Anti-nucleosome, anti-chromatin, anti-dsDNA and anti-histone antibody reactivity in systemic lupus erythematosus

Comparison of two anti-histones antibodies commercial assays in an immunology laboratory and systemic lupus erythematosus

BACKGROUND

Anti-histones antibodies (AHAs) are antibodies directed against histone proteins - structural proteins that provides scaffolding for DNA to be wrapped around. AHAs, measured in the serum, are diagnostically helpful in cases of systemic lupus erythematosus (SLE) and drug-induced lupus erythematosus (DILE). In the diagnostic laboratory, they may be measured by enzyme-linked immune-sorbent assay (ELISA) or line immunoassays (LIA); however, the performance of these have never been directly compared in the literature.

METHODS

We evaluated a commonly used commercial ELISA and LIA to compare the performance in our immunology laboratory. Retrospective and prospective analyses were undertaken over a 5.5-year period. We also examined their performance in the model disease of SLE and compared their performance to disease activity and the main clinical features.

RESULTS

One hundred and thirty-five patients were evaluated including 65 SLE patients. Based on the quantitative cut-offs, there was only moderate agreement between the two assays (κ = 0.444). Both assays only had modest agreement with the clinical situation of the evaluated patients. When considered within the SLE context, both assays were moderately correlated with disease activity. Positive AHAs by ELISA were associated with SLE cytopaenias, and both ELISA and LIA correlated with positive anti-double stranded DNA.

CONCLUSIONS

Moderate agreement analytically were seen between ELISA and LIA methods in a general laboratory cohort. Both assays were comparable in their diagnostic performance. ELISA detection of AHAs appears to have some clinical use in our cohort of SLE patients. Future studies are required to explore the clinical utility of AHAs in SLE and other disorders.

Clinical use of anti-histone antibodies in idiopathic and drug-induced lupus

Anti-histone antibodies (AHAs) make their appearance in a number of systemic autoimmune diseases including systemic lupus erythematosus (SLE) and drug-induced lupus erythematosus (DILE). Although being known for over 50 years, they are poorly studied and understood. There is emerging evidence for their use in predicting clinical features of SLE, diversifying their clinical use. AHAs, however, are probably less prevalent in DILE than once thought owing to a move away from older DILE drugs to modern biological agents which do not appear to elicit AHAs. This review examines the historical studies that have defined AHAs and looks at some of the recent work with these autoantibodies.

Epitope-Specific Anti-C1q Autoantibodies in Systemic Lupus Erythematosus

Objective

In patients with systemic lupus erythematosus (SLE) complement C1q is frequently targeted by autoantibodies (anti-C1q), that correlate best with active renal disease. Anti-C1q bind to largely unknown epitopes on the collagen-like region (CLR) of this highly functional molecule. Here we aimed at exploring the role of epitope-specific anti-C1q in SLE patients.

Methods

First, 22 sera of SLE patients, healthy controls and anti-C1q positive patients without SLE were screened for anti-C1q epitopes by a PEPperMAP^® microarray, expressing CLR of C1q derived peptides with one amino acid (AA) shift in different lengths and conformations. Afterwards, samples of 378 SLE patients and 100 healthy blood donors were analyzed for antibodies against the identified epitopes by peptide-based ELISA. Relationships between peptide-specific autoantibodies and SLE disease manifestations were explored by logistic regression models.

Results

The epitope mapping showed increased IgG binding to three peptides of the C1q A- and three of the C1q B-chain. In subsequent peptide-based ELISAs, SLE sera showed significantly higher binding to two N-terminally located C1q A-chain peptides than controls (p < 0.0001), but not to the other peptides. While anti-C1q were associated with a broad spectrum of disease manifestations, some of the peptide-antibodies were associated with selected disease manifestations, and antibodies against the N-terminal C1q A-chain showed a stronger discrimination between SLE and controls than conventional anti-C1q.

Conclusion

In this large explorative study anti-C1q correlate with SLE overall disease activity. In contrast, peptide-antibodies are associated with specific aspects of the disease suggesting epitope-specific effects of anti-C1q in patients with SLE.

