Electron-lucent Halo Research Articles

Merkel-like basal cells in the nasal septal island of dromedaries: Ultrastructure and possible functions

Unlike other Merkel cell types, the morphology and functions of the Merkel-like basal cells remain unclear. The aim of the present study was to investigate the ultrastructural features of Merkel-like basal cells in the nasal septal island (NSI) of dromedaries (Camelus dromedarius) using transmission electron microscopy and to speculate their potential functions. Ten pairs of nasal septal islands obtained from ten heads of dromedary camels were used for the current study. Interestingly, these cells have been identified in the basal layer of the neuroepithelium of the dromedary nasal septal island near the sensory nerve endings. These cells were ovoid to elliptical in shape and rested on the basal lamina. Their surface had spine like cytoplasmic processes which interwined with the adjacent basal cells. Their nuclei were large lobulated with 2–3 deep notches. Moreover, numerous dense-core granules surrounded by electron-lucent halo were aggregated in the basal portion of the cells close to the nerve ending as well as melanin pigments in the apical portion. The ultrastructural characteristics of the Merkel-like basal cells of NSI were typical to those of Merkel cells, but with some morphological differences, including their location, cellular attachments, and connections to other structures. The potential functions were discussed in the light of the cellular context and architecture. The Merkel-like basal cells of the NSI neuroepithelium might play a role in nociception and magnetoreception in dromedaries.

Determination of secretory granule maturation times in pancreatic islet β-cells by serial block-face electron microscopy

It is shown how serial block-face electron microscopy (SBEM) of insulin-secreting β-cells in wild-type mouse pancreatic islets of Langerhans can be used to determine maturation times of secretory granules. Although SBEM captures the β-cell structure at a snapshot in time, the observed ultrastructure can be considered representative of a dynamic equilibrium state of the cells since the pancreatic islets are maintained in culture in approximate homeostasis. It was found that 7.2 ± 1.2% (±st. dev.) of the β-cell volume is composed of secretory granule dense-cores exhibiting angular shapes surrounded by wide (typically ≳100 nm) electron-lucent halos. These organelles are identified as mature granules that store insulin for regulated release through the plasma membrane, with a release time of 96 ± 12 h, as previously obtained from pulsed 35S-radiolabeling of cysteine and methionine. Analysis of β-cell 3D volumes reveals a subpopulation of secretory organelles without electron-lucent halos, identified as immature secretory granules. Another subpopulation of secretory granules is found with thin (typically ≲30 nm) electron-lucent halos, which are attributed to immature granules that are transforming from proinsulin to insulin by action of prohormone convertases. From the volume ratio of proinsulin in the immature granules to insulin in the mature granules, we estimate that the newly formed immature granules remain in morphologically-defined immature states for an average time of 135 ± 14 min, and the immature transforming granules for an average time of 130 ± 17 min.

Morphology and chemical composition of the Koschewnikow gland of the honey bee Apis mellifera (Hymenoptera: Apidae) workers engaged in different tasks

The Koschewnikow gland is associated with the sting apparatus in the honey bee Apis mellifera Linnaeus, 1758, as a potential source of compounds used as an alarm pheromone. This study describes the histology, morphometry and ultrastructure, and chemical composition of the Koschewnikow gland in workers performing different tasks in the A. mellifera colony. The Koschewnikow gland shows well-developed globular secretory cells of class III with those of the nurse and foragers larger and in greater numbers than those of guard bees. At the ultrastructural level, the secretory cells of all worker bees are rich in mitochondria and smooth endoplasmic reticulum. Mitochondria had different ultrastructure among workers with membrane electron-dense granules in nurse and the electron-lucent halo surrounding the organelle in guard bees. Mitochondria in forager workers show degenerative features such as the disappearance of cristae, electron-lucent matrix, and accumulation of electron-dense aggregates. The chemical analyses of the Koschewnikow gland extract showed that of 23 compounds, 13 had different abundances between workers and of these, 10 were found in higher abundance in guard workers. These results suggest that the Koschewnikow gland has a different structure and chemical composition in honey bee workers engaged in different tasks.

The Muc2 mucin coats murine Paneth cell granules and facilitates their content release and dispersion.

