Mucosal tolerance and immunity: regulating the development of allergic disease and asthma

The relationship between IFN-γ, IL-10, IL-6 cytokines, and severity of the condition with serum zinc and Fe in children infected with Mycoplasma pneumoniae

Objective

To explore the relationship between cytokines such as interferon γ (IFN-γ), interleukin-10 (IL-10), and interleukin-6 (IL-6), as well as the severity of the condition, and serum zinc (Zn) and Fe levels in children with Mycoplasma pneumoniae infection.

Methods

A simple random sampling method was used to select 108 children with Mycoplasma pneumoniae infection admitted to the hospital from January to December 2022 as the study subjects. Collect demographic data such as gender, age, and course of disease from all patients, as well as inflammatory cytokines (InCs) such as IFN-γ, IL-10, and IL-6, the severity of the condition, and serum trace element information such as Zn, Fe, calcium (Ca), and potassium (K) from all patients. Spearman correlation analysis was used to examine the relationship between IFN-γ, IL-10, IL-6, severity of illness, and Zn, Fe, Ca, K in children infected with Mycoplasma pneumoniae. Additionally, receiver operating characteristic (ROC) curve analysis was used to test the predictive efficacy of Zn, Fe, Ca, and K on the severity of the patient's condition.

Results

This study included 108 children infected with Mycoplasma pneumoniae, of whom 6 had clinical data missing >10% and were all excluded. Finally, 102 complete clinical data were collected, with a data recovery efficiency of 94.44%. The differences in IFN-γ, IL-10, IL-6 levels, severity of the condition, as well as Zn, Fe, Ca, K levels among children of different ages, disease courses, body mass, and body temperature showed P < 0. 05. Spearman correlation analysis showed that the levels of IFN-γ, IL-10, IL-6, and severity of the condition in children with Mycoplasma pneumoniae infection were negatively correlated with Zn, Fe, Ca, and K (ρ = -0.319 to -0.827, P < 0.05). The ROC curve analysis results indicate that Zn, Fe, Ca, and K can all be used as indicators to predict the severity of the patient's condition (AUC = 0.710-0.759, P < 0.05).

Conclusion

There is a close relationship between InCs and the severity of the condition in children with Mycoplasma pneumoniae and serum trace elements. Therefore, clinical attention should be paid to monitoring the serum trace element levels of children, and reasonable measures should be taken to regulate them to accelerate the progress of disease treatment.

Interactions of thymic stromal lymphopoietin with interleukin-4 in adaptive immunity during Aspergillus fumigatus keratitis

AIM

To investigate the potential interactions of thymic stromal lymphopoietin (TSLP) with interleukin-4 (IL-4) in adaptive immunity during fungal keratitis (FK).

METHODS

An FK mouse model was induced with Aspergillus fumigatus (AF) hyphal infection. Mice were divided into several groups: untreated, phosphate buffer saline (PBS), infected with AF, and pretreated with a scrambled siRNA, a TSLP-specific siRNA (TSLP siRNA), murine recombinant TSLP (rTSLP), immunoglobulin G (IgG), murine recombinant IFN (rIFN-γ), murine recombinant IL-4 (rIL-4), rIL-13, murine recombinant IL-17A (rIL-17A), and murine recombinant IL-17F (rIL-17F) groups. Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) or Western blot were performed to determine mRNA and protein levels in the inflamed cornea. Cytokine locations were observed by immunofluoresence staining after AF hyphal infection.

RESULTS

Compared to those in the untreated group, TSLP and T helper type 1 (Th1) cytokine levels in the AF group were upregulated at 24h post infection (hpi), and those of T helper type 2 (Th2) and T helper type 17 (Th17) cytokines were increased at 5d post infection (dpi). Th2 cytokine levels were decreased in the TSLP siRNA-pretreated group and increased in the rTSLP-pretreated group compared with the AF group. The TSLP level was increased in the rIL-4-pretreated group, but there were no significant changes among the other groups. Immunofluorescence staining showed cytokine locations after AF hyphal infection.

CONCLUSION

TSLP induces a Th2 immune response and promots Th2 T cell differentiation in vivo. IL-4 promotes TSLP secretion. Therefore, TSLP with IL-4 regulates adaptive immunity in FK.

