Data of low-density neutrophils (LDN),the neutrophils in the peripheral blood mononuclear cells (PBMC) fraction,in sepsis is still less. As such,LDN (CD66b-positive cells in PBMC) was highest in intensive care unit (ICU) patients with sepsis (n=24) compared with non-sepsis (n=10) and healthy control (n=20),with a negative correlation with lymphocyte count and could predict secondary infection and mortality with the area under the curve (AUC) at 0.79 and 0.84,respectively. Compared with sepsis normal-density neutrophils (NDN),sepsis-LDN demonstrated higher expression of CD66b,CD63,CD11b,and CD184,but lower expression of CD62L and CD182 and defects of effector functions,including phagocytosis and apoptosis. The t-distributed stochastic neighbor embedding (t-SNEs) demonstrated high program cell death ligand-1 (PD-L1) in sepsis-LDN. In sepsis samples,the T cell proliferation in PBMC (T cells with LDNs) was lower than that in the isolated T cells (T cells alone) and incubation of anti-PD-L1 neutralizing antibody,but not a reactive oxygen species (ROS) scavenger (N-acetyl cysteine),improved the T cell suppression. Additionally,30 min lipopolysaccharide (LPS) activation altered healthy control NDN into LPS-LDN (reduced density) and LPS-NDN (maintain density) with similarly elevated CD66b,CD11B,and CD62L. However,LPS-LDN (in vitro LDN) showed lower expression of CD63,CD184,and PD-L1 compared with LDN from patients (sepsis-LDN),suggesting a partial LPS impact on LDN generation. From the microscopic-based method (Wright’s staining in PBMC),sepsis-LDN demonstrated a mixed population of mature and immature cells with a good correlation with the flow-based analysis (Bland–Altman analysis and AUC). In conclusion,LDN in sepsis,partly generated by LPS activation,was associated with secondary infection and T cell suppression,mainly through the expression of PD-L1,which might be an immune suppression biomarker,especially with a less expensive microscopic-based method.
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