A Paneth cell analogue in Xenopus small intestine expresses antimicrobial peptide genes: conservation of an intestinal host-defense system

Antimicrobial peptides are a widespread component of host defense. We characterized the tissue distribution and cellular localization of expression of the magainin family of antimicrobial peptide genes in Xenopus laevis. Two genes from this family, magainin and PGLa, are expressed at high levels in the skin and throughout the gastrointestinal tract. Magainin and PGLa mRNAs are synthesized in the granular multinucleated cell (GMC) of the gastric mucosa, a cell shown previously to contain magainin and PGLa peptides by immunohistochemical methods. In addition, we have localized magainin and PGLa mRNAs to distinct cells of Xenopus small intestine. Further characterization of this large, granule-filled cell by electron microscopy demonstrates features in common with the Paneth cell of mammalian small intestine, previously identified as a site of expression of antimicrobial peptide genes of the defensin family in mouse and human. Our identification of granule-laden, eosinophilic intestinal cells in Xenopus as a site of magainin and PGLa antimicrobial peptide gene expression suggests that these cells are functional analogues of mammalian Paneth cells and further supports a conserved role of antimicrobial peptides in host defense of the vertebrate small intestine.

Identification of interstitial cells of Cajal. Significance for studies of human small intestine and colon

BACKGROUND

Interstitial cells of Cajal (ICC) were described a century ago by Ramón y Cajal a.o. as primitive neurons in the intestines. In the period 1900-1960 a large number of light microscopical studies of ICC were published, in which ICC were identified by heir characteristic morphology. After 1960 electron microscopical studies emphasized similarities between ICC and fibroblasts. In our early studies of ICC in the external musculature of mouse small intestine, we identified ICC by their characteristic morphology and topography, and we analyzed the relation between ICC, autonomic nerves and smooth muscle. These studies strongly suggested that ICC were fundamental regulators of external muscle function. These hypotheses have since been supported by independent morphological and electrophysiological evidence, strongly suggesting a pacemaker role of some ICC populations as well as other regulatory functions (mechanoreceptive, mediating inhibitory nervous input). In spite of this possible fundamental importance for G-I motility, ICC have not been adequately described or even identified in human intestine, and hence, never included in ultrastructural studies of G-I neuropathology. This survey presents the concepts of ultrastructure necessary for identification and morphological studies of ICC in human intestine.

METHODOLOGY

Several light microscopical methods have been claimed selective for intestinal ICC (and nerves), including vital methylene blue, Golgi methods, silver impregnations and ZIO-methods. Unfortunately, even the most reliable of them (ZIO, vital methylene blue) do not work at all in some animal species and in some, regions of the intestinal wall. In our hands, the best results have been obtained in mouse small intestine with vital methylene blue staining (AP only) and with ZIO methods (all levels of the musculature). None of them have yet proved their value in human intestine, although we have occasionally stained ICC-SMP in human colon with ZIO methods. Optimal ultrastructural preservation of ICC for TEM studies in laboratory animals, has been achieved by fixation by vascular perfusion. In humans, the ultrastructural preservation was satisfactory, but not ideal, after optimizing the immersion fixatives (Karnovsky-types, addition of picrate).

RESULTS AND DISCUSSION

General architecture of musculature externa. ICC differ markedly in their organization and ultrastructure from one part of the gut and from one region to another. For understanding the extent and distribution of ICC plexuses it is therefore critical to preserve a stringency and uniformity with respect to terminologies and descriptions of topography. Auerbach's plexus (AP) designates the ganglionated plexus between the main muscle layers in small and large intestine, whereas we prefer to use the term myenteric plexus for all nerves in the external muscle. The deep muscular plexus (DMP) designates the two-dimensional, non-ganglionated nerve plexus between the thick outer and thin inner subdivision of the circular muscle layer in the small intestine. In our material a similar plexus was not present in colon. The submuscular plexus (SMP) indicates the non-ganglionated, two-dimensional nerve plexus present at the submucosal surface of the colonic circular muscle. The circular muscle in small- and large intestine of large animals (dogs, humans) is organized into lamellae, separated by main septa piercing the whole layer. Both in the small intestine and colon the innermost circular muscle cells, are smaller, and, particularly in colon, more irregular than the bulk of the circular muscle. Identification of ICC in laboratory animals. By TEM ICC are distinguishable as a separate cell type in the small- and large intestine of all species investigated.(ABSTRACT TRUNCATED)