Anti-dsDNA Testing Specificity for Systemic Lupus Erythematosus: A Systematic Review

BACKGROUND

Autoantibody specificity in autoimmune diseases is variable due to each patient's individual spectrum of autoantibodies and the inherent differences between detection methods and tests. Since false-positive results have downstream consequences, we conducted a comprehensive assessment of anti-double stranded DNA (anti-dsDNA) specificity from published studies of systemic lupus erythematosus (SLE).

METHODS

A systematic review (MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and Database of Abstracts of Reviews of Effects) identified cross-sectional or case-control studies published January 2004 to August 2019, reporting anti-dsDNA test accuracy data in SLE. Study quality was assessed using Quality Assessment Tool for Diagnostic Accuracy Studies, version 2. A meta-analysis was conducted to estimate specificity by test method or named test where feasible.

RESULTS

Thirty studies were included covering 43 different tests. The Crithidia luciliae indirect immunofluorescence test (CLIFT) and fluorescence enzyme immunoassay methods are likely to be ≥ 90% specific (Euroimmun 97.8% (95% CI 96.2%-98.7%) 4 studies; EliA 94.7% (95% CI 91.7%-96.7%), 6 studies; CLIFT 98.7% (95% CI 96.7%-99.5%), 8 studies/7 tests]. For other test methods, specificity was not fully demonstrated to be ≥ 90% and/or the control group included healthy patients possibly overestimating specificity. More studies are required for NOVA Lite [96.0% (95% CI 87.2%-98.9%), 5 studies], chemiluminescence immunoassays [92.3% (95% CI 83.6%-96.6%), 6 studies/4 tests], multiplex immunoassays [89.3% (95% CI 86.1%-91.8%), 4 studies/2 tests], and Farr fluorescent immunoassays (no estimate, 2 studies). Specificity data reported for Farr radioimmunoassays [93.8% (95% CI 85.4-97.5%), 11 studies, 9 tests] and enzyme-linked immunosorbent assays [93.4% (95% CI 89.9%-95.7%), 15 studies/16 tests] lacked consistency.

CONCLUSION

Anti-dsDNA testing shows considerable variation in test specificity, with potential impact on the management of SLE patients. This review may help laboratory specialists and clinicians choose and interpret the appropriate anti-dsDNA test for their setting.

Clinical Performance of Two Automated Immunoassays, EliA CTD Screen and QUANTA Flash CTD Screen Plus, for Antinuclear Antibody Screening

Background

Recently, two fully automated immunoassays for antinuclear antibody (ANA) screening were introduced EliA CTD Screen (Thermo Fisher Scientific, Freiburg, Germany) and QUANTA Flash CTD Screen Plus (Inova Diagnostics, San Diego, USA). We evaluated their clinical performance in comparison with the indirect immunofluorescence assay (IIFA) and analyzed samples with discrepant results.

Methods

In total, 406 serum samples (206 from patients undergoing routine checkups and 200 from rheumatology clinic patients) were assayed using EliA, QUANTA Flash, and IIFA. We evaluated assay concordance and agreement and confirmed the presence of anti-extractable nuclear antigen (ENA) antibodies in samples with discrepant automated immunoassay and IIFA results. Additionally, we compared the clinical performance of each assay in diagnosing ANA-associated rheumatic disease (AARD) and adjusted the cut-off values.

Results

In rheumatology clinic samples, the concordance and agreement were 91.5% and strong between EliA and QUANTA Flash, 79.0% and weak between EliA and IIFA, and 80.5% and moderate between QUANTA Flash and IIFA, respectively. In automated immunoassay-positive, IIFA-negative samples (N=15), all anti-ENA antibodies detected (6/15) were anti-Sjögren’s syndrome antigen A/Ro (Ro60) antibodies. The automated immunoassays and IIFA showed high accuracy for diagnosing AARD, and adjusted cut-off values improved their sensitivities (EliA with 0.56 ratio, 82.9% sensitivity; QUANTA Flash with 9.7 chemiluminescent units, 87.8% sensitivity).

Conclusions

The two automated immunoassays showed reliable performance compared with IIFA and can be efficiently used with the IIFA in clinical immunology laboratories. Clinical cut-off values can be adjusted according to the workflow in each laboratory.

