific inhibition experiments and associated with IFN regulatory factor (IRF)3 degradation. TLR-3-signalling had similar effects on SGECs obtained from SS patients and controls, whereas it did not affect the expression of these autoantigens in HeLa cells. TLR-3 signalling regulates the expression of autoantigens by SGECs, implicating innate immunity pathways in their over-expression in inflamed tissues and possibly in their exposure to the immune system.

B cell epitope spreading: mechanisms and contribution to autoimmune diseases

While a variety of factors act to trigger or initiate autoimmune diseases, the process of epitope spreading is an important contributor in their development. Epitope spreading is a diversification of the epitopes recognized by the immune system. This process happens to both T and B cells, with this review focusing on B cells. Such spreading can progress among multiple epitopes on a single antigen, or from one antigenic molecule to another. Systemic lupus erythematosus, multiple sclerosis, pemphigus, bullous pemphigoid and other autoimmune diseases, are all influenced by intermolecular and intramolecular B cell epitope spreading. Endocytic processing, antigen presentation, and somatic hypermutation act as molecular mechanisms that assist in driving epitope spreading and broadening the immune response in autoimmune diseases. The purpose of this review is to summarize our current understanding of B cell epitope spreading with regard to autoimmunity, how it contributes during the progression of various autoimmune diseases, and treatment options available.

Differential immunoglobulin class-mediated responses to components of the U1 small nuclear ribonucleoprotein particle in systemic lupus erythematosus and mixed connective tissue disease

OBJECTIVE

The objective of this paper is to determine whether patients with systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) possess differential IgM- and IgG-specific reactivity against peptides from the U1 small nuclear ribonucleoprotein particle (U1 snRNP).

METHODS

The IgM- and IgG-mediated responses against 15 peptides from subunits of the U1 snRNP were assessed by indirect enzyme linked immunosorbent assays (ELISAs) in sera from patients with SLE and MCTD and healthy individuals (n = 81, 41, and 31, respectively). Additionally, 42 laboratory tests and 40 clinical symptoms were evaluated to uncover potential differences. Binomial logistic regression analyses (BLR) were performed to construct models to support the independent nature of SLE and MCTD. Receiver operating characteristic (ROC) curves corroborated the classification power of the models.

RESULTS

We analyzed IgM and IgG anti-U1 snRNP titers to classify SLE and MCTD patients. IgG anti-U1 snRNP reactivity segregates SLE and MCTD from nondisease controls with an accuracy of 94.1% while IgM-specific anti-U1 snRNP responses distinguish SLE from MCTD patients with an accuracy of 71.3%. Comparison of the IgG and IgM anti-U1 snRNP approach with clinical tests used for diagnosing SLE and MCTD revealed that our method is the best classification tool of those analyzed (p ≤ 0.0001).

CONCLUSIONS

Our IgM anti-U1 snRNP system along with lab tests and symptoms provide additional molecular and clinical evidence to support the hypothesis that SLE and MCTD may be distinct syndromes.

A comprehensive review of autoantibodies in primary Sjögren's syndrome: clinical phenotypes and regulatory mechanisms

Sjögren's syndrome (SS) is a systemic autoimmune disease characterized by periepithelial lymphocytic infiltrates in affected tissues and the production of plethora of autoantibodies. Among them autoimmune responses against Ro/SSA and La/SSB are of major importance since their detection is routinely used for disease diagnosis and clinical characterization. Although the exact mechanisms underlying disease pathogenesis are not fully understood, the important role of salivary gland epithelial cells (SGEC) in the initiation and development of the local immune responses is well-established. SGECs are also capable to mediate the exposure of the Ro/SSA and La/SSB autoantigens to the immune system by elevated apoptosis and autoantigen release in apoptotic bodies and/or by the secretion of autoantigen-containing exosomes. The expression of these autoantigens in epithelial cells appears to be tightly regulated. Up-to-date, signaling of certain innate immunity receptors, such as TLR3, appear to be implicated in the regulation of Ro/SSA and La/SSB expression by SGECs, whereas the deregulated expression of certain miRNAs that are predicted to target them in SS patients suggests a regulatory feedback at the post-transcriptional level. In the periphery, the humoral autoimmune responses are further regulated by the development of an active network of idiotypic-antiidiotypic antibodies. The plethora of mechanisms suggests that autoimmune humoral responses in SS are tightly regulated. In this review, the major humoral autoimmune responses, recent advances on the role of epithelial cells in their development, as well as possible regulatory mechanisms will be discussed.

