Paneth cell function: phagocytosis and intracellular digestion of intestinal microorganisms. II. Spiral microorganism

Paneth cells as the cornerstones of intestinal and organismal health: a primer

Paneth cells are versatile secretory cells located in the crypts of Lieberkühn of the small intestine. In normal conditions, they function as the cornerstones of intestinal health by preserving homeostasis. They perform this function by providing niche factors to the intestinal stem cell compartment, regulating the composition of the microbiome through the production and secretion of antimicrobial peptides, performing phagocytosis and efferocytosis, taking up heavy metals, and preserving barrier integrity. Disturbances in one or more of these functions can lead to intestinal as well as systemic inflammatory and infectious diseases. This review discusses the multiple functions of Paneth cells, and the mechanisms and consequences of Paneth cell dysfunction. It also provides an overview of the tools available for studying Paneth cells.

Immunocytochemical localization of secretory component in Paneth cell secretory granules-rat Paneth cells participate in acquired immunity

With the marker of Paneth cells-lysozyme, secretory component (SC) immunoreactivity was demonstrated exclusively in Paneth cells of rat small intestine. The other types of epithelial cells (columnar, goblet, endocrine) were negative. On electron microscopic level, many SC-positive colloidal gold particles were found in rough endoplasmic reticulum, Golgi complexes, basal membrane and secretory granules of Paneth cells. These results suggest that SC is not a component of ingested immune complex, but a membrane receptor on Paneth cell. It may function as receptor for polymeric IgA and mediate its transport across the mucosal epithelium. Thus, Paneth cells are responsible for SC synthesis and participate in IgA-mediated acquired immunity in rat small intestine.

Mucispirillum schaedleri gen. nov., sp. nov., a spiral-shaped bacterium colonizing the mucus layer of the gastrointestinal tract of laboratory rodents

The mammalian gastrointestinal tract is covered by a layer of mucus that can harbour a range of bacterial species specifically adapted to colonize this ecological niche. Examination of 110 bacterial isolates cultivated from the gastrointestinal tract of 23 mice revealed the presence of a subgroup of 30 isolates that did not correspond genetically with genera commonly associated with this site, i.e. members of the epsilon-Proteobacteria such as Helicobacter and Campylobacter species. Instead this group of isolates was found to lie within the phylum Deferribacteres, a completely distinct lineage in the domain Bacteria. There was a high level of consensus in results obtained from the phenotypic and genotypic characterization of a number of the isolates, which showed they were distinct from other members of the Deferribacteres. As such, they are proposed to constitute a new genus and species, Mucispirillum schaedleri gen. nov., sp. nov. These organisms are anaerobic, Gram-negative, spiral-shaped rods with bipolar flagella. The type strain is HRI I17(T) (= ATCC BAA-1009(T) = ACM 5223(T)).

Defensins in granules of phagocytic and non-phagocytic cells

Antimicrobial proteins stored in lysosome-like granules of neutrophils and macrophages probably play an important role in killing phagocytosed microbes after delivery to the phagolysosome. Among the granules' antimicrobial armamentarium are defensins, peptides that kill a broad spectrum of microorganisms in vitro. Antimicrobial defensins were recently also isolated from non-phagocytic granulocytes of the mouse small intestinal epithelium, from where they are secreted into the lumen to function extracellularly. Clarification of the antimicrobial mechanisms of defensins in intracellular and extracellular environments will provide a key to understanding peptide-mediated host defence.

Emergence of diverse Helicobacter species in the pathogenesis of gastric and enterohepatic diseases

Since Helicobacter pylori was first cultivated from human gastric biopsy specimens in 1982, it has become apparent that many related species can often be found colonizing the mucosal surfaces of humans and other animals. These other Helicobacter species can be broadly grouped according to whether they colonize the gastric or enterohepatic niche. Gastric Helicobacter species are widely distributed in mammalian hosts and are often nearly universally prevalent. In many cases they cause an inflammatory response resembling that seen with H. pylori in humans. Although usually not pathogenic in their natural host, these organisms serve as models of human disease. Enterohepatic Helicobacter species are an equally diverse group of organisms that have been identified in the intestinal tract and the liver of humans, other mammals, and birds. In many cases they have been linked with inflammation or malignant transformation in immunocompetent hosts and with more severe clinical disease in immunocompromised humans and animals. The purpose of this review is to describe these other Helicobacter species, characterize their role in the pathogenesis of gastrointestinal and enterohepatic disease, and discuss their implications for our understanding of H. pylori infection in humans.

