Lymphoepithelial interactions in the mucosal immune system

Targeting Leukocyte Trafficking in Inflammatory Bowel Disease

In the last two decades, understanding of inflammatory bowel disease (IBD) immunopathogenesis has expanded considerably. Histopathological examination of the intestinal mucosa in IBD demonstrates the presence of a chronic inflammatory cell infiltrate. Research has focused on identifying mechanisms of immune cell trafficking to the gastrointestinal tract that may represent effective gut-selective targets for IBD therapy whilst avoiding systemic immunosuppression that may be associated with off-target adverse effects such as infection and malignancy. Integrins are cell surface receptors that can bind to cellular adhesion molecules to mediate both leukocyte homing and retention. In 2014, Vedolizumab (Entyvio^®) was the first anti-integrin (anti-α4ß7 monoclonal antibody) treatment to be approved for use in IBD. Several other anti-integrin therapies are currently in advanced stages of development, including novel orally administered small-molecule drugs. Drugs targeting alternative trafficking mechanisms such as mucosal addressin cellular adhesion molecule-1 and sphingosine-1-phosphate receptors are also being evaluated. Here, we summarise key established and emerging therapies targeting leukocyte trafficking that may play an important role in realising the goal of stratified precision medicine in IBD care.

Gut-Selective Integrin-Targeted Therapies for Inflammatory Bowel Disease

Integrins are cell surface receptors with bidirectional signalling capabilities that can bind to adhesion molecules in order to mediate homing of leukocytes to peripheral tissues. Gut-selective leukocyte homing is facilitated by interactions between α4β7 and its ligand, mucosal addressin cellular adhesion molecule-1 [MAdCAM-1], while retention of lymphocytes in mucosal tissues is mediated by αEβ7 binding to its ligand E-cadherin. Therapies targeting gut-selective trafficking have shown efficacy in inflammatory bowel disease [IBD], confirming the importance of leukocyte trafficking in disease pathobiology. This review will provide an overview of integrin structure, function and signalling, and highlight the role that these molecules play in leukocyte homing and retention. Anti-integrin therapeutics, including gut-selective antibodies against the β7 integrin subunit [etrolizumab] and the α4β7 integrin heterodimer [vedolizumab and abrilumab], and the non-gut selective anti-α4 integrin [natalizumab], will be discussed, as well as novel targeting approaches using small molecules.

Invited review: Enteric bacteria, lipopolysaccharides and related cytokines in inflammatory bowel disease: biological and clinical significance

Ulcerative colitis (UC) and Crohn's disease (CD) [inflammatory bowel disease (IBD)] are both characterized by an exaggerated immune response at the gut associated lymphoreticular tissue level. Such an abnormal and dysregulated immune response may be directed against luminal and/or enteric bacterial antigens, as also supported by murine models of inflammatory bowel disease (IBD) caused by organisms such as Citrobacter rodentium and Helicobacter hepaticus.

Bacterial endotoxins or lipopolysaccharides (LPS) have been detected in the plasma of IBD patients and an abnormal microflora and/or an increased permeability of the intestinal mucosa have been invoked as cofactors responsible for endotoxemia. At the same time, the evidence that phagocytosis and killing exerted by polymorphonuclear cells and monocytes and the T-cell dependent antibacterial activity are decreased in IBD patients may also explain the origin of LPS in these diseases.

In IBD, pro-inflammatory cytokines and chemokines have been detected in elevated amounts in mucosal tissue and/or in peripheral blood, thus suggesting a monocyte/macrophage stimulation by enteric bacteria and/or their constituents ( e.g. LPS).

On these grounds, in experimental models and in human IBD, anti-cytokine monoclonal antibodies and interleukin receptor antagonists are under investigation for their capacity to neutralize the noxious effects of immune mediators. Finally, the administration of lactobacilli is beneficial in human IBD and, in murine colitis, this treatment leads to a normalization of intestinal flora, reducing the number of colonic mucosal adherent and translocated bacteria.

Adaptive immune responses during Shigella dysenteriae type 1 infection: an in vitro stimulation with 57 kDa major antigenic OMP in the presence of anti-CD3 antibody

An effort was made to understand the role of the 57 kDa major antigenic fraction of Shigella outer membrane protein (OMP) in the presence of T-cell antigen receptor in activation of adaptive immune responses of the cell mediated immune (CMI) restored patients. The expression of HLA-DR/CD4 out of CD3(+) T-cells was significantly dominant over the HLA-DR/CD8 and comparable to unstimulated cells of infected or healthy controls. CD4(+) T-cell activation together with HLA-DR is associated with the expression of CD25(+) (IL2Ralpha) for IL-2 growth factors with decreased IL-4 levels, required for maintaining the homeostasis of CD4(+) T cell. Furthermore, the positive expression of the CD45 antigen is possibly required for acquiring the memory for CD4(+) cells signals and facilitates the interaction with CD54 antigen. As a result, antigen-specific secondary signal is generated for B-cell activation to produce IgG2a and IgG2b. This suggests that antibody mediated-adaptive immune responses are generated due to anti-CD3 induced helper T-cell activity. The above mentioned findings reflect that the antigen alone might not exacerbate the selective T-cell responses. But these antigens in the presence of anti-CD3 antibody might help to elicit adaptive immune response via T-cell receptor (TCR) activation.

Effects of early enteral glutamine supplementation on lymphocyte subpopulations in Peyer's patches in scalded rats

AIM: To investigate the changes in the number of total lymphocytes and each lymphocyte subpopulation in Peyer's patches in scalded rats receiving different nutrition support, and examine the effects of glutamine (Gln) supplementation on intestinal immunity.

METHODS: Healthy adult Sprague-Dawley rats were subjected to a 30% TBSA third-degree scald injury to induce scald injury. Scalded rats were randomly divided into standard enteral nutrition group (EN group) and glutamine supplementation group (EN plus Gln group). Rats in the EN group were fed standard enteral nutrition (Nutrison Multi Fibre) while those in the EN plus Gln group were fed standard enteral nutrition plus Gln. The number of total lymphocytes and each lymphocyte subpopulation in Peyer's patches were then determined by flow cytometry on days 1, 4, 7 and 10 after feeding.

RESULTS: The number of total lymphocytes, especially B lymphocytes, in Peyer's patches significantly decreased in response to scald induction. The number of total lymphocytes in Peyer's patches in rats in the EN plus Gln group, but not in the EN group, returned to normal on day 7 after scald induction [(5.29 ± 1.03) × 10⁶vs (6.13 ± 1.14) × 10⁶, P > 0.05]. The total number of B cells in Peyer's patches in rats in the EN plus Gln group on days 7 and 10 showed no significant changes when compared with pre-induction value [(2.87 ± 0.69) × 10⁶ and (3.05 ± 0.72) × 10⁶vs (3.29 ± 0.62) × 10⁶, respectively; both P> 0.05]. In contrast, the total number of B cells in Peyer's patches in rats in the EN group on day 10 was significantly lower than pre-induction value [(2.07 ± 0.63) × 10⁶vs (3.29 ± 0.62) × 10⁶; P < 0.05]. Scald induction had no significant effect on the number of CD4⁺ and CD8⁺ lymphocytes (both P > 0.05).

