The ultrastructure of the cell center in the enterocytes of mouse embryos and newborn mice

The centrosome structure was studied in differentiating small intestine enterocytes of mouse embryos (day 16 to 17 of gestation) and newborn mice. It is shown that fine structure of the centrosome in embryonic enterocytes differs from that found in cells of the adult mice. The centrosome of the crypt cells is more active: a greater number of cytoplasmic microtubules terminates there; mother centriole has two types of satellites; both centrioles are surrounded by fine fibrillar material. In 20% of crypt cells, replication of centrioles is observed. In the upper part of the villus of embryonic intestine, there still are two centrioles per cell, but they are located 3-7 um apart and devoid of any cytoplasmic microtubules attached to or directed toward them. In newborn mice, centrosomes of cells located at the bottom of the crypt are less active, as compared with centrosomes of embryonic cells. There are 1-3 satellites on mother centriole and few cytoplasmic microtubules closing to the centrosome. In 20% of cells from the bottom of the crypt centrioles are replicating. In the lateral part of the crypt, centrosome is inactive: centrioles are located 1-3 um apart and do not replicate. In the villus, centrioles undergo changes similar to those observed in the villus of adult mice. Centrioles loose portions of microtubule triplets. Near the top of the villus, only one centriole was found in two of 25 studied cells. In the enterocytes of the murine small intestine, centrioles are always located far from nuclei and close to the apical cell surface (1-3 um from the brush border). Centrioles never form a primary cilium and are not attached to the plasma membrane.     

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).     

Intraepithelial lymphocytes from villus tip and crypt portions of the murine small intestine show distinct characteristics

BACKGROUND & AIMS: Intraepithelial lymphocytes (IELs) are located between epithelial cells that are thought to display unique features and functions at the small intestinal villus tip and crypt levels. We have addressed whether the spatial differences in the intestinal epithelium extend to IELs and subsequent cross-talk between IELs and epithelial cells. METHODS: IELs were isolated from villus tip and crypt portions of mouse small intestine and then compared for spontaneous cytokine production and responsiveness to interleukin (IL)-2 and/or IL-7. RESULTS: No difference was observed between number of beta IELs in villus tips and crypts, whereas a trend toward increased frequencies of IELs bearing the gamma delta form of T-cell receptor was noted in villus tips. Interestingly, the number of beta IELs producing interferon gamma and IL-5 was significantly reduced in the cells from crypts compared with villus tips. Furthermore, villus tip beta IELs exhibited higher responses to stimulation signals provided by IL-2 and/or IL-7 than their crypt counterpart. Such functional differences were not observed with gamma delta IELs from the two intestinal sites. CONCLUSIONS: Distinct molecular cross-talk between IELs and epithelial cells occurs in intestinal villus tips and crypts.     

Ultrastructural changes in the cell center during enterocyte differentiation in the mouse

Centrioles in the enterocytes of murine small intestine are located far away from the nuclei and close to the apical surface of cells (1-3 microns from the brush border). Centrioles never form a primary cilium and are not attached to the plasma membrane. Centrosomes (cell center) in enterocytes undergo subsequent involution in respect to the position of cell in the crypt-villus system. Five zones were studied separately: the bottom of the crypt (approx. 1/3 of the appendix), the upper part of the crypt (before its transition into the villus), the basal part, the middle and top of the villus. A centrosome in the crypt contains two centrioles (maternal and daughter) located close to each other. In 10 of 27 cells studied centrioles were replicating. A maternal centriole has 2-3 pericentriolar satellites and appendages. Several cytoplasmic microtubules run towards mother centrioles. Centrioles at the upper part of the crypt split at a distance up to 1.5 microns from each other. The average number of cytoplasmic microtubules and pericentriolar satellites decreases. At the basal part of the villus, centrioles split a distance up to 5 microns from each other; seldom microtubules may be found in a radius of 1 micron around centrioles and none of them is attached to centrioles or satellites. Starting from the middle of the villus, centrioles sometimes may have incomplete triplets of microtubules at the distal and (or) the proximal end. At the upper part of the villus there is only one centriole per cell, that was found in 10 of 50 cells studied on a complete series of 0.2 micron thick sections.     

