(Auto)immunity to cartilage matrix proteins - a time bomb?

Serum and synovial cartilage oligomeric matrix protein levels in early and established rheumatoid arthritis

OBJECTIVE

To assess cartilage oligomeric matrix protein (COMP) levels in serum and synovial fluid in patients with early and established rheumatoid arthritis (RA), and to correlate the levels with clinical, laboratory and radiological characteristics.

PATIENTS AND METHODS

The study included 24 female RA patients. Full medical history was taken, thorough clinical examination and laboratory investigations performed, and body mass index (BMI) recorded. Radiological damage was assessed according to the modified Larsen score. Disease activity score 28 (DAS28) was calculated. The control group comprised 30 age- and gender-matched healthy subjects. Serum and synovial COMP levels were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Mean patient age was 44.04 ± 10.5 years. Of the 24 patients, 12 had early RA and 12 had established disease with joint destruction; 5 of each group had knee effusion. Serum COMP was significantly higher in patients (19.54 ± 5.47 µg/ml) compared to controls (5.93 ± 1.95 µg/ml; p < 0.001) and was also significantly higher in patients with established disease (23.9 ± 3.1 µg/ml) compared to those in early stages (15.1 ± 3.2 µg/ml; p < 0.001). Synovial COMP was also significantly increased in established compared to early-stage RA (31.2 ± 9.8 µg/ml vs. 51.6 ± 10.4 µg/ml; p = 0.013). Serum and synovial COMP significantly correlated with age, disease duration, BMI, DAS28 and modified Larsen score. On performing regression analysis in RA patients, only BMI could predict the serum level of COMP (p = 0.02).

CONCLUSION

COMP is a promising biomarker for disease activity in RA, making it a potential therapeutic target. The obvious correlation with the BMI throws light on the importance of weight control not only in osteoarthritis (OA), but also in RA.

Rheumatoid arthritis vaccine therapies: perspectives and lessons from therapeutic ligand epitope antigen presentation system vaccines for models of rheumatoid arthritis

The current status of therapeutic vaccines for autoimmune diseases is reviewed with rheumatoid arthritis as the focus. Therapeutic vaccines for autoimmune diseases must regulate or subdue responses to common self-antigens. Ideally, such a vaccine would initiate an antigen-specific modulation of the T-cell immune response that drives the inflammatory disease. Appropriate animal models and types of T helper cells and signature cytokine responses that drive autoimmune disease are also discussed. Interpretation of these animal models must be done cautiously because the means of initiation, autoantigens, and even the signature cytokine and T helper cell (Th1 or Th17) responses that are involved in the disease may differ significantly from those in humans. We describe ligand epitope antigen presentation system vaccine modulation of T-cell autoimmune responses as a strategy for the design of therapeutic vaccines for rheumatoid arthritis, which may also be effective in other autoimmune conditions.

Cartilage oligomeric matrix protein and its binding partners in the cartilage extracellular matrix: interaction, regulation and role in chondrogenesis

Thrombospondins (TSPs) are widely known as a family of five calcium-binding matricellular proteins. While these proteins belong to the same family, they are encoded by different genes, regulate different cellular functions and are localized to specific regions of the body. TSP-5 or Cartilage Oligomeric Matrix Protein (COMP) is the only TSP that has been associated with skeletal disorders in humans, including pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED). The pentameric structure of COMP, the evidence that it interacts with multiple cellular proteins, and the recent reports of COMP acting as a 'lattice' to present growth factors to cells, inspired this review of COMP and its interacting partners. In our review, we have compiled the interactions of COMP with other proteins in the cartilage extracellular matrix and summarized their importance in maintaining the structural integrity of cartilage as well as in regulating cellular functions.