Sm Antibody IgG ELISA Kit

Systemic lupus erythematosus (SLE) is a chronic, systemic rheumatic autoimmune disease characterized by the deposition of autoantibodies and immune complexes that can affect essentially any organ, leading to a range of clinical manifestations. In addition to clinical manifestations, serologic findings play an important role in the diagnosis. Because of the lack of diagnostic criteria, classification criteria that are primarily used to enroll patients in clinical studies are often used for diagnostic purposes, and these classification criteria have been revised to include fluorescent antinuclear antibodies (ANAs), native DNA antibodies, and antibodies to the anti-Smith (Sm) antigen, thereby improving the performance of the criteria.

The Smith antigen (Sm antigen) was named after the discovery of the antigen from the serum of a patient named Stephanie Smith. Sm antigens are not single proteins, but protein complexes consisting of a set of core proteins. To date, the proteins SmB1 (SmB), SmB2 (SmB'), SmB3 (SmN), SmD1, SmD2, SmD3, SmE, SmF, and SmG have been identified and are expressed in the nuclei of all cells. Sm proteins, together with ribonucleoprotein and small nuclear RNA (snRNA), form RNA-protein complexes or small nuclear ribonucleoprotein (snRNP), which are involved in precursor messenger RNA (mRNA) splicing, ultimately leading to the production of mature mRNAs. The Sm protein complex binds to snRNA in a ring-like structure, thereby protecting snRNA from nuclease degradation and supporting RNA processing. Different snRNAs are known to belong to different snRNPs (e.g., U1, U2, U4/U6 and U5). Of these, the U1-SnRNP is the best known and consists of U1-RNA, ribonucleoproteins RNP70, A and C, and Sm proteins.

Figure 1. The U1 small nuclear ribonucleoprotein complex
(Source: van Beers JJBC, et al. 2022)

Anti-Sm antibodies correlate with SLE disease activity and are a highly specific but less sensitive biomarker for the diagnosis of SLE. In addition, anti-Sm antibodies have been associated with lupus nephritis, and the presence of anti-Sm antibodies in patients with SLE suggests a future risk of developing lupus nephritis. High-titer anti-Sm antibodies are considered a predictor of silent lupus nephritis and predict early poor prognosis.

Anti-Sm IgG ELISA Kit
Anti-Smith IgG ELISA Kit
Anti-Sm antigen IgG ELISA Kit