A fluorimetric assay for human antibodies to all the histones

Antinuclear Autoantibodies in Health: Autoimmunity Is Not a Synonym of Autoimmune Disease

The incidence of autoimmune diseases is increasing. Antinuclear antibody (ANA) testing is a critical tool for their diagnosis. However, ANA prevalence in healthy persons has increased over the last decades, especially among young people. ANA in health occurs in low concentrations, with a prevalence up to 50% in some populations, which demands a cutoff revision. This review deals with the origin and probable physiological or compensatory function of ANA in health, according to the concept of immunological clearance, theory of autoimmune regulation of cell functions, and the concept of functional autoantibodies. Considering ANA titers ≤1:320 as a serological marker of autoimmune diseases seems inappropriate. The role of anti-DFS70/LEDGFp75 autoantibodies is highlighted as a possible anti-risk biomarker for autoimmune rheumatic disorders. ANA prevalence in health is different in various regions due to several underlying causes discussed in the review, all influencing additive combinations according to the concept of the mosaic of autoimmunity. Not only are titers, but also HEp-2 IFA) staining patterns, such as AC-2, important. Accepting autoantibodies as a kind of bioregulator, not only the upper, but also the lower borders of their normal range should be determined; not only their excess, but also a lack of them or "autoimmunodeficiency" could be the reason for disorders.

DNA-histone complexes as ligands amplify cell penetration and nuclear targeting of anti-DNA antibodies via energy-independent mechanisms

We have generated three monoclonal cell-penetrating antibodies (CPAbs) from a non-immunized lupus-prone (NZB × NZW)F1 mouse that exhibited high anti-DNA serum titres. These CPAbs are polyreactive because they bind to DNA and other cellular components, and localize mainly in the nucleus of HeLa cells, albeit with a distinct nuclear labelling profile. Herein, we have examined whether DNA-histone complexes (DHC) binding to CPAbs, before cell entry, could modify the cell penetration of CPAbs or their nuclear staining properties. By applying confocal microscopy and image analysis, we found that extracellular binding of purified CPAbs to DHC significantly enhanced their subsequent cell-entry, both in terms of percentages of positively labelled cells and fluorescence intensity (internalized CPAb amount), whereas there was a variable effect on their nuclear staining profile. Internalization of CPAbs, either alone or bound to DHC, remained unaltered after the addition of endocytosis-specific inhibitors at 37° or assay performance at 4°, suggesting the involvement of energy-independent mechanisms in the internalization process. These findings assign to CPAbs a more complex pathogenetic role in systemic lupus erythematosus where both CPAbs and nuclear components are abundant.

Chitosan-coated polystyrene microplate for covalent immobilization of enzyme

Microplates made of polystyrene have been widely used for immunoassays. Protein molecules that have been immobilized on a hydrophobic polystyrene microplate by passive adsorption lose their activity and suffer considerable denaturation. A new chitosan-coated microplate suitable for the covalent immobilization of enzymes has been developed. The primary amino groups of chitosan were exploited for this covalent coupling of proteins. The optical transmittance of the chitosan-coated microplate, at wavelengths of 400-800 nm, was estimated to be suitable for its application in chromogenic reaction-based bioassays. The immobilization efficiency of the chitosan-coated microplate was demonstrated to be far superior to that of a conventional microplate when tested using acetylcholinesterase (AChE) and β-glucosidase as model biomolecules, and the chitosan-coated microplate may thus have potential applications in biosensing and bioreactor systems.

