Structural requirements of DNA used in the Farr assay to detect antibodies directed against double-stranded DNA

Summary The measurement of antibodies to DNA in SLE requires the use of double-stranded DNA (dsDNA), demonstrably free of single-stranded regions. Such dsDNA preparations can, however, contain other structural components. In this study DNA preparations with defined structure, both secondary (single- and double-stranded and random base-paired) and tertiary (superhelical and open circular), were used in the Farr assay to measure the DNA binding of sera from patients with SLE and related connective-tissue diseases. The presence of true single-stranded DNA regions in denatured DNA, native DNA, and dsDNA containing single-stranded regions increased the DNA binding measured in all sera. DsDNA, whether intact or containing small regions of random base-pairing, was bound by sera from the majority of patients with SLE but not by non-SLE sera. Superhelical dsDNA from bacteriophage PM2 was bound by SLE sera to a greater extent than linear dsDNA was. Inhibition experiments suggested that this difference in binding to DNA according to tertiary, as opposed to secondary, structure is because there are fewer available binding sites on super-helical dsDNA. DNA binding, as measured by the Farr assay, can thus be influenced by both secondary and tertiary DNA structure. Using superhelical DNA, advantage can be taken of the dsDNA form plus tertiary structure to enhance DNA binding of SLE sera beyond the levels achieved using linear dsDNA.     

Analysis of the complement-fixing potential of dsDNA/anti-dsDNA immune complexes

Summary Prepared antibody/³H-dsDNA immune complexes have been analyzed with respect to both primary binding (the Farr assay) and complement fixation (the RBC-CF assay). In SLE sera an average of only one-third of the anti-dsDNA antibodies fix complement upon binding dsDNA. However, this proportion can vary considerably for different sera. In the case of bacteriophage PM2 dsDNA, 1 antibody molecule per molecule of dsDNA is sufficient for binding in the Farr assay. However, an average of 4±1 complement-fixing antibodies must be bound to give 50% binding in the RBC-CF assay. Through an independent proximity analysis it was calculated that two adjacent antibodies bound to the DNA are required to form a complement-fixing unit.     

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.     

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 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.     

A sensitive solid phase microradioimmunoassay for anti-double stranded DNA antibodies

A sensitive solid phase microradioimmu-noassay has been developed for measurement of antidouble stranded DNA (dsDNA) antibodies. In this procedure, advantage has been taken of the capacity of poly-L-lysine (PLL) to facilitate the binding of pure dsDNA to plastic surfaces. In the absence of PLL, binding did not occur. Diluted sera were incubated in PLL-treated dsDNA-coated microtitration trays and anti-dsDNA Ig was measured using affinity purified¹²⁵I-anti-Ig of high specific activity. The synthetic DNA, poly dA-dT, was used as a model for dsDNA. In initial experiments, specific anti-DNA binding could not be demonstrated because of high background binding of patient Ig to PLL-treated surfaces. This was reduced by diluting test sera and anti-Ig in buffer containing 2% BGG and 1% BSA. Specificity of the assay for DNA was demonstrated by absorbing the anti-DNA activity on DNA-coated plastic. The binding of systemic lupus erythema-tosus (SLE) patient serum Ig to poly dA-dT coated trays did not diminish after digestion with nuclease S¹, suggesting that the synthetic polymer is an appropriate model for dsDNA. Patient and normal sera were screened for anti-dsDNA activity using poly dA-dT as antigen. None of the 38 normal sera, 23 of 35 active SLE sera, 1 of 25 treated SLE, 4 of 35 rheumatoid arthritis, 3 of 35 scleroderma, and 1 of 13 polymyositis sera demonstrated positive anti-dsDNA activity. The anti-dsDNA values obtained in the radioimmunoassay correlated significantly with those obtained in the Crithidia luciliae assay.     

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     

Evaluation of an ELISA system for determination of class-specific antibodies to native and denatured DNA in man.