Role of colony stimulating factor-1 in the establishment and regulation of tissue macrophages during postnatal development of the mouse

Colony stimulating factor-1 (CSF-1) regulates the survival, proliferation and differentiation of mononuclear phagocytes. The osteopetrotic (op/op) mutant mouse is devoid of CSF-1 due to an inactivating mutation in the CSF-1 gene and is deficient in several mononuclear phagocyte subpopulations. To analyze more fully the requirement for CSF-1 in the establishment and maintenance of mononuclear phagocytes, the postnatal development of cells bearing the macrophage marker antigens F4/80 and MOMA-1, in op/op mice and their normal (+/op or +/+) littermates, were studied during the first three months of life. In normal mice, maximum expression of tissue F4/80+ cells was generally correlated with the period of maximum organogenesis and/or cell turnover. Depending on the tissue, the F4/80+ cell density either decreased, transiently increased or gradually increased with age. In op/op mice, tissues that normally contain F4/80+ cells could be classified into those in which F4/80+ cells were absent and those in which the F4/80+ cell densities were either reduced, normal or initially normal then subsequently reduced. To assess which F4/80+ populations were regulated by circulating CSF-1 in normal mice, op/op mice in which the circulating CSF-1 concentration was restored to above normal levels by daily subcutaneous injection of human recombinant CSF-1 from day 3 were analyzed. These studies suggest that circulating CSF-1 exclusively regulates both the F4/80+ cells in the liver, spleen and kidney and the MOMA-1+ metallophilic macrophages in the spleen. Macrophages of the dermis, bladder, bone marrow and salivary gland, together with a subpopulation in the gut, were partially restored by circulating CSF-1, whereas macrophages of the muscle, tendon, periosteum, synovial membrane, adrenals and the macrophages intimately associated with the epithelia of the digestive tract, were not corrected by restoration of circulating CSF-1, suggesting that they are exclusively locally regulated by this growth factor. Langerhans cells, bone marrow monocytes and macrophages of the thymus and lymph nodes were not significantly affected by circulating CSF-1 nor decreased in op/op mice, consistent with their regulation by other growth factors. These results indicate that important differences exist among mononuclear phagocytes in their dependency on CSF-1 and the way in which CSF-1 is presented to them. They also suggest that the prevalent role of CSF-1 is to influence organogenesis and tissue turnover by stimulating the production of tissue macrophages with local trophic and/or scavenger (physiological) functions. Macrophages involved in inflammatory and immune (pathological) responses appear to be dependent on other factors for their ontogenesis and function.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

The Caco-2 cell monolayer system as an in vitro model for studying bacterial-enterocyte interactions and bacterial translocation

Partly because of inherent limitations of in vivo models, the cellular mechanisms underlying the process of bacterial translocation across the intestinal epithelial barrier are incompletely understood. We therefore used the Caco-2 intestinal cell line as an in vitro model to examine the bacterial translocation process under controlled conditions. Caco-2 cells were grown on porous membranes in the upper compartment of a two-compartment system. Caco-2 cells were cultured for 7, 14, 21, or 28 days. Cellular confluence and tight junction integrity were verified by measurements of dextran permeability and transepithelial electrical resistance. Bacterial translocation was measured by culturing the bacteria (E. coli C25) that were able to cross the Caco-2 cell monolayer. The passage of E. coli C-25 and dextran across the Caco-2 monolayer was higher and the transepithelial electrical resistance lower after 7 days of culture than after 14 or 21 days of culture. The Caco-2 cells became impermeable to dextran blue after 14 days of culture with an average transepithelial electrical resistance of 173.1 +/- 9.24 ohms.cm2. When increasing doses of (10(2)-10(9) colony-forming units) of E. coli were tested in 14-day-old Caco-2 monolayers, bacterial translocation occurred in a time- and dose-dependent fashion. Once cellular confluence and tight junction integrity have been established, bacterial translocation across Caco-2 cells appears to be a time- and dose-dependent process.

