Development of a CENP-A/CENP-B-specific immune response in a patient with systemic sclerosis

Can Antinuclear Antibodies Have a Pathogenic Role in Systemic Sclerosis?

Systemic sclerosis (SSc) is a connective tissue disease characterized by extensive fibrosis of the skin and internal organs, associated with vasculopathy and autoimmune features. Antinuclear antibodies (ANA) are found in almost all SSc patients and constitute strong diagnosis and prognosis biomarkers. However, it remains unclear whether ANA are simple bystanders or if they can have a role in the pathophysiology of the disease. One might think that the nuclear nature of their targets prevents any accessibility to autoantibodies. Nevertheless, recent data suggest that ANA could be pathogenic or at least contribute to the perennation of the disease. We review here first the indirect clues of the contribution of ANA to SSc: they are associated to the disease subtypes, they may precede disease onset, their titer correlates with disease activity and severity, there is an association between molecular subsets, and some patients can respond to B-cell targeting therapy. Then, we describe in a second part the mechanisms of ANA production in SSc from individual genetic background to post-transcriptional modifications of neoantigens. Finally, we elaborate on the potential mechanisms of pathogenicity: ANA could be pathogenic through immune-complex-mediated mechanisms; other processes potentially involve molecular mimicry and ANA penetration into the target cell, with a focus on anti-topoisomerase-I antibodies, which are the most probable candidate to play a role in the pathophysiology of SSc. Finally, we outline some technical and conceptual ways to improve our understanding in this field.

Characterization of testicular macrophagesubpopulations in mice

Testis is an immune privileged site, a feature that prevents germ cells from eliciting an autoimmune response. Macrophages contribute to this state of tolerance by adopting an immunoregulatory phenotype. Here, we further characterized their features in mice by analyzing surface markers, anatomic localization as well as morphology and function. Testicular macrophages (TMF) were stained for various surface receptors, and MHCII and CD206 were found to be most suitable to discriminate between two subpopulations. Our immunohistochemical analysis further confirmed a predominant localization of CD206+ cells in the interstitial space. Imaging flow cytometry revealed that both subtypes of TMF differed in size and contrast, and to some extent also in their ability to engulf high-molecular dextran. To investigate whether the polarization of the immune system had any influence on the phenotype of TMF, we compared C57BL/6 and BALB/c mice. Importantly, our analysis revealed that the abundance of cells expressing either MHCII or any of the scavenger receptors CD206, CD163 and CD71 differed between both mouse strains. In addition, the presence of the glucocorticoid receptor in macrophages affected the ratio between individual subpopulations, which is consistent with a crucial role of glucocorticoids in macrophage polarization. Collectively, our results indicate that TMF are composed in a variable ratio of distinct subsets with characteristic features, which may shape the immune privilege of the testis also in humans.

Increased Autoantibodies Against Ro/SS-A, CENP-B, and La/SS-B in Patients With Kidney Allograft Antibody-mediated Rejection

Supplemental Digital Content is available in the text.

Antibody-mediated rejection (AMR) causes more than 50% of late kidney graft losses. In addition to anti-human leukocyte antigen (HLA) donor-specific antibodies, antibodies against non-HLA antigens are also linked to AMR. Identifying key non-HLA antibodies will improve our understanding of AMR.

A Bioinformatics Analysis Reveals Novel Pathogens as Molecular Mimicry Triggers of Systemic Sclerosis

A recent bioinformatic analysis revealing dominant B cell epitopes of systemic sclerosis-specific autoantibodies, including anti-centromere B, anti-topoisomerase I and anti-fibrillarin, has demonstrated the existence of several in silico antigenic mimics of pathogens that could act as triggers of the respective dominant autoepitopes. Based on those findings, the aim of the present study was to use a more comprehensive bioinformatic analysis. We demonstrated the presence of a plethora of novel microbial mimics, unnoticed by the studies so far conducted, which share remarkable amino acid similarities with the respective autoantigenic epitopes. This bioinformatic approach coupled by in vitro testing of the homologous self/non-self-mimics in serum samples from patients with systemic sclerosis may provide novel evidence of immunological cross-reactivity, implicating currently ignored or overlooked pathogens, which may indeed play a role in the induction of SSc-specific autoantibodies and assist efforts to understand the pathogenesis of this enigmatic disease.

