Characterization of a new antigen-antibody system (Su) in patients with systemic lupus erythematosus

Case report: Overlap syndrome of neuromyelitis optica spectrum disorder with anti-Argonaute antibodies

Aquaporin-4 antibodies (AQP4-Abs) are a diagnostic marker for patients with a demyelinating disease called neuromyelitis optica spectrum disorder (NMOSD). Anti-Argonaute antibodies (AGO-Abs) present as potential biomarkers of the overlap syndrome between NMOSD and other autoimmune diseases. In this paper, we present the case of an adult woman with numbness, tingling, and burning sensations in her arms and subsequent bilateral internuclear ophthalmoplegia. Brain-cervical-thoracic magnetic resonance imaging (MRI) showed T2 hyperintensities in the dorsal brainstem and around the midbrain aqueduct and longitudinally transverse myelitis with homogeneous enhancement on gadolinium-enhanced MRI. The contemporaneous detection of AQP4- and AGO-Abs led to a definite diagnosis of overlap syndrome of NMOSD with AGO-Abs. The patient was treated with immunosuppressive agents, including corticosteroids and immunoglobulins, and achieved remission. This case highlights a novel phenotype of NMOSD with AGO-Abs overlap syndrome, which presents with relapsing brainstem syndrome and longitudinally extensive myelitis with acute severe neurological involvement. The promising prognosis of the disease could serve as a distinct clinical profile. Broad screening for antibodies against central nervous system autoimmune antigens is recommended in suspected patients with limited or atypical clinical manifestations.

Anti-AGO1 Antibodies Identify a Subset of Autoimmune Sensory Neuronopathy

BACKGROUND AND OBJECTIVES

Autoantibodies (Abs) improve diagnosis and treatment decisions of idiopathic neurologic disorders. Recently, we identified Abs against Argonaute (AGO) proteins as potential autoimmunity biomarkers in neurologic disorders. In this study, we aim to reveal (1) the frequency of AGO1 Abs in sensory neuronopathy (SNN), (2) titers and IgG subclasses, and (3) their clinical pattern including response to treatment.

METHODS

This retrospective multicentric case/control study screened 132 patients with SNN, 301 with non-SNN neuropathies, 274 with autoimmune diseases (AIDs), and 116 healthy controls (HCs) for AGO1 Abs through ELISA. Seropositive cases were also tested for IgG subclasses, titers, and conformation specificity.

RESULTS

AGO1 Abs occurred in 44 patients, comprising significantly more of those with SNN (17/132 [12.9%]) than those with non-SNN neuropathies (11/301 [3.7%]; p = 0.001), those with AIDs (16/274 [5.8%]; p = 0.02), or HCs (0/116; p < 0.0001). Ab titers ranged from 1:100 to 1:100,000. IgG subclass was mainly IgG1, and 11/17 AGO1 Ab-positive SNN (65%) had a conformational epitope. AGO1 Ab-positive SNN was more severe than AGO1 Ab-negative SNN (e.g., SNN score: 12.2 vs 11.0, p = 0.004), and they more frequently and more efficiently responded to immunomodulatory treatments than AGO1 Ab-negative SNN (7/13 [54%] vs 6/37 [16%], p = 0.02). Regarding the type of treatments more precisely, this significant difference was confirmed for the use of IV immunoglobulins (IVIg) but not for steroids or second-line treatments. Multivariate logistic regression adjusted for potential confounders showed that AGO1 Ab positivity was the only predictor of response to treatment (OR 4.93, 1.10-22.24 95% CI, p = 0.03).

DISCUSSION

Although AGO Abs are not specific for SNN, based on our retrospective data, they may identify a subset of cases with SNN with more severe features and a possibly better response to IVIg. The significance of AGO1 Abs in clinical practice needs to be explored on a larger series.

