Identification of three types of granules in neutrophils of ruminants. Ultrastructure of circulating and maturing cells.

The production of three populations of granules during maturation and their occurrence in the neutrophils of a number of ruminants is described. Bone marrow samples from cows, sheep, and goats were fixed, reacted for peroxidase, and examined by transmission electron microscopy. Granule formation was found to occur at three subsequent stages. As in other species including man, it begins with the production of peroxidase-positive granules and is concluded with the production of moderately dark-staining, peroxidase-negative granules of similar size. These two organelles have the characteristics of the azurophil or primary and specific or secondary granules of other species. At an intermediate stage, a different type of peroxidase-negative granule, the large granule, is formed. Its profile is round and markedly larger than those of azurophil and specific granules. The large granules initially have a loose, undulated membrane and fill gradually with matrix which in early forms consists of a central core. Fully developed large granules have a sharply defined membrane and a pale, very uniform content. The two types of peroxidase-negative granules can be distinguished by their sizes and times of formation and also by the appearance of their content which is more coarse and darker in the specific granules. Mature neutrophils from cows, goats, sheep, and an ibex were also examined. Two features are common to all cells viewed: the presence of three types of granules and the preponderance of the large granule population. The results of this study, together with evidence from cell fractionation experiments, suggest that the large granules are a characteristic property of the neutrophils of ruminants.