False positive anti-Topoisomerase I (Scl-70) antibody results in clinical practice: A case series from a scleroderma referral center

PURPOSE

To determine if some patients who tested positive for anti-Scl-70 antibody in clinical practice, but did not have classifiable systemic sclerosis, were negative for anti-Scl-70 antibody by the more specific immunodiffusion method of testing.

METHODS

Patients evaluated by a rheumatologist at a Scleroderma referral center who had tested positive for anti-Scl-70 antibody prior to referral, but did not have classifiable SSc based on clinical criteria, were invited to undergo testing for anti-Scl-70 antibody by immunodiffusion. Patient demographics and clinical features were recorded at the time of their evaluation, and diagnostic testing results were reviewed using the medical records.

RESULTS

52 patients were enrolled over an 8-year period, with 48 (92.3%) testing negative and 4 (7.7%) testing positive for anti-Scl-70 antibody by immunodiffusion. Of the 48 patients who tested negative, 18 (37.5%) tested negative for ANA by indirect immunofluorescence, 33 (68.8%) did not have Raynaud's phenomenon, and 43 (89.6%) had ≤1 clinical criteria items based on the 2013 ACR/EULAR SSc classification criteria. Nevertheless, 21 (43.8%) patients who were negative for anti-Scl-70 antibody by immunodiffusion had undergone a chest CT and 14 (29.2%) had undergone an echocardiogram. A total of 23 patients had at least one follow up clinic visit. 3 out of 4 patients who were positive for anti-Scl-70 antibody by immunodiffusion, but none of the 19 patients who tested negative by immunodiffusion, developed sufficient criteria during follow up to be classified as SSc.

CONCLUSION

Assays for anti-Scl-70 antibody in commercial laboratories that are commonly utilized in clinical practice can produce false positive results. These results can lead to angst for patients, as well as unnecessary referrals and diagnostic evaluations.

The Effect of Anti-Scl-70 Antibody Determination Method on Its Predictive Significance for Interstitial Lung Disease Progression in Systemic Sclerosis

OBJECTIVE

The objective of this study was to assess the predictive significance of anti-Scl-70 (anti-topoisomerase I) antibodies, as determined by three different methods, for decline in forced vital capacity (FVC) within the first year of follow-up in patients with systemic sclerosis (SSc)-related interstitial lung disease (ILD).

METHODS

Patients in the Genetics Versus Environment in Scleroderma Outcome Study cohort who had ILD (verified by imaging) and available FVC% at enrollment, plus 12 to 18 months thereafter, were examined. All patients had a disease duration of 5 years or less at enrollment. The annualized percentage change in FVC% at 1 year follow-up was the outcome variable. Anti-Scl-70 antibodies were determined by passive immunodiffusion (ID) against calf thymus extract, chemiluminescent immunoassay (CIA), and line blot immunoassay (LIA).

RESULTS

Ninety-one patients with a mean disease duration of 2.36 years were included. Anti-Scl-70 antibodies by ID predicted a faster rate of FVC% decline (b = -0.06, P = 0.04). None of the other clinical or serological variables significantly predicted ILD progression. Interestingly, anti-Scl-70 antibodies as determined by CIA and LIA were not significant predictors of FVC decline (P = 0.26 and 0.64, respectively). The observed level of agreement between ID and LIA was moderate (κ = 0.568), whereas it was good between ID and CIA (κ = 0.66).

CONCLUSION

Anti-Scl-70 antibodies determined by ID predicted faster FVC decline in patients with SSc-related ILD. Notably, both CIA and LIA for the same antibody did not predict rate of FVC decline at their current cutoffs of positivity. The discrepancy observed between anti-Scl-70 antibody assays can have relevant implications for clinical care and trial enrichment strategies in SSc-ILD.