Conformation-stabilizing ELISA and cell-based assays reveal patient subgroups targeting three different epitopes of AGO1 antibodies

Autoantibodies (Abs) are biomarkers for many disease conditions and are increasingly used to facilitate diagnosis and treatment decisions. To guarantee high sensitivity and specificity, the choice of their detection method is crucial. Via cell-based assays, we recently found 21 patients with neurological diseases positive for antibodies against argonaute (AGO), 10 of which having a neuropathy (NP). Here, we established a simple and conformation-sensitive ELISA with the aim to distinguish between AGO1 Abs against conformational epitopes and non-conformational epitopes and to reveal further characteristics of AGO1 antibodies in NP and autoimmune disease (AID). In a retrospective multicenter case/control and observational study, we tested 434 patients with NP, 274 disease controls with AID, and 116 healthy controls (HC) for AGO1 Abs via conformation-stabilizing ELISA. Seropositive patients were also tested for conformation-specificity via comparative denaturing/stabilizing ELISA (CODES-ELISA), CBA positivity, AGO1 titers and IgG subclasses, and AGO2 reactivity. These parameters were statistically compared among different epitope-specific patient groups. We found Abs in 44 patients, including 28/434 (6.5%) NP, 16/274 (5.8%) AID, and 0/116 (0%) HC. Serum reactivity was consistently higher for AGO1 than AGO2. Globally among the 44 AGO1 Abs-positive patients, 42 were also tested in CBA for AGO1 Abs positivity and 15 (35.7%) were positive. Furthermore, 43 were tested for conformation-specificity and 32 (74.4%) bound a conformational epitope. Among the subgroups of highly positive patients (ELISA z-score &gt;14) with sera binding conformational epitopes (n=23), 14 patient sera were also CBA positive and 9 bound a second conformational but CBA-inaccessible epitope. A third, non-conformational epitope was bound by 11/43 (15.6%). Among the epitope-specific patient subgroups, we found significant differences regarding the Abs titers, IgG subclass, and AGO2 reactivity. When comparing AGO1 Abs-positive NP versus AID patients, we found the conformation-specific and CBA inaccessible epitope significantly more frequently in AID patients. We conclude that 1) conformational ELISA was more sensitive than CBA in detecting AGO1 Abs, 2) serum reactivity is higher for AGO1 than for AGO2 at least for NP patients, 3) AGO1 Abs might be a marker-of-interest in 6.5% of NP patients, 4) distinguishing epitopes might help finding different patient subgroups.

Argonaute Autoantibodies as Biomarkers in Autoimmune Neurologic Diseases

Objective

To identify and characterize autoantibodies (Abs) as novel biomarkers for an autoimmune context in patients with central and peripheral neurologic diseases.

Methods

Two distinct approaches (immunoprecipitation/mass spectrometry–based proteomics and protein microarrays) and patients' sera and CSF were used. The specificity of the identified target was confirmed by cell-based assay (CBA) in 856 control samples.

Results

Using the 2 methods as well as sera and CSF of patients with central and peripheral neurologic involvement, we identified Abs against the family of Argonaute proteins (mainly AGO1 and AGO2), which were already reported in systemic autoimmunity. AGO-Abs were mostly of immunoglobulin G 1 subclass and conformation dependent. Using CBA, AGO-Abs were detected in 21 patients with a high suspicion of autoimmune neurologic diseases (71.4% were women; median age 57 years) and only in 4/856 (0.5%) controls analyzed by CBA (1 diagnosed with small-cell lung cancer and the other 3 with Sjögren syndrome). Among the 21 neurologic patients identified, the main clinical presentations were sensory neuronopathy (8/21, 38.1%) and limbic encephalitis (6/21, 28.6%). Fourteen patients (66.7%) had autoimmune comorbidities and/or co-occurring Abs, whereas AGO-Abs were the only autoimmune biomarker for the remaining 7/21 (33.3%). Thirteen (61.9%) patients were treated with immunotherapy; 8/13 (61.5%) improved, and 3/13 (23.1%) remained stable, suggesting an efficacy of these treatments.