Paneth cells are a key subset of secretory epithelial cells found at the base of small intestinal crypts. Unlike intestinal goblet cells, which secrete the mucin Muc2, Paneth cells are best known for producing an array of antimicrobial factors. We unexpectedly identified Muc2 staining localized around Paneth cell granules. Electron microscopy (EM) confirmed an electron lucent halo around these granules, which was lost in Paneth cells from Muc2-deficient (-/-) mice. EM and immunostaining for lysozyme revealed that Muc2-/- Paneth cells contained larger, more densely packed granules within their cytoplasm, and we detected defects in the transcription of key antimicrobial genes in the ileal tissues of Muc2-/- mice. Enteroids derived from the small intestine of wild-type and Muc2-/- mice revealed phenotypic differences in Paneth cells similar to those seen in vivo. Moreover, lysozyme-containing granule release from Muc2-/- enteroid Paneth cells was shown to be impaired. Surprisingly, Paneth cells within human ileal and duodenal tissues were found to be Muc2 negative. Thus Muc2 plays an important role in murine Paneth cells, suggesting links in function with goblet cells; however human Paneth cells lack Muc2, highlighting that caution should be applied when linking murine to human Paneth cell functions. NEW & NOTEWORTHY We demonstrate for the first time that murine Paneth cell granules possess a halo comprised of the mucin Muc2. The presence of Muc2 exerts an impact on Paneth cell granule size and number and facilitates the release and dispersal of antimicrobials into the mucus layer. Interestingly, despite the importance of Muc2 in murine Paneth cell function, our analysis of Muc2 in human intestinal tissues revealed no trace of Muc2 expression by human Paneth cells.

Trypanosoma cruzi invasion in non-phagocytic cells: an ultrastructural study

Trypanosoma cruzi is the causative agent of Chagas disease. This parasite requires the intracellular niche in order to proliferate and disseminate the infection. After invasion, T. cruzi resides temporarily in an acidic vacuole which is lysed by a not well-understood mechanism. Transmission electron microscopy was used to describe the process of T. cruzi escape from the parasitophorous vacuole over the time. Using HeLa (non-professional phagocytic cells) as host cell, we observed that recently internalized parasites reside in a membrane-bounded vacuole. A few hours later, the first sign of vacuole disruption appeared as membrane discontinuities. This observation was followed by a progressive vacuole swelling as evidenced by an electron-lucent halo between the parasite and the vacuole membrane. Apparently, the vacuole membrane remnants reorganized as small vesicles that eventually disappeared from the vicinity of the parasites. Finally, parasites reach the host cell cytosol where replication takes place. The thorough ultrastructural description of this process set the base for a comprehensive understanding of the parasite-host cell interaction and, thus open the possibility of new therapeutic intervention strategies.

The mature and immature spermatozoa of the free-living marine nematode Daptonema sp. (Nematoda: Monhysterida: Xyalidae)

The immature spermatozoa stored in the testis and female postvulval uterine sac (PUS), and mature spermatozoa from the uterus of the free-living marine nematode Daptonema sp. (Monhysterida: Monhysterina: Xyalidae) were studied. The spermatozoa have a nucleus without a nuclear envelope. The central cytoplasm of the immature spermatozoa from the testis and the distal part of the PUS is occupied by a mass of pale fibrous bodies (FB) surrounded by mitochondria and osmiophilic membranous organelles (MO). The spermatozoa in the proximal half of PUS have a wide peripheral layer of electron lucent filamentous cytoplasm. The uterus lumen contains an aggregation of mature spermatozoa of which the periphery is transformed into pseudopods. The FB replaced by a voluminous electron-lucent halo bounded by a continuous layer of MO, mitochondria and fibrous matter. The MO may be intact, but numerous MO are fused with the plasma membrane, having been transformed into transparent pouches, each one opening to the exterior via a pore. Ultrastructural data showed that the activation is regulated in the female when spermatozoa migrate toward the uterus and transform into amoeboid mature spermatozoa. In general, the spermatozoa of Daptonema sp. and some other Monhysterina closely resemble those of the taxa belonging to the order Rhabditida. However, the `rhabditid' pattern of spermatozoon structure and development is most likely the plesiomorphic state in Rhabditida and close sister groups.

