Characterization of rat polymorphonuclear leukocyte subcellular granules

The bactericidal subcellular granules of rat peritoneal neutrophils were studied to determine selected physical and biochemical characteristics. Isopycnic centrifugation of these granules resolved them into three subpopulations: specific granules (buoyant density = 1.176) as well as light and heavy azurophil granules (buoyant density = 1.20 and 1.22, respectively). These buoyant densities corresponded closely to those of similarly isolated human granules. Specific granules of rat peritoneal neutrophil contained 68 per cent of the sedimentable alkaline phosphatase activity and part of the lysozyme of the whole rat peritoneal neutrophil. The light azurophil granules contained the remainder of the lysozyme, as well as a substantial portion of the beta-glucuronidase activity. Peroxidase was detected in both light and heavy azurophil granules, as was neutral protease. Morphologically, the rat specific granules were round or slightly ovoid organelles (0.10 to 0.13 micrometer in diameter). The azurophil granules were larger (0.3 micrometer) ellipsoid as well as round in shape, and stained strongly for peroxidase. These granules were significantly smaller than the crystal-containing granules of eosinophils.