Role of interleukin-6 in human and mouse mucosal IgA plasma cell responses

Comparison of oral and nasal immunization with inactivated porcine epidemic diarrhea virus on intestinal immunity in piglets

Porcine epidemic diarrhea virus (PEDV) has proven to be a major problem for the porcine industry worldwide. Conventional injectable vaccines induce effective systemic immune responses but are less effective in preventing PEDV at mucosal invasion sites, including the nasal or oral mucosa. Additionally, antigens delivered orally are easily degraded. Nasal immunization induces intestinal mucosal immune responses, which can aid in blocking viral invasion, and requires fewer antigen inoculation doses. Therefore, nasal immunizations are considered to be a potential approach to overcome viral infections. In the present study, nasal immunization of piglets was performed using inactivated PEDV combined with Bacillus subtilis as an immunopotentiator and the efficacy of nasal immunization was assessed. The results demonstrated that compared with oral immunization, piglets from the nasal immunization group exhibited higher levels of neutralizing antibodies (P<0.01) in the intestine, PEDV-specific immunoglobulin (Ig)G (P<0.01) in serum and PEDV-specific secretory IgA (SIgA) in saliva (P<0.01) and nasal secretions (P<0.01). An increased number of intestinal CD3⁺ T cells, IgA-secreting cells and intraepithelial lymphocytes (P<0.05) were also observed. Furthermore, the protein expression levels of interleukin-6 and interferon-γ, relative to the control PEDV infection, were also significantly elevated (P<0.05). The results of the present study indicate that nasal immunization is more effective at inducing the intestinal mucosal immune response, and provide new insights into a novel vaccination strategy that may be used to decrease the incidence of PEDV infections.

Orally administered heat-killed Lactobacillus paracasei MCC1849 enhances antigen-specific IgA secretion and induces follicular helper T cells in mice

Antigen-specific immunoglobulin (Ig) A plays a major role in host defense against infections in gut mucosal tissue. Follicular helper T (Tfh) cells are located in germinal centers and promote IgA production via interactions with germinal center B cells. Several studies have demonstrated that some lactic acid bacteria (LAB) strains activate the host’s acquired immune system, inducing IgA secretion in the intestine. However, the precise molecular mechanisms underlying the effects of LAB on IgA production and Tfh cells are not fully resolved. Lactobacillus paracasei MCC1849 is a probiotic strain isolated from the intestine of a healthy adult. In this study, we investigated the effects of orally administered heat-killed MCC1849 on IgA production in the intestine and on Tfh cell induction in vivo. We found that orally administered MCC1849 induced antigen-specific IgA production in the small intestine, serum and lungs. We also observed that MCC1849 increased the proportion of IgA⁺ B cells and Tfh cells in Peyer’s patches (PPs). In addition, MCC1849 increased the gene expression of IL-12p40, IL-10, IL-21, STAT4 and Bcl-6 associated with Tfh cell differentiation. These results suggest that orally administered MCC1849 enhances antigen-specific IgA production and likely affects Tfh cell differentiation in PPs.

Development of a nanogel-based nasal vaccine as a novel antigen delivery system

INTRODUCTION

Nasal vaccination is one of the most effective immunization methods because it can induce effective antigen-specific immune responses not only at the mucosal site of administration but also at distant mucosal surfaces, as well as in the systemic compartment. Based on this advantage, many nasal vaccines are being developed and some have been licensed and marketed for clinical use. However, some have been withdrawn because of unacceptable adverse events such as inactivated influenza vaccine administrated with a heat-labile enterotoxin of Escherichia coli as an adjuvant. Thus, it is important to consider both the efficacy and safety of nasal vaccines. Areas covered: This review describes the benefits of cholesteryl group-bearing pullulan (CHP) nanogels for nasal vaccine delivery and vaccine development identified on Pubmed database with the term 'Nanogel-based nasal vaccine'. Expert commentary: CHP nanogels have been developed as novel drug delivery system, and a cationic CHP nanogels have been demonstrated to induce effective immunity as a nasal vaccine antigen carrier. Since vaccine antigens incorporated into CHP nanogels have exhibited no brain deposition after nasal administration in mice and nonhuman primates, the vaccine seems safe, and could be a promising new delivery system.