Immunocytochemical localization of pancreatitis-associated protein in human small intestine

Pancreatitis-associated protein (PAP) is a lectin-related protein barely detectable in normal pancreas but overexpressed by this tissue during the acute phase of the pancreatitis. We describe in this report that PAP is constitutively expressed in the human intestinal tract. Northern blot analysis with pancreatic cDNA as probe shows the presence of a transcript in the jejunum that has the same electrophoretic mobility as the pancreatic mRNA. No signal was detected in colon, however. In addition, immunoblotting assays, utilizing specific rabbit immunosera prepared against PAP, revealed the presence of a protein of 16,000 Da (as in pancreatic juice) in the homogenate of jejunum, but not of the colon. When the same antibodies were used for tissule localization of the protein, positive immunoreactivity was observed on Paneth cells and in some goblet cells located in jejunum at the bottom of the crypts. No staining was observed in colon.

Bactericidal properties of murine intestinal phospholipase A2

We purified a molecule from the murine small intestine that killed both Escherichia coli and Listeria monocytogenes, and identified it as intestinal phospholipase A2 (iPLA2) by NH2-terminal sequencing and enzymatic measurements. The ability of iPLA2 to kill. L. monocytogenes was greatly enhanced by 5 mM calcium, inhibited by EGTA and abolished after reduction and alkylation, suggesting that enzymatic activity was required for iPLA2-mediated bactericidal activity. A mouse-avirulent phoP mutant, S. typhimurium 7953S, was 3.5-fold more susceptible to iPLA2 than its isogenic virulent parent, S. typhimurium 14028S (estimated minimal bactericidal concentrations 12.7 +/- 0.5 micrograms/ml vs. 43.9 +/- 4.5 micrograms/ml P < 0.001). Overall, these findings identify iPLA2 as part of the antimicrobial arsenal that equips Paneth cells to protect the small intestinal crypts from microbial invasion. Because iPLA2 is identical to Type 2 phospholipase A2 molecules found in other sites, including spleen, platelets and inflammatory exudate cells, this enzyme may also contribute to antibacterial defenses elsewhere in the body.

Isolation and characterization of "Flexispira rappini" from laboratory mice

A bacterium with an unusual ultrastructure and possessing a fusiform protoplasmic cylinder, spiral periplasmic fibers, and bipolar tufts of sheathed flagella was identified in the intestinal mucosae of laboratory mice. The organism was cultured under microaerophilic conditions and was found to rapidly hydrolyze urea. On the basis of 16S rRNA gene sequence analysis, the organism was shown to be "Flexispira rappini." "F. rappini" is closely related to members of the genus Helicobacter and has been reported to be associated with human gastroenteritis and ovine abortion. "F. rappini" has not previously been observed in the gastrointestinal tracts of mice.

Distribution of pancreatic (group I) and synovial-type (group II) phospholipases A2 in human tissues

The catalytic activity of phospholipase A2 (cat-PLA2) and the concentration of pancreatic (group I) phospholipase A2 (pan-PLA2) and synovial-type (group II) phospholipase A2 (syn-PLA2) were studied in 19 human tissues in order to find potential sources of circulating phospholipase A2. Five specimens of each tissue were collected at autopsies or from normal deliveries (placentas and amnionic membranes). The concentrations of pan-PLA2 and syn-PLA2 were measured by specific time-resolved fluoroimmunoassays. The cat-PLA2 was measured by radioactive dipalmitoyl phosphatidylcholine as substrate. The concentration of pan-PLA2 was negligible in all tissue homogenates except the pancreas. Immunoreactive syn-PLA2 was found in the homogenates of the digestive tract, cartilage, and prostatic and parotid glands. By immunohistochemistry, syn-PLA2 was localized in Paneth cell secretory granules, chondrocytes, cartilage matrix, and glandular cells of prostate.