Visualization of gene expression of short and long forms of prolactin receptor in rat digestive tissues

Several effects of prolactin have been characterized in various tissues of the gastrointestinal tract. In the present study, the expression of short and long forms of prolactin receptor was explored and quantified in the digestive tract and correlated to the prolactin specific functions. Sections of all digestive tissues were analyzed by in situ hybridization, using 35S-labeled oligoprobes unique to each form of receptor. Macroautoradiogram signals were quantified and expressed in arbitrary units. In rat liver, prolactin receptor mRNAs are expressed to a much greater degree in females than in males. The short-form transcript is significantly expressed to a greater degree in liver, whereas the long form predominates in the pancreas and esophagus. In the remainder of the gastrointestinal tract, there is an equivalent distribution of short- and long-form transcripts. Relatively high signal intensities are seen in the stomach, duodenum, jejunum, ileum, and colon, whereas the rectum is essentially negative. The identification of prolactin receptor gene expression to limited regions should help establish specific functions associated with this hormone in the digestive tissues.

Monoclonal antibodies to a zinc-binding protein of rat Paneth cells

Paneth cells are morphologically well characterized but their function has been not elucidated. Previously, we identified and purified a 90 KD zinc-binding protein (ZBPP-1) in rat intestine that was localized to Paneth cell granules, consistent with their high zinc content. To further elucidate the structure and function of ZBPP-1, we immunized Balb/c mice with purified ZBPP-1 and identified four independent monoclonal antibodies (MAb) producing MAb ZIP-1 (IgM), ZIP-2 (IgG1), ZIP-3 (IgM), and ZIP-4 (IgM). Immunohistochemistry (IHC) and immunoelectron microscopy (IEM) with these MAb showed positive staining of Paneth cell cytoplasmic granules. MAb ZBPP-1 also stained a population of mononuclear cells in the lamina propria of digestive tract mucosa and a few cells in spleen, presumably a subset of macrophages. These MAb will provide a useful tool to study the function of Paneth cells in human health and disease, since they cross-reacted with human intestinal Paneth cells and mucosal mononuclear cells.

Tissue and plasma concentrations of amidated and glycine-extended glucagon-like peptide I in humans

Using specific radioimmunoassays, we studied the occurrence of amidated and glycine-extended glucagon-like peptide I (GLP-I) molecules in the human small intestine and pancreas and in the circulation system in response to a breakfast meal. Through gel permeation chromatography of extracts of the human pancreas (n = 5), we found that 71% of the GLP-I immunoreactivity eluted as a large molecule corresponding to the major proglucagon fragment, 24% corresponded to GLP-I 1-36 amide, and 5% to GLP-I 1-37. By gel permeation chromatography of extracts of human small intestine (n = 6), we found that all immunoreactivity eluted in one peak at the common elution position of the two insulin-releasing peptides, GLP-I 7-36 amide and GLP-I 7-37. Of the GLP-I immunoreactivity, 80% corresponded to GLP-I 7-36 amide and 20% to GLP-I 7-37. The mean concentrations of amidated GLP-I and glycine-extended GLP-I in fasting plasma were 7 +/- 1 and 6 +/- 1 pM, respectively (n = 6). In response to a breakfast meal, the concentration of amidated GLP-I rose significantly amounting to 41 +/- 5 pM 90 min after the meal ingestion, whereas the concentration of glycine-extended GLP-I only rose slightly to a maximum of 10 +/- 1 pM. Thus, both amidated and glycine-extended GLP-I molecules are produced in the small intestine and in the pancreas in humans. Both amidated and glycine-extended GLP-I are measurable in fasting plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of I-plastin, a human fimbrin isoform expressed in intestine and kidney

