Role of the high affinity immunoglobulin E receptor in bacterial translocation and intestinal inflammation

Mouse and human FcR effector functions

Mouse and human FcRs have been a major focus of attention not only of the scientific community, through the cloning and characterization of novel receptors, and of the medical community, through the identification of polymorphisms and linkage to disease but also of the pharmaceutical community, through the identification of FcRs as targets for therapy or engineering of Fc domains for the generation of enhanced therapeutic antibodies. The availability of knockout mouse lines for every single mouse FcR, of multiple or cell-specific--'à la carte'--FcR knockouts and the increasing generation of hFcR transgenics enable powerful in vivo approaches for the study of mouse and human FcR biology. This review will present the landscape of the current FcR family, their effector functions and the in vivo models at hand to study them. These in vivo models were recently instrumental in re-defining the properties and effector functions of FcRs that had been overlooked or discarded from previous analyses. A particular focus will be made on the (mis)concepts on the role of high-affinity IgG receptors in vivo and on results from antibody engineering to enhance or abrogate antibody effector functions mediated by FcRs.

IgE-based immunotherapy of cancer: challenges and chances

Passive immunotherapy with monoclonal antibodies is an indispensable cornerstone of clinical oncology. Notably, all FDA-approved antibodies comprise the IgG class, although numerous research articles proposed monoclonal antibodies of the IgM, IgG, IgA and IgE classes directed specifically against tumor-associated antigens. In particular, for the IgE isotype class, several recent studies could demonstrate high tumoricidic efficacy. Therefore, this review specifically highlights the latest developments toward IgE-based immunotherapy of cancer. Possible mechanisms and safety aspects of IgE-mediated tumor cell death are discussed with special focus on the attracted immune cells. An outlook is given on how especially comparative oncology could contribute to further developments. Humans and dogs have a highly comparable IgE biology, suggesting that translational AllergoOncology studies in patients with canine cancer could have predictive value for the potential of IgE-based anticancer immunotherapy in human clinical oncology.

Modulation of anti-inflammatory response in lipopolysaccharide stimulated human THP-1 cell line and mouse model at gene expression level with indigenous putative probiotic lactobacilli

The anti-inflammatory potential of eight indigenous probiotic Lactobacillus isolates was evaluated in vitro in terms of modulating the expression of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) in human acute monocytic leukemia (THP-1) cells under inflammatory conditions. Amongst these, Lactobacillus plantarum Lp91 was the most potent anti-inflammatory strain as it evoked a significant (P < 0.001) down-regulation of TNF-α by -1.45-fold relative to the control in THP-1 cells. However, in terms of IL-6 expression, all the strains could up-regulate its expression considerably at different levels. Hence, based on in vitro expression of TNF-α, Lp91 was selected for in vivo study in lipopolysaccharide (LPS)-induced mouse model to look at the expression of TNF-α, IL-6, monocyte chemotactic protein-1 (MCP-1), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule (ICAM-1) and E-selectin in mouse aorta. In LPS challenged (2 h) mice group fed with Lp91 for 10 days, TNF-α, IL-6, MCP-1, VCAM-1, ICAM-1 and E-selectin expressions were significantly down-regulated by 3.10-, 10.02-, 4.22-, -3.14-, 2.28- and 5.71-fold relative to control conditions. In conclusion, Lp91 could serve as a candidate probiotic strain to explore it as a possible biotherapeutic anti-inflammatory agent against inflammatory diseases including cardiovascular disease.

Anti-inflammatory and immunomodulatory efficacy of indigenous probiotic Lactobacillus plantarum Lp91 in colitis mouse model

