PT - JOURNAL ARTICLE AU - Emily C. Suter AU - Eva M. Schmid AU - Erik Voets AU - Brian Francica AU - Daniel A. Fletcher TI - Antibody:CD47 ratio regulates macrophage phagocytosis through competitive receptor phosphorylation AID - 10.1101/2020.07.31.231779 DP - 2020 Jan 01 TA - bioRxiv PG - 2020.07.31.231779 4099 - http://biorxiv.org/content/early/2020/08/02/2020.07.31.231779.short 4100 - http://biorxiv.org/content/early/2020/08/02/2020.07.31.231779.full AB - Cancer immunotherapies often modulate macrophage effector function by introducing either targeting antibodies that activate Fc gamma receptors or blocking antibodies that disrupt inhibitory SIRPα-CD47 engagement. Yet how these competing signals are integrated is poorly understood mechanistically, raising questions about how to effectively titrate immune responses. Here we find that macrophage phagocytic decisions are regulated by the ratio of activating ligand to inhibitory ligand on targets over a broad range of absolute molecular densities. Using endogenous as well as chimeric receptors, we show that activating:inhibitory ligand ratios of at least 10:1 are required to promote phagocytosis of model antibody-opsonized CD47-inhibited targets and that lowering this ratio reduces FcγR phosphorylation due to inhibitory phosphatases recruited to CD47-bound SIRPα. We demonstrate that ratiometric signaling is critical for phagocytosis of tumor cells and can be modified by blocking SIRPα in vitro, indicating that balancing targeting and blocking antibodies may be important for controlling macrophage phagocytosis in cancer immunotherapy.Competing Interest StatementThe authors have declared no competing interest.