Application of anti-DFS70 antibody and specific autoantibody test algorithms to patients with the dense fine speckled pattern on HEp-2 cells

Discriminating between Homogeneous (AC-1) and Dense Fine Speckled (AC-2) Antinuclear Antibody Patterns: Re-Evaluation of Immunofluorescence Imaging

Antinuclear antibodies (ANAs) are essential diagnostic markers in systemic autoimmune rheumatic diseases. Among the 30 ANA patterns, homogeneous (AC-1) and dense fine speckled (AC-2) should be focused on owing to their somewhat indistinct presentation in immunofluorescence imaging and distinct correlation with clinical conditions. This study aimed to develop a flowchart to guide discrimination between AC-1 and AC-2 patterns and to re-evaluate ANA samples according to this flowchart to verify its detection ability. We re-evaluated immunofluorescence imaging of 62 ANA blood samples simultaneously subjected to solid-phase assays for autoantibodies against dsDNA, nucleosomes, histones, and DFS70. The results showed statistically significant odd ratios (ORs) of detection of anti-DFS70 using AC-2 after re-evaluation of total samples (OR 101.9, 95% CI 11.7-886.4, p-value < 0.001) and subgroup analysis of patients' samples (OR 53.8, 95% CI 5.9-493.6, p-value < 0.001). The OR of anti-nucleosome/histone/dsDNA detection using AC-1 in re-evaluated data increased to 5.43 (95% CI 1.00-29.61, p-value = 0.05). In the analysis of specific autoantibodies, more than half of the samples with an AC-2 pattern (54.2%) had specific autoantibodies other than anti-DFS70. We conclude that the flowchart for discriminating between AC-1 and AC-2 ANA patterns in this study is a viable practical guide for other laboratories when encountering equivocal ANA results.

The Prevalence and Clinical Relevance of the DFS Immunofluorescence Staining Pattern in a Large ANA-Positive Cohort

Background

Although the dense fine speckled (DFS) immunofluorescence staining pattern has been studied by various researchers in recent years, its clinical associations remain unspecified. Thus, we performed a retrospective study in a non-selective population to explore the prevalence of this enigmatic antinuclear antibody (ANA) pattern and to determine its possible clinical associations with any identifiable pathology.

Methods

We retrieved the results of ANA testing ordered by various departments in 2019 to study the prevalence of DFS pattern. Demographic characteristics and clinical features of these participants were also collected from the electronic medical record system. Correlation analysis was made to study its clinical associations and a p-value < 0.05 was considered statistically significant.

Results

The prevalence of ANA positivity was 37.4% among 72,204 serum samples of which the median age was 44 (interquartile range: 31, 56) years old and 68.0% were women. The prevalence of the DFS staining pattern was 1.1% in the total population and accounted for 3.1% in the ANA-positive population. There were 97.6% of these cases displaying the DFS pattern with a low titer of ANA (≤1:320; starting serum dilution: 1:100). We found that this pattern correlated with several pathological conditions, such as skin disorders (25.1%), alopecia (4.6%), and obstetric complications (6.6%).

Conclusion

The presence of the DFS immunofluorescence staining pattern may accompany several pathological conditions and may be a signal of localized inflammation within certain organs or tissues, especially the skin.

Anti-DFS70 Antibodies for Differentiating Systemic Autoimmune Rheumatic Disease in Patients with Positive ANA Tests: A Systematic Review and Meta-Analysis

Anti-DFS70 antibodies have been proposed as a marker to exclude systemic autoimmune rheumatic disease (SARD). We conducted this systematic diagnostic test accuracy review and meta-analysis to determine the performance of anti-DFS70 antibodies in patients with a positive anti-nuclear antibody (ANA) test result to exclude SARD. We searched PubMed, Embase, Web of Science, Scopus and the Cochrane Library up to 22 February 2021, and included studies examining the diagnostic accuracy of anti-DFS70 antibodies in patients with a positive ANA test result. The results were pooled using a hierarchical bivariate model and plotted in summary receiver operating characteristic curves. R software and Stata Statistical Software were used for the statistical analysis. Eight studies with 4168 patients were included. The summary sensitivity was 0.19 (95% confidence interval: 0.12–0.28) and the specificity was 0.93 (95% confidence interval: 0.88–0.96). The area under the curve was 0.69 (95% confidence interval: 0.64–0.72). The meta-regression analysis showed that targeting only ANA-associated rheumatic disease was associated with higher specificity. In addition, the studies with a non-SARD prevalence of <80% and using a chemiluminescence assay were associated with higher specificity. Anti-DFS70 antibodies have high specificity for the exclusion of SARD among patients presenting with a positive ANA test, but the sensitivity is low.

