Research in gastrointestinal immunology. State of the art

Absolute counts and distribution of lymphocyte subsets in small intestine of BALB/c mice change during weaning

The gut immune system is an essential part of the barrier function of the gut. At weaning, major changes can be expected in the number and subset composition of lymphocytes in the small intestine since the gut is exposed to a wide variety of food and microbial antigens, especially when human milk is gradually replaced by weaning foods. The purpose of this study was to evaluate the changes in small intestine lymphocyte subsets in mice during weaning. BALB/c male mice at weaning (3 wk old) were fed a nonpurified diet for 18 d and were killed at different times (0, 4, 7, 12 and 18 d). Lymphocyte populations from lamina propria (LPL), Peyer's patches (PPL) and intestinal epithelium (IEL) were isolated. The expression of different antigens (CD3, CD4, CD8alpha, CD8beta, CD22 and CD45R) in those lymphocyte populations was analyzed by flow cytometry. The percentages of cells expressing T-cell antigens, such as CD3, were significantly higher in LPL during weaning compared to d 0. The percentages of cells expressing CD8alpha and CD8beta increased in both IEL and LPL. However, the percentage of CD4+ cells tended (P = 0.07) to decrease in IEL and to increase in LPL. The percentages of cells expressing B-cell antigens, such as CD22 or CD45R in PPL increased. Changes in the specific phenotypes of intestinal lymphocyte populations at weaning are apparently related to the maturation of the intestinal immune system during early life. Thus, B cells increase in PPL and T cell increase in IEL and LPL.

Dietary gangliosides positively modulate the percentages of Th1 and Th2 lymphocyte subsets in small intestine of mice at weaning

We studied the influence of dietary gangliosides on the number of spontaneous cytokine-secreting cells from two intestinal lymphocyte populations: lamina propria lymphocytes and Peyer's patches lymphocytes in Balb/c mice for 28 days after weaning. Weanling mice were separated into two groups, designated as Control and BG. The Control group was fed with a semipurified diet without gangliosides and the BG group was fed with the semipurified diet supplemented with 47 mg/kg of a mixture of bovine brain gangliosides. Intestinal lymphocytes were isolated from mice killed at 3, 7, 14 and 28 days after weaning, and the percentages of spontaneous Th1 as well as Th2 cytokine-secreting lymphocytes were determined using the ELISPOT assay. The BG group animals showed an earlier development in the number of cytokine-secreting cells, which appeared one week later in Control animals. In addition, mice fed with the ganglioside-supplemented diet showed a significantly higher number of Th1 and Th2 cytokine-secreting lymphocytes than Control mice in lamina propria and Peyer's patches lymphocytes at the end of the experimental period (28 days). Our results suggest that dietary gangliosides influence the maturation process of the intestinal immune system that take place during weaning.

Development of immune function in the intestine and its role in neonatal diseases

This review has traced the ontogeny of the human mucosal immune system, speculating that appropriate gut immune responses are essential in preventing many significant neonatal enteric diseases. Because the gastrointestinal tract serves as the portal of entry for many potential antigens, its mucosal immune function is essential in controlling antigenic responses and ensuring systemic tolerance. A thorough under standing of the development of the entire immune system is essential in defining intestinal mucosal immune function. From the protective barrier covering the enterocyte to the intraepithelial T lymphocytes, these components work together to limit antigen passage from the gut lumen to the underlying immune cells and, thus, promote normal immunity and tolerance. When abnormalities exist or when this immune barrier has not matured fully, conditions afflicting newborns, especially preterm infants, occur. Necrotizing enterocolitis, milk-protein enteropathy, and enteric bacterial infections are only three clinical examples of how aberrant gut immune-mediated defenses may have a significant role in their pathogenesis. In clinical practice, it is not only important to recognize these conditions at their onset but also to understand the basis for the underlying illness and identify newborns who are at an increased risk of acquiring them.

