The study further analyzed the differentially expressed gene groups between cardiac MP/DCs in the control group and AF patients, and it found that the secreted phosphoprotein 1 (SPP1) and CCR2 genes and triggering receptor expressed on myeloid cells 2 (TREM2) and CD9 cell surface markers were increased in the MP/DCs of the left atrium in AF patients. The gene discussed is CD9; the disease is atrial fibrillation.