Close relationships between the cells of the immune system and the epithelial cells in the rat small intestine

Summary A possible contribution of the intestinal epithelium to the immune defence system was studied by electron microscopy in the rat small intestine. The cells of the immune system (CIS) such as lymphocytes, eosinophils and macrophages penetrate the basal lamina into the epithelium and make close relationships with the absorptive cells. At the points of close apposition, the two cell membranes run parallel at a regular distance of about 20 nm. On the other hand, about 5% of the intestinal absorptive cells also penetrate the basal lamina into the lamina propria via their basal protrusions and show a similar close association with CIS. The basal protrusions contain many microfilaments; this indicates that they are structures with a definite function rather than a simple hernia. These findings are discussed with respect to the transport of antigenic molecules and of intercellular communication between CIS and the intestinal epithelium.     

Transepithelial pathogen uptake into the small intestinal lamina propria

The lamina propria that underlies and stabilizes the gut lining epithelium is densely populated with strategically located mononuclear phagocytes. Collectively, these lamina propria macrophages and dendritic cells (DC) are believed to be crucial for tissue homeostasis as well as the innate and adaptive host defense. Lamina propria DC were recently shown to gain direct access to the intestinal lumen by virtue of epithelium-penetrating dendrites. However, the role of these structures in pathogen uptake remains under debate. In this study, we report that entry of a noninvasive model pathogen (Aspergillus fumigatus conidia) into the murine small intestinal lamina propria persists in the absence of either transepithelial dendrites or lamina propria DC and macrophages. Our results suggest the existence of multiple pathogen entry pathways and point at the importance of villus M cells in the uptake of gut lumen Ags. Interestingly, transepithelial dendrites seem altogether absent from the small intestine of BALB/c mice suggesting that the function of lamina propria DC extensions resides in their potential selectivity for luminal Ags, rather than in general uptake or gut homeostasis.     

Intestinal myofibroblasts: targets for stem cell therapy

The subepithelial intestinal myofibroblast is an important cell orchestrating many diverse functions in the intestine and is involved in growth and repair, tumorigenesis, inflammation, and fibrosis. The myofibroblast is but one of several α-smooth muscle actin-positive (α-SMA(+)) mesenchymal cells present within the intestinal lamina propria, including vascular pericytes, bone marrow-derived stem cells (mesenchymal stem cells or hematopoietic stem cells), muscularis mucosae, and the lymphatic pericytes (colon) and organized smooth muscle (small intestine) associated with the lymphatic lacteals. These other mesenchymal cells perform many of the functions previously attributed to subepithelial myofibroblasts. This review discusses the definition of a myofibroblast and reconsiders whether the α-SMA(+) subepithelial cells in the intestine are myofibroblasts or other types of mesenchymal cells, i.e., pericytes. Current information about specific, or not so specific, molecular markers of lamina propria mesenchymal cells is reviewed, as well as the origins of intestinal myofibroblasts and pericytes in the intestinal lamina propria and their replenishment after injury. Current concepts and research on stem cell therapy for intestinal inflammation are summarized. Information about the stem cell origin of intestinal stromal cells may inform future stem cell therapies to treat human inflammatory bowel disease (IBD).     

Immunological differences in intestine and rectum of Atlantic cod (Gadus morhua L.)

The defence system of the distal gut (hindgut and rectum) of Atlantic cod, (Gadus morhua L.) was studied using (immuno)histochemical, electron microscopical and real-time quantitative PCR techniques. The uptake and transport of macromolecules in the intestinal epithelium was also investigated.In this study we observed that cod has many and large goblet cells in its intestinal epithelium and that IgM⁺ cells are present in the lamina propria and their number is considerably higher in the rectum than in the intestine. Myeloperoxidase staining revealed low numbers of granulocytes in and under the epithelium of the distal intestine, whereas high numbers were found clustered in the submucosa of the rectum. Electron microscopy not only confirmed these observations, but also revealed the presence of lymphoid cells and macrophages within the intestinal epithelium. Acid phosphatase staining demonstrated more positive macrophage-like cells in the rectum than in the distal intestine. Antigen uptake studies showed a diffused absorption of horse radish peroxidase (HRP) and LTB-GFP, whereas ferritin uptake could not be detected.Basal gene expression of cytokines (IL-1β, IL-8 and IL-10) and immune relevant molecules (hepcidin and BPI/LPB) were compared in both the intestine and rectum and revealed approximately 2–9 times higher expression in the rectum, of which IL-1β expression showed the most prominent difference.The present results clearly indicate that intestinal immunity is very prominent in the rectum of cod.     

