Anti-Sm/RNP
Enzyme-linked immunosorbent assay method for the semi-quantitative determination of specific IgG autoantibodies to Sm/RNP in human serum.
The detection of Anti-Nuclear Antibodies (ANA’s) has long been an important tool in the diagnosis of systemic rheumatic diseases. The antigens used in their detection are purified by the saline extraction of human or animal nuclei, this has led to them being termed Extractable Nuclear Antigens (ENA’s). The most commonly measured ENA specifications are anti-SS-A/Ro, anti-SS-B/La, anti-Sm, anti-Sm/RNP, anti-Jo-1 and anti-Scl-70.
The intracellular antigen Sm/RNP is a complex of Sm and RNP components. While the Sm antigen can exist independently, the RNP antigen exists as part of the Sm/RNP complex. The Sm/RNP antigen complex is a target for immune response in many patients with Mixed Connective Tissue Disease (MCTD), Systemic Lupus Erythematosus (SLE), Primary Sjogren’s Syndrome (SS) and Progressive Systemic Sclerosis (PSS). Studies have shown that anti-Sm/RNP antibodies occur in over 90% of MCTD cases, 35-45% of patients with SLE and approximately 30% of patients with SS. The Sm/RNP antigen is a ribonuclear protein and under Western Blot produces a band at approximately 68kD.
The AutostatII assay for detection of autoantibodies is a solid phase immunosorbent assay (ELISA) in which the analyte is indicated by a colour reaction of an enzyme and substrate. The AutostatII wells are coated with purified antigen (1).
On adding diluted serum to the wells the antibodies (2) present bind to the antigen. After incubating at room temperature and washing away unbound material, horseradish peroxidase conjugated anti-IgG monoclonal antibody (3) is added, which binds to the immobilised antibodies.
Following further incubation and washing, tetra-methyl benzidine substrate (TMB) (4) is added to each well. The presence of the antigen-antibody-conjugate complex turns the substrate to a dark blue colour. Addition of the stop solution turns the colour to yellow.