Probiotics can affect the immune homeostasis by altering the gut microbial balance and enhancing the immune system of gut, thus benefits in Inflammatory Bowel Disease, including Crohn's disease and Ulcerative colitis. Relative gene expression of pro, anti-inflammatory cytokines and other molecules in 2,4,6-trinitrobenzene sulfonic acid-induced colitis mouse model against Lactobacillus plantarum Lp91 (L. plantarum Lp91) was investigated by reverse transcription-quantitative PCR (RT-qPCR) using relative expression software tool (REST 2008 V2.0.7). L. plantarum Lp91 evoked significant down regulation of TNF-α and COX2 to 0.026 and 0.077 fold in colitis mouse model. No significant difference in expression of IL-12a cytokine in colitis mouse challenged with L. plantarum Lp91 was also observed. IL-10 was significantly up-regulated to 37.813 and 1.327 fold in colitis and non-colitis mouse challenged with L. plantarum Lp91. While, other anti-inflammatory markers i.e. COX1, IL-4 and IL-6 were significantly up regulated in colitis mouse challenged with L. plantarum Lp91. MUC2 gene was significantly up regulated to 2.216 fold in non-colitis group. L. plantarum Lp91, an indigenous probiotic culture, the main subject of this project exhibited strong immunemodulatory properties under in vivo conditions in mouse colitis model.

Peanut-induced intestinal allergy is mediated through a mast cell-IgE-FcepsilonRI-IL-13 pathway

BACKGROUND

Although implicated in the disease, the specific contributions of FcepsilonRI and IL-13 to the pathogenesis of peanut-induced intestinal allergy are not well defined.

OBJECTIVES

We sought to determine the contributions of FcepsilonRI, IL-13, and mast cells to the development of intestinal mucosal responses in a murine model of peanut-induced intestinal allergy.

METHODS

Sensitized wild-type (WT), FcepsilonRI-deficient (FcepsilonRI(-/-)), and mast cell-deficient (Kit(W-sh/W-sh)) mice received peanut orally every day for 1 week. Bone marrow-derived mast cells (BMMCs) from WT, FcepsilonRI(-/-), IL-4(-/-), IL-13(-/-), and IL-4/IL-13(-/-) mice were differentiated and transferred into WT, FcepsilonRI(-/-), and Kit(W-sh/W-sh) recipients. BMMCs from WT and UBI-GFP/BL6 mice were differentiated and transferred into WT and Kit(W-sh/W-sh) mice. Blockade of IL-13 was achieved by using IL-13 receptor alpha2 (IL-13Ralpha2)-IgG fusion protein.

RESULTS

FcepsilonRI(-/-) mice showed decreased intestinal inflammation (mast cell and eosinophil numbers) and goblet cell metaplasia and reduced levels of IL4, IL6, IL13, and IL17A mRNA expression in the jejunum. Transfer of WT BMMCs to FcepsilonRI(-/-) recipients restored their ability to develop intestinal allergic responses unlike transfer of FcepsilonRI(-/-), IL-13(-/-), or IL-4/IL-13(-/-) BMMCs. FcepsilonRI(-/-) mice exhibited lower IL-13 levels and treatment of WT mice with IL-13 receptor alpha2 prevented peanut-induced intestinal allergy and inflammation.

CONCLUSIONS

These data indicate that the development of peanut-induced intestinal allergy is mediated through a mast cell-dependent IgE-FcepsilonRI-IL-13 pathway. Targeting IL-13 might be a potential treatment for IgE-mediated peanut-induced allergic responses in the intestine.

Suppressive functions of activated B cells in autoimmune diseases reveal the dual roles of Toll-like receptors in immunity

B lymphocytes contribute to immunity through production of antibodies, antigen presentation to T cells, and secretion of cytokines. B cells are generally considered in autoimmune diseases as drivers of pathogenesis. This view is certainly justified, given the successful utilization of the B cell-depleting reagent rituximab in patients with rheumatoid arthritis or other autoimmune pathologies. In a number of cases, however, the depletion of B cells led to an exacerbation of symptoms in patients with autoimmune disorders. In a similar manner, mice lacking B cells can develop an aggravated course of disease in several autoimmune models. These paradoxical observations are now explained by the concept that activated B cells can suppress immune responses through the production of cytokines, especially interleukin-10. Here, we review the stimulatory signals that induce interleukin-10 secretion and suppressive functions in B cells and the phenotype of the B cells with such characteristics. Finally, we formulate a model explaining how this process of immune regulation by activated B cells can confer advantageous properties to the immune system in its combat with pathogens. Altogether, this review proposes that B-cell-mediated regulation is a fundamental property of the immune system, with features of great interest for the development of new cell-based therapies for autoimmune diseases.