CONCLUSION: The number of total lymphocytes decreases significantly in response to scald induction. Early enteral glutamine supplementation can promote lymphocyte proliferation, increase the number of total lymphocytes (especially B cells) in Peyer's patches, and enhance intestinal immunity in scalded rats.

Transepithelial transport and mucosal defence I: the role of M cells

How do cells of the immune system encounter the majority of antigens that enter the body through the gut and airways? The epithelia lining these systems contain a remarkable cell type, the M cell, that delivers antigens across the epithelium to lymphocytes and macrophages. In this article, Marian Neutra and Jean-Pierre Kraehenbuhl describe the structure of the M cell, its function in promoting the immune response and its exploitation by invading pathogens. In the next issue of Trends in Cell Biology, these authors will review the other immunological function of epithelia, secretion of polymeric IgA.

Delayed viral replication and CD4+ T cell depletion in the rectosigmoid mucosa of macaques during primary rectal SIV infection

Rectal infection of macaques by SIV is a model for rectal HIV transmission. We focus here on the digestive tract during days 7-14 of primary rectal infection by SIV in 15 rhesus macaques. Surprisingly, we did not detect productively infected cells in the rectosigmoid colon at early stages of viral dissemination. This strongly suggests that there is no massive viral amplification in the rectosigmoid colon prior to viral dissemination. As dissemination proceeds, productively infected T cells are observed in the rectosigmoid colon and small intestine, with rectosigmoid colon showing the heaviest viral load. Lymphoid follicles are infected prior to lamina propria at both sites. When viral dissemination is widespread, inflammatory infiltrates are visible in the rectosigmoid colon, but not in the small intestine. An important decrease in CD4(+) T cells is then observed in the lamina propria of the rectosigmoid colon only.

Systemic and mucosal antibody responses following retroductal gene transfer to the salivary gland

Gene transfer to salivary glands by retrograde perfusion of the salivary duct has been shown to result in production of the encoded protein. We sought to determine if this technique would be useful for genetic immunization. In studies that compare delivery of DNA to either the salivary gland (SG) or muscle (im), mean plasma IgG and IgA titers obtained following SG delivery were 46- and 86-fold greater, respectively, than those following im delivery. We also tested the hypothesis that SG vaccination could generate mucosal responses in sites proximal and distal to DNA administration. SG-treated animals produced specific antibodies within saliva, vaginal fluid, and lung washes as well as demonstrating robust specific responses in Peyer's patches. In a test of functional immunity, animals vaccinated with DNA by SG retrograde perfusion were significantly more resistant to the effects of lethal anthrax challenge than im DNA-vaccinated animals. These data suggest that SG genetic immunization may offer advantages over conventional routes of vaccination.

High-throughput gene expression profiling indicates dysregulation of intestinal cell cycle mediators and growth factors during primary simian immunodeficiency virus infection

During primary simian immunodeficiency virus (SIV) infection, CD4+ T cells are severely depleted in gut-associated lymphoid tissue (GALT), while CD8+ T-cell numbers dramatically increase. To gain an understanding of the molecular basis of this disruption in T-cell homeostasis, host gene expression was monitored in longitudinal jejunum tissue biopsies from SIV-infected rhesus macaques by DNA microarray analysis. Transcription of cyclin E1, CDC2, retinoblastoma, transforming growth factor (TGF), fibroblast growth factor (FGF), and interleukin-2 was repressed while cyclins B1 and D2 and transcription factor E2F were upregulated, indicating a complex dysregulation of growth and proliferation within the intestinal mucosa. Innate, cell-mediated, and humoral immune responses were markedly upregulated in animals that significantly reduced their viral loads and retained more intestinal CD4+ T cells. We conclude that the alterations in intestinal gene expression during primary SIV infection were characteristic of a broad-range immune response, and reflective of the efficacy of viral suppression.

Innate immunity and the gut

The intestinal epithelium encounters a unique environment consisting of microbes, both commensals and pathogens, as well as dietary nutrients and antigens. This complex composition necessitates the presence of a dynamic system of defense to contain both pathogenic and commensal bacteria within the lumen yet allow for nutrient absorption. Tight junctions provide protection of the intercellular spaces while other surface molecules, such as intestinal trefoil factor, help to maintain the structural integrity of the epithelium. Other more active processes, including upregulated expression and activation of antimicrobial peptides and enhanced fluid secretion, provide a second level of innate defense. Despite providing the interface between an exuberant immune system and a highly antigenic lumenal environment, the intestinal epithelium must remain quiescent. As such, several novel antiinflammatory mechanisms were recently identified. Studies that elaborate the various aspects of these pathways are discussed in this review.

Saccharomyces boulardii stimulates sIgA production and the phagocytic system of gnotobiotic mice

The effect of Saccharomyces boulardii on the immune system was evaluated, comparing germ-free Swiss/NIH mice monoassociated with the probiotic with germ-free mice. Saccharomyces boulardii colonized the gut of germ-free mice and survived the gastrointestinal conditions. An increase in sIgA production, both total and anti-S. boulardii, was observed in the intestinal contents of monoassociated mice when compared with germ-free controls. The number of Kupffer cells was significantly higher in monoassociated mice than in germ-free controls. In S. boulardii-monoassociated mice, clearance of Escherichia coli B41 was higher than in germ-free controls. TNF-alpha, IFN-gamma and IL-12 serum levels were higher at earlier time points in monoassociated mice when compared with germ-free mice. These results show that the yeast S. boulardii modulates the host immune responses. This effect may be of interest for improving the resistance to enteropathogenic bacterial infections.

Total parenteral nutrition alters molecular and cellular indices of intestinal inflammation in neonatal piglets

BACKGROUND

The adverse effects of TPN on systemic immunity are well-documented; however, the impact of IV feeding on neonatal intestinal immunity is unknown.

METHODS

A piglet TPN model was used to compare immune cell composition within the intestinal epithelium and lamina propria of parenterally and orally fed piglets.

RESULTS

Small intestinal weight of piglets maintained intravenously was reduced 50% after 7 days. Intestinal atrophy in piglets fed parenterally was evidenced by decreased width of intestinal villi and colon cuffs and reduced intestinal crypt depth. The numbers of CD4+ and CD8+ T lymphocytes were threefold greater within the lamina propria of jejunal and ileal villi of piglets supported intravenously. Inverse correlations were observed between villus height or width and T-lymphocyte numbers (r = -.80; p < .05). Major histocompatibility complex class II mRNA expression, an indicator of localized inflammation, was increased in the ileum and colon of piglets receiving parenteral nutrition. Goblet cell numbers were two-fold greater in jejunal and ileal villi, and mast cells were more abundant in the colon of piglets fed parenterally. Furthermore, jejunal T-lymphocyte numbers were correlated with goblet cell numbers (r = .80; p = .01).

