The role of anti-collagen type II antibodies in the pathogenesis and prognosis of rheumatoid arthritis

Abstract: Rheumatoid arthritis (RA) which affects 0.5-1% of the world population and is characterised by joint erosions and presence of the autoantibodies anti-citrullinated protein antibodies (ACPA) and rheumatoid factor. Collagen II (CII) is a joint-specific antigen and we have shown that antibodies against CII (anti-CII) are present in around 8% of RA patients. RA patients with anti-CII are characterized by acute RA onset with elevated CRP and early joint erosions at the time of RA onset. Polymorphonuclear granulocytes (PMN) and peripheral blood mononuclear cells (PBMC) are abundant in RA synovial fluids, where they can interact with anti-CII, thus forming immune complexes (IC) with CII. In my thesis I have shown that PMN upregulated the cell surface markers CD66b and CD11b and downregulated CD16 and CD32 after stimulation with anti-CII IC. These changes in CD66b and CD16 associated to joint erosions to a larger extent than did PBMC responses to anti-CII IC. PMN cocultured with PBMC and stimulated with anti-CII IC showed augmented chemokine production that was dependent on TLR4 and functionally active PMN enzymes. This mechanism can lead to accumulation of inflammatory cells in joints of RA patients who are anti-CII positive around the time of RA diagnosis, and may thus help explain the acute onset RA phenotype associated with anti-CII.In a large Swedish RA cohort, anti-CII associated with elevations in clinical and laboratory measures of disease activity at diagnosis and until 6 months, whereas ACPA associated with late inflammation. Anti-CII seropositive RA was associated with improvements in clinical measurements and was negatively associated with smoking in contrast to ACPA that was associated with worseneing of clinical symptoms and associated positively with smoking. Anti-CII levels associated to  HLADRB1'03 and  HLADRB1'01 whereas ACPA showed negative association to HLA-DRB1'03. In a Malaysian RA cohort anti-CII also associated to elevated CRP at the time of diagnosis.Anti-CII seropositive RA represents a distinct phenotype, in many respects representing the converse  to the clinical, genetic and smoking associations described for ACPA. Early determinations of anti-CII in parallel to ACPA predict the inflammatory outcome in RA.