Background Particular emphasis has been placed on early identification of RA patients and joint damage risk stratification to improve patient outcomes. The 14-3-3η (eta) protein has been described as a mechanistic marker that is detectable in serum during the very early stages of RA development. 14-3-3η's extracellular expression in RA elicits a specific autoantibody (AAb) response that can be measured, and is postulated to be protective when it effectively clears systemic 14-3-3η.
Objectives This study examined the combined diagnostic strength of the 14-3-3η protein and its AAbs in early RA and whether the AAbs mark a favorable prognosis.
Methods 704 subjects were evaluated; 409 DMARD-naïve early RA patients from READE and 295 controls. Median age, disease duration, % females was 56 yrs, 4 mo, 73% with 69% and 63% being +ve for RF and ACPA. Controls included 106 healthy and 189 with either: connective tissue disease, OA, AS or autoimmune disorders. 14-3-3η protein levels were previously tested in this cohort using the 14-3-3η ELISA (+ve cut-off ≥0.19 ng/ml) and 67% of early RA patients were +ve. 14-3-3η AAb levels were measured on the MSD ECL platform. A diagnostic cut-off was determined by ROC curve analysis. The group that was 14-3-3η AAb-only +ve, in whom the 14-3-3η protein would have been cleared, was compared to the remainder of the cohort in terms of differences in radiographic progression over 3 yrs using the Mann-Whitney U-test. Fisher Exact test was used to determine the association between marker positivity and radiographic progression (SHS≥3 at yr 3).
Results Median (IQR) 14-3-3η AAb values were significantly higher in early RA [527U/ml (154-11762) vs all controls 264U/ml (96-1421), p<0.0001 delivering a ROC AUC of 0.85 (95%CI:0.82-0.88). When compared to healthy subjects, the ROC AUC was 0.92 (95%CI:0.89-0.95), p<0.0001 with the best cut-off of ≥380 U/ml delivering 93% specificity and 77% sensitivity with a likelihood ratio (LR) of 11.6. At this cut-off, 313 (77%) were 14-3-3η AAb +ve. Notably, 93% of early RA patients were +ve for either of the 14-3-3η markers and a Pearson correlation of r=-0.02 highlighted their complementary nature. Of the 409 patients, 105 (26%) were only +ve for the 14-3-3η AAbs and had significantly less joint damage progression at year 3, median (IQR) ΔSHS 0 (0-31) vs the rest of the cohort, 2 (-1–71), p<0.04. The Fisher exact test revealed that 14-3-3η AAb positivity (in the absence of the 14-3-3η protein) is associated with less radiographic progression at Year 3, LR=3.7 (p=0.04). Importantly, of the 105 AAb +ve patients, 37 (35%), 36 (34%) and 46 (44%) were +ve for ACPA, RF and ACPA/RF. Regression analysis in this group revealed that none of ACPA (p=0.3), RF (p=0.1) or the combination of RF/ACPA (p=0.2) were predictive of radiographic outcomes.
Conclusions 14-3-3η biomarkers identify 93% of early RA patients. Those who are uniquely positive for 14-3-3η AAbs have a favorable radiographic prognosis irrespective of ACPA or RF status. This is likely due to 14-3-3η AAbs' protective nature and effective clearance of deleterious 14-3-3η protein.
Disclosure of Interest D. van Schaardenburg: None declared, M. Murphy Employee of: Augurex Life Sciences Corp, S. Turk: None declared, V. Bykerk: None declared, E. Keystone: None declared, K. Siminovitch: None declared, A. Marotta Employee of: Augurex Life Sciences Corp, W. Maksymowych Consultant for: Augurex Life Sciences Corp