Detection of autoantibodies to citrullinated BiP in rheumatoid arthritis patients and pro-inflammatory role of citrullinated BiP in collagen-induced arthritis

Arthritis Res Ther. 2011;13(6):R191. doi: 10.1186/ar3520. Epub 2011 Nov 22.


Introduction: Anti-citrullinated protein/peptide antibodies (ACPAs) are highly specific to rheumatoid arthritis (RA) patients and are thought to have a close relationship with the pathogenesis of arthritis. Several proteins, including fibrinogen, vimentin, and alpha-enolase, were reported as ACPA-target antigens, and their importance in RA pathogenesis was widely proposed. We identified citrullinated immunoglobulin binding protein (citBiP) as another ACPA target in RA patients and examined its pro-inflammatory role in arthritis.

Methods: We measured the levels of anti-citBiP, anti-BiP, and anti-cyclic citrullinated peptide (CCP) antibodies in the serum of RA patients (n = 100), systemic lupus erythematosus (SLE) patients (n = 60), and healthy controls (n = 30) using ELISA and immunoblotting. Epitope mapping was performed using 27 citBiP-derived peptides. In the mouse study, after DBA/1J mice were immunized with BiP or citBiP, serum titers of ACPAs were measured by ELISA and immunohistochemistry. The development of collagen-induced arthritis (CIA) was observed in BiP- or citBiP-pre-immunized mice.

Results: The serum levels of anti-BiP and anti-citBiP antibodies were significantly increased in RA patients, although only anti-BiP antibodies were slightly increased in SLE patients. Interestingly, anti-citBiP antibody levels were higher than anti-BiP antibody levels in 72% of RA patients, whereas no significant increase in anti-citBiP antibody levels was detected in SLE patients and healthy controls. The serum levels of anti-CCP antibodies were correlated with those of anti-citBiP antibodies in RA patients (R2 = 0.41). Several citrulline residues of citBiP were determined to be major epitopes of anti-citBiP antibodies, one of which showed cross-reactivity with CCP. Immunization of DBA/1J mice with citBiP induced several kinds of ACPAs, including anti-CCP and anti-citrullinated fibrinogen antibodies. Pre-immunization with citBiP exacerbated CIA, and anti-CCP antibody levels were increased in citBiP-pre-immunized CIA mice.

Conclusions: CitBiP is a newly described ACPA target that may play a pro-inflammatory role in arthritis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Arthritis, Experimental / blood
  • Arthritis, Experimental / immunology*
  • Arthritis, Rheumatoid / blood
  • Arthritis, Rheumatoid / immunology*
  • Autoantibodies / blood
  • Autoantibodies / immunology*
  • Autoantigens / immunology
  • Citrulline / metabolism
  • Collagen Type II / immunology
  • Epitope Mapping / methods
  • Epitopes / chemistry
  • Epitopes / immunology
  • Female
  • Fluorescent Antibody Technique
  • Heat-Shock Proteins / chemistry
  • Heat-Shock Proteins / immunology*
  • Heat-Shock Proteins / metabolism
  • Humans
  • Immunoblotting
  • Lupus Erythematosus, Systemic / blood
  • Lupus Erythematosus, Systemic / immunology
  • Mice
  • Mice, Inbred DBA
  • Molecular Sequence Data


  • Autoantibodies
  • Autoantigens
  • Collagen Type II
  • Epitopes
  • Heat-Shock Proteins
  • Citrulline
  • molecular chaperone GRP78