Frontline Science: Nasal epithelial GM-CSF contributes to TLR5-mediated modulation of airway dendritic cells and subsequent IgA response

Flagellin, as a TLR5 agonist, is an established mucosal adjuvant for enhancing mucosal IgA responses by i.n. immunization. Nasal epithelial cells (NECs) are the first sentinel cells to be exposed to antigen and adjuvant in i.n. immunization, and it is suggested that they play an important role in the mucosal adjuvant activity of flagellin. However, the molecular mechanism leading to modulation and the response by flagellin-activated NECs remain unknown. We aimed to identify the soluble mediator(s) from flagellin-activated NECs that modulate the functions of airway dendritic cells (DCs) and enhance subsequent IgA response. In vitro studies showed that compared with the TLR4 agonist LPS, flagellin directly triggered slight up-regulation of CD80 on airway DCs but was insufficient to affect CD86 expression and DC-mediated IgA response. With the use of an in vitro system for culturing mouse primary NECs (mNECs), we demonstrated that flagellin-activated mNECs could functionally modulate airway DCs, which manifested as significant up-regulation of CD80/CD86 and enhancement of IgA production. The functional modulation of airway DCs was dependent on TLR5 activation of mNECs rather than direct TLR5 activation of airway DCs. With the use of cytokine array and antibody-blocking assays, we further identified that GM-CSF, a cytokine secreted from TLR5-activated mNECs, contributes to the activation of mNECs to airway DCs and subsequent IgA enhancement. In vivo blocking experiments confirmed that GM-CSF is an important factor in recombinant flagellin derived from Salmonella typhi (FliC)-induced airway DC activation and antigen-specific IgA enhancement. Our data directly demonstrate that nasal epithelial GM-CSF contributes to TLR5-mediated modulation of airway DCs and a subsequent IgA response.

Injury induces localized airway increases in pro-inflammatory cytokines in humans and mice

BACKGROUND

Secretory immunoglobulin A (sIgA) increases in the airways of humans and mice after injury to protect against infection. The pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 are linked molecularly to sIgA production and secretion and are required for sIgA increases in the airway after injury in a mouse model. We investigated the injury effect on airway and serum concentrations to determine the source of the cytokines involved in the airway IgA response.

METHODS

In the first experiment, TNF-α, IL-1β, and IL-6 concentrations in bronchoalveolar lavage (BAL) fluid and serum obtained from 11 ventilated trauma patients within 30 h of admission were compared with those in eight elective surgical patients. In the second experiment, male ICR mice received no injury (n = 7) or injury with sham celiotomy and neck incisions (n = 8) with sacrifice of all animals at 8 h for BAL fluid and serum cytokine measurements by enzyme-linked immunosorbent assay.

RESULTS

Injured patients had significantly higher BAL fluid and serum TNF-α, IL-1β, and IL-6 concentrations, with greater increases in the BAL fluid than in the serum. Injured mice had significantly increased BAL fluid concentrations of TNF-α, IL-1β, and IL-6 without significant changes in serum TNF-α or IL-1β. Serum IL-6 increased significantly.

CONCLUSIONS

Injury significantly increases human and mouse airway TNF-α, IL-1β, and IL-6. Increases are greater in the airway than in serum, implying a local rather than a systemic stress response to injury.

Small intestine mucosal immune system response to injury and the impact of parenteral nutrition

BACKGROUND

Both humans and mice increase airway immunoglobulin A (IgA) after injury. This protective response is associated with TNF-α, IL-1β, and IL-6 airway increases and in mice is dependent upon these cytokines as well as enteral feeding. Parenteral nutrition (PN) with decreased enteral stimulation (DES) alters gut barrier function, decreases intestinal IgA, and decreases the principal IgA transport protein pIgR. We investigated the small intestine (SI) IgA response to injury and the role of TNF-α, IL-1β, IL-6, and PN/DES.

