Perinuclear accumulation of hepatitis A virus proteins, RNA, and particles and ultrastructural alterations in infected cells

The exact intracellular site of hepatitis A virus (HAV) production is unknown, possibly due to its usually slow and inefficient replication. Using immunocytochemistry and in-situ RT-PCR, we show that in cells infected with the rapidly replicating HAV strain HAS-15, viral proteins and RNA are scattered throughout the cytoplasm and accumulate in the perinuclear cytoplasmic area. Various ultrastructural alterations were found in infected cells, such as large polyribosomes, swelling of the perinuclear space and the ER, and dilatation of Golgi cisternae. In addition, HAV infection induced the formation of large arrays of annulate lamellae. Direct visualization of HAV particles was scarce. The various ultrastructural alterations described here might represent different phases of the replicative cycle of HAV that is asynchronous in the infected cell layer.

Subcellular localization of thrombopoietin in human blood platelets and its release upon thrombin stimulation

Thrombopoietin (TPO) is a major regulator of platelet production. The concentration of circulating TPO seems to be determined by its binding and internalization by megakaryocytes and platelets. To elucidate the platelet compartments involved in TPO metabolism, we investigated intraplatelet TPO by post-embedding immunoelectron microscopy, incubated platelets with recombinant human (rh)TPO coupled to colloidal gold and visualized the TPO uptake using electron microscopy. TPO concentrations were measured in 12 platelet concentrates (PC) before and after stimulation with thrombin and after disruption of platelets by freezing-thawing. In resting platelets, immunogold labelling revealed a prevailing cytoplasmic localization of TPO antigen and minor labelling within the surface-connected canalicular system (SCCS); storage granules were devoid of labelling. In tracer experiments, TPO-gold was observed on the plasma and SCCS membranes and within the cytoplasm. Upon thrombin stimulation, endogenous TPO was still detected within the cytoplasm by immunolabelling, and tracer experiments revealed TPO-gold within the cytoplasm and on fibrin fibres. After thrombin stimulation of PC, the plasma TPO levels increased to an average of 535%, and after platelet lysis to an average of 1625% compared with plasma values in unstimulated PC. We conclude that platelets contain releasable immunoreactive TPO within the SCCS and within their cytoplasm, but not within granular compartments. Stored immunoreactive TPO is released upon thrombin stimulation, but only to a minor degree.

Production of trypsin by cells of the exocrine pancreas is paralleled by the expression of the KH protein vigilin

Vigilin, a protein with a continuous series of 14 KH motifs, forms part of a multiprotein complex containing tRNA. Several lines of evidence have suggested that vigilin expression is enhanced in those cells which were actively engaged in protein synthesis. Accordingly, we show here by immunoelectronmicroscopy a close association of vigilin with the rough endoplasmic reticulum in rat pancreatic cells. Histological examination of these cells furthermore demonstrates the highest intensity of vigilin staining in the perinuclear, intranuclear, and basolateral regions where the endoplasmic reticulum is mainly amassed. In vivo challenge of starving rats fed prior to sacrifice raised in parallel the protein levels of both trypsin and vigilin when compared to unchallenged animals and was associated with enhanced expression of the vigilin gene. In contrast, in human and rat cell lines of pancreatic tumors with a constitutively high expression of vigilin no further stimulation by cholecystokinin treatment could be achieved. Our data provide circumstantial evidence that vigilin may play a crucial role in the ability of an organ, e.g., pancreas, to cope with the physiological demand to upregulate protein synthesis.

Endocytosis, storage, and release of IgE by human platelets: differences in patients with type I allergy and nonatopic subjects

