Luminal uptake of Vibrio (Listonella) anguillarum by shed enterocytes--a novel early defence strategy in larval fish.

As adhesion and translocation through fish gut enterocytes of the pathogen Vibrio (Listonella) anguillarum are not well investigated, the effective cause of disease and mortality outbreaks in larval sea bass, Dicentrarchus labrax, suffering from vibriosis is unknown. We detected V. anguillarum within the gut of experimentally infected gnotobiotic sea bass larvae using transmission electron microscopy and immunogold labelling. Intact bacteria were observed in close contact with the apical brush border in the gut lumen. Enterocytes contained lysosomes positive for protein A-gold particles suggesting intracellular elimination of bacterial fragments. Shed intestinal cells were regularly visualized in the gut lumen in late stages of exposure. Some of the luminal cells showed invagination and putative engulfment of bacterial structures by pseudopod-like formations. The engulfed structures were positive for protein A-colloidal gold indicating that these structures were V. anguillarum. Immunogold positive thread-like structures secreted by V. anguillarum suggested the presence of outer membrane vesicles (MVs) hypothesizing that MVs are potent transporters of active virulence factors to sea bass gut cells suggestive for a substantial role in biofilm formation and pathogenesis. We put forward the hypothesis that MVs are important in the pathogenesis of V. anguillarum in sea bass larvae.

The effect of hyperoxygenation and reduced flow in fresh water and subsequent infectious pancreatic necrosis virus challenge in sea water, on the intestinal barrier integrity in Atlantic salmon, Salmo salar L.

In high intensive fish production systems, hyperoxygenation and reduced flow are often used to save water and increase the holding capacity. This commonly used husbandry practice has been shown to be stressful to fish and increase mortality after infectious pancreatic necrosis virus (IPNV) challenge, but the cause and effect relationship is not known. Salmonids are particularly sensitive to stress during smoltification and the first weeks after seawater (SW) transfer. This work aimed at investigating the impact of hyperoxygenation combined with reduced flow in fresh water (FW), on the intestinal barrier in FW as well as during later life stages in SW. It further aims at investigating the role of the intestinal barrier during IPNV challenge and possible secondary infections. Hyperoxygenation in FW acted as a stressor as shown by significantly elevated plasma cortisol levels. This stressful husbandry condition tended to increase paracellular permeability (P(app)) as well as translocation of Aeromonas salmonicida in the posterior intestine of Atlantic salmon. After transfer to SW and subsequent IPNV challenge, intestinal permeability, as shown by P(app), and translocation rate of A. salmonicida increased in the anterior intestine, concomitant with further elevation in plasma cortisol levels. In the anterior intestine, four of five fish displayed alterations in intestinal appearance. In two of five fish, IPNV caused massive necrosis with significant loss of cell material and in a further two fish, IPNV caused increased infiltration of lymphocytes into the epithelium and granulocytes in the lamina propria. Hyperoxygenation and reduced flow in the FW stage may serve as stressors with impact mainly during later stages of development. Fish with an early history of hyperoxygenation showed a higher stress response concomitant with a disturbed intestinal barrier function, which may be a cause for the increased susceptibility to IPNV infection and increased susceptibility to secondary infections.

Histological changes in intestine of Atlantic salmon (Salmo salar L.) following in vitro exposure to pathogenic and probiotic bacterial strains.

Furunculosis and vibriosis are diseases that cause severe economic losses in the fish-farming industry. The foregut of the Atlantic salmon (Salmo salar L.) was exposed in vitro to two fish pathogens, Aeromonas salmonicida (causative agent of furunculosis) and Vibrio anguillarum (causative agent of vibriosis), and to one probiotic strain, Carnobacterium divergens, at 6 x 10(4) or 6 x 10(6) viable bacteria per milliliter. Histological changes following bacterial exposure were assessed by light and electron microscopy. Control samples (foregut exposed to Ringer's solution only) and samples exposed only to C. divergens had a similar appearance to intact intestinal mucosal epithelium, with no signs of damage. However, exposure of the foregut to the pathogenic bacteria resulted in damaged epithelial cells, cell debris in the lumen, and disorganization of the microvilli. Co-incubation of the foregut with a pathogen and C. divergens did not reverse the damaging effects caused by the pathogen, although these were alleviated when probiotic bacteria were used. Based on these results, we suggest that the probiotic bacterium, C. divergens, is able to prevent, to some extent, pathogen-induced damage in the Atlantic salmon foregut.

