Objective:To evaluate the effect of activation of splenic plasmacytoid dendritic cells (pDCs) on myocardial ischemia-reperfusion (I/R) injury in mice.Methods:The experiment was performed in two parts. Animal experiment Thirty-six SPF healthy male C57BL/6J mice, aged 10 weeks, weighing 22-27 g, were assigned to 3 groups ( n=12 each) using a random number table method: sham operation group (Sham group), myocardial ischemia group (MI group) and myocardial I/R group (MI/R group). The myocardial ischemia was induced by occluding the left anterior descending coronary artery for 40 min in MI group, while the model of myocardial I/R was established by occlusion of the left anterior descending coronary artery for 40 min followed by 1-h reperfusion in MI/R group. Following successful preparation of the model, 3 animals from each group were randomly selected, and their hearts were removed for determination of myocardial infarct size through a combination of TTC and methylene blue double staining. Another 3 animals from each group were randomly selected, and their hearts were removed for examination of pathological changes of myocardial tissues using HE staining. Blood samples were collected from the abdominal aorta of 6 mice left in each group for determination of plasma interferon alpha (IFN-α) concentrations by enzyme-linked immunosorbent assay. Then the animals were sacrificed and hearts were harvested for collection of cardiac perfusate (CP). Cell experiment Twelve SPF healthy male C57BL/6J mice, aged 10 weeks, weighing 22-27 g, were selected and the splenic pDCs were isolated using anti-mPDCA-1 MicroBeads according to the manufacturer′s instructions (with a positivity rate of >85% for the isolated cells). The cells were divided into 4 groups: group pDCs stimulated by CP in Sham group (pDCs+ CP-Sham group), group pDCs stimulated by CP in MI group (pDCs+ CP-MI group), group pDCs stimulated by CP in MI/R group (pDCs+ CP-MI/R group) and pDCs stimulated by PBS group (pDCs+ PBS group). The CP in Sham, MI and MI/R groups and PBS were used to induce and culture pDCs for 8 h. Flow cytometry was employed to detect the expression of CD45 and co-stimulatory molecules CD80, CD86 and Major Histocompatibility Complex Ⅱ (MHC Ⅱ) on the surface of pDCs. The levels of IFN-α in the cell culture supernatant were determined using enzyme-linked immunosorbent assay. Results:Animal experiments Compared with Sham group and MI group, the percentage of myocardial infarct size was significantly increased, the concentrations of plasma IFN-α were increased ( P<0.05), and cardiomyocytes displayed evident vacuolar degeneration, severe myocardial fiber rupture, and infiltration of a substantial number of inflammatory cells in MI/R group. There was no significant difference in each parameter between Sham group and MI group ( P>0.05). Cell experiment Compared with pDCs+ CP-Sham group, the expression of CD80, CD86 and MHCⅡ was significantly up-regulated in pDCs+ CP-MI group ( P<0.05), and no significant change was found in the aforementioned parameters in pDCs+ CP-MI/R group ( P>0.05). The expression of aforementioned parameters was significantly up-regulated in pDCs+ CP-MI group as compared with pDCs+ CP-MI/R group ( P<0.05). Compared with pDCs+ CP-Sham group and pDCs+ CP-MI/R group, the concentrations of IFN-α in the cell culture supernatant were significantly increased in pDCs+ CP-MI group ( P<0.05). There was no statistically significant difference in the concentrations of IFN-α between pDCs+ CP-MI/R group and pDCs+ CP-Sham group ( P>0.05). Conclusions:The mechanism underlying myocardial I/R injury may be related to activation of splenic pDCs leading to the production of IFN-α following myocardial ischemia in mice.