The diagnostic value of anti-DNA antibodies depends on the technic used for their detection

Three anti-native DNA antibody detecting assays were compared using sera from 948 patients with clinical symptoms of connective tissue disease and 55 definite systemic lupus erythematosus patients. The Farr assay was more effective than the two other assays in the diagnosis of lupus. Anti-DNA antibody detection by ELISA was as sensitive as the Farr assay; in contrast indirect immunofluorescence on Crithidia luciliae had a significantly lower sensitivity, detecting less than one out of two cases of lupus detected. Particularly ELISA but also indirect immunofluorescence may give positive results in the absence of lupus, so that results obtained by each of these assays must be confirmed by the Farr assay if they are used in the diagnosis of lupus. The significance of antibodies detected by one assay but not by the others is discussed.     

DETECTION OF ANTI-DNA ANTIBODIES: A COMPARISON BETWEEN TWO FARR ASSAYS, CRITHIDIA LUCILIAE AND A HUMAN CHROMOSOMAL SUBSTRATE ASSAY

Four commercially available assays were compared with a ¹⁴CDNA Farr assay for their ability to detect anti-DNA antibodiesin 119 sera from 109 patients with systemic lupus erythematosus(SLE) and 25 control sera. The ¹⁴C DNA Farr assay was the mostsensitive and specific assay (SLE, 57% positive, controls, 0%).A commercial ¹²⁵I DNA Farr assay was significantly less sensitive(SLE, 39% positive). The fluorescence human chromosomal preparationassay was as sensitive as the ¹⁴C DNA Farr assay (SLE, 58% positive)but less specific (controls, 8% positive). The immunofluorescenceCrithidia luciliae assay was specific, but less sensitive (SLE,37% positive) than the MC DNA Farr assay. Adaptation of Crithidiato immunoperoxidase did not alter its sensitivity or performance.These results confirm that the ¹⁴C DNA Farr assay, locally refinedand performed by experienced hands, is the most sensitive andspecific assay for anti-DNA antibodies. The ¹²⁵I DNA Farr wasno more sensitive than the Crithidia assay but considerablymore laborious. The human chromosomal preparation may be suitableas a rapid screening test for anti-DNA antibodies. KEY WORDS: Anti-DNA antibodies, Systemic lupus erythematosus, Crithidia luciliae, Fair assay     

Enzyme immunoassay for antibodies to native DNA. Specificity and quality of antibodies

An enzyme immunoassay was developed to detect antibodies to native DNA; DNA coating conditions that maximized sensitivity, specificity, and reproducibility were selected. Sera of patients with systemic lupus erythematosus (SLE) were positive more frequently by this immunoassay than by the Crithidia luciliae assay or by counterimmunoelectrophoresis. By enzyme immunoassay, 94% of sera with active SLE and 70% of sera from patients with inactive SLE were positive, as were 16% from those suspected of having SLE, and 2.5% of normal persons. Specificity for native DNA was shown for both SLE and normal sera by inhibition studies and by S1 nuclease treatment of polystyrene-bound native DNA. The enzyme immunoassay correlated more with serum hemolytic complement levels that did the other 2 assays, suggesting that it detects biologically more relevant anti-DNA antibodies than do the other 2 tests.     

Enzyme immunoassay for antibodies to native DNA

An enzyme immunoassay was developed to detect antibodies to native DNA; DNA coating conditions that maximized sensitivity, specificity, and reproducibility were selected. Sera of patients with systemic lupus erythematosus (SLE) were positive more frequently by this immunoassay than by the Crithidia luciliae assay or by counterimmunoelectrophoresis. By enzyme immunoassay, 94% of sera with active SLE and 70% of sera from patients with inactive SLE were positive, as were 16% from those suspected of having SLE, and 2.5% of normal persons. Specificity for native DNA was shown for both SLE and normal sera by inhibition studies and by S1 nuclease treatment of polystyrene-bound native DNA. The enzyme immunoassay correlated more with serum hemolytic complement levels than did the other 2 assays, suggesting that it detects biologically more relevant anti-DNA antibodies than do the other 2 tests.     