Effect of Fluoxetine on the Pancreas of Adult Male Albino Rats and the Possible Protective Role of Omega-3: Light and Electron Microscopic Study

Depression is linked with a high risk of type 2diabetes (T2D). The affiliation between depression and diabetes might be correlated to depression itself and, or medications recommended. Significantly, the usage of selective serotonin reuptake inhibitors (SSRIs), the most commonly antidepressants increased the hazard of developing T2D. Nevertheless, the mechanism underlying this suggestion remains vague. Omega-3 had antioxidant and anti-inflammatory activity. So, there is developing evidence that consumption of omega-3 could be expedient. The present study was carried out to investigate the potential effect of omega-3 in the fluoxetine induced alterations in the pancreas of adult male albino rats. Forty adult male albino rats were divided into four groups. Group I served as a control group. Group II received a single daily dose of 300 mg/kg of omega-3. Group III received 24 mg/kg bw/day of fluoxetine hydrochloride. Group IV received omega-3 and fluoxetine as group II and III for 30 days. Light and electron microscopic investigations were carried out. Histological examination using H & E and Masson’s Trichrome stain were carried out. The insulin expression in β cells was evaluated using immunohistochemistry. Morphometric results were subjected to statistical analysis. Investigation of group III (Fluoxetine group) showed distorted exocrine pancreas with thick interlobular septa that contained dilated congested blood vessels, cellular infiltration, and fat cells. Marked shrunken of the pancreatic islets was observed. Masson’s trichrome stain showed increased collagen fibers deposition. Electron microscopic examination revealed that most of the acinar cells had irregular shaped nuclei with peripheral heterochromatin and wide capillaries. The cytoplasm of β cells had a variety of secretory granules. Most of them had an electron dense core with increased electron lucent halo however, few β granules were empty and coalesced. Omega- 3 supplementation improved the morphology of Langerhans compared to fluoxetine group. Importantly, some pancreatic duct cells revealed a positive reaction against anti-insulin antibodies. The current results demonstrated that fluoxetine harmfully affected the histological structure of the pancreas. Omega-3 diminished effectively some histological, immunohistochemical and electron microscopic changes in a fluoxetine induced pancreatic injury. Omega-3 could stimulates β-cell regeneration from potent islet progenitor cells present in the ductal cells and these might lead to repair of the functional accomplishments of the injured pancreas to a great extent.

Quantification of endocrine cells and ultrastructural study of insulin granules in the large intestine of opossum Didelphis aurita (Wied-Neuwied, 1826)

This study aimed to investigate the distribution of argyrophil, argentaffin, and insulin-immunoreactive endocrine cells in the large intestine of opossums (Didelphis aurita) and to describe the ultrastructure of the secretory granules of insulin-immunoreactive endocrine cells. Fragments of the large intestine of 10 male specimens of D. aurita were collected, processed, and subjected to staining, immunohistochemistry, and transmission electron microscopy. The argyrophil, the argentaffin, and the insulin-immunoreactive endocrine cells were sparsely distributed in the intestinal glands of the mucous layer, among other cell types of the epithelium in all regions studied. Proportionally, the argyrophil, the argentaffin, and the insulin-immunoreactive endocrine cells represented 62.75%, 36.26%, and 0.99% of the total determined endocrine cells of the large intestine, respectively. Quantitatively, there was no difference between the argyrophil and the argentaffin endocrine cells, whereas insulin-immunoreactive endocrine cells were less numerous. The insulin-immunoreactive endocrine cells were elongated or pyramidal, with rounded nuclei of irregularly contoured, and large amounts of secretory granules distributed throughout the cytoplasm. The granules have different sizes and electron densities and are classified as immature and mature, with the mature granules in predominant form in the overall granular population. In general, the granule is shown with an external electron-lucent halo and electron-dense core. The ultrastructure pattern in the granules of the insulin-immunoreactive endocrine cells was similar to that of the B cells of pancreatic islets in rats.

The effects of experimental aflatoxicosis on the pancreas of adult male albino rats and the role of ginger supplementation