CONCLUSIONS

These data identify molecular and cellular indices of intestinal inflammation that are responsive to IV feeding in neonates and provide a novel framework to investigate mechanisms underlying gut atrophy during TPN.

Cytokine mRNA expression in lymphoid organs associated with the expression of IgA response in the rat

The T-helper dependency of the IgA antibody response has been investigated in rats injected intravenously with Schistosoma mansoni eggs. This method, allowing the trapping of parasite eggs in the lung tissue, led to a strong anti-egg IgA antibody response in the bronchoalveolar lavage but not in the serum. To characterize the cytokine pattern associated with the IgA response, kinetic analysis of the cytokine mRNA expression in the lungs, periaortic nodes (PN) and spleen was undertaken. Under such conditions, significant levels of mRNA encoding IL-5 and IL-10 were recorded in spleen during the early period following egg injection, as well as a more prolonged expression of TGF-beta and IL-6 mRNAs. However, neither IFN-gamma nor IL-4 mRNA could be detected in these samples. Finally, in lungs and in PN, RT-PCR analysis revealed delayed production of cytokine mRNA. Taken together our data suggest that the rat mucosal IgA antibody response is predominantly linked to a Th2 response.

Immune control of Chlamydial growth in the human epithelial cell line RT4 involves multiple mechanisms that include nitric oxide induction, tryptophan catabolism and iron deprivation

The antimicrobial activity of T cell-derived cytokines, especially interferon (IFN)-gamma, against intracellular pathogens, such as Chlamydia trachomatis, involves the induction of 3 major biochemical processes: tryptophan catabolism, nitric oxide (NO) induction and intracellular iron (Fe) deprivation. Since the epithelial cell is the natural target of chlamydial infection, the presence of these antimicrobial systems in the cell would suggest that they may be involved in T cell control of intracellular multiplication of Chlamydia. However, the controversy over whether these 3 antimicrobial processes are present in both mice and humans has precluded the assessment of the relative contribution of each of the 3 mechanisms to chlamydial inhibition in the same epithelial cell from either mice or humans. In the present study, we identified a Chlamydia-susceptible human epithelial cell line, RT4, that possesses the 3 antimicrobial systems, and we examined the role of nitric oxide (NO) induction, and deprivation of tryptophan or Fe in cytokine-induced inhibition of chlamydiae. It was found that the 3 antimicrobial systems contributed to cytokine-mediated inhibition of the intracellular growth of Chlamydia. NO induction accounted for approximately 20% of the growth inhibition; tryptophan catabolism contributed approximately 30%; iron deprivation was least effective; but the combination of the 3 systems accounted for greater than 60% of the inhibition observed. These results indicate that immune control of chlamydial growth in human epithelial cells may involve multiple mechanisms that include NO induction, tryptophan catabolism and Fe deprivation.

Migration of intestinal intraepithelial lymphocytes into a polarized epithelial monolayer

Intraepithelial lymphocytes (IEL) are a phenotypically distinct population of lymphocytes that reside in mucosal epithelia, below the intercellular tight junctions. Although adhesive functions of this population have been previously studied, relatively little is known about IEL migration from the microvasculature into the epithelium. We demonstrated that cultured human IEL were capable of migration into polarized epithelial cells in vitro, where they assumed a subjunctional position, identical to that observed in vivo. The migration was rapid and efficient and was directionally polarized, such that IEL migrated into epithelial monolayers from the basolateral, but not the apical, aspect. After a 4-h period of residence, up to one-half of the IEL then exited the monolayer basolaterally. Migration was partially inhibited by pertussis toxin, suggesting a potential mechanism for IEL migration by chemokine receptor-mediated signaling. The conditions and ligand pairs used in IEL migration were different from those for neutrophils, another cell type known to migrate through epithelia. This system may serve as a model for microenvironmental homing of IEL into the epithelium.

Inflammatory bowel disease. 1. Origins, presentation, and course

The exact cause of inflammatory bowel disease remains undiscovered, but its destructive nature is clearly recognized. In this article, the authors summarize what is known about the pathogenesis and epidemiology of ulcerative colitis and Crohn's disease and how to distinguish between the two, both clinically and pathologically. They also describe disorders that may mimic inflammatory bowel disease. In part 2 of this article, beginning on page 86, the authors discuss some of the therapeutic options that are the commonly used as well as some that are investigational but show promise for patients with this chronic and relapsing disease.

Postnatal development of lymphocyte subpopulations in the intestinal mucosa in goat

The incidence and location of CD2+, CD4+, CD8+ and gamma/delta T-lymphocytes and B-lymphocytes were studied in the intestinal mucosa in goats of one week, one month, three months and seven months old, using monoclonal antibodies and immunohistochemical methods. At all ages CD2+ lymphocytes were the major subpopulation in the intestinal mucosa, more numerous in the small than in the large intestine and in the villi than in the crypt region. In one week-old animals most of CD2+ lymphocytes were scattered in the lamina propria and the number of lymphocytes that expressed CD4 was less than those that expressed CD8, resulting in a CD4/CD8 ratio less than 1. CD2+ lymphocytes increased markedly until one month old, with a higher increase of CD4+ subpopulation than CD8+ with an inversion of the CD4/CD8 ratio. CD4+ lymphocytes were localised in the lamina propria forming clusters, whereas CD8+ lymphocytes were scattered peripherally under the epithelium and in older animals from three month old, CD8+ lymphocytes were also abundant between epithelial cells. The gamma/delta T-lymphocytes recognised with the mAb CACTB6A represented a minor subpopulation located between epithelial cells or in the lamina propria, no evident changes were observed with age. IgM+ cells were a minor subpopulation in all animals (never higher than 1 cell per 1500 microns-2) located in the crypt region of the lamina propria.

Enteral nutrition modifies gut-associated lymphoid tissue in rat regardless of the molecular form of nitrogen supply

BACKGROUND

It has been suggested that beneficial effect of elemental enteral diets in the treatment of inflammatory bowel diseases could be mediated by the suppression of protein dietary antigens. The objective of the present work was to study the effect of enteral diet on gut associated lymphoid tissue and on gastric Lactobacillus flora, in rat.

METHODS

The effects of three molecular forms of nitrogen supply: amino acids, oligopeptides or whole casein, were compared in rats on continuous enteral diet. Frozen sections of small bowel were studied with monoclonal antibodies anti-CD5, -CD4, -CD8, -CD25, -macrophages, -MHC II. The Lactobacillus flora was also enumerated in the stomach, in order to assess the effect of ED on rat flora.