The binding of antihistone antibodies to Crithidia luciliae kinetoplasts is growth cycle-dependent

The Crithidia luciliae immunofluorescence (CLIF) assay is widely used to test for native DNA (nDNA) antibodies in the diagnosis and management of systemic lupus erythematosus. However, sera from patients with drug-induced lupus erythematosus or rheumatoid arthritis, which should not contain nDNA antibodies, occasionally react with the CL kinetoplast. We examined 36 sera from patients with systemic lupus erythematosus, rheumatoid arthritis, Sj?gren's syndrome, and drug-induced lupus erythematosus, who had positive CLIF tests. All 36 sera were also antinuclear antibody-positive with homogeneous and/or peripheral staining patterns on mouse kidney substrates. After hydrochloric acid extraction of the CL smears to remove histone and other nuclear protein antigens, 14 of the 36 sera no longer produced a positive result on the CLIF test. Ten of these 14 sera again gave a positive CLIF result after the hydrochloric acid-extracted Crithidia substrate had been reconstituted with purified histone. These studies demonstrated that kinetoplast binding was due to antihistone antibodies in at least 10 of 36 initially CLIF-positive sera. Antihistone antibodies were then purified with a histone-affinity column, and these purified antibodies were reactive with CL kinetoplasts. Thus, the CLIF test is not specific for nDNA antibodies. Additional studies using CL from different days of culture indicated that histone antigen expression in the CL kinetoplast was a function of the life cycle of this organism and is most readily detected 2 days after initiation of culture.     

Identification of antinative DNA antibodies in cryoglobulinemic states.

Antinative DNA antibodies have previously been demonstrated in serum and in cryoglobulins of patients with systemic lupus erythematosus. We have studied serum and isolated cryoglobulins from patients with bacterial infection (four patients), essential mixed cryoglobullnemia (four patients), glomerulonephritis (four patients) and systemic lupus erythematosus (four patients), and have analyzed them for the presence of antinuclear and antinative DNA antibodies. Although six of 16 patients' cryoglobulins had peripheral antinuclear antibodies (ANA) at neutral pH, in 15 of 16 patients' specimens ANA was demonstrable after preincubation with acid buffer. Similarly, antinative DNA antibodies of the IgG class were demonstrable in four of 16 cryoprecipitates at neutral pH, whereas 15 of 16 were positive for IgG antinative DNA after acid incubation. IgG antinative DNA antibodies were shown to be concentrated in the cryoprecipitate with respect to serum antibody content. Native DNA was present in the cryoglobulins of 13 of 14 patients. Antinative DNA antibodies are, therefore, present in cryoglobulins in disease states other than systemic lupus erythematosus. The add incubation technic, which was employed in the determination of cryoglobulin antibody content, enhanced the measurable antibody titer, suggesting immune bound antibodies.     

Antideoxyribonucleic acid antibodies in Graves' disease

Antidouble stranded DNA (dsDNA) antibodies have been detected by a sensitive RIA in the sera of 28-100% of patients with Graves' disease, but it remains unclear whether these assays have detected authentic dsDNA antibodies. We have obtained sera from 42 patients with active Graves' disease and no known connective tissue disorders. All sera were tested for dsDNA antibodies by 2 quantitative RIAs (Farr assay and Millipore filter assay; normal, less than 20% for both assays) and by an enzyme-linked immunosorbant assay for antibodies to dsDNA and to single stranded DNA (ssDNA). All sera were negative for dsDNA antibodies by the Farr assay and by enzyme-linked immunosorbant assay, 2 of 42 had mildly elevated levels (33% and 23%) by the Millipore filter assay, and 7 of 42 were positive for ssDNA antibodies. The 2 positive sera for dsDNA antibodies were also tested using the Crithidia luciliae indirect immunofluorescence assay, and both were negative. Patients with Graves' disease have been reported to have an increased prevalence of antinuclear antibodies, but the more recent findings of dsDNA antibodies in these patients is of interest because dsDNA antibodies are considered to be specific for systemic lupus erythematosus. Our data suggest that true immunoglobulin G dsDNA antibodies are not elevated during active Graves' disease, and positive assay results may be due to measurement of ssDNA antibodies, immunoglobulin M dsDNA antibodies, or nonantibody DNA binding.     

Measurement of anti-DNA antibodies: a reappraisal using five different methods.

