CD47 inhibits phagocytosis through Vav dephosphorylation.

CD47 on viable cells protects against phagocytosis. CD47 is recognized by SIRPα, an inhibitory receptor expressed by macrophages and other myeloid cells. Activated SIRPα recruits SHP-1 and SHP-2 phosphatases, but the inhibitory signaling cascade downstream of these phosphatases is unclear. Here, we used time-lapse imaging to measure how CD47 impacts the kinetics of phagocytosis. Targets with IgG antibodies were primarily phagocytosed through a Rac-based reaching mechanism. Targets also containing CD47 were only phagocytosed through a less frequent Rho-based sinking mechanism. Hyperactivating Rac2 eliminated the suppressive effect of CD47, suggesting that CD47 prevents activation of Rac and reaching phagocytosis. During IgG-mediated phagocytosis, the tyrosine kinase Syk phosphorylates the GEF Vav, which activates Rac to drive F-actin rearrangement and target internalization. CD47 inhibited Vav phosphorylation without impacting Vav recruitment to the phagocytic synapse or Syk phosphorylation. Macrophages expressing a hyperactive Vav were no longer sensitive to CD47. These data suggest that Vav is a key target of the CD47 signaling pathway.