Effect of anti-mouse CD52 monoclonal antibody on mouse intestinal intraepithelial lymphocytes

BACKGROUND

CD52 monoclonal antibody (mAb) has been used therapeutically in lymphocytic leukemia, autoimmune disease, and organ transplantation. But the effect of CD52 mAb on intestinal intraepithelial lymphocytes (IELs) was unknown. The aim of this study was to assess the influence of anti-mouse CD52 mAb on IELs.

METHODS

Twenty male C57BL/6 mice were randomly assigned to a treatment or a control group. The treatment group received anti-mouse CD52 mAb (20 mug, subcutaneously), whereas the control group received the same volume of phosphate-buffered solution. On the seventh day after treatment, mice were killed, and ileum and colon were obtained for histopathology and immunohistochemistry examination, IELs were isolated for flow cytometric analysis and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis. Furthermore, the intestinal permeability was measured by lactulose-mannitol test.

RESULTS

The number and viability of IELs were decreased significantly in treatment compared with the control group. There were significant differences between the two groups considering IELs phenotypes. In addition, the proportion of apoptotic IELs in CD52 mAb treatment group was significantly higher than the control group (19.59%+/-3.13% and 2.02%+/-0.33%, respectively; P<0.05). Furthermore, lactulose-mannitol test showed a marked increase intestinal permeability after CD52 treatment (90.38%+/-5.96% and 46.02%+/-6.40%, respectively; P<0.05).

CONCLUSION

Anti-mouse CD52 mAb could induce more IELs to apoptosis and result in reducing the number of IELs, which may disrupt intestinal barrier function.

Immunoglobulin E antibodies enhance pulmonary inflammation induced by inhalation of a chemical hapten

BACKGROUND

Occupational exposure to chemicals is an important cause of asthma. Recent studies indicate that IgE antibodies enhance sensitization to chemicals in the skin.

OBJECTIVE

We investigated whether IgE might similarly promote the development of airway inflammation following inhalation of a contact sensitizer.

METHODS

A model of chemical-induced asthma is described in which introduction of the low-molecular-weight compound, trinitrobenzene sulphonic acid (TNBS), via the respiratory tract was used for both sensitization and challenge. The role of IgE antibodies in the immune response to inhaled TNBS in this model was assessed by comparing the responses of wild-type (WT) and IgE-deficient (IgE(-/-)) mice on the BALB/c background. Reconstitution of circulating IgE levels by intravenous injection of IgE antibodies into IgE(-/-) mice before sensitization was performed to confirm the role of IgE in any differences observed between the responses of WT and IgE(-/-) mice.

RESULTS

Intranasal challenge of TNBS-sensitized (but not sham-sensitized control mice) induced intense pulmonary inflammation. Macrophages, eosinophils and lymphocytes, including T, B, natural killer and natural killer T cells, were recruited to the airway and the animals displayed bronchial hyperresponsiveness (BHR) to methacholine. Serum levels of murine mast cell protease-1 (mMCP-1) were elevated suggesting mast cell activation. In contrast, the development of airway inflammation, recruitment of lymphocytes, induction of BHR and production of mMCP-1 were all significantly attenuated in IgE-deficient mice. Reconstitution of IgE(-/-) mice with IgE (of unrelated antigen specificity) before sensitization partially restored these features of asthma.

CONCLUSION

Our data indicate that IgE antibodies non-specifically enhance the development of airway inflammation induced by exposure to chemical antigens.