Uptake of ferritin by follicle-associated epithelium in the colon of calves

Uptake of macromolecules (e.g., ferritin) by M cells in follicle-associated epithelium in small and large intestine was investigated in three healthy, conventionally raised, 2- to 3-week-old, female Holstein Frisian calves. A 2.5% solution of ferritin was injected into the ligated loops in mid-jejunum, in terminal ileum, in the ascending colon adjacent to the ileocecal junction, and in the proximal loop of the ascending colon containing gut-associated lymphoid tissue. After exposure times that ranged from 82 to 165 minutes, ferritin was detected in M cells of domes in the small intestine, as well as in cells in follicle-associated epithelium of proprial lymphoid nodules and lymphoglandular complexes of colon that morphologically resembled M cells of small intestine. Ferritin was found in apical invaginations, apical vesicles, multivesicular bodies, basal vesicles, and adjacent intercellular spaces. In addition to ferritin, apical vesicles, multivesicular bodies, and intercellular spaces contained 50-nm membrane-bound particles. More ferritin was endocytosed by M cells of the small intestine than by M cells of the large intestine. In the large intestine, higher amounts of ferritin were found in M cells of follicle-associated epithelium overlying proprial lymphoid nodules than in M cells of follicle-associated epithelium in the depth of lymphoglandular complexes. Based on these results, we concluded that M cells of follicle-associated epithelium in the colon of calves provide a route for antigen uptake into the intestinal lymphoid system.

Mast cells and multiple sclerosis: a light and electron microscopic study of mast cells in multiple sclerosis emphasizing staining procedures

In the brains of 7 patients with multiple sclerosis, mast cells were observed within the demyelinated plaques, in the border zone of the plaques as well as in seemingly normal white matter. The cells were mostly located in close connection with small vessels. The routine staining with toluidine blue for the demonstration of mast cells is not adequate as compared with staining of similar sections in pinacyanol erythrosine. Mast cells may be a hitherto underestimated contributor to the demyelinating process of multiple sclerosis.

The tissue distribution of Ia- and IgM-positive cells in adult and newborn miniature pigs

Distribution of Ia- and IgM-positive cells was compared in tissues of adult and newborn miniature pigs, using indirect immunoperoxidase and immunofluorescent techniques with monoclonal antibodies. The different distribution patterns were found mainly in adult jejunum and kidney. Both IgM- and Ia-staining were ascertained in the lamina propria between the Lieberkühn crypts and in the lymphoid follicles of the jejunum. Moreover, IgM-positive cells were demonstrated in the crypts while Ia-reaction was seen in the lamina propria of the villi. In the kidney, IgM-staining was limited to the glomeruli. On the contrary, a distinct Ia-reaction was found mainly in intertubular structures. Small differences in IgM- and Ia-positive cell distribution were also noted in the mesenteric lymph nodes and in the spleen. Developmental changes of the adult distribution patterns (chiefly that of IgM-positive cells) were found in all tissues studied at 2 days of age.

The enteric immune response to shigella antigens

Mucosal immunity to some enteropathogens occurs naturally following infection. By learning how to optimize initiation of the mucosal immune response it will be possible to develop vaccines against a wide variety of enteropathogens and their toxic products. In the past few years, we have examined stimulation of the mucosal response to Shigella antigens. We have found that the mucosal memory response to Shigella LPS can be stimulated by oral immunization with live, but not with killed Shigella. This primes specific B lymphocytes which, following rechallenge, quickly migrate from the Peyer's patches to mesenteric lymph nodes, the spleen, and back to the Peyer's patches. We have found that the uptake of S. flexneri is the initial step in developing a mucosal immune response to Shigella. Whereas there is little difference between the initial uptake of virulent and avirulent bacteria by M cells, pathogenic strains of Shigella are able to replicate following their uptake by the specialized M cells located in the follicle-associated epithelium of the gut. This likely serves as the source of the ulcerative lesions found in dysentery. Lastly, we have detected a vigorous secretory IgA response to Shiga toxin. The titer of IgA activity to Shiga toxin from these loop secretions correlated well with the ability to prevent Shiga toxin cytotoxin effects in vitro. The extremely vigorous mucosal immune response to Shiga toxin makes this an attractive alternative to cholera toxin to potentiate the secretory IgA immune response.