RESULTS

Growth and mucosa morphology were identical in control and enteral groups. Rats on enteral diet showed, whatever was the molecular form of nitrogen supply, a decrease in CD5+, CD4+ and CD8+ intraepithelial cell numbers, but not in lamina propria cell number, and a decreased MHC II epithelial expression, when compared to control rats. The enterally fed rats also showed a decrease in Lactobacillus gastric contents.

CONCLUSIONS

The current study demonstrates that continuous enteral nutrition modifies MHC II epithelial expression and gut associated lymphoid tissue cell number in rat, whatever is the molecular form of nitrogen supply. Intestinal flora could be responsible, at least for part, for these results.

Experimental autoimmune uveitis: molecular mimicry and oral tolerance

Intraocular inflammatory disease or uveitis, which affects the uveal tract and the retina of the eyes in human, is the major cause of visual impairment. Experimental autoimmune uveitis (EAU) is a T-cell-mediated autoimmune disease directed against retinal proteins and has been studied in several mammalian species including subhuman primates as a model for human posterior uveitis. Autoimmune responses provoked by molecular mimicry occur when the nonself and host determinants are similar enough to cross-react yet different enough to break immunological tolerance, and is one of the proposed mechanisms for induction of autoimmune diseases. Therapeutic immunomodulatory strategies have been used to induce antigen-specific peripheral immune tolerance in animal models of T-cell-mediated autoimmune diseases by oral administration of autoantigens. Oral tolerance leads to unique mechanisms of tissue and disease-specific immunosuppression, which would circumvent the immunotherapeutic problem of multiple target tissue autoreactivity. Several groups have investigated the effects of delivering autoantigens across gastric mucosal surfaces. This review briefly discusses molecular mimicry and the mechanism of induction of oral tolerance with respect to immunopathogenesis of T-cell-mediated autoimmune disease in general and EAU in particular.

Alterations of the mucosal immune system in inflammatory bowel disease

The normal intestinal immune system is under a balance in which proinflammatory and anti-inflammatory cells and molecules are carefully regulated to promote a normal host mucosal defense capability without destruction of intestinal tissue. Once this careful regulatory balance is disturbed, nonspecific stimulation and activation can lead to increased amounts of potent destructive immunologica and inflammatory molecules being produced and released. The concept of balance and regulation of normal mucosal immune and inflammatory events is indicative of how close the intestine is to developing severe inflammation. The normal intestinal mucosal immune system is constantly stimulated by lumenal contents and bacteria. The stimulatory molecules present in the intestinal lumen that activate and induce subsequent mucosal immunologic and inflammatory events include bacterial cell wall products, such as peptidoglycans and lipopolysaccharides, as well as other chemotactic and toxic bacterial products that are produced by the many different types of bacteria within the gastrointestinal tract. These highly stimulatory bacterial cell wall products are capable of activating macrophages and T lymphocytes to release potent proinflammatory cytokines, including interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-alpha). IL-1, IL-6, and TNF-alpha increase the presence of human leukocyte antigen (HLA) class II antigen-presenting molecules on the surfaces of epithelial cells, endothelial cells, macrophages, and B cells, thus increasing their ability to present lumenal antigens and bacterial products. The proinflammatory cytokines IL-1 and TNF-alpha also increase the ability of epithelial cells, endothelial cells, macrophages, and fibroblasts to secrete potent chemotactic cytokines, such as interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1), which serve to increase the movement of macrophages and granulocytes from the circulation into the inflamed mucosa. Thus, through lumenal exposure to potent, nonspecific stimulatory bacterial products, the state of activation of the intestinal immune system and mucosal inflammatory pathways are markedly up-regulated. This raises the question of whether there is a deficiency in effective down-regulation through the absence of normally suppressive cytokines such as interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), interleukin-4 (IL-4), and IL-1 receptor antagonist. Normally, the turning off of the active and destructive immunologic and inflammatory events should occur following the resolution of a bacterial or viral infection that has been appropriately defended against and controlled by the mucosal immune system. In inflammatory bowel disease (IBD), however, the down-regulatory events and processes that should turn off the immunologic and inflammatory protective processes, once the pathogenic agent has been cleared, appear to be deficient or only partially effective. We may find that we ultimately are dealing with disease processes that have more than one genetic or cellular basis. The improved understanding of the immunopathophysiology of IBD will allow exploration of novel immunologic and genetic approaches, such as gene replacement therapy, administration of a suppressor cytokine or an altered cell surface antigen, the administration of humanized monoclonal antibodies directed against proinflammatory cytokines, or the development of newer strategies against fundamental cell biologic mechanisms such as adhesion molecules.

Antigen sampling across epithelial barriers and induction of mucosal immune responses

Epithelial barriers on mucosal surfaces at different sites in the body differ dramatically in their cellular organization, and antigen sampling strategies at diverse mucosal sites are adapted accordingly. In stratified and pseudostratified epithelia, dendritic cells migrate to the outer limit of the epithelium, where they sample antigens for subsequent presentation in local or distant organized lymphoid tissues. In simple epithelia, specialized epithelial M cells (a phenotype that occurs only in the epithelium over organized lymphoid follicles) deliver samples of foreign material by transepithelial transport from the lumen to organized lymphoid tissues within the mucosa. Certain pathogens exploit the M cell transport process to cross the epithelial barrier and invade the mucosa. Here we review the features of M cells that determine antigen and pathogen adherence and transport into mucosal lymphoid tissues.

Immune functions and immunopathology of the mucosa of the upper respiratory pathways

The specific defence of airway mucosae depends primarily on secretory immunity. The B cells involved are initially stimulated in organized mucosa-associated lymphoid tissue, apparently including the tonsils and adenoid. From these inductive sites, memory cells migrate to secretory effector sites where they differentiate terminally to immunoglobulin (Ig)-producing plasma cells. Locally produced Ig consists mainly of J chain-containing dimers and larger polymers of IgA (pIgA) that are selectively transported through glandular cells by an epithelial receptor called secretory component or the pIg receptor. IgG can participate in immune exclusion because it reaches the secretions by passive diffusion. However, its proinflammatory properties render IgG antibodies of local immunopathological importance when elimination of penetrating antigens is unsuccessful. T helper (Th) cells activated in this process may by a Th2 cytokine profile promote persistent inflammation with extravasation and priming of eosinophils. This development appears to be part of the late-phase allergic reaction, perhaps initially driven by interleukin-4 (IL-4) released from mast cells that are subjected to IgE-mediated activation, and subsequently also by Th2 cell activation. Eosinophils are potentially tissue-damaging, particularly after priming with IL-5. Various cytokines up-regulate adhesion molecules on endothelial and epithelial cells, thereby enhancing migration of eosinophils into the mucosa, and perhaps in addition causing aberrant immune regulation within the epithelium. Soluble antigens bombarding the epithelial surfaces normally seem to induce several immunosuppressive mechanisms, but mucosal homeostasis appears less patent in the airways than oral tolerance to dietary antigens operating in the gut.