Effects of natural winter pasture and commercial pellet on the ultrastructure of small intestinal epithelium in reindeer.

Segments of small intestine (duodenum, jejunum and ileum) from slaughtered reindeer (Rangifer tarandus tarandus) grazing natural winter pastures (n=3) and reindeer fed commercially available pellets (RF-80) in winter (n=5) were collected and immediately fixed in McDowell's fixative. Transmission electron microscopy was employed to investigate the ultrastructural features of the epithelium and lamina propria along the small intestine and to relate these to the different diets. Major differences in ultrastructural features were observed between the small intestinal enterocytes of reindeer fed the two diets. Enterocytes in reindeer fed the natural diet displayed a normal appearance with a dense cytoplasm and distinct microvilli. In contrast, reindeer fed the commercial diet showed damaged enterocytes amongst the normal cells. Abnormal changes included disintegration and loss of microvilli, cytoplasmic swelling, loss of membrane integrity and increases in the width of intercellular spaces, especially in the jejunum.

Morphologic changes in tubular cells from in situ kidneys following experimental hypothermia and rewarming.

Although renal failure may occur following rewarming from deep accidental hypothermia, this subject has received little attention in experimental hypothermia and clinical case reports. In order to explore the integrity of hypothermic and posthypothermic renal morphology we used an experimental animal model of accidental hypothermia where the heart supports the circulation throughout cooling and rewarming without accompanying cardioplegia or ischemia. Ultrastructural changes in renal tubular cells from three groups of pentobarbital anesthetized Wistar rats: 1) controls (n=6) maintained at 37 degrees C for 4 h, 2) hypothermic rats (n=6) core-cooled and maintained at 15-13 degrees C for 4 h, and 3) rewarmed rats (n=10), were studied as a sensitive indicator of renal damage. Electron micrographs (EM) from hypothermic kidneys showed rounded up mitochondria with loss of contrast. These changes were observed in several though not all of the biopsies, but they were found in all kidneys. Areas exhibiting focal tubular necrosis were seen on most EM from three of these kidneys. EM from rewarmed kidneys showed alterations of mitochondrial ultrastructure with similarities to those observed after hypothermia, but in general the changes were more prominent. Extracellular edema, intracellular edema, swelling of mitochondria, margination of chromatin, necrosis of single tubular cells, and disrupting necrotic debris into tubular lumen could be found in micrographs from 7 of the 10 kidneys examined. Rewarming from experimental hypothermia, without episodes of ischemia or hypoxia, thus induces ultrastructural changes in renal tubular cells similar to changes observed in acute tubular necrosis, associated with renal failure.

Fluid pressure in human dermal fibroblast aggregates measured with micropipettes.

Previous studies indicated that connective tissue cells in dermis are involved in control of interstitial fluid pressure (Pif). We wanted to develop and characterize an in vitro model representative of loose connective tissue to study dynamic changes in fluid pressure (Pf) over a time course of a few minutes. Pf was measured with micropipettes in human dermal fibroblast cell aggregates of varying size (<100- and >100-microm diameter) and age (days 1-4) kept at different temperatures (approximately 15, 25, and 35 degrees C). Pressures were measured at different depths of micropipette penetration and after treatment with prostaglandin E1 isopropyl ester (PGE1), latanoprost (PGF2alpha), and ouabain. Pf was positive (more than +2 mmHg) during control conditions and increased with increasing aggregate size (day 2), age (day 4 vs. day 1), temperature, and depth of micropipette penetration. Pf decreased from 2.9 to 2.0 mmHg during the first 10 min after application of 10 microl of 1 mM PGE1 (P < 0.001). Pf increased from 3.0 to 4.8 mmHg (P < 0.01) after administration of 10 microl of 1.4 microM ouabain and from 3.1 to 4.4 mmHg after addition of 5 microl of 1.42 mM PGF2alpha (P > 0.05). In conclusion, we have developed and validated a new in vitro method for studying fluid pressure in loose connective tissue elements with the advantage of allowing reliable and rapid screening of substances that have a potential to modify Pf and studying in more detail specific cell types involved in control of Pf. This study also provides evidence that fibroblasts in the connective tissue can actively modulate Pf.