Quadruple colocalization of calretinin,calcitonin gene-related peptide,vasoactive intestinal peptide,and substance P in fibers within the villi of the rat intestine

Double-labeling immunofluoresenct histochemistry demonstrates that calretinin, a calcium-binding protein, coexists with calcitonin gene-related peptide, vasoactive intestinal peptide, and substance P in the fibers innervating the lamina propria of the rat intestinal villi. An acetylcholinesterase histochemical stain revealed that the majority of calretinin-containing cells in the myenteric ganglia were cholinergic and that about one half of the submucosal calretinin-containing cells colocalized with acetylcholinesterase. In situ hybridization studies confirmed the presence of calretinin mRNA in the dorsal root ganglia, and a ribonuclease protection assay verified the presence of calretinin message in the intestine. The coexistence of calretinin in calcitonin-gene-related-peptide-containing cells that also contained substance P and vasoactive intestinal polypeptide in the dorsal root ganglia suggest that these ganglia are the source of the quadruple colocalization within the sensory fibers of the villi. Although the function of calretinin in these nerves is unknown, it is hypothesized that the coexistence of three potent vasodilatory peptides influences the uptake of metabolized food products within the vasculature of the villi.     

Effects of the oral administration of the exopolysaccharide produced by Lactobacillus kefiranofaciens on the gut mucosal immunity

The probiotic effects ascribed to lactic acid bacteria (LAB) and their fermented dairy products arise not only from whole microorganisms and cell wall components but also from peptides and extracellular polysaccharides (exopolysaccharides) produced during the fermentation of milk. There is a lack of knowledge concerning the immune mechanisms induced by exopolysaccharides produced by lactic acid bacteria, which would allow a better understanding of the functional effects described to them. The aim of this study was to investigate the in vivo immunomodulating capacity of the exopolysaccharide produced by Lactobacillus kefiranofaciens by analyzing the profile of cytokines and immunoglobulins induced at the intestinal mucosa level, in the intestinal fluid and blood serum. BALB/c mice received the exopolysaccharide produced by L. kefiranofaciens for 2, 5 or 7 consecutive days. At the end of each period of administration, control and treated mice were sacrificed and the numbers of IgA+ and IgG+ cells were determined on histological slices of the small and large intestine by immunofluorescence. Cytokines (IL-4, IL-6, IL-10, IL-12, IFNgamma and TNFalpha) were also determined in the gut lamina propria as well as in the intestinal fluid and blood serum. There was an increase of IgA+ cells in the small and large intestine lamina propria, without change in the number of IgG+ cells in the small intestine. This study reports the effects of the oral administration of the exopolysaccharide produced by L. kefiranofaciens in the number of IgA+ cells in the small and large intestine, comparing simultaneously the production of cytokines by cells of the lamina propria and in the intestinal fluid and blood serum. The increase in the number of IgA+ cells was not simultaneously accompanied by an enhance of the number of IL-4+ cells in the small intestine. This finding would be in accordance with the fact that, in general, polysaccharide antigens elicit a T-independent immune response. For IL-10+, IL-6+ and IL-12+ cells, the values found were slightly increased compared to control values, while IFNgamma+ and TNFalpha+ cells did not change compared to control values. The effects observed on immunoglobulins and in all the cytokines assayed in the large intestine after kefiran administration were of greater magnitude than the ones observed in the small intestine lamina propria, which may be due to the saccharolytic action of the colonic microflora. In the intestinal fluid, only IL-4 and IL-12 increased compared to control values. In blood serum, all the cytokines assayed followed a pattern of production quite similar to the one found for them in the small intestine lamina propria. We observed that the exopolysaccharide induced a gut mucosal response and it was able to up and down regulate it for protective immunity, maintaining intestinal homeostasis, enhancing the IgA production at both the small and large intestine level and influencing the systemic immunity through the cytokines released to the circulating blood.     

