Immunohistochemical analysis of mucosal gamma-interferon production in coeliac disease

Molecular mechanisms of the adaptive, innate and regulatory immune responses in the intestinal mucosa of celiac disease patients

Celiac disease is a complex genetic disorder that affects the small intestine of genetically predisposed individuals when they ingest gluten, a dietary protein. Although several genome screens have been successful in identifying susceptibility loci in celiac disease, the only genetic contributors identified so far are the human leukocyte antigen (HLA)-DQ2/DQ8 molecules. One of the most important aspects in the pathogenesis of celiac disease is the activation of a T-helper 1 immune response, when the antigen-presenting cells that express HLA-DQ2/DQ8 molecules present the toxic gluten peptides to reactive CD4(+) T-cells. Recently, new insights into the activation of an innate immune response have also been described. It is generally accepted that the immune response triggers destruction of the mucosa in the small intestine of celiac disease patients. Hence, the activation of a detrimental immune response in the intestine of celiac disease patients appears to be key in the initiation and progression of the disease. This review summarizes the immunologic pathways that have been studied in celiac disease thus far, and will point to new potential candidate genes and pathways involved in the etiopathogenesis of celiac disease, which should lead to novel alternatives for diagnosis and treatment.

Serum cytokine elevations in celiac disease: association with disease presentation

Celiac disease (CD) is an autoimmune disorder that is triggered by an immune response to gluten in genetically predisposed individuals. Although considered a primary gastrointestinal disease, CD is now known to have widespread systemic manifestations. We attempted to define the nature and role of systemic cytokine levels in the pathophysiology of CD. Multiplex cytokine assays were performed on four different groups of adult patients; patients with active CD (ACD), patients on a gluten-free diet (GFD) with positive TTG IgA antibodies, patients on a GFD with negative antibodies, and those with refractory CD (RCD). The results were compared with values in healthy adult controls. Patients with active CD and those on GFD with positive antibodies had significantly higher levels of proinflammatory cytokines, such as interferon-gamma, interleukin (IL)-1beta, tumor necrosis factor-alpha, IL-6 and IL-8, and also T(h)-2 cytokines such as IL-4 and IL-10, compared with normal controls and patients on GFD without antibodies. Interestingly patients on GFD for less than 1 year had significantly higher levels of both proinflammatory cytokines and T(h)2 cytokines compared with the patients on GFD for more than 1 year. In addition, a statistically significant correlation between levels of TTG IgA titers and serum levels of T(h)-2 cytokines IL-4 (p < 0.001), IL-10 (p < 0.001) and inflammatory cytokines such as IL-1alpha (p < 0.001), IL-1beta (p < 0.005), and IL-8 (p < 0.05) was observed.

Spontaneous T(H)1 cytokine production by intraepithelial but not circulating T cells in infants with or without food allergies

BACKGROUND

It has been established that the maintenance of immunological tolerance to dietary antigen and the intestinal flora (oral tolerance) is an actively-maintained process dependent upon mucosal lymphocyte populations. Early life exposures appear critical in the development of such tolerance. However little is known about the activation status of mucosal lymphocytes in human infancy and childhood.

PATIENTS AND METHODS

We have performed flow cytometric analysis for cell lineage and cytokine-production status in peripheral blood and duodenal intraepithelial lymphocytes taken during endoscopy from 20 children [median age 2.9 +/- 0.6 years (median +/- SE)] in whom investigation found no intestinal abnormalities (histologically normal controls) and 30 children (median age 1.6 +/- 0.4 years) with confirmed allergy to cow's milk and other dietary antigens.

RESULTS

Regardless of clinical status, spontaneous production of cytokines was low or undetectable in peripheral blood cells. By contrast, intraepithelial CD4 and CD8 cells isolated from the small intestine were often activated, with 5% or more showing spontaneous production of T(H)1 type [interleukin-2, interferon (IFN)-gamma] cytokines in both normal controls and food-allergic children. Stimulation in vitro strongly induced cytokine production in peripheral blood but not intraepithelial lymphocytes. Immunohistochemistry showed similar density of IFN-gamma(+) intraepithelial lymphocytes in controls and allergic children.

CONCLUSIONS

Duodenal intraepithelial lymphocytes in human infants show a state of increased spontaneous activation compared with peripheral blood lymphocytes, and show no significant impairment of T(H)1 responses in food allergic children.

