The CN-index of hnRNP-DL Predicts an Individual 'Window of Treatment Success' in RA Patients

BackgroundThere is a need for biomarker to identify patients ‘at risk’ for rheumatoid arthritis (risk-RA) and to better predict the therapeutic response and in this study we tested the hypothesis that novel native and citrullinated heterogeneous nuclear ribonucleoprotein (hnRNP)-DL autoantibodies could be possible biomarkers.MethodsUsing Protein macroarray and ELISA, epitope recognition against hnRNP-DL was analysed in sera from different developed RA disease and diagnosed SLE patients. Toll-like receptor (TLR) 7/9 and myeloid differentiation primary response gene 88 (MyD88)-dependency were studied in sera from murine disease models. HnRNP-DL expression in cultivated cells and synovial tissue was analysed by indirect immunofluorescence, immunoblot and immunohistochemistry. ResultshnRNP-DL was highly expressed in stress granules, citrullinated in the rheumatoid joint and targeted by autoantibodies either as native or citrullinated proteins in patient subsets with different developed RA disease. Structural citrullination dependent epitopes (SCEs) of hnRNP-DL were detected in 58% of the SLE patients although 98% of these sera were α-CCP2-negative. To obtain a specific citrullinated signal value, we subtracted the native antibody value from the citrullinated signal. This CNDL (Citrullinated-Native-hnRNP-DL)-index identified and the bioinformatic value was explored, as a new value for an “individual window of treatment success” in early RA and for the detection of RF-IgM/α-CCP2 seronegative RA patients (24-46%). Negative CNDL-index was found in SLE patients, risk-RA- and early RA-cohorts such as EIRA where the majority of these patients are DAS28-responders to methotrexate (MTX) treatment (87%). High positive CNDL-values were associated with more severe RA, shared epitope and parenchymal changes in the lung. Specifically, native α-hnRNP-DL is TLR7/9-dependent, associated with pain and ROC-analysis revealed an association to initial MTX or etanercept treatment response, especially in seronegative RA patients.ConclusionCNDL-index defines patients is a possible biomarker for develop RA and the “window of treatment success” thereby potentially closing the sensitivity gap.