Neutrophil apoptosis induced by E coli. The indicated concentrations of E coli were incubated with neutrophils as described in Materials and Methods. (The ratios of bacterial particles to neutrophils were between 20 and 460 bacteria/neutrophil.) Results are expressed as percentage of cells with hypodyploid DNA as measured by the PI assay and represent the mean ± SEM of three separate experiments. (*)Indicates where E colialone caused significantly greater apoptosis than control buffer.