Interferon-gamma-secreting T cells localize to the epithelium in coeliac disease

Increased levels of interferon-gamma (IFN-gamma) transcripts have previously been found in duodenal biopsy specimens from patients with untreated coeliac disease (CD). Such samples and duodenal control mucosa were therefore studied to locate and phenotype cells spontaneously secreting IFN-gamma. Specimens were collected from consecutively recruited patients with untreated (seven), treated (four) or refractory (three) CD and from five histologically normal controls. Morphological and immunohistochemical examinations were performed, and epithelial and lamina propria cell suspensions were prepared from parallel samples. Unstimulated viable cells secreting IFN-gamma were identified and phenotyped with a new fluorescence-activated cell sorter-based assay, and IFN-gamma messenger RNA (mRNA) was analysed in snap-frozen aliquots of the same suspensions. Untreated CD cases had the highest fraction of IFN-gamma+ cells in the epithelial compartment (median 2.6%, range 1.6-6.2%) and, less strikingly, in the lamina propria compartment (1.6%, range 0.3-3.6%), followed by refractory (1.4%, 1.0-1.9%; and 0.3%, 0.0-1.2%) and treated (0.8%, 0.5-0.9%; and 0.7%, 0.2-1.1%) disease and finally the controls (0.5%, 0.3-0.9%; and 0.2%, 0.1-0.7%). IFN-gamma mRNA data supported these findings. IFN-gamma+ intraepithelial lymphocytes were mostly CD3+ and CD8+, whereas many positive lamina propria cells were CD8-. We conclude that isolated T cells spontaneously secreting IFN-gamma localize preferentially in the epithelium of patients with classical and refractory CD.

Human leukocyte antigen class II alleles in white Brazilian patients with celiac disease

BACKGROUND

Celiac disease (CD) is a permanent gluten intolerance disorder characterized by malabsorption, intestinal mucosa villus atrophy, and crypt hyperplasia. Clinical and histologic features improve in persons consuming a gluten free diet. The pathogenesis of CD involves environmental, genetic, and immunologic factors.

METHODS

The frequencies of human leukocyte antigen (HLA) class II alleles were evaluated in white Brazilian patients who had CD and compared with those observed in healthy individuals from the same geographical area (Ribeirão Preto, São Paulo) and of similar ethnic background. Twenty-five patients with CD, 11 females and 14 males, and 91 control individuals were studied. The HLA class II alleles were typed using amplified DNA hybridized with sequence-specific primers. Statistical analysis was performed using the two-tailed Fisher exact test. The relative risk (RR), etiologic fraction (EF), and preventive fraction (PF) were also estimated. The EF represents the attributable risk for the development of CD at the population level, whereas PF represents the protective risk.

RESULTS

The frequency of the HLA-DRB1*03, HLA-DRB1*07, and HLA-DQB1*02 alleles was significantly increased in patients. The RR conferred by these alleles was 5.35, 7.15, and 10.6, respectively, and the EF was 48.7%, 44.7%, and 76%, respectively. The frequency of HLA-DQB1*06 alleles was significantly decreased in CD patients, conferring an RR of 0.08 and a PF of 48%.

CONCLUSIONS

The results show that HLA-DRB1*03, HLA-DRB1*07, and HLA-DQB1*02 alleles conferred susceptibility to CD in Brazilian patients. In contrast, HLADQB1*06 alleles conferred protection against development of the disease.

Sodium butyrate blocks interferon-gamma (IFN-gamma)-induced biosynthesis of MHC class III gene products (complement C4 and factor B) in human fetal intestinal epithelial cells

Human intestinal epithelial cells have been established as local sites for complement biosynthesis. In this study, we investigated the effects of IFN-gamma and sodium butyrate on biosynthesis of MHC class III gene products (complement C4 and factor B) in the human fetal intestinal epithelial cell line INT-407. IFN-gamma induced a dose- and time-dependent increase in C4 and factor B secretion. However, sodium butyrate dose-dependently inhibited IFN-gamma-induced C4 and factor B secretion. These effects were also observed at the mRNA level. Immunoblotting indicated that IFN-gamma induced a rapid activation of Stat1alpha, and fluorescence immunohistochemistry detected a translocation of Stat1alpha into the nucleus within 1 h. However, the translocation of Stat1alpha was not affected by the addition of sodium butyrate. Nuclear run-on assay indicated that IFN-gamma induced a weak increase in the transcription rate of factor B gene, and sodium butyrate did not affect this response. IFN-gamma and sodium butyrate induced a counter-regulatory effect on C4 and factor B secretion: IFN-gamma acted as a potent inducer, but sodium butyrate potently abrogated these responses. These are mainly regulated through the post-transcriptional mechanism.

