A specific feature of rheumatoid arthritis is the presence of citrullinated antigen and production of anti-citrullinated protein autoantibodies (ACPA) which can appear years prior to disease onset to trigger immune responses. In this study, the serum citrulline-containing antigens from RA patients were screened and the significance of the antibodies against citrullinated lipopolysaccharide binding protein (anti-cLBP) was studied.
Polypeptides isolated from the serum of patients with RA were identified by the Orbitrap high-precision proteomic technology. And then the citrulline-containing proteins was demonstrated.We synthesized citrullinated LBP peptide based on its richness and possible antigenity. The levels of anti-cLBP were determined in sera of 100 RA, 27 OA, 20 SLE and 50 healthy controls by indirect enzyme-linked immunosorbent assay (ELISA).
A total of 11 citrulline-containing antigens were identified in proteins from sera of RA patients. By using citrullinated LBP, the antibodies (anti-cLBP) was detected in RA patients, healthy and disease controls. We found that the levels of anti-cLBP were significantly increased in RA patients. The sensitivity and specificity of anti-cLBP antibody were 28.00% and 95.92%, respectively. In anti-CCP-negative and RF-negative RA patients, the prevalences of anti-cLBP were 19.05% (4/21) and 20.59% (7/34), respectively. In addition, in RA patients of anti-CCP and RF-double negative, anti-cLBP was also detectable in 16.67% (3/18) of the patients. Further analysis of the clinical relevance, we found that anti-cLBP antibody was associated with disease activities in RA. It was noticed that the level of anti-cLBP was closely related with a high incidence of infection in patients with RA.
Anti-cLBP autoantibody is a novel biomarker in RA, especially in seronegative RA, and associated with disease severity.