Molecular mechanisms of erythrophagocytosis: flow cytometric quantitation of in vitro erythrocyte phagocytosis by macrophages.

A rapid, sensitive, and reproducible flow cytofluorimetric procedure is described for quantitation of erythrophagocytosis based on the use of red blood cells (RBCs) labeled with the fluorescent probe PKH-26. The procedure involves the following steps: i) incubation of PKH-26-labeled erythrocytes with macrophages, ii) removal of un-bound red blood cells, iii) lysis of membrane-bound RBCs, and iv) measurement of extent of phagocytosis by direct flow-cytometric analysis of intact macrophages. Each step was controlled by fluorescence microscopy. Use of fluorescent, instead of radio-labeled RBCs, makes the method more sensitive, rapid, and avoids radioactive hazards. Furthermore, this approach is multi-parametric and can distinguish different populations of macrophages with reference to their erythrophagocytic potential. This technology moreover, has broad applications from the initial step of contact (between effector and target cells to study the specific receptor mediated attachment) to the subsequent cascade of time-dependent changes resulting from that signal transduction.