Fine specificity of anti-citrullinated peptide antibodies discloses a heterogeneous antibody population in rheumatoid arthritis

Anti-citrullinated peptide antibodies (ACPA) are highly specific for rheumatoid arthritis (RA). However, the predominant B cell epitopes have not yet been defined. The aim of this study was to examine the reactivity of ACPA against different peptides derived from citrullinated proteins and to investigate whether or not these antibodies constitute a homogeneous population. For this purpose, sera from patients with RA (n = 141), systemic lupus erythematosus (SLE) (n = 60), Sjögren's syndrome (SS) (n = 54) and healthy controls (n = 100) were tested for their reactivity against six citrullinated peptides derived from peptidyl arginine deiminase (PAD), vimentin (vim), alpha-enolase (enol), fibrin, type II collagen (col-II) and filaggrin, respectively. A non-citrullinated control peptide derived from PAD was used as control (ctrlPAD(621-40)). Antibody reactivity against each individual peptide was evaluated by enzyme-linked immunosorbent assay (ELISA). Specificity and cross-reactivity of ACPA were tested by using two prototype sera with homologous and cross-inhibition assays. Specificity of ACPA from two prototype sera was confirmed by purification of anti-peptide antibodies and homologous-inhibition experiments. We found that sera from patients with RA reacted diversely with the six citrullinated peptides. More specifically, PAD(211-30) displayed 29·08% sensitivity, vim(60-75) 29·08%, enol(5-21) 37·59%, fibrin(617-31) 31·21%, col-II(358-75) 29·97% and filaggrin(306-24) 28·37%, while control ctrlPAD(621-40) showed no reactivity. All reactive peptides were found to be highly specific for RA. A notable cross-reaction (>70%) was found mainly between filaggrin and the majority of anti-citrullinated peptide antibodies. We concluded that ACPA in RA constitute a heterogeneous population with limited cross-reactivity and without a predominant epitope.

Autoantibody profiling to follow evolution of lupus syndromes

INTRODUCTION

Identification of patients who are in early stages of lupus is currently done through clinical evaluation and is not greatly facilitated by available diagnostic tests. Profiling for patient characteristics and antibody specificities that predict disease would enhance the ability of physicians to identify and treat early cases prior to onset of organ damaging illness.

METHODS

A group of 22 patients with 4 or fewer diagnostic criteria for lupus were studied for changes in clinical and autoantibody profiles after a mean follow up period of 2.4 years. An array with more than 80 autoantigens was used to profile immunoglobulin G (IgG) and immunoglobulin M (IgM) autoantibodies. Correlations with clinical disease progression were examined.

RESULTS

3 of the 22 patients (14%) added sufficient criteria during follow up to satisfy a diagnosis of systemic lupus erythematosus (SLE) or to acquire a diagnosis of SLE renal disease. Patients who progressed were all females and were younger than those who did not progress (P=0.00054). IgG but not IgM autoreactivity showed greater increases in the progressor group than in the non-progressor group (P=0.047). IgG specificities that were higher at baseline in progressors included proliferating cell nuclear antigen (PCNA), beta 2 microglobulin, C1q and hemocyanin (P<0.019). Progressors had significant increases in La/SSB and liver cytosol type 1 (LC1) IgG autoantibodies over the period of evaluation (P≤0.0072). A quantitative risk profile generated from baseline demographic and autoantibody variables yielded highly different scores for the progressor and non-progressor groups (P=1.38 × 10⁻⁷)

CONCLUSIONS

In addition to demographic features, autoantibody profiles using an expanded array of specificities were correlated with the risk of progressive disease in patients with lupus. These findings suggest the feasibility of developing a simple diagnostic that could be applied by nonspecialists to screen for lupus and permit effective triage for specialty care.

Autoantibodies in Sjögren's syndrome: clinical presentation and regulatory mechanisms

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease mostly affecting the exocrine glands. A large number of autoantibodies have been detected in the serum of patients with pSS. Among them, anti-Ro/SSA and anti-La/SSB autoantibodies are the most common; they serve as disease markers and are involved in the pathogenesis of neonatal lupus syndrome (NLS). Other autoantibodies are associated with significant clinical phenotypes, such as cryoglobulins with development of non-Hodgkin's lymphoma, anti-centromere antibodies with Raynaud's phenomenon and anti-mitochondrial antibodies with liver pathology. As a result, pSS patients can be schematically categorized in subgroups according to their serological profile. Although the clinical utility of these autoantibodies is appreciated, little is known about the mechanisms related to their production and the regulation of the autoimmune response. In the present review, the clinical subsets of patients with pSS related to different autoantibodies as well as the regulating mechanisms of their production with special emphasis on idiotypic/anti-idiotypic network are discussed.

