The Role of Anti-cyclic Citrullinated Peptide Antibody from Joint to Brain

Anti-cyclic citrullinated peptide (CCP) antibodies are highly specific and predictive for rheumatoid arthritis (RA). Recently، existence of anti-CCP in several other inflammatory conditions from psoriatic arthritis to neurodegenerative disorder like Alzheimer''s disease (AD) has been reported. We compared the level of anti-CCP titer between the patients with mild cognitive impairment (MCI) and Alzheimer''s disease; then، we compared it between the patients with mild rheumatoid arthritis and Alzheimer''s disease. In this cross-sectional study، 40 patients with rheumatoid arthritis، 29 patients with Alzheimer''s disease، 30 patients with mild cognitive impairment and 30 healthy controls were enrolled. Anti-CCP titer was measured by solid phase enzyme immunoassay kit. Statistical analysis was performed using one-way analysis of variance and post-hoc Tukey tests. Level of anti-CCP titer (mean ± SD) was higher significantly in patients with Alzheimer''s disease (13. 6 ± 1. 6) was higher than healthy subjects (4. 2 ± 1. 1) and patients with mild cognitive impairment (4. 8 ± 1. 3) (P = 0. 0100 for both). Anti-CCP serum level in 32. 1% of patients with Alzheimer''s disease and 95. 5% of patients with mild rheumatoid arthritis was higher than normal range. In addition، the antibody level was significantly higher in patients with rheumatoid arthritis (54. 7 ± 4. 8) compared to patients with Alzheimer''s disease (P = 0. 0001). We obviously observed differences in Anti-CCP titer between patients with Alzheimer''s disease and those with mild rheumatoid arthritis. It was expected since anti-CCP has a high specificity for rheumatoid arthritis and become positive in early stages of disease with a high predictive value. However، we found that in early stages of cognitive impairment، we could not use this biomarker as a diagnostic test but during disease progression، a significant difference was observed between patients with mild cognitive impairment and those with Alzheimer''s disease. It needs more studies to confirm the role of anti-CCP antibody production in patients with Alzheimer''s disease.