Rotavirus infection reduces sucrase-isomaltase expression in human intestinal epithelial cells by perturbing protein targeting and organization of microvillar cytoskeleton

Rotavirus infection is the most common cause of severe infantile gastroenteritis worldwide. These viruses infect mature enterocytes of the small intestine and cause structural and functional damage, including a reduction in disaccharidase activity. It was previously hypothesized that reduced disaccharidase activity resulted from the destruction of rotavirus-infected enterocytes at the villus tips. However, this pathophysiological model cannot explain situations in which low disaccharidase activity is observed when rotavirus-infected intestine exhibits few, if any, histopathologic changes. In a previous study, we demonstrated that the simian rotavirus strain RRV replicated in and was released from human enterocyte-like Caco-2 cells without cell destruction (N. Jourdan, M. Maurice, D. Delautier, A. M. Quero, A. L. Servin, and G. Trugnan, J. Virol. 71:8268-8278, 1997). In the present study, to reinvestigate disaccharidase expression during rotavirus infection, we studied sucrase-isomaltase (SI) in RRV-infected Caco-2 cells. We showed that SI activity and apical expression were specifically and selectively decreased by RRV infection without apparent cell destruction. Using pulse-chase experiments and cell surface biotinylation, we demonstrated that RRV infection did not affect SI biosynthesis, maturation, or stability but induced the blockade of SI transport to the brush border. Using confocal laser scanning microscopy, we showed that RRV infection induces important alterations of the cytoskeleton that correlate with decreased SI apical surface expression. These results lead us to propose an alternate model to explain the pathophysiology associated with rotavirus infection.     

Adaptive changes in intestinal mucosa of the small intestine as a result of intraluminal stress

Under physiological conditions, the intestinal mucosa is the site of a delicate balance between cell proliferation in the crypt region and cell desquamation at the villus tips. This balance can be deranged by a number of endogenous or exogenous factors, oneof which is the intraluminal contents. This review discusses the effects of different modifications of the luminal milieu on the structure and function of the mucosa. Following intestinal resection or loop transposition, the contents reaching the remnant or the transposed loop differ markedly from those with which they come into contact under normal conditions. Hyperplasia without zonal transformation then develops in the experimental loop. The villi do not become wider, and changes in the strucutre of the epithelium are not observed. There are conflicting resutls in the literature concerning the enzyme activities in the individual enterocytes resulting from this hyperplasia. However, the epithelium its functionally immature, since transport capacities measured in vitro are reduced. On the other hand, the hyperplasia of the mucosa is such that absorptive capacities in vivo, when expressed in terms of intestinal length, are larger than normal. When the intestine is subjected to prolonged infusion of lactic acid, the enterocytes are damaged and increased exfoliation results. A similar result is obtained in the blind-loop syndrome, where the accumulation of bile acids and bacteria provides the stress responsible for the destruction of the enterocytes, and in non-tropical spure, where the epithelium is attacked by noxious peptides in the diet. The first consequence of the accelerated desquamation is epithelial hyperplasia without zonal transformation, though the enterocytes are damaged - in contrast to those of the resected intestine - and apparently possess reduced enzyme activities. If the application of the stress is continued, a stage is reached in which the cell proliferation does not suffice to counteract the cell loss at the villus tips. Then a zonal transformation occurs whereby, despite the lengthened crypts, the villi become shorter and wider until, in extreme cases, the mucosa is completely devoid of villi. The transport capacity in vitro and in vivo - even when expressed in terms of unit-length is reduced, and good correlations exist between the reduction in function and the diminution in surface area of the intestine. In a self-emptying blind loop, the intestine is devoid of all contact with nutritional material. Under these circumstances, hypoplasia of the mucosa develops in which the enterocytes appear unchanged, though in extreme cases they may possess reduced enzyme levels, and the absorption capacity in vivo is consequently reduced.     

The effects of sodium ricinoleate on small intestinal function and structure

The mechanism of hydroxy fatty acid-induced secretion was investigated in perfused hamster small intestine in vivo. Sodium ricinoleate at an 8-mM concentration resulted in not only secretion of water and sodium, but an increase in intestinal clearance of inulin and a 16,000 mol wt dextran as well. A concentration of ricinoleate (2 mM) which did not affect water transport, however, did not alter intestinal permeability. Ricinoleate-induced intestinal secretion was also accompanied by increased mucosal cell exfoliation as measured by the appearance of DNA in the perfusate and by apparent injury to epithelial cell membranes as judged by measurement of sucrase activity and phospholipid in cell-free aliquots of luminal fluid. Light and electron microscopic studies demonstrated substantial mucosal architectural changes with 8 mM ricinoleate with villus shortening and injury to epithelial cells at the villus tips. In contrast, cholera enterotoxin caused marked secretion of sodium and water, presumably by a cyclic AMP mechanism, but did not alter inulin clearance or enhance DNA or sucrase appearance in the lumen. These studies suggest that at least a component of ricinoleate-induced intestinal secretion is related to structural alterations of the mucosa.     