Assessment of antinuclear antibodies (ANA): National recommendations on behalf of the Croatian society of medical biochemistry and laboratory medicine

Antinuclear antibodies (ANA) represent a family of autoantibodies targeting ubiquitous cellular constituents and are a hallmark of systemic inflammatory autoimmune rheumatic diseases named connective tissue diseases (CTD). The gold standard method for ANA determination is indirect immunofluorescence (IIF) on the human laryngeal epidermoid carcinoma cell line type 2 substrate (HEp-2), but with increasing demand for ANA testing, novel methods eased for automation emerged, which allows testing by staff less experienced in this specific field of laboratory diagnostic. In 2016 The working group (WG) for laboratory diagnostics of autoimmune diseases as part of the Committee for the Scientific Professional Development of the Croatian Society of Medical Biochemistry and Laboratory Medicine (CSMBLM) published the data of a survey regarding general practice in laboratory diagnostics of autoimmune diseases in Croatia. Results indicated high diversity in the performance of autoantibody testing as well as reporting of the results and indicated the need of creating recommendations for the assessment of ANA that would help harmonize diagnostics of systemic autoimmune rheumatic diseases in Croatia. This document encompasses twenty-seven recommendations for ANA testing created concerning indications for ANA testing, preanalytical, analytical, and postanalytical issues, including rational algorithm and quality control assurance. These recommendations are based on the relevant international recommendations and guidelines for the assessment of ANA testing and relevant literature search and should help to harmonize the approach in ANA testing and clarify differences in interpretation of the results obtained using different methods of determination.

Twenty years of research on the DFS70/LEDGF autoantibody-autoantigen system: many lessons learned but still many questions

The discovery and initial characterization 20 years ago of antinuclear autoantibodies (ANAs) presenting a dense fine speckled (DFS) nuclear pattern with strong staining of mitotic chromosomes, detected by indirect immunofluorescence assay in HEp-2 cells (HEp-2 IIFA test), has transformed our view on ANAs. Traditionally, ANAs have been considered as reporters of abnormal immunological events associated with the onset and progression of systemic autoimmune rheumatic diseases (SARD), also called ANA-associated rheumatic diseases (AARD), as well as clinical biomarkers for the differential diagnosis of these diseases. However, based on our current knowledge, it is not apparent that autoantibodies presenting the DFS IIF pattern fall into these categories. These antibodies invariably target a chromatin-associated protein designated as dense fine speckled protein of 70 kD (DFS70), also known as lens epithelium-derived growth factor protein of 75 kD (LEDGF/p75) and PC4 and SFRS1 Interacting protein 1 (PSIP1). This multi-functional protein, hereafter referred to as DFS70/LEDGF, plays important roles in the formation of transcription complexes in active chromatin, transcriptional activation of specific genes, regulation of mRNA splicing, DNA repair, and cellular survival against stress. Due to its multiple functions, it has emerged as a key protein contributing to several human pathologies, including acquired immunodeficiency syndrome (AIDS), leukemia, cancer, ocular diseases, and Rett syndrome. Unlike other ANAs, "monospecific" anti-DFS70/LEDGF autoantibodies (only detectable ANA in serum) are not associated with SARD and have been detected in healthy individuals and some patients with non-SARD inflammatory conditions. These observations have led to the hypotheses that these antibodies could be considered as negative biomarkers of SARD and might even play a protective or beneficial role. In spite of 20 years of research on this autoantibody-autoantigen system, its biological and clinical significance still remains enigmatic. Here we review the current state of knowledge of this system, focusing on the lessons learned and posing emerging questions that await further scrutiny as we continue our quest to unravel its significance and potential clinical and therapeutic utility.

