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Autoantibodies to ribosomal P proteins in systemic lupus erythematosus.

Systemic lupus erythematosus is considered the prototype of systemic autoimmune diseases in which autoantibody production is the prominent feature of the immune system dysregulation. These autoantibodies are directed against fundamental intracellular antigens, mainly of nuclear but also of cytoplasmic origin or localization in the cell. Among the anti-cytoplasmic antibodies, anti-ribosomal protein antibodies are the most predominant and the ribosomal P proteins the major targeted antigens [1,2]. The P proteins are three highly conserved phosphorylated proteins (P0, P1, P2) of 38, 19 and 17 kDa apparent molecular weight, respectively, located within the large 60S subunit of the eukaryotic ribosome. The anti-P immunodominant epitope has been identified as a single linear sequence within the 22 amino acid carboxy-terminal peptide (C22) common to the three P proteins 3], even though the antibody binding seems to be mediated also by conformational determinants on P proteins [3].