The complete cDNA sequence of human intestine-specific plastin (I-plastin) was determined from a clone derived by PCR. It consists of a 97-bp 5' untranslated region, a 1,887-bp coding region, and a 1,655-bp 3' untranslated region. The coding region predicts a 629-residue polypeptide whose sequence displays 86, 75, and 73% identities with chicken intestine fimbrin, human T-plastin, and human L-plastin, respectively. Recombinant I-plastin cross-linked actin filaments into bundles in the absence but not in the presence of calcium. The I-plastin gene was mapped by PCR to human chromosome 3; the L- and T-plastin genes were previously mapped to chromosomes 13 and X, respectively. I-plastin mRNA was detected in the small intestine, colon, and kidneys; relatively lower levels of expression were detected in the lungs and stomach. In contrast, L-plastin expression was restricted to the spleen and other lymph node-containing organs, while T-plastin was expressed in a variety of organs, including muscle, brain, uterus, and esophagus. In contrast to the situation for the intestine, high levels of L- and T-plastin mRNAs were detected in Caco-2, a human colon-derived cell line. Immunofluorescence microscopy detected I-plastin in the brush border of the small intestine and colon. These results identify I-plastin as the human homolog of chicken intestine fimbrin and as a third plastin isoform in humans.

Generation of one set of murine monoclonal antibodies specific for globo-series glycolipids: evidence for differential distribution of the glycolipids in rat small intestine

We generated four murine monoclonal antibodies (MAbs) specific for globo-series glycolipids by immunizing C3H/HeN mice with these purified glycolipids adsorbed to Salmonella minnesota followed by fusion with mouse myeloma cells. By use of a wide variety of glycolipids, the precise structures recognized by these MAbs were elucidated through an enzyme-linked immunosorbent assay and an immunostaining on thin-layer chromatography. These four MAbs, designated as BGR23, BGR47, BMR26, and BGR27, exhibited highly restricted binding specificities, reacting only with the globo-series glycolipids Gb3Cer, III3Gal alpha-Gb3Cer, Gb4Cer, and IV3GalNAc alpha-Gb4Cer, respectively, which were used for immunization. None of the other various glycolipids or gangliosides were recognized. We determined the localization of these globo-series glycolipids in adult rat small intestine by means of an immunofluorescence technique with these MAbs. Our study revealed that there is a differential distribution of these glycolipids in the rat tissue. III3Gal alpha-Gb3Cer was demonstrated on the cryptic cells and circular muscle, whereas Gb4Cer was localized on both the circular and longitudinal muscles. The expression of Gb3Cer was associated with the epithelium and the capillary endothelial cells in the lamina propria mucosae as well as with the tunica submucosa, whereas IV3GalNAc alpha-Gb4Cer was detected on the epithelium, capillary endothelial cells in the lamina propria mucosae, and both the muscle layers.

Reciprocal expression of laminin A-chain isoforms along the crypt-villus axis in the human small intestine

BACKGROUND/AIMS

Intestinal epithelial cell proliferation, migration, and differentiation are susceptible to various influences along the crypt-villus axis including compositional changes in the basement membrane and differential expression of receptors for these components. However, laminin has been consistently detected at the epithelial basement membrane without significant variation in relation to the crypt-villus functional unit. The aim of this study was to examine the distribution of individual laminin chains.

METHODS

The patterns of distribution of laminin A, M (an A-chain variant), B1, and B2 chains as well as the integrins alpha 6 beta 1 and alpha 6 beta 4, two laminin receptors, were determined by indirect immunofluorescence in the adult human small intestine.

RESULTS

Markedly distinct patterns of laminin chain expression were observed along the crypt-villus axis. The A chain was found predominantly associated with the differentiated epithelial cells on the villus whereas the M chain was restricted to the basement membrane of crypts. However, both B1 and B2 chains were detected all along the intestinal basement membrane. Furthermore, alpha 6 beta 1 and alpha 6 beta 4 integrins were found to be expressed by all enterocytes.

CONCLUSIONS

These observations show a reciprocal expression of laminin isoforms along the crypt-villus axis and support the concept that the intestinal epithelial basement membrane is subjected to intricate compositional changes.

