Objective: To analyze the correlation between the expression of peptidyl arginine deiminase 4(PAD4) and the levels of rheumatoid factor(RF), anti-cyclic citrullinated peptide(CCP) antibody, the disease activity score using 28 joint counts(DAS28) in rheumatoid arthritis(RA) patients,and to explore the significance of PAD4 for the diagnosis and therapy of RA. Methods: The serum of 90 RA patients and 76 healthy controls were collected. At the same time, the clinical data of RA patients were collected. The expression level of PAD4,RF-IgA,RF-IgG and anti-CCP antibody in serum of RA patients and healthy controls was detected by enzyme linked immunosorbent assay(ELISA). In addition, EDTA anticoagulant blood of 39 RA patients and 22 healthy controls were collected, the peripheral blood mononuclear cells(PBMC) were separated by lymphocyte separation solution. The expression level of PAD4 mRNA of RA patients was detected by real-time fluorescence quantitative PCR, and the levels of rheumatoid factor in serum of RA patients were detected by BN Ⅱ System. The proliferation of PBMC was detected by CCK-8, and the apoptosis of PBMC was detected by flow cytometry. Results: The serum concentration of PAD4 in RA patients was(5.94±0.37) ng·ml-1, which was higher than(2.30±0.18) ng·ml-1 in healthy controls, the difference was statistically significant(P<0.05). The area under receiver operating characteristic(ROC)curve of PAD4 in diagnosing RA was 0.875. The expression level of PAD4 in RA patients was positively correlated with RF-IgM(r=0.22, P=0.039). The level of PAD4 in patients with positive anti-CCP antibody was positively correlated with anti-CCP antibody(r=0.258,P=0.033), moreover the level of PAD4 in patients with negative anti-CCP antibody were high. However, there was no correlation between level of PAD4 and RF-IgA, RF-IgG, DAS28. The best time and concentration of F-amidine, which was an inhibitor of PAD4, on PBMC were 48 h and 15 μmol·L-1 respectively. F-amidine could increase the proportion of apoptosis in PBMC. The expression level of PAD4 mRNA in RA patients was 7.23±9.57, which was higher than 1.00±0.00 in healthy controls, the difference was statistically significant(P<0.05),which was positively correlated with anti-CCP antibody(r=0.390,P=0.023). However, there was no correlation between level of PAD4 mRNA and RF, DAS28. Conclusion: The expression level of PAD4 in RA patients can be used as an indicator for the diagnosis of RA, PAD4 is expressed in 73.7% RA patients with negative anti-CCP antibody. It is suggested that PAD4 can be used as the target of RA treatment.
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