Autoantibodies directed against the ribosomal P proteins are not only directed against a common epitope of the P0, P1 and P2 proteins

The autoantibodies (aAbs) directed against the ribosomal P proteins (RPP aA bs) are known to react mainly against epitopes localized within the common C-terminal sequence of the three acidic ribosomal P proteins, P0, P1 and P2 . In order to investigate the opportunity to select short recombinant pepti des of this common C-terminal sequence to detect the RPP-aAbs, the location of the epitopes recognized by ribosomal proteins (RP) aAb(+) sera of syste mic lupus erythematosus patients (SLE) was investigated. Immunoblotting and ELISA techniques using extracted or recombinant, entire or cleaved RPP sho wed that 55% of the RP aAbs were directed against the three ribosomal PO, P 1, and P2 proteins. The epitopes recognized by the RPP aAbs are located not only within the C-terminal sequence common to the three proteins but also within the N-terminal sequence of the P2 or P1 protein. The other RP aAbs s era (45%) did not react with all three proteins but with some of them, and showed the following pattern: P0(+) P1(+); P1(+); P2(+); P0(+) and P1(+) Th ey recognized epitopes located in the region of the C-terminal sequence of the protein but not common to the three proteins. In addition two out of th e six monoclonal Abs produced by immunization of mice using the P1 protein did not react with the peptide N-65 or N-71 of the P2 protein or with the C -terminal sequence of the three proteins. In conclusion this study showed t hat the RPP aAb in SLE patients are not only directed against epitopes with in the C-terminal sequence shared by the three acidic ribosomal P proteins. In view of these data it seems necessary to be cautious in using only a C- terminal peptide of ribosomal P proteins in tests performed to detect RPP a Ab in human sera. (C) 1999 Academic Press.