Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease with genetic susceptibility. It is characterized by chronic synovitis and progressive joint destruction. There is synovial infiltration by inflammatory cells, activation of synovial fibroblasts, and production of a wide range of inflammatory cytokines. Sustained high disease activity results in a poor disease outcome so assessment of inflammatory activity in RA is of pivotal importance for the optimal treatment in these patients. Disease activity of RA patients is assessed by clinical examination, laboratory tests and radiographic assessment (e.g. ultrasonography). Laboratory assessment of RA activity is done routinely by measuring acute phase reactants such as an erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), which are elevated in most patients with RA. It has been demonstrated that more than 40% of RA patients have normal ESR or CRP (false negative results). Therefore, new serum markers that can more accurately reflect real inflammatory activity in RA patients are needed. Calprotectin (CLP) is a calcium binding leucocyte protein consisting of the heterocomplex of S100A8/ A9 (myeloid-related protein, MRP8/MRP14), as well as being a major monocyte/macrophage protein which has gained interest as a marker of inflammation in RA. Calprotectin has been identified as an important endogenous alarmin, one of the damage-associated molecular pattern (DAMP) molecules that acts as a ligand for the TLR4 receptor and amplifies the inflammation cascade via NF-kB and p38 mitogen-activated protein kinase. Calprotectin levels are higher in the serum of RA patients compared with healthy subjects or patients with osteoarthritis (OA), Still, no cut-off levels have been identified to help in the diagnosis of RA. Calprotectin is involved in cartilage damage in OA. Synovial lining macrophages play a role in the OA process and in cartilage damage. Moderate calprotectin increase has been observed in the serum of OA patients compared with healthy controls also serum calprotectin levels were found higher in OA patients with synovial inflammation compared with those without.
Assessment of the serum level of calprotectin in patients with rheumatoid arthritis and osteoarthritis.