Excess IL-12 but not IL-23 accompanies the inflammatory bowel disease associated with common variable immunodeficiency

The role of chronic norovirus infection in the enteropathy associated with common variable immunodeficiency

OBJECTIVES

A severe enteropathy of unknown etiology can be associated with common variable immunodeficiency (CVID).

METHODS

S tool and archived small intestinal mucosal biopsies from patients with CVID enteropathy were analyzed by PCR for the presence of Norovirus RNA. The PCR products were sequenced to determine the relationship of viral isolates. Stool samples from 10 patients with CVID but no enteropathy served as controls.

RESULTS

All eight patients in our CVID cohort with enteropathy showed persistent fecal excretion of Norovirus. Analysis of archived duodenal biopsies revealed a strong association between the presence of Norovirus and villous atrophy over a period of up to 8 years. Analysis of the viral isolates from each patient revealed distinct strains of genogroup II.4. Sequence analysis from consecutive biopsy specimens of one patient demonstrated persistence of the same viral strain over a 6-year period. CVID patients without enteropathy showed no evidence of Norovirus carriage. Viral clearance occurred spontaneously in one patient and followed oral Ribavirin therapy in two further patients, and resulted in complete symptomatic and histological recovery. However, Ribavirin treatment in two further patients was unsuccessful.

CONCLUSIONS

Norovirus is an important pathogen for patients with CVID and a cause of CVID enteropathy, as viral clearance, symptom resolution, and histological recovery coincide. Ribavirin requires further evaluation as a potential therapy.

Cytokines in common variable immunodeficiency as signs of immune dysregulation and potential therapeutic targets - a review of the current knowledge

Common variable immunodeficiency (CVID) is characterized by low levels of circulating immunoglobulins and compromised specific antibody response leading to frequent infections. Cytokines play an important role in the orchestration of the antibody response. Several previous studies have attempted to identify distinct cytokines responsible for the inflammatory changes and different manifestations of CVID, but there are conflicting results regarding the cytokine profiles in CVID patients. In light of this, an extensive review regarding the level of various cytokines and their potential therapeutic role in CVID patients was performed. This review delineates the contribution of interleukin (IL)-1, IL-2, IL-4, IL-5, IL-6, IL-7, IL-10, IL-12, IL-21, interferons, tumor necrosis factor (TNF)-α, IL-17, APRIL (a proliferation inducing ligand) and BAFF (B cell activating factor) in CVID disease and outline their potential therapeutic implications in these patients.

The role of the immune system in governing host-microbe interactions in the intestine

The mammalian intestinal tract harbors a diverse community of trillions of microorganisms, which have co-evolved with the host immune system for millions of years. Many of these microorganisms perform functions critical for host physiology, but the host must remain vigilant to control the microbial community so that the symbiotic nature of the relationship is maintained. To facilitate homeostasis, the immune system ensures that the diverse microbial load is tolerated and anatomically contained, while remaining responsive to microbial breaches and invasion. Although the microbiota is required for intestinal immune development, immune responses also regulate the structure and composition of the intestinal microbiota. Here we discuss recent advances in our understanding of these complex interactions and their implications for human health and disease.

Bridging immunity and lipid metabolism by gut microbiota

The human gut is a unique organ in which hundreds of different microbial species find their habitat and in which different host physiologic functions, such as digestion, nutrition, and immunity, coexist. Although all these players were studied separately for decades, recently, there has been an explosion of studies demonstrating the essential role for interactions between these components in gut function. Furthermore, new systems biology methods provide essential tools to study this complex system as a whole and to identify key elements that define the crosstalk between the gut microbiota, immunity, and metabolism. This review is devoted to several human diseases resulting from the disruption in this crosstalk, including immunodeficiency-associated and environmental enteropathies, celiac disease, inflammatory bowel disease, and obesity. We describe findings in experimental models of these diseases and in germ-free animals that help us understand the mechanisms and test new therapeutic strategies. We also discuss current challenges that the field is facing and propose that a new generation of antibiotics, prebiotics, and probiotics coupled with novel, systems biology-driven diagnostics will provide the basis for future personalized therapy.

