Syk is required for optimal phagocytosis and killing of rag1^−/− serum-opsonized bacteria. (A) Phagocytosis was determined by flow cytometric analysis of FITC-labeled S aureus or E coli by WT, syk^−/−, CD11b^−/−, or CD18^−/− neutrophils. (B) Intracellular bacterial killing capacity assessed by viable S aureus or E coli colony-forming units (CFUs). Data are the mean (n = 3 replicates) of the percentage remaining CFU relative to the addition of gentamicin (set as time = 0 minutes). (C) Cytospins of TNF-α primed neutrophils stimulated for 2 hours with S aureus or E coli and stained with 4,6-diamidino-2-phenylindole (DNA/red), antihistone antibody (green), and phalloidin (actin/blue). White arrowheads indicate cells classified as NETs. (D) NETs quantified by both loss of nuclear structure and exclusion of the actin cytoskeleton, expressed as a percentage of total neutrophils scored. Error bars represent ± SD. Data are representative of 3 independent experiments. *P < .05, **P < .01, #P < .001 by ANOVA.