Effects of the oral administration of the exopolysaccharide produced by Lactobacillus kefiranofaciens on the gut mucosal immunity

The probiotic effects ascribed to lactic acid bacteria (LAB) and their fermented dairy products arise not only from whole microorganisms and cell wall components but also from peptides and extracellular polysaccharides (exopolysaccharides) produced during the fermentation of milk. There is a lack of knowledge concerning the immune mechanisms induced by exopolysaccharides produced by lactic acid bacteria, which would allow a better understanding of the functional effects described to them. The aim of this study was to investigate the in vivo immunomodulating capacity of the exopolysaccharide produced by Lactobacillus kefiranofaciens by analyzing the profile of cytokines and immunoglobulins induced at the intestinal mucosa level, in the intestinal fluid and blood serum. BALB/c mice received the exopolysaccharide produced by L. kefiranofaciens for 2, 5 or 7 consecutive days. At the end of each period of administration, control and treated mice were sacrificed and the numbers of IgA+ and IgG+ cells were determined on histological slices of the small and large intestine by immunofluorescence. Cytokines (IL-4, IL-6, IL-10, IL-12, IFNγ and TNFα) were also determined in the gut lamina propria as well as in the intestinal fluid and blood serum. There was an increase of IgA+ cells in the small and large intestine lamina propria, without change in the number of IgG+ cells in the small intestine. This study reports the effects of the oral administration of the exopolysaccharide produced by L. kefiranofaciens in the number of IgA+ cells in the small and large intestine, comparing simultaneously the production of cytokines by cells of the lamina propria and in the intestinal fluid and blood serum. The increase in the number of IgA+ cells was not simultaneously accompanied by an enhance of the number of IL-4+ cells in the small intestine. This finding would be in accordance with the fact that, in general, polysaccharide antigens elicit a T-independent immune response. For IL-10+, IL-6+ and IL-12+ cells, the values found were slightly increased compared to control values, while IFNγ+ and TNFα+ cells did not change compared to control values. The effects observed on immunoglobulins and in all the cytokines assayed in the large intestine after kefiran administration were of greater magnitude than the ones observed in the small intestine lamina propria, which may be due to the saccharolytic action of the colonic microflora. In the intestinal fluid, only IL-4 and IL-12 increased compared to control values. In blood serum, all the cytokines assayed followed a pattern of production quite similar to the one found for them in the small intestine lamina propria. We observed that the exopolysaccharide induced a gut mucosal response and it was able to up and down regulate it for protective immunity, maintaining intestinal homeostasis, enhancing the IgA production at both the small and large intestine level and influencing the systemic immunity through the cytokines released to the circulating blood.     

Eosinophilic granule cells and endocytic cells in intestinal wall of pearl gouramy (Anabantidae: Teleostei)

The localization and frequency of eosinophilic granule cells (EGCs) and endocytic cells in the intestinal wall of a teleost, pearl gouramy (Trichogaster leeri), a stomach-containing anabantid, are described. EGCs occurred in high numbers in lamina propria and epithelial layer throughout the entire intestine. They often embraced blood capillaries, but were unable to take up foreign ferritin, i.e. they seem not to play any blood cleansing role in this tissue. Only some of the EGCs granules reacted with Schmorl's solution, suggesting that they are at a different stage of development or of different types in these cells. The granule content is probably secreted close to the intestine blood stream where it may play important local immunological roles. The present results suggest that the number of intestinal EGCs can be high in teleosts even in species with a putative well-developed acid-based defence in the digestive tract. Also, endocytic cells capable of taking up and storing much foreign ferritin were frequently seen in this tissue; such cells may play significant cleansing and scavenger roles throughout the entire intestine in pearl gouramy.     

Immunocytochemical localization of prostaglandin endoperoxide synthase in the bovine intestine

The localization of prostaglandin (PG) endoperoxide synthase in bovine intestine was examined immunocytochemically with polyclonal antibody raised against PG endoperoxide synthase purified from bovine seminal glands. The most intense positive staining reaction for the enzyme was present in mast cells. Mast cells were found to be widely distributed in the intestinal wall, and were particularly numerous in the lamina propria. Most of the mast cells in the lamina propria of the intestinal villi were elongated and oriented with their long axis parallel to the plane of the absorptive epithelium. In whole mount preparations of jejunal villi, mast cells were seen to form a two-dimensional network in the lamina propria. In addition to mast cells, smooth muscle cells of the inner circular muscle layer and muscularis mucosae, nerve cells and fibers, endothelial cells of arterioles, and serosal epithelial cells also showed faint to moderate staining for the enzyme. These results suggested that mast cells are the major source of PGs in the bovine intestinal wall. The characteristic arrangement of mast cells in the intestinal villi may be related to their functions in this portion of the bovine intestine.     