Bethanechol and a G-protein activator, NaF/AlCl3, induce secretory response in Paneth cells of mouse intestine

Paneth cells located at the bottom of intestinal crypts may play a role in controlling the bacterial milieu of the intestine. Using morphometry to clarify the secretory mechanism of the Paneth cells, we studied the ultrastructural changes in mouse Paneth cells produced following intra-arterial perfusion with Hanks' balanced salt solution containing a cholinergic muscarinic secretagogue (bethanechol), a neuroblocking agent (tetrodotoxin), or a G-protein activator (NAF/AlCl3). Bethanechol (2 x 10(-4) mol/l) induced Paneth-cell secretion. Many Paneth cells massively exocytosed their secretory material into the crypt lumen; the enhanced secretion caused degranulation and vacuole formation. However, tetrodotoxin (2 x 10(-6) mol/l) did not prevent the bethanechol-enhanced secretion by the Paneth cells. NaF (1 x 10(-2) mol/l) and AlCl3 (1 x 10(-5) mol/l) induced massive exocytosis of the Paneth cells; the exocytotic figures were similar to those observed in mice stimulated by bethanechol. G-protein activation was followed by a sequence of intracellular events, resulting in exocytosis.

Cryptdins: antimicrobial defensins of the murine small intestine

Paneth cells are specialized small intestine epithelial cells that contain lysozyme, possess phagocytic properties, and secrete cytoplasmic granules into the intestinal crypt lumen after the entry of bacteria. Recent studies by Ouellette and associates (A. J. Ouellette, R. M. Greco, M. James, D. Frederick, J. Naftilan, and J. T. Fallon, J. Cell Biol. 108:1687-1695, 1989) indicated that murine Paneth cells produce prodefensin mRNA, but the properties of its peptide product were not reported. We purified two closely related defensins, cryptdin 1 and cryptdin 2, from a subcellular fraction of murine small intestine cells that was enriched in Paneth cells. Both peptides contained 35 amino acid residues, including the characteristic defensin "signature" of six invariantly conserved cysteines. Cryptdins 1 and 2 were approximately 90 to 95% homologous to each other and to the carboxy-terminal domain of the 93-amino-acid defensin precursor, cryptdin A, described by Ouellette and associates (Ouellette et al., J. Cell Biol. 108:1687-1695, 1989). Both cryptdins exerted bactericidal activity against Listeria monocytogenes EGD and Escherichia coli ML-35p in vitro. Their potency exceeded that of human neutrophil defensin HNP-1 but was considerably lower than that of NP-1, a defensin produced by rabbit neutrophils and alveolar macrophages. Both cryptdins killed mouse-avirulent Salmonella typhimurium 7953S (phoP) much more effectively than its phoP+, mouse-virulent, isogenic counterpart, S. typhimurium 14028S. Our data indicate that mouse intestinal prodefensins are processed into 35-amino-acid mature defensins (cryptdins) with broad-spectrum antimicrobial properties. The production of defensins and lysozyme by Paneth cells may enable them to protect the small intestine from bacterial overgrowth by autochthonous flora and from invasion by potential pathogens that cause infection via the peroral route, such as L. monocytogenes and Salmonella species.

Paneth cell degranulation and lysozyme secretion during acute equine alimentary laminitis

The equine Paneth cell response to a shift in the microbial balance of the intestinal tract was studied by inducing an acute episode of alimentary laminitis in 6 mature ponies. The normal bacterial population of the gut was modified by administration of a carbohydrate-rich ration. During acute laminitis a dramatic degranulation of the Paneth cells occurred in the intestinal glands throughout the duodenum, jejunum, and ileum. Bacteriocidal lysozyme, which was immunohistochemically identified as a component of the Paneth cell secretory granule, was evident in the glandular lumina and in degranulated Paneth cells. These results indicate that lysozyme is secreted by the equine Paneth cell in an apparent attempt to regulate the changing microbial population induced by carbohydrate overload of the gut. From these observations, it is suggested that the Paneth cell plays a role in the mucosal defense system of the equine intestinal tract.

