Surface topography of leukocytes in situ: cells of mouse peritoneal milky spots.

Identical peritoneal lymphocytes, macrophages, and mast cells, fixed in situ, on the surface of milky spots of mouse omentum and mesentery, were identified in the light microscope and then studied in the scanning electron microscope. Undisturbed, in their natural environment, the lymphocytes' surface ranged from highly villous to totally bald, and their shape varied from spherical to that of a “hand-mirror”. The macrophage surface was rugose, but also had microvilli, and its shape ranged from discoid with a regular outline to flat with an irregular outline. The mast cell was usually discoid and had an undulating surface with few microvilli and the frequent impression of underlying granules. The microvilli of the lymphocytes, and the ridges and folds of the macrophages, had also characterized these cells in vitro following their removal from the peritoneal cavity and incubation on artificial substrates (Orenstein and Shelton, 1975). However, there were pronounced differences in their appearance in situ as compared to in vitro. In vitro the lymphocyte was very regular in shape and varied little in the number of its microvilli, while the macrophage had an uneven distribution of surface features and could even be totally smooth. The elongated processes that were frequently directly between neighboring cells in vitro occurred less frequently in situ, where there was more intimate contact between cells. Processes that appeared to be of a similar nature frequently joined the cells of the substrate to the cells resting on their surface.     

A study by scanning electron microscopy of the bladder epithelium of the guinea pig

Under scanning electron microscopy (SEM) the surface cells of the guinea pig bladder have pentagonal or hexagonal outlines. Their borders are clearly defined since they are elevated. They possess a large reserve of surface membrane which is markedly folded and wrinkled when the bladder is empty. The folds disappear and the cells become flat during distension. The luminal surface is characterized by numerous reticular ridges which are a remarkably constant feature and persist even under acute artificial distension. A small proportion of the surface cells are small and have less than five sides. Since they show only sparse microvilli as a surface feature, they have a smooth appearance. These are believed to be young surface cells which have just emerged from the intermediate layer, and have not yet acquired the ridged pattern of mature cells.     

Scanning electron microscopy of epiplexus cells (macrophages) in the fetal rat brain

Intraventricular macrophages were observed with the scanning electron microscope on the choroid plexus in developing rat brains. Cell membrane configurations of these large, epiplexus cells (8-10 μm) were typified by folds, flange-like surface projections and long, thin pseudopodia interdigitating with subjacent brain cell microvilli; discrete, periodic enlargements were observed at intervals along the pseudopodial processes.     

Surface morphology of human aorta as revealed by the scanning electron microscope.

Human aorta was prepared for scanning electron microscopy using critical point drying. The aortic surface is lined by a continuous layer of squamous endothelial cells. The luminal surface of these cells contains many microvilli or microappendages and pinocytotic vesicles. In addition, at the periphery of each cell, larger marginal appendages or microfolds are present which allow the observer to see the cell boundaries clearly. The marginal folds are superficial to the cell junctions and could be observed without any staining procedures. These observations on human aorta are generally in agreement with our findings on the rabbit and guinea pig aorta and vena cava but in contrast to others who have reported the presence of ridges, intercellular bridges, and "hair-like" processes on the endothelial surfaces.     

Surface morphology of human aorta as revealed by the scanning electron microscope

Human aorta was prepared for scanning electron microscopy using critical point drying. The aortic surface is lined by a continuous layer of squamous endothelial cells. The luminal surface of these cells contains many microvilli or microappendages and pinocytotic vesicles. In addition, at the periphery of each cell, larger marginal appendages or microfolds are present which allow the observer to see the cell boundaries clearly. The marginal folds are superficial to the cell junctions and could be observed without any staining procedures. These observations on human aorta are generally in agreement with our findings on the rabbit and guinea pig aorta and vena cava but are in contrast to others who have reported the presence of ridges, intercellular bridges, and “hair-like” processes on the endothelial surfaces.     

