Phagocytosis of brushite crystals by pig neutrophils

Neutrophils from pig blood were disrupted by homogenisation or sonication and placed on an analytical sucrose gradient. Pig neutrophil azurophil granules were less dense than the specific granules, unlike those from neutrophils of most other mammalian species. Brushite crystals, which stimulate the respiratory burst in pig neutrophils, were found by electron microscopy to be phagocytosed. Membrane-limited vesicles containing crystals were obtained from a dense region of the sucrose gradient loaded with a homogenate of crystal treated cells. Intake of crystals involved preferential mobilisation of cytochrome b from the plasma membrane and the fusion of both specific and azurophil granules with the primary phagosome. Plasma membrane and granule markers appear in a crystal-containing region of the sucrose gradient when cells are treated with crystals. They are present in much lower concentration at this location in gradients from cells untreated with a crystal stimulus.