Autoantibodies spectrum in lupus nephritis in a cohort of Egyptian patients: relation to disease activity and prognostic value

Background

Specific autoantibodies are considered as an important marker in autoimmune rheumatic diseases and are of great value for the diagnosis and prognosis of systemic lupus erythematosus (SLE) patients. A total of eighteen autoantibodies were analyzed for their positivity in SLE patients and we evaluated the clinical relevance of the five most frequent autoantibodies: anti-dsDNA, anti-nucleosome, anti-histone, anti-Ro60, and anti-Ro52 on disease activity and renal affection in SLE Egyptian patients.

Results

Immunological profile and correlation of the five autoantibodies with disease activity and histopathological pattern of renal involvement were analyzed for 190 SLE patients. Lupus nephritis (LN) patients showed much worse constitutional and mucocutaneous manifestations than patients without nephritis. Autoantibody profile showed a significant increased frequency of anti-dsDNA, anti-nucleosome, anti-histone, anti-Ro-60, and anti-Ro52 antibodies in LN patients. The impact of the co-positivity of the autoantibodies on the renal function was obvious. Moreover, the disease activity increased by the increased frequency of autoantibodies positivity in LN patients. ROC curve analysis showed that anti-nucleosome had the highest sensitivity; 93% followed by anti-dsDNA 83.3% then anti-histone 73.8%, but anti-Ro60 and anti-Ro52 showed a humble sensitivity. Furthermore, the highest frequency of positivity for the five autoantibodies was found in class-III and class-IV LN patients.

Conclusion

Detection of anti-dsDNA, anti-nucleosome, anti-histone, and anti-Ro60 in SLE patients may be important for predicting disease progression and kidney affection. Moreover, anti-nucleosome and anti-dsDNA show high sensitivity and specificity for lupus nephritis, thus patients with four to five positive autoantibody panels should be kept under close monitoring as they may warrant considering aggressive therapy to control their disease and prevent renal damage.

Reconstructing a 3-dimensional image of the results of antinuclear antibody testing by indirect immunofluorescence

Indirect immunofluorescence anti-nuclear antibody testing (IIF-ANAT) is an essential screening tool in the diagnosis of various autoimmune disorders. ANA titer quantification and interpretation of immunofluorescence patterns are determined subjectively, which is problematic. First, we determined the examination conditions under which IIF-ANAT fluorescence intensities are quantified. Next, IIF-ANAT was performed using homogeneous, discrete speckled, and mixed serum samples. Images were obtained using Bio Zero BZ-8000, and 3-dimensional images were reconstructed using the BZ analyzer software. In the 2-dimensional analysis, homogeneous ANAs hid the discrete speckled pattern, resulting in a diagnosis of homogeneous immunofluorescence. However, 3-dimensional analysis of the same sample showed discrete speckled-type ANA in the homogeneous background. This study strengthened the current IIF-ANAT method by providing a new approach to quantify the fluorescence intensity and enhance the resolution of IIF-ANAT fluorescence patterns. Reconstructed 3-dimensional imaging of IIF-ANAT can be a powerful tool for routine laboratory examination.

Redefining the Scl-70 indirect immunofluorescence pattern: autoantibodies to DNA topoisomerase I yield a specific compound immunofluorescence pattern

Objectives. To report on a novel IIF pattern specifically associated with antibodies to DNA topo I.

Methods. A novel compound IF pattern, designated Scl-70 pattern, was characterized in routine ANA-HEp-2 IIF screening. Within the last 3 years, all serum samples presenting the Scl-70 pattern at the ANA-HEp2 IIF screening were tested for anti-topo I reactivity. Conversely, 16 serum samples with known anti-topo I reactivity and affinity-purified anti-topo I antibody preparations were tested for the Scl-70 pattern.

Results. The Scl-70 pattern comprised the staining of five cellular regions: nucleus, nucleolus and cytoplasm in interphase cells; nucleolar organizing region (NOR) and chromosomes in mitotic cells. All 81 serum samples selected as Scl-70 pattern reacted with topo I. All 16 anti-topo I samples and antibody preparations reproduced the Scl-70 pattern. This compound IF pattern was consistently observed in different commercial HEp-2 cell slides and in home-made slides with HEp-2 cells and human fibroblasts fixed with alternative protocols. Double IIF experiments demonstrated the co-localization of topo I and human upstream binding factor at the NOR.