The gut associated addressins: lymphocyte homing in the gut

The process of lymphocyte trafficking is mainly regulated by receptors that belong to a group of molecules referred to as adhesion molecules. These molecules can be divided, according to their molecular structure, into three broad families: the integrins; the selectins; and the immunoglobulin superfamily members. The alpha 4 beta 7 integrin is expressed on some lymphocytes with hallmarks of gut tropism. alpha 4 beta 7, among others, serves as a ligand for the mucosal vascular addressin MadCAM-1, which is selectively expressed on mucosal lymphoid organ high endothelial venules and on gut lamina propria venules. It is tempting to believe that related integrin receptors play a crucial role in the recirculation of activated lymphocytes between the gut mucosa and the synovial membrane.

Intestinal immune function is unaffected by parenteral nutrition in man

BACKGROUND

Animal studies have demonstrated intestinal immunoglobulin production is decreased when luminal nutrition is withheld and nutrition is provided solely on the basis of total parenteral nutrition (TPN).

METHODS

Eight normal volunteers were hospitalized in the Clinical Research Center for three weeks. The subjects received TPN as an exclusive means of nutritional support for 14 days followed by 5 days of enteral feeding with either standard or a glutamine- and arginine-supplemented formula in which the protein source was primarily free amino acids and peptides. Endoscopic jejunal biopsies obtained before and after TPN and following enteral refeeding were evaluated by immunofluorescence for the number of IgA, IgM and IgG-producing cells; T and B cells as well as intraepithelial and lamina propria lymphocytes were also counted. Serum immunoglobulins and the molecular forms of serum IgA were determined at the same intervals.

RESULTS

The number of intestinal IgA-, IgM- and IgG-producing cells was unaffected by TPN (676 +/- 58 vs. 643 +/- 38, 101 +/- 14 vs. 98 +/- 18, 10 +/- 1 vs. 11 +/- 2 per low power field). The total number of intestinal lymphocytes, and CD3+ lymphocytes in the intraepithelial area was unaffected by TPN (10.4 +/- 0.4 vs. 10.2 +/- 1.3, 7.3 +/- 0.8 vs. 8.6 +/- 1.6 per 100 epithelial cells). Similarly, the total number of lymphocytes and CD3+ lymphocytes in the intestinal lamina propria was unaffected by TPN (4.4 +/- 0.2 vs. 6.2 +/- 0.8, 3.3 +/- 0.7 vs. 4.5 +/- 0.8). A small, but statistically significant increase in serum IgA and IgM was seen with TPN 314 +/- 11 vs. 342 +/- 16 mg/dL and 154 +/- 25 vs. 226 +/- 47 mg/dL, although IgG remained unchanged (1262 +/- 69 vs. 1207 +/- 57 mg/dL). The proportion of polymeric and monomeric serum IgA remained unchanged after TPN (19.2 vs. 22.1% polymeric).

CONCLUSIONS

The use of TPN is not associated with intestinal immune dysfunction in man. A small, but statistically significant increase in serum IgM, and a borderline statistically significant increase in serum IgM were associated with TPN. The etiology and clinical significance of these observations is unclear.

Induction of systemic immune responses to measles virus synthetic peptides administered intranasally

A systemic antibody response was induced when a chimeric peptide containing two copies of a promiscuous T-cell epitope and one copy of a B-cell epitope (TTB) from the fusion protein of measles virus (MV) was administered to mice intranasally without adjuvant. A higher antibody titre was produced when the peptide was administered intranasally with cholera toxin B subunit (CTB) as an adjuvant and these antibodies crossreacted with the MV. Furthermore, splenocytes from intranasally immunized mice proliferated in vitro in the presence of the TTB peptide. The immune response following intranasal immunization with the peptide was influenced by the MHC haplotype of the strain of mice used. Thus CBA and BALB/c mice were high responders whereas C57BL/6 mice were low responders. Although peptide administered intranasally with CTB to CBA mice induced an immune response, no significant protection was observed against intra-cranial challenge with canine distemper virus which is antigenically related to MV.

Intraepithelial and lamina propria leucocyte subsets in inflammatory bowel disease: an immunohistochemical study of colon and rectal biopsy specimens

AIMS

To gain new insights into the pathogenesis and differential diagnosis of ulcerative colitis and colonic Crohn's disease.

METHODS

Immunohistochemistry for different leucocyte subsets was performed in biopsy specimens of the sigmoid colon and rectum from 55 patients with inflammatory bowel disease and 11 healthy controls.

RESULTS

Colonic biopsy specimens from patients with active ulcerative colitis had significantly higher numbers of CD45+ and CD3+ leucocytes compared with those from patients with inactive disease, and higher numbers of total leucocytes and macrophages than those from patients with Crohn's disease. Rectal biopsy specimens from patients with Crohn's disease had greater numbers of intraepithelial leucocytes (CD45, CD3 and CD8 cells) than specimens from patients with active or inactive ulcerative colitis, or from healthy controls.

CONCLUSIONS

Because of the phenotypic differences in the inflammatory infiltrate in the mucosa from the sigmoid colon and the rectum, the segment of the intestine to be biopsied should be specified. Assessment of the leucocytic component of the intraepithelial infiltrate in rectal biopsy specimens was more useful than examination of colonic biopsy specimens in the differential diagnosis of ulcerative colitis and Crohn's disease.

Heat shock protein 70 and HLA-DR molecules tissue expression. Prognostic implications in colorectal cancer

PURPOSE

The expression of 70,000-Da heat shock protein (HSP 70) and HLA-DR molecules on cancer cells influences immunologic mechanisms that may be of some prognostic significance. The purpose of this study was to examine the relationship among immunohistochemical HSP 70, HLA-DR expression, and clinicopathologic tumor variables, as well as patient survival in a series of 128 colorectal carcinomas.

METHOD

A three-step immunoperoxidase staining technique was undertaken for detection of both markers.

RESULTS

Of the examined carcinomas 77.3 percent were HSP 70-positive and 74.2 percent were HLA-DR-positive. Increased HSP 70-positive expression correlated significantly with low differentiation (P < 0.05), showed a tendency to characterize advanced stages of disease, and was clearly associated with worse overall survival (P < 0.05). The highest rate of HLA-DR positivity was demonstrated in early stages and was significantly associated with more favorable prognosis (P < 0.001). HSP 70-positive/HLA-DR-negative patients had worse overall survival compared with the rest (P < 0.001).

CONCLUSIONS

The resulting opposite effects on prognosis of examined markers seem to be related to different pathophysiologic functional roles on tumor immunology.

