Absence of IgG-Fc core fucose enhances platelet phagocytosis through FcγRIII on PMNs and monocytes. Platelets were haptenized with TNP; labeled for phagocytosis with pHrodo; opsonized with either isotype antibody, anti-TNP low- or high-fucose antibodies; subjected to phagocytosis by either neutrophils (PMNs; A), FcγRIIIa⁺ monocytes (B), or FcγRIIIa^– monocytes (C) as effector cells; and expressed as anti-TNP–specific phagocytosis (Mean Fluorescence Intensity (MFI) anti-TNP − MFI isotype IgG). Anti-TNP IgG1 antibodies with low fucose displayed increased phagocytosis compared with highly fucosylated anti-TNP antibodies using PMNs or FcγRIIIa⁺ monocytes (A-B, respectively) as effector cells, but not with FcγRIIIa^– monocytes (C). Platelets were labeled with pHrodo, opsonized with 35 AU of anti-HPA-1a antibodies from maternal FNAIT sera, and subjected to phagocytosis by neutrophils (D). Phagocytosis was expressed as anti-HPA-1a–specific phagocytosis (MFI anti-HPA-1a from maternal FNAIT sera − MFI isotype IgG from NHS). Statistical analyses: 1-tailed unpaired Student t test (A-C) and Pearson correlation (D). *P ≤ .05; **P ≤ .01. NS, nonsignificant.