Expression of interleukin-4 and interferon-gamma in the small bowel of patients with dermatitis herpetiformis and isolated gluten-sensitive enteropathy

Although possessing a morphologically similar small bowel abnormality to patients with isolated gluten-sensitive enteropathy (GSE), patients with dermatitis herpetiformis (DH) have few gastrointestinal symptoms and exhibit blistering skin lesions and cutaneous IgA deposits. To determine whether clinical discrepancies between these gluten-sensitive conditions might be the result of different patterns of small bowel cytokine expression, duodenal biopsies were obtained from eight DH patients and nine isolated GSE patients. Biopsies were evaluated for interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) expression by reverse-transcriptase polymerase chain reaction (message) and immunohistochemistry (protein). In DH patients, most of whom had no gut symptoms, IFN-gamma mRNA expression was significantly less than in isolated GSE patients with symptomatic gut disease. Conversely, IL-4 mRNA expression in DH patients was greater than that found among isolated GSE patients. These findings suggest that the different clinical phenotypes of gluten sensitivity may be caused by variation in cytokine expression in the small bowel response to gluten.

Intestinal crypt cell apoptosis in murine acute graft versus host disease is mediated by tumour necrosis factor alpha and not by the FasL-Fas interaction: effect of pentoxifylline on the development of mucosal atrophy

BACKGROUND

Murine T cell mediated acute semiallogeneic graft versus host disease (GVHD) is characterised by lymphocytic infiltrates, crypt hyperplasia, and villous atrophy. It has been shown that programmed cell death (apoptosis) of the crypt epithelium takes place during the intestinal manifestation of acute GVHD.

AIMS

To investigate which of the two most investigated inductors of apoptosis (Fas ligand (FasL) and tumour necrosis factor alpha (TNF-alpha)) is responsible for the induction of apoptosis in this animal model.

METHODS

Animals undergoing acute semiallogeneic GvH reaction were treated with neutralising anti-TNF-alpha, two different anti-FasL antibodies, or pentoxifylline.

RESULTS

Anti-TNF-alpha application inhibited the appearance of apoptotic cells in the intestinal mucosa, whereas anti-FasL antibodies had no influence on mucosal apoptosis. In addition, the transfer of FasL deficient (gld) donor lymphocytes still induced crypt cell apoptosis, villous atrophy, and crypt hyperplasia. Furthermore, when the animals were treated with pentoxifylline, a known inhibitor of TNF-alpha secretion in vitro and in vivo, there was significant normalisation of the intestinal morphology accompanied by inhibition of epithelial apoptosis.

CONCLUSIONS

The FasL-Fas interaction is not involved in the induction of apoptosis during acute GVHD. However, neutralisation of TNF-alpha by an antibody or by pentoxifylline inhibits the occurrence of apoptosis and of mucosal atrophy in this animal model. These results have implications for the treatment of immunologically mediated human atrophic gut diseases-for example, diet refractory cases of coeliac disease.

Cytokine-producing cells in peripheral blood of children with coeliac disease secrete cytokines with a type 1 profile

Coeliac disease (CoD) is a small intestinal disorder characterized by crypt cell hyperplasia and villous atrophy, and the production of cytokines from T cells and macrophages are of importance for the histological changes seen in CoD. A peroral immunization with an antigen, which gives rise to a mucosal immune response, may increase the levels of circulating cytokine-producing cells, and we wanted to obtain a better picture of an eventual emergence of activated circulating T cells in the peripheral blood in children with CoD. The cytokine expression of interferon-gamma (IFN-gamma), IL-4, IL-6 and IL-10 was measured at the single-cell level by an ELISPOT method in 38 children with CoD. The numbers of IFN-gamma-producing cells in the peripheral blood was increased in children with untreated CoD (P < 0.01) and after gluten challenge (P < 0.05) compared with healthy controls. Also, the numbers of IL-6-producing cells were increased (P < 0.05) after gluten challenge compared with the healthy controls. A paired comparison showed that the numbers of IFN-gamma-producing cells increased after gluten challenge (P < 0.05), whereas no such change was seen for IL-4- or IL-10-producing cells. There were no differences in the numbers of IFN-gamma-producing cells between the group of children with treated CoD and the groups of untreated or challenged CoD children. IL-4 production correlated with serum levels of total IgE. These results show that circulating mononuclear cells in children with active CoD secrete cytokines compatible with a type 1 response.