Exploring Impact of Rare Variation in Systemic Lupus Erythematosus by a Genome Wide Imputation Approach

The importance of low frequency and rare variation in complex disease genetics is difficult to estimate in patient populations. Genome-wide association studies are therefore, underpowered to detect rare variation. We have used a combined approach of genome-wide-based imputation with a highly stringent sequence kernel association (SKAT) test and a case-control burden test. We identified 98 candidate genes containing rare variation that in aggregate show association with SLE many of which have recognized immunological function, but also function and expression related to relevant tissues such as the joints, skin, blood or central nervous system. In addition we also find that there is a significant enrichment of genes annotated for disease-causing mutations in the OMIM database, suggesting that in complex diseases such as SLE, such mutations may be involved in subtle or combined phenotypes or could accelerate specific organ abnormalities found in the disease. We here provide an important resource of candidate genes for SLE.

Bicaudal D2 is a novel autoantibody target in systemic sclerosis that shares a key epitope with CENP-A but has a distinct clinical phenotype

We studied the clinical correlations and epitopes of autoantibodies directed to a novel autoantigen, Bicaudal D (BICD2), in systemic sclerosis (SSc) and reviewed its relationship to centromere protein A (CENP-A). 451 SSc sera were tested for anti-BICD2 using a paramagnetic bead immunoassay and then univariate and multivariate logistic regression was used to study the association between anti-BICD2 and demographic and clinical parameters as well as other SSc-related autoantibodies. Epitope mapping was performed on solid phase matrices. 25.7% (116/451) SSc sera were anti-BICD2 positive, of which 19.0% had single specificity anti-BICD2 and 81.0% had other autoantibodies, notably anti-CENP (83/94; 88.3%). Compared to anti-BICD2 negative subjects (335/451), single specificity anti-BICD2 subjects were more likely to have an inflammatory myopathy (IM; 31.8% vs. 9.6%, p=.004) and interstitial lung disease (ILD; 52.4% vs. 29.0%, p=.024). Epitope mapping revealed a serine- and proline-rich nonapeptide SPSPGSSLP comprising amino acids 606-614 of BICD2, shared with CENP-A but not CENP-B. We observed that autoantibodies to BICD2 represent a new biomarker as they were detected in patients without other SSc-specific autoantibodies and were the second most common autoantibody identified in this SSc cohort. Our data indicate that the major cross-reactive epitope is associated with anti-CENP-A but, unlike anti-CENP, single specificity anti-BICD2 antibodies associate with ILD and IM.

Anticentromere antibody-positive primary Sjögren's syndrome: Epitope analysis of a subset of anticentromere antibody-positive patients

OBJECTIVES

Anticentromere antibody (ACA) is generally considered to be a serological marker for systemic sclerosis (SSc). ACA-positive patients with primary Sjögren's syndrome (pSS) have also been reported. ACA often recognizes centromere proteins (CENPs): CENP-A, CENP-B, and CENP-C, and sometimes reacts to heterochromatin protein 1 (HP1)α. We compared the reactivity against six different epitopes for three ACA-positive clinical subgroups: 29 patients with pSS, 36 SSc patients with sicca symptoms, and 28 SSc patients without sicca symptoms.

METHODS

We utilized enzyme-linked immunosorbent assays (ELISAs) with recombinant proteins covering six different epitope regions of ACA (the amino terminus (Nt) of CENP-A, CENP-B, and CENP-C, the carboxyl terminus (Ct) of CENP-B and CENP-C, and HP1α).

RESULTS

The patients with pSS were found to have IgG-class autoantibodies against CENP-C-Nt and HP1α, and IgA-class autoantibodies against CENP-C-Ct with significantly higher frequencies than the SSc patients with or without sicca symptoms. The positive predictive value and the negative predictive value of the combination of these three autoantibodies for pSS were 73% and 82%, respectively, for pSS.

CONCLUSIONS

Based on the result that reactivities against CENP-C and HP1α in patients with pSS differ from those in patients with SSc, we propose ACA-positive pSS as a clinical subset of SS that is independent of SSc.

Correlation between centromere protein-F autoantibodies and cancer analyzed by enzyme-linked immunosorbent assay

Background

Centromere protein-F (CENP-F) is a large nuclear protein of 367 kDa, which is involved in multiple mitosis-related events such as proper assembly of the kinetochores, stabilization of heterochromatin, chromosome alignment and mitotic checkpoint signaling. Several studies have shown a correlation between CENP-F and cancer, e.g. the expression of CENP-F has been described to be upregulated in cancer cells. Furthermore, several studies have described a significant correlation between the expression of autoantibodies to CENP-F and cancer.

