Effect of IAV on neutrophil uptake of E coli.Mean neutrophil fluorescence after exposure to various concentrations of FITC-labeled E coli alone or in combination with IAV was assessed using flow cytometry as described. All samples were incubated with Trypan blue to quench extracellular fluorescence. (A) Results of incubating various concentrations of E coli alone (lower curve) or in combination with a fixed concentration of IAV (70 μg/mL). (*)Indicates where IAV caused a significantly increased (P < .05) binding of E coli in (A). (B) The effect of preincubating neutrophils with various concentrations of IAV followed by washing off unbound virus and testing binding of FITC-labeled E coli (“IAV Pre-incubation”; lower curve) or of simultaneously incubating various concentrations of IAV along with a fixed concentration of E coli (250 μg/mL) with neutrophils (“IAV simultaneous with E.coli”; upper curve). Results represent mean ± SEM of three separate experiments. In (B) all concentrations of IAV simultaneously incubated with neutrophils enhanced E coli binding significantly (P ≤ .05). The enhancement of uptake was significantly greater with 7.2 μg/mL of IAV than with any other concentration of the virus. For neutrophils preincubated with IAV (lower curve), only the highest concentration of IAV enhanced E coli binding.