Epithelium-associated bacteria in the gastrointestinal tract of Arctic charr (Salvelinus alpinus L.). An electron microscopical study.

AIMS: The primary aim was to use transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to define the location of epithelium-associated bacteria in the digestive tract of the salmonid fish, Arctic charr (Salvelinus alpinus). METHODS AND RESULTS: TEM and SEM examination of the gastrointestinal tract demonstrated substantial numbers of ovoid and rod-shaped bacterial cells associated with the microvillous brush borders of enterocytes. Bacteria were found at the tips of microvilli as well as between adjacent microvilli. Endocytosis of bacteria by epithelial cells was observed in two regions (pyloric caeca and midgut). CONCLUSION: Electron microscope examination of the gut is an important tool for evaluating the microbial ecology of the fish digestive tract ecosystem. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the current study clearly demonstrate that the intestine is involved in bacterial endocytosis.

The effect of a low molecular weight inhibitor of lipid peroxidation on ultrastructural alterations to ischemia-reperfusion in the isolated rat heart.

The effects of H290/51, a novel indenoindole derivative inhibitor of lipid peroxidation, on ultrastructural changes during cardiac ischemia-reperfusion injury were investigated. Langendorff-perfused rat hearts were exposed to 30 minutes of global ischemia followed by 20 minutes of reperfusion: Group A: Control hearts with standard buffer perfusion with vehicle added. Group B: H290/51 (10(-6) mol/l) added to buffer throughout stabilisation and reperfusion. In an additional Group C, where hearts were given H290/51, but not subjected to ischemia, the ultrastructure was preserved till the end of reperfusion. Absolute volumes and calculated volume fractions (Vv) of tissue and subcellular components were assessed with quantitative stereologic morphometry. After ischemia the increase in volume of extracellular interstitium was inhibited by H290/51 (247 +/- 80 vs. 159 +/- 50 microl, mean +/- SD, groups A and B, respectively, p<0.05). The Vv (interstitium/myocard) was higher in control hearts (0.318 +/- 0.062 vs. 0.206 +/- 0.067, p<0.05). Vv (cell edema/myocyte) was higher in the control group (0.144 +/- 0.07 vs. 0.083 +/- 0.033, p<0.05). Vv (myocyte/myocard) was higher in group B after ischemia than in the control group (0.622 +/- 0.071 vs. 0.707 +/- 0.052, p<0.05). The decreased Vv (capillary/myocard) after ischemia was inhibited by H290/51. After reperfusion there was no difference between groups. Treatment with H290/51 reduced edema and ensured better preserved sarcolemmal membrane structure during ischemia. The effect was no longer present after reperfusion.

Altered cytokine and nitric oxide secretion in vitro by macrophages from diabetic type II-like db/db mice.

Macrophage dysfunction is a likely mechanism underlying common diabetic complications such as increased susceptibility to infection, accelerated atherosclerosis, and disturbed wound healing. There are no available studies on the function of tissue macrophages in diabetes in humans. We have therefore studied peritoneal macrophages from diabetic type 2-like db/db mice. We found that the release of tumor necrosis factor-alpha and interleukin-1beta from lipopolysaccharide plus interferon-gamma-stimulated macrophages and vascular endothelial growth factor from both stimulated and nonstimulated macrophages was significantly reduced in diabetic animals compared with nondiabetic controls. Nitric oxide production from the stimulated db/db macrophages was significantly higher than that in the db/+ cultures, whereas there was no difference in their ability to generate reactive oxygen species. When studied both at light and electron microscopic levels, macrophages in diabetic animals had an altered morphological appearance compared with those of normal controls. We conclude that the function and morphology of the macrophages are disturbed in db/db mice and that this disturbance is related to the mechanisms underlying common inflammatory and degenerative manifestations in diabetes.