Diagnosis and treatment of gastrointestinal disorders in patients with primary immunodeficiency

Gastrointestinal disorders such as chronic or acute diarrhea, malabsorption, abdominal pain, and inflammatory bowel diseases can indicate immune deficiency. The gastrointestinal tract is the largest lymphoid organ in the body, so it is not surprising that intestinal diseases are common among immunodeficient patients. Gastroenterologists therefore must be able to diagnose and treat patients with primary immunodeficiency. Immune-related gastrointestinal diseases can be classified as those that develop primarily via autoimmunity, infection, an inflammatory response, or malignancy. Immunodeficient and immunocompetent patients with gastrointestinal diseases present with similar symptoms. However, intestinal biopsy specimens from immunodeficient patients often have distinct histologic features, and these patients often fail to respond to conventional therapies. Therefore, early recognition of symptoms and referral to an immunologist for a basic immune evaluation is required to select appropriate treatments. Therapies for primary immunodeficiency comprise immunoglobulin replacement, antibiotics, and, in severe cases, bone marrow transplantation. Treatment of immunodeficient patients with concomitant gastrointestinal disease can be challenging, and therapy with immunomodulators often is required for severe disease. This review aims to guide gastroenterologists in the diagnosis and treatment of patients with primary immunodeficiency.

Nodular regenerative hyperplasia in common variable immunodeficiency

PURPOSE

Patients with Common Variable Immunodeficiency (CVID) are subject to the development of a liver disease syndrome known as nodular regenerative hyperplasia (NRH). The purpose of this study was to define the characteristics and course of this complication of CVID.

METHODS

CVID patients were evaluated by retrospective and prospective clinical course review. Liver biopsy specimens were evaluated for evidence of NRH and studied via RT-PCR for cytokine analysis.

RESULTS

NRH in our CVID patient population occurred in approximately 5 % of the 261 patients in our total CVID study group, initially presenting in most cases with an elevated alkaline phosphatase level. While in some patients the disease remained static, in a larger proportion a more severe disease developed characterized by portal hypertension, the latter leading to hypersplenism with neutropenia and thrombocytopenia and, in some cases, to ascites. In addition, a substantial proportion of patients either developed or presented initially with an autoimmune hepatitis-like (AIH-like) liver disease that resulted in severe liver dysfunction and, in most cases to death due to infections. The liver histologic findings in these AIH-like patients were characterized by underlying NRH pattern with superimposed interface hepatitis, lymphocytic infiltration and fibrosis. Immunologic studies of biopsies of NRH patients demonstrated the presence of infiltrating T cells producing IFN-γ, suggesting that the NRH is due to an autoimmune process.

CONCLUSION

Overall, these studies provide evidence that NRH may not be benign but, can be a severe and potentially fatal disease complication of CVID that merits close monitoring and intervention.

Common variable immunodeficiency: crossroads between infections, inflammation and autoimmunity

Common variable immunodeficiency is a collection of diseases characterized by primary hypogammaglobulinemia. The causes of CVID are extremely heterogeneous and may affect virtually every pathway linked to B cell development and function. Clinical manifestations of CVID mainly include recurrent bacterial infections, but autoimmune, gastrointestinal, lymphoproliferative, granulomatous, and malignant disorders have also been frequently reported as associated conditions. We aimed to focus on the state of the art of the relationship between infections, inflammation and autoimmunity in CVID.

Circulating levels of interleukin (IL)-12 and IL-13 in Helicobacter pylori-infected patients, and their associations with bacterial CagA and VacA virulence factors

OBJECTIVE

The aim of this study was to determine the association of the Helicobacter pylori virulence factors, cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA) antibodies, with serum levels of interleukin (IL)-12 and IL-13 in H. pylori-infected duodenal ulcer (DU) patients and H. pylori-infected asymptomatic (AS) carriers in order to elucidate any correlation between them.

METHODS

A total of 67 DU patients, 48 AS individuals, and 26 healthy H. pylori-negative subjects were enrolled in this study. Serum concentrations of IL-12 and IL-13 were determined by enzyme-linked immunosorbent assay (ELISA) method. Patient sera were tested by Western blot method to determine the presence of serum antibodies to bacterial virulence antigens p120 (CagA) and p95 (VacA). Serum concentrations of IL-12 and IL-13 were compared in 9 groups, including 4 AS phenotypes (CagA⁺VacA⁺, CagA⁺VacA⁻, CagA⁻VacA⁺, CagA⁻VacA⁻), 4 DU phenotypes (CagA⁺VacA⁺, CagA⁺VacA⁻, CagA⁻VacA⁺, CagA⁻VacA⁻), and 1 control group.

