Abstract

Low-density neutrophils (LDNs) have been described in tumors and various autoimmune diseases, where they exhibit immune dysfunction and alter disease progression. Nevertheless, LDNs have been rarely reported in sepsis. We studied sepsis patients admitted to the intensive care unit. Wright-Giemsa stain assay and Transmission electron microscopy were performed to detect the morphology of neutrophils. Flow cytometry was used to analyze the number and function of LDNs. Concentration of cytokines was measured using ELISA. Neutrophil chemotaxis was examined using an under-agarose chemotaxis model. We found that LDNs were significantly elevated in patients with sepsis. Phenotypes and morphological characteristics suggest that LDNs may be formed by mixtures of neutrophils at various maturation stages. In vitro experiments showed that LDN formation was closely associated with neutrophil degranulation. We preliminarily discussed changes in immune function in LDNs. Compared with high-density neutrophils, expression levels of CXC chemokine receptor 4 on LDN surfaces were increased, phagocytotic capacity was decreased, and life span was prolonged. The chemotactic ability of LDNs was significantly reduced, possibly related to the increased expression of P2X1. These data suggest that LDNs are essential components of neutrophils in sepsis. To clarify the source and dysfunction mechanism of LDN in sepsis may be helpful for the diagnosis and treatment of sepsis in the future.

Highlights

  • Low-density neutrophils (LDNs) have been described in tumors and various autoimmune diseases, where they exhibit immune dysfunction and alter disease progression

  • We found that a high proportion of CD66b-neutrophils were found in peripheral blood mononuclear cells (PBMCs)

  • In patients 3, 16, and 21, CD66bpositive neutrophils were the main component of PBMCs (87.93%, 82.20% and 83.90%, respectively)

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Summary

Introduction

Low-density neutrophils (LDNs) have been described in tumors and various autoimmune diseases, where they exhibit immune dysfunction and alter disease progression. We collected the peripheral blood of sepsis patients and purified neutrophils using density gradient centrifugation (Fig. 1A). Gating strategy using flow cytometry showed that PBMCs in sepsis patients included neutrophils, monocytes, and lymphocytes (Fig. 1D).

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