Secretion of human meprin from intestinal epithelial cells depends on differential expression of the alpha and beta subunits

Human meprin (N-benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase, EC 3.4.24.18), an astacin-type metalloprotease, is expressed by intestinal epithelial cells as a dimeric protein complex of alpha and beta subunits. In transfected cells, intracellular proteolytic removal of the membrane anchor from the alpha subunit results in its secretion, while the beta subunit and alpha/beta heterodimers are retained at the cell membrane. We investigated the consequence of differential intracellular processing of alpha and beta subunits in the human small and large intestine using subunit-specific immunohistochemistry, in situ hybridization and biosynthetic studies in organ culture. In the ileum, both subunits localize to the brush-border membrane of villus enterocytes. In contrast, the beta subunit is not expressed in the colon, which leads to the secretion of the alpha subunit. We conclude that differential expression of meprin alpha and beta subunits is a unique means of targeting the proteolytic activity of the alpha subunit either to the brush-border membrane in the ileum or to the lumen in the colon, suggesting dual functions of cell-associated and luminal meprin. Meprin alpha and beta subunits are also coexpressed in distinct lamina propria leukocytes, suggesting an additional role for this protease in leukocyte function in the intestinal mucosa.     

Intraepithelial gamma delta T cells are closely associated with apoptotic enterocytes in the bovine intestine

The T cell population in the intestinal epithelium, comparable in size to the T cell pool in the spleen, is characterized by the predominant distribution of T cells bearing gamma delta T cell receptors. To determine the functional significance of the intraepithelial lymphocytes, we observed gamma delta T cells present in the jejunal epithelium in cattle, in which there is predominance of gamma delta T cells. Immunohistochemistry of frozen sections demonstrated that gamma delta T lymphocytes were densely distributed in the villous epithelium but there were fewer in the lamina propria and they were not present in the crypt epithelium. Ultrastructurally, intraepithelial gamma delta T cells were characterized by possessing electron-dense granules and interdigitating with enterocyte cytoplasm. Enterocytes, which were inserted by processes of intraepithelial lymphocytes or contacted by their cell bodies, showed morphologic changes seen in apoptotic cell death, such as elevated electron density of the cytoplasm and condensation of the chromatin. Apoptotic cells and cell debris were found in macrophages, which gathered in the subepithelial region of villus tips. These findings suggest that in the small intestine of cattle, gamma delta T cells are involved in the renewal of epithelial cells by inducing apoptosis of epithelial cells.     

Rat intestinal glycolipids. II. Distribution and biosynthesis of glycolipids and ceramide in villus and crypt cells

Intestinal epithelial cells were isolated from rat intestine and grouped into villus and crypt cell fractions. Glycolipids were purified from each cell fraction and quantitated by fluorimetric determination of glycolipid sphingosine. Significant quantities of ceramide were found in all cell fractions and accounted for approximately 15% of total glycolipid sphingosine. While villus and crypt cell fractions quantitatively contained differing amounts of sphingosine, all cell fractions contained proportionally similar quantities of sphingosine when compared to cellular cholesterol or phospholipid. Individual glycolipids, however, showed significant differences in distribution between villus and crypt cells. Hematoside and glucosylceramide were proportionally increased in villus cells, while crypt cells showed an increase in trihexosylceramide and ceramide content. The rate of UDPglucose : hydroxy fatty acid ceramide glucosyltransferase was higher in villus cells while the rate of UDPgalactose : lactosylceramide galactosyltransferase was 3--4 times increased in crypt cells. These studies demonstrate that significant differences in both the distribution and biosynthesis of individual glycolipids occur in crypt and villus cells of rat intestine and are of possible importance in the process of intestinal cell differentiation.     