RESULTS

The results revealed that DU patients positive for CagA, independent of the anti-VacA antibody status, showed drastically elevated levels of IL-12 (251 ± 43 pg/ml) when compared with the other groups (p = 0.0001). No significant difference was found between groups regarding levels of IL-13 (p > 0.05).

CONCLUSIONS

Our findings indicate that in the DU group, the serum concentrations of IL-12 but not of IL-13 were influenced by bacterial CagA, independent of the VacA status, suggesting that high IL-12 levels may contribute to susceptibility to DU in CagA-positive individuals. These findings could possibly be considered to improve the predictive or prognostic values of inflammatory cytokines for DU, and also to design possible novel therapeutic approaches.

The significance of duodenal mucosal atrophy in patients with common variable immunodeficiency: a clinical and histopathologic study

Gastrointestinal manifestations and villous atrophy can be seen in patients with common variable immunodeficiency (CVID). In some patients, infectious agents may be responsible, whereas in others, celiac disease (CD) may be the cause. In this study, we investigate the causes and the histopathologic features seen in patients with CVID. Eleven patients with CVID and villous atrophy underwent duodenal biopsies, human leukocyte antigen (HLA) typing, and testing for all celiac antibodies. Fifteen patients with CVID and normal villi and 6 patients with CD but without CVID served as controls. Histologic response to a gluten-free diet (GFD) allowed a diagnosis of CD in 3 of 11 patients. In the remaining 8, the lack of a histologic response to a GFD or HLA typing excluded CD. Celiac antibodies gave conflicting results and were of no help. Polymorphonuclear infiltrates and lesions like graft-versus-host disease are seen more often in flat mucosa unresponsive to a GFD. However, the specificity of these findings remains to be determined and response to a GFD remains the only diagnostic criteria for CD in these patients. Villous atrophy was gluten-sensitive in 3 of 11 patients with CVID. It was not related to gluten-responsive CD in most patients.

Crosstalk between B lymphocytes, microbiota and the intestinal epithelium governs immunity versus metabolism in the gut

Using a systems biology approach, we discovered and dissected a three-way interaction between the immune system, the intestinal epithelium and the microbiota. We found that, in the absence of B cells, or of IgA, and in the presence of the microbiota, the intestinal epithelium launches its own protective mechanisms, upregulating interferon-inducible immune response pathways and simultaneously repressing Gata4-related metabolic functions. This shift in intestinal function leads to lipid malabsorption and decreased deposition of body fat. Network analysis revealed the presence of two interconnected epithelial-cell gene networks, one governing lipid metabolism and another regulating immunity, that were inversely expressed. Gene expression patterns in gut biopsies from individuals with common variable immunodeficiency or with HIV infection and intestinal malabsorption were very similar to those of the B cell-deficient mice, providing a possible explanation for a longstanding enigmatic association between immunodeficiency and defective lipid absorption in humans.

Primary B-cell deficiencies reveal a link between human IL-17-producing CD4 T-cell homeostasis and B-cell differentiation

IL-17 is a pro-inflammatory cytokine implicated in autoimmune and inflammatory conditions. The development/survival of IL-17-producing CD4 T cells (Th17) share critical cues with B-cell differentiation and the circulating follicular T helper subset was recently shown to be enriched in Th17 cells able to help B-cell differentiation. We investigated a putative link between Th17-cell homeostasis and B cells by studying the Th17-cell compartment in primary B-cell immunodeficiencies. Common Variable Immunodeficiency Disorders (CVID), defined by defects in B-cell differentiation into plasma and memory B cells, are frequently associated with autoimmune and inflammatory manifestations but we found no relationship between these and Th17-cell frequency. In fact, CVID patients showed a decrease in Th17-cell frequency in parallel with the expansion of activated non-differentiated B cells (CD21(low)CD38(low)). Moreover, Congenital Agammaglobulinemia patients, lacking B cells due to impaired early B-cell development, had a severe reduction of circulating Th17 cells. Finally, we found a direct correlation in healthy individuals between circulating Th17-cell frequency and both switched-memory B cells and serum BAFF levels, a crucial cytokine for B-cell survival. Overall, our data support a relationship between Th17-cell homeostasis and B-cell maturation, with implications for the understanding of the pathogenesis of inflammatory/autoimmune diseases and the physiology of B-cell depleting therapies.