Generation of neomucosa in vivo by transplantation of dissociated rat postnatal small intestinal epithelium

A novel method to study the generation of rat small intestinal mucosa, by transplantation of disaggregated postnatal rat small intestinal epithelium is described. Cellular aggregates, comprised of epithelium with attached proliferative cells and closely associated stromal tissue, were isolated from postnatal rat small intestine by enzymatic digestion, then grafted immediately to the subcutaneous plane of adult recipients. On graft retrieval after 14 days, 39% of cellular transplants to nude mice, and 84% of cellular transplants to inbred rats had developed into small intestine-like structures. These structures were comprised of a circumferential layer of epithelium surrounding a central mucin filled lumen. This neomucosal layer exhibited well formed crypts and villi, and contained all epithelial stem cell lineages i.e. absorptive enterocytes, goblet cells, Paneth's cells and entero-endocrine cells. Proliferative activity within this neomucosa was confined to crypt regions as in normal postnatal small intestine. Developmental maturation within the regenerated neomucosa was demonstrated by organotypic morphogenesis, i.e. formation of mature crypts and villi, and progressive cytodifferentiation with increased numbers of goblet cells, entero-endocrine cells and Paneth's cells. Altered patterns of brush border enzyme expression further confirmed a temporal progression of development within neomucosal enterocytes. It is concluded that after "extensive" mucosal disaggregation, postnatal small intestinal epithelial progenitor cells retain the capacity for organotypic regeneration of neomucosa when transplanted to ectopic sites in adult recipients. These small aggregates of epithelium and stroma are capable of generating the topographical signals necessary for the three dimensional regeneration of this tissue. Furthermore, the multipotent generative potential of the stem cells within these cellular aggregates is maintained with production of all progeny.

Molecular species analysis of glycosphingolipids from small intestine of Japanese quail, Coturnix coturnix Japonica by HPLC/FAB/MS

Neutral glycosphingolipids were isolated from quail small intestine and their structures were analysed. They contained: Gal beta 1-4GlcCer(LacCer), Gal alpha 1-4GalCer(Ga2Cer), Gal alpha 1-4Gal beta 1-4GlcCer(Gb3Cer), GlcNAc beta 1-3Gal beta 1-4GlcCer(Lc3Cer), GalNAc beta 1-4Gal beta 1-4GlcCer(Gg3Cer), GalNAc beta 1-4[GalNAc beta 1-3] Gal beta 1-4GlcCer(LcGg4Cer), and GalNAc alpha 1-3GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4GlcCer (Forssman glycolipid) as well as glucosylceramide, galactosylceramide (Nishimura K et al. 1984) Biochim Biophys Acta 796:269-76) and the LeX glycolipid, III3 Fuc alpha-nLc4Cer (Nishimura K et al. (1989) J. Biochem (Tokyo) 101:1315-18). The molecular species compositions of these glycosphingolipids were examined using fast atom bombardment-mass spectrometry linked with reversed-phase high-performance liquid chromatography. By such analysis, we could classify the quail glycosphingolipids into at least three classes: glycolipids rich in species having four hydroxyl groups in the ceramides (GalCer, Gg3Cer, LcGg4Cer and LeX), those rich in the ceramides of N-acyl trihydroxysphinganine with normal fatty acids (Lc3Cer), and glycolipids rich in the ceramides of N-acyl sphingenine with normal fatty acids (LacCer, Gb3Cer and Forssman glycolipid). Immunohistochemical observation implies that the differences in the hydrophobic moieties specified the localization of glycosphingolipids in the tissue.

Voltage- and time-dependent K+ channel currents in the basolateral membrane of villus enterocytes isolated from guinea pig small intestine

Patch-clamp studies were carried out in villus enterocytes isolated from the guinea pig proximal small intestine. In the whole-cell mode, outward K+ currents were found to be activated by depolarizing command pulses to -45 mV. The activation followed fourth order kinetics. The time constant of K+ current activation was voltage-dependent, decreasing from approximately 3 ms at -10 mV to 1 ms at +50 mV. The K+ current inactivated during maintained depolarizations by a voltage-independent, monoexponential process with a time constant of approximately 470 ms. If the interpulse interval was shorter than 30 s, cumulative inactivation was observed upon repeated stimulations. The steady state inactivation was voltage-dependent over the voltage range from -70 to -30 mV with a half inactivation voltage of -46 mV. The steady state activation was also voltage-dependent with a half-activation voltage of -22 mV. The K+ current profiles were not affected by chelation of cytosolic Ca2+. The K+ current induced by a depolarizing pulse was suppressed by extracellular application of TEA+, Ba2+, 4-aminopyridine or quinine with half-maximal inhibitory concentrations of 8.9 mM, 4.6 mM, 86 microM and 26 microM, respectively. The inactivation time course was accelerated by quinine but decelerated by TEA+, when applied to the extracellular (but not the intracellular) solution. Extracellular (but not intracellular) applications of verapamil and nifedipine also quickened the inactivation time course with 50% effective concentrations of 3 and 17 microM, respectively. Quinine, verapamil and nifedipine shifted the steady state inactivation curve towards more negative potentials. Outward single K+ channel events with a unitary conductance of approximately 8.4 pS were observed in excised inside-out patches of the basolateral membrane, when the patch was depolarized to -40 mV. The ensemble current rapidly activated and thereafter slowly inactivated with similar time constants to those of whole-cell K+ currents. It is concluded that the basolateral membrane of guinea pig villus enterocytes has a voltage-gated, time-dependent, Ca(2+)-insensitive, small-conductance K+ channel. Quinine, verapamil, and nifedipine accelerate the inactivation time course by affecting the inactivation gate from the external side of the cell membrane.

