POSTECH: Selectively Staining Neutrophils in White Blood Cells
White blood cells act as the first line of defense in the immune system and are often referred to as an army that protects our body. Neutrophils account for the largest portion (55-70%) of white blood cells in humans and fight against bacteria or fungi – and their lack causes abnormalities in the immune system. They usually circulate in the blood and move to sites where tissues are infected or inflamed. Recently, a POSTECH research team has developed a method for deciphering live neutrophils.
Professor Young-Tae Chang of the Department of Chemistry at POSTECH (Associate director of Center for Self-assembly and Complexity, an Institute for Basic Science), Sun Hyeok Lee of the School of Convergence Science and Technology, and Min Gao of the Institute for Basic Science – in joint research with the Ulsan University Hospital – have reported the first fluorescent probe NeutropG for the specific distinction and imaging of active neutrophils.*1 In recognition of its academic excellence, this study was published on August 19, 2021 in the international edition of Angewandte Chemie, a world-renowned chemistry journal.
A fluorescent probe is a reporter that indicates whether a specific ion or substance is recognized by emitting a light signal. Identifying live neutrophils in humans is important not only for clinical diagnosis, but also for finding treatments for infections or inflammations. However, small molecule-based probes for differentiating live neutrophils among granulocytes have not been developed so far.
Antibodies are useful in detecting specific cells, but those with low cell permeability have limitations in identifying biomarkers inside cells. Cell fixation and permeation processes are required to identify biomarkers, but when they undergo the pre-treatment process, their state becomes altered from the live state. These differences limit the selection of antibodies when studying live cells.
To this, the research team tried to use the low-molecule fluorescent compound with relatively high cell permeability to overcome the shortcomings of antibodies. NeutropG, developed in this study, is selectively labeled on neutrophils through the lipid droplet biosynthesis*2, and occurs from the different rate of enzyme gene expression of long-chain acyl-CoA synthetases (ACSL)*3 and diglyceride acyltransferase (DGAT).*4
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It was confirmed that NeutropG changes into triacylglycerol (TAG), a component of the lipid droplet, by the action of these enzymes using a unique mechanism called the Metabolism-Oriented Live-cell Distinction (MOLD), which is completely different from the conventional Holding Oriented Live-cell Distinction (HOLD) or the Gating Oriented Live-cell Distinction (GOLD).
NeutropG was used to observe the phagocytosis process of neutrophils and through this, the researchers proved that the staining can stay stable for a long time and does not significantly affect the native functions of neutrophils.
This study has verified that NeutropG selectively stains healthy neutrophils and through its application, the researchers were able to accurately quantify neutrophil levels in fresh blood samples. This high selectivity of neutrophil demonstrated the potential to be applicable in clinical diagnosis.
“NeutropG is the first case for specific distinction and imaging of active neutrophils in blood samples,” explained Professor Chang who led the study. “In particular, the metabolism-oriented live-cell distinction has the strength to selectively identify healthy neutrophils.”