Conclusions

AGO-Abs might be potential biomarkers of autoimmunity in patients with central and peripheral nonparaneoplastic neurologic diseases. In 7 patients, AGO-Abs were the only biomarkers; thus, their identification may be useful to suspect the autoimmune character of the neurologic disorder.

Classification of Evidence

This study provides Class III evidence that AGO-Abs are more frequent in patients with autoimmune neurologic diseases than controls.

From the Argonauts Mythological Sailors to the Argonautes RNA-Silencing Navigators: Their Emerging Roles in Human-Cell Pathologies

Regulation of gene expression has emerged as a fundamental element of transcript homeostasis. Key effectors in this process are the Argonautes (AGOs), highly specialized RNA-binding proteins (RBPs) that form complexes, such as the RNA-Induced Silencing Complex (RISC). AGOs dictate post-transcriptional gene-silencing by directly loading small RNAs and repressing their mRNA targets through small RNA-sequence complementarity. The four human highly-conserved family-members (AGO1, AGO2, AGO3, and AGO4) demonstrate multi-faceted and versatile roles in transcriptome’s stability, plasticity, and functionality. The post-translational modifications of AGOs in critical amino acid residues, the nucleotide polymorphisms and mutations, and the deregulation of expression and interactions are tightly associated with aberrant activities, which are observed in a wide spectrum of pathologies. Through constantly accumulating information, the AGOs’ fundamental engagement in multiple human diseases has recently emerged. The present review examines new insights into AGO-driven pathology and AGO-deregulation patterns in a variety of diseases such as in viral infections and propagations, autoimmune diseases, cancers, metabolic deficiencies, neuronal disorders, and human infertility. Altogether, AGO seems to be a crucial contributor to pathogenesis and its targeting may serve as a novel and powerful therapeutic tool for the successful management of diverse human diseases in the clinic.

Autoantibodies to Su/Argonaute 2 in Japanese patients with inflammatory myopathy

BACKGROUND

Anti-Su antibodies are found in 5-20% of cases of various systemic autoimmune rheumatic diseases and in 5-10% of dermatomyositis (DM)/polymyositis (PM) patients. In 2006, the 100kDa Su antigen was identified as argonaute2 (Ago2), and it was found to play a major role in RNA interference. However, immunoprecipitation (IP) remains the main method for detecting anti-Su and the clinical significance of the antibodies is uncertain.

METHODS

Sera from patients with DM/PM (n=224) were screened by an ELISA that uses recombinant biotinylated Ago2 protein. Some serum samples were tested by IP and by indirect immunofluorescence (IIF) analysis.

RESULTS

Seventeen (7.5%, 17/224) sera from DM/PM were positive in ELISA. Of the 33 IP-tested sera (17 ELISA-positive and 16 ELISA-negative with high background), 13 were found to be anti-Ago2/Su-positive in IP and ELISA. Only one IP-positive serum was judged to be ELISA-negative. Among the 13 patients with anti-Su/Ago2, 7 cases also had myositis-specific autoantibodies. Six sera that were positive by both IP and ELISA showed the GW body pattern in IIF. Interestingly, one ELISA-positive serum with an inconclusive result in IP also showed the GW body pattern.

CONCLUSION

Our novel ELISA appears to be useful for screening anti-Su/Ago2 antibodies (sensitivity: 93%, specificity: 79%).

Dynamic nature of noncoding RNA regulation of adaptive immune response

Immune response plays a fundamental role in protecting the organism from infections; however, dysregulation often occurs and can be detrimental for the organism, leading to a variety of immune-mediated diseases. Recently our understanding of the molecular and cellular networks regulating the immune response, and, in particular, adaptive immunity, has improved dramatically. For many years, much of the focus has been on the study of protein regulators; nevertheless, recent evidence points to a fundamental role for specific classes of noncoding RNAs (ncRNAs) in regulating development, activation and homeostasis of the immune system. Although microRNAs (miRNAs) are the most comprehensive and well-studied, a number of reports suggest the exciting possibility that long ncRNAs (lncRNAs) could mediate host response and immune function. Finally, evidence is also accumulating that suggests a role for miRNAs and other small ncRNAs in autocrine, paracrine and exocrine signaling events, thus highlighting an elaborate network of regulatory interactions mediated by different classes of ncRNAs during immune response. This review will explore the multifaceted roles of ncRNAs in the adaptive immune response. In particular, we will focus on the well-established role of miRNAs and on the emerging role of lncRNAs and circulating ncRNAs, which all make indispensable contributions to the understanding of the multilayered modulation of the adaptive immune response.

