title: Label-free in vivo imaging of human leukocytes using two-photon excited endogenous fluorescence.
abstract: We demonstrate that two-photon excited endogenous fluorescence enables label-free morphological and functional imaging of various human blood cells. Specifically, we achieved distinctive morphological contrast to visualize morphology of important leukocytes, such as polymorphonuclear structure of granulocyte and mononuclear feature of agranulocyte, through the employment of the reduced nicotinamide adenine dinucleotide (NADH) fluorescence signals. In addition, NADH fluorescence images clearly reveal the morphological transformation process of neutrophils during disease-causing bacterial infection. Our findings also show that time-resolved NADH fluorescence can be potentially used for functional imaging of the phagocytosis of pathogens by leukocytes (neutrophils) in vivo. In particular, we found that free-to-bound NADH ratios measured in infected neutrophils increased significantly, which is consistent with a previous study that the energy consumed in the phagocytosis of neutrophils is mainly generated through the glycolysis pathway that leads to the accumulation of free NADH. Future work will focus on further developing and applying label-free imaging technology to investigate leukocyte-related diseases and disorders.
authors.affiliation: Hong Kong University of Science and Technology, Department of Electronic and Computer Engineering, Biophotonics Research Laboratory, Clear Water Bay, Kowloon, Hong Kong SAR, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zeng
authors.forename: Bo
authors.initials: B
authors.lastname: Yan
authors.forename: Qiqi
authors.initials: Q
authors.lastname: Sun
authors.forename: Seng Khoon
authors.initials: SK
authors.lastname: Teh
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Zilong
authors.initials: Z
authors.lastname: Wen
authors.forename: Jianan Y
authors.initials: JY
authors.lastname: Qu
mesh_terms: D004926:Escherichia coli / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000097:blood; D006801:Humans; D007962:Leukocytes / Q000737:chemistry* / Q000166:cytology* / Q000382:microbiology; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D009243:NAD
chemical_list: D009243:NAD