Abstract： Objective:To investigate the role of caspase recruitment domain protein 9(card9) from macrophage in pancreatic acinar-to-ductal metaplasia.Methods:Card9 siRNA1, card9 siRNA2 and card9 siRNA3 were constructed; fluorescence microscopy was used to investigate the fluorescence intensity of macrophages, and real-time quantitative PCR method was performed to detect the expressed level of card9 mRNA to obtain the best transfection rate. 100 μg/ml β glucan was added into 5×10 5 macrophages in vitro culture for 12 or 24 hours, which were divided into positive group (macrophages), β glucan-stimulated positive group (β dextran+ macrophage), negative group (card9 -/- macrophage) and β glucan-stimulated negative group (β dextran+ card9 -/- macrophages). Western blotting was applied to determine the protein level of card9 in macrophages. Then, 1×10 5 macrophages and 1×10 5 pancreatic acinar cells were co-cultured in upper and lower transwell chamber in vitro for 120 hours, which were divided into positive group (macrophages+ acinar cells), 100 μg/ml and 500 μg/ml β glucan-stimulated positive group, negative group (card9 -/- macrophage+ acinar cell), 100 μg/ml and 500 μg/ml β glucan-stimulated negative group. Pancreatic acinar cells in the lower chamber were collected and immunofluorescence was applied to assay the duct metaplasia marker CK19 protein expression. Results:At 24 hours of transfection using siRNA, the intracellular fluorescence intensity in macrophages reached a peak. Card9 siRNA at the concentration of 200 nmol/l showed the highest interference efficiency. Card9 protein in positive group, β glucan-stimulated positive group, negative group, and β glucan-stimulated negative group were 0.81±0.05, 1.46±0.05, 0.42±0.06 and 0.46±0.06, respectively; card9 expression in β glucan-stimulated positive group was obviously higher than that in positive cell group, and the difference was statistically significant ( P<0.05). Finally, after 100 or 500 μg/ml β glucan stimulation, the green fluorescence in pancreatic acinar cells increased significantly compared with positive group, exhibiting β glucan concentration dependence. Conversely, CK19 protein in negative group and 100 and 500 μg/ml β glucan-stimulated negative group was obviously decreased compared with positive group. Conclusions:The expression level of card9 in macrophages can induce acinar-to-ductal metaplasia, indicating that card9 may mediate in the pathogenesis of pancreatic cancer.