Lipophilic fluorochrome trackers of membrane transfers between immune cells

Cell-to-cell transfers of membrane molecules between lymphoid cells (sometimes referred to as trogocytosis) is frequent and has multiple physiological consequences. Although difficult to visualize through the tracking of defined cell surface proteins, this process can be readily monitored by inserting PKH or CellVue Maroon fluorochromes into the plasma membranes of donor cells. We discuss here parameters that determine its detection by a flow-cytometry-based in vitro assay and present examples of application, including time-lapse video-microscopy analysis of transfers at the immunological synapse. By combining detection of cell-to-cell transfer and of cell surface CD107, it is possible to discriminate lymphoid cells binding target cells with and without perforin release. This could prove useful for identifying cells that destruct known target cells in autoimmune pathologies.