Anti-Sm

Anti-Sm (Anti-Smith antibody)

This is antibody to a ribonuclear protein antigen.

It is associated with central nervous system involvement and nephritis in SLE. The HLA-markers associated with SLE and anti-dsDNA are HLA-DR2 and HLA-DQw6.

The Sm antigen represents not a single protein but a protein complex consisting of a group of core proteins (1)

• at present, several proteins, being SmB1 (SmB), SmB2 (SmB’), SmB3 (SmN), SmD1, SmD2, SmD3, SmE, SmF and SmG, have been identified, which are expressed in the nuclei of all cells

Anti-sm antibodies are seen in less than 30% of SLE patients but have 99% specificity for SLE (2):

• in SLE are usually always associated with Anti-U1-RNP antibodies, which are present in up to 30% of SLE patients

Notes:

• the name Smith antigen is derived from a patient named Stephanie Smith, who was diagnosed with SLE in 1959
  • her physician dr. Tan, discovered a specific SLE antigen using the Ouchterlony agar diffusion method with her serum
  • this specific SLE antigen became known as the Smith antigen or Sm antigen

Reference:

1. van Beers JJBC, Schreurs MWJ. Anti-Sm antibodies in the classification criteria of systemic lupus erythematosus. J Transl Autoimmun. 2022 Apr 13;5:100155.
2. Justiz Vaillant AA, Goyal A, Varacallo MA. Systemic Lupus Erythematosus. 2023 Aug 4. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–.