Scanning and transmission electron microscopy of the rat kidney

This study utilized scanning and transmission electron microscopy of renal tissue to provide new information on the gross and microscopic structure of the kidney. The luminal surface of the proximal convoluted tubule was characterized not only by the border of microvilli, but also by crater-like depressions, and circumferential folds. In tissue processed for scanning electron microscopy the proximal tubular cells separated along their lateral surfaces clearly exposing the topography of the lateral cell projections of cytoplasm which have been generally unavailable for viewing because of their interdigitation with adjacent cells. The various segments of the nephron were identified on the basis of position in the kidney, general morphology, and the distribution and form of apical microvilli, cilia, or flaps. The external surface of the papillary tip had several parallel furrows into which the collecting ducts opened. Large plaquelike depressions lined the papillary surface. The opposed surface of the renal pelvis had small plaque-like depressions separated by narrow ridges. Transmission electron microscopy of plastic-embedded tissue specimens which had been previously dehydrated by the critical point drying method demonstrated that little damage occurred from this procedure.     

The choroid plexus of the mature and aging rat: the choroidal epithelium.

The choroid plexus of mature and old rats has been examined by both scanning and transmission electron microscopy. It has been shown that the macrophages lying upon the ventricular surface of the choroid plexus have a close association with burr-like protrusions that extend from the apical surfaces of the choroidal epithelial cells. These protrusions have a dark cytoplasm filled with vesicles and tubules, and projecting from them are thin, shrunken microvilli. It is suggested that these protrusions are phagocytosed by the macrophages and that they are the source of some of the inclusions which become increasingly common within the cytoplasm of macrophages in older rats. The lateral surfaces of the choroidal epithelial cells have also been examined in the scanning electron microscope after exposure of the surfaces by dissection. In such preparations it is apparent that the elaborate interdigitations between adjacent cells are effected by irregular and vertically arranged folds confined to the basal portions of the lateral cell surfaces. Lastly, it has been shown that at the junction between the choroid plexus and the ependyma in the lateral ventricle, there are two modes of transition between the choroidal and ependymal epithelia. In one, typical choroidal and ependymal epithelial cells lie next to each other to produce a distinct and continuous bondary. In the other mode the boundary is also continuous, but there are modified ependymal cells present. These modified cells have short, relatively sparsely distributed microvilli and not more than one or two cilia.     

The choroid plexus of the mature and aging rat: The choroidal epithelium

The choroid plexus of mature and old rats has been examined by both scanning and transmission electron microscopy. It has been shown that the macrophages lying upon the ventricular surface of the choroid plexus have a close association with burr-like protrusions that extend from the apical surfaces of the choroidal epithelial cells. These protrusions have a dark cytoplasm filled with vesicles and tubules, and projecting from them are thin, shrunken microvilli. It is suggested that these protrusions are phagocytosed by the macrophages and that they are the source of some of the inclusions which become increasingly common within the cytoplasm of macrophages in older rats. The lateral surfaces of the choroidal epithelial cells have also been examined in the scanning electron microscope after exposure of the surfaces by dissection. In such preparations it is apparent that the elaborate interdigitations between adjacent cells are effected by irregular and vertically arranged folds confined to the basal portions of the lateral cell surfaces. Lastly, it has been shown that at the junction between the choroid plexus and the ependyma in the lateral ventricle, there are two modes of transition between the choroidal and ependymal epithelia. In one, typical choroidal and ependymal epithelial cells lie next to each other to produce a distinct and continuous boundary. In the other mode the boundary is also continuous, but there are modified ependymal cells present. These modified cells have short, relatively sparsely distributed microvilli and not more than one or two cilia.     

Surface morphology of macrophages in the regressing corpus luteum, as revealed by scanning electron microscopy