One hundred and thirty coded sera, 60 from patients with systemic lupus erythematosus (SLE) and 70 from patients with other autoimmune rheumatic diseases were tested for deoxyribonucleic acid (DNA) binding activity by five different types of assay. These were enzyme linked immunosorbent assay (ELISA) (distinguishing IgG and IgM anti-ssDNA and anti-dsDNA), Crithidia luciliae, a nitrocellulose filter assay, the Amersham kit, and another modified Farr assay, the radioimmunoassay (RIA) (UK). The Crithidia test was the most specific, none of the controls was positive, but the least sensitive (13% positive only). The RIA (UK) was the most sensitive (57% positive). In most of the assays 3-9% of the controls were positive. When the SLE sera were analysed according to disease activity the IgG anti-dsDNA ELISA, all three RIA values, and the Crithidia test values were raised in all the patients with severely active disease. Some patients with inactive disease, however, were positive in each of the tests. The best interassay correlations (r less than 0.49) were found between RIA (UK), and ss IgG and the Amersham kit; and between ds IgG and ss IgG. In the main, however, it was clear that different assays are dependent upon distinctive properties of DNA antibodies. It seems inevitable that most major rheumatology units will require more than one anti-DNA antibody assay.     

Detection of anti-dsDNA as diagnostic tool.

The diagnostic significance of anti-dsDNA determinations was evaluated in 2 different groups of patients. When the immunofluorescence technique (IFT) with Crithidia luciliae and the Farr assay with 3H-labelled-PM2 DNA were applied to a selected panel of 536 sera from patients with various well-defined autoimmune diseases, positive results were obtained only with serum samples from patients with systemic lupus erythematosus (SLE). On the other hand when we screened 4431 sera sent to our laboratory for diagnostic reasons, we observed a high incidence of antibodies to dsDNA in patients who did not fulfil the preliminary American Rheumatism Association's criteria for SLE and did not have the diagnosis SLE. Furthermore, a significant number of the positive sera showed peculiar behaviour in that they were positive only in the IFT on Crithidia luciliae and not in the Farr assay.     

Anti-nucleosome antibodies in the diagnosis of systemic lupus erythematosus

OBJECTIVE: To study the prevalence and diagnostic significance of antibodies against nucleosomes in patients with systemic lupus erythematosus (SLE) as compared to five anti-nuclear antibody (ANA) assays. METHODS: The study included 305 patients with SLE, 125 patients with other autoimmune rheumatic diseases, and 415 healthy controls. Anti-nucleosome antibodies were measured by an enzyme-linked immunosorbent assay (ELISA) and ANA by immunofluorescence (IF) using Hep-2 cells. Anti-double-stranded DNA (anti-dsDNA) antibodies were measured by three commercial ELISAs and by IF using Crithidia luciliae as antigen. RESULTS: Compared to three ELISAs for anti-dsDNA, the anti-nucleosome assay was less sensitive (30% vs. 29-69%) but equally specific (90% vs. 77-95%) for SLE. The most sensitive test was ANA (76%), and the least sensitive was Crithidia (13%). The correlations between the different assays were good (p < 0.001 for all comparisons). CONCLUSION: The anti-nucleosome antibody assay does not offer additional information compared to conventionally used anti-dsDNA tests in the differential diagnosis of SLE.     

The clinical significance of measuring different anti-dsDNA antibodies by using the Farr assay, an enzyme immunoassay and a Crithidia luciliae immunofluorescence test.

Anti-double-stranded DNA (dsDNA) antibodies are highly specific for the diagnosis of systemic lupus erythematosus (SLE) but are heterogeneous in respect to, for example, avidity, class and cross-reactivity. Sera from 2061 patients were measured by three methods: an enzyme-linked immunosorbent assay (ELISA), an indirect immunofluorescence test with Crithidia luciliae as substrate (CLIF), and the Farr assay, a radioimmunological method based on the ammonium sulfate precipitation of immune complexes. The different anti-dsDNA antibody determinations were evaluated by analysis of patient records. The reason for a reactive Farr assay in 14 patients was predominantly the measurement of antibodies of the IgM class, which are not detected by the ELISA. The detection of additional antibodies to dsDNA of the IgA class, to single-stranded DNA or to histones plays a minor role. In comparison with the Farr assay, we found more positive results with the ELISA, which additionally detects anti-dsDNA antibodies of low avidity. The ELISA might also yield positive values in conditions such as chronic liver diseases, various infections and connective tissue diseases other than SLE. Avoiding the disadvantages of radioactivity, the ELISA is well suited as a screening test for dsDNA antibodies. However, positive results should be confirmed by the CLIF test or preferably by the Farr assay, thus combining sensitivity with specificity.     

Titration emulation: a computer-assisted technique that simplifies the quantification of anti-dsDNA antibodies using the Crithidia luciliae assay.

