Ultrastructure of phagocytes from mammary glands of non-pregnant heifers

Results of ultramicroscopic investigations of phagocytes isolated from non- secreting and abberantly secreting juvenile mammary glands of non-pregnant heifers are presented. The two types of phagocytes observed in cell suspens ions obtained by lavage of mammary gland cavities were polymorphonuclear le ukocytes and macrophages. Polymorphonuclear leukocytes were spherical or ir regular in shape and contained segmented nuclei. Azurophilic and specific e lectron-dense granules, mitochondria, glycogen particles, phagosomes and ph agolysosomes in cytoplasma and characteristic pseudopodia on the cell surfa ce were observed. In addition to these normal polymorphonuclear leukocytes, degenerating cells, characterized by spherical nuclei, total absence of ps eudopodia, merged nuclear segments and altered granules, other cellular org anelles and plasmalemma were present. Two types of macrophages, i.e, vacuol ized and non-vacuolized, could be distinguished. Typical of the non-vacuoli zed type was a kidney-shaped nucleus, a rich Golgi complex, and a large amo unt of lysosomes in the cytoplasm. The vacuolized macrophages contained a l arge amount of electron-dense vacuoles in the cytoplasm. Unlike non-secreti ng glands, the cell suspensions collected from aberrantly secreting juvenil e mammary glands contained only vacuolized macrophages. The vacuolization r esults from phagocytosis of corpuscular particles of aberrant milk plasma.