Clinical significance of antibodies to native DNA as measured by a DNA binding technique in patients with articular features of rheumatoid arthritis

Detection of antibodies to DNA: a technical assessment

Antibodies to DNA can be found in the circulation of the majority of patients with Systemic Lupus Erythematosus (SLE). They are quite specific for this disease, which makes their detection an important diagnostic aid to the clinician. Fluctuations in the level of anti-dsDNA in an individual patient generally parallel the clinical state of that patient. Furthermore, the presence of anti-dsDNA may precede the diagnosis of SLE by more than a year. Four methods relevant for the measurement of anti-dsDNA antibodies are discussed in this paper: the ELISA, the indirect immunofluorescence test on Crithidia luciliae, the PEG assay, and the Farr assay. Each of these methods detects a part of the spectrum of anti-dsDNA antibodies present in the circulation of an individual patient. The ELISA is the most sensitive method, whereas the Farr assay is the most specific for SLE. However, with the latter method only antibodies of a relative high avidity for DNA are detected. Mild forms of SLE, where patients only have anti-dsDNA of a low avidity in their circulation, may easily be missed by this technique. Clinically, high avidity anti-dsDNA is related with the more frequent occurrence of nephritis, whereas low avidity anti-dsDNA antibodies are more often found in patients with central nervous system involvement.

Anti-dsDNA: choice of assay in relation to clinical value

Antibodies to DNA are quite specific for systemic lupus erythematosus (SLE) and occur in the majority of SLE patients. Therefore, their detection is an important diagnostic aid to the clinician. Detection of anti-dsDNA may precede the diagnosis of SLE by more than a year. Fluctuations in the level of anti-dsDNA in an individual patient may give important information on the clinical status of the patient. Four of the most important methods developed for the measurement of anti-dsDNA antibodies will be discussed in this paper: the Farr assay, the PEG assay, the indirect immunofluorescence test on Crithidia luciliae and the ELISA. They will also be compared with one commercially available (Farr) assay, the Amersham anti-dsDNA kit. Each method, detects a part of the spectrum of anti-dsDNA antibodies produced by a patient. The Farr assay is the most specific for SLE; however, milder forms of the disease in which patients have only low avidity anti-dsDNA may easily be missed by this technique. Clinically, high avidity anti-dsDNA is related more frequently to the occurrence of nephritis, whereas low avidity anti-dsDNA antibodies are found more often in patients with central nervous system involvement. Traditionally, SLE is considered an immune-complex disease, in which inflammatory processes are initiated by local deposition of DNA/anti-dsDNA complexes. More recently, a major role was thought to be played by crossreactions of anti-dsDNA with tissue constituents. Our current view, however, is that such a crossreactivity plays only a minor role; we postulate that binding to glomerular constituents is caused by anti-dsDNA antibodies complexed with DNA and histones.

A comparison of assays used for the detection of antibodies to DNA

In this paper we will briefly compare four assays in use in our institute for the measurement of antibodies to DNA: the anti-DNA ELISA, the PEG assay, the indirect immunofluorescence test on Crithidia luciliae and the Farr assay. Although with the use of sera from defined patients with systemic lupus erythematosus (SLE) quite good correlations were obtained between the various assays, these correlations were lost upon the use in routine screening of sera of undefined patients. It will be shown that the Farr assay has the highest specificity to systemic lupus erythematosus, whereas the ELISA and the PEG assay are the most sensitive methods. In its present form, however, the ELISA is not suited for the detection of IgM anti-DNA. Furthermore, this technique alone also detects DNA/-anti-DNA complexes present in sera or hybridoma culture supernatants.

Antinuclear antibody determination: the present state of diagnostic and clinical relevance

Determination of antinuclear antibodies (ANA) will gain in diagnostic significance if a specific type of ANA can be related to a defined clinical disorder. The past decade has brought us quite a lot of papers dedicated to this subject. Yet, with exception of the DNA/anti-DNA system, observed correlations have remained scarce or contradictory. Also, still little is known about the pathogenic role of ANA. Perhaps more recent approaches using biochemical technologies will provide us with highly purified nuclear antigens necessary to study possible correlations at a more sophisticated level.