Structure and mucous histochemistry of the intestinal respiratory tract of the mud loach, Misgurnus anguillicaudatus (Cantor)

The straight intestinal tract of the mud loach Misgurnus anguillicaudatus was divided into an intestine and rectum which consisted of a mucosa (epithelial layer), lamina propria‐submucosa, muscularis and serosa. The intestine and rectum have shorter mucosal folds and a thinner wall. Extensive vascular capillary networks were present in the mucosa of the intestine and the rectum. The diffusion distance between the vascular capillaries and the lumen in the intestinal and rectal mucosal epithelium was about 11.2 μm (±1.12). The majority of the epithelial mucous cells contain acidic mucins although there are small amounts of a mixture of acidic and neutral mucins. The intestinal tract of M. anguillicaudatus is probably modified to suit its role of respiration for the deficient oxygen supply within their environment.     

Antigen sampling by mucosal dendritic cells

The mucosal immune system is the first line of defence against bacterial and viral infections and is crucial in maintaining mucosal homeostasis. In the gut, mucosal dendritic cells offer an alternative pathway to epithelial cells for antigen uptake, to initiate antigen-specific immune responses. It has recently been shown that lamina propria dendritic cells of the small intestine actively sample gut bacteria through the formation of transepithelial dendrites by a mechanism that is dependent on the expression of the chemokine receptor CX3CR1.     

Determinants of the localization, magnitude, and duration of a specific mucosal IgA plasma cell response in enterically immunized rats

The origin and fate of specific IgA plasma cells in intestinal lamina propria were studied in rats immunized enterically with cholera toxin (CT). Our major goal was to define how an anti-CT response is focused and sustained at the site of antigen challenge. To distinguish antigen-dependent from antigen-independent mechanisms, CT exposure was restricted to defined portions of intestine and, in some studies, the distribution of antitoxin-containing plasma cells (ACC) was examined in nonimmune adoptive recipients of post-challenge thoracic duct lymphocytes. After enteric priming and challenge, ACC appeared throughout the gut, but were most numerous at the challenged site. About 25% of ACC appearing at the site of jejunal challenge were due to antigen-driven proliferation of memory cells within the lamina propria; the remainder arose elsewhere, apparently in mucosal follicles or mesenteric lymph nodes, and migrated systemically as antitoxin-containing plasmablasts before homing to the lamina propria. The homing of these migrating ACC precursors was not affected by mucosal exposure to CT, nor did they undergo appreciable antigen-driven division after arrival in gut lamina propria. However, homing was specific for the organ from which they arose, i.e., precursors arising from duodenal challenge homed selectively to jejunum, whereas those from colonic challenge homed to the colon. The organ specificity of homing was determined during the challenge response and was independent of the origin of memory cells participating in the response. The survival of migrating ACC precursors did not differ in segments of gut exposed or nonexposed to CT. However, CT exposure at the time of their migration evoked another secondary-type response, due to stimulation of comigrating memory cells, thus sustaining the secondary response at a high level. These results and those in a previous report identify important mechanisms that affect the localization, magnitude, and duration of a specific IgA response, at least in the intestine. These include: 1) organ-specific homing of migrating IgA plasmablasts, 2) antigen-driven generation of IgA plasma cells from memory cells within the lamina propria, 3) enhanced memory at the site of mucosal priming compared to that a distant mucosae, and 4) regeneration of memory cells during the secondary response.     

Tissue distribution of immunoglobulin-secreting cells in normal and IgA-deficient chickens.

A reverse hemolytic plaque assay was employed to enumerate lymphoid cells actively secreting either immunoglobulin (Ig)G, IgA, or IgM in the small intestine, lungs, and lymphoid organs of normal and IgA-deficient chickens. In normal birds, intestinal lamina propria lymphocytes were proportionately richest in cells secreting IgG and IgA whereas the bone marrow was richest in IgM-secreting cells. The highest ratio of IgA to IgG secreting cells was also found in the lamina propria lymphocytes of the intestine (0.9), followed by the IgA to IgG ratios in the intestinal epithelium (0.31), and the lungs (0.19). The IgA to IgG ratios in the bone marrow (0.08) and the spleen (0.02) were considerably lower. Thus, both the intestine and the lungs were relatively enriched in cells actively secreting IgA. These IgA-secreting cells are the likely source of the IgA found in such quantities in intestinal and respiratory secretions. The tissue distribution of Ig-secreting cells was also studied in two generations of birds with experimentally induced IgA deficiency. There was a striking diminution of IgA-secreting cells in all tissues, including the intestine and lungs, whereas cells secreting IgG and IgM were normal or increased. The lack of IgA-secreting cells in these birds represents the effects of donor suppressor T cells having specificity for IgA.     