Ultrastructure of Paneth cells in the intestine of various mammals

Paneth cells in the following species were observed under an electron microscope: human, rhesus monkey, hare, guinea pig, rat, nude rat, mouse, golden hamster, and insect feeder bat. Secretory granules containing homogeneous electron-dense materials were observed in the Paneth cells of humans, monkeys, hares, guinea pigs, and bats; mouse Paneth-cell granules were bipartite (central core and peripheral halo), and the Paneth cells in rats and golden hamsters had secretory granules showing various electron densities. In humans, monkeys, and bats, immature granules near the Golgi apparatus sometimes showed bipartite substructure. The number and size of secretory granules were also diverse among various animal species. Some lysosome-like bodies were commonly observed in peri- or supranuclear regions, though the size and shape of the bodies differed from cell to cell. In apical cytoplasm, small clear vesicles (100-200 nm diameter) were more-or-less observed in all species examined, and it was especially note that rat Paneth cells contained many clear vesicles. Small dense-cored vesicles (150-200 nm diameter) were rare. It is unlikely that the various ultrastructural features of Paneth cells correlate with the phylogenetical classification.

Spirochetes autochthonous to the rat gastrointestinal tract

Spirochetes are structurally unique microorganisms found in the gastrointestinal tracts of most mammals. In an attempt to determine the ecological status of these bacteria, enumeration and distribution of morphologically distinct spirochetes were studied in the tracts of conventional laboratory rats. Five different types were seen to colonize infant rats between 19 and 26 days of age and subsequently to form stable communities in all 15 adults examined. Two types were found predominantly in lumen contents of the large bowel. The other three were consistently seen in the mucous blanket, attached to enterocyte surfaces or deep in the glands of the cecum and proximal colon. One type inhabiting the mucosal environment was also seen to pass into and through epithelial cells with no detectable host response. We conclude that spirochetes fulfill all the criteria for autochthonicity to the rat gastrointestinal tract.

Effect of live and heat-killed bacteria on the secretory activity of Paneth cells in germ-free mice

Germ-free mice were given live or heat-killed facultative anaerobes, and the ultrastructure of ileal Paneth cells was quantitatively examined with special reference to secretory granules showing a bipartite substructure (central core and peripheral halo). After administering live or heat-killed bacteria, there was a decrease in the area occupied by the cores of secretory granules in Paneth cells, and exocytosed core material was observed in the crypt lumen. There were no changes in the area occupied by the halo of secretory granules. None of the examined Paneth cells phagocytosed bacteria. It is concluded that certain bacteria may affect the secretion of antibacterial agents contained in the secretory granules of Paneth cells.

Quantitative electron microscopic observations on Paneth cells of germfree and ex-germfree Wistar rats

Ultrastructural changes of Paneth cells of germfree (GF) rats which had been inoculated with bacteria-containing feces from conventionally-reared (SPF) rats were quantitatively examined. 12 and 24 h after inoculation, the Paneth cells showed a striking decrease in the number of secretory granules and the occurrence of large vacuoles. Phagosomes containing bacteria were not seen. After 4 days, the secretory granules reaccumulated and smooth-surfaced apical vesicles increased in number. It is discussed that the large vacuoles may be related to membrane-retrieval events following the massive extrusion of secretory granules whereas the apical vesicles appear to serve this function when exocytosis is not pronounced. In addition to the large secretory granules ca. 10% of Paneth cell profiles contained a few dense-cored vesicles measuring about 150 nm in diameter which resemble peptidergic neurosecretory granules.