Enzyme-linked immunosorbent assays (ELISA) have been set up for determination of plasma IgG and IgM antibodies to native (n) and denatured (d) DNA. Normal male and female donors generally gave low values in the assays for IgG; IgM control values were higher, particularly in females. Mean values for patients with systemic lupus erythematosus (SLE) were greatly raised in all four categories of assay in relation to the control (female) group. Levels of IgG anti-nDNA in SLE correlated well with a standard diagnostic test (Farr), and this ELISA assay was more successful than Farr in discriminating between patients and normal females. No such correlation with Farr was found for IgM anti-nDNA. Correlations were found in SLE between levels of antibodies to nDNA and dDNA. Inhibition tests--including those with a plasmid DNA preparation containing no single-stranded regions--showed that most of the IgG antibodies determined in the 'native' assay were able to bind to nDNA and dDNA with comparable avidity, whereas most of those reacting in the 'denatured' assay could only bind dDNA. The former antibodies were probably directed against shared determinants on the deoxyribose-phosphate backbone and the latter against base-dependent structures not exposed in nDNA. Inhibition results for IgM assays were similar, though the predominance of antibodies specific for dDNA appeared less marked. ELISA assays could well prove more useful than established methods in diagnosis and monitoring of SLE and other diseases.     

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 for 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.     

Cross-reactivity of antiidiotypic antibodies with DNA in systemic lupus erythematosus

OBJECTIVE: To assess the functional relationship between antibodies reactive with DNA and antibodies reactive with the idiotypes (idiopeptides) of anti-DNA antibodies that are associated with systemic lupus erythematosus (SLE) in mice. METHODS: Antiidiotypic antibodies that appeared spontaneously in lupus mice, and others that were induced by immunization of normal, non-lupus mice, were analyzed for their reactivity by a range of direct binding, competition enzyme-linked immunosorbent assay (ELISA), and surface plasmon resonance (SPR) methods. Their reactions were assessed against synthetic peptides representing sequences of the V(H) region of anti-DNA monoclonal antibody (mAb) V-88, against the native mAb itself, and against mammalian DNA. RESULTS: In lupus mice, only sera with the highest reactivity against double-stranded DNA (dsDNA) also reacted with idiopeptides in ELISA, and this showed a strong statistical correlation. However, there was no significant relationship between antiidiotypic antibodies and anti-single-stranded DNA antibodies. Immunization of (BALB/c x NZW)F1 mice with idiopeptides p64 (V(H) residues 64-80) or p92 (V(H) residues 92-105) induced antibodies that reacted not only against the respective peptides, but also against the native parent anti-DNA mAb V-88. Furthermore, the immune antiidiopeptide antibodies cross-reacted with dsDNA. Competition SPR experiments with the BIAcore system supported this observation. The binding reaction of V(H) peptide p64 (representing the CDR-H2/FR-H3 region of V-88) with antiidiopeptide antibodies was inhibited by dsDNA. CONCLUSION: This study identified a unique set of autoantibodies in SLE. They react with both autoantibody idiotopes and with dsDNA, thus having a dual specificity for 2 autoantigens. Because these antiidiotope antibodies arise naturally during the development of lupus disease, and because they bind also to dsDNA, this provides a mechanism whereby the production of anti-dsDNA antibodies is stimulated. These idiotopes on autoantibodies in lupus act as natural mimotopes for inducing anti-dsDNA antibodies, which, due to their dual specificity, may significantly contribute to the pathology of nephritis in SLE.     

Anti-nucleosome antibody: significance in lupus patients lacking anti-double-stranded DNA antibody

OBJECTIVE: To investigate the clinical significance of anti-nucleosome antibodies in SLE patients lacking anti-double stranded DNA (dsDNA) antibodies. METHODS: IgG anti-nucleosome antibodies were detected by enzyme-linked immunosorbent assays (ELISA) in the sera of SLE patients. Anti-dsDNA antibodies were measured by Farr assays and ELISA, not only in the samples taken for anti-nucleosome testing, but also in sera obtained regularly during the follow-up. RESULTS: Ninety-eight (76.0%) out of 129 patients with SLE had anti-nucleosome antibodies. Twenty-five patients (19.4%) consistently showed little or no anti-dsDNA reactivity during the course of their disease, and among these anti-nucleosome antibodies were present in the sera of 15 (60.0%). Of the patients with anti-dsDNA-negative SLE, renal disorders were present in 8 patients (32.0%), all of whom had anti-nucleosome antibodies. Renal disorders were not found in patients (n = 10) who had neither anti-dsDNA nor anti-nucleosome antibodies. Other autoantibodies such as anti-Ro, anti-Sm and anti-cardiolipin were not associated with renal disorders in this group. The levels of anti-nucleosome antibody strongly correlated with the SLEDAI scores, but inversely correlated with serum complement levels in anti-dsDNA negative SLE patients. CONCLUSION: Our data suggest that the anti-nucleosome antibody may be a useful marker for diagnosis and activity assessment of anti-dsDNA negative SLE. Anti-nucleosome antibody may be an important factor for renal involvement in this subgroup of patients.     

