Autoantibodies to the 20-kDa Ribosomal Proteins: Identification, Characterization, and New Aspects on Prevalence in Systemic Lupus Erythematosus

Autoantibodies to the 20-kDa ribosomal proteins (L12/S10) are not well studied, especially in juveniles with systemic lupus erythematosus (SLE). Randomly selected sera from American juveniles and adults with SLE were screened for antibodies to either 20-kDa protein and P proteins and then assayed for anti-L12 and anti-S10 by immunoblot assays. In a pilot study of patients with anti-P (Cohort 1), IgG antibodies to either 20-kDa protein and, specifically, to L12 were observed in 72 and 42% of juveniles and adults, respectively. IgG antibodies to S10 were detected less frequently. In Cohort 2 patients who were chosen irrespective of autoantibody status, twice as many juveniles as adults had IgG antibodies to either 20-kDa protein. Prevalences of IgG anti-L12 and IgG anti-S10 antibodies in the juveniles were 28 and 16% and in the adults were 13 and 12%, respectively. Anti-L12 were strongly but not invariably associated with anti-P, and usually arose temporally to these antibodies. Anti-S10 activity was due to anti-Sm antibodies. We conclude that IgG anti-L12 are more prevalent in SLE than previously reported, and are responsible for the majority of activity toward the 20-kDa ribosomal proteins, especially in juveniles.