Insights from advances in research of chemically induced experimental models of human inflammatory bowel disease

Inflammatory bowel disease (IBD), the most important being Crohn's disease and ulcerative colitis, results from chronic dysregulation of the mucosal immune system in the gastrointestinal tract. Although the pathogenesis of IBD remains unclear, it is widely accepted that genetic, environmental, and immunological factors are involved. Recent studies suggest that intestinal epithelial defenses are important to prevent inflammation by protecting against microbial pathogens and oxidative stresses. To investigate the etiology of IBD, animal models of experimental colitis have been developed and are frequently used to evaluate new anti-inflammatory treatments for IBD. Several models of experimental colitis that demonstrate various pathophysiological aspects of the human disease have been described. In this manuscript, we review the characteristic features of IBD through a discussion of the various chemically induced experimental models of colitis (e.g., dextran sodium sulfate-, 2,4,6-trinitrobenzene sulfonic acid-, oxazolone-, acetic acid-, and indomethacin-induced models). We also summarize some regulatory and pathogenic factors demonstrated by these models that can, hopefully, be exploited to develop future therapeutic strategies against IBD.

New developments in FcepsilonRI regulation, function and inhibition

The high-affinity Fc receptor for IgE (FcepsilonRI), a multimeric immune receptor, is a crucial structure for IgE-mediated allergic reactions. In recent years, advances have been made in several important areas of the study of FcepsilonRI. The first area relates to FcepsilonRI-mediated biological responses that are antigen independent. The second area encompasses the biological relevance of the distinct signalling pathways that are activated by FcepsilonRI; and the third area relates to the accumulated evidence for the tight control of FcepsilonRI signalling through a broad array of inhibitory mechanisms, which are being developed into promising therapeutic approaches.

The B-cell system in inflammatory bowel disease

Secretory immunity is the best-defined part ot the mucosal immune system. This adaptive humoral defense mechanism depends on a fine-tuned cooperation between secretory epithelia and local plasma cells. Such mucosal immunocytes produce preferentially dimers and larger polymers of immunoglobulin A (collectively called pIgA), which contain J chain and therefore can bind to the epithelial secretory component (SC). This transmembrane glycoprotein functions as pIg receptor (pIgR) that also translocates pentameric IgM to the epithelial surface. B cells with a high level of J-chain expression and pIg-pIgR interactions at mucosal effector sites are thus necessary for the generation of secretory antibodies (SIgA and SIgM). Secretory antibodies perform immune exclusion in a first-line defense, thereby counteracting microbial colonization and mucosal penetration of soluble antigens. However, local production of pIgA is significantly down-regulated in inflammatory bowel disease (IBD), as revealed by strikingly decreased J-chain expression. Although the total increase of the immunocyte population in IBD lesions probably compensates for the relatively reduced pIgA production, decreased pIgR/SC expression in regenerating and dysplastic epithelium signifies that the SIgA system is topically deficient. There is, moreover, a significant shift from IgA2 to IgA1 production, the latter subclass being less resistant to proteolytic degradation. These changes--together with activation of mucosal macrophages and a dramatic increase of IgG-producing cells--may reflect local establishment of a second defense line which, however, is unsuccessful in its attempt to eliminate antigens derived from the indigenous microbial flora. Such a 'frustrated' local humoral immune system results in altered immunological homeostasis and jeopardized mucosal integrity. Complement activation observed in relation to epithelium-bound IgG1 in ulcerative colitis indicates, moreover, that the surface epithelium is subjected to immunological attack by an autoimmune reaction. These luminal deposits regularly contain terminal cytotoxic complement, and often also C3b as a sign of persistent activation. Comparison of identical twins, discordant with regard to ulcerative colitis, suggests that the markedly skewed local IgG1 response seen in this IBD entity may be genetically determined. The initial event(s) eliciting B-cell driven immunopathology in IBD remains unknown. Abrogation of oral tolerance to certain antigens from commensal bacteria has been suggested as a putative early mechanism, and lymphoid neogenesis and hyperplasia in the lesions most likely signify massive microbial overstimulation of the local B-cell system. Such ectopic lymphoid microcompartments may contribute substantially to the proinflammatory systemic-type of B-cell responses occurring in established IBD lesions.

