Human Anti-Histones ELISA (IgG)
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.
PRINCIPLE OF THE ASSAY
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.
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.
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.