Clinical significance of anti-DFS70 antibody in antinuclear antibody-positive samples with a dense fine speckled pattern

Background

When the dense fine speckled (DFS) pattern-antinuclear antibodies (ANA) are detected in the indirect immunofluorescence (IIF) assay, the presence of anti-dense fine speckles 70 (DFS70) antibodies has been suggested to facilitate the exclusion of ANA-associated rheumatic diseases (AARD). We evaluated the potential use of anti-DFS70 antibodies for verifying AARD in patients with a positive ANA result of the DFS pattern.

Methods

A total of 5509 patients who were requested ANA testing were included. The DFS pattern was confirmed using two IIF assays. Semiquantitative DFS70 ELISA (Euroimmun, Germany) was examined in samples with the DFS pattern.

Results

Among 639 ANA-positive patients, 19.6% displayed the DFS pattern. And 17.6% of patients with the DFS pattern were diagnosed with AARD. The low titer of 1:80 was more prevalent in the non-AARD group than in the AARD group (64.1% vs. 4.5%, p < 0.0001). Anti-DFS70 antibodies were positive in 60.0% of patients with the DFS pattern. The frequency of anti-DFS70 positivity was higher in the non-rheumatic disease (NRD) group (74.2%) than in the other rheumatic disease group (43.2%, p = 0.003) and the AARD group (45.5%, p = 0.019).

Conclusions

The DFS pattern is present in both AARD and non-AARD cases. In the DFS pattern, a low titer of 1:80 and isolated anti-DFS70 antibodies without AARD-associated antibodies represent a low likelihood of AARD. The presence of anti-DFS70 antibodies cannot exclude AARD and should be analyzed in combination with AARD-associated antibodies in the diagnostic algorithm.

Prevalence and serological profile of anti-DFS70 positive subjects from a routine ANA cohort

Anti-Dense Fine Speckled 70 (DFS70) antibodies are a common finding in clinical laboratory referrals. High prevalence of DFS70 autoantibodies in healthy population and usual negative association with Antinuclear Antibody (ANA)-associated autoimmune rheumatic diseases (AARD) were reported. The aim of this study was to evaluate the prevalence of DFS70 autoantibodies and their association with other autoantibodies in the context of a routine ANA referral cohort. Consecutive sera submitted for ANA screening were analyzed for anti-DFS70 antibodies by indirect immunofluorescence (IIF) (n = 3175, 1030 men and 2145 women) then confirmed by immunoblotting. Anti-DFS70 positive samples were also assayed for a large spectrum of other circulating autoantibodies. The prevalence of anti-DFS70 antibodies was 1.7% in the whole population and 4.6% in the ANA-positive samples. Comparison between DFS70 IIF and immunoblotting showed an excellent correlation between the two methods. The prevalence of anti-DFS70 positive was significantly higher in females (2.1%, 45/2145) than in males (1.0%, 10/1030). Of note, no concomitant autoantibodies were found in the DFS70-positive male group compared with DFS70-positive females group that showed other serum autoantibodies in the 51% of cases. Anti-DFS70 reactivity in male population may represent an useful biomarker predicting the absence of other autoantibodies. On the contrary, the serological profile of DFS70-positive females required further investigations in order to define the presence of concomitant disease-marker autoantibodies.

Recognition and Relevance of Anti-DFS70 Autoantibodies in Routine Antinuclear Autoantibodies Testing at a Community Hospital

