Peptide stimulation of phagocytosis in Amoeba proteus

Summary Normal articular cartilages from the weightbearing areas of the femoral condyles of the knee joints of 11 patients (3–20 years old) and of 35 Schwarzkopf sheep (3 months to 2 years old) were studied using the electron microscope. The study has shown that the matrix of normal articular cartilage is not only composed of collagen fibrils and proteoglycans, but also contains two types of elastic system fibres. Small elastic fibres can be identified in the superficial and lower radiate zones of cartilage of man and sheep. Similar to elastic fibres in other tissues, they consist of a central amorphous core and are surrounded by aggregates of 10 nm microfibrils. Another type of elastic system fibres, oxytalan fibres, are found in the intermediate and upper radiate zones of the articular cartilage.     

Prostaglandins may play a signal-coupling role during phagocytosis in Amoeba proteus

Summary Phagocytosis in Amoeba proteus can be induced with prostaglandins (PG). In addition, arachidonic acid (the fatty acid precursor to the PG-2 series) also induces phagocytosis. The induction of phagocytosis with arachidonic acid can be partially inhibited by the cyclooxygenase inhibitor indomethacin. Phagocytosis in the amoeba can also be induced with the chemotactic peptide N-formylmethionyl-leucylphenylalanine (NFMLP). The peptide presumably induces phagocytosis by interacting with receptors on the amoeba surface, which may initiate the release of arachidonic acid from membrane lipids. NFMLP-induced phagocytosis can also be partially inhibited by indomethacin. It is suggested that PG's or biochemically related substances may play a signal-coupling role during phagocytosis in the amoeba.     

"New membrane" formation in Amoeba proteus upon injury of individual cells. Electron microscope observations

Changes in the plasma membrane complex following the injury of single cells of Amoeba proteus were examined with the electron microscope. Two types of injury were employed in this study; cells were either pinched ("cut") in half or speared with a glass microneedle, and quickly fixed. Speared cells, when fixed in the presence of the ruthenium violet (a derivative of ruthenium red), revealed the presence of an extra trilaminar structure outside of each cell. This structure, called the "new membrane," was separated from the plasma membrane complex by a distance of less than a micron. The trilaminar structure of the new membrane strikingly resembled the image of the plasma membrane in all cells examined, except for its increased width (30%). This new membrane appeared nearly to surround the injured amebae. Attempts were made to demonstrate the possible origin of the new membrane, its reality, and its sensitivity to calcium. Also, some evidence is shown concerning the role of the small dense droplets (100–1200 A in diameter) normally present in the cytoplasm of amebae. Their frequent contact with the plasma membrane of the cell as the result of injury is interpreted as indicating their involvement in the formation and expansion of the plasma membrane.     

Scanning electron microscope observations of the rat subcommissural organ.

Under the scanning electron microscope, the rat subcommissural organ (SCO) appears as an oval zone, rich in kinocilia and well delimited from the non-specific ependymal epithelium. This zone surrounds the cranial and posterior part of the mesencephalic canal's entrance. The ependymal cells of the SCO show coniform processes with microvilli and kinocilia. In contact with the apical pole of the peripheric SCO-ependymocytes lie scarce supraependymal axons. The Reissner's fiber is composed by the twining of the fibrillary structures emerging from the area of the SCO.     

Scanning Electron Microscope Observations of Amoeba proteus During Phagocytosis*

SYNOPSIS. Phagocytosing Amoeba proteus at different stages of forming foodcups have been observed by scanning electron microscopy. A nonphagocytosing ameba is characterized by dorsal and lateral ridges running longitudinally over the posterior half of the cell and its attachment to the substrate over small areas. When stimulated by prey organisms, the ameba loses polarity and ridges, and adheres to the substrate more firmly over a wider area of contact. Then it forms broad pseudopods to surround its prey and this results in the formation of foodcups. The surface of all amebae is covered with small projections, and membranous blebs are often seen on the surface of phagocytosing organisms.     

Binding characteristics of receptors for phagocytosis on the surface of Amoeba proteus

Summary Binding of the tripeptide n-formylmethionyl-leucylphenylalanine (NFMLP) to phagocytic receptors on the surface of Amoeba proteus was examined. Peptide-binding is reversible and demonstrates saturation kinetics. The receptors for phagocytosis are internalized by a temperature-sensitive process with indications that the receptors are recycled. The amoeba is capable of down-regulating its receptors for phagocytosis in response to constant external peptide levels, and also increasing the number of surface receptors in response to food deprivation. On the basis of competition studies, there is evidence that Amoeba proteus has separate surface receptors for both pinocytosis and phagocytosis.     