Dendritic cell expression of the signaling molecule TRAF6 is required for immune tolerance in the lung

Immune tolerance in the lung is important for preventing hypersensitivity, such as allergic asthma. Maintenance of tolerance in the lung is established by coordinated activities of poorly understood cellular and molecular mechanisms, including participation of dendritic cells (DCs). We have previously identified DC expression of the signaling molecule TRAF6 as a non-redundant requirement for the maintenance of immune tolerance in the small intestine of mice. Because mucosal tissues share similarities in how they interact with exogenous antigens, we examined the role of DC-expressed TRAF6 in the lung. As with the intestine, we found that the absence TRAF6 expression by DCs led to spontaneous generation of T_h2-associated immune responses and increased susceptibility to model antigen-induced asthma. To examine the role of commensal microbiota, mice deficient in TRAF6 in DCs were treated with broad-spectrum antibiotics and/or re-derived on a germ-free (GF) background. Interestingly, we found that antibiotics-treated specific pathogen-free, but not GF, mice showed restored immune tolerance in the absence of DC-expressed TRAF6. We further found that antibiotics mediate microbiota-independent effects on lung T cells to promote immune tolerance in the lung. This work provides both a novel tool for studying immune tolerance in the lung and an advance in our conceptual understanding of potentially common molecular mechanisms of immune tolerance in both the intestine and the lung.

The role of endosomal toll-like receptors in asthma

Asthma is a heterogeneous inflammatory disease caused by association of genetic and environmental factors and its incidence has significantly increased over the latest years. The clinical manifestations of asthma are the result of airway hyper-reactivity to a variety of triggers such as aeroallergens, viral and bacterial components. Toll-like receptors (TLRs) are pathogen associated molecular pattern receptors, which are also expressed in the lung tissue as well as in several cells of the innate and adaptive immune system. Ligation of TLRs results in alterations in the expression of several inflammatory and anti-inflammatory mediators, which are known to be involved in the pathogenesis of asthma. The endosomal TLRs have been shown to be associated with the induction of asthmatic inflammation (TLR3), and with disease exacerbations (TLR7, TLR8 and TLR9). Targeting these receptors seems to be an effective choice for suppressing airway inflammation, eosinophilia and airway hyperresponsiveness in asthmatic patients. In this review we provide information regarding endosomal TLRs and their role in the pathogenesis of asthma as well as their potential use as targets for the development of novel treatments for the therapy of asthma.

Probiotics as additives on therapy in allergic airway diseases: a systematic review of benefits and risks

BACKGROUND

We conducted a systematic review to find out the role of probiotics in treatment of allergic airway diseases.  

METHODS

A comprehensive search of the major electronic databases was done till March 2013. Trials comparing the effect of probiotics versus placebo were included. A predefined set of outcome measures were assessed. Continuous data were expressed as standardized mean difference with 95% CI. Dichotomous data were expressed as odds ratio with 95% CI. P value < 0.05 was considered as significant.

RESULTS

A total of 12 studies were included. Probiotic intake was associated with a significantly improved quality of life score in patients with allergic rhinitis (SMD -1.9 (95% CI -3.62, -0.19); P = 0.03), though there was a high degree of heterogeneity. No improvement in quality of life score was noted in asthmatics. Probiotic intake also improved the following parameters: longer time free from episodes of asthma and rhinitis and decrease in the number of episodes of rhinitis per year. Adverse events were not significant.

CONCLUSION

As the current evidence was generated from few trials with high degree of heterogeneity, routine use of probiotics as an additive on therapy in subjects with allergic airway diseases cannot be recommended.

