Fig. 4.
Electron micrograph of a human neutrophil that has ingested E. coli minicells; the neutrophil was subsequently reacted for the cytochemical detection of MPO activity using the DAB method with exogenous H2O2. Black electron dense deposits are present in intracellular granules, the azurophil granules (asterisks), and within a population of phagosomes (arrows). Under these incubation conditions, there were some phagosomes that had not yet acquired MPO (double arrows). The cytochemical reaction for the detection of MPO activity following ingestion of minicells was carried out as we have described (Fox et al. 1987). Bar: 1 μm