Immunoglobulin E-bearing antigen-presenting cells in atopic dermatitis

Human antigen-presenting cells (APCs) bind monomeric immunoglobulin E (IgE) via the high-affinity IgE receptor, Fc epsilon RI. Surface expression of this trimeric structure is strongly associated with the atopic status of the donors, and maximal levels are observed on Langerhans cells (LC) and inflammatory dendritic epidermal cells (IDEC) in atopic dermatitis (AD). Although intracellular expression of the Fc epsilon RI alpha-chain is induced by interleukin-4 (IL-4), the upregulation of surface levels on dendritic cells (DC) from atopics is due to enhanced expression of the Fc epsilon RI gamma-chain and stabilization by binding of its ligand IgE. A characteristic function of Fc epsilon RI-bearing APCs is the specific uptake and processing of IgE-bound allergens, which is followed by T-cell stimulation. In AD, DC-mediated presentation of aeroallergens penetrating the epidermis is thought to induce an IgE-mediated, delayed-type hypersensitivity reaction. In addition, different Fc epsilon RI-bearing APC subsets in AD skin might regulate inflammatory processes through the production of Th1/Th2-polarizing signals, proinflammatory cytokines, chemokines, and factors that are involved in the induction of tolerance.

Mast cells are required for experimental oral allergen-induced diarrhea

Gastrointestinal allergic disorders represent a diverse spectrum of inflammatory diseases that are occurring with increasing incidence and severity. An essential question concerning these disorders is to determine the specific cells and mediators responsible for specific clinical manifestations. With this in mind, we developed a murine model of oral allergen-induced intestinal inflammation accompanied by strong Th2-associated humoral and cellular responses and focused on the immunopathogenesis of allergic diarrhea. Exposure of OVA/alum-sensitized mice to repeated doses of intragastric OVA induced genetically restricted, dose-dependent, acute diarrhea associated with increased intestinal permeability, eosinophilia, and mastocytosis. Mice developed limited systemic manifestations of anaphylaxis, even though they developed marked intestinal mucosal mast cell degranulation. Notably, experiments involving mast cell depletion (with anti-c-kit mAb), anti-IgE treatment, and Fc epsilon RI-deficient mice indicated a critical effector role for mast cells in mediating allergic diarrhea. Furthermore, allergic diarrhea was dependent upon synergistic signaling induced by serotonin and platelet-activating factor (PAF), but not histamine. These results demonstrate that oral allergen-induced diarrhea associated with experimental Th2 intestinal inflammation is largely mast cell, IgE, serotonin, and PAF dependent.

Dysbiosis in inflammatory bowel disease

Abundant data have incriminated intestinal bacteria in the initiation and amplification stages of inflammatory bowel diseases. However, the precise role of intestinal bacteria remains elusive. One theory has suggested a breakdown in the balance between putative species of "protective" versus "harmful" intestinal bacteria--this concept has been termed "dysbiosis". Arguments in support of this concept are discussed.

The biology of IGE and the basis of allergic disease

Allergic individuals exposed to minute quantities of allergen experience an immediate response. Immediate hypersensitivity reflects the permanent sensitization of mucosal mast cells by allergen-specific IgE antibodies bound to their high-affinity receptors (FcepsilonRI). A combination of factors contributes to such long-lasting sensitization of the mast cells. They include the homing of mast cells to mucosal tissues, the local synthesis of IgE, the induction of FcepsilonRI expression on mast cells by IgE, the consequent downregulation of FcgammaR (through an insufficiency of the common gamma-chains), and the exceptionally slow dissociation of IgE from FcepsilonRI. To understand the mechanism of the immediate hypersensitivity phenomenon, we need explanations of why IgE antibodies are synthesized in preference to IgG in mucosal tissues and why the IgE is so tenaciously retained on mast cell-surface receptors. There is now compelling evidence that the microenvironment of mucosal tissues of allergic disease favors class switching to IgE; and the exceptionally high affinity of IgE for FcepsilonRI can now be interpreted in terms of the recently determined crystal structures of IgE-FcepsilonRI and IgG-FcgammaR complexes. The rate of local IgE synthesis can easily compensate for the rate of the antibody dissociation from its receptors on mucosal mast cells. Effective mechanisms ensure that allergic reactions are confined to mucosal tissues, thereby minimizing the risk of systemic anaphylaxis.