Methods

Autoantibodies to CENP-F were detected in a small number of samples during routine indirect immunofluorescence (IIF) analysis for anti-nuclear antibodies (ANA) using HEp-2 cells as substrate. Using overlapping synthetic peptides covering a predicted structural maintenance of chromosomes (SMC) domain, we developed an enzyme-linked immunosorbent assay (ELISA) for detection of CENP-F antibodies.

Results

Analyzing the reactivity of the sera positive in IIF for CENP-F antibodies to overlapping CENP-F peptides, we showed that autoantibodies to several peptides correlate with the presence of antibodies to CENP-F and a diagnosis of cancer, as increased CENP-F antibody expression specific for malignant cancer patients to five peptides was found (A9, A12, A14, A16, A27). These antibodies to CENP-F in clinical samples submitted for ANA analysis were found to have a positive predictive value for cancer of 50%. Furthermore, the expression of cancer-correlated CENP-F antibodies seemed to increase as a function of time from diagnosis.

Conclusion

These results conform to previous findings that approximately 50% of those patients clinically tested for ANA analyses who express CENP-F antibodies are diagnosed with cancer, confirming that these antibodies may function as circulating tumor markers. Thus, a peptide-based CENP-F ELISA focused on the SMC domain may aid in identifying individuals with a potential cancer.

Autoantibodies recognizing the amino terminal 1-17 segment of CENP-A display unique specificities in systemic sclerosis

Centromere-associated protein A (CENP-A), a common autoimmune target in a subset of systemic sclerosis patients, appears to have no role to explain why its corresponding auto-antibodies are more frequently found in the limited than the diffuse form of systemic sclerosis. Therefore, we investigated the fine specificity of anti-CENP-A antibodies as a first step to understanding their role in systemic sclerosis pathology. We focused on the amino-terminal portion of CENP-A spanning amino acids 1 to 17 (Ap(1-17)), which represents, along with Ap(17-30), an immunodominant epitope of the protein. Peptide Ap(1-17) was used to purify antibodies from 8 patients with systemic sclerosis. Anti-Ap(1-17) antibodies specifically reacted with human CENP-A but did not cross-react with CENP-B or Ap(17-30). Panning of a phage display peptide library with anti-Ap(1-17) antibodies from 2 patients identified two novel, partially overlapping motifs, <(5)Rx(st)xKP(10)> and <(9)KPxxPxR(15)> as the result of the alignment of specific phage clone insert sequences. Anti-Ap(1-17) IgG from the 8 patients had different reactivities to isolated phage clone insert sequences. Scanning the Swiss-Prot database revealed a large number of different types of proteins containing the two Ap(1-17) antigenic motifs. These data show that anti-CENP-A(1-17) antibodies are generated independently from anti-CENP-B antibodies and display great heterogeneity in their specificity by recognizing different motifs within that peptide sequence. This finding, along with the widespread interspecies and human tissue distribution of the two motifs, suggests that the number of motif-expressing proteins which can be the potential target of these antibodies is markedly higher than that estimated from the peptide-based epitope spreading model.

Evaluation of a new multi-parallel line immunoassay for systemic sclerosis-associated antibodies in an Asian population

OBJECTIVES

To compare the SSc-line immunoassay (LIA) with conventional techniques of antibody detection, to evaluate its diagnostic utility and to describe clinical associations of antibodies in Asian SSc patients.

METHODS

Stored sera from patients with SSc (n = 68), SLE (n = 49), OA (n = 41) and normal controls (NCs, n = 32) were evaluated. Cohen's κ and Bland-Altman plots were used to evaluate agreement.

RESULTS

There was good agreement between LIA and ELISA for anti-Scl-70 (κ = 0.97), anti-CENPA (κ = 0.83), anti-CENPB (κ = 0.96) and anti-PmScl100 (κ = 1.00) (5.48-8.22% of values outside the 95% limits of agreement using Bland-Altman plots), and between LIA and IIF for anti-CENPA (κ = 0.81) and anti-CENPB (κ = 0.77) (P < 0.001). Using LIA, of 32 (32/68, 47%) SSc patients negative for anti-Scl-70 and anti-CENPA/B, 5 (5/32, 15%) were positive for anti-Ku, -Nor90, -fibrillarin and -RP155. Specificity of each antibody for SSc was at least 97% (vs OA/NC) and 94% (vs SLE), except for anti-Ro52 (63%). Anti-CENPB was associated with joint pain [odds ratio (OR) 0.17], interstitial lung disease (OR 0.24) and telangiectasia (OR 4.00) (P < 0.05). Anti-Ro60 was associated with pulmonary arterial hypertension (OR 3.89, P = 0.041).

