Temporal shifts from Sm to ribonucleoprotein reactivity in systemic lupus erythematosus.

The Sm and RNP autoantibodies, found in the sera of many patients who have connective tissue diseases, recognize determinants on small nuclear ribonucleoprotein particles (snRNP). Numerous techniques have been used to distinguish between the subsets of snRNP proteins recognized by these two antibody systems. Using protein and snRNP immunoprecipitation, as well as a competitive enzyme-linked immunosorbent assay, antibodies in the sera of Sm patients have been observed to include variable quantities of RNP-like reactivity. To analyze changes in these autoantibodies, 2 patients with anti-Sm antibodies were followed temporally. The autoantibodies in the sera of both patients underwent shifts from predominant Sm reactivity to predominant RNP reactivity. In 1 patient the shift occurred gradually over several years, while in the other the shift occurred within 8 weeks.