MicroRNAs in systemic rheumatic diseases

MicroRNAs (miRNAs) are endogenous, non-coding, single-stranded RNAs about 21 nucleotides in length. miRNAs have been shown to regulate gene expression and thus influence a wide range of physiological and pathological processes. Moreover, they are detected in a variety of sources, including tissues, serum, and other body fluids, such as saliva. The role of miRNAs is evident in various malignant and nonmalignant diseases, and there is accumulating evidence also for an important role of miRNAs in systemic rheumatic diseases. Abnormal expression of miRNAs has been reported in autoimmune diseases, mainly in systemic lupus erythematosus and rheumatoid arthritis. miRNAs can be aberrantly expressed even in the different stages of disease progression, allowing miRNAs to be important biomarkers, to help understand the pathogenesis of the disease, and to monitor disease activity and effects of treatment. Different groups have demonstrated a link between miRNA expression and disease activity, as in the case of renal flares in lupus patients. Moreover, miRNAs are emerging as potential targets for new therapeutic strategies of autoimmune disorders. Taken together, recent data demonstrate that miRNAs can influence mechanisms involved in the pathogenesis, relapse, and specific organ involvement of autoimmune diseases. The ultimate goal is the identification of a miRNA target or targets that could be manipulated through specific therapies, aiming at activation or inhibition of specific miRNAs responsible for the development of disease.

Are the Ro RNP-associated Y RNAs concealing microRNAs? Y RNA-derived miRNAs may be involved in autoimmunity

Here we discuss the hypothesis that the RNA components of the Ro ribonucleoproteins (RNPs), the Y RNAs, can be processed into microRNAs (miRNAs). Although Ro RNPs, whose main protein components Ro60 and La are targeted by the immune system in several autoimmune diseases, were discovered many years ago, their function is still poorly understood. Indeed, recent data show that miRNA-sized small RNAs can be generated from Y RNAs. This hypothesis leads also to a model in which Ro60 acts as a modulator in the Y RNA-derived miRNA biogenesis pathway. The implications of these Y RNA-derived miRNAs, which may be specifically produced under pathological circumstances such as in autoimmunity or during viral infections, for the enigmatic function of Ro RNPs are discussed.

Anti-argonaute2 (Ago2/Su) and -Ro antibodies identified by immunoprecipitation in primary anti-phospholipid syndrome (PAPS)

OBJECTIVES

Primary anti-phospholipid syndrome (PAPS) is an autoimmune condition defined by anti-phospholipid antibodies (aPL) and thrombotic or obstetric events. Some PAPS can evolve into systemic lupus erythematosus (SLE) during follow-up. Few studies systematically examined lupus autoantibodies and their clinical significance in PAPS. The aim of our study is to analyze the clinical and laboratory correlations with lupus-related autoantibodies, detected by immunoprecipitation (IP), a technique not yet systematically applied to investigate autoantibodies in this condition.

METHODS

Sera from 52 PAPS patients were screened by indirect immunofluorescence (IIF) antinuclear antibodies (ANA), IP of ³⁵S-labeled K562 cell extract, and ELISA [anti-Argonaute2 (Ago2, Su), 60kRo, 52kRo, La, dsDNA)]. Anti-Ago2/Su positive sera were also tested for anti-GW bodies (GWBs) by IIF double staining, using rabbit anti-Rck/p54 serum.

