Histones are cationic proteins which associate with DNA in the nucleus of eukaryotic cells to form nucleosomes. Anti-histone antibodies occur in a number of clinical conditions, primarily in systemic lupus erythematosus (SLE) and drug-induced lupus (DIL), and also in other systemic and organ-specific autoimmune diseases, and certain neurological and infectious diseases. Anti-histone antibodies are found in up to 80% of SLE patients, and 95% of the cases with DIL by procainamide, hydralazine, chlorpromazine, and quinidine. Despite of SLE and DIL, anti-histone antibodies are commonly seen in other rheumatic diseases, including myositis and systemic sclerosis (SSc). Therefore, anti-histone antibodies are a common biomarker for evaluating the autoimmune diseases.

The determination of anti-histone antibodies is based on an indirect enzyme linked immune reaction. The micro-plate is pre-coated with purified total histones, which bind to the anti-histone antibodies presented in the Standards and samples. After incubation and washing, any unbound antibodies will be removed. Then Goat anti-human IgG-HRP conjugates are added, which bind to the captured anti-histone antibodies. After incubation and washing, any unbound conjugates will be also removed. Then substrate is catalyzed by the HRP to produce a blue color that changes to yellow after adding the stopping buffer. The density of the yellow coloration is directly proportional to the amount of captured anti-histone antibodies in the plate. The light absorbance (OD value) under 450nm wavelength of the wells is determined using a microplate reader. The antibody concentration of the unknown sample can be estimated with the provided calibrators in the kit. Since no international standard has been established for anti-histone antibodies, the standards are calibrated against Anti-Nuclear Factor Serum (Homogeneous) Human (NIBSC code: W1064, non WHO reference material), and presented as relevant unit (RU) per mL. The kit offers semiquantitative and quantitative interpretation of the data, which is in the section of INTERPRETATION.

A.Linearity:

The linearity of Anti-dsDNA ELISA (IgG) was determined by assaying 8 serial dilutions of 5 serum samples. The linear regreassion was calculated, calculated, R2 amounting to >0.98 within the concentration range of 10 RU/mL to 300 RU/mL.

B.Reproducibility:

The reproducibility of the test was investigated by determine the intra- and inter-assay coefficients of variation using 3 sera. The Intra-assay CVs are based on 20 determinations and the inter-assay CVs on 4 determinations performed in 6 different plates.