METHODS

Expt 1: Murine kinetics of SI washing fluid (SIWF) IgA; SI, SIWF and serum TNF-α, IL-1β, and IL-6, was determined by ELISA from 0 to 8 hours after a limited surgical stress injury (laparotomy and neck incisions). Expt 2: Mice received chow or PN/DES before injury and SIWF IgA and SI pIgR levels were determined at 0 and 8 hours. Expt 3: Mice received PBS, TNF-α antibody, or IL-1β antibody 30 minutes before injury to measure effects on the SIWF IgA response. Expt 4: Mice received injury or exogenous TNF-α, IL-1β, and IL-6 to measure effects on the SIWF IgA response.

RESULTS

Expt 1: SIWF IgA levels increased significantly by 2 hours after injury without associated increases in TNF-α or IL-1β whereas IL-6 was only increased at 1 hour after injury. Expt 2: PN/DES significantly reduced baseline SIWF IgA and SI pIgR and eliminated their increase after injury seen in Chow mice. Expt 3: TNF-α and IL-1β blockade did not affect the SIWF IgA increase after injury. Expt 4: Exogenous TNF-α, IL-1β, and IL-6 increased SIWF IgA similarly to injury.

CONCLUSION

The SI mucosal immune responds to injury or exogenous TNF-α, IL-1β, and IL-6 with an increase in lumen IgA, although it does not rely on local SI increases in TNF-α or IL-1β as it does in the lung. Similar to the lung, the IgA response is eliminated with PN/DES.

Proinflammatory cytokine surge after injury stimulates an airway immunoglobulin a increase

BACKGROUND

: Injury stimulates an innate airway IgA response in severely injured patients, which also occurs in mice. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β stimulate the production of polymeric immunoglobulin receptor, the protein required to transport immunoglobulin A (IgA) to mucosal surfaces. Blockade of TNF-α and IL-1β eliminates the airway IgA response to injury. IL-6 stimulates differentiation of B cells into IgA-secreting plasma cells at mucosal sites. We investigated the local and systemic kinetics of TNF-α, IL-1β, and IL-6 after injury in mice. We also hypothesized that injection of exogenous TNF-α, IL-1β, and IL-6 would replicate the airway IgA response to injury.

METHODS

: Experiment 1: male Institute of Cancer Research mice were randomized to uninjured controls (n = 8) or to surgical stress with laparotomy and neck incisions, with killing at 1, 2, 3, 5, or 8 hours after injury (n = 8/group). Bronchoalveolar lavage (BAL) and serum levels of TNF-α, IL-1β, and IL-6 were analyzed by enzyme-linked immunosorbent assay. Experiment 2: male Institute of Cancer Research mice were randomized to uninjured controls (n = 6), injury (surgical stress that was similar to experiment 1 except the peritoneum was left intact, n = 6), or cytokine injection with intraperitoneal injection of recombinant TNF-α, IL-1β, and IL-6. Animals were killed at 2 hours after injury, and nasal airway lavage and BAL IgA were analyzed by enzyme-linked immunosorbent assay.

RESULTS

: Experiment 1: BAL TNF-α, IL-1β, and IL-6 levels increased in bimodal pattern after injury at 3 hours and 8 hours versus controls (p < 0.05). Serum IL-6 did not increase at 3 hours, but did show a significant increase by 5 hours versus control (p < 0.05). Serum levels of TNF-α and IL-1β did not change. Experiment 2: both Injury and combination TNF-α, IL-1β, and IL-6 cytokine injection significantly increased IgA levels in airway lavage (BAL + nasal airway lavage) compared with control (p < 0.01 for both).