康氏粉蚧蜡泌物的扫描电镜观察

采用制作玻片标本和扫描电镜技术研究了康氏粉蚧Pseudococcus comstocki(Kuwana)在不同发育阶段的显微形态特征及蜡泌物的超微形态。结果表明:三格腺是康氏粉蚧最主要的腺体,随着虫体的发育,数量增多,分布变广,每个腺孔分泌一根蜡丝,覆盖体表;管腺只在特定的时期分泌长的空心蜡管构成卵囊;多格腺分泌多棱形卷曲的小蜡丝粘附在卵粒上,防止其相互粘连。     

Chemical stimulation of phagocytosis in Amoeba proteus and the influence of external calcium

Summary The process of phagocytosis in Amoeba proteus was examined by following the uptake of Tetrahymena pyriformis and agarose beads. The ciliates are taken up in a time dependent and saturable manner. T. pyriformis apparently emits a water-soluble substance that acts as a chemoattractant to the amoebae. Plain agarose beads are not engulfed by A. proteus, but those beads having reducedglutathione with the -SH group exposed are taken up almost to the same extent as T. pyriformis. Phagocytosis of the glutathione beads is calcium-dependent with maximum bead uptake at 10^-4M Ca⁺⁺. Glutathione applied to A. proteus brings about pseudopod formation, increased phagocytosis and displacement of surface-associated calcium.     

Scanning electron microscope observations on the miracidium of Schistosoma

Miracidia of two species of Schistosoma, viz. haematobium and japonicum, were studied with the scanning electron microscope to more clearly visualize what is seen with the light microscope and the transmission electron microscope, and more specifically, to relate the structure of the apical papilla to its function in snail penetration.The apical papilla of schistosome miracidia is composed of corrugated areas which form tiny suckerlike cups, presumably used by the miracidium to facilitate attachment to the snail during penetration. A lateral opening (secretory pore) on the apical papilla and short stubby apical cilia (tactile or sensory) are also demonstrated.     

Scanning electron microscope observations on the spore of Nosema apis Zander

A simple Epon block fracture technique was used to process spores of Nosema apis for scanning clectron microscope examination. The mature spore was egg-shaped with a pointed anterior pole. The young spore was more elongated. The surface of both stages was smooth. A large number of midgut epithelial cells which harbour N. apis were also observed. The cell surfaces of the epithelial cells were also smooth.     

Scanning electron microscope observations of the spores of some species of Polystichum

Five species of Polystichum are studied under the scanning electron microscope and a comparison made with the light microscope studies of the same species published earlier. The SEM studies present a clear picture of the surface topography, supplying additional information.     

Amoeba proteus: the nuclear periphery.

This study extends previous work on the nuclear envelope and associated structures. It illustrates that the cylindrical structures of the honeycomb lattice are not attached to the nuclear envelope, although generally perpendicular and closely apposed to it, and that there is a complex arrangement of fibrillar material between the cylinders of the lattice. The relationship of nuclear helices to these structures is described and the possible mode of their transfer from nucleus to cytoplasm is discussed.     

Scanning electron microscopic observations of early stages of phagocytosis of E. coli by human neutrophils

Summary Changes in surface morphology, as observed by scanning electron microscopy, appear rapidly when human polymorphonuclear neutrophils (PMN) are challenged with bacteria. Monolayers of PMN adhering to glass were incubated with opsonized E. coli from 5 sec to 10 min, and then fixed and prepared for SEM. As early as 5 sec after phagocytic challenge, E. coli are found in contact with PMN and in the process of engulfment into open cavities formed by lamellipodia. The shape of the mouth of the forming phagocytic vacuole is related to the orientation of bacteria during entry. Bacteria engulfed into early forming phagosomes are surrounded by a large open space between the bacteria and the phagosome wall. As phagocytosis proceeds, the space is reduced and the loose fit around the entering bacteria becomes tight. By 30 sec, bacteria may be completely internalized and by 1 min phagocytized E. coli are packed into bulging PMN. The observations reveal the variability and rapidity of the phagocytic response and confirm the presence of sensitive mechanisms for host defense by PMN.This work was supported by research grants from the University of North Carolina Research Council and the National Institutes of Health (A1 02430)