Immunohistochemical observations of immunoglobulin A in the Paneth cells of germ-free and formerly-germ-free rats

The localization of secretory immunoglobulin A (IgA) in Paneth cells was immunohistochemically studied in germ-free (Gf) and ex-Gf rats that had been injected with feces obtained from specific-pathogen-free (SPF) rats. In Gf as well as SPF rats, the secretory granules of Paneth cells and the brush borders of crypt cells exhibited IgA immunoreactivity. At 12 and 24 h after inoculation, it was found that, concomitant with the occurrence of considerable degranulation, the IgA immunoreactivity in Paneth cells disappeared, except of the margin of supranuclear vacuoles. In contrast, the IgA immunoreactivity of the crypt-cell brush borders was unchanged. Four days after inoculation, secretory granules exhibiting IgA immunoreactivity reaccumulated in Paneth cells. The present study suggests that Paneth cells regulate the bacterial milieu in the intestine by releasing secretory granules containing IgA into the crypt lumen.

Immunohistochemical localization of intestinal phospholipase A2 in rat paneth cells

Using the peroxidase-anti-peroxidase (PAP) technique with a specific rabbit anti-swine intestinal-phospholipase-A2 serum, the immunoreactivity of this phospholipase A2 was localized in rat-intestinal Paneth cells. The specific rabbit anti-swine intestinal-phospholipase-A2 serum did not stain the rat-pancreatic acinar cells which were stained by a specific rabbit anti-swine pancreatic-phospholipase-A2 serum. Specific rabbit anti-swine pancreatic-phospholipase-A2 serum did not stain rat-intestinal Paneth cells. Therefore, there is no cross-immunoreactivity between pancreatic and intestinal phospholipases.

Bacterial infection of the common bile duct in chronic fascioliasis in the rat

Bile taken from rats infected with the liver fluke, Fasciola hepatica contained spiral bacteria whereas bile from uninfected rats was free from spiral bacteria. The bacterium and its relationship to the bile duct epithelium and the liver fluke was studied with a combination of light microscopy, scanning and transmission electron microscopy. Its morphological characteristics suggest that the bacterium belongs to the genus Spirillum. In contrast to many other co-infections of bacteria and helminths, the present one seems to be a fairly passive relationship so that neither the helminth nor the rat suffers from the presence of bacteria. The presence of the bacteria is thought to be due to changes in the biliary environment, produced as a result of the fluke infection; these changes subsequently allow a multiplication of bacteria normally present in the uninfected animal.

Isolation and characterization of a spiral bacterium from the crypts of rodent gastrointestinal tracts

Spiral-shaped bacteria with a distinctive morphology were isolated from the intestinal mucosa of rats and mice on a campylobacter selective medium using microaerophilic incubation. These bacteria have been shown by other authors to be present in the intestinal tracts of several animal species but have not been cultured previously. The results of electron microscopic examinations and biochemical testing have shown that these organisms do not correspond to any known genus. Colonization experiments with pure cultures in gnotobiotic rodents have shown these bacteria to be mucosa associated, with a particular affinity for intestinal crypts. The pattern of colonization of the intestinal crypts in gnotobiotes known to be free of other mucosa-associated organisms differed from the colonization occurring in conventional animals that possess a normal mucosa-associated flora.

Light microscopic morphometric analysis of rat ileal mucosa: II. Component quantitation of Paneth cells

A quantitative light microscopic morphometric analysis of lysozyme- and IgA-containing Paneth cells within the ileal mucosa of physiologically manipulated and control (sham operation) animals was performed. The experimental groups of rats included animals raised in a gnotobiotic environment (microbial reduction) and animals with ileal self-filling blind (microbial proliferation) and Thiry-Vella (intestinal discontinuity) loops. The unlabeled antibody enzyme immunohistochemical localization technique was employed for the identification of intracellular lysozyme and IgA. Component quantitation was performed by use of a micrometer component quantitator. Marked Paneth cell hyperplasia was noted in association with gnotobiosis and with the Thiry-Vella fistula. This observation quantitatively confirms previous subjective impressions of increased Paneth cell differentiation in association with those physiologic states. Since the neurovascular component of the Thiry-Vella fistula is intact, the normal intraluminal succus entericus would appear to be involved in modulation of Paneth cell differentiation. The recognition of Paneth cell hyperplasia in association with the Thiry-Vella fistula suggests that this may be a useful experimental model for an evaluation of the life cycle and functional characteristics of this cell population. The results also revealed that no significant change in the volume percentage of Paneth cells and a decreased volume percentage of Paneth cells containing IgA occurred in association with the self-filling blind loop. A decreased volume percentage of IgA-containing immunocytes in association with the blind loop has previously been reported. The data are most consistent with the interpretation that the Paneth cell and immunocyte response to antigenic stimulation are interrelated and that the Paneth cell population has a restricted latitude of response to microbial proliferation.