Solid-phase immunoassay of serum antibodies to peptides. Covalent antigen binding to adsorbed phenylalanine-lysine copolymers

Two small peptide antigens, glucagon and enkephalin (5-L-leucine), were covalently immobilised using either glutaraldehyde or bis-(sulphosuccinimidyl) suberate to an adsorbed layer of phenylalanine-lysine copolymer (PL) or partially acetylated PL (APL) on polystyrene. Both copolymers formed stable layers, particularly APL after adsorption from solution in distilled water. Adsorption of the copolymers under these conditions and subsequent coupling of the antigens yielded solid phases with low non-specific immunoglobulin binding characteristics in an enzyme-linked immunosorbent assay (ELISA) to detect peptide-specific antibodies in rabbit serum. The signal-to-noise ratio in this ELISA was dependent on the combination of copolymer, antigen and coupling reagent employed. Removal from the solid-phase of weakly bound antigen by washing with solutions containing Tween 20 or sodium dodecyl sulphate (SDS) increased assay sensitivity, which was 2-4-fold greater than when simple antigen adsorption was utilised. In the ELISA, the coefficient of variation was lower when covalent antigen coupling was employed.

Antibodies to the five histones and poly(adenosine diphosphate-ribose) in drug induced lupus: implications for pathogenesis

Certain drugs are a frequent source of antinuclear antibody (ANA) induction, and ANA is invariably present in the few patients who progress to the drug induced lupus syndrome. This report concerns the fine specificity of the ANA response to hydralazine, penicillamine, and sulphasalazine therapy. Using highly purified individual histones in fluorimetric assays, antihistone antibodies are always detectable, often in large amounts, but the pattern of response to individual histones is variable and not drug specific. In addition to the response to the three histones H1, H2B, and H3 reminiscent of idiopathic systemic lupus erythematosus, antibody to histone H2A predominates in some drug induced cases. Contrary to previous thought, histones are not the sole target of the antinuclear response: we also demonstrate a significant correlation between ANA titre and antibody to poly(adenosine diphosphate-ribose). Like the histones, this is a macromolecule that can bind to deoxyribonucleic acid (DNA). It is proposed that drug induced damage to chromatin leads to ANA production, while drug induced impairment of complement activity may then enable these autoantibodies to mediate the lupus syndrome.

Detection of antibodies to total histones and their subfractions in systemic lupus erythematosus patients and their asymptomatic relatives

Sera drawn from 75 patients with systemic lupus erythematosus, 141 healthy relatives (from the families of 51 patients), and 115 healthy control subjects were examined, by enzyme-linked immunosorbent assay, for IgG and IgM antibodies to total histones and their subfractions. Compared with the controls, statistically significant numbers of patients and their relatives had antihistone antibodies of both isotypes. Among the relatives, the sera from females, notably sisters of the patients, contained the highest levels of anti-total histone antibody. Anti-H2A/H2B and H3 antibodies were most prevalent among the lupus patients, but many of the relatives had IgM anti-H4 antibodies. These findings indicate that antihistone antibodies can serve as a genetic marker in patients with systemic lupus erythematosus.

Patterns of antihistone antibody specificity in systemic rheumatic disease. I Systemic lupus erythematosus, mixed connective tissue disease, primary sicca syndrome, and rheumatoid arthritis with vasculitis

A new fluorimetric assay was used to measure the relative amounts of antibodies to individual nuclear histones in sera from 102 patients with systemic lupus erythematosus (SLE), mixed connective tissue disease, primary sicca syndrome, and rheumatoid arthritis with vasculitis. In SLE sera, the predominant responses were to histones H-1, H-2B, and H-3, with marked elevations of binding to H-1 and H-2B in one-third of the patients, and to H-3 in one-fourth; antibodies of both the IgG and IgM classes were also detected. In a few SLE sera, the pattern of histone response differed or was restricted to 1 immunoglobulin class. In mixed connective tissue disease, only 2 of 9 sera showed elevated histone binding activity, the response being predominantly to H-3 in 1 patient and to H-1 and H-2B in the other. Binding to H-2B was also prominent in 2 of 3 patients with primary sicca syndrome. The highest antihistone reactivity and the most heterogeneous response patterns were observed in patients who had rheumatoid arthritis with vasculitis; 6 of 8 of those sera had elevated histone reactivity. In SLE, the highest histone binding results were found among patients with a history of photosensitivity. Histones are closely associated with DNA in the nucleosome, and we speculate that antihistone antibodies could arise as a result of damage to DNA, induced by drugs or irradiation.