Ultrastructure and C-Type Particles in Myeloid Leukemia of a Pig

13* Is There have been no studies on the ultrastructural cell morphology of swine myeloid leukemia, although ultrastructure of hereditary lymphoma has been ob~erved.~ A two- or three-year-old Landrace crossbred sow was brought to an abattoir due to reproductive disorders. Myeloid lesions with uniform, slight green color were detected in bone marrow, spleen, lymph nodes, liver, ovaries, renal cortices, pancreas, endometrium, and mammary glands. Neoplastic cells which were similar to promyelocytes had broad cytoplasms and stained weakly basophilic to eosinophilic with a faint granular appearance by hematoxylin and eosin. On electron microscopy, neoplastic cells contained large nuclei and well-defined nucleoli. The condensed chromatin area along the nuclear membrane was narrow. Ribosomes were found abundantly in the cytoplasm. Well-developed Golgi apparatus, luxuriant rough-surfaced endoplasmic reticulum, and a moderate number of medium-sized, round mitochondria appeared in the cytoplasm. Round or rod-like granules surrounded by unit membranes were identified as azurophilic granules or primary granules; they dispersed in various numbers according to cell maturation (fig. 1). Distinct peroxidase activity was demonstrated in these granules by electron microscopy in spite of a faint positive reaction by optical microscopy (fig. 2). Some granules were surrounded by Golgi cisterna. Fibrillar formation rarely was striated and occasionally was seen in the cytoplasm-but seldom in the nucleus. Erythrophagia occasionally was found. In lymph nodes and kidneys, neoplastic cells revealed intracellular vesicles including numerous particles (presumably C-type) (fig. 3). Some vesicles contained various types of bodies, and a few vesicles were surrounded by clear zones. Budding of particles through cell membranes was detected (fig. 3, inset), but few particles were found in intercellular spaces. The size of these particles and their nucleocapsids, which were measured in high magnification, was approximately 110 to 120 nm and 80 to 90 nm, respectively, in diameter (fig. 4). A knob-like structure was found only in the last stage of budding. In freeze-replica preparations, C-type particles also were visualized in vesicles-corresponding to those observed in thin sections (fig. 5). The cleaved concave and convex surfaces of particle envelopes were smooth, with only one or two tiny particles which were under 10 nm in size (fig. 5, inset). With examination by electron microscopy after peroxidase staining, neoplastic cells corresponded to promyelocytes.'. I I They differed from those of hypergranular promyelocytic leukemia in man-there wasno atypia. Judging from the lack of hemorrhage and thrombosis, the present case seems to correspond to myeloblastic leukemia with maturation in man.3 A number of particles, presumably C-type, were present in vesicles and appeared in tumor cells, but no budding through the membrane of vesicles was observed. Some vesicles contained various types of bodies other than C-type particles. They probably were degenerated organelles. Erythrophagia was detected in the present case and also was reported in an erythroleukemic cat.14 It is supposed, therefore, that phagocytosis of particles occurs in neoplastic cells. C-type. particles were observed in myeloid leukemia of miniature swine induced by strontium 90'O as well as in macrophages in hereditary lymphoma.' Although the porcine lymphoma C-type particles isolated from the permanent tissue culture line were investigated l7 the relation