Characterization of Autoantibodies against the E1α Subunit of Branched-Chain 2-Oxoacid Dehydrogenase in Patients with Primary Biliary Cirrhosis

Primary biliary cirrhosis (PBC) is characterized by antimitochondrial antibodies (AMAs) that react with the lipoyl-containing E2 subunits of 2-oxoacid dehydrogenase complexes such as BCOADC and PDC. The lipoyl domains of E2 contain the major epitopes essential for immunopathology. However, the non-lipoyl-containing E1 subunits are also frequently targeted. Since anti-E1 antibodies always appear in combination with anti-E2 antibodies, the mechanisms underlying the autoimmunity against E1 may be linked to, but distinct from, those against E2. Here, we demonstrate that intermolecular and intramolecular determinant spreading underlies the autoimmunity against E1. We performed characterizations and epitope mapping for anti-BCOADC-E1α antibodies from both the intermolecular and intramolecular points of view. The antibody reactivities form a cluster against the BCOADC complex that is distinct from that against the PDC complex, and the anti-BCOADC-E1α antibodies arise as part of the cluster against the BCOADC complex. Multiple epitopes are present on the surface of the BCOADC-E1α molecule, and the major epitope overlaps with the active center. Sera with anti-BCOADC-E1α antibodies strongly inhibited the enzyme activity. These findings suggest that the E1α subunit as part of the native BCOADC complex is an immunogen, and that determinant spreading is involved in the pathogenesis of AMA production.

The complexity of Sjögren's syndrome: novel aspects on pathogenesis

In Sjögren's syndrome, like in most other autoimmune diseases, the enigma leading to a pathogenic attack against self has not yet been solved. By definition, the disease must be mediated by specific immune reactions against endogenous tissues to qualify as an autoimmune disease. In Sjögren's syndrome the autoimmune response is directed against the exocrine glands, which, as histopathological hallmark of the disease, display persistent and progressive focal mononuclear cell infiltrates. Clinically, the disease in most patients is manifested by two severe symptoms: dryness of the mouth (xerostomia) and the eyes (keratoconjunctivitis sicca). A number of systemic features have also been described and the presence of autoantibodies against the ubiquitously expressed ribonucleoprotein particles Ro (Sjögren's-syndrome-related antigen A - SSA) and La (SSB) further underline the systemic nature of Sjögren's syndrome. The original explanatory concept for the pathogenesis of Sjögren's syndrome proposed a specific, self-perpetuating, immune mediated loss of acinar and ductal cells as the principal cause of salivary gland hypofunction. Although straightforward and plausible, the hypothesis, however, falls short of accommodating several Sjögren's syndrome-related phenomena and experimental findings. Consequently, researchers considered immune-mediated salivary gland dysfunction prior to glandular destruction and atrophy as potential molecular mechanisms underlying the symptoms of dryness in Sjögren's syndrome. Accordingly, apoptosis, fibrosis and atrophy of the salivary glands would represent consequences of salivary gland hypofunction. The emergence of advanced bio-analytical platforms further enabled the identification of potential biomarkers with the intent to improve Sjögren's syndrome diagnosis, promote the development of prognostic tools for Sjögren's syndrome and the long-term goal to identify possible processes for therapeutic treatment interventions. In addition, such approaches allowed us to glimpse at the apparent complexity of Sjögren's syndrome.

Idiotype, anti-idiotype network of autoantibodies: pathogenetic considerations and clinical application

A common serologic finding in autoimmune diseases is the presence of autoantibodies against intracellular autoantigens. Recent data suggest that an anti-idiotypic network exists in these diseases, regulating the production of autoantibodies (idiotypic response). The anti-idiotypic antibodies can be monitored using complementary epitopes, designed according to the “molecular recognition” theory. The role of antiidiotypic antibodies in neonatal lupus and type 1 diabetes are discussed. In neonatal lupus, mothers with high anti-idiotypic antibody activity against anti-La autoantibodies are at lower risk of giving birth to an un-healthy child, as compared with mothers without anti-idiotypic antibodies. Similarly,the lack of particular anti-idiotypic antibodies against anti-GAD65 autoantibodies predispose in type 1 diabetes. These findings imply that antiidiotypic antibodies may confer protection from the harmful effect of autoantibodies in certain autoimmune diseases [corrected].