CONCLUSION

The SSc-LIA has good agreement with conventional techniques for selected antibodies and has good diagnostic utility.

Clinical Correlates of CENP-A and CENP-B Antibodies in a Large Cohort of Patients with Systemic Sclerosis

Objective.

To study the clinical phenotypes of centromeric proteins (CENP)-A- and CENP-B-positive patients with systemic sclerosis (SSc) and to compare them to anticentromere antibody (ACA)-positive and negative SSc patients.

Methods.

Sera samples were collected from 802 patients with SSc enrolled in a multicenter cohort study. Antibodies to CENP-A and B were detected by ELISA, and ACA by indirect immunofluorescence. Associations with clinical and other serological manifestations of SSc were investigated.

Results.

CENP-A antibodies were detected in 276 (34%), CENP-B in 286 (36%), and ACA in 279 (35%) patients. Patients having ACA, CENP-A, and/or CENP-B resembled each other and differed from the remainder of the cohort in the following respects: older chronologically and at disease onset; more commonly women; more likely to have limited disease and lower skin scores; less likely to have finger ulcers, digital tuft resorption, or finger contractures; more likely to have pulmonary hypertension; less likely to have interstitial lung disease, scleroderma renal crisis, inflammatory arthritis, and inflammatory myositis; and having lower overall disease severity. CENP-A and/or B status was predictive of the extent of skin involvement over time. Patients with limited disease who were CENP-A-negative at baseline were more likely to progress to diffuse disease compared to CENP-A-positive patients (OR 2.55, 95% CI 1.37, 4.85, p = 0.004).

Conclusion.

Clinical immunology laboratories are increasingly using high-throughput ELISA tests for CENP antibodies, with or without ACA detected by indirect immunofluorescence. The phenotype of CENP-A and/or B-positive patients is generally similar to that associated with ACA.

Clinical and serological evaluation of a novel CENP-A peptide based ELISA

Introduction

Anti-centromere antibodies (ACA) are useful biomarkers in the diagnosis of systemic sclerosis (SSc). ACA are found in 20 to 40% of SSc patients and, albeit with lower prevalence, in patients with other systemic autoimmune rheumatic diseases. Historically, ACA were detected by indirect immunofluorescence (IIF) on HEp-2 cells and confirmed by immunoassays using recombinant CENP-B. The objective of this study was to evaluate a novel CENP-A peptide ELISA.

Methods

Sera collected from SSc patients (n = 334) and various other diseases (n = 619) and from healthy controls (n = 175) were tested for anti-CENP-A antibodies by the novel CENP-A enzyme linked immunosorbent assay (ELISA). Furthermore, ACA were determined in the disease cohorts by IIF (ImmunoConcepts, Sacramento, CA, USA), CENP-B ELISA (Dr. Fooke), EliA^® CENP (Phadia, Freiburg, Germany) and line-immunoassay (LIA, Mikrogen, Neuried, Germany). Serological and clinical associations of anti-CENP-A with other autoantibodies were conducted in one participating centre. Inhibition experiments with either the CENP-A peptide or recombinant CENP-B were carried out to analyse the specificity of anti-CENP-A and -B antibodies.

Results

The CENP-A ELISA results were in good agreement with other ACA detection methods. According to the kappa method, the qualitative agreements were: 0.73 (vs. IIF), 0.81 (vs. LIA), 0.86 (vs. CENP-B ELISA) and 0.97 (vs. EliA^® CENP). The quantitative comparison between CENP-A and CENP-B ELISA using 265 samples revealed a correlation value of rho = 0.5 (by Spearman equation). The receiver operating characteristic analysis indicated that the discrimination between SSc patients (n = 131) and various controls (n = 134) was significantly better using the CENP-A as compared to CENP-B ELISA (P < 0.0001). Modified Rodnan skin score was significantly lower in the CENP-A negative group compared to the positive patients (P = 0.013). Inhibition experiments revealed no significant cross reactivity of anti-CENP-A and anti-CENP-B antibodies. Statistically relevant differences for gender ratio (P = 0.0103), specific joint involvement (Jaccoud) (P = 0.0006) and anti-phospholipid syndrome (P = 0.0157) between ACA positive SLE patients and the entire SLE cohort were observed.

