Diagnostic use and biological signiticance of peptide mimotopes for nucleosome specific autoantibodies in systemic lupus erythematosus (SLE) identified by random peptide phage display libraries
05 / 2000 - 05 / 2004
The cardinal feature of systemic lupus erythematosus (SLE) is the formation of antinuclear antibodies. The nucleosome is a major auto-antigen that drives the T cell dependent autoantibody response, as exemplified by the presence of nucleosome-specific T helper cells and the high prevalence of nucleosome-specific autoantibodies (NSA). Nucleosomes are also important for mediating tissue lesions, especially glomerulonephritis. Via their cationic histone part, nucleosomes mediate the binding of anti-nuclear antibodies to HS in the GBM. In lupus nephritis nucleosomes, NSA and nucleosome/IgG complexes have been identified in the glomerular immune deposits. Therefore, measurements of NSA provides an important diagnostic tool in SLE patients. However, this is hampered by the fact that in assays employing nucleosomes, also anti-dsDNA and anti-histone antibodies will bind. Until now, NSA can only be measured after absorption of anti-dsDNA and anti-histone antibodies, which precludes routine analysis. A method circumventing these absorption procedures would be of great clinical importance. The availability of the random peptide phage display technique (PDT) provides such a possibility, since with this PDT, peptide mimotopes have been identified mimicking non-protein conformational epitopes in DNA and RNA. In this project several peptide phage display libraries will be screened by monoclonal NSA derived from lupus mice. After several selection and amplification rounds positive phages will be screened for binding to anti-dsDNA or anti-histone mAbs, because recognition by these mAbs precludes their use for NSA screening. From phages remaining after these selections, peptide sequences will be determined, and consensus peptides will be derived and synthesized. These mimotopes will be used for: - diagnostic purposes to screen sera from SLE patients with or without nephritis, with active and quiescent non-renal disease manifestations, controls and patients with non-SLE systemic autoimmune diseases - immunization in normal and premorbid lupus mice to analyse their impact on anti-nuclear antibody response - analysis of renoprotection since mimotopes can compete with the nucleosome for binding to NSA, thereby acting as a decoy molecule. This will be probed both after i.p. inoculation of NSA secreting hybridomas, known to lead to glomerular deposition as well as in MRL/Ipr mice.