PROTEIN AND RNA IMMUNOPRECIPITATION FOR THE IDENTIFICATION OF SPECIFIC SERUM AUTOANTIBODIES IN SYSTEMIC AUTOIMMUNE RHEUMATIC DISEASES.

Serum autoantibodies play a key role in systemic autoimmune rheumatic diseases for diagnostic, classification and prognostic purposes. Research of new autoantibodies has been very active in the last decade in rare connective tissue diseases such as systemic sclerosis and poly/dermatomyositis, with new biomarkers entering the clinical practice. Immunoprecipitation of protein and/or RNA components of the target autoantigens constitutes the gold standard method for the discovery of new autoantibodies in a screening setting but is considered time- and labor-intensive and, accordingly, is performed only in a few laboratories worldwide. As a result, alternative techniques such as ELISA and immunoblotting are often preferred for large-scale testing, despite the lack of standardization. The aims of the present project are (1) to set up protein- and RNA- immunoprecipitation in our laboratory and (2) to describe serum autoantibodies identified in our series of patients affected by systemic autoimmune rheumatic diseases. During the PhD program we were able to perform correctly protein-and RNA-immunoprecipitation in our laboratory as demonstrated by positive reference sera, and then by the identification of known but also new and rare autoantibodies, as represented by two new patterns immunoprecipitated in systemic sclerosis, corresponding to serum anti-hnRNP-L and anti-mitochondrial antibodies. In psoriatic arthritis we also analyzed the concentration of circulating levels of LL37, a recently established target of autoimmune response at the skin level, and we identified an increased production in a subset of patients. In conclusion, performing protein- and RNA-immunoprecipitation as a screening method in our laboratory allows a more complete and specific autoantibody analysis that cannot be performed by the commercial techniques available nowadays, and further analysis of the role of LL37 in psoriatic arthritis patients may help in the identification of a new biomarker in this condition.