Immunohistochemical expression of C-myc oncogene, heat shock protein 70 and HLA-DR molecules in malignant cutaneous melanoma

The clinical course of malignant melanomas is frequently unpredictable, although a number of prognostically useful variables can be identified. There is a need for additional markers of prognostic value. In a series of 60 malignant cutaneous melanomas, we analysed the immunohistochemical expression of c-myc proto-oncogene, heat shock protein 70 (HSP70) and HLA-DR molecules in order to investigate their prognostic significance. C-myc, HSP70 and HLA-DR were expressed in 43.3%, 56.6% and 38.3% of all melanoma cases, respectively. Advanced Clark levels (Clark III-V) were significantly associated with c-myc expression rate (P < 0.05), HSP70 detection (P < 0.01) and HLA-DR positivity (P < 0.01). Increased Breslow thickness (> 1.5 mm) was related to HLA-DR expression (P < 0.05). High mitotic rate was closely associated with c-myc positivity (P < 0.05), while HSP70 and HLA-DR expression separately correlated to clinical stage of the disease (P < 0.05). The evaluation of these variables may be of immunological and prognostic significance. They were found to be associated with melanocyte subpopulations of the vertical growth phase which are arguably characterized by an increased invasive potential.

Antigenaemia during acute graft versus host disease

AIMS

Animal studies have shown that antigens present within the gut play an important role in the development of acute graft versus host disease (GvHD) following allogeneic bone marrow transplantation (BMT). In previous studies, inert sugars have been found to penetrate the small bowel mucosa after conditioning therapy for BMT; endotoxaemia can also occur during acute GvHD. Data on absorption of antigenic proteins across the gut following BMT in humans have not been presented as yet.

METHODS

Six patients undergoing allogeneic BMT were studied to determine whether enteric ovalbumin absorption increased or endotoxaemia developed during acute GvHD.

RESULTS

Three patients had minimal antigenaemia and no detectable endotoxaemia before receiving conditioning therapy. At the onset of acute GvHD, however, much higher ovalbumin concentrations were detected in those patients with severe antigenaemia. Serum concentrations of specific antiovalbumin IgG and IgA, or antiendotoxin IgM or IgG had no bearing on detectable IgG or IgM ovalbumin or endotoxin concentrations. In five of six patients, small bowel permeability increased, as tested by the lactulose/mannitol sugar absorption test, but detectable ovalbumin absorption increased in only three of these and only two developed endotoxaemia.

CONCLUSIONS

Antigens present within the gut can cross the mucosal epithelium during acute GvHD, probably resulting in an enhanced immune response.

Immunocompetent cells of the upper airway: functions in normal and diseased mucosa

Secretory immunity is central in primary defense of the airway mucosa. B cells involved in this local immune system are initially stimulated in mucosa-associated lymphoid tissue, including tonsils and adenoids, and then migrate to secretory effector sites where they become immunoglobulin (Ig)-producing plasma cells. Locally produced Ig consists mainly of J-chain-containing dimers and larger polymers of IgA (pIgA) that are selectively transported through glandular cells by an epithelial receptor called secretory component or pIgR. Secretory antibodies perform surface protection by immune exclusion of soluble antigens as well as infectious agents. IgG can also participate in this primary defense because it reaches secretions by passive diffusion similar to IgE. However, the inflammatory properties of antibodies belonging to the latter two classes explain their involvement in mucosal immunopathology when elimination of penetrating antigens is unsuccessful. T helper (Th) cells activated in this process may by a Th2 profile of cytokines promote persistent inflammation with extravasation and priming of eosinophils. This mechanism appears to occur in the late-phase allergic reaction, perhaps driven mainly by interleukin-4 (IL-4) released from mast cells subjected to IgE-mediated degranulation. Eosinophils are potentially tissue-destructive cells, particularly after priming with IL-5. Cytokines also up-regulate adhesion molecules on vascular endothelium and epithelium, thereby enhancing migration of eosinophils and other leukocytes into the mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in the mucosal immune system in ulcerative colitis and Crohn's disease

Emphasis is now being placed upon obtaining a better understanding of the regulatory cytokines that normally downregulate acute intestinal inflammation. These inhibitory cytokines appear to be missing or not functioning properly in patients with inflammatory bowel disease (IBD), thereby leading to perpetuation of inflammation. As we obtain an increased understanding of immune and inflammatory regulatory processes in the intestine, we will be able to devise better future therapeutic strategies for use in our IBD patients.

An in vitro model for immune control of chlamydial growth in polarized epithelial cells

A polarized epithelial culture system and chlamydia-specific T-cell lines and clones were employed to investigate the ability and mechanisms by which T cells control the growth of chlamydiae in epithelial cells. Monolayers of polarized mouse epithelial cells were infected with the Chlamydia trachomatis agent of mouse pneumonitis (MoPn) and then exposed to antigen-stimulated MoPn-specific T-cell lines and clones. The results revealed that in vivo-protective MoPn-specific T-cell lines and clone 2.14-0 were capable of inhibiting the growth of MoPn in polarized epithelial cells. In contrast, the nonprotective MoPn-specific T-cell clone 2.14-3, naive splenic T cells, and a control T-cell clone could not inhibit the growth of MoPn in epithelial cells. Transmission electron microscopic analysis of infected epithelial cells which were exposed to clone 2.14-0 confirmed the absence of an established infection, as deduced from the virtual absence of inclusions in the cells. Antigen-specific activation of clone 2.14-0 was required for the MoPn-inhibitory function, since the absence of antigenic stimulation or stimulation with a heterologous chlamydial agent did not result in MoPn growth inhibition. Activation of clone 2.14-0 resulted in acquisition of the capacity to inhibit growth of both homologous (MoPn) and heterologous chlamydial agents. Close interaction between epithelial cells and clone 2.14-0 was required for the MoPn-inhibitory action, because separation of the cell types by a filter with a pore size of 0.45, 3.0, or even 8.0 microns abrogated MoPn inhibition. Protective T cells may act at close range in the epithelium to control chlamydial growth, possibly involving short-range-acting cytokines. The ability of antigen-stimulated T-cell lines and clones to inhibit chlamydial growth in polarized epithelial cultures could be a useful method for identifying protective T-cell clones and antigenic peptide fragments containing protective epitopes.

Malignant lymphoma in coeliac disease: various manifestations with distinct symptomatology and prognosis?

OBJECTIVES

To study the different forms of malignant lymphoma complicating coeliac disease in a low-prevalence area, according to extranodal-nodal and extraintestinal-intestinal manifestations.

SUBJECTS AND SETTING

Patients recruited from two University Hospitals (Amsterdam, Leiden) and from PALGA (National Dutch data-bank) over a 16-year period.

DESIGN

Review of hospital charts with respect to clinical presentation and treatment of both coeliac disease and malignant lymphoma. Re-evaluation of morphology and staging by immunoperoxidase, enzyme- and immunohistochemical stainings on unstained and frozen materials.

MAIN OUTCOME MEASURES

Clinical behaviour and T- or B-cell morphology of extranodal intestinal, extranodal extraintestinal and nodal intestinal disease.

