Objective:To investigate the expression and clinical significance of decoy receptor 3 (DcR3) and its signal pathway-related molecules in PBMCs of patients with ankylosing spondylitis (AS).Methods:Peripheral blood samples, clinical data and laboratory test results were collected from 100 patients with ankylosing spondylitis [50 patients with AS activity (ASA), 50 patients with AS stability (ASS)], 30 patients with osteoarthritis and 30 patients with gouty arthritis (as disease control group), and 60 healthy controls (HC). The mRNA expression levels of DcR3 and its signal pathway related genes (DR3, TL1A, Fas, FasL, LIGHT, LIGHTR, LTβR) were measured by real-time fluorescence quantitative polymerase chain reaction. Measurement data among the three groups in normal distribution were analyzed by t test or one-way analysis of variance, pairwise comparisons using LSD- t test, non-normal distribution data were analyzed by Mann-Whitney test or Kruskal-Wallis H test, χ2 test was used for correlation analysis of categorical variables. Correlation analysis between variables were analyzed using Spearman correlation analysis. Results:① By comparing the AS group, disease control group and HC group, the expression levels of DcR3 mRNA and DR3 mRNA in the AS group were lower than those in disease control group and HC group, and DcR3 mRNA and DR3 mRNA in disease control group were lower than those in the HC group {DcR3mRNA: [6.21 (3.89, 10.70)]×10 -4vs [9.51 (5.89, 16.65)]×10 -4vs [17.81 (11.27, 24.20)]×10 -4, H=55.28, P<0.001; DR3 mRNA: [41.05 (24.09, 66.95)]×10 -4vs [58.28 (28.41, 94.38)]×10 -4vs [94.79 (54.07, 144.51)]×10 -4, H=37.10, P<0.001}. The expression level of TL1A mRNA in the AS group was higher than that in disease control group {[14.71(4.91, 42.22)]×10 -4vs [4.00(1.07, 16.60)]×10 -4vs [7.70 (3.52, 27.83)]×10 -4, H=17.71, P<0.001}; The expression level of Fas mRNA in AS group and disease control group was lower than that in HC group {[20.99(4.63, 62.89)]×10 -4vs [23.97(15.82, 38.99)]×10 -4vs [78.45 (27.32, 146.46)]×10 -4, H=31.17, P<0.001}. The expression level of FasL mRNA in AS group was higher than that in disease control group and HC group {[42.87(6.57, 91.21)]×10 -4vs [5.45(2.83, 10.32)]×10 -4vs [6.88 (4.57, 23.79)]×10 -4, H=46.42, P<0.001}. The expression level of LIGHTR mRNA in AS group was lower than that in disease control group {[52.66 (7.20, 143.21)]×10 -4vs [98.80 (53.11, 166.24)]×10 -4vs [63.47(40.85, 138.07)]×10 -4, H=11.96, P<0.001}. There were no significant differences in LIGHT mRNA and LTβR mRNA among all groups ( H=0.86, P>0.05; H=3.18, P>0.05). ②The expression levels of DcR3 mRNA, DR3 mRNA and Fas mRNA in ASA group and ASS group were lower than those in HC group. DcR3 mRNA in ASA group was higher than that in ASS group, and DR3 mRNA in ASA group was lower than that in ASS group {DcR3 mRNA: [7.28 (4.92, 16.56)]×10 -4vs [4.59 (2.49, 7.03)]×10 -4vs [17.81 (11.27, 24.20)]×10 -4, H=62.63, P<0.001; DR3 mRNA: [30.93(16.18, 66.66)]×10 -4vs [47.17(29.91, 67.40)]×10 -4vs [94.79(54.07, 144.51)]×10 -4, H=41.48, P<0.001; Fas mRNA: [20.04(3.29, 62.30)]×10 -4vs [22.49(5.63, 64.79)]×10 -4vs [78.45(27.32, 146.46)]×10 -4, H=23.54, P<0.001}. The expression levels of TL1A mRNA and LTβR mRNA in the ASA group were higher than those in the ASS group and the HC group {TL1A mRNA: [32.36(10.09, 97.84)]×10 -4vs [9.98(1.29, 21.63)]×10 -4vs [7.70(3.52,27.83)]×10 -4, H=21.14, P<0.001; LTβR mRNA: [6.13(2.16,20.06)×10 -4vs [2.13(0.53,8.04)]×10 -4vs [2.72 (1.24,5.73)]×10 -4, H=12.86, P<0.001}. The expression level of FasL mRNA in the ASA group and the ASS group was higher than that in the HC group {[60.70 (8.16, 106.16)]×10 -4vs [30.14 (5.37, 78.40)]×10 -4vs [6.88 (4.57, 23.79)]×10 -4, H=18.99, P<0.001}. The expression level of LIGHTR mRNA in ASS group was lower than that in HC group {[49.79(10.75, 168.48)]×10 -4vs [15.92(3.27, 105.91)]×10 -4vs [63.47(40.85, 138.07)]×10 -4, H=11.80, P<0.001]. There was no significant difference in LIGHT mRNA among all groups ( H=4.15, P>0.05). ③Spearman correlation analysis showed that DcR3 level was positively correlated with BASDAI score and hsCRP in AS patients ( r=0.52, P<0.001; r=0.35, P<0.01), and DR3 level was negatively correlated with BASDAI score, ESR and hsCRP level ( r=-0.28, P<0.001; r=-0.25, P<0.001; r=-0.31, P<0.001). TL1A was positively correlated with BASDAI score, ESR and hsCRP level ( r=0.23, P=0.046; r=0.26, P=0.015; r=0.25, P=0.017). Conclusion:DcR3 and its signal pathway-related molecules are differentially expressed in PBMCs of patients with AS, suggesting that they may participate in the occurrence and development of AS.