Ileal Paneth cells and IgA system in rats with severe zinc deficiency: an immunohistochemical and morphological study

Morphological abnormalities in Paneth cells occur in patients with acrodermatitis enteropathica, a hereditary disease associated with zinc deficiency; furthermore, rat Paneth cells contain large amounts of zinc. This study was conducted to assess the effect of severe zinc deficiency in Sprague-Dawley rats on various parameters of Paneth cells. Morphology at both the light microscopical and ultrastructural levels, Paneth cell numbers per crypt and the intracellular distribution of lysozyme were not altered by zinc deficiency. A weak correlation (r = +0.38, P = 0.05) was noted between ileal zinc concentration and numbers of IgA-containing Paneth cells per crypt. These findings indicate that the morphological abnormalities noted in human Paneth cells in patients with acrodermatitis enteropathica cannot be reproduced by experimental severe zinc deficiency in rats. Furthermore, these generally negative findings suggest that the severe diarrhoea often associated with zinc deficiency is not attributable to abnormalities induced in Paneth cells by zinc deficiency.

Renal cortical tubules in experimental malakoplakia. Phagocytic alteration of tubular epithelium

Intrarenal injection of a crude E. coli extract (endotoxin-antigen-complex) induced malakoplakia in rats. Beside the granulation tissue the proximal tubular epithelium showed a strong phagolysosomal response--especially in two-three weeks--, thus becoming very similar to the Hansemann cells of the malakoplakia granulation tissue. This malakoplakia alteration of the epithelium if very severe sometimes led to necrosis or it was segregated inside the epithelial cells. Later on an atrophy of the tubules developed similar to the atrophy of different etiology, but the remaining cells often contained a striking number of residual bodies. It is suggested that the tubular granulated cells of megalocytic interstitial nephritis regarded as identical with renal cortical malakoplakia also have a tubular epithelial origin.

Morphological study of the Paneth cell. Paneth cells in intestinal metaplasia of the stomach and duodenum of man

The Peneth cells in intestinal metaplasia of stomach and the duodenum in human subjects were studied ultrastructurally, and the fine structures of these cells were compared. Paneth cells showed the ultrastructure of serozymogenic cells and secreted their secretory granules by merocrine process. The rod or tubular dense bodies were observed in the apical region of some Paneth cells. The structures may have some relation to the secretion of the secretory granules. The secretory granules with less dense layer in the periphery, which had never been described in the Paneth cell of man, were also observed. Morphologically intermediate cells between Paneth cell and goblet cell were found. Some of the Paneth cells might be phagocytized by undifferentiated crypt cells. The Paneth cells in intestinal metaplasia were fundamentally the same as those in duodenum at least in morphology. Difference between them was that Paneth cells with many phagolysosomes in the lower cytoplasm were observed more frequently in the duodenum than in intestinal metaplasia of the stomach. The physiological functions of the Paneth cell have been discussed.

Immunoglobulins within human small-intestinal Paneth cells

Human duodenal, jejunal, and ileal samples obtained at necropsy and by peroral and surgical biopsy, were studied by light microscopy using the unlabelled antibody enzyme method for imunocytochemical staining of lysozyme and immunoglobulins. Paneth cells contained IgA and IgG, but not IgD IgE, or IgM. Staining intensity indicated that IgA and IgG were present in amounts greater than in other epithelial cells. There was pronounced variation in the immunoglobulin content of Paneth cells. Rat Paneth cell containing IgA and lysozyme and are capable of the phagocytosis and degradation of microorganisms. These observations suggest that human Paneth cells may have similar functional capabilities.