CONCLUSIONS

: Airway levels of TNF-α, IL-1β, and IL-6 increase in a bimodal pattern after injury with peaks at 3 hours and 8 hours, which do not correspond to serum changes. The peak at 8 hours is consistent with the known increase in airway IgA after injury. Intraperitoneal injection of a combination exogenous TNF-α, IL-1β, and IL-6 replicates the airway IgA increase after injury. This effect is not seen with individual cytokine injections.

Mucosal vaccines: novel advances in technology and delivery

Mucosal vaccines are considered the most suitable type of vaccines to combat emerging and re-emerging infectious diseases because of their ability to induce both mucosal and systemic immunity. Considerable advances have been made toward the development of mucosal vaccines against influenza virus and rotavirus. Many additional mucosal vaccines are in development, including vaccines against cholera, typhoid, traveler's diarrhea and respiratory infections. In addition to oral and nasal vaccines, transcutaneous (or skin patch) and sublingual immunizations are now part of a new generation of mucosal vaccines. Furthermore, a rice-based oral vaccine (MucoRice) has been receiving global attention as a new form of cold chain-free vaccine, because it is stable at room temperature for a prolonged period. This review describes recent developments in mucosal vaccines with promising preclinical and clinical results.

Role of retinoic acid in the imprinting of gut-homing IgA-secreting cells

Antibody-secreting cells (ASCs) lodging in the mucosa of the small intestine are derived from activated B cells that are thought to arise in gut-associated lymphoid tissues (GALT). Upon leaving the GALT, B cells return to the blood where they must express the gut-homing receptors alpha4beta7 and CCR9 in order to emigrate into the small bowel. Recent evidence indicates that gut-associated dendritic cells (DCs) in GALT induce gut-homing receptors on B cells via a mechanism that depends on the vitamin A metabolite retinoic acid (RA). In addition, although ASC associated with other mucosal tissues secrete IgA in an RA-independent fashion, the presence of high levels of RA in intestine and GALT can promote B cell class switching to IgA and thus, boost the production of IgA in the intestinal mucosa. Here, we discuss the role of RA in the imprinting of gut-homing ASC and the evidence linking RA with the generation of intestinal IgA-ASCs.

Differentiation and homing of IgA-secreting cells

Most antibody-secreting cells (ASCs) in mucosal tissues produce immunoglobulin A (IgA), the most abundant immunoglobulin in the body and the main class of antibody found in secretions. IgA-ASCs differentiate in the mucosal-associated lymphoid tissues and are usually considered as a homogeneous population of cells. However, IgA-ASCs that travel to the small intestine have unique characteristics in terms of their migratory requirements. These IgA-ASCs require the homing molecules alpha4beta7 and CCR9 to interact with their ligands, mucosal addressin cell adhesion molecule-1 and CCL25, which are constitutively expressed in the small intestine. Indeed, recent work has shown that IgA-ASCs specific for the small bowel are generated under different conditions as compared with IgA-ASCs in other mucosal compartments. Moreover, the mechanisms inducing IgA class switching may also vary according to the tissue where IgA-ASCs differentiate. Here we describe the mechanisms involved in the differentiation of IgA-ASCs in mucosal compartments, in particular those involved in the generation of gut-homing IgA-ASCs.

Homing imprinting and immunomodulation in the gut: role of dendritic cells and retinoids