Spontaneous secretion of interferon gamma and interleukin 4 by human intraepithelial and lamina propria gut lymphocytes

BACKGROUND

Cytokines secreted by intestinal T lymphocytes probably play a critical role in regulation of the gut associated immune responses.

AIMS

To quantify interferon gamma (IFN-gamma) and interleukin 4 (IL-4) secreting cells (SC) among human intraepithelial (IEL) and lamina propria (LPL) lymphocytes from the duodenum and right colon in non-pathological situations and in the absence of in vitro stimulation.

PATIENTS

Duodenal and right colonic biopsy specimens were obtained from patients with no inflammation of the intestinal mucosa.

METHODS

Intraepithelial and lamina propria cell suspensions were assayed for numbers of cells spontaneously secreting IFN-gamma and IL-4 by a two site reverse enzyme linked immunospot technique (ELISPOT).

RESULTS

The relatively high proportion of duodenal lymphocytes spontaneously secreting IFN-gamma (IEL 3.6%; LPL 1.9%) and IL-4 (IEL 1.3%; LPL 0.7%) contrasted with the very low numbers of spontaneously IFN-gamma SC and the absence of spontaneously IL-4 SC among peripheral blood mononuclear cells. In the basal state, both IFN-gamma and IL-4 were mainly produced by CD4+ cells. Within the colon, only 0.2% of IEL and LPL secreted IFN-gamma in the basal state, and 0.1% secreted IL-4.

CONCLUSIONS

Compared with peripheral lymphocytes substantial proportions of intestinal epithelial and lamina propria lymphocytes spontaneously secrete IFN-gamma and/or IL-4. These cytokines are probably involved in the normal homoeostasis of the human intestinal mucosa. Disturbances in their secretion could play a role in the pathogenesis of gastrointestinal diseases.

Majority of gliadin-specific T-cell clones from celiac small intestinal mucosa produce interferon-gamma and interleukin-4

An abnormal mucosal cell-mediated immune response plays a fundamental role in the pathogenesis of celiac disease. To characterize locally infiltrating T cells, gliadin-specific T-cell clones were isolated from two treated celiac patients. Mucosal biopsies were cultured in vitro for 24 hr with a peptic-tryptic digest (PT) of gliadin. T-cell clones (TCC) were then isolated by limiting dilution. The production of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) was evaluated by ELISA in culture supernatants obtained after a short incubation with anti-CD3 and PMA, or with antigen. Twenty-two TCC were specific for gliadin and/or PT. All were CD3+, CD4+, CD8-, TCR alphabeta+. In one such clone the PT-specific response was inhibited by an anti-DQ, but not by an anti-DR antibody. Of the five gliadin-specific TCC examined, four produced IL-4 and high levels of IFN-gamma; the remaining one initially produced only IL-4, but subsequently also IFN-gamma. All clones obtained from the celiac mucosa, including the gliadin-specific ones, produced high levels of IFN-gamma, in most cases with IL-4. This cytokine profile could explain most of the immunological features of the celiac mucosa.

The anatomical basis of intestinal immunity

The lymphoid tissues associated with the intestine are exposed continuously to antigen and are the largest part of the immune system. Many lymphocytes are found in organised tissues such as the Peyer's patches and mesenteric lymph nodes, as well as scattered throughout the lamina propria and epithelium of the mucosa itself. These lymphocyte populations have several unusual characteristics and the intestinal immune system is functionally and anatomically distinct from other, peripheral compartments of the immune system. This review explores the anatomical and molecular basis of these differences, with particular emphasis on the factors which determine how the intestinal lymphoid tissues discriminate between harmful pathogens and antigens which are beneficial, such as food proteins or commensal bacteria. These latter antigens normally provoke immunological tolerance, and inappropriate responses to them are responsible for immunopathologies such as food hypersensitivity and inflammatory bowel disease. We describe how interactions between local immune cells, epithelial tissues and antigen-presenting cells may be critical for the induction of tolerance and the expression of active mucosal immunity. In addition, the possibility that the intestine may act as an extrathymic site for T-cell differentiation is discussed. Finally, we propose that, under physiological conditions, immune responses to food antigens and commensal bacteria are prevented by common regulatory mechanisms, in which transforming growth factor beta plays a critical role.

