Rheumatoid arthritis sera antibodies to citrullinated collagen type II bind to joint cartilage

Abstract

Objective To investigate the occurrence and frequency of anti-citrullinated protein antibodies (ACPA) to cyclic citrullinated type II collagen (COL2) epitope with a capacity to bind joint cartilage. Methods Luminex immunoassay was used to analyze serum antibody reactivity to 10 COL2-citrullinated peptides (ACC10) and corresponding arginine peptide controls in rheumatoid arthritis (RA), osteoarthritis (OA), and healthy individuals’ cohorts. Top ten “promiscuous” sera (cross-reactive with all ACC10) and top ten “private” sera (restrictedly reactive with one ACC10 peptide) from RA and OA cohorts were selected. Enzyme-linked immunosorbent assay (ELISA) was used to detect response to native COL2. Sera were analyzed with naive and arthritic joints from DBA/1J mice by immunohistochemistry, using monoclonal ACPAs and COL2 reactive antibodies with human Fc as comparison. Staining specificity was confirmed with C1 (a major antibody epitope on COL2) mutated mice and competitive blocking with epitope-specific antibodies. Results All patient sera bound ACC10 compared with control peptides but very few (3/40) bound native triple-helical COL2. Most sera (27/40) specifically bound to arthritic cartilage, whereas only one private RA serum bound to healthy cartilage. Despite very low titers, private sera from both RA and OA showed an epitope-specific response, documented by lack of binding to cartilage from C1-mutated mice and blocking binding to wild-type cartilage with a competitive monoclonal antibody. As a comparison, monoclonal ACPAs visualized typical promiscuous, or private reactivity to joint cartilage and other tissues. Conclusion ACPA from RA and OA sera, reactive with citrullinated non-triple-helical COL2 peptides, can bind specifically to arthritic cartilage.

A subset of antibodies targeting citrullinated proteins confers protection from rheumatoid arthritis

“…The binding of E4 to joint cartilage raised the question whether it also binds to other tissues. Our recent study showed a specific binding of E4 limited to structures located in certain non-joint tissues, such as psoriatic skin and esophagus 34 , demonstrating that E4 has a more restricted binding pattern in vivo, in contrast to the in vitro binding to citrullinated peptides. In this study, we showed the strong staining by E4 as well as L2 on the keratinocytes in naïve/arthritic joint skin tissues (Fig.…”

“…3A and Supplementary Fig. 4B ) and in cartilage from the mice with collagen-induced arthritis 34 . We also stained arthritic joint tissues from FCGR2B KO mice one day after the injection of arthritogenic antibodies, these mice are highly sensitive to inflammation and CAIA can be rapidly induced within one day.…”

Shift in perspective: autoimmunity protecting against rheumatoid arthritis

“…In addition, the antibody response is polyclonal, and antibodies with different specificities carrying different functions are mixed. However, an interesting observation was that the binding capacity to the cartilage of polyclonal ACPA reactive to citrullinated COL2 could be visualized by staining of RA and osteoarthritis sera on the arthritic cartilaginous joints, suggesting that this is commonly seen by ACPA-containing RA sera 50…”

“…There are only a few examples of isolated private ACPA clones, which all are derived from mice. The private cross-reactive ACC1 clone cross-reacts to COL2 and binds to the cartilage but also citrullinated filaggrin in the oesophagus and induces severe arthritis 18 50 53. The private specific antibody ACC4 binds to citrullinated COL2 alpha chains and can only bind to the cartilage when it is already destabilised and therefore only enhances arthritis together with other arthritogenic antibodies 18.…”

Significance of Type II Collagen Posttranslational Modifications: From Autoantigenesis to Improved Diagnosis and Treatment of Rheumatoid Arthritis

“…Recently, more than 150 citrullinated cellular and extracellular proteins have been identified in RA synovia, comprising the so-called RA-associated citrullinome, which has been suggested to play an essential role in disease pathogenesis and the generation of ACPA [ 94 , 98 ]. Despite this variety of detected citrullinated antigens, autoimmunity towards COL2 that has been modified by citrullination has been well determined in the RA disease course [ 99 , 100 , 101 , 102 , 103 ]. Anti-citrullinated COL2 antibodies can induce and exacerbate arthritis in experimental murine models [ 100 , 104 , 105 ].…”