Objectives: Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterised by autoantibody production. This study aims to identify biomarkers involving citrullinated peptides that can be used for SLE diagnosis.
Methods: After a negative selection step with serum from healthy controls (HCs), a phage library of 12 peptides was used for three rounds of screening with sera from 30 SLE patients. After four rounds of biopanning, 21 positive peptides were sequenced. We produced 37-feature arrays containing 16 recombinant citrullinated peptides. The microarrays were tested with an independent validation set of serum samples from 50 HCs, 60 SLE patients, and 60 rheumatoid arthritis (RA) patients.
Results: Microarray analysis showed that the positive rates of 13S1212Cit3-IgM (60.0%), 13S1210-IgG (43.33%), and 13S1212Cit3-IgG (41.67%) were increased in SLE patients compared with HCs and RA patients. The area under the receiver operating characteristic curve (AUC) was 0.770, 0.687 and 0.698, respectively. The combination of 13S1212Cit3-IgM and 13S1210-IgG (termed COPSLE, for combination of peptides for SLE) was more efficient for SLE diagnosis, with a larger AUC (0.830) and a positive rate of 73.33%. COPSLE could be used to identify 80.0% of SLE patients who were negative for anti-Smith (Sm), anti-double-stranded DNA (ds-DNA), and anticardiolipin (ACA). The Spearman rank correlation indicated that COPSLE increased with albumin, serum level of C3 and platelet distribution width, but had negative correlations with decreased C3 and discoid lupus.
Conclusions: A citrullinated/non-citrullinated peptide panel is a valuable diagnostic marker of SLE, even for patients who are negative for anti-Sm, anti-ds-DNA and ACA.