Antinuclear autoantibodies (ANA) displaying a dense fine speckled pattern (DFS, ICAP AC-2) on HEp-2 cells are frequently observed in clinical laboratory referrals, often associated with anti-DFS70 specificity. Anti-DFS70 positive patients rarely develop systemic autoimmune rheumatic disease (SARD), especially in the absence of clinical evidence or additional anti-extractable nuclear antigen (ENA) antibodies, prompting suggestions that an isolated DFS70-specific ENA may be an exclusionary finding for SARD. In this study, the frequency and diagnostic significance of anti-DFS70 autoantibodies was investigated in a community hospital cohort of patients undergoing routine ANA testing. ANA screening was performed by HEp-20-10-based indirect immunofluorescence, followed by ENA profiling using a multiparametric line immunoassay (LIA). Of 6,511 patient samples tested for ANA in 2016, the DFS pattern was identified in 1,758 (27.0%), 720 (41.0%) of which were anti-DFS70 positive by LIA. Of these, 526 (73.1%) revealed isolated anti-DFS70 reactivity, while 194 (26.9%) showed additional ENA specificities. Among 1,038 anti-DFS70 negative or borderline samples, 778 (75.0%) were ENA profile negative, while the remaining 260 (25.0%) showed a varied presence of other ENA specificities. Chart reviews of patients with an isolated anti-DFS70 ANA affirmed that ANA-related SARD is rare in the absence of clinical evidence or other ENA specificities, there being no case thus far identified. Rheumatoid arthritis patients occasionally had an isolated anti-DFS70 ANA and were positive for rheumatoid factor and anti-cyclic citrullinated peptide antibodies. In conclusion, the recognition of a DFS ANA pattern using a mitotic-rich HEp-2 substrate, followed by confirmation of anti-DFS70 specificity should be a routine ANA testing service. Use of an expanded ENA profile and clinical correlation is necessary to affirm the "isolation" of anti-DFS70 as the cause of an ANA. Recognition of isolated anti-DFS70 ANA enables reassurance of patients that SARD is unlikely, thus avoiding referral for more extensive testing. The presence of significant elevations of other ENAs may reflect SARD and warrants close clinical correlation and follow-up.

Simultaneous Distinction of Monospecific and Mixed DFS70 Patterns During ANA Screening with a Novel HEp-2 ELITE/DFS70 Knockout Substrate

Systemic autoimmune connective tissue disorders are characterized by circulating antinuclear antibodies (ANA). Although there are several technologies available for ANA screening, indirect immunofluorescence (IIF) using Human epithelial cells-2 (HEp-2) substrate remains the primary and recommended method because of its superior sensitivity. HEp-2 substrates can detect a multitude of patterns resulting from autoantibody binding to various protein and nucleic acid autoantigens distributed throughout the nucleus and cytoplasm of the cells. The great diversity of monospecific and mixed patterns resulting from positive reactions on HEp-2 substrate also complicate the interpretation and accuracy of reporting. One specific example which received utmost attention recently is the dense fine speckled 70 (DFS70) pattern resulting from autoantibodies that specifically bind to a protein called lens epithelium derived growth factor (LEDGF). Lack of clear association with a specific systemic autoimmune disease and high prevalence in healthy populations have made accurate interpretation of DFS70 pattern important. Accurate distinction of DFS70 pattern from disease-associated patterns using conventional HEp-2 substrate is challenging. Moreover, frequent co-occurrence of DFS70 pattern along with disease-associated patterns such as homogeneous, speckled, and mixed homogeneous-speckled patterns complicate the IIF interpretation. The goal of this paper is to demonstrate the utility of a novel engineered HEp-2 IIF substrate that retains all advantages of conventional HEp-2 substrate while simultaneously providing the ability to distinguish DFS70 pattern with high confidence in both monospecific and mixed ANA positive examples. The new substrate is further able to unmask disease-associated ANA patterns previously concealed by DFS70 pattern.