Activated macrophages phagocytize moribund luteal cells and thus play a central role in the postpartum regression of corpora lutea in guinea pigs (Paavola, '79). When viewed by transmission electron microscopy (TEM), these luteal macrophages exhibit many surface protrusions. To characterize more fully the nature and extent of these evaginations, as well as to gain further understanding of phagocytes in their natural surroundings, luteal macrophages were studied in situ by scanning electron microscopy of regressing corpora lutea. Correlated TEM was carried out to confirm the identity of the various cell types. Even in low power scanning electron micrographs, macrophages are consipicuous, and can be readily distinguished from luteal cells by their surface topography. Luteal cell surfaces bear low ridge-like folds and sparse microvilli. In contrast, macrophages characteristically exhibit highly developed surface projections, the most common of which are knob-like or clubbed processes of varying size and shape. Other distinctive surface modifications displayed by luteal macrophages include long, slender filopodia, and well developed pseudopodia. These processes generally have an uneven distribution over the cell; thus, luteal macrophages may appear polarized with regard to surface activity. Both filopodia and pseudopodia occur in close contact with luteal cell surfaces. In addition, occasional luteal macrophages have surfaces that are covered with large, crater-like depressions. The phagocytosis of cells and cellular debris by macrophages was also observed. In summary, the highly pleomorphic surface activity of luteal macrophages appears to be correlated with their role in the removal of senescent luteal cells.     

Ultrastructural changes of cultured human amnion cells by Clostridiu difficile toxin.

The ultrastructure of the surface of primary human amnion monolayer cells undergoing cytopathology induced by Clostridium difficile toxin was examined by scanning electron microscopy. Our observations indicated that the type and distribution of cell surface projections were altered dramatically by this toxin. The patterns of such surface changes were specific for the two different types of cells found in this cell culture. Cells with demarcated borders showed rearrangement of microvilli into globular chains or ridges which lined up with the branching membrane. Cells without demarcated borders exhibited studlike microvilli, all arranged into ridges or globular chains. These changes were noted after 1 h of toxin exposure and persisted without further progression, in spite of continued toxin exposure, up to 48 h. These data indicate that C. difficile produces a cytolytic toxin and that scanning electron microscopy may be useful in determining toxin-cell interactions.     

Effects of colchicine and cytochalasin B on vasopressin- and cyclic adenosine monophosphate-induced changes in toad urinary bladder

Coincident with an increase in water permeability, the ridge-like surface structures of toad bladder granular cells transform to individual microvilli after stimulation with vasopressin (VP) or cyclic adenosine monophosphate (cAMP) by a mechanism that is yet to be defined. To explore the possible role of microtubules and microfilaments in this cell response, colchicine and cytochalasin B were employed to determine whether interference with the function of these components of the cytoskeletal system would prevent the VP- and cAMP-induced conversion of ridges to microvilli. Incubation of toad urinary bladders in 10(-4) M colchicine for 4 hours or 10(-5) M cytochalasin B for 90 minutes before stimulation with 20 mU. per ml. of VP markedly inhibited osmotic water flow. However, neither agent prevented the striking conversion of ridges to surface microvilli induced by VP and cAMP as seen with scanning electron microscopy. In addition, the ridges characteristic of granular cells were maintained in control bladders incubated with colchicine or cytochalasin B, but left unstimulated. Under the conditions of these experiments, these findings suggest that microtubules and microfilaments are not essential for maintenance of normal surface configuration in granular cells of toad urinary bladder, and that they are not involved in the mechanism responsible for VP- and cAMP-induced surface changes that occur in association with increased water permeability of this epithelium.     

Morphological changes in isolated lymphocytes during preparation for SEM: Freeze drying versus critical-point drying

A quantitative comparison of isolated lymphocytes prepared for SEM by the critical-point drying (CPD) and freeze drying (FD) methods revealed that the mean cellular diameter dropped from 7.9 μm after fixation to a final diameter of 6.9 μm after FD, and to 5.7 μm after CPD. In addition to their larger sizes, FD lymphocytes were immediately distinguishable by their more complex surfaces, featuring wider microvilli which often emanated from ridges on the cell surface and branched extensively near their bases. The mean width of microvilli was 0.22 μm after FD and 0.12 μm after CPD. The number of microvilli per cell was essentially the same by the two methods. In view of these findings, a critical comparison of the CPD and FD methods using the particular cells or tissue to be investigated is an essential prelude to a rigorous SEM study.     

Surface ultrastructure of the epithelia lining the normal human lower urinary tract.

