Interactions between macrophages and neutrophils in vivo. (A) Interactions between macrophages (red represents photoconverted Kaede) and neutrophils (green represents EGFP) in Tg(mpeg1:Gal4-VP16/UAS:Kaede/mpx:EGFP) compound transgenic F1 embryos. Two examples of apoptotic neutrophils being phagocytosed by macrophages at the wound margin. The first occurs at 340 minutes by macrophage 1 (Mϕ-1) at the top of frame followed by the second at 348 minutes by Mϕ-2. Loss of green neutrophil fluorescence is evident in the Mϕ-1 after 76 minutes and within Mϕ-2 occurs in 45 minutes. Stills from supplemental Video 3. Bar represents 10 μm. (B) Demonstration that the loss of cytoplasmic neutrophil fluorescence is dependent on macrophage phagocytosis. At 568 to 571 minutes, partial phagocytosis of a segment of a neutrophil. At 572.5 to 634 minutes, loss of fluorescence in the phagocytosed fragment occurs after approximately 6 hours (dotted circle represents region of lost EGFP fluorescence). Providing an internal control for this process, an unphagocytosed still-fluorescing neutrophil fragment remains stationary throughout the first phagocytic phase, until it is subsequently engulfed by the same macrophage at 727.5 minutes, with loss of its EGFP fluorescence at 736.5 minutes. Stills from supplemental Video 4. Bar represents 10 μm. In both panels, white arrowheads and yellow arrowheads indicate unphagocyted and phagocytosed states, respectively, of neutrophil corpse. (C-D) Two examples of cytoplasmic transfer from live neutrophils (green represents EGFP) to macrophages (red represents photoconverted Kaede). (C) A neutrophil/macrophage interaction near a wound margin results in a cytoplasmic fragment from a live neutrophil transferring to within a macrophage. (Top panel) Merged images. (Bottom panel) EGFP channel only. Dashed outlines indicate position of macrophage (blue) and neutrophil/fragment. Stills extracted from supplemental Video 5. Bar represents 20 μm. (D) A neutrophil/macrophage interaction in the trunk of the embryo. Merged fluorescence and bright-field images clearly demonstrate interaction resulting in cytoplasm transfer from neutrophil to macrophage. Stills from supplemental Video 6. Bar represents 20 μm. In both examples, white arrowheads and yellow arrowheads indicate unphagocytosed and phagocytosed states, respectively, of the transferring neutrophil cytoplasmic fragment. Neutrophil viability throughout the process is demonstrated by its subsequent migration out of the field of view (direction of white arrow in subpanels iv and v).