SPI1 and atrial fibrillation: After incubation of the PU.1-OE or PU.1 siRNA macrophages with FITC-labelled AF conidia, laser scanning confocal microscopy showed that PU.1-OE macrophages exhibited stronger phagocytosis against AF conidia than the control group (**P < 0.01) (Fig. 3A and B).