Anti-dsDNA antibody assay: high specificity and sensitivity with a filtration radioassay in comparison to low specificity with the standard ELISA

OBJECTIVE: To evaluate whether a new fluid-phase filtration radioassay possesses both high sensitivity and specificity compared with the currently used ELISA and Farr assays. METHODS: Sequential sera (25 samples) from 9 patients with systemic lupus erythematosus (SLE), sera from 20 patients with SLE possessing anti-dsDNA antibodies by the Crithidia assay, 75 patients with rheumatoid arthritis possessing rheumatoid factors, 50 healthy control subjects, 767 from patients with type 1 diabetes, and a commercial standard serum sample were tested for anti-dsDNA antibodies with the 3 different assays. RESULTS: Of serial dilutions of a standard anti-dsDNA antibody sample, only the highest positive sample (50 IU/ml) in the ELISA and the highest 2 positive samples (50 and 25 IU/ml) in the Farr assay were above the normal range. In contrast, all dilutions (to 2.5 IU/ml) of the standard anti-dsDNA antibody sample were above the normal range in the filtration radioassay. Using the values of 50 healthy control subjects in each assay to define the normal range, all 25 sequential sera from 9 patients with SLE were positive. In addition, 20/20 of the SLE individual sera, 2/75 (2.7%) of the RA sera, and 12/767 (1.6%) of the diabetes sera were positive (signal above normal range) in the filtration radioassay. The SLE sera were further examined in 2 additional assays, ELISA and Farr assay, and both assays were less sensitive and specific compared with the filtration radioassay. CONCLUSION: The fluid-phase filtration radioassay demonstrated high sensitivity and specificity for the detection of anti-dsDNA antibodies in SLE, with the standard ELISA exhibiting lower specificity. We suggest that testing for anti-dsDNA antibodies can be improved using a fluid-phase filtration radioassay in comparison to commercial assays.     

Presence of antibodies against a cell-surface protein, cross-reactive with DNA, in systemic lupus erythematosus: a marker of the disease

Antibodies against a cell-surface protein, cross-reactive with double-stranded DNA, were detected in the serum of 25 patients with active human systemic lupus erythematosus (SLE), defined on the basis of the revised American Rheumatism Association classification. Among these sera, two did not display anti-DNA antibodies, as shown by Farr assay, solid-phase radioimmunoassay, and Crithidia luciliae test. Five other SLE patients were consecutively studied in active and remission states. Antibodies against the protein were detected in the serum of the 5 SLE patients when they were in active phase but not in the serum of the same patients in inactive phase of the disease. The anti-protein antibodies were not found in the serum of 10 inactive SLE patients or in the sera of 10 normal human controls, 10 patients with rheumatoid arthritis, 5 patients with scleroderma, and 4 patients with primary sicca syndrome. Taken together, these results strongly suggest that antibodies against this cell-surface protein could provide a better diagnosis marker and activity index than anti-DNA antibodies in SLE.     

Immunochemical conditions affecting the measurement of DNA antibodies using ammonium sulfate precipitation

The binding of serum to native DNA as detected by the Farr ammonium sulfate technic is subject to considerable variation dependent on reaction conditions. DNA-binding activity of normal sera was significantly increased in buffers of low pH or ionic strength, to the range of SLE sera. Conversely, without incubation at 37 C and 4 C, many SLE sera were within the normal range. Serum nuclease activity did not account for the absence of DNA-binding in normal sera. The presence or absence of serum complement did not affect binding. Both precipitating and nonprecipitating antibodies are detected using ammonium sulfate precipitation. Optimal conditions for specificity and sensitivity included use of a buffer of pH 8 with conductivity of 12.5 millimhos (equivalent of 0.15M sodium chloride), and incubation for one hour at 37 C and 24 hours at 4 C prior to addition of saturated ammonium sulfate.     