Introduction Aflatoxin contamination of foods is a worldwide problem, especially in developing countries. Ginger has antioxidant properties. Aim of the study To study the histological and biochemical changes in the pancreas of rats with experimental aflatoxicosis, and to evaluate the role of ginger supplementation. Materials and methods Forty-five adult male albino rats were equally divided into three groups. Group I that served as the control group. Group II that received 250 μg/kg body weight/day of aflatoxin B1 dissolved in olive oil using a gastric tube for 5 days/week for 4 weeks. Group III that received both aflatoxin as in group II and 400 mg/kg body weight/day of ginger orally for 5 days/week for 4 weeks. At the end of the experiment, all rats were anesthetized, and their pancreases were extirpated and divided into two parts to be processed for light and electron microscopic examinations. Morphometrical analysis for area percentage of collagen fibers and biochemical analysis for glucose, insulin, and serum amylase were performed and statistically analyzed. Results Examination of group II revealed thick interlobular septa that contained congested blood vessels, cellular infiltration, mast, and fat cells. Pancreatic acinar cells showed decreased secretory granules, vacuolization, and dilated fragmented rough endoplasmic reticulum. Few acinar cells showed rarified areas of cytoplasm. Some acinar cells had small condensed heterochromatic nuclei. Most of the islets of Langerhans were formed of cells separated by dilated congested capillaries. Most of the nuclei of β cells were euchromatic, whereas some were small heterochromatic. The cytoplasm of β cells had a variety of secretory granules. Most of them had an electron-dense core and an electron-lucent halo, whereas others had homogenous moderate density. Some granules coalesced. A few cells had cytoplasmic areas depleted of granules. Pancreatic ducts were dilated. Examination of group III revealed that pancreatic lobules were separated by thin interlobular septa. Acini had numerous apical acidophilic secretory granules, a few vacuoles, and basal euchromatic nuclei. Beta cells of the islets of Langerhans had euchromatic nuclei and numerous secretory granules with an electron-dense core and a wide electron-lucent halo. Biochemical analysis of glucose and serum amylase showed a highly significant increase, whereas that of insulin showed a highly significant decrease, in group II in comparison with group I. The glucose and serum amylase levels were significantly decreased, whereas the insulin level was significantly increased in group III compared with group II. Conclusion Aflatoxin had a deleterious effect on the histological structure of the rats' pancreas, and ginger minimized these effects.

Late Postoperative Opacification of Hydrogel Intraocular Lenses: Analysis of 13 Explanted Lenses

We report the clinical, morphological, and ultrastructural findings of 13 consecutively explanted opacified Hydroview(R) (hydrogel) intraocular lenses (IOLs). Our purpose was to provide a comprehensive account on the possible factors involved in late postoperative opacification of these IOLs. Thirteen consecutive opacified hydrogel IOLs (Hydroview H 60 M, Bausch & Lomb) were explanted due to the significant visual impairment they caused. The IOLs underwent macroscopical examination, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrophoresis for protein detection. Three unused control Hydroview IOLs served for comparison. Macroscopical examination showed a diffuse or localized grey-whitish opacification within the IOL optic. TEM confirmed the presence of lesions inside the optic in all the explanted IOLs and revealed 3 patterns of deep deposits: a) diffuse, thick, granular, electron-dense ones; b) small, thin, lattice-like ones, with prominent electron-lucent areas; and c) elongated electron-dense formations surrounded by electron-lucent halos. SEM showed surface deposits on four IOLs. EDS revealed oxygen and carbon in all IOLs and documented calcium, phosphorus, silicon and/or iron in the deposits. Two of the patients with iron in their IOLs had eye surgery prior to their phacoemulsification. Iron correlated well with the second TEM pattern of deep lesions, whereas calcium with the third TEM pattern. No protein bands were detected on electrophoresis. Control lenses did not show any ultrastructural or chemical abnormality. The present study supports the presence of chemical alterations inside the polymer of the optic in late postoperative opacification of Hydroview IOLs. This opacification does not follow a unique pathway but may present under different ultrastructular patterns depending on the responsible factors. Mechanical stress during surgery may initiate a sequence of events where ions such as calcium, phosphorus, silicon, and/or iron, participate in a biochemical cascade that leads to gradual alteration of the polymer network. Intraocular inflammation due to previous operation may be a factor inducing opacification through increase of iron-binding capacity in the aqueous humour. Calcification accounts only partially for the opacification noted in this type of IOL.