Characterization of immunologic defects in patients with common variable immunodeficiency (CVID) with intestinal disease

BACKGROUND

Common variable immunodeficiency (CVID) is a heterogeneous disorder commonly presenting with recurrent sinopulmonary infections. In all, 6%-10% of CVID patients develop an inflammatory bowel disease (IBD)-like disorder, making these patients a unique population to investigate immune-mediated gastrointestinal disease. This study examined whether defects in peripheral and/or intestinal lymphocytes are involved in disruption of the intestinal mucosa in CVID patients with inflammatory intestinal diseases.

METHODS

Peripheral blood (PB) T cells from healthy controls; CD or UC; CVID; and CVID with IBD were stimulated for 48 hours with anti-CD3+CD28 or phytohemagglutinin (PHA) + phorbol 12-myristate 13-acetate (PMA); cytokine production was measured by enzyme-linked immunosorbent assay (ELISA). Cytokine expression from unstimulated lamina propria lymphocytes (LPLs) was compared by real-time polymerase chain reaction (PCR). Immunohistochemistry of mucosal biopsies was performed. Cell populations were quantified by morphometry.

RESULTS

CVID/IBD PB T cells stimulated by anti-CD3+CD28 had trends for reduced IL-2, IL-10, IFN-γ, and TNF-α compared to controls. These differences were not apparent following stimulation by PHA/PMA. Constitutive production of inflammatory cytokines by LPLs was not detected. Histologically, CVID patients had reduced/absent plasma cells with reductions in intestinal IgM and IgA. CVID patients with and without gastrointestinal (GI) disease exhibited increased CD3+ T cells, specifically CD8+, in the colon compared to normal and IBD controls, suggesting immune dysregulation.

CONCLUSIONS

Intestinal inflammation in CVID patients with IBD-like disease may be mediated by abnormal cytokine production through a T-cell receptor-mediated pathway. However, the variability observed suggests multiple, rather than singular, mechanisms are involved. Histologic features such as reduced intestinal plasma cells and lack of intestinal immunoglobulins may be useful markers in diagnosing CVID in a patient with GI disease refractory to conventional therapies.

"A rose is a rose is a rose," but CVID is Not CVID common variable immune deficiency (CVID), what do we know in 2011?

Common variable immune deficiency (CVID) is the commonest symptomatic primary immunodeficiency and represents a heterogenous collection of disorders resulting mostly in antibody deficiency and recurrent infections. However, autoimmunity, granulomatous inflammation and malignancy frequently occur as part of the syndrome. The etiology of the condition has been poorly understood although in recent years, significant progress has been made in elucidating genetic mechanisms that can result in a CVID phenotype. In parallel to this, advances in treatment of the condition have also resulted in improved survival and quality of life for patients. There still remains significant work to be done in improving our understanding of the disease. In addition, recognition of the condition remains poor with significant diagnostic delays and avoidable morbidity. In this article, we review CVID with a particular focus on the areas of improving diagnosis and classification, recent developments in understanding the underlying etiology and genetics; and current treatment and monitoring recommendations for patients.

Inflammatory bowel diseases in patients with adaptive and complement immunodeficiency disorders

Crohn's disease and ulcerative colitis are idiopathic chronic inflammatory diseases that primarily affect the gastrointestinal tract. The underlying causes remain poorly understood, but there is a growing body of evidence advocating a likely primary pathogenic role for immunodeficiency in the development of Crohn's lesions. Concordantly, a number of congenital immunodeficiencies disrupting the cellular innate immune system strongly predispose to noninfectious, Crohn's-like inflammatory bowel disease. There are case reports and series suggesting that the same may be true for some of the congenital adaptive and complement immunodeficiencies. This review considers and critiques these potential associations.

The enteropathy associated with common variable immunodeficiency: the delineated frontiers with celiac disease

OBJECTIVES

The enteropathy associated with common variable immunodeficiency (CVID) is poorly characterized, and its possible relationships with well-defined causes of enteropathy, such as celiac sprue (CS), remain debated. We aimed to assess the clinical and histopathological features of the enteropathy associated with CVID.

