SAA enhances neutrophil phagocytosis of E coli but not S pneumoniae. (A) Typical FACS profiles of E coli-GFP association with neutrophils in the absence or presence of SAA (1 μg/mL). Percentage of GFP⁺ cells within the region shown with bar were determined. (B) Time course of phagocytosis of E coli-GFP shows increases at approximately 15 minutes. Phagocytosis (difference in % GFP⁺ cells in the absence and presence of cytochalasin D) is expressed as Δ GFP⁺ in the presence of SAA (1 μg/mL) minus absence of SAA. (C-D) Binding and uptake of E coli-GFP () by human neutrophils was increased in the presence of SAA at all concentrations tested. This response was due to phagocytosis, since no increase was seen when cytochalasin D treatment was included (). Phagocytosis of S pneumoniae-PKH67 (□) was not increased by SAA but was increased by NHS. (C) Relative ratio of percentage of GFP⁺/PKH67⁺ cells in region denoted by bar calculated from values obtained with bacteria + SAA or NHS over values obtained with bacteria alone. (D) Relative ratio of mean fluorescence intensity (MFI) of cells in region denoted by bar calculated from values obtained with bacteria + SAA or NHS over values obtained with bacteria alone. The dotted line represents unaltered bacterial association in the absence of SAA. Data represent mean ± SEM of 11 donors for E coli, 6 for E coli + cytochalasin D, and 4 for S pneumoniae. Statistical significance of samples with bacteria + SAA or NHS versus bacteria alone was calculated from raw percentage of GFP⁺ cells by Wilcoxon matched pair test (^*P < .05; ^**P < .01; ^***P < .001).