Characterization of obestatin- and ghrelin-producing cells in the gastrointestinal tract and pancreas of rats: an immunohistochemical and electron-microscopic study

Both ghrelin and obestatin are derived from preproghrelin by post-translational processing. We have morphologically characterized the cells that produce obestatin and ghrelin in new-born and adult Sprague-Dawley rats that were freely fed, fasted, or subjected to gastric bypass surgery or reserpine treatment. Tissue samples collected from the gastrointestinal tract and pancreas were examined by double-immunofluorescence staining, immunoelectron microscopy, and conventional electron microscopy. Obestatin was present in the stomach, duodenum, jejunum, colon, and pancreas. In the stomach, differences were noted in the development of obestatin- and preproghrelin-immunreactive (IR) cells on the one hand and ghrelin-IR cells on the other, particularly 2 weeks after birth. Preproghrelin- and obestatin-IR cells were more numerous than ghrelin-IR cells in the stomach, suggesting the lack of ghrelin in some A-like cells. Most obestatin-producing cells in the stomach were distributed in the basal part of the oxyntic mucosa; these cells co-localized with chromogranin A (pancreastatin) and vesicle monoamine transporters type 1 and 2, but not with serotonin or histidine decarboxylase. Immunoelectron microscopy revealed the obestatin- and ghrelin-producing cells to be A-like cells, characterized by numerous highly electron-dense granules containing ghrelin and obestatin. Some granules exhibited an even electron density with thin electron-lucent halos, suggestive of monoamines. Feeding status, gastric bypass surgery, and reserpine treatment had no obvious effect on the A-like cells. In the pancreas, obestatin was present in the peripheral part of the islets, with a distribution distinct from that of glucagon-producing A cells, insulin-producing beta cells, and cells producing pancreatic polypeptide Y. Thus, obestatin and ghrelin co-localize with an anticipated monoamine in A-like cells in the stomach, and obestatin is found in pancreatic islets.

Ultrastructure of mature spermatozoa in the lumen of the spermatheca and middle vas deferens of Paratelphusa hydrodromous (Crustacea)

Mature spermatozoa of P. hydrodromous are spherical or ellipsoidal, composed of an acrosome surrounded by a cup shaped nucleus. The acrosome is divided into a distal apical cap and an acrosomal vesicle, which is enclosed in the cup shaped nucleus. The apical cap is raised in its middle to form the apical cone. Below the apical cap is the subcap region. The acrosomal vesicle has a central canal, which encloses dense tubules. A thin inner layer, middle acrosomal rays layer and an outer acrosomal vesicle layer surrounds the central canal. Radial arms are absent. Along the posterior region of the spermatozoa are posterior median processes. Within the lumen of the mid vas deferens, spermatozoa are seen encased in oval or spherical spermatophores. Spermatophores are without distinct lining membranes. In the spermatophore lumen spermatozoa exist free or two to three of them tightly packed to form a unit. Each unit is surrounded by an electron-lucent halo, embedded in a moderately dense spermatophore ground substance. The spermatozoa are seen embedded in a flocculent material possibly the seminal plasma. There was hardly any structural difference between spermatozoa present in the lumen of the spermatheca and those present in the mid vas deferens (MVD). KEY WORDS: Spermatheca, middle vas deferens, ultrastructure, crabs, spermatozoa. Tropical Freshwater Biology, 10 (2001) 35 - 46

Androgen-dependent synthesis/secretion of caltrin, calcium transport inhibitor protein of mammalian seminal vesicle.

Effects of androgen status on the synthesis and secretion of rat caltrin have been studied by three different procedures: a) immunocytochemistry in seminal vesicle tissues; b) polyacrylamide gel electrophoresis and Western immunostaining of seminal vesicle secretion; and c) evaluation of trypsin inhibitory activity of the seminal vesicle secretion. Rat caltrin has been immunolocalized in cells of the secretory epithelium, specifically in the electron-lucent halo of secretory granules which store and transport proteins to the lumen. No caltrin immunoreaction was detected 14 days postcastration, and the ultrastructure of the epithelial cells was markedly altered. SDS-PAGE and Western blotting of the seminal vesicle secretion revealed alterations in the protein pattern and loss of the caltrin-related immunoreactive bands. The 54-kDa caltrin-precursor protein and the 6.2-kDa active caltrin were absent. Trypsin inhibitory activity of the seminal secretion was reduced about 50% in castrated animals. Daily testosterone administration restored both the protein pattern and immunoreactivity of the seminal vesicle secretion, and, as expected, reversed the morphological alterations of the gland after 7 days of treatment. Trypsin--inhibitor effect of the secretion also returned to normal levels after fourteen days of testosterone administration. Data suggest that the synthesis and secretion of caltrin are testosterone-dependent processes.