RESULTS

First, 56% of PAPS patients (29/52) were ANA positive, mainly with speckled pattern. Anti-Ago2/Su antibodies were found in 13% (7/52), anti-Ro/SSA in 10% (5/52), anti-La in one case. The clinical profile of patients did not seem to be related to the presence of these antibody specificities. However, levels of IgG anti-β2 glycoprotein I antibodies were lower in anti-Ago2/Su positive patients (p = 0.02). None of anti-Ago2/Su or -Ro patients developed SLE during a 2-year follow-up. Ago2 is a key component of GWBs, however, only 1/7 anti-Ago2/Su serum showed a typical cytoplasmic GWBs staining.

CONCLUSIONS

Anti-Ago2/Su and -Ro antibodies are the two autoantibodies detected by IP in our PAPS cohort. Clarifying why Ago2/Su and Ro are specific targets of autoimmunity may help to understand the mechanisms of autoantibody production.

Autoimmune targeting of key components of RNA interference

RNA interference (RNAi) is an evolutionarily conserved mechanism that is involved in the post-transcriptional silencing of genes. This process elicits the degradation or translational inhibition of mRNAs based on the complementarity with short interfering RNAs (siRNAs) or microRNAs (miRNAs). Recently, differential expression of specific miRNAs and disruption of the miRNA synthetic pathway have been implicated in cancer; however, their role in autoimmune disease remains largely unknown. Here, we report that anti-Su autoantibodies from human patients with rheumatic diseases and in a mouse model of autoimmunity recognize the human Argonaute (Ago) protein, hAgo2, the catalytic core enzyme in the RNAi pathway. More specifically, 91% (20/22) of the human anti-Su sera were shown to immunoprecipitate the full-length recombinant hAgo2 protein. Indirect immunofluorescence studies in HEp-2 cells demonstrated that anti-Su autoantibodies target cytoplasmic foci identified as GW bodies (GWBs) or mammalian P bodies, structures recently linked to RNAi function. Furthermore, anti-Su sera were also capable of immunoprecipitating additional key components of the RNAi pathway, including hAgo1, -3, -4, and Dicer. Together, these results demonstrate an autoimmune response to components of the RNAi pathway which could potentially implicate the involvement of an innate anti-viral response in the pathogenesis of autoantibody production.

The RNA interference pathway: a new target for autoimmunity

Many intracellular macromolecular complexes that are involved in the production or degradation of RNAs are targeted by autoantibodies in systemic autoimmune diseases. RNA interference (RNAi) is a recently characterized gene silencing pathway by which specific mRNAs are either degraded or translationally suppressed. In a recent issue of Arthritis Research and Therapy, Andrew Jakymiw and colleagues reported that the enigmatic Su autoantigen complex contains key components of the RNAi machinery. Anti-Su autoantibodies from both human patients with rheumatic diseases and a mouse model of autoimmunity recognize the endonucleolytic Argonaute and Dicer proteins, both crucial enzymes of the RNAi pathway. These data raise the question of how the anti-Su response is triggered. So far, it is unknown whether molecular modifications may be involved, as has been proposed for other intracellular autoantigens. The implication of RNAi in anti-viral defence may suggest a role for virus infection in this process.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.

Pristane induces high titers of anti-Su and anti-nRNP/Sm autoantibodies in BALB/c mice. Quantitation by antigen capture ELISAs based on monospecific human autoimmune sera