Bacterial penetration into tonsillar surface epithelium during infectious mononucleosis.

Bacterial penetration into epithelial cells, scraped from the palatine tonsils of 14 patients (10 males, four females; median age 16 years) with current infectious mononucleosis and concomitant membranous tonsillitis, was studied using the transmission electron microscopic (TEM) technique. Bacteria were seen to adhere to and penetrate the epithelial cells, some of which were completely filled with bacteria. This finding suggests intracellular proliferation of bacteria. Epstein-Barr virus, the causative agent of infectious mononucleosis, especially when associated with growth of beta-haemolytic streptococci on the palatine tonsils, induces bacterial penetration into tonsillar tissue, that in turn might be a causative mechanism in the development of peritonsillar abscess.

Proliferation, differentiation and apoptosis in villous trophoblast at 13-41 weeks of gestation (including observations on annulate lamellae and nuclear pore complexes).

Ultrastructural, immunochemical, fluorescence and stereological studies were undertaken on human villous trophoblast from 13 weeks of gestation to term. The aim was to describe and quantify morphological changes during proliferation, differentiation and apoptosis in cytotrophoblast and syncytial regions of non-aggregated and aggregated nuclei. Numbers of trophoblast nuclei increased continuously from 13 weeks. In term placentae, intrasyncytial differentiation was characterized ultrastructurally by gradual decreases in nuclear size and packing density accompanied by nucleolar regression, and increasing heterochromatinization, envelope convolution and packing density of nuclear pore complexes. In densely packed areas, nuclear profiles resembled interlocking jigsaw pieces. Occasionally, these 'pre-apoptotic' nuclei were associated with annulate lamellae. Rarely, nuclear changes terminated in apoptosis with a characteristic pattern of condensed peripheral chromatin, a central island of euchromatin, no nucleoli and no discernible nuclear pores. Apoptotic nuclei were seen singly and within dense nuclear aggregations. Similar spatial patterns of nuclei and chromatin were seen in propidium iodide-stained sections at 13-41 weeks. Whilst the relative incidence of intensely fluorescent nuclei remained constant, absolute numbers increased linearly during gestation and correlated positively with the volume of syncytial knots. Nuclei labelled for DNA fragmentation occurred very infrequently and were also found in nuclear clusters as well as singly. We suggest that nuclear differentiation in syncytium has two phases: on entering syncytium, nuclei become committed to a long programmed pre-apoptotic phase which leads to a short apoptotic execution phase. We propose further that clustered nuclei (pre-apoptotic and apoptotic) in syncytial knots probably represent the extrusion component of normal continuous epithelial turnover.

The initial phase of myocardial reperfusion is not associated with aggravation of ischemic-induced ultrastructural alterations in isolated rat hearts exposed to prolonged global ischemia.

The present study focuses on the qualitative and sequential development of myocardial ultrastructural changes during the first 10 min of reperfusion in isolated rat hearts exposed to 60 min of global ischemia. The frequency of and the association between ultrastructural changes were examined by semiquantitative morphometry using the micrograph as unit. In each micrograph the subcellular components of the myocytes (sarcolemma, mitochondria, myofilaments and nucleus) and the endothelial cells were evaluated and graded as slightly, moderately, or severely altered. Ischemia alone induced moderate to severe ultrastructural alterations. The myocytes revealed sarcolemmal disattachment or rupture. The myocytic mitochondria had a clear matrix with abundant broken cristae and amorphous matrix densities. The myofilamental pattern was irregular or even disrupted, and most nuclei had reduced density and showed margination of chromatin. The endothelium showed vacuolization, rupture of the plasma membrane, and extracellular accumulation of cellular debris. During the first 2 min of reperfusion severe ultrastructural alterations were partly reversed. After 10 min of reperfusion both the frequency and grade of myocardial ultrastructural alternations were similar to that observed after ischemia. Cristal adhesions occurred predominately during reperfusion and were associated with moderately and severely altered myocytic mitochondrial alterations. In conclusion, the results showed that ischemic-induced ultrastructural alterations were transiently improved upon reperfusion. With exception of the development of cristal adhesions, the acute phase of reperfusion was not associated with additional ultrastructural changes in isolated buffer-perfused rat hearts exposed to prolonged ischemia.