The finding of cells with pleomorphic microvilli in urinary sediments has been proposed as an indicator for urothelial neoplasia. Recently, in addition to such cells, others with less bizarre, non-pleomorphic microvilli have also been found in urothelial cancers, and these cells are similar in appearance to others detected in the urinary sediments of healthy people. When using scanning electron microscopy as a diagnostic tool, these cells are a possible source of confusion. The entire lower urinary tracts from people free of urothelial neoplasia have therefore been examined to delineate the normal surface appearance of all cell types which could appear in the urine. There are 4 predominant cell types: the large, flat squamous cells of the urethral meatus which have abundant microridges; cells with mucus-coated, short, stubby microvilli lining the urethra and renal papilla; immature urothelial cells with chains and ridges of bleb-like processes in the ureters and bladder; and, also in the ureters and bladder, mature urothelial cells with microridges or ruffles. The lining epithelia of the normal urethra and renal papilla may thus contribute cells with non-pleomorphic stubby microvilli to urine sediments, which cannot be differentiated by scanning electron microscopy alone from similar cells derived from urothelial neoplasms. However, the normal complement of cells lining the adult lower urinary tract does not include any with prolific, long, pleomorphic microvilli such as characterize transitional-cell carcinomas of the urothelium.     

In situ degranulation of human nasal mucosal mast cells: ultrastructural features and cell-cell associations

Mucosal mast cells in human nasal turbinates obtained at surgery were studied by electron microscopy before and after exposure en bloc to a degranulating stimulus. Mast cells occurred as solitary cells and in islets typically containing one mast cell and one to three mononuclear cells. All islets and most solitary mast cells were associated with thin cytoplasmic processes of distinctive, branched stromal cells that also phagocytosed debris from pyknotic mast cells. Mast cells were grouped into three categories based largely on published ultrastructural criteria. Resting (nondegranulating) mast cells possessed secretory granules that typically packed the cytoplasm and contained a densely stained amorphous material and scroll-like crystalline profiles. Granules in some resting cells were larger, more polymorphic, and appeared nearly homogeneous. Secretory granules of degranulating mast cells possessed crystalline, scroll-like, or reticular constituents predominantly with interspersed amorphous material. Granules were fewer in number and were often concentrated in the peripheral cytoplasm. Few degranulating mast cells exhibited labyrinth formation or exocytosis of granule contents. Largely degranulated mast cells had few if any typical granules but possessed small vacuoles containing recognizable granule remnants. Resting and degranulating mast cells possessed very long cell surface projections that, in places, interdigitated to form stacks of parallel folds above the plasmalemma, resulting in a threefold increase in cell-surface area. The surface membrane of the folds appeared to be continuous with that lining intracytoplasmic channels extending from the cell surface to the Golgi zone.     

Ultrastructural studies on the interaction between Salmonella typhimurium 395 M and HeLa cells.

The interaction of Salmonella typhimurium 395 MS and its rough Rd-mutant 395 MR10 with HeLa cells was studied by transmission and scanning electron microscopy. The bacteria attached to central as well as more marginal positions of the HeLa cell surface. Bacteria associated preferentially to HeLa cells with a relatively low number of microvilli, in which they often were entangled. Bacteria attached to the cell border were sometimes surrounded by membrane folds, possibly as a response to their attachment. Infected cells had longer and more slender microvilli compared with noninfected cells. Some parts of the attached bacteria were in close contact with the HeLa cell membrane, whereas other parts were separated from the latter by a gap. Bacteria adhered preferentially to microvilli without obvious membrane damage. Most of the intracellular bacteria were surrounded by a membrane, often appearing as a vacuole, which sometimes contained more than one bacterium. Intracellular bacteria seemed to be morphologically intact. We propose that S. typhimurium enter HeLa cells by a process of phagocytosis.     

大鼠大网膜表面的扫描电镜观察

大白鼠大网膜不同结构区——薄膜区、脂肪和血管区的表面均有一层间皮和散在的乳斑。同皮细胞间借突起相接。突起之间可见宽窄不一的间隙。薄膜区间隙较大,呈网络状。间皮细胞表面有疏密不均的微绒毛。微绒毛或离散分布,或连接成网。在微绒毛稀少区的细胞表面可见散在的小孔。在脂肪和血管区有丰富的乳斑,薄膜区乳斑少见且较少。乳斑的细胞多数位于间皮细胞间的间隙内或其表面。乳斑细胞的绝大部分裸露于腹膜腔。乳斑的细胞成分主要为巨噬细胞和淋巴细胞,有少数颗粒白细胞和红细胞,偶见肥大细胞。     