Conclusions. The Scl-70 pattern belongs to the group of compound IF patterns that hold strong association with the respective autoantibody specificities, such as that observed with centromere protein F (CENP-F) and nuclear mitotic apparatus-1 (NuMA-1) protein. The identification of the Scl-70 pattern at routine ANA-HEp-2 IIF screening may lead to implementation of specific tests for the identification of anti-topo I antibodies. In addition, the Scl-70 pattern outlines cellular domains other than those previously reported for topo I, which is of interest for further understanding the roles of this enzyme in cell biology.

Anti-chromatin and anti-histone antibodies in Egyptian patients with systemic lupus erythematosus

There has been a renewed interest in anti-chromatin and anti-histone antibodies in the last few years. To assess the prevalence of anti-chromatin and anti-histone antibodies in patients with systematic lupus erythematosus (SLE) and to correlate serum levels of these antibodies with clinical features of the disease, the presence of anti-chromatin and anti-histone antibodies in 38 patients with SLE was investigated by an enzyme-linked immunosorbent assay (ELISA). To determine the specificity of these antibodies, 15 patients with rheumatoid arthritis, 15 patients with systemic sclerosis, and 15 normal controls were also tested. Sensitivity of anti-chromatin antibodies in SLE patients was 89.5% and specificity was 80.0%, while sensitivity of anti-histone antibodies was 92.1% and specificity was 82.2%. Significant associations were found between the levels of anti-chromatin antibodies and arthritis, malar rash, oral ulcer, pulmonary affection (P < 0.05) also, lupus nephritis (P < 0.01), and disease activity score as measured by SLE disease activity index (SLEDAI; P < 0.001). Significant association was found between anti-histone antibodies and fatigue (P < 0.05). The incidence of positive anti-chromatin and anti-histone antibodies was significantly higher than that of anti-dsDNA antibodies in early stage of the disease. We conclude that anti-chromatin and anti-histone antibodies are both sensitive and specific for SLE and could be a useful addition to the laboratory tests that can help in the diagnosis of SLE. Anti-chromatin antibodies seem to be a promising marker useful in early diagnosis and assessment of disease activity in SLE patients especially in patients who are negative for anti-dsDNA antibodies.

Anti-histones antibodies in systemic lupus erythematosus: prevalence and frequency in neuropsychiatric lupus

To investigate the specificity, sensitivity, and concomitant presence of antibodies against histones (H), histone H1 (H1), and histone H3 (H3) in patients with systemic lupus erythematosus (SLE) and analyze their association with SLE. Serum IgG anti-histones antibodies were detected by enzyme-linked immunosorbent assay in 144 SLE patients consisting of 24 neuropsychiatric lupus (NPSLE), 65 lupus nephritis (LN), and 55 SLE, 100 other rheumatic diseases patients, as well as 40 healthy controls. Clinical and biological parameters of the patients were also evaluated. Anti-H, anti-H1, and anti-H3 antibodies yielded a sensitivity of approximately 33% and a specificity of more than 93% for SLE, which was comparable to that found for anti-double-stranded DNA (anti-dsDNa) antibodies. More significantly, anti-histone antibody is found in approximately 50% of patients with NPSLE compared with LN. Moreover, the titers of anti-histones antibodies of NPSLE patients were significantly higher than that of patients with SLE and LN. The sequential analysis revealed a close correlation of anti-H and anti-H1 antibodies with SLE disease activity. There was an approximate 30% positive rate of anti-histones antibodies in 144 SLE patients lacking anti-nucleosome, anti-mDNA, anti-Sm, and anti-dsDNA antibodies. Antibodies to histones H1 and H3 are markers with high specificity of 93.6-96.4% for SLE. The anti-histone antibody markers are prevalent in approximately 50% of NPSLE. Furthermore, there was a strong correlation with SLE disease activity index and levels of antibodies to histones and H1.

