Characterization of canine neutrophil granules

The purpose of this study was to isolate distinct populations of canine neutrophil granules and to compare them with neutrophil granules from other species. Size, shape, density, and content of canine neutrophil granules were determined. Neutrophils obtained by Ficoll-Hypaque sedimentation were homogenized, and granule populations were separated by isopycnic centrifugation on a linear sucrose gradient (ρ, 1.14 to 1.22 g/ml). The most dense granule population (ρ, 1.197 g/ml) contained all of the myeloperoxidase, β-glucuronidase, and elastase, more than half of the acid β-glycerophosphatase, and most of the lysozyme. The population with intermediate density (ρ, 1.179 g/ml) contained lactoferrin, vitamin B₁₂-binding protein, and the remainder of the acid β-glycerophosphatase and lysozyme. The least dense granule population did not contain a major peak of any of the enzymes or binding proteins tested but was distinguished by density and morphology. The size and shape of the granules were determined from scanning electron micrographs and assessment of shape was aided by transmission electron micrographs. By these methods three populations of canine neutrophil granules were characterized and named: myeloperoxidase granules, vitamin B₁₂-binding protein granules, and low-density granules.