Hemorrhage in mice produces alterations in intestinal B cell repertoires

Abnormalities in immune response play a major role in the increased susceptibility to infection after hemorrhage and trauma. Infections occurring after injury often originate in the intestine. In order to determine the effects of hemorrhage on intestinal B cell function, we examined hemorrhage-induced alterations in available (clonal precursors) and actual (plasma cells) B cell repertoires among intestinal lamina propria and Peyer's patch cells. Hemorrhage resulted in complete suppression of the increase in levan-specific lamina propria and Peyer's patch plasma cell numbers following oral immunization with this bacterial polysaccharide antigen. The absolute frequency of clonal precursors specific for levan among lamina propria B cells decreased by more than twofold following hemorrhage. These results demonstrate that hemorrhage produces marked alterations in intestinal B cell repertoires, which may contribute to postinjury abnormalities in host defenses.     

Fat intestinal absorption in the catfish--a histochemical study in glycol methacrylate embedded tissue

The intestinal absorption of lipids was investigated in plastic sections from glycol methacrylate embedded intestine after fat administration. In the catfish, the lipids are absorbed by the enterocytes of the proximal intestinal segment, thus forming fat cytoplasmic inclusions that were demonstrated by Sudan black B staining. The histochemical characterization of lipids by the Nile blue sulphate test revealed the neutral or triglyceride nature of the cytoplasmic droplets, both after the corn oil and oleic acid feeding. There is lipid accumulation in the lamina propria and lymphatic vessels.     

Evidence for vasopressin production in the human gastrointestinal system.

In the present study we performed immunohistochemical examination of segments from the human gastrointestinal system for the presence of cells containing vasopressin (VP) and vasopressin-associated human neurophysin (VP-HNP). VP immunoreactivity was found in crypt cells of the stomach and small intestine, and in mononuclear cells within the lamina propria and submucosa. VP-HNP was demonstrated in the crypt and lamina propria regions of the small intestine, and was colocalized with vasopressin in crypt cells. This colocalization indicates local vasopressin synthesis by these cells and raises the possibility that they may perform an endocrine or exocrine function in the human gastrointestinal system.     

Simian immunodeficiency virus infection in neonatal macaques

Children with human immunodeficiency virus infection often have higher viral loads and progress to AIDS more rapidly than adults. Since the intestinal tract is a major site of early viral replication and CD4(+) T-cell depletion in adults, we examined the effects of simian immunodeficiency virus (SIV) on both peripheral and intestinal lymphocytes from 13 neonatal macaques infected with SIVmac239. Normal neonates had more CD4(+) T cells and fewer CD8(+) T cells in all tissues than adults. Surprisingly, neonates had substantial percentages of CD4(+) T cells with an activated, memory phenotype (effector CD4(+) T cells) in the lamina propria of the intestine compared to peripheral lymphoid tissues, even when examined on the day of birth. Moreover, profound and selective depletion of jejunum lamina propria CD4(+) T cells occurred in neonatal macaques within 21 days of infection, which was preceded by large numbers of SIV-infected cells in this compartment. Furthermore, neonates with less CD4(+) T-cell depletion in tissues tended to have higher viral loads. The persistence of intestinal lamina propria CD4(+) T cells in some neonates with high viral loads suggests that increased turnover and/or resistance to CD4(+) T-cell loss may contribute to the higher viral loads and increased severity of disease in neonatal hosts.     

Trichinella spiralis: peroxidase activity in isolated cells from the rat intestine

An understanding of physiologic events underlying resistance to parasitic worms depends on a knowledge of metabolic interactions between parasites and specific cells at the host-parasite interface. In the case of invasive intestinal parasites this interaction involves contact with epithelial cells and cells of the lamina propria. This investigation deals with the collection of epithelial cells and lamina propria cells from the small intestine of control rats and rats infected with the nematode, Trichinella spiralis, and measurement of peroxidase activity in these cells. Lamina propria cells were isolated by collagenase digestion of everted gut segments previously denuded of epithelium by treatment with hyaluronidase. Mean peroxidase activity in homogenates of lamina propria cells was equivalent to 40 nmoles H₂O₂ decomposed/min/mg of cell protein from control rats compared to 413 nmoles from infected animals. Epithelial cell peroxidase activity in homogenates of epithelial cells from both control and infected rats was less than 2 nmoles H₂O₂ decomposed/min/mg cell protein. The degree of contamination of lamina propria cells with epithelial cells was determined by measuring disaccharidase activity in both cell populations. The specific activity of maltase, sucrase, and trehalase in lamina propria cells was between 10 and 17% of that in epithelial cells. This work is a requisite for a study in which the role of intestinal cell peroxidase in resistance to Trichinella will be evaluated.