Class II MHC expression on rat intestinal intraepithelial lymphocytes

The expression of class II major histocompatibility complex (MHC) on rat intestinal intraepithelial lymphocytes (IELs) and mesenteric lymph node cells (MLNCs) were examined by immunofluorescence and flow cytometry. As expected, MLNCs contain eight small populations of CD4+ class II MHC+ T-cells in addition to classical antigen presenting cells. In contrast, rat IELs include a significant population of class II MHC+ T-cells, predominantly in the CD8+ CD4-alpha beta TCR+ subset. IEL samples with a relatively high percentage of class II MHC+ cells also include some CD4+ class II MHC+ cells; IEL samples with a low percentage of class II MHC+ cells also include some CD4- CD8- class II MHC+ cells. The role of lymphocyte subpopulations in the intestinal epithelium may need to be revisited in consideration of these findings.

Induction of ileum muscarinic cholinoceptor signal transduction pathways by rat interferon-gamma

We have recently shown that rat interferon-gamma (IFN gamma) can trigger a cholinergic muscarinic response upon interaction with isolated rat atria, decreasing both the contractile tension and cAMP synthesis, and increasing cGMP production. Because the intestine is rich in cholinergic muscarinic receptors, and IFN gamma-producing cells are normal components of the mucosal immune system, we investigated whether IFN gamma could also modulate the muscarinic cholinergic activity of the intestine. Our results indicate that IFN gamma may interact with ileum cholinergic muscarinic receptors by inhibiting binding of the radiolabelled antagonist quinuclidinyl benzylate (3H-QNB), decreasing cAMP formation and increasing cGMP synthesis. These effects are associated with increased mechanical activity of the isolated ileum strips, and can be blunted by pretreatment of the tissue with atropine.

Gluten specific, HLA-DQ restricted T cells from coeliac mucosa produce cytokines with Th1 or Th0 profile dominated by interferon gamma

Coeliac disease is precipitated in susceptible subjects by ingestion of wheat gluten or gluten related prolamins from some other cereals. The disease is strongly associated with certain HLA-DQ heterodimers, for example, DQ2 (DQ alpha 1*0501, beta 1*0201) in most patients and apparently DQ8 (DQ alpha 1*0301, beta 1*0302) in a small subset. Gluten specific T cell clones (TCC) from coeliac intestinal lesions were recently established and found to be mainly restricted by HLA-DQ2 or HLA-DQ8. Antigen induced production of cytokines was studied in 15 TCC from three patients, 10 being DQ2 and five DQ8 restricted. Cell culture supernatants were prepared by stimulation with gluten peptides in the presence of DQ2+ or DQ8+ Epstein-Barr virus transformed B cells as antigen presenting cells (APC). Supernatants were analysed for cytokines by bioassays, ELISA, and CELISA. Cellular cytokine mRNA was analysed semi-quantitatively by slot blotting and polymerase chain reaction (PCR). All TCC were found to secrete interferon (IFN) gamma, often at high concentrations (> 2000 U/ml); some secreted in addition interleukin (IL) 4, IL 5, IL 6, IL 10, tumour necrosis factor (TNF), and transforming growth factor (TGF) beta. The last TCC thus displayed a Th0-like cytokine pattern. However, other TCC produced IFN gamma and TNF but no IL 4, or IL 5, compatible with a Th1-like pattern. In conclusion, most DQ8 restricted TCC seemed to fit with a Th0 profile whereas the DQ2 restricted TCC secreted cytokines more compatible with a Th1 pattern. The TCC supernatants induced upregulation of HLA-DR and secretory component (poly-Ig receptor) in the colonic adenocarcinoma cell line HT-29.E10, most probably reflecting mainly the high IFN gamma concentrations. This cytokine, particularly in combination with TNF alpha, might be involved in several pathological features of the coeliac lesion. The characterised cytokine profiles thus support the notion that mucosal T cells activated in situ by gluten in a DQ restricted fashion play a central part in the pathogenesis of coeliac disease.