Specificity in systemic lupus erythematosus of antibodies to double-stranded DNA measured with the polyethylene glycol precipitation assay

Recently, a new radioimmunoassay--the polyethylene glycol (PEG) assay--was introduced to measure antibodies to double-stranded (ds) DNA. In this method, polyethylene glycol precipitation of formed 3H-DNA/antiDNA complexes is used instead of the ammonium sulfate precipitation used in the Farr assay. In contrast to the Farr assay, with which only high-avidity antibodies to dsDNA are detected, the PEG assay also reportedly measures anti-dsDNA of relatively low avidity. We studied whether this gain in antibody measurement results in loss of specificity for systemic lupus erythematosus. When the PEG assay was applied to a selected panel of 440 sera from patients with various well-defined autoimmune diseases and to a group of 197 normal human control sera, matched sex and age to the patients, the method was found to be fairly specific for systemic lupus erythematosus, although the sera from some patients with myasthenia gravis and some with autoimmune liver disease were also found positive. Screening of 352 additional serum specimens, sent to our laboratory for diagnostic reasons, revealed that, with the PEG assay, an extra population of relatively low-avidity antibodies to dsDNA--missed by the Farr assay--was detected. Upon clinical evaluation, we found that the patients in whom such antibodies were detected generally fulfilled a number of the preliminary criteria of the American Rheumatism Association for systemic lupus erythematosus, but that this diagnosis often was not made. We claim that the presence of low-avidity antiDNA characterizes a milder form of the disease in which patients often show only a single clinical feature of the disease. We conclude that results of the PEG assay add valuable diagnostic and clinical information to results obtained by the Farr assay.

[The Crithidia luciliae immunofluorescence test for detection of antibodies to double-stranded DNA (author's transl)]

For measurement of antibodies of double-stranded DNA (ds DNA) the Crithidia luciliae immunofluorescence test (C1-IFT) was compared with the Farr precipitation technique in diagnosis and management of systemic lupus erythematosus (SLE). The C1-IFT proved to be less sensitive in SLE patients without clinical disease activity, but the sensitivity of the test in those with active disease was comparable to that of the Farr test. In 76.9% of the patients' sera identical test results were obtained by both assays. In some sera antibodies were detected only by the C1-IFT. Positive test results in patients with diseases other than SLE were found more often with the Farr test. Thus, The C1-IFT seemed to be more specific for diagnosis of SLE. Measurement of titers using the C1-IFT provides a simple method to survey SL E disease activity. It allows to analyze the immunoglobulin classes of the reacting antibodies and their complement fixation ability in vitro. All three major immunoglobulin classes (IgG, IgM, IgA) were found to be present in the sera with high antibody titers, complement fixation in the C1-IFT could predominantly be detected is sera with high antibody titers.

DNA in synovial fluid and the circulation of patients with arthritis

DNA levels were measured in synovial fluids and sera of 106 patients with rheumatoid arthritis (RA), osteoarthritis (OA), gout, pseudogout, and posttraumatic arthritis (TRA). In synovial fluids, the highest concentration was found in rheumatoid arthritis (mean +/- SE 18 +/- 3 microgram/ml for seropositive and 9 +/- 1 microgram/ml for seronegative variants), gout and pseudogout (17 +/- 3 microgram/ml). In contrast, the levels in patients with OA or acute TRA were very low: 0.8 +/- 0.1 microgram/ml an 1.1 +/- 0.2 microgram/ml, respectively. The differences between the means of the first disease group and OA or TRA is statistically significant. A similar pattern was observed for DNA levels in the circulation: in rheumatoid arthritis, the mean concentration was 135 +/- 28 ng/ml and 164 +/- 39 ng/ml for seropositive and seronegative RA, respectively. Again the levels in OA and TRA were much lower, 52 +/- 18 ng/ml and 0 ng/Ml, respectively. The latter are not significantly different from the mean levels of 95 normal, healthy controls (14 +/- 3 ng/ml), whereas the concentration of DNA in the serum of RA patients is significantly higher than in OA, TRA, or normal controls. Serial determinations of DNA and other criteria of disease activity (leukocytes and protein levels in synovial fluid, blood sedimentation rate) in individual patients revealed a strong correlation of elevated values with active episodes. THe results suggest that these parameters reflect tissue damage.