Relation of antivimentin antibodies to anticardiolipin antibodies in systemic lupus erythematosus.

Tests for antivimentin antibodies (AVA) were performed on 50 systemic lupus erythematosus (SLE) and 63 control sera by indirect immunofluorescence and enzyme linked immunosorbent assay (ELISA). The prevalence was significantly raised in SLE (38% and 50% of sera positive for IgM-AVA and IgG-AVA, respectively, by immunofluorescence; 36% and 64% of sera positive for IgM-AVA and IgG-AVA, respectively, by ELISA) in comparison with the control sera. A significant correlation existed between IgM-AVA, on the one hand, and anticardiolipin antibodies (ACA) and anti-single-stranded DNA (ssDNA), on the other. A stepwise principal component analysis demonstrated that IgM-AVA and IgG-AVA accounted for 71% of the total variance in SLE (50 patients x 5 parameters = total variance). Twenty ACA positive serum samples from patients with syphilis were therefore tested for the presence of AVA, but hardly any were found to be positive. IgM-AVA from patients with SLE were inhibited by cardiolipin and absorbed with ssDNA. An association between AVA positivity and arthralgia was also shown in SLE.     

Autoantibodies in Greek juvenile chronic arthritis patients.

The aim of this study was to investigate sera of Greek patients with juvenile chronic arthritis (JCA) for the presence of autoantibodies and correlate these antibodies with the clinical picture and disease activity. Sera from 69 JCA patients and sera from 66 healthy children matched for sex and age, were tested for antinuclear antibodies (ANAs), antibodies to extractable cellular antigens (ENAs), rheumatoid factor (RF), immunoglobulins (IgG, IgM), antibodies to double stranded (ds) DNA and anticardiolipin (CL). Our results indicate that: (a) autoantibodies to dsDNA are a not uncommon finding in JCA sera; (b) these autoantibodies have a low affinity for the antigen since they are found in low titers only by ELISA, while the Farr assay and Crithidia lucilliae immunofluorescence assay (IF) are negative; and (c) active JCA patients express many autoantibodies.     

Assessment of antibodies to double-stranded DNA induced in rheumatoid arthritis patients following treatment with infliximab, a monoclonal antibody to tumor necrosis factor alpha: findings in open-label and randomized placebo-controlled trials

OBJECTIVE: To compare the incidence of anti-double-stranded DNA (anti-dsDNA) antibodies in rheumatoid arthritis (RA) patients receiving either single or multiple doses of a chimeric anti-tumor necrosis factor alpha (anti-TNFalpha) antibody or placebo infusions, with or without methotrexate, in open-label, randomized, placebo-controlled trials. METHODS: Multiple sera obtained from 156 patients before and after treatment with infliximab and from 37 patients treated with placebo infusions were tested for anti-dsDNA antibodies by 3 methods: Crithidia luciliae indirect immunofluorescence test (CLIFT), a commercial Farr assay (Ortho Diagnostics radioimmunoassay [RIA]) in which the antigen source is mammalian DNA, and a Farr assay employing 125I-labeled circular plasmid DNA (Central Laboratory of The Netherlands Red Cross Blood Transfusion Service [CLB] RIA). Patients with positive findings on the CLIFT were also tested for antibodies to histones (H1-H5) and chromatin and for IgM rheumatoid factors (IgM-RFs). RESULTS: None of the RA patients had a serum sample that was positive for anti-dsDNA antibodies by the CLIFT prior to infliximab therapy. Of the 22 patients who developed a positive CLIFT result, 11 (7% of 156 exposed to infliximab) also had positive findings on the Ortho RIA at a concentration of >10 units/ml and another 8 (5%) were positive at a concentration of >25 units/ml. In all but 1 patient, the anti-dsDNA antibodies were solely of the IgM isotype. Only 1 patient had detectable anti-dsDNA antibodies by the CLB RIA. All sera containing anti-dsDNA by the CLIFT contained antibodies to chromatin, and sera from 2 patients also contained antibodies to histones. IgM-RF titers showed a significant reduction following infliximab therapy in these 22 patients. One patient developed anti-dsDNA antibodies of IgG, IgA, and IgM isotype and had positive results on both Farr assays (peaking at 22 weeks and resolving by 54 weeks); this was associated with a reversible lupus syndrome. CONCLUSION: Anti-dsDNA antibodies of IgM class are induced by infliximab therapy; the frequency is dependent on the assay method used. Only 1 of the 156 patients who were treated with infliximab developed a self-limiting clinical lupus syndrome; that patient developed high titers of anti-dsDNA antibodies of IgG, IgM, and IgA class, as detected by the CLIFT and by 2 different Farr assays.     