Apoptotic process in the monkey small intestinal epithelium: I. Association with glutathione level and its efflux

The apoptotic process in the normal gastrointestinal mucosa is of interest due to its possible role in physiological cell renewal. The aim of this study was to identify the apoptotic process in the monkey small intestine and the association of glutathione level and its efflux in this process. Monkey small intestinal epithelial cells were separated in to different fractions consisting of villus, middle and crypt cells. Apoptosis was identified by DNA ladder pattern and Hoechst staining. The level of glutathione, its efflux and the enzymes involved in its metabolism were quantitated in these fractions. Apoptotic cells were identified predominantly in the villus tip cell fractions by both DNA ladder pattern and Hoechst dye staining. Glutathione level was 7 fold higher in the crypt cells as compared to villus tip cells the middle cells showing a gradual decrease. A similar pattern was seen in mitochondrial content of glutathione. As the cells mature from crypt to villus, there is increased efflux of GSH, which may be responsible for the decreased level of GSH in apoptotic villus cells. In the monkey small intestine, apoptotic cells are seen in the villus tip fractions and the glutathione level and its efflux may play a role in this process.     

Ultrastructure of the digestive system of adult Sanguinicola inermis

The alimentary tract of adult Sanguinicola inermis Plehn, 1905 (Digenea: Sanguinicolidae) was studied by transmission electron microscopy. A highly developed muscular region, likely to be a modified sucker, is present anteriorly to the oesophagus. The tegumental oesophagus, on the basis of the characteristics of the surface cytoplasm, is differentiated into anterior, median and posterior regions with the apical cytoplasm of the median oesophagus drawn into extracellular vesicles from which arise surface knobs. The oesophagus leads to a cellular intestine composed of a single layer of epithelial cells. The apical surface of the intestine is drawn into short luminal projections and the intestinal cells contain numerous organelles and secretory granules. No host cells or cell debris were evident within the alimentary tract, although the intestinal lumen was filled with electron-dense material.     

Antisecretory factor enhances in vivo internalization of cholera toxin and of horseradish peroxidase into rat enterocytes

The in vivo effect of antisecretory factor (ASF, derived from pig plasma) on the ability of cholera toxin (CT) and of horseradish peroxidase (HRP) to bind to and penetrate into epithelial cells of the rat small intestine was evaluated in the absence of anesthetics. The potency of intravenously administrated ASF was demonstrated by some 70% inhibition of CT-induced secretion in ligated small intestinal loops. Using immunohistochemical methods for visualization, we found ASF to enhance internalization of both CT and HRP after 30 to 60 min of challenge, without interfering with the initial binding to the enterocyte brush border region. The internalization process started in the upper 2/3 of the villus region. After 5 h, no CT or HRP could be seen bound to the enterocytes. The results suggest that ASF might enhance small intestinal absorption.     

Effects of cereal type and feed particle size on morphological characteristics, epithelial cell proliferation, and lectin binding patterns in the large intestine of pigs

The present study was undertaken to investigate the effects of cereal type and feed particle size on the morphological characteristics and epithelial cell proliferation of the large intestinal tissue in pigs. Forty pigs, weighing approximately 30 kg, were fed diets containing either coarsely or finely milled barley or wheat for a period of 4 wk. Tissue samples were taken from the cecum and from the proximal, medial, and distal colon at slaughter. The pigs fed the coarse diets had significantly larger crypts, in terms of height as well as volume, than did pigs fed the fine diets. The cereal type had no effect on the mucosal architecture. The epithelial cell proliferation, in terms of counted native mitoses in the crypts, was significantly higher in pigs fed the coarse barley diet than in pigs fed the coarse wheat diet or the fine diets. The volume of the mucin granules in the crypts constituted from 32 to 52% of the crypt volume and was greatest in the pigs fed the coarse diets. This effect of feed particle size was observed for neutral as well as for acidic mucins and sulfomucins. Lectin binding patterns indicated that more of the terminal sugars on glycoconjugates of the apical membrane on the mucosal surface were the sialic acid alpha-2,3 neuraminic acid, but less were mannose in the pigs fed the coarse barley diet. Distinct regional differences were observed among the intestinal sites. These included a decline in the epithelial cell proliferation and an increase in the volume of mucin in the crypts along the intestinal tract. Furthermore, the sialic acid alpha-2,3 neuraminic acid was more abundant in the medial colon than in the cecum; the contrary was seen for mannose and galactose. This study shows that the feed particle size of barley and wheat diets, more than the cereal type itself, affects the mucosal architecture, epithelial cell proliferation, and production and composition of the mucins in the large intestine of pigs. The study suggests that pigs fed a coarse diet are better protected against intestinal infections than pigs fed a fine diet.     