Platelets of atopic individuals differ in alpha-granular contents and in the amount of biologically active mediators released compared with platelets of nonatopic subjects. Because platelets carry the low-affinity IgE receptor (CD23), they may contribute to long-lasting IgE sensitivity by serving as a storage pool for IgE. We compared 45 atopic individuals with immediate-type allergies and 25 nonatopic control subjects with respect to storage and release of IgE by their platelets. Platelets of atopic individuals were characterized by a 10-fold higher median IgE content compared with those of nonatopic control subjects. The platelet IgE content correlated with the serum IgE level in the four atopic individuals with seasonal allergies who were followed up monthly over 1 year. Platelet stimulation with platelet activating factor, but not with thrombin or adenosine diphosphate, resulted in a release of 65% of the stored IgE. Conversely, platelet stimulation with monoclonal IgE/kappa resulted in the release of the chemokine RANTES. Platelet alpha-granules were identified as the main storage compartment for IgE by postembedding immunocytochemistry. Although more than half of the alpha-granules showed gold labeling for IgE, additional labeling was found on the external face of the plasma membrane and within the open canalicular system, indicating endocytosis and exocytosis of IgE. Moreover, the detection of CD23 not only on the plasma membrane but also on membranes of the alpha-granules further supports the existence of an exchange of IgE between the blood plasma and an internal storage compartment. Endocytosis could be confirmed by the uptake of an IgE myeloma protein coupled to colloidal gold. We conclude that platelets of atopic individuals may contribute to allergic inflammation by serving as a storage pool for IgE and by their increased capacity to liberate further mediators of allergy in response to IgE stimulation.

Platelets and inflammation

Besides their functions in the haemostatic process and in thrombus formation after an endothelial injury, blood platelets also take part in the processes of inflammation and tissue repair that follows. For this purpose, they closely collaborate with all types of leukocytes. Activated platelets secret chemotactic substances, they facilitate the binding of leukocytes to the endothelium and their subsequent extravasation, and they may influence the inflammatory responses of leukocytes in both stimulating and inhibiting ways. However, platelets themselves also contain an array of potent proinflammatory substances, and therefore they are regarded as mediator and effector cells in inflammation. Their capability to interact with bacteria, parasites, and other foreign materials is possibly a phylogenetic vestige and may explain the existence of IgE-dependent killing mechanisms of platelets. On the other hand, the connection between IgE and platelets, besides the platelet-induced eosinophil infiltration, offers a functional basis for the involvement of platelets in allergic processes, particular in the skin and the airways.

Clathrin-mediated endocytosis of high density lipoprotein3 in human intestinal Caco-2 cells. A post-embedding immunocytochemical study

The mechanism by which high density lipoprotein (HDL) removes excess cholesterol from intracellular sites has been the subject of much controversy. There is some evidence that HDL binds to specific cell surface receptors without internalization. Other evidence suggests that HDL is taken up by endocytosis, enters a pathway of endosomal trafficking and is resecreted from the cells (retroendocytsosis). In the present study, we investigated the distribution of apolipoprotein AI, the major protein constituent of HDL, in cultured intestinal Caco-2 cells employing post-embedding immunocytochemistry on LR White-embedded material. Cells grown under control conditions showed label for apolipoprotein AI in the endoplasmic reticulum. After incubation with native apolipoprotein E-free high density lipoprotein3 (HDL3) additional label for apolipoprotein AI was found in endosomes. These endosomes were observed near lipid droplets and in the basolateral cytoplasm. Further, it was demonstrated that label for apolipoprotein AI was colocalized with label for clathrin on the basolateral membrane. Our results support the concept that HDL3 is internalized and subsequently processed in an endosomal pathway in Caco-2 cells besides de novo synthesis of apolipoprotein AI.

The storage lesion of platelets: ultrastructural and functional aspects

When prepared and stored as concentrates, platelets undergo a lot of structural, biochemical and functional alterations that lead to an impaired function after transfusion. Besides signs of activation like disc-to-sphere transformation, extension of pseudopodes and loss of storage granules, platelets may display a swollen open canalicular system and changes in the structure of their alpha-granules. These partly reversible morphological alterations correspond to a deterioration of basic metabolic parameters and a decrease in the reactivity of stored platelets to weak agonists. All these changes occur to a very different degree depending on the methods of preparation and storage. With the introduction of acetate-containing additive solutions, the storage conditions could be greatly improved, and platelets from pooled buffy coats and stored in an acetate-containing medium with at least 20% autologous plasma show the best structural integrity over 8 days of storage.