Autoantibodies to lipoprotein lipase and dyslipidemia in systemic lupus erythematosus

OBJECTIVE: To demonstrate the binding of bovine lipoprotein lipase (LPL) by IgG from sera obtained from patients with systemic lupus erythematosus (SLE) and other rheumatic diseases, and the relationship of anti-LPL to triglyceride levels in SLE. METHOD: Binding of LPL by IgG from sera obtained from patients with SLE and other rheumatic diseases was measured by an enzyme-linked immunosorbent assay technique. Lipid profiles for fasting blood samples obtained from SLE patients and control subjects were determined. RESULTS: Sera obtained from 105 patients with SLE were assessed for reactivity with LPL, and 49 (47%) of the results were positive. Sera obtained from patients with rheumatoid arthritis (RA) (n = 80), Sj?gren's syndrome (n = 30), polymyositis and dermatomyositis (n = 30), and progressive systemic sclerosis (n = 31) were also studied, and 10 (13%), 3 (10%), 12 (40%), and 13 (42%), respectively, were positive for reactivity with LPL. It was determined that all affinity-purified anti-double-stranded DNA (dsDNA) antibodies and 4 of 5 monoclonal anti-dsDNA antibodies bound to LPL. The binding of IgG depleted of anti-dsDNA to LPL indicates a second anti-LPL activity in SLE. Measurements of fasting lipid levels in SLE patients with anti-LPL revealed a strong positive correlation of antibody levels and total serum triglycerides, apolipoprotein B, and apolipoprotein E concentrations. CONCLUSION: Antibodies to LPL occurred in 47% of SLE patients and in a similar percentage of patients with polymyositis or systemic sclerosis. The prevalence of these antibodies was less in patients with RA or Sj?gren's syndrome. It is hypothesized that the elevated triglyceride levels in SLE patients are in part attributable to anti-LPL, and this lipid abnormality could contribute to the premature atherosclerosis known to be present in patients with SLE.     

Low avidity antibodies to dsDNA as a diagnostic tool.

An evaluation of the diagnostic value of low avidity antibodies to double stranded DNA (dsDNA) measured by the polyethylene glycol (PEG) assay was undertaken. By routine screening low avidity anti-dsDNA were detected in the serum samples of 106 hitherto unknown patients. Clinical data of these patients were collected and when only low avidity anti-dsDNA was present (n = 92) a varied disease spectrum was observed. A diagnosis of systemic lupus erythematosus (SLE) was established in 48/92 (52%), lupus-like disease in 21/92 (23%), autoimmune hepatitis in 9/92 (10%), rheumatoid arthritis in 8/92 (9%), and mixed connective tissue disease in 2/92 (2%) of all patients. Patients with definite SLE were all older than 45 years and predominantly female (46/48, 96%). They showed a remarkably low incidence of renal disease (2/69, 3%). When high avidity antibodies to dsDNA as measured by the Farr assay were present as well (n = 14) a diagnosis of SLE could be established in 12/14 (86%) of all patients, indicating the secondary importance of low avidity anti-dsDNA in these patients.     

Anti-gamma-globulin activity, DNA and antibodies to DNA in nonlupoind cryoglobulinemias.

Anti-gamma-globulin activity, free DNA, and DNA binding were studied in 19 cryoglobulinemias: 8 patients with Waldenstr?m's disease (WD), 9 patients with essential cryoglobulinemia (EC), and 2 with chronic aggressive hepatitis (CAH). Antihuman gamma-globulin activity was detected in all sera and dissolved cryoprecipitates but two from EC and one from the CAH group. By diphenylamine assay we found DNA in two sera from WD and in one serum and cryoprecipitate from EC. An antibody to denaturated DNA was shown only in sera from the two patients with CAH and from one patient with EC. Nonspecific binding was more frequent.