METHODS

The medical files of 50 CVID patients with gastrointestinal symptoms were analyzed retrospectively. Histological, phenotypic, and molecular analysis of intestinal endoscopic specimens was centrally performed.

RESULTS

Chronic diarrhea was the most frequent gastrointestinal symptom (92%), and biological evidence of malabsorption was observed in 54% of patients. Chronic gastritis associated or not with pernicious anemia and microscopic colitis were the most frequently observed histopathological features in gastric and colonic mucosa, respectively. Small-bowel biopsies available in 41 patients showed moderate increase in intestinal intraepithelial lymphocytes in 31 patients (75.6%) and villous atrophy in 21 patients (51%). Distinctive features from CS were a profound depletion in plasma cells and follicular lymphoid hyperplasia. Presence of peripheral blood CD8+ hyperlymphocytosis was predictive of intestinal intraepithelial hyperlymphocytosis. Intravenous (i.v.) immunoglobulin (Ig) therapy had no effect on enteropathy-related symptoms. Gluten-free diet improved only two out of 12 patients with villous atrophy, whereas all patients (7/7) responded to steroid therapy.

CONCLUSIONS

Several distinctive features differentiate CVID enteropathy from other causes of enteropathy including CS. Replacement i.v. Ig therapy is insufficient to improve gastrointestinal symptoms. Steroids are effective in reducing inflammation and restoring mucosal architecture.

B-cell and T-cell phenotypes in CVID patients correlate with the clinical phenotype of the disease

BACKGROUND

Common variable immunodeficiency (CVID) is a heterogeneous disorder characterized by recurrent infections and defective immunoglobulin production.

METHODS

The DEFI French national prospective study investigated peripheral T-cell and B-cell compartments in 313 CVID patients grouped according to their clinical phenotype, using flow cytometry.

RESULTS

In patients developing infection only (IO), the main B-cell or T-cell abnormalities were a defect in switched memory B cells and a decrease in naive CD4(+) T cells associated with an increase in CD4(+)CD95(+) cells. These abnormalities were more pronounced in patients developing lymphoproliferation (LP), autoimmune cytopenia (AC), or chronic enteropathy (CE). Moreover, LP and AC patients presented an increase in CD21(low) B cells and CD4(+)HLA-DR(+) T cells and a decrease in regulatory T cells.

CONCLUSION

In these large series of CVID patients, the major abnormalities of the B-cell and T-cell compartments, although a hallmark of CVID, were only observed in half of the IO patients and were more frequent and severe in patients with additional lymphoproliferative, autoimmune, and digestive complications.

Gastrointestinal manifestations in primary immune disorders

The gastrointestinal tract is the largest lymphoid organ in the body containing T and B lymphocytes, macrophages, and dendritic cells. Despite the fact that these cells are constantly confronted with antigen primarily in the form of food and bacteria, immune responses in the gut are tightly regulated to maintain homeostasis. Without this balance of active immunity and tolerance, mucosal inflammation may ensue, and manifest as Crohn's disease, ulcerative colitis, pernicious anemia, or celiac sprue. Therefore, it is not unreasonable that inflammatory diseases of the gut are commonly encountered in patients with primary immune deficiencies. The exact pathogenesis of gastrointestinal diseases in the setting of primary immunodeficiency remains unknown, however, both humoral and cell-mediated immunity appear to play a role in preventing intestinal inflammation. Patients presenting with atypical gastrointestinal disease and/or failure to respond to conventional therapy should be evaluated for an underlying primary immune disorder in order to initiate appropriate treatment, such as immunoglobulin or in more severe cases bone marrow transplantation, to prevent long term complications.

Pathogenesis and treatment of gastrointestinal disease in antibody deficiency syndromes

Primary humoral immune deficiencies are characterized by limited antibody responses secondary to either impaired B-lymphocyte development or B-cell responses to T-lymphocyte signals. Given that the gastrointestinal tract is the largest lymphoid organ in the body, it is not surprising that intestinal diseases are common in immunodeficiency. These gastrointestinal diseases can be classified into one of 4 groups, infection, malignancy, inflammatory, and autoimmune, and can mimic other known disease processes, such as inflammatory bowel disease and celiac sprue. The exact pathogenesis of these gastrointestinal disorders in the setting of systemic immunodeficiency is still under investigation. However, studies suggest that defects in antibody deficiency alone do not result in gastrointestinal disease but rather that defects in cellular immunity are also involved. Treatment is difficult given an already immunocompromised state, and often therapy with immunomodulators is required for more severe processes.