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.

The clinical significance of the antinuclear antibody test as a screening procedure for DNA antibodies in SLE

During the two-year period (1st October 1974-30th September 1976), 2979 sera were tested for DNA antibodies by the Farr test. One thousand six hundred and ninety-five of these were tested because they had high ANA titres (1/256 or greater). In this group 285 sera were found to have raised DNA binding capacities (DNA-bc), 86 of which were found in patients having diagnoses other than SLE. When the diagnoses were reviewed following the finding of a raised DNA-bc, 55 of these patients were found to be suffering from SLE. Of the 1284 sera tested for DNA antibodies without the prior ANA screening procedures, 288 were positive, 36 of which came from patients not considered to have SLE; 30 of these patients were subsequently shown to have SLE. Thus the DNA-bc test is an important tool in the diagnosis of SLE, and the ANA test appears to be a valuable screening procedure. The level of DNA-bc was not of any diagnostic value.

Anti-native DNA detection by the Crithidia luciliae method: an improved guide to the diagnosis and clinical management of systemic lupus erythematosus

The clinical value of the Crithidia luciliae (CL) method for detection of antibodies to native DNA (nDNA) was assessed. Significant titers were limited almost exclusively to patients with active systemic lupus erythematosus (SLE). Evaluation of sera from patients at the onset of active lupus demonstrated elevated anti-nDNA levels in 80% of subjects with active disease and in 94% of patients with clinically evident lupus nephritis. In longitudinal studies, rising titers of anti-nDNA were invariably accompanied by exacerbation of lupus activity. These findings suggest that the CL method correlates more closely with active SLE than do other anti-DNA methods in common use and indicate that it will prove highly useful in the diagnosis and management of SLE.

Diagnostic significance of antibody to native deoxyribonucleic acid in children with juvenile rheumatoid arthritis and other connective tissue diseases

Sera of children with juvenile rheumatoid arthritis and other connective tissue diseases were tested for antibodies to native DNA by a radiolabeled-binding assay. Normal values were obtained in 130 children with JRA, including 28 with uveitis and 14 with selective IgA deficiency. Normal values were also found in sera from children with dermatomyositis, scleroderma, polyarteritis, ankylosing spondylitis, and a variety of other nonconnective tissue diseases. The only sera with elevated DNA-binding assays were from children with systemic lupus erythematosus. On the basis of these data, increased levels of antibodies to native DNA distinguished patients with active SLE from children with JRA.

A controlled study of ANA+ RF- arthritis

Thirty (7.5%) of 401 adult rheumatoid arthritis (RA) patients were antinuclear antibody positive (ANA+) and rheumatoid factor negative (RF-), and 15 of 16 patients who were followed for a year or longer remained so. Clinical, other laboratory, and radiographic parameters were compared among this group and 90 matched RA controls divided into ANA+RF+, ANA-RF+, and ANA-RF- groups. All groups were identical, except the ANA-RF- group, which had significantly fewer nodules and less destructive disease than the other three.

The clinical manifestations of systemic lupus erythematosus: a Cairo-Glasgow co-operative study

The clinical features of 78 patients with SLE seen in Cairo and Glasgow are reviewed. Raynaud's phenomenon was recorded more frequently here than in previous series. The value of serial measurements of anti-DNA antibodies, C3 and C4 in the management of SLE is discussed. Although antibodies to native DNA paralleled the disease course in only a minority of SLE patients anti-DNA antibodies were present during all major SLE exacerbations and could be diagnostically useful. Serious systemic infections complicating the management of SLE patients could occur and their diagnosis is discussed.