Ultrastructure of blebbing and phagocytosis of blebs by hyperplastic thyroid epithelial cells in vivo.

In addition to pseudopods, somewhat pleomorphic blebs were consistently found protruding from the apical surfaces of hyperplastic rat thyroid epithelial cells into the follicular lumens in vivo. Many blebs were knobby, roughly hemispherical protrusions, with a diameter of 2-3 mum. Such blebs had a densely packed microfilamentous core and contained numerous apparent ribosomes. They were morphologically similar to blebs that have been observed in a variety of cultured cells. Other blebs were larger, more elongate, and less knobby, but had a similar ultrastructural organization. Blebs of all sizes appeared to be phagocytosed on some occasions by nearby epithelial cells. The phagocytic process involved partial engulfment of the bleb by a typical epithelial pseudopod, followed by an apparent pinching-off process, presumably resulting in the separation of the bleb from its cells or origin. The pinching-off process was associated with a band of approx. 6-nm diameter microfilaments that developed within the pseudopod cytoplasm surrounding the base of the bleb and is postulated to function as a contractile ring. The finding of blebbing is an intact tissue in vivo indicates that this phenomenon is not restricted to cultured cells, and thus tends to extend the significance of in vitro observations of the process. In relation to their occurrence in the hyperplastic thyroid gland in vivo, possible interconversions are considered between different types of blebs, and between blebs and pseudopods.

Vascular injury and lysis of basement membrane in vitro by neutral protease of human leukocytes.

Frozen and thawed granules of human, peripheral-blood leukocytes rapidly produce hemorrhage when injected into animal tissues. The effect is blocked by inhibitors of proteolysis. The granule extract can digest vascular basement membrane in vitro at neutral pH. In addition, basement membranes of blood vessels damaged in vivo by the leukocyte fraction are found to be attenuated when examined by electron microscopy. The proteases of human leukocyte granules differ in several important respects from known lysosomal cathepsins and trypsin-like esterases. Polymorphonuclear neutrophils are a major source of the neutral proteases present in circulating white cells, and release these enzymes during phagocytosis of immune complexes.

Blood capillary enlargement during the development of thyroid hyperplasia in the rat.

To study blood capillary growth in the hyperplastic thyroid gland, rats were fed 0.25% thiouracil in a low iodine diet for time intervals up to 100 days. Thyroids were fixed by vascular perfusion and embeded in Epon. Whole lobes were sectioned from pole to pole and slides were prepared of sections every 0.3 mm. Capillaries were clearly enlarged by 3 days and they enlarged progressively thereafter. By 3 days, the cells of many neighboring capillaries came into close apposition and from this time on, there was evidence of fusion of capillary walls in the form of partial septa in the capillary lumens. Fusion continued until 20 days, when follicles were almost completely surrounded by a continuous endothelial sheet and unfused capillary walls were separated by connective tissue. The vascular pattern around peripheral follicles changed in a way similar to interior follicles, except that in places, capillaries were gradually excluded from the space between epithelium and thyroid capsule. Vascular enlargement was restricted to the thyroid blood vessels. There was no obvious enlargement of the blood capillaries of the parathyroid despite its close proximity to the thyroid.

Association of centrioles with clusters of apical vesicles in mitotic thyroid epithelial cells. Are centrioles involved in directing secretion?

The ultrastructure of thyroid epithelial cells in mitosis has been investigated. A spatial association is described between clusters of apical vesicles (believed to contain thyroglobulin destined for secretion into the follicular lumen) and centrioles, in late prophase and late telophase cells. Quantitative techniques demonstrate the statistical significance of this association and suggest that it is not related to proximity of the Golgi apparatus or to the location of the centriole in the cell, which changes considerably during these phases of mitosis. The physical basis for this association remains uncertain, but microtubules emanating from the pericentriolar area may be involved. In interphase cells, centrioles are located very close to the follicular lumen, where the majority of apical vesicles are also found. The association of centrioles with clusters of apical vesicles also in mitotic cells suggests that in interphase cells the apically located centrioles may serve as a focus for apical vesicles, helping to direct these secretory vesicles toward the follicular lumen and to maintain cellular polarization. Previous studies demonstrating that centrioles can act as microtubule organizing centers in interphase cells and studies linking microtubules and secretion also tend to support this hypothesis.

Ultrastructure of the degradation of erythrocytes by thyroid epithelial cells in vivo.

The ultrastructure of the degradation of red blood cells (RBCs) in vivo by rat thyroid epithelial cells was studied. Two morphologically distinct degradative pathways appeared evident. The granular pathway was characterized by a finely mottled appearance of RBC phagosomes, first observed about the RBC periphery and later extending to the entire RBC matrix. Such phagosomes became gradually smaller, less electron dense, and indistinguishable from cellular lysosomes. The hemolytic degrative pathway was characterized by a progessive, usually homogenous decrease in the density of the RBC matrix except at the periphery of the RBC, where a thin, dense layer persisted for some time. Such phagosomes often appeared swollen relative to freshly ingested RBCs and resembled RBC ghosts. In later stages, they became irregular, smaller, and gradually indistinguishable from cellular lysosomes. Both degradative pathways were associated with ferritin-like particles. The earliest visualization of ferritin was in the cytoplasm, but in later stages it was also found to be concentrated within lysosomes and phagolysosomes.