Titers of anti-double-stranded (ds) DNA antibodies in sera from patients with systemic lupus erythematosus (SLE) using the Crithidia luciliae assay method were compared by conventional titration vs the titration emulation method (ImageTiter) to evaluate whether the latter assay can replace manual titration. Titers by the two methods were identical or within one dilution in 98% (41/42) of samples. A single sample showed a two-dilution difference. Titration emulation showed a tendency to under-estimate the titer of high titer anti-dsDNA samples, although the difference was small. Titration emulation is a suitable alternative to the conventional titration method, offering an accurate and cost-effective approach to quantification of anti-dsDNA antibodies.     

Anti-DNA antibodies of IgA class in patients with systemic lupus erythematosus

Summary Sera obtained from 53 patients with systemic lupus erythematosus (SLE) were investigated for the presence of immunoglobulin class-specific antibodies against native (ds)DNA and denatured (ss)DNA. The methods employed were the Crithidia luciliae test and an enzymelinked immunosorbent assay (ELISA), respectively. Anti-dsDNA antibodies of IgG class were seen in 42%, IgM-anti-dsDNA antibodies in 43%, and IgA-anti-dsDNA antibodies in 30% of the patients. There was an association between the presence of both IgG- and IgA anti-dsDNA antibodies and the activity of the disease. Patients with active nephritis also had anti-dsDNA antibodies of IgG and IgA class significantly more often than patients with inactive nephritis or without renal disease. IgG-anti-ssDNA antibodies were seen in 89%, IgM-anti-ssDNA antibodies in 51%, and IgA-anti-ssDNA antibodies in 66% of the patients. Patients with nephritis had low levels of antibodies to ssDNA of IgM class. We suggest that immunoglobulin class-specific anti-DNA antibodies should de determined in the diagnosis and monitoring of SLE.     

Antidouble stranded DNA antibody assays in systemic lupus erythematosus: correlations of longitudinal antibody measurements

To determine whether different assays of antidouble stranded DNA (anti-dsDNA) antibodies provide comparable information in quantitative antibody assessment over time, longitudinal correlations between 3 anti-dsDNA antibody methods were derived. Determinations of anti-dsDNA antibody levels on serial samples from 9 patients with systemic lupus erythematosus (SLE) were performed by filter binding radioimmunoassay, enzyme linked immunosorbent assay, and Crithidia indirect immunofluorescence. Substantial pairwise correlations among assay methods were found (r = 0.544 to 0.804; p less than 0.001). In addition, anti-dsDNA antibody levels as measured by each assay were inversely correlated with levels of the 3rd component of complement. Our results indicate that changes in antibody levels as determined by these 3 methods closely parallel each other over time, and suggest that the array of anti-dsDNA antibodies detected in patient sera remains relatively constant over time.     

The significance of discrepant Farr and Crithidia luciliae tests

The most specific serological test for systemic lupus erythematosus (SLE) is the detection of anti-dsDNA antibodies by the Farr or Crithidia luciliae (CL) assay. Serological interpretation is difficult when these assays give discrepant results (i.e., one is positive and the other negative). In the present study 34 patients with discrepant results (18 CL positive Farr negative; 16 CL negative Farr positive) were reviewed to determine whether they fulfilled ARA criteria for SLE at presentation or at follow up 1-50 months (mean 15.8 months) later. Only 2 patients had SLE, both of whom fulfilled ARA criteria at presentation. Discrepant CL and Farr assays are associated with SLE uncommonly and rarely precede the development of clinical lupus.     

Effect of fibronectin on the Crithidia luciliae test for anti-double-stranded DNA antibodies.

The various tests for anti-double-stranded DNA antibodies do not always agree. Plasma fibronectin specifically binds DNA, is a component of immune complexes, and shows variations in concentration with disease activity in systemic lupus erythematosus. It may therefore interfere with the detection of DNA autoantibodies. This possibility was examined in a series of studies using the Crithidia luciliae test. Studies were based on serum samples received during one year (250 samples). Serum samples from 50 patients which were positive or weakly positive in the C luciliae test were used. In blocking experiments fibronectin was added either to the wells or to the serum. In a second series of experiments fibronectin was depleted by affinity chromatography from six serum samples with weak anti-DNA staining. Preincubation of wells with fibronectin or addition of fibronectin to serum invariably blocked the interaction of anti-DNA antibodies with the C luciliae kinetoplast. When fibronectin was removed from serum the intensity of staining was increased. These results indicate that fibronectin influences the detection of anti-double-stranded DNA antibodies using C luciliae and may explain the disparity between the results of different tests for DNA antibodies. Furthermore, the unmasking of positive reactivity when fibronectin is removed from serum has implications for the diagnosis and treatment of systemic lupus erythematosus.     

