Natural fluorescence of white blood cells: spectroscopic and imaging study.

Autofluorescence has been proved to be an intrinsic parameter of biological substrates that may aid in both the characterization of the physiological state and the discrimination of pathological from normal conditions of cells, tissues and organs. In this work, the fluorescence properties of human white blood cells have been studied in suspension and on single cells at microscopy. The results indicate that suspensions of agranulocytes and granulocytes differ in the amplitude of the fluorescence signal on excitation at wavelengths in the range 250-370 nm. The differences are particularly enhanced when excitation is performed in the 250-265 nm range. Microspectrofluorometric analysis, performed on single cells, allows several leukocyte families to be characterized. Lymphocytes, monocytes, neutrophils and eosinophils can be distinguished according to the intensity and spectral shape of the autofluorescence emission in the visible range from 440 to 580 nm. Both the nature and extent of the differences change when the excitation wavelength is moved from 366 to 436 nm. Differences in the intrinsic metabolic engagement, rather than in the cell dimensions, seem to be responsible for the differences observed between the leukocyte populations. The results identify interesting perspectives for autofluorescence as a discriminating parameter in the differential counting of human white blood cells.