Conclusions

Anti-CENP-A antibodies as determined by peptide ELISA represent a sensitive, specific and independent marker for the detection of ACA and are useful biomarkers for the diagnosis of SSc. Our data suggest that anti-CENP-A antibodies are a more specific biomarker for SSc than antibodies to CENP-B. Furthers studies are required to verify these findings.

Elevated immunoglobulin G antibodies to the proline-rich amino-terminal region of Epstein-Barr virus nuclear antigen-2 in sera from patients with systemic connective tissue diseases and from a subgroup of Sjögren's syndrome patients with pulmonary involvements

Associations of Epstein-Barr virus (EBV) and autoimmune diseases have been hypothesized. We have analysed IgG antibodies to EBV nuclear antigen (EBNA)-2 in sera from Japanese patients with autoimmune systemic connective tissue diseases (CTD), exemplified by systemic lupus erythematosus (SLE), primary Sjogren's syndrome (SS), rheumatoid arthritis (RA), systemic sclerosis (SSc) and secondary SS (classical CTDs complicated with SS). An enzyme-linked immunosorbent assay (ELISA) which uses glutathione-S-transferase polypeptides fused to EBV nuclear antigen (EBNA)-2 and EBNA-1 was developed. Ratios of IgG antibody reactivity to whole IgG concentrations of sera were calculated to normalize EBNA-2 and EBNA-1 antibody levels to the hypergammaglobulinaemia that occurs in CTD. The ELISA optical density OD(450) readings of IgG antibodies to both the amino-terminal aa 1-116 of EBNA-2 and carboxyl-terminal aa 451-641 of EBNA-1 were elevated significantly in patients with SLE, primary SS, RA, SSc and secondary SS when compared to EBNA-1. The OD readings were divided by serum IgG concentrations to normalize for the hypergammaglobulinaemia. The specific levels of IgG antibodies to the amino-terminal region of EBNA-2 were elevated in patients with SLE, primary SS or RA, as well as those with secondary SS complicated with SLE or RA. The EBNA-2 amino-terminal region contains a polyproline tract and a proline-rich sequence and has considerable amino acid sequence homology with many cellular proline-rich proteins. High ratios of EBNA-2 aa 1-116 to EBNA-1 aa 451-641 IgG antibody levels which probably suggest reactivation of EBV latent infection were associated significantly with pulmonary involvement in SS patients. These results are consistent with the hypothesis that the sequence similarity between the amino-terminal region of EBNA-2 and proline-rich cellular proteins is associated with pathogenesis in a subpopulation of CTD patients, possibly by the molecular mimicry-epitope shift mechanism.

Identification of a SmD3 epitope with a single symmetrical dimethylation of an arginine residue as a specific target of a subpopulation of anti-Sm antibodies

Anti-Sm antibodies, identified in 1966 by Tan and Kunkel, are highly specific serological markers for systemic lupus erythrematosus (SLE). Anti-Sm reactivity is found in 5-30% of SLE patients, depending on the autoantibody detection system and the racial background of the SLE population. The Sm autoantigen complex comprises at least nine different polypeptides. All of these core proteins can serve as targets of the anti-Sm B-cell response, but most frequently the B and D polypeptides are involved. Because the BB'Sm proteins share cross-reactive epitopes (PPPGMRPP) with U1 specific ribonucleoproteins, which are more frequently targeted by antibodies that are present in patients with mixed connective tissue disease, the SmD polypeptides are regarded as the Sm autoantigens that are most specific to SLE. It was recently shown that the polypeptides D1, D3 and BB' contain symmetrical dimethylarginine, which is a component of a major autoepitope within the carboxyl-terminus of SmD1. In one of those studies, a synthetic dimethylated peptide of SmD1 (amino acids 95-119) exhibited significantly increased immunoreactivity as compared with unmodified SmD1 peptide. Using immobilized peptides, we confirmed that the dimethylated arginine residues play an essential role in the formation of major SmD1 and SmD3 autoepitopes. Moreover, we demonstrated that one particular peptide of SmD3 represents a more sensitive and more reliable substrate for the detection of a subclass of anti-Sm antibodies. Twenty-eight out of 176 (15.9%) SLE patients but only one out of 449 (0.2%) control individuals tested positive for the anti-SmD3 peptide (SMP) antibodies in a new ELISA system. These data indicate that anti-SMP antibodies are exclusively present in sera from SLE patients. Thus, anti-SMP detection using ELISA represents a new serological marker with which to diagnose and discriminate between systemic autoimmune disorders.