Ultrastructural pattern of glucagon producing-cells in the gastric mucosa of the developing opossum Didelphis albiventris (Marsupialia)

Gastric glucagon-producing cells of the pouch young, weaned and adult opossum Didelphis albiventris were investigated by immunocytochemical and ultrastructural methods. In sections of the oxyntic mucosa stained by immunoperoxidase it was observed that glucagon-immunoreactive cells increased in number during pouch development (from 7.9 +/- 4.7 to 35.4 +/- 5.9 cells/mm2), decreasing progressively to weaned (14.2 +/- 4.8 cells/mm2) and adult animals (10.4 +/- 3.0 cells/mm2). The glucagon-immunoreactive cells presented numerous electrondense, round cytoplasmic granules surrounded by a membrane. Frequently, the dense core of the granules was separated from the enveloping membrane by a delicate electronlucent halo or by a less electrondense peripheral halo. This pattern of the granular component was similar to the ultrastructural morphology observed in pancreatic islet glucagon-producing cells and A-like cells of the gastric mucosa of those eutherian mammals studied so far.

Fine structural and histochemical study of equine Paneth cells.

Ultrastructure, lysozyme and glycoconjugate activity in duodenal Paneth cells were observed concurrently in the horse. Paneth cells were seen to uniformly line the base of the equine intestinal glands. The round secretory granules have centrally located electron densities with peripherally located electron lucent halos. Histochemically, the peripheral halo layer was positively stained for carbohydrates by the periodic acid-thiocarbohydrazide-silver protein-physical development (PA-TCH-SP-PD) method and the entire granules reacted positively to the WGA. The central core area reacted with anti-lysozyme. We identified a young (Type I) and an old (Type II) cell population in the same crypt, but we suggest that the observed populations are variations of the same cell type with the varied appearance due to aging of the secretory granules.

Infection by intracellular bacterium in red claw crayfish, Cherax quadricarinatus (Von Martens), in Ecuador

An intracellular bacterium was detected on several occasions in commercial farms in Ecuador culturing red claw crayfish, Cherax quadricarinatus (Von Martens). Cases A, B and C presented mortality rates of 80%, 45% and 80%, respectively. Each incident occurred in grow-out ponds. Moribund crayfish were observed at the edge of the ponds in some cases. Affected crayfish presented no external differences from healthy ones, except their smaller size. Histological examination of affected red claw crayfish revealed that the cytoplasm of cells in the hepatopancreas, cuticular epithelium, and connective tissue of all organs had been replaced by massive granular and basophilic material. In the hepatopancreas, the tubules were intact but the intertubular connective tissue was replaced by Gram-negative microcolonies. Columnar cells in the cuticular epithelium also contained Gram-negative microcolonies and were necrotic. The heart and nerve cords also contained basophilic material. Transmission electron microscopy showed that the microcolonies consisted of a rod-shaped, obligately intracellular bacterium. The bacterium was delimited by a cell membrane that was composed of two electron-dense zones. Cells contained a single, compact, cytoplasmic condensation that was circumscribed by an electron-lucent halo. The bacterium replicated within the cytoplasm of host cells, which is pathognomic of rickettsiales infections. No host cell nuclei were infected.

Electron microscopic immunolocalization of caltrin proteins in guinea pig seminal vesicles.

Caltrins, the small, basic proteins of the seminal vesicle secretion that inhibit calcium transport into epididymal spermatozoa, and consequently the onset of the acrosome reaction and the hyperactivated motility, were localized in the epithelial cells and the lumen of the seminal vesicles of the guinea pig by an immunocytochemical procedure and electron microscopy. Rabbit antisera against each protein (caltrin I or II), and goat anti-rabbit IgG antiserum labeled with colloidal gold were used to detect the caltrin immunoreaction. The subcellular distribution of the gold labeling was occasionally localized in the rough endoplasmic reticulum but mainly within big secretory vacuoles containing low electron-dense material, which are components of the Golgi complex known as condensing vacuoles. These are involved in the intracellular transport, storage, and discharge of secretory proteins. Gold-labeled material released to the lumen was also detected. There was no clear evidence that the discharge was mediated by an exocytotic process. Immunoreaction was observed neither in the electron-dense core nor in the electron-lucent halo of the typical secretory granules of the epithelial cells of the seminal vesicles. Using light microscope immunocytochemistry, intense positive immunoreactivity was detected in the material secreted to the lumen but not on the epithelial cell layer. Only those cells undergoing a degenerative process and showing a picnotic nucleus and condensed cytoplasmic matrix exhibited detectable immunoreaction when gold label and silver intensification were applied. The same distribution of the immunoprobes was obtained by electron or light microscopy when antiserum to either I or II was used. It would appear that the two caltrin proteins of the guinea pig are synthesized in the rough endoplasmic reticulum of the epithelial cells and transported quickly to the Golgi complex where the secretory vacuoles (condensing vacuoles) are formed. The proteins are transported by the secretory vacuoles to the apical ends of the cells to be discharged into the lumen.

