Express FRET Labeling and Analysis of Phagocytic Clearance.

Lysosomal DNase II in phagocytic digestion produces DNA ends with 3'PO4 /5'OH, which differ from those created in apoptotic DNA fragmentation, and can be used to label phagocytic clearance of cell death. Here, we describe the use of these specific DNA ends as selective markers of phagocytic reaction in cell suspensions. The approach does not require cell fixation. It selectively labels blunt-ended DNA breaks with terminal 5'OH. The detection is performed by ultra-fast FRET probes in a single step, closed-tube procedure. It takes 3 min and is signaled by fluorescence. The full step-by-step protocol is presented as well as instructions on analysis and representation of the results.The described DNA-end-based phagocytosis marker and the new rapid FRET assay can be useful in studies of phagocytosis, apoptosis and in immune system assessments.