Histamine release from serosal mast cells by intermediate products of arachidonic acid metabolism

In the present paper we report the results of experiments carried out to measure the release of histamine from isolated rat mast cells during the metabolic activation of arachidonic acid. Arachidonic acid (10^–8–10^–4 M) and the terminal products (10^–6 M) of the arachidonic acid pathways were devoid of any significant histamine releasing properties. A substantial amount of histamine was released from rat mast cells by low concentrations of arachidonic acid during incubation with prostanoid generating systems, such as guinea-pig lung microsomes, rat serosal macrophages and polymorphonuclear cells and prostaglandin-H-synthase from calf seminal vesicles. The release of histamine was not accompanied by a leakage of lactate dehydrogenase and was blocked byd-mannitol and by lipoxygenase and cyclo-oxygenase pathway inhibitors. The data are consistent with the hypothesis that free radical derivatives of arachidonic acid, originating from hydroperoxy fatty acids, are generated during catalysis, causing mast cell histamine release.     

The surface ultrastructure of Gaucher cells.

The Gaucher cells of seven patients with Gaucher's disease were examined by both transmission and scanning electron microscopy. The ultrastructure of the cells, as seen by transmission electron microscopy, did not differ from that reported in the literature. The surface structure varied not only in the different patients but also in the same individual. The cells were oval or round, most of them with a rough surface due to presence of microvilli, ruffles, ridges, and blebs of various numbers and shapes. In two patients the Gaucher cells showed phagocytosis. The appearance of the surface ultrastructure of the Gaucher cells supports the accepted view that they are related to the cells of the reticuloendothelial system.     

Macrophage fusion and multinucleated giant cell formation, surface morphology

Crude supernatants from BCG sensitized lymphocytes incubated with BCG were capable of mediating the in vitro fusion of and subsequent multinucleated giant cell (MGC) formation of either alveolar or peritoneal macrophages obtained from normal rabbits. The crude supernatant fluids which contained a lymphokine termed Macrophage Fusion (MFF) mediated the fusion of over 88% of the macrophages present in the experimental system. MGC possesing several hundred nuclei per cell were commonly observed with dimensions of over 1.5 mm. Control supernatants in most instances did not induce cell fusion. The surfaces of BCG-induced multinucleated giant cells of alveolar macrophage origin were examined using the scanning electron microscope. The surface of many MGC which were spread out onto the plastic substrate possessed four distinct morphological areas: a central area with a dense array of membranous veils, a transitional area with few veils, a peripheral area composed of pits and ridges giving an undulating appearance, and terminal edges which were smooth or possessed filopodia. Occasionally an atypical morphology consisting of dendritic-like structures were present on small sites on the MGC surface. Frequently many alveolar macrophages possessing typical membranous veils were attached to the MGC surface. It was concluded that the surface morphology of multinucleated giant cells was similar to that of macrophages.     

Epithelial migration in organ culture. A morphological and time lapse cinematographic analysis of migrating stratified squamous epithelium.

The migration of stratified squamous epithelium in organ cultures of rat palatal explants has been studied using scanning and transmission electron microscopy. The scanning microscope revealed plate-like folds at the margins, and microvilli on the bodies of cells. These structures were most highly developed on those cells nearest the leading edge of the sheet of cells and are interpreted as an index of cells that are migrating. The cells at the leading edge have broad flat pseudopodia in direct contact with the collagen bundles. A time lapse cinemicrographic study showed that the net forward movement of cells (nuclei) remote from the leading edge was at least as great as that at the leading edge immediately in front of them and the distance they travelled was greater than that of the leading edge. In transmission electron micrographs of these migrating epithelial cells from in vivo wounds, profiles that could correspond to the microvilli and plate-like folds could be found on the surface of the migrating cells. The results of this study suggest a simple model for the particular type of movement that occurs in stratified squamous epithelium in healing wounds where a mass of cells is produced that can both migrate into the wound and undergo stratification and cornification. A tracked vehicle shedding a broken track is used as an analogy of the model proposed.