Use of mouse models to evaluate the persistence, safety, and immune modulation capacities of lactic acid bacteria

Recent clinical and experimental observations showed that specific probiotic microorganisms may provide therapeutic benefits in inflammatory bowel disease. However, a rigorous screening for new candidate probiotic strains with optimized therapeutic properties necessitates also determining possible adverse interactions with the host, particularly in individuals who are not healthy. We have evaluated the persistence of strains of lactic acid bacteria (LAB) in the digestive tracts of mice, their immunomodulation capacity, and their safety in healthy animals and in a colitis model. Following daily administration of 10(9) CFU of viable LAB orally, intragastrically, or intrarectally, the animals' feces were examined for bacterial excretion and cytokines were quantified in intestinal samples by quantitative reverse transcription-PCR. The level of bacterial translocation was assessed in healthy mice and in mice suffering from colitis induced by 2,4,6-trinitrobenzene sulfonic acid (TNBS). Irrespective of the route of administration, the potential probiotic strain Lactobacillus plantarum NCIMB8826 was found to persist for up to 10 days in the digestive tracts of mice. This strain did not induce detrimental effects in healthy or in TNBS-treated animals, as was reflected by the absence of weight loss, intestinal inflammation, modification of cytokine levels in the ileum and colon (healthy mice), and bacterial dissemination (healthy and colitic animals). Moreover, the translocation of endogenous microflora to the mesenteric lymph nodes and spleen was greatly reduced in the TNBS-treated mice after administration of LAB. This property, together with the strain's persistence capacity and innocuousness renders L. plantarum NCIMB8826 an attractive candidate as a probiotic to be used in the prevention or treatment of chronic inflammation.

Immune networks in animal models of inflammatory bowel disease

The animal models of inflammatory bowel disease provide a framework to define the immunopathogenesis of intestinal inflammation. Studies in these models support the hypothesis that exaggerated immune responses to normal enteric microflora are involved in the initiation and perpetuation of chronic intestinal inflammation. A major pathway involves development of acquired immune responses by the interactions of CD4+ T-cell receptor alphabeta T cells with antigen-presenting cells (dendritic cells). Immunoregulatory cells, including Tr1 cells, Th3 cells, and CD4+ CD25+ T cells and B cells, directly or indirectly affect the T-cell receptor alphabeta T cell-induced immune responses and bridge innate and acquired immunity. The study of these complicated immune networks provides the rationale for the development of new therapeutic interventions in inflammatory bowel disease.

Inhibition of intestinal bacterial translocation with rifaximin modulates lamina propria monocytic cells reactivity and protects against inflammation in a rodent model of colitis

BACKGROUND

A modification of the intestinal flora and an increased bacterial translocation is a common finding in patients with inflammatory bowel disease as well as in animal model of colitis. Rifaximin, a non-absorbable derivative of rifamycin, is an effective antibiotic that acts by inhibiting bacterial ribonucleic acid synthesis.

AIMS

In the present study, we investigated the effect of the administration of rifaximin (10, 30 and 50 mg/kg/day) or prednisolone (10 mg/kg/day) in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in mice.

METHODS

Colitis was induced in mice by intrarectal administration of TNBS (1.5 mg/mouse in 50% ethanol) and disease severity assessed clinically and by histologic scoring of colon damage, determination of interleukin (IL)-2, IL-12, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha (protein and mRNA and myeloperoxidase (MPO) activity in the colon. Cytokines production by the lamina propria mononuclear cells (LPMC) and luminal bacteria were also measured.

RESULTS

Rifaximin administration (30 or 50 mg/kg/day) increased survival rates of colitic mice and reduced colitis severity as demonstrated by improvement of wasting syndrome, histologic scores, decrease in colon IL-2, IL-12, IFN-gamma and TNF-alpha (protein and mRNA) levels, and diminished colon MPO activity. Rifaximin administration caused a significant reduction of colon bacterial translocation towards mesenteric lymph nodes. LPMC obtained from rifaximin-treated mice released significantly lower amount of IFN-gamma in response to ex vivo stimulation with agonistic anti-CD3 and anti-CD28 antibodies. Rifaximin (50 mg/kg/day) significantly accelerates recovery in mice with established colitis.