Cardiac abnormalities in patients with systemic lupus erythematosus.

OBJECTIVE: To determine the prevalence of cardiac abnormalities in patients with systemic lupus erythematosus. DESIGN: Prospective survey. SETTING: Rheumatic diseases unit of a university hospital. PATIENTS: Volunteer sample comprising 83% of patients with systemic lupus erythematosus followed annually in the rheumatic disease unit (93 patients; mean age 46 +/- 13 years; female 79, male 14). These patients were age-matched with 16 female control volunteers (mean age 43 +/- 5 years) recruited from hospital staff. INTERVENTIONS: Electrocardiograms, two-dimensional echocardiograms and radionuclide angiograms were performed in patients and controls. Anticardiolipin antibodies were measured by enzyme-linked immunosorbent assay in the systemic lupus erythematosus patients. MAIN RESULTS: At least one cardiac abnormality was detected in 44 of 93 systemic lupus erythematosus patients (47%). These abnormalities included: aortic valve thickening 12%; mitral valve thickening, prolapse, vegetations or stenosis 23%; left ventricular segmental dysfunction 4%; left ventricular global hypokinesis 4%; right ventricular hypokinesis 4%; left ventricular hypertrophy 14%; left ventricular diastolic dysfunction 16%; and pericardial effusion 2%. Three of the 16 controls (19%) had cardiac abnormalities consisting of mitral valve prolapse (one), right ventricular hypokinesis (one) and pericardial effusion (one). Cardiac abnormalities were more common in the systemic lupus erythematosus group compared with controls (47% versus 19%, P less than 0.05). Raised anticardiolipin antibodies were specific (88%) but not sensitive (33%) for the presence of cardiac abnormalities in systemic lupus erythematosus patients. Renal disease and prednisone therapy were more common in systemic lupus erythematosus patients with cardiac involvement than in such patients without evidence of cardiac disease (40% versus 16%, P = 0.03; and 81% versus 59%, P = 0.04, respectively). CONCLUSIONS: Cardiac abnormalities can be identified noninvasively in 47% of patients with systemic lupus erythematosus.     

An immunofluorescent method using Crithidia luciliae to detect antibodies to double-stranded DNA.

The immunochemical specificity of the immunofluorescent Crithidia luciliae method for detection of antibodies to double-stranded DNA (dsDNA) was confirmed by demonstrating abolition of staining by DNase digestion and by absorption with dsDNA. This method was less sensitive than a Millipore filter method for detecting antibodies to DNA. It was positive only in subjects with systemic lupus erythematosus or drug-induced antinuclear factors. This technique appears suitable for study of the immunochemical characteristics fo antibodies to dsDNA.     

Autoantibodies in alcoholic liver disease

PURPOSE: To test the hypothesis that since only a proportion of heavy drinkers develop significant alcoholic liver disease (ALD), an autoimmune pathogenesis is likely. PATIENTS AND METHODS: Autoimmune markers were measured in 47 patients with biopsy-proven ALD and compared to measurements in 20 alcoholics without clinical and hematologic evidence of ALD and 28 patients with autoimmune chronic active hepatitis (CAH). RESULTS: Twenty-two percent of patients with ALD were antinuclear antibody-positive, compared to 71% of patients with CAH. Approximately 60% of patients with ALD had either anti-single-stranded or anti-double-stranded DNA antibodies, slightly more than the patients with CAH. Another marker of autoimmunity, as in systemic lupus erythematosus, is the presence of IgM antibodies to autologous and heterologous lymphocytes, which are cytotoxic at 4 degrees C. Seventy-two percent of patients with CAH had positive antilymphocyte antibodies, compared to 59.6% of patients with ALD. Furthermore, more than 90% of the sera from ALD and CAH patients displayed lymphocytotoxicity. Thirty-two percent and 25.5% of CAH and ALD patients, respectively, had all three autoantibodies present. CONCLUSION: These results suggest that autoimmune mechanisms may indeed play a role in the pathogenesis of ALD in at least some patients.