Epithelial integrity, cell death and cell loss in mammalian small intestine.

In recent years, the different mechanisms of epithelial cell loss which occur in mammalian and avian small intestine have been re-investigated. Information is now available for a variety of mammalian types and mechanisms can be divided into two major classes: [i] those preserving epithelial integrity by maintaining intercellular tight junctions throughout early-to-late stages of cell extrusion; and [ii] those which compromise integrity by introducing breaches in epithelial continuity. Both classes are associated with the activity and/or proximity of non-epithelial cells (mainly lymphocytes and mononuclear phagocytes) located in the epithelium or underlying lamina propria. Intraepithelial lymphocytes may be involved in enterocyte targetting and killing whilst lamina propria (LP) macrophages sequester cell debris. Where epithelial integrity is maintained, two types of loss can be identified. In the first (type 1), complete cells are extruded into the lumen. In the second (type 2), only anucleate apical cell fragments pass into the lumen. There are two variants of type 2 loss distinguishable by the fate of the nucleated basal portions of cells. One variant (type 2a) creates large intercellular spaces extending from the preserved apical cap to the basal lamina and containing enterocyte debris for phagocytosis. The second (type 2b) involves the gradual shrinkage of individual cells (which become more electron-dense) and in situ degeneration of their nucleated subapical portions in increasingly narrower intercellular spaces between adjacent healthy enterocytes. The mechanism of removal of these fragments is unclear but may be via macrophages or surrounding enterocytes. Apoptosis has been implicated in both type 1 and type 2 extrusion. In contrast, type 3 loss involves morphological changes in enterocytes which are reminiscent of those seen in necrosis and is accompanied by breaks in epithelial continuity following cell swelling, a decrease in cell electron density and total or subtotal degradation of organelles and membranes. It ends in loss of either an abnormal cell apex (with subsequent exposure of the degraded cell contents and their spillage into the lumen) or a complete cell remnant (extruded into the lumen before total disintegration of plasma membranes).

Further evidence of species variation in mechanisms of epithelial cell loss in mammalian small intestine: ultrastructural studies on the reindeer (Rangifer tarandus) and seal (Phoca groenlandica).

Ultrastructural studies were conducted on mechanisms of epithelial cell loss in the small intestine of seal and reindeer. Mechanisms maintaining epithelial integrity were distinguished from those that did not and the non-epithelial cell types involved were identified. Three types of cell extrusion were noted. In two, tight junctional integrity was preserved and anucleate apical cell fragments (rather than complete cells) were lost into the lumen. In reindeer (type 1), this involved creating large intercellular spaces extending from the preserved apical cap to the lamina propria and containing enterocyte debris probably phagocytosed by subepithelial macrophages. A variant of this process (type 2) involved the gradual shrinkage of individual cells, which became more electron-dense, and the in situ degeneration of their nucleated subapical portions. Degenerated cell fragments and membrane whorls were confined to narrow intercellular spaces between approximating adjacent healthy enterocytes. The mechanism of removal of these fragments was unclear. In both cases, the proximity of intraepithelial lymphocytes suggested that they were involved in cell targetting and killing. Evidence of apoptotic nuclei was not found but nucleated cell fragments could have been washed out of the lumen during tissue preparation. Type 2 cell loss was seen in both species, as was another mechanism (type 3) reminiscent of necrosis. In contrast to other mechanisms, this was accompanied by breaks in epithelial continuity following gradual loss of cell electron density and total or subtotal degradation of organelles and membranes. In seal, this terminated in the loss of an abnormal cell apex and exposure of the contents of the cell remnant to the lumen. In reindeer, all the cell remnants may have been extruded before total membrane degeneration but, in both species, the otherwise tight epithelial barrier was clearly breached. Again, intraepithelial lymphocytes were associated with sites of necrosis. These findings provide evidence for further species differences in mechanisms of epithelial cell extrusion and suggest that necrotic cell loss may be more common than previously admitted.

