Deoxyribonuclease I treatment of histones for the detection of anti-histone antibodies in solid-phase immunoassays. Effect of protease contamination in commercial deoxyribonuclease I preparations

The Role of Non-Chromosomal Histones in the Host Defense System

Histone H1 is located at the inter-nucleosome and more correctly at both ends of the double-stranded DNA that protrude from the nucleosome unit. It has long been recognized to be localized only inside the nuclei as a constituent for packaging nucleosome into chromatin. Thus, it could be hardly believed that detatched or solubilized histone H1 plays the role of a host defense molecule. Given the old reports on histone-like basic proteins that show bacteriostatic functions, I herein chose some recent related articles and tried review them. Recent advances in research on the cell death mechanism makes it possible to understand that programmed cell death, (i.e. apoptosis) could serve as a good source of soluble histones. Some forms of them are highly probable to be bacteriostatic.

Dual reactivity of several monoclonal anti-nucleosome autoantibodies for double-stranded DNA and a short segment of histone H3

We have shown previously that four IgG monoclonal autoantibodies (mAbs) reacted in ELISA with both double-stranded (ds) DNA and peptide 83-100 of histone H3. The peptide 83-100 contains a cysteine residue at position 96 and readily dimerizes at pH 7-8. We describe here that only the 83-100 dimers, and not the 83-100 monomers, are recognized by the four antibodies and inhibit in ELISA the binding of mAbs to dsDNA. The equilibrium affinity constants (Ka) and kinetic rate constants of two of these mAbs were measured in a biosensor system. Ka values were significantly higher when these mAbs were tested with dsDNA as compared with the 83-100 dimer. Further higher Ka values were measured with mononucleosomes containing DNA and histones. It is proposed that these four mAbs are directed against a topographic determinant formed by DNA and the region 83-100 of H3 present as a dimer at the surface of nucleosome, and that they react, although significantly less well, with DNA and peptide dimer tested separately. This study provides a quantitative and kinetic basis to interaction between several antibodies and distinct antigenic structures and allows us to better understand the structural basis of apparent autoantibody cross-reactivity.

Detection of 5-bromo-2-deoxyuridine (BrdUrd) incorporation with monoclonal anti-BrdUrd antibody after deoxyribonuclease treatment

We studied the effects of deoxyribonucleases on the detection of 5-bromo-2-deoxyuridine (BrdUrd) by anti-BrdUrd monoclonal antibodies (mAbs). After DNase I treatment, BrdUrd was detected in cells fixed on slides with the anti-BrdUrd mAbs, B44 and BMC9318. The level of detection related to the degree of DNA digestion. DNA digestion of 25-75% resulted in levels of staining comparable to control preparations in which DNA was denatured by heating with formamide. Staining with the mAbs of DNase I-treated cells was abolished with S1 nuclease, a single-stranded DNA-specific nuclease. When exonuclease III was used after DNase I treatment, the staining intensity of cells fixed on slides increased, and BrdUrd could be detected in suspended cells by flow cytometry. Since this enzymatic method leading to the detection of BrdUrd does not involve cell loss, or destruction of either cellular morphology or epitope reactivity, as occurs with traditional DNA denaturation procedures, it is useful for kinetic studies of phenotypically mixed populations. Furthermore, staining with anti-BrdUrd mAb of cells treated with exonuclease III offers a simple approach to quantitation of apoptotic cells, in which an endogenous endonuclease is activated.

Occurrence of antibodies to protease-treated histones in a patient with vasculitis

We describe the presence of IgG antibodies reacting with histones previously treated with proteases in a patient with vasculitis. The patient's serum did not react with nontreated histones and when several enzymes were tested separately, only alpha-chymotrypsin reproduced the effect. Reactivity was directed against histone fraction H2B and no other autoantibody was found in the patient's serum. This could represent an autoantigen-driven response, histones hydrolyzed in vivo with proteases being the immunogenic stimulus. Diagnostic and pathogenic implications derived from the existence of such autoantibodies are discussed.