The Clinical Relevance of Anti-DFS70 Autoantibodies

Despite all the progress in the establishment of specific autoantibody assays, screening for antinuclear antibodies (ANA) by indirect immunofluorescence on HEp-2 cells for quality-oriented laboratory diagnosis of ANA associated rheumatic diseases (AARD) remains indispensable but is not without limitations. Recent data on the relevance of the dense fine speckled (DFS) pattern and anti-DFS70 antibodies disclosed novel possibilities to optimize the serological stepwise diagnostics of AARD. The DFS pattern on HEp-2 cells is well differentiated from the classic "homogeneous" ANA pattern associated with dsDNA antibodies. This is the most frequent pattern in high titer ANA-positive healthy persons. The most characteristic ANA specificity associated with DFS pattern is the anti-DFS70 antibody (synonym LEDGF antibody). The prevalence of anti-DFS70 antibodies in AARD patients is significantly lower compared with the prevalence in ANA-positive healthy persons. There is a negative association between anti-DFS70 antibodies and AARD, especially if no concomitant AARD-specific autoantibodies are found. Isolated anti-DFS70 antibodies are detectable in less than 1 % of AARD but are detectable in 2-22 % of healthy persons. In the presence of an isolated anti-DFS70 antibody, the posttest probability for AARD is reduced significantly. The significance of anti-DFS70 antibodies as a criterion that helps to exclude AARD is also confirmed by follow-up studies on anti-DFS70 antibodies of positive, healthy individuals, who did not develop any AARD during a 4 year observation period. Consequently, anti-DFS70 antibodies are valuable novel biomarkers for better interpretation of positive ANA in cases of negative AARD-associated autoantibodies and should be integrated in modified test algorithms to avoid unnecessary referrals and examinations of ANA-positive persons.

Analysis of DFS70 pattern and impact on ANA screening using a novel HEp-2 ELITE/DFS70 knockout substrate

Indirect immunofluorescence (IIF) using human epithelial cell (HEp-2) substrate is a widely used and the recommended method for screening of antinuclear antibodies (ANA). Dense fine speckled (DFS70) pattern on HEp-2 has been widely reported in various healthy and disease groups. Interpretation of DFS70 pattern can be challenging on a conventional HEp-2 substrate due to its similarity to some of the disease associated patterns. The high prevalence of DFS70 autoantibodies in normal population, lack of association with a particular disease group and a general negative association with systemic and ANA associated autoimmune rheumatic diseases (SARD/AARD) necessitates the confirmation of DFS70 pattern. Results using available commercial assays for confirmation of DFS70 autoantibodies do not always agree with IIF screening results further complicating the lab work flow and ANA algorithms. In this review, we discuss the prevalence of DFS70 antibodies and factors affecting the performance of IIF and DFS70 specific confirmatory assays. Factors that contribute to disagreement between DFS70 suspicion by IIF and confirmatory assays will also be discussed. In addition, we also describe a novel IIF HEp-2 substrate, and its positive impact on DFS70 reporting and ANA screening-confirmation algorithm.

The prevalence and determinants of anti-DFS70 autoantibodies in an international inception cohort of systemic lupus erythematosus patients

Autoantibodies to dense fine speckles 70 (DFS70) are purported to rule out the diagnosis of SLE when they occur in the absence of other SLE-related autoantibodies. This study is the first to report the prevalence of anti-DFS70 in an early, multinational inception SLE cohort and examine demographic, clinical, and autoantibody associations. Patients were enrolled in the Systemic Lupus International Collaborating Clinics (SLICC) inception cohort within 15 months of diagnosis. The association between anti-DFS70 and multiple parameters in 1137 patients was assessed using univariate and multivariate logistic regression. The frequency of anti-DFS70 was 7.1% (95% CI: 5.7–8.8%), while only 1.1% (95% CI: 0.6–1.9%) were monospecific for anti-DFS70. In multivariate analysis, patients with musculoskeletal activity (Odds Ratio (OR) 1.24 [95% CI: 1.10, 1.41]) or with anti-β2 glycoprotein 1 (OR 2.17 [95% CI: 1.22, 3.87]) were more likely and patients with anti-dsDNA (OR 0.53 [95% CI: 0.31, 0.92]) or anti-SSB/La (OR 0.25 [95% CI: 0.08, 0.81]) were less likely to have anti-DFS70. In this study, the prevalence of anti-DFS70 was higher than the range previously published for adult SLE (7.1 versus 0–2.8%) and was associated with musculoskeletal activity and anti-β2 glycoprotein 1 autoantibodies. However, ‘monospecific’ anti-DFS70 autoantibodies were rare (1.1%) and therefore may be helpful to discriminate between ANA-positive healthy individuals and SLE.