Analysis of DNA structure by hydroxyapatite columns and ethidium bromide fluorescence techniques. A comparative study and effect on DNA binding

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

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 superhelical 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.

Measurement of serum DNA binding in chronic active hepatitis and systemic lupus erythematosus using the Farr assay

Antibodies to double-stranded DNA (dsDNA), generally regarded as highly specific for systemic lupus erythematosus (SLE), have also been reported in chronic active hepatitis (CAH). Using the Farr assay and E. coli DNA, fractionated by benzoylated-naphthoylated-DEAE cellulose chromatography into dsDNA and dsDNA containing single-stranded regions, we compared the serum DNA binding of CAH and SLE patients. Although CAH sera were found to have dsDNA binding significantly above the normal control group such binding was of low level and we could find no evidence of markedly elevated dsDNA binding in CAH. However 12 of the 20 CAH sera studied did bind preferentially to dsDNA containing single-stranded regions suggesting the presence of anti-single-stranded DNA antibodies. We conclude that the description of elevated anti-dsDNA antibodies, as measured by the Farr assay, in CAH is due to the interaction of anti-single-stranded DNA antibodies or other serum components with single-stranded DNA contaminating dsDNA preparations.

Efficient generation in vitro, from human peripheral blood cells, of monoclonal Epstein-Barr virus transformants producing specific antibody to a variety of antigens without prior deliberate immunization

This paper describes a simple protocol for the efficient generation of large numbers of human monoclonal antibody-producing cells. This system is based on initial limiting-dilution culture after Epstein-Barr virus exposure of highly enriched precursors selected from peripheral blood mononuclear cells. Precursors can be enriched by using rosetting or panning approaches. Antibodies to erythrocytes, a mouse mammary carcinoma, DNA, and sperm antigens, produced without any deliberate immunization, are described. Large-scale human monoclonal antibody production may be facilitated by a combination of this protocol with a human cellular fusion system. For efficient precursor analysis and short-term (2 months or more) monoclonal antibody production, however, the system described here may be sufficient.

Neutropenia in rheumatoid arthritis: studies on possible contributing factors

Twenty-five patients with rheumatoid arthritis (RA) and neutropenia, of whom 19 had a palpable spleen, were compared with 24 patients with uncomplicated RA, and 16 patients with RA and associated splenomegaly without neutropenia. Clinically patients with neutropenia had evidence of a more systemic disease as assessed by prevalence of rheumatoid nodules, weight loss, and recurrent infections. However, there was less evidence of active synovitis than in the other 2 groups. Marrow neutrophil reserve was studied by means of a hydrocortisone stimulation test and was found to be lower in all 3 groups than in normal persons but with most marked depletion in the neutropenic group. Removal of the spleen in some patients with neutropenia resulted in a significant increase in marrow neutrophil reserve. Circulating immune complexes as detected by anticomplementary activity and platelet aggregation tests were detected in 68% of the RA neutropenia group, 31% of the RA splenomegaly group, and 8% of the uncomplicated RA group. Our results show that, assessed both clinically and by the above tests, patients with neutropenia have a greater prevalence of abnormalities which may be directly related to their neutropenia. Patients with splenomegaly alone closely resemble patients with uncomplicated RA.

A simple, rapid ELISA method for the detection of DNA antibodies

Employing an enzyme-linked immunosorbent assay (ELISA) technique the serum antibodies against native (double stranded) and denatured (single stranded) deoxyribonucleic acid (DNA) have been measured in various disease groups and a group of blood donor sera. The ELISA method has been compared with a radioimmunoassay method using native (double stranded) DNA is substrate antigen and a latex-fixation technique using particles coated with soluble deoxyribonucleoprotein (SNP). It is concluded that ELISA offers an economic and reliable alternative to isotope techniques for the assessment of antibody content in systemic lupus erythematosus (SLE) and related disease states for the clinical laboratory.

Seronegative chronic polyarthritis: clinical and serological correlates

Twenty-seven patients with chronic, active, seronegative polyarthritis were assessed clinically and serologically by accepted criteria for evidence of connective tissue diseases. The patients were divided into 2 groups, 13 positive for fluorescent antinuclear antibody (FANA) and 14 that were negative. All but 1 patient fulfilled the clinical criteria for the diagnosis of definite rheumatoid arthritis. Four patients (2 in each group) fulfilled the preliminary criteria for the classification of systemic lupus erythematosus. Antiperinuclear factor was positive in 5 of the FANA-negative patients, consistent with a diagnosis of rheumatoid arthritis. By contrast, this factor was absent in all the FANA-positive patients. Positive DNA binding was found in 7 of the FANA-positive patients, in high titre in 4, consistent with a diagnosis of 'minimal lupus' with predominantly 'unisystem' disease. DNA binding was positive in low titre in 2 of the FANA-negative patients. Antibodies to extractable nuclear antigens (ENA) were found in 4 patients with a positive FANA and in only 1 FANA-negative patient. The current clinical criteria showed poor discriminatory value in classifying cases of seronegative polyarthritis, which may represent mild cases of other connective tissue disease presenting with synovitis in the absence of extra-articular disease manifestations.

Antibody to synthetic poly dAT: correlation with antibody to native DNA and specificity for SLE

Antibodies to synthetic 3H-poly dAT have the advantage over antibody to native DNA in that they have a higher degree of specificity for systemic lupus erythematosus (SLE). This is because poly dAT eliminates the problem of measurement of single stranded antibodies that are not specific for any one condition but which may be detected by native DNA preparations which usually contain single stranded regions. The overall degree of correlation between the two antibodies is good in SLE. Antibodies to poly dAT correlate well with clinical evidence of disease activity but in this study were not particularly associated with the presence of renal disease.