Objective To investigate the effects of caspase recruitment domain-containing protein 9 (CARD9)expression in peritoneal macrophages on severe acute pancreatitis(SAP)in rats and its mechanism.Methods A total of 60 male Sprague Dawley rats were divided into control group(n=6), SAP group(n=18),small interfering RNA(siRNA)control group(n=18)and siRNA CARD9 group (n=18).SAP rat models were established.At three,six and twelve hours after the models were established,ascites was collected,peritoneum was lavaged and peritoneal macrophages were isolated and cultured.The expressions of CARD9,nuclear factor-kappaB(NF-κB),p38 mitogen-activated protein kinase(p38MA PK)at mRNA level in peritoneal macrophages was measured by real-time polymerase chain reaction(RT-PCR).The levels of tumor necrosis factor-α(TNF-α),interleukin(IL)-1β and IL-6 in peripheral blood were detected by enzyme-linked immunosorbent assay(ELISA).LSD or Tamhane′s T2 methods were performed for statistical analysis.Results At three,six and twelve hours after the models were established,CA RD9 mRNA levels of peritoneal macrophages in SAP group were 1.63 ± 0.05,1.68 ± 0.24 and 2.61 ± 0.02,respectively,which were all higher than that of control group(1.01 ± 0.23),and the differences were statistically significant(t=25.97,6.86 and 131.59;all P<0.05);the levels of CA RD9 mRNA of siRNA CARD9 group were 1.45 ± 0.02,1.24 ± 0.03 and 1.63 ± 0.03,respectively,which were lower than that of SAP group at the same time points,and the differences were statistically significant(t=-7.81,-4.46 and -62.13;all P< 0.05).At three,six and twelve hours after the models were established,the mRNA levels of NF-κB and p38MA PK of peritoneal macrophages of rats in SAP group were 1.51 ± 0.08,1.81 ± 0.10,2.30 ± 0.05 and 1.37 ± 0.13,1.69 ± 0.18,2.42 ± 0.23,respectively, which were higher than those of control group(1.00 ± 0.01,1.03 ± 0.08),and the differences were statistically significant(tNF-κB=15.10,19.95 and 60.36;tp38MAPK=5.37,8.34 and 14.11;all P<0.05);the levels of N F-κB mRNA in siRNA CARD9 group were 1.38 ± 0.05,1.57 ± 0.06 and 1.76 ± 0.09, respectively,which were lower than that of SAP group at the same time points,and the differences were statistically significant(t= -3.32,-5.07 and -12.70;all P<0.05).At six and twelve hours after the models were established,the p38MA PK mRNA levels of siRNA CARD9 group were 1.50 ± 0.10 and 2.00 ± 0.09,respectively,which were lower than that of SAP group,and the differences were statistically significantly(t= -2.30 and -4.17,both P< 0.05).At three,six and twelve hours after the models were established,the levels of TNF-α,IL-1β and IL-6 in peripheral blood of SAP group were(53.49 ± 21.64)pg/mL,(108.62 ± 22.76)pg/mL and(139.00 ± 15.35)pg/mL;(43.86 ± 18.30)pg/mL, (87.51 ± 17.10)pg/mL and(117.27 ± 14.57)pg/mL;(78.38 ± 32.70)pg/mL,(156.39 ± 30.56)pg/mL and(209.56 ± 26.09)pg/mL,respectively,which were higher than those of control group((2.79 ± 1.17),(7.13 ± 4.52),(12.73 ± 8.08)pg/mL),and the differences were statistically significant(tTNF-α=5.73,11.37 and 21.69;tIL-1β=4.77,11.13 and 17.68;tIL-6=4.77,11.32 and 17.68;all P<0.05).At six and twelve hours after the models were established,the levels of TNF-α,IL-1β and IL-6 of siRNA CARD9 group were(75.73 ± 16.93)pg/mL,(108.23 ± 14.02)pg/mL;(63.05 ± 11.98)pg/mL, (91.56 ± 14.28)pg/mL and(112.67 ± 21.40)pg/mL,(163.62 ± 25.51)pg/mL,respectively,which were lower than those of SAP group,and the differences were statistically significant(tTNF-α= -2.84,-3.63;tIL-1β= -2.88,-3.09;tIL-6= -2.88,-3.09;all P< 0.05).Conclusions There are CARD9-related NF-κB and p38MAPK pathways in peritoneal macrophages of SAP rats.Intervention of the expression of CARD9 in peritoneal macrophages,especially at early stage of SAP may relieve the inflammation reaction and pancreatic injury,which may provide a new method for SAP treatment.