A fundamental role of mAbp1 for phagocytosis and bacterial clearance in vivo. (A) Confocal microscopy images of dHL-60 cells and murine PMNs phagocytosing serum-opsonized Alexa 594–conjugated E coli (red). mAbp1 (green) was enriched at the site of particle binding (arrows). Bar = 10 μm. (B) Maximal 3D projection of confocal images taken with an interval of 0.4 μm of a dHL-60 cell expressing mAbp1-EGFP (green) phagocytosing Alexa 594–labeled E coli (red). Please see supplemental Figure 1 and supplemental Video 1 for three-dimensional (3D) animation. Bar = 5 μm. (C) Confocal spinning disc microscopy of a dHL-60 cell expressing mAbp1-EGFP during phagocytosis of serum-opsonized Alexa 594–conjugated E coli. Consecutive images at indicated time points were extracted from the original recording that was performed with a frame rate of 1 picture per second (please see supplemental Video 2). For better visualization, the EGFP fluorescence intensity was processed to pseudocolors. mAbp1 was dynamically enriched at the binding site (arrows) of the E coli particle (dotted line). Bar = 10 μm. Phagocytosis of serum-opsonized E coli particles by (D) siAbp1 dHL-60 cells or (E) murine mAbp1^−/− PMNs compared with siControl (100%) or mAbp1^+/+ PMNs (100%). (D-E) Mean relative phagocytosis ± SD; n = 4. (F) Phagocytosis of serum-opsonized S typhimurium invasion-deficient strain SB161 by murine mAbp1^−/− and mAbp1^+/+ PMNs. Mean number of CFU per 10⁵ PMN; n = 3. (G) Bacterial load of spleens of mAbp1^+/+ and mAbp1^−/− mice 48 hours after oral infection with 5 × 10⁷ CFU of S typhimurium wild-type strain SL1344. Mean CFU × 10⁵/g spleen ± SEM; n = 4; *P < .05; **P < .005.