Immunocytochemical localization of vigilin, a tRNA-binding protein, after cell fractionation and within the exocrine pancreatic cell of the rat

A polyclonal antibody against a fusion protein composed of two vigilin domains and gamma-galactosidase was used to localize the tRNA-binding protein vigilin at the ultrastructural level. Immunoreactivity for vigilin was found on membranes bearing ribosomes within the microsome fraction derived from rat livers and on the rough endoplasmic reticulum in rat exocrine pancreatic cells, synthesis corroborating the involvement of vigilin in protein synthesis. Gold labeling was also found in the nucleus and in the microsome fraction in an osmiophilic substance resembling heterochromatin. Both of these localizations, the rough endoplasmic reticulum and the nucleus, are in line with the observation that a vigilin-containing ribonucleoprotein complex binds tRNA.

Platelets stored in a glucose-free additive solution or in autologous plasma--an ultrastructural and morphometric evaluation

We evaluated a new glucose-free citrate-acetate-NaCl platelet additive solution (PAS 2). In series I, platelet concentrates (PC) were prepared by apheresis and subsequently stored either in plasma (n = 16) or in PAS 2 (n = 15). In series II, PCs were prepared from pools of four buffy coats (BC) and stored in plasma (n = 12) or in PAS 2 (n = 11). By means of ultrastructural morphometry, the volume fractions of alpha-granules, the open canalicular system (OCS) and the fraction of storage granules secreted into the OCS were analyzed during storage for up to 8 days. Additionally, we determined pH, glucose, lactate, pCO2, HCO3-, lactate dehydrogenase and platelet factor 4. Apheresis platelets stored in plasma showed no changes in their contents of alpha-granules and in the fractions of the OCS. In contrast, apheresis platelets stored in PAS 2 displayed a decrease of their relative volume fraction of alpha-granules from 9.1 +/- 1% on day 1 to 3.7 +/- 0.9% on day 5. The fraction of the OCS increased from 7.4 +/- 0.8% on day 1 to 17.1 +/- 1.4% on day 3. On day 8, 93 +/- 9% of all platelets were lysed. Levels of glucose were significantly lower in these preparations and after day 3 glucose consumption decreased to zero. Among PC derived from pooled BC, differences between storage in PAS 2 or plasma were less striking. Only the fraction of alpha-granules secreted into the OCS was significantly greater in BC derived PC stored in PAS 2 on all days. These PCs stored in PAS 2 had a higher plasma carryover (30%) in comparison to apheresis PC stored in PAS 2 (10%). We conclude that plasma is superior to PAS 2 for storage of both apheresis and buffy coat platelets. For preservation of the structural integrity of platelets, the use of PAS 2 requires a minimum of 30% plasma carryover.

Immunocytochemical localization of the chemokines RANTES and MIP-1 alpha within human platelets and their release during storage

The cytokines RANTES and MIP-1 alpha are 8-kD peptides which belong to the C-C subfamily of chemokines. They are both potent chemotactic factors for basophils and eosinophils. Apart from lymphocytes, the RANTES peptides was recently shown to be released from human platelets stimulated with thrombin [Kameyoshi et al: J Exp Med 1992;176:587-592]. Employing postembedding immunocytochemistry, we could detect RANTES and for the first time also MIP-1 alpha within the alpha-granules of human platelets. To date, MIP-1 alpha was not reported to occur in platelets. In slightly activated platelets, as found in stored platelet concentrates (PC), label for RANTES and MIP-1 alpha could also be observed within cisterns of the open canalicular system and on the plasma membrane, indicating a release of both peptides. These findings were confirmed by in vitro studies in PC, by investigation of RANTES and MIP-1 alpha release into the suspending medium. Over a period of 8 days, RANTES was steadily released in relatively high amounts, whereas MIP-1 alpha was measured in rather small amounts in the suspending medium. As RANTES and MIP-1 alpha, besides their chemotactic activity on eosinophils and basophils, are able to mediate the release of histamine, it is tempting to speculate about a participation of platelets in inflammatory reactions in which eosinophils and basophils are involved.