CONCLUSIONS

Luminal bacterial microflora plays a role in the pathogenesis of TNBS-induced colitis in mice. Rifaximin administration reduces the development of colitis and accelerates healing of established disease by preventing bacterial translocation.

Role of activator protein 1, nuclear factor-kappaB, and nuclear factor of activated T cells in IgE receptor-mediated cytokine expression in mature human mast cells

BACKGROUND

On activation by cross-linking the high-affinity IgE receptor (FcepsilonRI), expression of TNF-alpha, IL-3, IL-5, and IL-13 is induced in human intestinal mast cells.

OBJECTIVE

We sought to examine, for the first time, FcepsilonRI signaling in mature human mast cells.

METHODS

Mast cells were isolated from intestinal tissue and cultured in the presence of stem cell factor. The cells were treated with specific inhibitors before stimulation by means of FcepsilonRI cross-linking. Cytokine mRNA expression was analyzed by means of RT-PCR, and activation of signaling molecules was determined by means of immunocytochemistry, RT-PCR, Western blotting, and protein kinase C (PKC) assay.

RESULTS

We found that nuclear factor-kappaB (NF-kappaB), as well as c-Fos and c-Jun, the components of activator protein 1 (AP-1), are activated after FcepsilonRI cross-linking in human intestinal mast cells. Treatment of the cells with specific inhibitors revealed an involvement of NF-kappaB and nuclear factor of activated T cells, as well as the necessity of extracellular signal-regulated kinase 1/2 (ERK-1/2), PKC, and AP-1 for the induced cytokine gene expression. Consistently, we found that activation of c-Fos corresponds with the induced cytokine gene expression and that ERK-1/2, an activator of c-Fos, was activated in response to FcepsilonRI cross-linking.

CONCLUSION

Our data on human mast cells show that the activity of ERK-1/2, PKC, and subsequent activation of AP-1 are necessary for the FcepsilonRI-mediated cytokine expression. Nuclear factor of activated T cells and NF-kappaB seem to be necessary for the induction of TNF-alpha, IL-3, and IL-13 but are less important for the transcription of IL-5.

Unraveling the mission of FcepsilonRI on antigen-presenting cells

A decade ago, the discovery of the high-affinity receptor for IgE (FcepsilonRI) on epidermal Langerhans cells documented the end of the dogma that FcepsilonRI is only expressed on effector cells of anaphylaxis. Since then, the functional significance of this receptor on antigen-presenting cells (APCs) has been an area of intense research work. Scientists have focused on a better understanding of the molecular structure, regulation, and role of FcepsilonRI on APCs in the human immune system. Insights into the cellular events linked to the activation of APCs on ligation of FcepsilonRI by IgE and allergens might provide the basis for new aspects in the pathophysiology of allergic diseases and the design of future diagnostic and therapeutic strategies. This review is dedicated to the 10th anniversary of the discovery of FcepsilonRI on APCs and describes the numerous areas of research in this field.

Differential localization of colitogenic Th1 and Th2 cells monospecific to a microflora-associated antigen in mice

BACKGROUND & AIMS

Clonal expansion of T cells is associated with inflammatory bowel diseases, which indicates antigenic activation of the T cells. We investigated whether the introduction of CD4 T cells specific to a microflora would initiate colitis and assessed the cytokine requirements for colitogenic CD4 T cells.

METHODS

Severe combined immunodeficiency disease (SCID) mice were reconstituted with CD4 T cells, which were either deficient in interleukin (IL)-4/interferon (IFN)-gamma production or differentiated in vitro to T-helper (Th) 1/Th 2 and bearing a transgenic T-cell receptor (TCR) specific to ovalbumin (OVA), and then inoculated with an Escherichia coli-producing OVA (ECOVA). Clinical and histologic manifestations of colitis were assessed.

RESULTS

Mice with ECOVA colonization and OVA-specific CD4 T cells developed colitis with histologic features of focal infiltration by mononuclear cells, destruction of crypts, and loss of goblet cells. Further, infiltration was initiated in pre-existing lymph follicles. Th1- and IL-4 deficient T cells were diffusely localized in the lamina propria and submucosa, whereas Th2- and IFN-gamma-deficient T cells were localized preferentially in lymph follicles.

