Delta-aminolevulinic acid-induced fluorescence in normal human lymphocytes

Endogenously generated protoporphyrin IX (PpIX) from exogenous delta-aminolevulinic acid (ALA) has the photodynamic capacity to inactive cancer cells of different origins. The aim of this study was to characterize the ability of normal lymphocytes to transform ALA into PpIX in order to appreciate through further studies changes in pathologic lymphocytes. We investigated in this study PpIX synthesis by normal human lymphocytes using a confocal laser microspectrofluorometer. Live lymphocytes were identified by monoclonal antibody fluorescent labeling. B and T lymphocytes synthesized PpIX (80-100 counts), with a maximum being reached after 4 h ALA incubation. When T subpopulations of lymphocytes were labeled, T4 and T8 changes in fluorescence kinetics were similar, reaching a maximum after 5 h ALA incubation. The influence of monoclonal antibody labeling on this delayed increase for maximum fluorescence is considered. Phytohemagglutinin (PHA, incubation for 72 h) lymphocyte stimulation induced a 100% increase in PpIX fluorescence for T lymphocytes, whereas pokeweed mitogen activation produced an increase of about 50% in the B- or T-lymphocyte signal. Finally, the scanning fluorescence image clearly indicated the inhomogeneity of cytoplasmic ALA-induced PpIX fluorescence, which was probably due to the distribution of mitochondria. The influence of this heterogeneity on PpIX photosensitivity effects is discussed.