A device architecture for three-dimensional, patterned paper immunoassays

Diagnostic assays can provide valuable information about the health status of a patient, which include detection of biomarkers that indicate the presence of an infection, the progression or regression of a disease, and the efficacy of a course of treatment. Critical healthcare decisions must often be made at the point-of-care, far from the infrastructure and diagnostic capabilities of centralized laboratories. There exists an obvious need for diagnostic tools that are designed to address the unique challenges encountered by healthcare workers in limited-resource settings. Paper, a readily-available and inexpensive commodity, is an attractive medium with which to develop diagnostic assays for use in limited-resource settings. In this article, we describe a device architecture to perform immunoassays in patterned paper. These paper-based devices use a combination of lateral and vertical flow to control the wicking of fluid in three-dimensions. We provide guidelines to aid in the design of these devices and we illustrate how patterning can be used to tune the duration and performance of the assay. We demonstrate the use of these paper-based devices by developing a sandwich immunoassay for human chorionic gonadotropin (hCG) in urine, a biomarker of pregnancy. We then directly compare the qualitative and quantitative results of these paper-based immunoassays to commercially available lateral flow tests (i.e., the home pregnancy test). Our results suggest paper-based devices may find broad utility in the development of immunoassays for use at the point-of-care.

IgM, IgG, and IgA anti-DNA topoisomerase I antibodies in systemic sclerosis

BACKGROUND

Anti-DNA topoisomerase I (anti-topo I) antibodies have been broadly studied in systemic sclerosis (SSc). The use of different native and molecularly cloned antigens has shown a predominant IgG response, and a variable frequency of positive IgM and IgA tests. We report herein the serological findings of SSc using a recombinant topo I obtained through a standard bacterial system.

METHODS

Anti-topo I antibodies were studied in 45 SSc patients and 85 healthy controls through ELISA and western blot. Escherichia coli XL1-blue strain and pT7-7 vector were used to amplify a DNA topo I cDNA clone, and to obtain the recombinant polypeptide. The latter was purified by affinity chromatography, and the enzymatic and antigenic properties were evaluated through specific tests. A native antigen was included for comparison.

RESULTS

The SSc group disclosed positive IgM (20%), IgG (86.6%), and IgA (26.6%) anti-topo I tests with the recombinant polypeptide, and a purified calf thymus antigen yielded similar results. IgG autoantibodies were frequently associated with skin involvement, esophageal dysfunction, and restrictive lung disease. The recombinant protein showed a molecular weight of 86.6 kDa, a positive topo I activity using a supercoiled pBR322 DNA relaxation test, and its carboxyl terminus region was recognized by specific antibodies.

CONCLUSION

This report confirms that different immunoglobulin classes with anti-topo I activity may occur in SSc. IgG was the predominant serological feature with both, the recombinant and native antigens. The study also demonstrates the association between high levels of these autoantibodies and some clinical manifestations of SSc.

Screening Autoantibody Profiles in Systemic Rheumatic Disease with a Diagnostic Protein Microarray That Uses a Filtration-Assisted Nanodot Array Luminometric Immunoassay (NALIA)

Background: We developed a cost-efficient modular system for multiplex analysis of the multiple autoantibodies that characterize systemic rheumatoid diseases.

Methods: The nanodot array luminometric immunoassay (NALIA) system consists of conventional 96-well membrane-bottomed plates in which antigens or antibodies are adsorbed onto the underside of the membrane. Current arrays use a 5 × 5 format (25 dots/well), which allows 10 analytes to be measured in duplicate: double-stranded DNA (dsDNA), centromere protein B (CENP-B), PCNA, Sm, Sm ribonucleoprotein (Sm-RNP), U1-snRNP, Scl70, SSA/Ro, SSB/La, Jo-1, and controls. The test fluid, control sera, and subsequent reagents are drawn through the membrane. The captured analytes are quantified by monitoring chemiluminescence with a charge-coupled device (CCD) and analyzed with commercial array software.

Results: The assay can detect <20 × 103 IU/L of anti-dsDNA. The interwell CV was 10%–14%. There was an 83% concordance (κ = 0.56) between the NALIA results obtained for anti-dsDNA assayed by β-testing in a routine immunology diagnostic laboratory and the results obtained with a conventional ELISA reagent set. The concordance values for Ro, La, Sm, and RNP were 98% (κ, 0.92), 93% (κ, 0.41), 97% (κ, 0.62), and 97% (κ, 0.73), respectively.

Conclusion: The NALIA approach promises to provide a highly economical platform for a wide range of applications that require assays of multiple analytes. The degree of concordance of our results with a conventional reagent set was no less than that occurring between different commercial products. A sample of serum from a finger stick provides a volume sufficient to perform the array assay.

−238 and +489 TNF-α along with TNF-RII gene polymorphisms associate with the diffuse phenotype in patients with Systemic Sclerosis

OBJECTIVE

To investigate possible associations of TNF-alpha and TNF-RII gene polymorphisms with diffuse or limited skin involvement phenotype in a cohort of Systemic Sclerosis (SSc) patients.