Effect of irradiation on hepatic natural killer cells

The rat liver contains a population of natural killer cells consisting of two morphologically and functionally different subsets, a low-density and a high-density fraction. In this work we describe the influence of low-dose radiation on hepatic natural killer activity. The effect on the cytotoxicity against YAC-1 lymphoma and CC531 colon adenocarcinoma tumor cells was measured in chromium-51 assays, and morphological changes were analyzed by means of electron microscopy. The low-density natural killer fraction showed increased cytotoxicity against YAC-1 which was associated with an increased binding of natural killer cells to the YAC-1 tumor cells shortly after irradiation. These phenomena were paralleled by an increased number of multivesicular bodies and cytoplasmic granules with an electron-lucent halo. In contrast, the other hepatic natural killer cell fraction, the high-density natural killer cells, did not show increased cytotoxicity, binding or morphological alterations. The radiation-stimulated lysis of YAC-1 cells was also observed when in vivo irradiated cells were isolated and tested immediately for in vitro lysis of YAC-1 cells. Sixteen hours after in vitro or in vivo irradiation, the cytotoxicity of hepatic natural killer cells against YAC-1 was no longer enhanced. The cytolysis of and binding of hepatic natural killer cells to CC531 colon adenocarcinoma cells was not stimulated by in vitro irradiation. From these experiments, we conclude that low-dose radiation stimulates the cytotoxicity of hepatic low-density natural killer cells against YAC-1 lymphoma cells immediately after irradiation as the result of enhanced binding of the cells to the tumor cells, in addition to the synthesis of new cytotoxic granules.

Effect of irradiation on hepatic natural killer cells

The rat liver contains a population of natural killer cells consisting of two morphologically and functionally different subsets, a low-density and a high-density fraction. In this work we describe the influence of low-dose radiation on hepatic natural killer activity. The effect on the cytotoxicity against YAC-1 lymphoma and CC531 colon adenocarcinoma tumor cells was measured in chromium-51 assays, and morphological changes were analyzed by means of electron microscopy. The low-density natural killer fraction showed increased cytotoxicity against YAC-1 which was associated with an increased binding of natural killer cells to the YAC-1 tumor cells shortly after irradiation. These phenomena were paralleled by an increased number of multivesicular bodies and cytoplasmic granules with an electron-lucent halo. In contrast, the other hepatic natural killer cell fraction, the high-density natural killer cells, did not show increased cytotoxicity, binding or morphological alterations. The radiation-stimulated lysis of YAC-1 cells was also observed when in vivo irradiated cells were isolated and tested immediately for in vitro lysis of YAC-1 cells. Sixteen hours after in vitro or in vivo irradiation, the cytotoxicity of hepatic natural killer cells against YAC-1 was no longer enhanced. The cytolysis of and binding of hepatic natural killer cells to CC531 colon adenocarcinoma cells was not stimulated by in vitro irradiation. From these experiments, we conclude that low-dose radiation stimulates the cytotoxicity of hepatic low-density natural killer cells against YAC-1 lymphoma cells immediately after irradiation as the result of enhanced binding of the cells to the tumor cells, in addition to the synthesis of new cytotoxic granules. (HEPATOLOGY 1994;19:1453–1458.)

Electron Microscopic Studies on the in vitro Proliferation of Spotted Fever Group Rickettsia Isolated in Japan

Rickettsia was isolated from a patient with Japanese spotted fever, and its proliferation in cultured green monkey kidney cells was observed by electron microscopy. In the course of this study, we observed fusion of infected cells to uninfected cells which may be a way of spreading the rickettsiae from a cell to another. On the other hand, whirlpool-like, multilayer membranous structures, similar to the mesosomes of gram-negative bacteria, were sometimes seen in the rickettsial cells. The other profiles common to the other rickettsiae in spotted fever group were observed, such as the electron-lucent halo zone around the rickettsiae, and external fibrous materials on their surface, but intranuclear multiplication was rarely observed.