C3 ruffles FcγR's claim over phagocytic cups.

Phagocytosis plays diverse roles in biology, but our understanding of the purpose, interplay and cell signaling mechanisms associated with different modes of phagocytosis is limited, without being able to capture and visualize each step in this rapid process from beginning to end. A new study by Walbaum et al. uses stunning time-lapse 3D imaging of the engulfment of erythrocytes by macrophages via sinking, ruffling and cup formation, unequivocally confirming a visionary 44-year-old theory derived from still electron microscopy photos, that phagocytosis mediated by complement receptor CR3 occurs via a sinking mechanism, and antibody-mediated phagocytosis occurs via phagocytic cup formation. The paper also challenges dogma, showing that phagocytic cup formation is not unique to antibody receptor-phagocytosis, rather CR3 plays a complex role in different modes of phagocytosis. For example, inhibition of antibody mediated phagocytosis leads to a compensatory upregulation of CR3-mediated sinking phagocytosis. These findings animate, in vivid colors, processes previously only captured as stills, exposing interactions between different phagocytic mechanisms and altering our basic understanding of this important process.