[Adrenergic and cholinergic regulation of respiratory efficiency of secretory cells]

The influence of sympathetic and parasympathetic systems on the secretory cell respiration is mediated at the subcellular level by adreno- and cholinoreceptors of plasmatic membranes and is related to selective oxidation of two different substrates of the Krebs cycle: succinate and alpha-ketoglutarate, both being involved into two reciprocal mediator-hormonal-substrate-nucleotide systems: catecholamines-succinate-cAMP-ATP and acetylcholint-alpha-ketoglutarate-cGMP-GTP. The reciprocation of these systems is necessary for regulation of cell oxygen demand and effective oxygen utilization for ATP-synthesis and synthesis of other macroergical compounds depending on the functional state of a cell.

Unique properties of a cytotoxic CD4+CD8+ intraepithelial T-cell line established from the mouse intestinal epithelium

Growth factor-dependent gut intraepithelial lymphocyte (IEL) cell lines were established from a long-term in vitro culture of BALB/c IEL with syngeneic irradiated spleen cells in the presence of concanavalin A-stimulated spleen supernatant fluids. The cell lines were preferentially consisted of very limited thymoindependent subsets of IEL; i.e., Thy-1+CD5-TCR alpha beta+CD4+CD8 alpha+beta- (double-positive; DP) IEL and Thy-1+CD5-TCR alpha beta+CD4-CD8 alpha+beta- (CD8 single-positive; CD8 SP) IEL. The CD8 SP IEL cell line had cytotoxic activities and was triggered to proliferate by T-cell receptor (TCR)-directed stimuli. The DP IEL cell line expressed high levels of the CD3-TCR alpha beta, exhibited cytotoxic activity in redirected lysis assays, and had perforin in the cytoplasm, indicating the functional maturity of this cell line. However, the DP IEL cell line did not proliferate in response to TCR alpha beta-directed stimuli, which indicated that TCR alpha beta-mediated signalling was able to initiate cytotoxic function but not to induce proliferation of the DP IEL cell line. Although both cell lines were shown to have functional competence, they expressed J11d antigen which marks immaturity in thymocyte differentiation pathways. These results indicate that the established thymoindependent DP and CD8 SP IEL cell lines have unique properties distinct from DP thymocytes and CD8 SP peripheral T cells. Together with a recent report on freshly isolated DP IEL (10), the unique properties of the DP IEL cell line seems to support the notion that DP IEL may undergo a unique maturation process in the gut microenvironment.

Neuroendocrinimmune modulation of secretory component production by rat lacrimal, salivary, and intestinal epithelial cells

PURPOSE

To evaluate the kinetics, receptor specificity, molecular basis, and site selectivity of the endocrine and neural regulation of secretory component (SC) synthesis by rat lacrimal gland acinar cells.

METHODS

Acinar cells from the rat lacrimal and submandibular glands, as well as epithelial cells (IEC-6) from the rat small intestine, were cultured in supplemented, serum-free media and treated with dihydrotestosterone, cholera toxin, carbachol, vehicle, or other agents for varying time periods. Media SC levels were measured by radioimmunoassay.