Autoantibodies to Su and anti-nRNP/Sm are common in human and murine systemic lupus erythematosus (SLE), and are also produced by BALB/c mice with SLE-like autoimmunity induced by pristane. Antigen capture ELISAs employing monospecific human autoimmune IgG were developed to quantitate the production of anti-Su and anti-nRNP/Sm autoantibodies in 77 sera from BALB/c mice with pristane-induced autoimmunity. The sensitivity and specificity of the anti-Su antigen capture ELISA were 100% compared with immunoprecipitation of 35S-labeled cellular proteins. All 16 immunoprecipitation positive sera were positive in the anti-nRNP/Sm antigen capture ELISA (100% sensitivity), whereas 55/61 immunoprecipitation negative sera were negative by ELISA (90% specificity). The 6/61 immunoprecipitation negative sera that were ELISA positive were probably true positives because subsequent sera obtained from the same mice were positive by both techniques. Thus, the antigen capture ELISA may be somewhat more sensitive than immunoprecipitation. The titers of anti-Su and anti-nRNP/Sm positive antibodies in the sera were as high as 1:25,000-1:250,000 by ELISA, suggesting that autoantibodies may be produced in pristane-primed BALB/c mice at levels comparable to those seen in spontaneous autoimmune disease. We conclude that antigen capture ELISAs based on human autoimmune sera were highly sensitive and specific for detecting murine anti-Su and anti-nRNP/Sm antibodies. This technique will be useful for quantitating antibodies in murine autoimmune disease models, since antigen capture ELISA avoids the use of denatured or recombinant antigens, permitting antibodies recognizing tertiary and quaternary structures to be detected.

Extraction and differentiation of the Su autoantigen from calf thymus nuclei

Antibodies to Su antigen have been reported previously as a distinct antigen-antibody system associated with connective tissue diseases; most specifically systemic lupus erythematosus and undifferentiated connective tissue disease. The Su antigen was first identified by double immunodiffusion using calf thymus nuclear extract (CTNE) as a source for Su antigen. In this report, enhanced extraction of Su antigen was achieved using deoxyribonuclease I (DNase) for preparation of CTNE. Only the Sm antigen was found in comparable quantities in the DNase CTNE. Western immunoblotting and immunoprecipitation employing DNase CTNE and extracts of [35S]methionine-labeled HeLa cells respectively were used for further characterization and differentiation of the Su antigen. Sera from patients positive for Su antibodies by double immunodiffusion were found to react most specifically with antigen components in a molecular weight range of approximately 50-55 kDa. These methods should assist in further understanding the biochemical properties of the Su antigen.

Clinical findings in patients with SLE whose sera contain antibodies to ribosomal ribonucleoprotein

In a clinical and serological study performed on a large series of patients with different connective tissue diseases, anti-ribosomal ribonucleoprotein (rRNP) antibodies were detected only in a small proportion of sera with systemic lupus erythematosus (SLE). SLE patients positive for anti-rRNP autoantibodies showed a significantly higher incidence of hemolytic anemia. The reasons for this surprising association are still unclear; however, this finding suggests that rRNP precipitin might be considered as a useful marker of a particular subgroup of patients with SLE.

The autoimmune antigen Me is distinct and related to undifferentiated connective tissue disease

Using prototype Me serum, a new autoantibody-antigen system has been identified by Ouchterlony immunodiffusion and indirect immunofluorescence. Although immunologically distinct, the Me antigen has physiochemical and biochemical properties similar to those of the Sm antigen. Immunoblot assays indicate that Me sera commonly recognize 4 peptides of molecular weights approximating 100K, 65K, 21K, and 16K. The last of these may be identical to the D peptide recognized by Sm antibodies. The Me antigen may be associated with the RNP-Sm macromolecular complex. Me-positive patients have few clinical symptoms, and the most common diagnosis is undifferentiated connective tissue disease.

The SL autoantibody-antigen system: clinical and biochemical studies

A recently described autoantibody, SL, was found in serum from 27 patients with autoimmune disease, including 20 with systemic lupus erythematosus (SLE) where the frequently was 7%. Analysis of clinical, serological, and HLA data from 119 SLE patients showed no positive associations with anti-SL antibody apart from a higher frequency of non-infective fever. Most SL positive sera contained other precipitins, notably antibodies to Ro(SS-A) and the proliferating cell nuclear antigen, PCNA. Anti-SL IgG recognised a protein of 32 000 daltons without associated RNA. This polypeptide was distinguished from a similarly sized component of the Sm and RNP ribonucleoprotein particles by demonstrating different products of partial proteolysis. Although anti-SL antibody is of limited clinical importance, it occurs with twice the frequency of anti-SM antibody in white patients with SLE. Preliminary studies indicate that SL and the Japanese Ki system are identical.