Lymphocyte migration is at the heart of chronic inflammatory ailments, including inflammatory bowel disease (IBD). Whereas naïve lymphocytes migrate to all secondary lymphoid organs, they are mostly excluded from nonlymphoid peripheral tissues. Upon activation, lymphocytes change their pattern of adhesion receptors and acquire the capacity to migrate to extralymphoid tissues. Antigen-experienced T cells are subdivided into different subsets based on their expression of homing receptors that favor their accumulation in specific tissues, such as the skin and the gut mucosa. B cells and antibody-secreting cells (ASC) also show tissue-tropism, which is somewhat correlated with the class of immunoglobulin that they produce. In fact, IgA-ASC are located in mucosal tissues, where they produce IgA, the main class of antibodies found in secretions. Although IgA-ASC are usually considered as a homogeneous pool of cells, those located in the small bowel have some unique migratory characteristics, suggesting that they are generated under different conditions as compared to IgA-ASC in other mucosal compartments. Foxp3(+) regulatory T cells (T(REG)) can also exhibit tissue-specific migratory potential and recent evidence suggests that T(REG) can be imprinted with gut-specific homing. Moreover, foxp3(+) T(REG) are enriched in the small bowel lamina propria, where they can be generated locally. The present review addresses our current understanding of how tissue-specific homing is acquired and modulated on T cells, B cells, and ASC, with a special emphasis on the intestinal mucosa. Harnessing these mechanisms could offer novel, effective, and more specific therapeutic strategies in IBD.

Experimental infection of ponies with equine influenza A2 (H3N8) virus strains of different pathogenicity elicits varying interferon and interleukin-6 responses

The production of interferon (IFN), interleukin-6 (IL-6), and tumor necrosis factor (TNF) was monitored in horses during the course of influenza A2 virus infections. The effects of two virus strains, Newmarket/2/93 and Sussex/89, were compared, of which the latter is considered the more pathogenic in terms of clinical signs. Ten naive ponies were infected with influenza A/equine/Sussex/89 and 10 with influenza A/equine/Newmarket/2/93, respectively. As expected ponies infected with Sussex/89 showed the most pronounced clinical signs but there was no notable difference in viral excretion compared with Newmarket/2/93. IFN was detected in nasal secretions of all ponies infected with Sussex/89 but only in 2 ponies infected with Newmarktet/2/93. IFN was not detected in serum of any animal. IL-6 activity was detected in nasal secretions of all experimental animals from day 2 and onwards, but showed markedly higher IL-6 responses were observed in ponies infected with Sussex/89. No TNF activity was detected in any of the samples collected. In summary, equine influenza A 2 infections elicited local, and in some cases systemic, IFN and IL-6 responses in the ponies. Interestingly, there was some evidence that the duration and levels of cytokine responses may be related to the pathogenicity of the influenza strains.

Cyclooxygenase-2 mediates interleukin-6 upregulation by vomitoxin (deoxynivalenol) in vitro and in vivo

Interleukin-6 (IL-6) is a central mediator of immunotoxicity that is associated with exposure to the trichothecene vomitoxin (VT). The purpose of this investigation was to test the hypothesis that the inducible cyclooxygenase-2 (COX-2) and its metabolites contribute to VT-induced IL-6 upregulation. VT at 100 to 250 ng/ml readily induced COX-2 protein expression in the RAW 264.7 murine macrophage cell line. Superinduction of lipopolysaccharide (LPS)-mediated IL-6 production by VT in these cells was significantly reduced by the COX inhibitors indomethacin and NS-398, whereas the inhibitors did not affect direct induction of IL-6 by LPS alone. Mice that had been gavaged orally with 5 and 25 mg/kg VT exhibited elevated COX-2 mRNA expression in Peyer's patches and spleen with peak induction occurring 2 h after VT exposure. IL-6 mRNA was also induced by VT in vivo, however, peak expression occurred from 2 to 4 h after toxin exposure, suggesting that maximal COX-2 gene upregulation preceded or was concurrent with that for IL-6. Also consistent with a putative contributory role for COX-2 was the finding that both induction of splenic IL-6 mRNA and serum IL-6 by VT were significantly reduced by pretreating mice with the COX inhibitors indomethacin or NS-398. Finally, COX-2 knockout mice showed significantly reduced splenic IL-6 mRNA and serum IL-6 responses to oral VT exposure compared to their parental wild type. Taken together, these in vitro and in vivo data suggest that VT-induced COX-2 gene expression and resultant COX-2 metabolites contributed, in part, to subsequent upregulation of IL-6 gene expression, which has been previously shown to be a hallmark of VT-mediated immunotoxicity.