Cytokine mRNA expression in the mucosa of treated coeliac patients after wheat peptide challenge

This study investigated the presence of mRNA coding for interferon gamma (IFN gamma), tumour necrosis factor alpha (TNF alpha), and interleukins 2 (IL2) and 6 (IL6), in the mucosa of four coeliac patients in remission who had been challenged with either gliadin or synthetic gliadin oligopeptides. Jejunal biopsy specimens from these patients, taken before and at two, four, and six hours after challenge, were hybridised with specific 35S-labelled DNA oligonucleotide probes. The lamina propria of all the patients contained significantly increased numbers of cytokine mRNA expressing cells four hours after challenge with gliadin or an oligopeptide corresponding to amino acids 31-49 of A-gliadin (peptide A). No significant changes were seen with the peptides corresponding to aminoacids 202-220 (peptide B) or 3-21 (peptide C) of A-gliadin, with the exception of one patient who showed a significant increase in the number of TNF alpha mRNA expressing cells four hours after challenge with peptide B. In vivo studies in coeliac disease have shown that significant histological changes occur in the mucosa of treated coeliac patients four hours after challenge with either gliadin or peptide A. These findings suggest that the histological changes seen previously in the mucosa of coeliac patients after wheat peptide challenge may be caused by increased expression of cytokines within the mucosa.

Expression of tumour necrosis factor-alpha, interleukin-6, and interleukin-2 mRNA in the jejunum of patients with coeliac disease

BACKGROUND

A T-cell-mediated immune response may be responsible for the enteropathy seen in coeliac disease (CD), but it is unclear whether this is initiated in the epithelium or the lamina propria. We studied the site and number of cells expressing mRNA encoding the cytokines interleukin-2 (IL-2), IL-6, and tumour necrosis factor-alpha in jejunal biopsy specimens from patients with untreated or treated CD and normal controls.

METHODS

Tissue sections were hybridized with 35S-labelled DNA oligonucleotide probes specific for each cytokine RNA sequence. Positive cells were counted in the lamina propria and epithelial compartments.

RESULTS

For each cytokine significantly greater numbers of positive cells were found in the lamina propria of untreated CD patients. Few positive cells were detected in the epithelium of all three groups.

CONCLUSIONS

This study shows that the immune response to gliadin appears to occur in the lamina propria and supports cell-mediated immunity in the pathogenesis of coeliac disease.

Detection of interferon gamma mRNA in the mucosa of patients with coeliac disease by in situ hybridisation

In situ hybridisation has been used to study interferon gamma (IFN gamma) mRNA expression in the small intestine of patients with coeliac disease. Sections of jejunal biopsies were obtained from five patients with treated and five with untreated coeliac disease and five disease controls. These sections were hybridised with radiolabelled specific DNA oligonucleotide probes. The lamina propria of untreated coeliac disease patients contained a significantly increased number of IFN gamma producing cells compared with controls but there was no significant difference between the coeliac patients treated with a gluten free diet and controls. The results suggest that IFN gamma may play a part in the immunopathogenesis of coeliac disease.

Interferon-gamma modulates cAMP-induced mucin exocytosis without affecting mucin gene expression in a human colonic goblet cell line

The regulation of intestinal mucin secretion by cytokines, soluble factors released by mucosal activated immune cells, is so far unknown. The aim of the present study was (1) to investigate the regulatory effects of interferon-gamma on baseline and stimulated mucin secretion elicited by an increase in intracellular cAMP, either a short-term increase (induced by vasoactive intestinal peptide or by forskolin) or a long-term increase (cholera toxin-induced), and (2) to attempt to delineate the site of action of interferon-gamma. The in vitro model used was the human colonic goblet cell line Cl.16E, which has already been shown to respond to physiological secretagogues in terms of mucin secretion. We examined the effects of interferon-gamma 1) on mucin exocytosis, measured as release of [3H]glucosamine-labeled macromolecules trapped at the stacking/running gel interface of polyacrylamide gels, and 2) on mucin biosynthesis, examined at the RNA level using a cDNA probe directed to the MUC2 mucin gene. We demonstrated that, while interferon-gamma did not alter baseline Cl.16E mucin secretion and MUC2 gene expression, it strongly inhibited the protein kinase A-dependent secretory response to VIP, forskolin, or cholera toxin. However, interferon-gamma had no effect on the protein kinase A-dependent MUC2 over-expression induced by cholera toxin. We thus concluded that the target for interferon-gamma inhibition of cAMP-stimulated Cl.16E mucin secretion is distal to protein kinase A and might be a component of the exocytotic machinery. Together, our results establish interferon-gamma as a pharmacologically powerful tool to specifically inhibit stimulated secretory processes without affecting baseline secretion.