Human Peyer's patches: lympho-epithelial relationships and characteristics of immunoglobulin-producing cells

Human Peyers patches (PP) were studied by immunohistochemistry to characterize functional properties of the follicle-associated epithelium (FAE) including the "membrane" (M) cells. The FAE had no transporting capacity for polymeric IgA (pIgA) because it did not express the secretory component (SC) which acts as a pIgA receptor. However, it expressed MHC class II (HLA-DR) determinants, except for the M cells (which were tentatively identified by absence of brush border alkaline phosphatase). It is possible, therefore, that the FAE generally performs class II-restricted transport and presentation to T cells of antigens which have been adequately processed in the gut lumen. The function of M cells may be limited to transport of particulate or undegraded antigens to subjacent macrophages for processing and subsequent presentation. There were significantly more intra- and subepithelial T cells in PP than in distant villi, and the T cells were concentrated adjacent to M cells. The proportion of the CD4+ phenotype (putative helper T cells) was much higher in FAE (approximately 40%) than in villous epithelium where the CD8+ (putative suppressor) phenotype predominated strikingly (approximately 90%). This disparity might reflect differences in capacity for positive and negative immune regulation at the two sites. The B cells terminating with Ig production in PP and adjacent to solitary lymphoid follicles apparently belonged to relatively mature memory clones as they showed a large proportion of IgG immunocytes and reduced J-chain expression. Conversely, both IgG and IgA immunocytes in lamina propria (LP) showed a high percentage of J-chain positivity (80-100%); such positivity was also considerable (45-60%) in mesenteric lymph nodes (MLN) in contrast to peripheral lymph nodes (PLN) and palatine tonsils (PT). Moreover, there was a decreasing percentage of IgA2 immunocytes in the order of PP (52%), distant ileal LP (40%), MLN (32%), PLN (11%), and PT (5%). Taken together, our results suggested that dissemination of relatively immature memory B-cell clones with high J-chain expression takes place from PP through MLN and that preferential settlement of such clones occurs in LP.

A major peritoneal reservoir of precursors for intestinal IgA plasma cells

Studies presented examine the origin of IgA plasma cells in B lineage chimeric mice constructed by reconstituting lethally irradiated mice with a mixture of syngeneic bone marrow cells and peritoneal cells from Ig heavy chain allotype congenic donors. In these mice, essentially all B cells in spleen and Peyer's patches are derived from the bone marrow donor; however Ly-1 B lineage cells which have been mainly detected in the peritoneum are derived from the peritoneal cell donor. Surprisingly, roughly half of the IgA plasma cells in the lamina propria of the gut are also derived from the peritoneal cell donor, suggesting an important role for peritoneally-derived B cells in the mucosal immune response.

Lymphoepithelial interactions in the mucosal immune system

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Gastrointestinal food allergy and its role in large domestic animals

The significance of food allergy as a primary cause for gastrointestinal disturbances in domestic animals, especially calves and piglets, is discussed. The immunological backgrounds and pathogenesis are described in some detail. The clinical and pathological manifestations in animals are related to those in man. Diagnostic possibilities, therapy and prevention, as far as known in animals, are mentioned and, based on human experiences, further extensions are proposed.

Immunobarriers of the mucosa of the upper respiratory and digestive pathways

The mucosa that lines the upper respiratory and digestive pathways is protected by a secretory immune system which is under complex and only partly understood immunoregulatory control. B cells of relatively immature memory clones with a potential for J-chain expression, are initially stimulated in mucosa-associated lymphoid tissue (probably including the tonsils) and migrate thereafter through lymph and blood to glandular sites where they are subjected to terminal differentiation and become immunoglobulin (Ig)-producing immunocytes. Most locally produced Ig is normally dimeric IgA which is selectively transported through the serous type of glandular cells by means of an epithelial receptor protein called the secretory component (SC). IgM is also subjected to SC-mediated transport. In patients with selective IgA deficiency, secretory IgA is lacking, but may be satisfactorily replaced by protective secretory IgM. In other IgA-deficient patients, however, immunoregulatory compensation gives rise to a large number of IgD-producing cells in respiratory mucosa. IgD cannot act as a secretory antibody and these patients are prone to have recurrent infections. These observations show that there are large individual variations in the secretory immune system.

Cryptosporidiosis and the follicle-associated epithelium over the ileal Peyer's patch in calves

Three calves were studied in stages of spontaneous cryptosporidial infection with particular reference to the relation of the cryptosporidia to the follicle-associated epithelium (fae) over the ileal Peyer’s patch (ipp). In early infection scanning electron microscopy and streptavidin immunoperoxidase staining showed marked predilection of cryptosporidia for the fae. Cryptosporidial antigen was also found in subepithelial tissue, both in the domes over the ipp and in villi, apparently in macrophages, where the parasites seemed to be progressively degraded. The fae showed long tightly spaced microvilli, replacing normal low folds and protrusions, particularly in late infection. Endocytosis of indian ink was restricted to the cell periphery in late infection, contrasting the normal, more even distribution of endocytosis in the fae apical cytoplasm. Few parasites were seen in the intestinal mucosa at this stage. At convalescence the fae was normal, but all stages of infection were characterised by elongation of microvilli in absorptive cells.