RESULTS

The authors' findings with lacrimal gland acinar cells demonstrate that: a significant, temporal delay exists between the initiation of stimulatory or inhibitory signals and the eventual cellular SC response to regulatory compounds; the parasympathetic analogue, carbachol, exerts a dual effect on SC output, i.e., an early stimulation (hours) followed by an extended suppression (days); the androgen and cholinergic control of SC is receptor-mediated; and the androgen modulation of SC may involve the induction of gene expression. In addition, the authors' results show that distinct, tissue-specific variations occur in the nature of SC regulation: Compounds that control SC output by lacrimal acinar cells do not necessarily alter SC production by epithelial cells from the rat submandibular gland or small intestine.

CONCLUSIONS

These findings advance the authors' understanding of the neuroendocrine regulation of SC synthesis in acinar cells from the lacrimal gland. Moreover, the authors' results indicate that the nature of the neural, endocrine, and immune control of lacrimal SC may be unique.

T cell migration during development: homing is not related to TCR V beta 1 repertoire selection

T cell precursors enter the chick thymus in three waves during embryonic life. Each wave of thymocyte precursors colonizing the thymus gave rise to a similar TCR V beta repertoire in thymus, spleen and intestine both in terms of V beta 1 and J beta usage as well as in the length of V beta-D beta-J beta junctions. Seventeen V beta 1s were utilized, and a new J beta segment was found. In the progeny of the third wave, more nucleotides were deleted at the 5' end of the J beta segment, but the overall size of the CDR3 was conserved by a concomitant increase of N nucleotide addition at the V beta-D beta-J beta junctions during rearrangement. This CDR3 modification was observed in the spleen but not in the intestine, implying that progeny of the third wave migrate preferentially to the spleen, a possibility that was confirmed by adoptive cell transfers into congenic chickens. Very low frequencies of non-productive rearrangements in the intestine suggested that negative selection may occur in this organ. The present analysis indicates that V beta 1+ T cells in spleen and intestine are primarily of thymic origin, this colonization of both organs occurs in waves and is not characterized by preselection of the TCR V beta 1 repertoire.

Calpain from rat intestinal epithelial cells: age-dependent dynamics during cell differentiation

Micromolar and millimolar Ca(2+)-requiring neutral protease (calpain I and calpain II) along with their endogenous inhibitor calpastatin were isolated and partially purified from the same preparation of rat intestinal epithelial cells. Calpain I and II were partially purified by 1300 and 900-fold with 57 and 53 per cent yield, respectively. The optimum assay conditions revealed pH 7.5, 20 min incubation at 25 degrees C and 0.24% casein substrate for both calpains. The optimum calcium concentration obtained for calpain I and II were 25 microM and 4 mM, respectively. Distribution of rat intestinal epithelial cells calpain I and II along with calpastatin during cell differentiation stages in weanling to senescence age were studied. Calpain I in weanling rats was in an increasing order from villus to crypt regions. Adult rats indicated well expressed consistent calpain I throughout the differentiation stages. Whereas, significant lowering towards crypt region cells were evident in old rats. Calpain II in weanling and adult rats was found to be consistent throughout the differentiation stages. Old animals revealed an increasing trend from villus to crypt region with insignificant activity present in upper villus cells. Concomitantly, different concentrations of calpastatin were observed throughout the differentiation stages in all the age groups. Moreover, the levels of calpains exceeded that of calpastatin in most of the epithelial cell populations during developmental stages. In addition to casein, intestinal epithelial cell membranes were found to be equally good substrates for calpains. Proteolytic susceptibility of weanling, adult and old rat membrane proteins varied significantly all along the ageing process in rats. Simultaneous age-dependent calpastatin response were also evident. Taken together the results obtained provided strong evidence that calpain plays significant role in rat intestinal cell differentiation and ageing process with calpastatin as its specific regulatory protein.

Structure and diversity of the murine cryptdin gene family

Cryptdins are antimicrobial peptides of the defensin family produced by mouse intestinal Paneth cells. Characterization of genomic and cDNA clones of cryptdins 1-3, 5, and 6 revealed that each of these genes has a two-exon structure. The prepro- and mature peptide coding regions are found on different exons separated by an intron of approximately 550 bp. The 5' ends of cryptdin mRNAs are distinguished by a 45-nucleotide untranslated sequence (UTS) encoded completely by the first exon. This feature contrasts with the extended 5' UTS of myeloid defensin mRNAs, which are coded by a third exon that appears to be unique to defensin genes expressed in hematopoietic cells. Sequencing of cryptdin cDNAs from both C3H/HeJ and 129/SVJ mouse small intestine demonstrated the presence of at least 16 different mRNAs, identifying cryptdins as the largest known defensin family. Amplification of these two-exon crypt defensin genes, followed by mutation-induced divergence at a limited number of positions, may have played an important role in the development of a broad-spectrum enteric defense system in the mouse.

