Abstract
Antibody dependent cellular phagocytosis (ADCP) removes malignant, immunologically aberrant, and infected cells in response to therapeutic antibodies and vaccines by recognition of cell surface antigens. Using lattice light sheet and TIRF microscopies we show that the phagocyte overcomes target cell restrictions on antigen mobility and drives microclustering of FcγR-IgG-antigen complexes and then reorganizes them into large patches that recruit Syk kinase, promote phosphorylation and trigger engulfment. Increased mobility of CD20-Rituximab in actin-disrupted B lymphoma cells enhanced microcluster reorganization, Syk recruitment and ADCP. Conversely, immobilization of CD20-Rituximab by chemical fixation had the opposite effects. Polarized-TIRF analysis revealed dynamic membrane topography between leading edge and podosome-like structures when IgG was presented fluid bilayers versus flat surfaces on immobile bilayers. The microcluster organization and engulfment depended on Syk and Arp2/3, indicating previously unrecognized complexity for the clearance of cells displaying surface-mobile antigens.
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