Differential expression of inducible nitric oxide synthase messenger RNA along the longitudinal and crypt-villus axes of the intestine in endotoxemic rats

OBJECTIVES: To characterize the mechanisms leading to excessive production of nitric oxide within the gut as a consequence of endotoxemia. We sought to: a) determine the time course of inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) expression in the intestine after challenging rats with lipopolysaccharide (LPS); and b) investigate whether there is differential expression of iNOS in enterocytes along the longitudinal or crypt-villus axes of the intestine in rats after LPS administration. DESIGN: Prospective, randomized, unblinded study. SETTING: Research laboratories at a large university-affiliated medical center. SUBJECTS: Male Sprague-Dawley rats. INTERVENTIONS: At T = 0 hr, rats were injected with O111:B4 Escherichia coli LPS (5 mg/kg) or a similar volume of the saline vehicle. At various time points thereafter, samples of duodenum, jejunum, ileum, colon, and liver were harvested for subsequent extraction of RNA. In some cases, populations of enterocytes enriched in either crypt or villus cells were harvested from the ileum. In some studies, rats were injected with cycloheximide (25 mg i.p.) 15 mins before being challenged with LPS or dexamethasone (2 mg i.p.) 30 mins before being injected with LPS. MEASUREMENTS AND MAIN RESULTS: iNOS mRNA was undetectable in ileal tissue from rats under basal conditions, but was evident by T = 1 hr and was maximal at T = 2 hrs after injection of LPS. Thereafter, ileal iNOS mRNA concentrations decreased and were undetectable again at T = 24 hrs. At T = 2 hrs after LPS injection, there was marked expression of iNOS mRNA in the ileum, whereas much lower concentrations of iNOS mRNA were detected in the jejunum and colon, and no iNOS mRNA was detected in the duodenum. At T = 3 hrs after LPS injection, expression of iNOS mRNA was up-regulated in both villus and crypt cells, although LPS-induced iNOS mRNA was more prominent in the former than the latter cell type. Pretreatment of rats with dexamethasone virtually abrogated the expression of iNOS mRNA in ileal samples obtained 3 hrs after the injection of LPS. Prior treatment of rats with the protein synthesis inhibitor, cycloheximide, also blunted LPS-induced iNOS mRNA expression. CONCLUSIONS: LPS-induced iNOS expression is differentially regulated along both the longitudinal and crypt villus axes of the intestinal mucosa, being most prominent in the villus cells of the ileum. LPS-induced iNOS expression is blunted by pretreating rats with dexamethasone or cycloheximide. The latter finding suggests that LPS-induced expression of iNOS mRNA in the gut requires new protein synthesis. Differential regulation of nitric oxide production along the longitudinal and crypt-villus axes of the gut may be a determinant of the pattern of sepsis-induced intestinal damage.     

Formation of isomorphic desolvates: creating a molecular vacuum

BACKGROUND: Microvillus inclusion disease is a congenital disorder characterized by secretory diarrhea. Patients demonstrate villus atrophy, loss of microvilli, and internalized inclusions of microvilli within the cytoplasm of small intestinal enterocytes. The exact molecular defect in these patients is not known. Two infants are described in this report with microvillus inclusion disease. Case 1 was a 3-month-old boy who developed secretory diarrhea shortly after birth. Case 2 was a 9-month-old boy who had abrupt onset diarrhea at 2 weeks of age resulting in weight loss and dehydration. Light microscopy revealed total villus atrophy with minimal crypt hyperplasia, and electron microscopic examination revealed variably shortened microvilli and cytoplasmic microvillus inclusions in both patients. METHODS: Poly (A)+ RNA was purified from duodenal biopsies and RT-PCR reactions were performed. Normal human intestinal RNA was used as a positive control. Primers specific for human NHE-1, NHE-2, NHE-3 (2 sets), sodium-glucose transporter (SGLT1), and beta-actin were used. RESULTS: Results showed that NHE-1 and beta-actin cDNAs amplified to similar levels in both patient and control samples. However, the expression of NHE-2 and SGLT1 was much higher in the control sample than in the patient samples. Additionally, NHE-3 mRNA was not detected in the patient samples using two sets of NHE-3 specific primers. CONCLUSIONS: The patients with microvillus inclusion disease have defects in apical but not basolateral membrane transport systems, and these defects are related to the pathogenesis of the disease.     

