Fluorescence lifetime imaging is able to recognize different hematopoietic precursors in unstained routine bone marrow films.

Fluorescence lifetime imaging (FLIM) has been used in living cells to measure metabolic activity and demonstrate cell differentiation. The aim of this study was to investigate whether the FLIM technique could be able to demonstrate cell maturation during myelopoiesis and erythropoiesis in unlabeled routine bone marrow (BM) preparations. Air-dried, unstained smears of BM aspiration samples of 32 patients without BM disease and a normal morphology on May-Grünwald-Giemsa (MGG) stained smears entered the study. FLIM images were captured with a Zeiss LSM 780 NLO multiphoton microscope equipped with a Becker & Hickl SPC-830 TCSPC FLIM module and HPM-100-40 hybrid detector. The samples were irradiated by two-photon excitation at 800 nm with a titanium-sapphire laser of the LSM 780 NLO. FLIM images were compared with those obtained by autofluorescence high resolution imaging. FLIM images of unstained smears were highly contrasted. Different cell types could be easily recognized as they were similar to those seen in MGG stained preparations. Cytoplasm of cells from the erythroid lineage revealed relatively short fluorescence lifetimes due to the presence of hemoglobin, and therefore could easily be distinguished from granulocytic precursors. Nuclear fluorescence lifetimes of all cell types were higher than those of the corresponding cytoplasm. So, FLIM of unstained BM smears obtained under routine real-life conditions permits an easy identification of BM cells, by highlighting differences of their physicochemical properties.