Demonstration of acidity in intestinal vacuoles of the suckling rat and pig

Fluorescence staining characteristics of "large vacuoles," i.e. vacuoles ranging up to almost cell size, were studied in suckling rats and pigs. In the distal epithelium of the small intestine of suckling rat, yellow autofluorescence and accumulation of orally administered FITC-dextran were observed in the supranuclear vacuole. In both species the weakly basic amino dye acridine orange (AO) stained the nuclei at neutral pH bright yellow-green and the transport and digestive vacuoles bright red or orange. It is concluded that trapping and accumulation of the dye (red shift) were due to the acidity of the vacuolar interior. Assessment of the vacuolar pH in rat enterocytes is in agreement with published data on lysosomal pH values. Acidic buffers, lysosomotropic and destructive agents, or illumination with bright light induced irreversible fading of AO-stained vacuoles; the color of the porcine transport vacuoles was the most labile. This fading was used to differentiate vacuoles from other structures, e.g., vacuolar inclusion bodies and goblet cells. In suckling rat, staining characteristics of the gut epithelium changed on Days 19 and 20 of postnatal age. Detection of acidity in the distal (digestive) vacuoles supports the lysosome-like nature of their function. They appear to constitute an auxiliary, intracellular digestive system for the young animal. However, the function of acidity in the non-digestive transport vacuoles of newborn pig is unclear.

Aflatoxin B1-adduct formation in rat and human small bowel enterocytes

BACKGROUND/AIMS

Hepatic CYP3A enzymes have been implicated in the bioactivation of aflatoxin B1 (AFB1) to DNA binding metabolites. CYP3A enzymes are also abundant in the small bowel, and we therefore examined the ability of this tissue to form intracellular AFB1 adducts.

METHODS

Immunohistochemistry using a antibody to the stable AFB1-DNA adduct was performed on small bowel sections obtained from rats orally gavaged with AFB1 and on human small bowel biopsy specimens maintained in explant culture. 3H-AFB1 was instilled into a loop of small bowel of untreated rats and rats pretreated with the CYP3A inducer dexamethasone during vivisection. DNA was isolated from the loop 2 hours later and assayed for specific activity.

RESULTS

In both rats and humans, AFB1-adducts were detected exclusively in mature enterocytes in a pattern similar to the distribution of CYP3A enzymes. Induction of enterocyte CYP3A in rats resulted in an increase in enterocyte immunoreactive AFB1 adducts and in a 1.8-fold increase in 3H-AFB1-nucleic acid adducts (P = 0.01).

CONCLUSIONS

Intracellular AFB1 adducts are formed in the small intestine, and this reflects, at least in part, the catalytic activity of CYP3A enzymes. Because these AFB1 adducts should ultimately pass in stool, enterocyte CYP3A may represent a regulatable barrier to dietary aflatoxins.

Heparin stimulates the proliferation of intestinal epithelial cells in primary culture

Heparin is a sulphated glycosaminoglycan derived from mast cells and has a number of functions including the inhibition of proliferation in several cell types and interactions with a range of heparin-binding growth factors. We report that heparin is a trophic factor in primary cultures of rat small intestinal epithelium. Heparin elicits a dose-dependent increase in epithelial proliferation and inhibits the growth of associated mesenchyme. The trophic effect of this molecule is not reproduced by other glycosaminoglycans including heparan sulphate but is dependent upon extensive molecular sulphation. Highly sulphated polysaccharides that are structurally unrelated to heparin (e.g. dextran sulphate and pentosan polysulphate) also stimulate epithelial proliferation in primary cultures. Heparin may act by the potentiation of mesenchyme-derived heparin-binding growth factors and these data suggest an in vivo role for mast cell-derived heparin in mucosal wound regeneration.