Association of 16/6 and SA1 anti-DNA idiotypes with anticardiolipin antibodies and clinical manifestations in a large cohort of SLE patients. European Concerted Action on the Immunogenetics of SLE.

The SA1 and 16/6 idiotypes can be found in some patients with systemic lupus erythematosus (SLE) or anti-phospholipid syndrome (APS). The aim of this study was to ascertain the prevalence of these idiotypes in a large cohort of SLE patients, and to determine whether their presence is correlated with the anticardiolipin (aCL) and anti-dsDNA antibodies or with the clinical manifestations of SLE. 492 SLE patients were evaluated for clinical manifestations of SLE and were assigned a disease severity score. ds-DNA autoantibodies, aCL autoantibodies of the IgM, IgG and IgA isotypes, and SA1 and 16/6 idiotypes were also determined in these patients. The prevalence of the SA1 and 16/6 idiotypes in the 492 SLE patients was found to be 11% and 5.1%, respectively, and these idiotypes were significantly more prevalent in the patients who had aCL antibodies of either the IgG, IgM or IgA isotypes. Moreover, while the 16/6 idiotype was not associated with the clinical manifestation of either SLE or APS, the SA1 idiotype was found significantly more frequently in patients who had vascular events Raynaud's phenomenon or hemolytic anemia (p = 0.016, 0.01, 0.01, respectively). SLE patients with the SA1 idiotype may run a higher risk of developing vascular events, Raynaud's phenomenon or hemolytic anemia. These clinical manifestations can be attributed to both SLE and secondary APS when aCL autoantibodies are also found. These results indicate that the possible pathogenicity of certain idiotypes in SLE cannot be excluded.