Dynamic quantitative assays of phagosomal function.

Much of the activity of the macrophage as an effector cell is performed within its phagocytic compartment. This ranges from the degradation of tissue debris as part of its homeostatic function to the generation of the superoxide burst as part of its microbicidal response to infection. We have developed a range of real-time readouts of phagosomal function that enable these activities to be rigorously quantified. This unit contains descriptions of several of these assays assessed by different methods of quantitation, including a fluorescence resonance emission transfer (FRET) assay for phagosome/lysosome fusion measured by spectrofluorometry, a fluorogenic assay for the superoxide burst measured by flow cytometry, and a fluorogenic assay for bulk proteolysis measured by confocal microscopy. These assays illustrate both the range of parameters that can be quantified and the flexibility of instrumentation that can be exploited for their quantitation.