Characteristics of immunity system in postoperative delirium patients by single-cell transcriptomic analysis

Background: Postoperative delirium (POD) is the most complication after cardiac surgery, and associated with increased mortality and decreased long term cognition ability. Our study aimed to explore the characteristics of immunity system in POD patients. Methods: This prospective study included patients scheduled for selective on-pump cardiac surgeries, who were divided into Non-POD and POD group according to whether POD occurred within 30 days after surgery. Multi-channel spectral flow cytometry, single-cell sequencing and plasma cytokines measurement were performed to describe the characteristics of immunity system in POD patients before surgery and at 24 hours after surgery. Results: A total of 120 patients were included, and 12 were diagnosed as POD within 30 days after surgery. T cells and B cells were activated in POD patients before and after surgery, and the upregulation of related genes contributed to the activation of chemotaxis in GZMK+ CD8+ T cells and memory B cells, which was confirmed by the elevation of CCL3 and CXCL8 concentration in plasma and the increased expression of chemotaxis related ligands-receptors pairs (CCL16_CCR1 and CXCL13_CXCR5). The inflammation response was enhanced in CD4+ T cells, which was confirmed by the activation of many cytokines related pathways and increased plasma level of IL-17 and IL-4 in POD patients before and after surgery. In monocytes, antigen presentation process and complement response were enhanced in POD patients before and after surgery, which was confirmed by the increased relative abundance of antigen presentation related surface markers (CD80, HLA-DR), activation of gene sets related to antigen binding and complement activation, and increased expression of related ligands-receptors pair (HLA-A_KIR3DL1 and C3_C3AR1). Overall design: We performed single-cell RNA sequencing of peripheral blood mononuclear cells from patients with or without POD at Pre-surgery and at 24 hours after surgery. The sequencing profiles were used to cluster the cells into the following four immune cell types based on expression of well-established markers: monocytes, T cells, B cells, and natural killer cells.