Immunological studies on nucleic acids: an investigation of the antigenic determinants of denatured deoxyribonucleic acid (DNA) reactive with rabbit anti-DNA antisera by a radioimmunoassay technique

Detection of DNA Fragmentation in Human Breast Cancer Tissue by an Antibody Specific to Single-stranded DNA

While there have been many reports concerning the clinical significance of bcl-2 expression in human breast cancer, little is known about apoptosis in primary breast cancers. We immunohistochemically examined DNA fragmentation in 107 primary human breast cancers from Japanese women using an antibody specific to single-stranded DNA. The apoptosis index calculated as the product of the positive cell number and the cellularity coefficient, ranged from 0 to 48. The average incidence of apoptosis was calculated as 0.1% of tumor cells. No relationships were observed among the apoptosis index, expression of bcl-2, and the histological grade of the tumors. Almost all apoptotic cells were phagocytosed by surrounding tumor cells immediately after DNA fragmentation. Apoptotic body formation was rare. The apoptotic cells seemed to be degraded within phagocytes, leaving no trace of apoptosis except the tiny shells of nuclei. The intensive phagocytic reaction might be one of the main reasons for the low incidence of apoptosis in human breast cancers.

Binding specificity of a monoclonal anti-DNA antibody

To investigate the interaction of DNA and anti-DNA antibodies in the immune complex disease of systemic lupus erythematosus, the fine specificity of binding of a monoclonal anti-DNA antibody was determined. This antibody, termed Cll, was derived from the fusion of spleen cells from an autoimmune MRL-lpr/lpr mouse with the myeloma cell line M45. In a solid-phase ELISA assay to measure anti-DNA activity, Cll showed preference for single stranded compared to double stranded DNA of animal origin. The Cll antibody also bound some deoxyribohomopolymers as well as ribohomopolymers, but failed to bind synthetic DNA duplexes. Defined size oligonucleotides with a size range of 2-(12-18) failed to inhibit the binding of Cll to single stranded DNA. This pattern of binding is consistent with the recognition of a unique structural determinant that can be represented by a variety of nucleic acids. The absence of antigenic activity among the oligonucleotides suggests that an extended polynucleotide structure is required for antibody binding, possibly because of a bivalent or 'monogamous' mode of interaction. The binding properties of Cll further suggest that its ability to participate in immune complex formation may be limited by the nature of the available DNA antigen.

Secondary structure in denatured DNA is responsible for its reaction with antinative DNA antibodies of systemic lupus erythematosus sera

Experiments were designed to determine the basis for the strong competitive reaction of denatured DNA with systemic lupus erythematosus (SLE) antinative DNA antibodies. Secondary structure in denatured DNA was reflected in hyperchromicity upon heating and in multiphase kinetics of its digestion by S1 nuclease. Partial digestion by S1 nuclease completely eliminated the ability of denatured DNA to react with antidenatured DNA antibodies, but not its ability to react with SLE sera. S1 nuclease-resistant cores were isolated from extensively digested denatured DNA. These cores had secondary structure, including some stable fold-back helical regions. The cores, from 20 to several hundred base pairs in size, competed with native DNA for binding by SLE sera. Other experiments measured reactions of denatured DNA under conditions that affected its secondary structure content. Its competitive activity decreased as temperature was increased from 0 degrees to 37 degrees C, whereas the activity of native DNA was not altered in this temperature range. With DNA pieces of 90-110 base pairs, native fragments were much more effective than the denatured fragments, in which stable helical structure is less likely to occur than in high molecular weight denatured DNA. Competitive assays with mononucleotides, oligonucleotides, homopolymers, and RNA-DNA hybrids also indicated that two strands of polydeoxyribonucleotide were required for optimal reactions with these SLE serum antibodies. The antibodies can measure stable helical regions in denatured DNA; they may also stabilize short helical regions that occur in an equilibrium of conformational forms.

Reaction of systemic lupus erythematosus antinative DNA antibodies with native DNA fragments from 20 to 1,200 base pairs

Double-stranded DNA fragments of varying sizes were isolated and tested for binding to systemic lupus erythematosus (SLE) antinative DNA antibodies. Fragments of 20-25, 40-50, 90-110, and 160-180 base pairs (bp), along with intermediate-size pieces were isolated by preparative gel electrophoresis of a limited micrococcal nuclease digest of calf thymus DNA. Larger helical polynucleotides of 160-200, 380, 600-1,000, and 1,200 bp were isolated by preparative gel electrophoresis of DNA from chicken erythrocyte nucleosomes and oligonucleosomes. The fragments behaved as base-paired structures as tested by thermal denaturation, resistance to S1 nuclease, and serological assays with antibodies to native or denatured DNA. At a concentration of 0.27 muM, fragments of 20-25 bp were able to react with two SLE sera in competition with native DNA. With these and two other sera, DNA of 40-50 bp was a much more effective competitor. One serum required DNA greater than 180 bp for competition in the concentration range tested. Denatured fragments were much less effective than native fragments. The results emphasize the heterogeneity of SLE antinative DNA antibodies, confirm that secondary structure of the antigen is important for specific binding to these antibodies, and support the suggestion that bivalent binding to one molecule may be important for high functional affinity.

Rapid separation of DNA constituents, bases, nucleosides and nucleotides, under the same chromatographic conditions using high-performance liquid chromatography with a reversed-phase column

Four components of three sets of DNA constituents, bases, deoxyribonucleosides and deoxyribonucleoside 5'-monophosphate, were sufficiently resolved under one set of chromatographic conditions using high-performance liquid chromatography with a reversed-phase column (Zorbax ODS) and the solvent 0.4 M NH4H2PO4 (pH 3.5). The effect of pH and salt concentration in the solvent on the retention of these compounds in the column was thoroughly investigated. Proportionality of peak height to the content, and reproducibility and recovery of the four bases were satisfactory under appropriate conditions and as little as 1 microgram of DNA could be analysed for its base composition by this method.

Reduction of the non-specific binding of DNA to gamma-globulin in Farr radioimmunoassay by addition of dextran sulfate and calcium chloride

The effect of non-specific binding caused by the interaction between gamma-globulin and denatured DNA was markedly reduced by addition of dextran sulfate or CaCl2 at alkaline pH. This method was shown to be applicable in the detection of anti-DNA antibodies in sera from cases of human systemic lupus erythematosus.

An adjuvant effect of poly A - poly U on production of antibodies to DNA in rabbits

The effect of polyadenylate-polyuridylate copolymer (poly A-poly U) on the formation of anti-DNA antibodies in rabbits was investigated. 1) Poly A-poly U proved to be an effective adjuvant for production of antibodies to DNA. These were elicited in rabbits at high titer and were formed at an early stage of immunizations. 2) The antiserum obtained reached potently with denatured DNA, but with neither methylated bovine serum albumin (MBSA) used as carrier protein nor poly A-poly U used as adjuvant. This was demonstrable both by C-fixation and double diffusion tests. 3) The antibodies occurred exclusively in the IgG fraction separated by Sephadex G-200 column chromatography.