Antinucleosome antibodies correlate with the disease severity in children with systemic lupus erythematosus

We compared the serum levels of antinucleosome antibodies (anti-NCS Abs) in thirty pediatric systemic lupus erythematosus (SLE) patients by using enzyme-linked immunosorbent assay (ELISA) to 29 adult SLE patients, 30 healthy controls, 21 juvenile idiopathic arthritis (JIA) and 23 Henoch-Schonlein purpura (HSP) patients as autoimmune disease controls. The mean anti-NCS Ab titer in the pediatric SLE patients was 1552.7+/-1842.2 U/ml, higher than those of adult SLE patients (194.3+/-402.7 U/ml), normal controls (9.5+/-5.7 U/ml) and disease controls (JIA: 7.7+/-4.0 U/ml, HSP: 5.7+/-4.4 U/ml) (p<0.05). The prevalence of both anti-NCS Ab (90%) and anti-ds DNA Ab (76.7%) in pediatric SLE patients were higher (p<0.05) than that of adult SLE patients (58.6% and 48.3%). A positive correlation was demonstrated between anti-NCS Ab and anti-dsDNA Ab as well as the SLEDAI scores in pediatric and adult patients (p<0.05). The inverse correlation of anti-NCS Ab levels with C3 was observed in both pediatric and adult SLE patients (pediatrics, r=-0.61, p=0.0003; adult, r=-0.44, p=0.02). Our data suggested that in pediatric SLE patients, anti-NCS Ab could be as good a marker for SLE diagnosis and disease activity assessment as in adult SLE patients.

Present and future of the autoimmunity laboratory

At present, autoimmunity laboratories are very dynamic owing to the constant and increasing availability of new tests, mainly due to the detection of new autoantibodies. The main characteristic of the autoimmunity laboratory and the one that differentiates it from other laboratories that use immunoassays as basic techniques is that it determines antibodies (autoantibodies) and not antigens. For this reason, immunoassay techniques must employ antigens as reagents. Indirect immunofluorescence has and continues to be a basic technique in autoimmunity studies. However, over the last few years, a significant trend at autoimmunity laboratories has been the gradual replacement of immunofluorescence microscopy by immunoassay. Of the several different forms of immunoassay, the enzyme-linked immunosorbent assay (ELISA) format is the one most used in autoimmunity laboratories. Recombinant DNA technology has allowed the production of large quantities of antigens for autoantibody analysis. Flow cytometry for the analysis of microsphere-based immunoassays allows the simultaneous measurement of several autoantibodies. Likewise, autoantigen microarrays provide a practical means to analyse biological fluids in the search for a high number of autoantibodies. We are now at the beginning of an era of multiplexed analysis, with a high capacity of autoantibody specificities. Future trends in this field include immunoassays with greater analytical sensitivity, simultaneous multiplexed capability, the use of protein microarrays, and the use of other technologies such as microfluidics.

The Relevance of Autoantigen Source and Cutoff Definition in Antichromatin (Nucleosome) Antibody Immunoassays

In the last few years, several reports have shown that chromatin (nucleosome) represents the main autoantigen-immunogen in systemic lupus erythematosus (SLE) and that specific antibodies are an important marker of the disease. To verify the clinical sensitivity and specificity of antinucleosome autoantibodies (ANuAs), we evaluated three ELISA immunoassay methods using different autoantigen preparations: Quanta Lite Chromatin, Medizym Anti-nucleo, and Nucleosome IgG Elisa. We compared the results with those obtained using two ELISA assays for determining anti-native DNA (anti-nDNA) antibodies: Axis-Shield and EliA dsDNA. We tested sera from 321 patients: 101 with SLE and 220 controls-48 with infectious diseases; 73 with autoimmune rheumatic disease (20 with rheumatoid arthritis, 30 with systemic sclerosis, and 23 with primary Sjögren's syndrome), and 99 healthy subjects. Using the manufacturer-recommended cutoff, the sensitivity for the three kits was 69%, 78%, and 74%, and specificity was 100%, 94.6%, and 95.0%, respectively. Using the cutoff corresponding to 95% specificity, the sensitivity of the methods for the ANuA assay was 86%, 77%, and 74%-higher than obtained with the two ELISA methods for anti-nDNA (65% and 64%). This study demonstrates that (1) the commercial reagents employed in clinical laboratories for ANuA detection show good sensitivity and high specificity; (2) ANuAs are more sensitive than anti-nDNA antibodies for diagnosing SLE; and (3) different solid-phase antigen preparations and methods used to define cutoff levels may affect a test's clinical performance.