The fibrillarin (Scl-34) autoantibody in systemic scleroderma

Reexamination of ANA positive sera with nucleolare fluorescence staining on HEp-2 cells and hamster liver imprints revealed 3 sera with an uniform characteristic pattern. It is characterized by: 1. Strong clumpy fluorescence of nucleoli in the interphase. 2. Missing nucleoplasma staining (pure nucleolar). 3. Characteristic granular staining of the cytoplasma from the condensed chromosoma in mitosis. 4. Additive fluorescence of a nucleolus-like body. 5. Extremely high antibody titers. 6. Negative immunodiffusion. This nucleolar staining pattern was described by Bernstein et al. as a clumpy nucleolar pattern. It is produced through an antibody to the dense fibrillar component of the nucleolus (fibrillarin). This antigen is a protein of the U3 RNP with a molecular weight 34 kDa. Clinically is the fibrillarin antibody highly specific for systemic scleroderma especially with diffuse skin involvement. We found it in 1% of scleroderma patients. Its pathogenetic importance is not known.