METHODS

One-hundred and fourteen consecutive SSc patients attending the referral centres of three academic hospitals in Italy (University of Naples, Pavia and Udine), 56 with the diffuse (dcSSc) and 58 with limited (lcSSc) skin involvement subsets, and 170 healthy blood donors (HBDs) were included in the study. The extracted DNA was genotyped for the following polymorphisms: TNF-alpha (-238, +489) and TNF-RII (+196), using the polymerase chain reaction (PCR) and the restriction enzymes BamHI, HpyCH4 IV and NlaIII, respectively.

RESULTS

The AG/AA (presence of allele A) genotypes in position -238 and the AG genotype in position +489 of the TNF-alpha gene were found significantly increased in SSc, as a whole, when compared with healthy blood donors (chi(nu=2)(2)=4.48, p=0.03 for -238 and chi(nu=2)(2)=7.82, p=0.02 for +489, respectively). The rare GG genotype in exon 6 (codon 196) of the TNF-RII gene was also found increased in SSc compared to HBDs, even though the difference did not show statistical significance (chi(nu=2)(2)=3.56, p=0.17). The strength of the association was mainly due to the dcSSc phenotype (Fisher test, p=0.04 for -238, chi(nu=2)(2)=10.07, p<0.01 for +489 and chi(nu=2)(2)=6.25, p=0.04 for the +196 TNF-RII, respectively).

CONCLUSIONS

TNF-alpha and TNF-RII gene polymorphisms seem to contribute to the development of SSc and in particular to the diffuse phenotype.

Accuracy of semiquantitative immunoenzymatic methods in quantitation of anti-topoisomerase I (Scl-70) antibodies

Reports of a possible correlation between anti-Scl-70 antibody concentration and clinical manifestations in systemic sclerosis patients have recently appeared in the scientific literature. The goal of our study was to evaluate, by means of a multicenter study, the analytical reliability of immunoassay systems in the quantitative measurement of Scl-70 antibodies. Three blind samples (H, M, L) at different anti-Scl-70 antibody concentrations, and a low concentration antibody serum (LPC) used as a common calibrator, were sent three times in a 6-month time span to 39 Italian clinical laboratories. Each laboratory was asked to calculate dosages following the enzyme-linked immunosorbent assay (ELISA) method they used and report the optical density values of each sample (ODs), of the cutoff serum provided by the manufacturer of the kit used (ODco) and of LPC (ODLPC). The overall analytical imprecision (between methods and between laboratories) of the three different determinations of the values respectively expressed in ODs, ODs/ODco and ODs/ODLPCratio was 47.1, 52.8 and 34.0% for sample H, 56.2, 47.4% and 34% for sample M and 84.6, 86.0 and 86.6% for sample L. The average intra-method analytical imprecision was, respectively, 20.7, 29.8 and 18.6% for sample H, 24.6, 26.5 and 19.3% for sample M, and 30.6, 28.1 and 20.2% for sample L. The commercial ELISA methods currently used to determine the presence of anti-Scl-70 autoantibodies show considerable differences in the quantitative determination. The best results for reproducibility analyses have been obtained when the values were expressed as a ratio between the ODs of the sample and of the common calibrator (ODs/ODLPC). Forward-looking clinical studies that can clarify the usefulness of quantitative determination of anti-Scl-70 antibodies in the monitoring of diffuse scleroderma patients can be performed only when standard serum with a known antibody concentration and calibration curves for quantitative ELISA measurements are made available.

Guidelines for the laboratory use of autoantibody tests in the diagnosis and monitoring of autoimmune rheumatic diseases

The Italian Society of Laboratory Medicine Study Group on the Diagnosis of Autoimmune Diseases has generated a series of guidelines for the laboratory diagnosis and monitoring of systemic autoimmune rheumatic diseases intendedfor the use of clinical pathologists and laboratory physicians. These guidelines are based on a systematic review of published works and expert panel discussion and consist of 13 recommendations for antinuclear antibodies, anti-double-stranded native DNA, and antinuclear specific antibodies. To improve analytic performances and help select the most appropriate test for specific autoantibodies, as well as provide education and guidance in the use of these tests, special emphasis is placed on laboratory methods.