[Background/Purpose ] Systemic lupus erythematosus (SLE) is characterized by the production of a variety of autoantibodies and is considered a prototype immune complex disease. Anti-dsDNA antibodies contribute to the pathogenesis of lupus nephritis (LN). However, since anti-dsDNA antibodies are not sufficient for the diagnosis, prognosis or evaluation of disease activity, other autoantibodies associated with LN need to be identified. Using an N-terminal biotinylated protein library (BPL) we screened for autoantigens reacting with LN patient sera and then further characterize these autoantigens.
[Methods ] We screened for autoantigens using the AlphaScreen method with the sera from 3 SLE patients with different disease complications; thrombocytopenia, nephritis or serositis. Antigens used for screening were created using the 2296 cDNA library from a wheat cell-free protein production system in the Ehime University Cell-Free Sciences and Technology Research Center. The proteins characteristic of nephritis were selected, and immunoprecipitation was performed using serum from patients with LN. Immunohistochemical staining of renal tissues was carried out with antibodies against proteins positive in the immunoprecipitation. The specificity of the identified autoantigens was analyzed by an enzyme-linked immunosorbent assay (ELISA) with serum from approximately 250 patients with various autoimmune diseases such as polymiositis/dermatomyositis, systemic sclerosis, and rheumatoid arthritis.
 [Results ] We screened 66 proteins which reacted with LN patient sera at a high levels. Of these, ten proteins showed strong reaction specifically to SLE sera with immunoprecipitation.  Immune complex deposition of these ten proteins was confirmed by immunohistochemical staining of renal biopsy tissue and autopsy renal tissue of LN. Clear deposition of 2 proteins, ribosomal RNA processing 8 (RRP8) and transition protein 1 (TNP1), was seen in some renal tissues. ELISA analysis showed that RRP8 and TNP1 reacted to the sera from some SLE patients but have little or no reaction with those from other autoimmune diseases. In addition, anti-RRP8 and anti-TNP1 antibodies were detected in 5 and 7 out of 11 LN patients, respectively.
[Conclusion ] The AlphaScreen method using BPL created by wheat germ cell-free protein synthesis proved to be useful for autoantibody screening. We have identified RRP8 and TNP1 as new LN autoantigens. RRP8 and TNP1 may play an important role in the pathogenesis of LN.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/new-autoantigens-associated-with-lupus-nephritis/