Functional and ultrastructural changes in alveolar macrophages from rabbits colonized with Bordetella bronchiseptica.

Alveolar macrophages from rabbits colonized with Bordetella bronchiseptica in their respiratory tract exhibited significant decreases in cell adherence, phagocytic uptake, and bactericidal activity compared with macrophages from uncolonized animals. These dysfunctions were accompanied by ultrastructural changes, including a decrease in overall cell density, a vacuolation of the rough endoplasmic reticulum, and an increase in organelle-poor cell surface projections.

The course and nature of acinar cell death following pancreatic ligation in the guinea pig.

The course and nature of acinar cell death (ACD) following pancreatic ligation in the guinea pig was studied as a possible model for human disease. Ultrastructural studies after various periods of ligation suggested a biphasic pattern of ACD. Early phase ACD involved only a small portion of acinar cells and occurred within a few hours of ligation. It was preceded by swelling and vesiculation of the rough endoplasmic reticulum. Morphometric measurements disclosed celular swelling at this time, and NaCl equilibration studies demonstrated a change in cellular osmoregulation. Late phase ACD, characterized by cellular wasting and autophagic vacuole formation, became prominent several days after ligation. Marked increases in lysosomal enzyme activities were found in tissue homogenates at this time, and acid phosphatase electron histochemistry localized the majority of this increased activity to lysosomes and autophagic vacuoles within the acinar cells. The etiology and nature of both phases of ACD are discussed.

Ultrastructural changes in thyroid epithelium during involution of the hyperplastic thyroid gland.

The ultrastructure of the thyroid epithelial cell was examined at various time intervals after induction of involution of the hyperplastic thyroid gland. Thyroids were made hyperplastic by the feeding of thiouracil in a Remington low-iodine diet to male Fischer rats for 3 weeks. Involution was induced by replacing the thiouracil-containing diet with Purina Laboratory Chow, a high-iodine diet. During involution, organelles that play a role in the synthesis and secretion of thyroglobulin, such as the rough endoplasmic reticulum, Golgi apparatus, and apical vesicles, were well preserved and prominent features of the epithelial cell. The apical plasma membrane of many cells was highly irregular for approximately 2 weeks with signs suggesting rapid discharge of apical-vesical contents into the lumen of the follicle. Pseudopods and colloid droplets were present but were not very prominent features of the cell. No signs of extensive autophagy or obvious increased incidence of lysosomes were present, although there was an elevation in the incidence of small dense bodies starting about day 8, and prominent by 15 days. Some of these may be phagosomes formed from luminal debris. The observations indicate that involution of the hyperplastic thyroid in which there is maintenance of the protein synthetic apparatus and little sign of autophagy or death of the epithelial cells is remarkably different from phenomena occurring during involution of prostate or mammary glands.

Maturation of the rabbit alveolar macrophage during animal development. I. Perinatal influx into alveoli and ultrastructural differentiation.

Rabbit alveolar macrophages (AM's) were collected by tracheobronchial lavege at sequential times during animal development. The total number of cells recovered by this technique was found to increase markedly shortly before birth (Fig. 4). This apparent influx of macrophages into the alveoli continued during the first postnatal week, and, at a reduced rate, throughout the first postnatal month of life (Fig. 3). Ultrastructurally, AM's of the prenatal period resembled their monocyte precursors, and contained modest numbers of lysosomes and mitochondria, scant lamellae of ribosome-studded endoplasmic reticulum (RER), and a small Golgi apparatus (Fig. 12). A considerable amount of phagocytosed material was observed in these AM's, and consisted largely of cellular debris and two forms of surfactant-related phospholipids, termed tubular and lamellar myelin (Figs. 12-15). The quantity of these ingested phospholipids increased dramatically shortly after birth, in correlation with the known release of similar material from type II pneumocytes at this time. (Figs. 16 and 19). During the first postnatal week AM's showed a considerable increase in number of mitochondria and in the development of the RER and Golgi apparatus (Fig. 22). Increased accumulations of lipid droplets were also noted during this period. Ingested material continued to consist largely of surfactant-related phospholipids, but was less abundant at this time. By 28 days after birth, AM's were nearly morphologically mature (Fig. 25). They showed large numbers of lysosomes and mitochondria, and well developed RER and Golgi apparatuses. Ingested phospholipid material was still visualized, and the incomplete degradation of this material appeared to give rise to the dense intraphagolysosomal whorls characteristic of the mature AM.