RESULTS

Fourteen cases of enteropathy-associated lymphoma could be traced, 10 with a history of coeliac disease, four primarily presenting with malignant lymphoma. The usual extranodal intestinal lymphoma (eight cases) presented with abdominal pain, weight loss, and malabsorption. Six had atypical disease: four presented with extranodal extraintestinal disease, located in the skin or the respiratory tract; two patients had intractable malabsorption and oedema caused by a nodal intestinal lymphoma. Re-evaluation with additional immunohistochemical stainings in 11 patients showed a pleomorphic malignant infiltrate of histiocyte-like cells of T-cell origin, with a pattern of CD3+; CD4-; CD5 +/-; CD7+ and CD8-. It also established a more appropriate diagnosis in four, an 0.6-year earlier diagnosis in six, and an upgraded stage of disease in two patients. A more extensive spread and poorer outcome appeared to become more probable in the ranking order of extranodal intestinal, extranodal extraintestinal and nodal intestinal lymphoma.

CONCLUSIONS

A proper and timely diagnosis of enteropathy-associated lymphoma requires clinical vigilance and unrelentless perseverance to obtain adequate fresh and frozen tissue for histochemical staining. Further research in a larger number of patients is warranted to investigate the relation between the primary site of the lymphoma, i.e. extranodal intestinal, extranodal extraintestinal, or nodal intestinal, and (its impact on) clinical presentation and prognosis.

Stimulation of lamina propria lymphocytes by intestinal epithelial cells: evidence for recognition of nonclassical restriction elements

We have addressed the restriction elements involved in the interaction of lamina propria lymphocytes (LPL) and intestinal epithelial cells using the model of primary mixed cell culture reaction. Whereas peripheral blood T cells proliferate in response to both allogeneic non T cells and class II antigen-bearing intestinal epithelial cells (non T cells >> epithelial cells), LP T cells appear to proliferate preferentially in response to intestinal epithelial cells. The interaction between these cells does not appear to be restricted by conventional products of the major histocompatibility complex as neither monoclonal antibodies to class I nor to class II antigens inhibit the mixed cell cultures, whereas they are inhibitory in conventional mixed lymphocyte reactions. Furthermore, treatment of epithelial cells with interferon gamma fails to augment the cells' ability to induce proliferation of LPL while successfully enhancing proliferation of peripheral blood T cells in parallel cultures. Taken together, these data suggest that alternate restriction elements or mucosa-specific accessory molecules may exist on intestinal epithelial cells that are preferentially recognized by LPLs. Such a distinct regulatory network may be critical to the maintenance of immunologic homeostasis in the gut.

Secretory immunity in the female reproductive tract

PROBLEM

Antibodies and antibody-producing cells display a different and characteristic distribution in body fluids and tissues.

METHOD

We have investigated the tissues of the female reproductive tract to determine whether the distribution of immunoglobulin-producing cells and the contents of cervical secretions were similar to those found in tissues of the secretory immune system.

RESULTS

Immunohistochemical examinations of female genital tissues revealed the presence of plasma cells that secrete IgA (and in lower numbers IgM and IgG) especially in the subepithelial layers of the uterine endo- and ectocervix, fallopian tubes, and vagina. Both IgA1- and IgA2-producing plasma cells were found in approximately equal proportions. The presence of J-chain in the IgA-secreting cells suggests the synthesis of polymeric IgA (pIgA). Epithelial cells lining the fallopian tube and endocervix were positive for secretory component (SC), which is required for the transepithelial transport of pIgA into external secretions. Cervical mucus was collected and the molecular forms of IgA were separated using column chromatography. Approximately 80% of IgA in cervical mucus was polymeric compared with 55% in the vaginal fluid.

CONCLUSIONS

These data indicate that all effector components of the mucosal immune system are present in the female reproductive tract. The immunization routes that lead to a secretory IgA (S-IgA) response need to be further explored.

Number and distribution of T lymphocytes in the small intestinal mucosa of calves inoculated with rotavirus

An understanding of the immune response to rotavirus is needed to develop effective prophylaxis. There is evidence that cell-mediated responses may be involved and to extend these observations, rotavirus antigen and the three major T cell subsets, BoCD4+, BoCD8+, and BoWC1+ gamma/delta lymphocytes were immunostained in tissue sections from calves killed at 2, 4, 6, 8 and 10 days post inoculation and quantified by image analysis. It was established that in control calves, BoCD4+ lymphocytes were predominantly in the lamina propria, while the majority of BoCD8+ and BoWC1+ gamma/delta lymphocytes were in the epithelium. Rotavirus infection was seen throughout the small intestine with the greatest amount of viral antigen detected at 4 days post inoculation in the mid and distal small intestine. Increased numbers of all subsets were detected; small increases in intraepithelial BoCD4+ and BoWC1+ gamma/delta T lymphocytes were observed especially in the distal small intestine, while larger increases in BoCD8+ cells were detected in the epithelium and lamina propria of the proximal, mid and distal small intestine. The timing and location of these increases in T lymphocyte subsets is indicative of a specific immune response involving BoCD8+ and BoWC1+ gamma/delta T lymphocytes.

Spontaneous cytotoxicity of intestinal intraepithelial lymphocytes: clues to the mechanism

Human intestinal intraepithelial lymphocytes (IEL) demonstrate target cell-restricted spontaneous cytotoxic (SC) activity that is due to CD2+CD3+CD8+CD16-CD56- effector cells; they kill epithelial cell (EC) tumours (such as DLD-1 colon cancer cells), but not natural killer (NK)-sensitive K-562 cells. The present study shows that the measured levels of SC activities by IEL correlated with those of autologous lamina propria lymphocytes (LPL), but not with those of peripheral blood lymphocytes (PBL). Also, the susceptibilities of DLD-1 cell clones to lysis by IEL and PBL effector cells did not correlate, suggesting different mechanisms of lysis. Antibody blocking experiments showed that the main surface molecules involved in lysis depended on the effector cell type: alpha E beta 7 (HML-1) on IEL and CD16 on PBL. No antibody-dependent cell-mediated cytotoxicity (ADCC) was demonstrated by IEL, even after stimulation with interferon-gamma (IFN-gamma). Few IEL expressed Fc receptors for IgG. This study describes further differences between the SC activities of IEL and PBL.

Intestinal epithelial function: the case for immunophysiological regulation. Implications for disease (2)

Substantial amounts of data have been reported showing a role for immunomodulation of epithelial function (particularly ion secretion and permeability) using animal models of anaphylactic reactions. In part one of this review we outlined the main immune cell types and mediators/cytokines that are currently known to influence epithelial physiology either directly, or indirectly via an intermediate cell type. Here we will expand on the significance of these studies and show how antigenic activation of the mucosal immune system can evoke changes in epithelial function that may be beneficial to the host by mediating loss/inactivation of the antigen. However, a continued and inappropriate immune stimulation can lead to pathophysiological reactions and disease. Thus, we will present data on immune regulation of epithelial function with direct applicability to understanding the mechanism underlying human intestinal inflammatory and secretory disease. Finally, we highlight key strategic points in the cascade of immune events that can control epithelial function and thus may be of relevance in the formulation of new therapeutic approaches to intestinal inflammation.