Changes in myocardial ultrastructure induced by cooling as well as rewarming.

The aim of the present study was to investigate if hypothermia and rewarming, without accompanying cardiac ischaemia or cardioplegia, causes myocardial damage. Anaesthetized rats were subjected to a cooling procedure (4 h at 15-13 degrees C) where spontaneous cardiac electromechanical activity was maintained, followed by rewarming. Control rats, hypothermic rats and posthypothermic rats were perfusion-fixed, the hearts removed and the ventricles examined using an electron microscope. Based on morphometric methodology volume fractions as well as absolute volumes of cellular and subcellular components of the ventricles were assessed. In hypothermic hearts capillary volume fraction was significantly decreased, which was probably due to a decrease in perfusion pressure. The cytosolic volume increased in both absolute values and as a fraction of the myocyte: from 25 +/- 11 in controls to 43 +/- 8 microliters and from 0.067 +/- 0.023 to 0.102 +/- 0.013, respectively. There was a corresponding relative decrease in the volume fraction of myofilaments from 0.598 +/- 0.030 to 0.548 +/- 0.024. In posthypothermic hearts significant tissue swelling was apparent, dominated by a significant increase in myocyte volume from 372 +/- 66 in controls to 522 +/- 166 microliters. Similar changes were measured in mitochondrial and cytosolic volumes. In conclusion, the myocardial ultrastructure was altered during hypothermia as well as after rewarming. Posthypothermic myocardium showed generalized cellular swelling and areas of cellular necrosis.

Selective attachment of beta-haemolytic streptococci group A to oropharyngeal epithelium in health and disease.

Localization and semiquantification of beta-haemolytic streptococci, Group A (GABHS), GABHS attachment and general bacterial attachment to epithelial cells (bacterial number and morphology) were studied during GABHS-positive acute tonsillitis and pharyngitis infections and among healthy GABHS carriers. Samples were collected from various areas of the oropharynx (palatine tonsils, posterior oropharyngeal wall, palatoglossal arch and buccal mucosa). During acute tonsillitis and pharyngitis, GABHS grew in samples obtained from the palatine tonsils and posterior oropharyngeal wall. The ratio of GABHS colonies to other aerobic colonies increased, and GABHS became attached to epithelial cells of both palatine tonsils and posterior oropharyngeal wall. In GABHS carriers, GABHS were found mainly on the palatine tonsils, but these microorganisms were not attached to the epithelium. Overall bacterial attachment to tonsillar and oropharyngeal epithelial cells increased during active tonsillitis and pharyngitis.

Reversible ultrastructural alterations in the myocytic mitochondria of isolated rat hearts induced by oxygen radicals.

The present study focuses on reversible mitochondrial ultrastructural alterations in myocardial myocytes that correspond or accompany reversible metabolic depression observed after oxygen radical exposure. The myocytic mitochondrial membranes and matrix of isolated Langendorff-perfused rat hearts were examined by semiquantitative morphometry using the electron micrograph as unit. The hearts were exposed to either standard perfusion (group A), 10 min of oxygen radicals together with superoxide dismutase and catalase followed by 35 min of recovery (group B), 10 min of oxygen radicals alone (group C), or 10 min of oxygen radicals followed by 35 min of recovery (group D). Mitochondrial ultrastructural alterations were detected in only a few micrographs in groups A and B. The frequency of micrographs with mitochondrial ultrastructural alterations was 69% in group C and 62% in group D. In the group exposed to 10 min of oxygen radicals without recovery (group C) condensed pentalaminar membranous profiles arranged in parallel, interpreted to be closely adhering cristae, were detected in the intracristal compartment of myocytic mitochondria in 50% of the micrographs. The cristal adhesions were associated with other mitochondrial ultrastructural changes. Cristal adhesions were not present in group A or B, and were rarely found in the group exposed to 10 min of oxygen radicals followed by 35 min of recovery (group D). Thus, the cristal adhesions appear to be reversible alterations caused by exposure to oxygen radicals.