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.

Exogenous IL-6 promotes enhanced intestinal antibody responses in vivo

It is well documented that IL-6 plays a critical role in B cell terminal differentiation, and in mucosal sites it stimulates proliferation and large-scale secretion of immunoglobulin by B cells, especially those committed to IgA production. The close juxtaposition of IL-6 mRNA+ cells to plasma cells in the intestinal lamina propria supports the proposition that IL-6 production in situ is an important factor determining the outcome of antibody responses at that site. However, it has not been established previously whether exogenous IL-6 could boost antibody responses in the intestine if administered with a challenge antigen. Using a resected gut loop (Thiry-Vella loop) model, we have been able to demonstrate that in mice with double loops, antibody containing cell responses to lumenal administration of ovalbumin were 50% greater in loops given intralumenal recombinant IL-6 with the challenge antigen, than in loops challenged with antigen alone. This demonstrates the efficacy of IL-6 in promoting accumulation of antibody secreting cells in the gut, and suggests a potential therapeutic role for IL-6 to enhance responses to mucosal vaccines.

In vitro production of TNFα, IL-6 and sIL-2R in Chinese patients with ulcerative colitis

AIM: To determine the tumor necrosis factor alpha (TNFα), interleukin 6 (IL-6) and soluble interleukin 2 receptor (sIL-2r) from peripheral blood mononuclear cells (PBMC) in 25 Chinese patients with ulcerative colitis and 20 healthy controls.

METHODS: PBMC were isolated by density gradient centrifugation of heparinized blood and cultures for 24 or 48 h by stimulation with LPS or PHA. TNFα and sIL-2r were measured by ELISA method and IL-6 measured by biossay.

RESULTS: TNFα production stimulated by LPS and sIL-2r production by PHA in ulcerative colitis were significantly lower than in healthy controls (TNFα 509 (46-7244) ng/L vs 1995 (117-18950) ng/L, P < 0.05; sIL-2r 320 U/mL ± 165 U/mL vs 451 U/mL ± 247 U/mL, P < 0.05). Spontaneous TNFα and sIL-2r production were not significantly different between ulcerative colitis and controls (TNFα 304 (46-7044) ng/L vs 215 (46-4009) ng/L, P > 0.05; sIL-2r 264 U/mL ± 115 U/mL vs 236 U/mL ± 139 U/mL, P > 0.05). IL-6 production by spontaneous release from PBMC in ulcerative colitis group was 109 U/mL ± 94 U/mL vs 44 U/mL ± 39 U/mL for those in healthy controls, P < 0.01. IL-6 stimulated by LPS in ulcerative colitis group was (261 U/mL ± 80 U/mL) higher than in healthy controls (102 U/mL ± 54 U/mL, P < 0.01). No correlation of TNFα, IL-6, sIL-2r production was found to disease activity, disease location and medication.

CONCLUSION: Cytokine production from PBMC was also disturbed in Chinese patients with ulcerative colitis.

Mucosal interleukin-6 secretion in ulcerative colitis. Effects of anti-inflammatory drugs and T-cell stimulation

BACKGROUND

We have studied modulation of mucosal interleukin-6 (IL-6) secretion by T-cell activation and by anti-inflammatory agents in inflammatory bowel disease.

METHODS

In vitro secretion of IL-6 by biopsy specimens from patients with active ulcerative colitis was investigated in the presence of cyclosporin-A (CsA) and drugs that have other anti-inflammatory actions. Biopsy specimens from patients with quiescent ulcerative colitis or controls were stimulated with anti-CD3 antibody to activate mucosal T cells.

RESULTS

Stimulation of control specimens increased IL-6 secretion (median increase, 147%; p < 0.003), which was prevented by CsA. In quiescent ulcerative colitis there was enhanced spontaneous secretion of IL-6 but a smaller, non-significant increase after T-cell activation (125%). Dexamethasone inhibited secretion in active ulcerative colitis (p < 0.006). 5-Aminosalicylic acid, 6-mercaptopurine, methotrexate, and indomethacin had no effect. There also tended to be a small reduction with CsA, but this just failed to reach statistical significance.