HLA-DR expression, natural killer cells and IgE containing cells in the jejunal mucosa of coeliac children

The expression of HLA-DR by surface and crypt epithelium and the numbers of cells of natural killer (NK) phenotype and of IgE containing cells were studied with monoclonal antisera using the peroxidase technique. We examined 48 jejunal biopsy specimens taken from 35 coeliac children before treatment (11), during gluten free diet (20) and after gluten challenge (17), and 13 control specimens. The luminal surface of the epithelial cells stained with HLA-DR antiserum in all specimens, but the cytoplasm of the surface epithelial cells took up the stain more frequently in the specimens from the controls (5/13) than those from the coeliacs (2/48) (p less than 0.01). In 21/28 specimens taken from coeliacs when on a gluten containing diet the crypt epithelium showed strong HLA-DR expression, while only 4/20 (p less than 0.01) specimens of coeliacs on a gluten free diet and 1/13 specimens of controls had similar staining. Among the intraepithelial lymphocytes no cells of NK phenotype were found in specimens from patients or controls. As compared with control specimens biopsy specimens from untreated coeliac patients showed smaller numbers of NK cells in the lamina propria. No difference was found in the numbers of IgE containing cells between the patients and controls. The strong expression of HLA-DR by the crypt epithelial cells in coeliac children on a normal diet suggest that these cells are involved in the presentation of the antigen.

The anatomical basis for the immune function of the gut

The barrier function of the gut wall can be divided into different histotopographically defined lines of defence. These consist not only of lymphoid cells but also of goblet cells, entero-endocrine cells, macrophages and mast cells. Subsets of lymphoid cells are found preferentially within the epithelium (T suppressor) or in the lamina propria (T helper). Most plasma cells produce IgA. Peyer's patches are described in detail as typical organized lymphoid structures of the gut. In man, they are present well before birth and are found in large numbers even in old age. They are not only typical for the ileum but are also present in the duodenum and jejunum. The four compartments in Peyer's patches, i.e. follicle, corona, interfollicular area and the dome, are defined by the typical localization of lymphocyte subsets and by their different functions. Typical features of the epithelium of the dome are the lack of villi and goblet cells and the presence of specialized epithelial cells (M cells) which are important for the uptake of particulate antigen from the gut lumen. Precursor cells of IgA producing plasma cells leave the intestinal wall via the lymphatics and return preferentially to the gut mucosa, and this is summarized by the term gut-associated lymphoid tissue (GALT). Other organs with mucous membranes, such as mammary and salivary glands, bronchial and genital tract, are also included in this circulatory route and this is expressed by the term mucosa-associated lymphoid tissue (MALT). Mast cells in the gut mucosa can be classified as connective tissue or mucosa mast cells. These differ in their sensitivity to formaldehyde as a fixative, contain different granules and mediators, have different origins, and show major differences in the effectiveness of antiallergic compounds on the stabilizing of the cell membrane. Mucosa mast cells have also been demonstrated in the human gut. The histotopographical relationship of many cell types such as goblet and M cells in addition to cells of the immune system such as lymphoid cells, macrophages and mast cells, is essential in the understanding of the barrier function of the gut wall.

Helminth-induced intestinal inflammation

Gastrointestinal inflammation is a prominent feature of protective reactions in animals immune against helminths. Infiltration into the inflamed mucosa of various cells and their subsequent activation result in the elaboration of an array of pharmacologically and biologically active substances. The release of mediators is also associated with alterations in the epithelial layer. Furthermore, increased smooth muscle reactivity and enhanced secretory function of the mucosal tissue contribute to the development of an unfavourable environment and lead to worm expulsion. Mediators elaborated from inflammatory cells, whether associated with cell granules (i.e., preformed) or de novo-generated from membrane phospholipids, possess a number of potent vasoactive and spasmogenic properties which may contribute to events leading to worm elimination. The lipoxygenase metabolites of arachidonic acid (leukotrienes) derived from cell membranes probably contribute to the state of intestinal hypersensitivity against helminths. The measurement of elevated levels of these lipid mediators following worm challenge of immune, but not control, rats suggests that leukotrienes may play a role in amplifying and augmenting the inflammatory process associated with worm expulsion.