Identification of Streptococcus pyogenes on tonsillar epithelium during infection.

Epithelial cells were swabbed from the tonsillar surfaces of 5 patients with acute tonsillitis culture-positive for Streptococcus pyogenes. By using 10 nm gold particles conjugated to antiserum to S. pyogenes it was possible to trace the actual microorganisms when examined in a transmission electron microscope. The S. pyogenes bacteria, usually in pairs, were attached to the epithelial surface by their pili. The bacteria often formed a hollow in the epithelial cell surface. Coccus-shaped bacteria expressing positive affinity to immunogold-labelled antiserum were intermingled with bacteria, often rods, having no affinity whatsoever to the antiserum. With the immunocytological technique outlined in this study it is possible to study more closely cellular/bacterial adhesion mechanisms.

In situ localization of Streptococcus pyogenes during acute tonsillitis: an immunocytochemical study with gold markers.

Epithelial cells were harvested from the surface of the palatine tonsils of seven patients with current acute tonsillitis, proven culture-positive for Streptococcus pyogenes. The epithelial cells harboured attached bacteria, which expressed positive affinity to gold-labelled antiserum to S. pyogenes. The gold particles adhered selectively to the bacterial capsules. The microorganisms were held in place by projections protruding from the epithelial cells, which were in close contact with the pili of the bacteria. In some areas, positive immunogold-labelled bacteria intermingled with bacteria lacking such labelling. None of the culture-negative controls harboured epithelial cells with positive immunogold-labelled bacteria. Orally administered phenoxymethylpenicillin caused a significant reduction in both culture-positive S. pyogenes and bacteria displaying positive coating with specific gold-labelled antiserum to S. pyogenes.

Endothelin-1 causes sequential trapping of platelets and neutrophils in pulmonary microcirculation in rats.

We previously showed that endothelin-1 (ET-1) causes accumulation of leukocytes in the pulmonary microvasculature and increases vascular permeability in isolated rat lungs provided the presence of leukocytes in the perfusate. In the present study, we examined the time sequence for morphological changes induced by ET-1 in rat alveolar tissue. For this purpose we used morphometric analysis based on lung transmission electron micrographs. Morphometry was performed by point counting, and data were expressed as relative volume density. ET-1 (0.06, 0.6, and 6 nmol/kg) was infused into the internal jugular vein, and the animals were killed at certain points of time. The lungs were fixed by endotracheal instillation of McDowell's fixative. Infusion of ET-1 (0.06 or 0.6 nmol/kg) caused no significant morphological changes in the rat alveolar tissue as assessed by morphometric examination. A sevenfold increase in volume density of platelets was seen 5 min after infusion of ET-1 6 nmol/kg. The platelets were loosely aggregated, adhered partly to the endothelium, and some of them had a spherical shape with vacuoles, indicating activation. The volume density of erythrocytes increased threefold, lasting 30 min. At 120 min, the volume density of polymorphonuclear leukocytes (PMN) increased 10-fold. The PMN adhered closely to the endothelium and partly occluded the capillary lumen. Simultaneously, the endothelial cell surface showed morphological signs of injury. No significant changes were observed in the volume density of alveolar macrophages or monocytes. No significant changes were seen in lung volumes or the volume of the alveolar tissue compartment. The results showed that ET-1 causes a time- and dose-dependent sequential entrapment of platelets and neutrophils in the pulmonary circulation.