CONCLUSIONS

In quiescent ulcerative colitis the enhanced spontaneous secretion of IL-6 may be a consequence of mucosal T-cell or macrophage activation: the smaller increase after T-cell stimulation suggests that one or both of these two cell types are already pre-activated.

Enhanced secretion of tumour necrosis factor-alpha, IL-6, and IL-1 beta by isolated lamina propria mononuclear cells from patients with ulcerative colitis and Crohn's disease

The perpetuation of inflammation in ulcerative colitis and Crohn's disease may be regulated in part by an increased secretion of proinflammatory cytokines due to either an appropriate response to initial stimulating agents, and/or due to an impaired down-regulation of cytokine secretion. The aim of this study was to determine the secretion patterns of the proinflammatory cytokines tumour necrosis factor-alpha (TNF-alpha), IL-6 and IL-1 beta, from isolated lamina propria mononuclear cells (LPMNC) isolated from colonic biopsies from patients with untreated ulcerative colitis or Crohn's disease. LPMNC isolated from involved inflammatory bowel disease (IBD) mucosa spontaneously produced increased amounts of TNF-alpha, and IL-6, and IL-1 beta. The TNF-alpha secretion from IBD LPMNC could be further enhanced by pokeweed mitogen stimulation. The secretion patterns of TNF-alpha and IL-1 beta by LPMNC from patients with either ulcerative colitis or Crohn's disease demonstrated a close correlation with the degree of tissue involvement and mucosal inflammation. LPMNC from non-involved ulcerative colitis mucosa secreted markedly increased levels of IL-6 compared with non-involved Crohn's disease mucosa or control mucosa. The heightened IL-6 secretion from LPMNC from non-involved ulcerative colitis mucosa without visible or microscopic signs of inflammation indicates that the pathophysiologic mechanisms involved in the initiation of inflammation may differ between ulcerative colitis and Crohn's disease. The determination of proinflammatory cytokine secretion by isolated LPMNC from colonoscopic biopsies may be a sensitive method for monitoring the severity of mucosal inflammation in IBD patients.

Cholera toxin enhances alloantigen presentation by cultured intestinal epithelial cells

In the present study we show that cholera toxin (CT) strongly potentiates antigen presentation by intestinal epithelial cells, probably by enhancing co-stimulation. This was demonstrated in an allogeneic system using cells from the IEC-17 rat epithelial cell line as antigen presenting cells (APC). These cells were induced by optimal concentrations of IFN-gamma to express good amounts of Ia antigen and cultured for 24-48 h in the presence or absence of CT. Thereafter the cells were thoroughly washed and added to cultures containing MHC-incompatible spleen cells as responder cells. Epithelial cells exposed to CT demonstrated greatly enhanced ability to trigger allogen-specific T-cell proliferation as compared with IEC-17 cells treated with IFN-gamma alone. The mechanism for the enhanced APC function was investigated by analysing CT-treated IEC-17 cells for increased class II MHC antigen expression or enhanced production of cytokines with known co-stimulatory function. We found no significant increase in class II MHC antigen expression. By contrast, CT strongly promoted, in a dose-dependent fashion, the production of both IL-1 and IL-6 cytokines by IEC-17 cells as compared with untreated epithelial cells. This effect of CT was specific and not due to contaminating endotoxin because excess amounts of soluble toxin receptor, ganglioside GM1, added to the IEC-17 cultures completely abrogated the cytokine response to CT. These results together with our previous findings of enhanced antigen presentation by macrophages stimulated by CT suggest that the potent adjuvant function of CT for induction of mucosal immune responses might be attributed to an enhanced co-stimulating ability of several putative APC in the mucosal immune system: macrophages, B cells and epithelial cells.