Interferon-gamma stimulation of messenger RNA for human secretory component (poly-Ig receptor) depends on continuous intermediate protein synthesis

Secretory component (SC or poly-Ig receptor) plays a key role in mucosal external body fluids. The aim of this study was to elucidate the molecular events underlying IFN-gamma-dependent up-regulation of SC. Using a human SC cDNA clone isolated by our laboratory, we found that IFN-gamma up-regulated SC mRNA levels in a time- and concentration-dependent manner. Moreover, in situ hybridization showed a striking increase of SC mRNA-positive HT-29 cells after IFN-gamma treatment. Inhibition with 5,6-dichloro-1-beta-ribofuranosyl-benzimidazole (DRB) indicated a half-life for IFN-gamma-induced SC mRNA of approximately 1 h. Cycloheximide (CHX) abolished the IFN-gamma-induced accumulation of SC mRNA in a reversible manner; the time-course suggested that de novo synthesis of protein factor(s) with a turnover time shorter than 6 h was required for accumulation of SC message. IFN-gamma-stimulated up-regulation of SC expression therefore appears to depend on molecular events similar to those taking place for the activation of several other genes in the Ig supergene family.

Induction of mucosal immunity by intranasal application of a streptococcal surface protein antigen with the cholera toxin B subunit

The level and distribution of isotype-specific antibodies in various secretions and of antibody-secreting cells in corresponding lymphoid organs and tissues were compared in mice immunized with Streptococcus mutans surface protein antigen I/II (AgI/II) conjugated to the cholera toxin B subunit (CTB), given intranasally (i.n.) or intragastrically (i.g.), with or without free cholera toxin (CT) as an adjuvant. Immunization i.n. induced stronger initial antibody responses to AgI/II in both serum and saliva than immunization i.g., but salivary immunoglobulin A (IgA)-specific antibody responses to immunization about 3 months later were not increased relative to total salivary IgA concentrations. Specific antibodies induced by i.n. immunization were as widely distributed in serum, saliva, tracheal wash, gut wash, and vaginal wash as those induced by i.g. immunization. Likewise, specific antibody-secreting cells were generated in the spleen, salivary glands, intestinal lamina propria, and mesenteric and cervical lymph nodes by either route of immunization. The strongest salivary IgA antibody response was induced by AgI/II-CTB conjugate given i.n., but the addition of CT did not further enhance it. However, free CTB could effectively replace CT as an adjuvant in i.n. immunization with unconjugated AgI/II. Booster i.n. immunization with AgI/II plus either free CT or CTB induced stronger recall serum antibody responses than conjugated AgI/II-CTB with or without CT as an adjuvant. Therefore, i.n. immunization with a protein antigen and free or coupled CTB is an effective means of generating IgA antibody responses expressed at several mucosal sites where protective immunity may be beneficial.

Cytotoxic activity of human lymphocytes against differentiated intestinal tumour cell lines

The natural killer (NK) and lymphokine-activated killer (LAK) cytotoxic activity of human peripheral blood lymphocytes (PBL) against various human tumour cell lines from intestinal origin (WIDR, HT29, Caco-2) has been investigated. The differentiated Caco-2 cells were then used as a model to investigate the cytotoxic activity against enterocyte-like target cells. Caco-2 were seeded on polycarbonate filters and maintained in culture for at least 15 days to allow the differentiation and formation of tight junctions. The integrity of tight junctions was assayed by measuring [3H]mannitol flux from apical to basolateral compartment. Cytotoxic analysis showed that both differentiated and undifferentiated Caco-2 cells were similarly susceptible to NK and LAK activity. The capacity of cytotoxic lymphocytes to kill enterocyte-like cells with intact junctional complex may suggest a direct role of cytotoxic lymphocytes in causing intestinal lesions under inflammatory conditions.

T-cell receptor-gamma delta association with lymphocyte populations in sheep intestinal mucosa

T cells expressing T-cell receptor (TcR)-gamma delta and CD8 represent a significant population in mouse and chicken intra-epithelial lymphocytes (IEL) but represent a minor population in human IEL. We examined the TcR-gamma delta usage and co-expression of CD5, CD4, CD8 and major histocompatibility complex (MHC) class II on isolated sheep IEL and lamina propria lymphocytes (LPL), and compared them with the TcR-gamma delta + cells in peripheral blood, intestinal lymph and jejunal Peyer's patches (PP). There were a number of notable differences. TcR-gamma delta + cells comprised 18% of IEL and 10% of LPL. Among the population of TcR-gamma delta + IEL, 24% were CD8+ and 54% were CD5+, which contrasts with the TcR-gamma delta + cells in blood and intestinal lymph that were universally CD5+ CD4- CD8-. A notable feature of the IEL was the presence of distinct CD8+ and TcR-gamma delta + populations that lacked CD5. Also a high percentage of IEL and LPL were CD2+ and MHC class II+. Analysis of the expression of MHC class II on T-cell subsets, as an indicator of activation, showed that 60-95% of the various IEL and LPL subsets were MHC class II+ compared with only 5-40% in jejunal PP, lymph nodes, spleen and blood. Therefore, it is possible that the circulating TcR-gamma delta + and CD8+ cells that localize in the gut epithelium might become activated and stop the expression of CD5 under the influence of the local microenvironment. These cells appear not to emigrate while still expressing the TcR-gamma delta + (CD8+) CD5- MHC class II+ phenotype. Our data, together with those from other studies, show that there is much heterogeneity in the use of TcR-gamma delta and accessory T-cell molecules by IEL.

Expression and regulation of adhesion molecules ICAM-1 (CD54) and LFA-3 (CD58) in human intestinal epithelial cell lines

T cells and other leucocytes regularly occur within and subjacent to the gut epithelium. Recent data suggest that intestinal epithelial cells may exert accessory immunological functions. Although interactions between leucocytes and accessory cells usually require expression of adhesion molecules, intestinal epithelium has generally been considered negative for intercellular adhesion molecule-1 (ICAM-1) by immunohistochemical techniques. We therefore studied the expression of ICAM-1 and lymphocyte function-associated antigen-3 (LFA-3) by two colonic epithelial cell lines and found that both adhesion molecules were constitutively present at low levels. ICAM-1 protein expression could be enhanced within 4 h by cytokines, particularly after co-incubation with interferon-gamma (IFN) and tumour necrosis factor-alpha (TNF), interleukin-1 beta (IL-1), or IL-6. IFN also resulted in accumulation of ICAM-1 mRNA. Conversely, the LFA-3 expression was virtually unaffected by cytokine stimulation. These data imply that intestinal epithelial cells under certain conditions may bear adhesion molecules required for cooperation with juxtaposed leucocytes in situ, and that the expression of some of these molecules is modulated by cytokines from activated mucosal leucocytes.