457 Circulating Low-Density Neutrophils in Acute Myocardial Infarction

Abstract

Cardiac repair following AMI is orchestrated by a dynamic inflammatory process, which is significantly shaped by the activity of neutrophils. A novel sub-population of low-density neutrophils (LDNs) existing within the peripheral blood mononuclear cell (PBMC) fraction of whole blood has been described to promote pathological inflammation in sterile inflammatory conditions. However, the extent to which LDNs are involved in propagating inflammation following AMI is yet to be determined. We therefore aimed to characterise LDNs in the setting of AMI. Normal-density (NDNs) and low-density neutrophils from AMI patients (n=7) and healthy controls (n=4) were isolated from granulocyte and PBMC fractions of whole blood, respectively. The cell-surface expression of markers for identifying (CD15) neutrophils and assessing neutrophil activation (CD66b, CD11b, CD33, CD16) were examined by flow cytometry. We observed a distinct pattern of neutrophil cell-surface activation markers in LDNs compared to NDNs. In a pooled cohort (n=11), LDNs expressed significantly higher levels of CD66b (118% higher), CD15 (115% higher) and CD33 (158% higher) than NDNs, whilst expression of CD11b and CD16 were significantly decreased in LDNs (27% and 72% lower respectively). We observed that LDNs from AMI patients (0.93%±0.77) represent a significantly greater proportion of granulocytes than healthy controls (0.27%±0.23). Our results are consistent with the view that LDNs and NDNs exhibit marked differences in activation. The presence of a phenotypically-distinct subset of neutrophils increasing in frequency during AMI may be functionally important, highlighting the need for further investigation.