Immunocytochemical colocalization of adhesive proteins with clathrin in human blood platelets: further evidence for coated vesicle-mediated transport of von Willebrand factor, fibrinogen and fibronectin

Coated membranes and vesicles play an important role in receptor-mediated endocytosis and intracellular trafficking in various cell types, and are also present in blood platelets. Platelets take up certain proteins from the blood plasma, such as von Willebrand factor and fibrinogen, and these substances are transferred to storage granules. The receptors for these plasma proteins on the platelet plasma membrane have been well characterized, but morphological evidence for their transport to the storage granules is not yet available. In an attempt to clarify this aspect, we employed postembedding immunocytochemistry on platelets embedded in the acrylic resin LR White. Clathrin as the major coat component of coated vesicles was localized in the cytoplasm, on the plasmic faces of alpha-granules and the open canalicular system, and on the plasmic face of the plasma membrane. Colocalizations of the adhesive proteins, von Willebrand factor, fibrinogen and fibronectin, with clathrin could be observed at the same typical locations as coated vesicles were seen in Araldite-embedded material. These colocalizations have not been reported to date and furnish further evidence for a coated vesicle-mediated transport of blood plasma-derived adhesive proteins from their receptors on the outer plasma membrane to the alpha-granules.

Storage lesion of human platelets as revealed by ultrathin sections and freeze-fracture replicas

We report the ultrastructural changes occurring in human platelets during eight days of storage. Extension of pseudopodia is frequently observed, but a concentration of organelles in the centre of the platelets is found only in a minor fraction (approximately 5%). Striking changes can be observed in both the granules and the open canalicular system. In fresh platelets, the latter often has the form of stacked membranes that have no lumen, but these membranes separate and spread with increasing storage time. However, the openings of this system on the outer surface of the platelet remain unchanged. Some of these features differ from the morphological description of platelets activated by thrombin or ADP, and suggest that the storage lesion is the result of a prolonged weak activation that leads to an incomplete release reaction within the first five days.

Morphological changes in thrombocytes during blood bank storage. An ultrastructural morphometric study

Monitoring the storage lesion of platelet concentrates (PC) is commonly done by determining metabolic parameters, release of cytoplasmic markers and granules contents and watching the light microscopical appearance of platelets. Descriptions of ultrastructural changes are rare, and so we ascertained the changes in two important organelles, the alpha- and lysosomal granules and the open canalicular system (OCS), by morphometric analysis. Single donor PC's were prepared with a CS-3000 plus (Baxter) processor and stored under routine conditions. The volume fraction of the granules displayed a decrease to 43% after 8 days of storage, and the OCS fraction increased to 143%. Moreover, changes in the morphology of granules and the development of OCS channels are described, and ballooning and even complete lysis of some platelets could be observed after only three days. Furthermore, the membrane flux in the formation of pseudopodia is discussed. Our results stress the need to establish better preparation and storage conditions for platelet concentrates.

The perinatal development of glucose-6-phosphatase activity distribution pattern in rat liver. A microdensitometrical study

The ontogenetic development of the intralobular distribution pattern of glucose-6-phosphatase activity in the rat liver is described in terms of histochemical changes determined with microdensitometry. A newly developed cerium-lead technique was employed and compared with the common lead technique optimized by Teutsch (1978a). The cerium technique has advantages, meets the prerequisites for quantitative determinations and yields results comparable to biochemically obtained data from microdissected tissue. The first signs of a heterogeneous distribution pattern of glucose-6-phosphatase activity are observed on the 3rd d after birth, and differences between periportal and centrolobular areas are largest around 10th and 15th d. At 30th d after birth, the adult pattern is complete with a centrolobular glucose-6-phosphatase activity of 67% of the periportal value.

The binding of a polyclonal antibody against human band 3 to in vitro aged erythrocytes

In vitro aged human erythrocytes were checked for their anti-band-3-antibody loading by means of a protein A-gold technique. The in vitro-ageing procedures are introduced as an alternative to the questionable preparation of in vivo aged cells. They include the influences of NaF in various concentrations, of heat (49 degrees C) and urea. After the treatment with 20 mmol/l NaF and more, the IgG loading increases significantly. In contrast to that, however, exovesiculation induced by heat and urea lower the IgG loading. Possible mechanisms for the growing accessibility of the epitopes concerned are discussed in connection with changes occurring during the physiological ageing processes.