CONCLUSIONS

A microbe-associated antigen, non-cross-reactive to colonic tissue, can drive antigen-specific CD4 T cells to cause colitis in SCID mice. Although the presence of IFN-gamma and IL-4 in the effector CD4 T cells was not an absolute requirement for the development of colitis, they seemed to regulate it in part by modulating migration of the effector T cells.

Chronic intestinal inflammatory condition generates IL-10-producing regulatory B cell subset characterized by CD1d upregulation

B cells possess a variety of immune functions that are involved in normal and abnormal immune responses, including autoimmune disorders. Through murine models of intestinal inflammation, we here demonstrate a B cell subset that is induced in gut-associated lymphoid tissues and is characterized by CD1d upregulation. This B cell subset appears under a chronic inflammatory environment, produces IL-10, and suppresses progression of intestinal inflammation by downregulating inflammatory cascades associated with IL-1 upregulation and STAT3 activation rather than by altering polarized T helper responses. This study indicates that B cells, by producing cytokines such as IL-10, can act as regulatory cells in immunologically mediated inflammatory reactions.

Inflammatory bowel disease: is the intestine a Trojan horse?

Inflammatory bowel disease (IBD) is a chronic relapsing inflammatory condition of the intestines that is clinically heterogenous. The cause(s) of IBD are currently unknown but the mechanisms of injury are immunological. Increasingly there is an emphasis on the study of the complex interactions at the interface of self and non-self--the gastrointestinal epithelial surface--in relationship to the pathogenesis of disease. There is mounting evidence that a lack of tolerance to the normal commensal flora of the intestine may underlie the disease pathogenesis. Several genetic loci that are markers of disease susceptibility have been identified. These loci map to areas of the genome that are concerned with antigen presentation or cytokine secretion and suggest a genetic heterogeneity that underlies the clinical differences. Overall a picture is emerging of defects in epithelial barrier function and, or immunoregulation leading to immune responses that are triggered or exaggerated by the antigenic components of the normal flora.

IgE receptors

IgE receptors are implicated as important components of the immunological pathway in allergic and inflammatory diseases. Recent investigations have begun to unravel the structure, signal transduction and function of IgE receptors from different cell types in rodent and human systems. Studies of the mechanisms involved might provide opportunities for therapeutic intervention strategies in the treatment of allergic and hypersensitivity reactions.

Inflammatory bowel disease: clinics and pathology. Do inflammatory bowel disease and periodontal disease have similar immunopathogeneses?

Inflammatory bowel disease (IBD) comprises two chronic, tissue-destructive, clinical entities Crohn disease (CD) and ulcerative colitis (UC) both apparently caused by immunological overreaction (hypersensitivity) to commensal gut bacteria. Under normal conditions the intestinal immune system shows a down-regulating tone ('oral tolerance') against dietary antigens and the indigenous microbiota. This local homeostasis is disturbed in IBD, leading to hyperactivation of T helper 1 (Th1) cells with abundant secretion of interferon-gamma and tumor necrosis factor (TNF) and production of IgG antibodies against commensal bacteria. In addition, UC includes genetically determined autoimmunity, particularly IgG1-mediated cytotoxic epithelial attack. Breaching of the epithelium is the best-defined event underlying abrogation of oral tolerance, but immune deviation caused by cytokines fiom irritated epithelial cells or subepithelial elements (for example, mast cells, natural killer cells, macrophages) may also be involved. Endogenous infection with local hypersensitivity likewise causes periodontal disease, reflecting 'frustrated' immune elimination mechanisms entertained by antigens from dental plaque. Altogether, perturbation of a tightly controlled cytokine network, with abnormal crosstalk between several cell types, apparently explains the progressive immunopathology of chronic inflammatory mucosal diseases in general. This adverse development will be influenced by numerous immunity genes, the dosage and potential pathogeniciy of commensal bacteria, general health, nutritional status, and psychological factors. Several targets for new therapy have tentatively been identified to block immunopathological mechanisms in IBD, and inhibition of TNF has a striking beneficial effect in CD, supporting a central role of this cytokine.