Serum monomeric C-reactive protein autoantibodies in systemic lupus erythematosus and its correlation with disease activity

Autoantibodies against C-reactive protein [anti-CRP] were measured and correlated with disease activity measures in serum samples from 25 patients with systemic lupus erythematosus [SLE]. Two samples were collected from each patient, one during the control state and the other during disease flare according to the Systemic Lupus Erythematosus Disease Activity Index [SLEDAI]. The presence of anti-CRP was analysed with enzyme-linked immunosorbent assay [ELISA]. The cut-off for positive anti-CRP test was set at the 95th centile of 100 healthy blood donor sera. Serum levels of CRP, anti-DNA antibodies, complement components and blood cell counts were evaluated in the two samples of each patient. Of the fifty serum samples, 20 [40%] contained antibodies reactive with monomeric CRP, and all patients with active lupus nephritis were positive for anti-CRP at flare. Anti-CRP data from all patients were positively correlated with SLEDAI scores and anti-DNA antibody levels, whereas significant inverse relationships were noted for complement factors Clq, C3 and C4, and for lymphocyte counts. This study confirms the high prevalence of anti-CRP autoantibodies in SLE and that the antibody levels are correlated with clinical and laboratory disease activity measures. This indicates that anti-CRP antibodies might have biological functions in the pathogenesis of SLE. Further clinical and experimental studies on effects mediated by anti-CRP antibodies are warranted

Cathepsin K as a marker of bone destruction in rheumatoid arthritis

Cathepsin K plays an essential role in bone remodeling and resorption in diseases such as osteoporosis, osteolytic bone metastasis and rheumatoid arthritis. Cathepsin K is a cystein protease that plays a pivotal role in osteoclast function and in the degradation of protein components of the bone matrix by cleaving proteins such as collagen type I, collagen type II and osteonectin. Our study aimed at measuring cathepsin K in the serum of rheumatoid arthritis patients. Our study group consisted of 50 patients with active longstanding rheumatoid arthritis and 50 age and sex matched healthy controls. Standardized clinical examination was performed for each patient, with stress on tender joint count, pain on motion, soft tissue swelling, swollen joint count and swollen proximal interphalangeal score. We found increased levels of cathepsin K compared with the control group and a significant correlation with radiological destruction measured by the Larsen score. Inhibition of cathepsin K may therefore be a new target for preventing bone erosion and joint destruction in rheumatoid arthritis. However, further studies have to be performed to prove that cathepsin K is a valuable parameter for bone metabolism in patients with early rheumatoid arthritis