Identification of elicitor-induced cytochrome P450s of soybean (Glycine max L.) using differential display of mRNA

Magnesium (Mg) absorption across the intestinal epithelium is crucial for Mg homeostasis in all vertebrates. Besides paracellular transport, it involves a cell-mediated component, and this predicts the presence of specific Mg carriers at both the apical and basolateral pole of the epithelial cells. Although the mechanism of transmembrane Mg transport in enterocytes, as in most cell types, has remained an elusive topic for many years, recent studies have provided promising new insights. We here recapitulate the progress that has been made in this field, and advance evidence for membrane carriers that are involved in transcellular Mg transport in the intestine.     

Membrane-bound carbonic anhydrase IV is expressed in the luminal plasma membrane of the human gallbladder epithelium

Alkaline hepatic bile is acidified in the gallbladder to prevent calcium precipitation and gallstone formation. Because membrane-bound carbonic anhydrase (CA) isoenzyme IV participates with cytoplasmic CA II in the acidification of urine in the kidney, we studied its expression in different regions of the human biliary tract using immunohistochemical techniques. The enzyme was expressed in the apical plasma membrane of the gallbladder epithelial cells and in the endothelium of the subepithelial capillaries. In the liver, some epithelial cells of the large bile ducts showed positive staining. Its presence in the gallbladder epithelium could be confirmed by Western blotting, which showed a single 35-kd polypeptide band, corresponding in molecular weight to the intact enzyme. The majority of the enzyme was phased to Triton X-114 detergent phase. A small amount of 35-kd polypeptide was also seen in the water phase. Smaller proteolytic fragments of the enzyme were not seen, suggesting that the tissue sample was well preserved. The results show that CA IV is expressed in abundance in the human gallbladder epithelium, where it may participate together with cytoplasmic CA II and ion transporters in acidification of the gallbladder bile via bicarbonate reabsorption.     

Determination of mean energies and impact parameters characteristic of charge-changing reactions

A guinea pig passage-adapted strain of the arena-virus Pichinde (adPIC) is highly virulent in inbred guinea pigs, whereas the related strain PIC3739 is attenuated. Both viruses were macrophage tropic and infected peritoneal, splenic, liver, and alveolar macrophages during experimental Pichinde virus infection. Infection with the virulent strain was associated with unlimited viral replication in the face of exaggerated delayed-type hypersensitivity response, manifested by the macrophage disappearance reaction. Histopathological lesions unique to adPIC-infected guinea pigs included intestinal villus blunting with mucosal infiltration by pyknotic debris-laden macrophages and apoptosis of crypt epithelial cells. Splenic red pulp necrosis was also significantly associated with adPIC infection but not PIC3739 infection. These findings may provide clues to the pathogenesis of a group of poorly understood human viral hemorrhagic fevers.     

Paneth cells and innate immunity in the crypt microenvironment

Paneth cells release granules into the lumen of the crypts of Lieberkuhn in the small intestine where their component proteins participate in mucosal immunity. The granules contain a number of proteins associated with roles in host defense, including lysozyme, secretory phospholipase A2, and alpha-defensins, termed cryptdins. Mouse cryptdins 1-6 and recombinant human Paneth cell alpha-defensin HD-5 are potent antimicrobial agents against certain microorganisms. As defensins, they kill microbes by disruption of the target cell membrane. The peptides are coded by individual, two-exon genes that map to homologous regions of chromosome 8 in mice and humans, and the differential expression of certain mouse cryptdin genes provides markers for studies of crypt ontogeny and epithelial cell differentiation and lineage determination. Neutrophil alpha-defensin peptides exhibit numerous biological activities in addition to antimicrobial function including regulation of cell volume, chemotaxis, mitogenicity, and inhibition of natural killer cell activity. When administered apically, mouse cryptdins 2 and 3 can reversibly stimulate human T-84 intestinal epithelial cells to secrete chloride ion, suggesting that alpha-defensins from Paneth cells also may be multifunctional. Thus, cryptdins and varied Paneth cell secretory products seem to contribute both to innate immunity of the crypt lumen and to defining the apical environment of neighboring cells.