Inflammatory bowel disease causes reversible suppression of osteoblast and chondrocyte function in mice

Decreased bone density and stature can occur in pediatric patients with inflammatory bowel disease (IBD). Little is known about how IBD broadly impacts the skeleton. To evaluate the influence of an acute episode of IBD on growing bone, 4-wk-old mice were administered 5% dextran sodium sulfate (DSS) for 5 days to induce colitis and their recovery was monitored. During active disease and early recovery, trabecular bone mineral density, bone volume, and thickness were decreased. Cortical bone thickness, outer perimeter, and density were also decreased, whereas inner perimeter and marrow area were increased. These changes appear to maintain bone strength since measures of moments of inertia were similar between DSS-treated and control mice. Histological (static and dynamic), serum, and RNA analyses indicate that a decrease in osteoblast maturation and function account for changes in bone density. Unlike some conditions of bone loss, marrow adiposity did not increase. Similar to reports in humans, bone length decreased and correlated with decreases in growth plate thickness and chondrocyte marker expression. During disease recovery, mice experienced a growth spurt that led to their achieving final body weights and bone length, density, and gene expression similar to healthy controls. Increased TNF-alpha and decreased IGF-I serum levels were observed with active disease and returned to normal with recovery. Changes in serum TNF-alpha (increased) and IGF-I (decreased) paralleled changes in bone parameters and returned to normal values with recovery, suggesting a potential role in the skeletal response.

Update in understanding common variable immunodeficiency disorders (CVIDs) and the management of patients with these conditions

The common variable immunodeficiency disorders are a mixed group of heterogeneous conditions linked by lack of immunoglobulin production and primary antibody failure. This variability results in difficulty in making coherent sense of either immunopathogenesis or the role of various genetic abnormalities reported in the literature. The recent attempt to collate the varied complications in these conditions and to define particular clinical phenotypes has improved our understanding of these diseases. Once refined and confirmed by other studies, these definitions will facilitate improved accuracy of prognosis and better management of clinical complication. They may also provide a method of analysing outcomes as related to new immunopathological and genetic findings.

[Gastrointestinal diseases in primary immunodeficiency disorders]

Gastrointestinal symptoms are common and often reveal primary immunodeficiency. Although they mimic gastrointestinal diseases observed in immunocompetent patients, there have diagnostic and therapeutic specificities that should be known for optimal management of these patients. This review describes the gastrointestinal diseases found in primary immunodeficiency and proposes some diagnostic and therapeutic strategies.

Anti-tumour necrosis factor-alpha therapy for severe enteropathy in patients with common variable immunodeficiency (CVID)

We present three common variable immunodeficiency (CVID) patients with severe inflammatory bowel disease of unknown aetiology, resistant to steroid treatment, treated with infliximab. After exclusion of any infection, infliximab was given at a dose of 5 mg/kg every 4 weeks for a 3 month induction followed by every 4-8 weeks depending on clinical response. Two of these patients had predominantly small bowel disease; they both showed clinical response to infliximab with weight gain and improvement of quality of life scores. The third patient had large bowel involvement with profuse watery diarrhea; this patient improved dramatically within 48 hours of having infliximab treatment. All three patients have been maintained on infliximab treatment for between 5 and 53 months (mean 37 months) with no evidence of increased susceptibility to infections in the patients with small bowel disease, although the third patient developed two urinary tract infections and a herpes zoster infection following therapy. This is the first small case series to show that infliximab is a useful addition to current therapy in this rare group of patients with potentially life threatening enteritis.

The fundamental basis of inflammatory bowel disease

Two broad hypotheses have arisen regarding the fundamental nature of the pathogenesis of inflammatory bowel diseases (IBDs, which include ulcerative colitis and Crohn disease). The first contends that primary dysregulation of the mucosal immune system leads to excessive immunologic responses to normal microflora. The second suggests that changes in the composition of gut microflora and/or deranged epithelial barrier function elicits pathologic responses from the normal mucosal immune system. Here we examine these hypotheses and conclude that IBD is indeed characterized by an abnormal mucosal immune response but that microbial factors and epithelial cell abnormalities can facilitate this response.