Intranasal delivery of E-selectin reduces atherosclerosis in ApoE-/- mice

Mucosal tolerance to E-selectin prevents stroke and protects against ischemic brain damage in experimental models of stroke studying healthy animals or spontaneously hypertensive stroke-prone rats. A reduction in inflammation and neural damage was associated with immunomodulatory or “tolerogenic” responses to E-selectin. The purpose of the current study on ApoE deficient mice is to assess the capacity of this stroke prevention innovation to influence atherosclerosis, a major underlying cause for ischemic strokes; human E-selectin is being translated as a potential clinical prevention strategy for secondary stroke. Female ApoE−/− mice received intranasal delivery of E-selectin prior to (pre-tolerization) or simultaneously with initiation of a high-fat diet. After 7 weeks on the high-fat diet, lipid lesions in the aorta, serum triglycerides, and total cholesterol were assessed as markers of atherosclerosis development. We also assessed E-selectin-specific antibodies and cytokine responses, in addition to inflammatory responses that included macrophage infiltration of the aorta and altered gene expression profiles of aortic mRNA. Intranasal delivery of E-selectin prior to initiation of high-fat chow decreased atherosclerosis, serum total cholesterol, and expression of the leucocyte chemoattractant CCL21 that is typically upregulated in atherosclerotic lesions of ApoE−/− mice. This response was associated with the induction of E-selectin specific cells producing the immunomodulatory cytokine IL-10 and immunosuppressive antibody isotypes. Intranasal administration of E-selectin generates E-selectin specific immune responses that are immunosuppressive in nature and can ameliorate atherosclerosis, a major risk factor for ischemic stroke. These results provide additional preclinical support for the potential of induction of mucosal tolerance to E-selectin to prevent stroke.

Guidance for substantiating the evidence for beneficial effects of probiotics: prevention and management of allergic diseases by probiotics

Allergy is a hypersensitivity reaction mediated by specific antibody-mediated or cell-mediated immunologic mechanisms and clinically manifested as atopic eczema, allergic rhinoconjunctivitis, or asthma. During the recent decades there has been an increase in allergy prevalence, which is attributed to changes in environmental factors. The so-called "hygiene hypothesis" suggests that a lack of exposure to microbial stimulus early in childhood is a major factor involved in this trend. This provides a rationale for using probiotics to modify the gut microbiota and thereby shaping the immune response of the host, especially in infancy. Most success has been obtained in primary prevention of atopic eczema. A limited number of studies also provided evidence for a beneficial effect of different probiotics in the management of allergic diseases (atopic eczema, allergic rhinitis). However, choice of probiotic strains as well as timing of the intervention are important variables. The exact in vivo mechanism of probiotics in shaping the immune response still needs to be determined. Future studies should use uniform criteria for diagnosis and symptom scoring of atopic diseases and may identify the genes predisposing to allergic disease. There is encouraging evidence that specific probiotics can become valuable tools in the prevention and management of allergic diseases.

Suppression of lymphocyte proliferation and regulation of dendritic cell phenotype by soluble mediators from rat lacrimal epithelial cells

Lacrimal epithelial cells appear to constitutively secrete autoantigens to their underling stroma. The present experiments address the hypothesis that they also secrete soluble factors that regulate immune responses. Epithelial cells, spleen cells and lymphocytes were obtained from rabbits or rats and cultured in various configurations. Monocytes from rat bone marrow were matured to dendritic cells (DC) ex vivo. Proliferation was measured by [3H]-thymidine incorporation; surface MHC Class II and CD86 using flow cytometry; and mRNA relative abundances using real time RT-PCR. Microporous culture inserts containing rat lacrimal cells inhibited proliferation of rabbit lymphocytes co-cultured with autologous lacrimal cells and of rat lymphocytes co-cultured with TNF-alpha-stimulated DC. They inhibited CD86 and MHC Class II surface expression by maturating DC and reversed surface expression of CD86 but not MHC Class II by partially matured DC. Subsequent exposure of partially matured DC to mediators from rat lacrimal cells reversed the ability to stimulate lymphocyte proliferation. TGF-beta(1) and IL-10 mRNAs increased somewhat when rat lacrimal cells were isolated but decreased markedly in rabbit lacrimal cells. Antibodies to TGF-beta prevented soluble factors from rat lacrimal cells from inhibiting proliferation of rabbit lymphocytes co-cultured with rabbit lacrimal cells, but recombinant TGF-beta alone did not mimic the soluble factors. IL-10 immunopositivity was detected in epithelial cells of interlobular ducts and occasional interstitial cells in rabbit lacrimal gland. Rat lacrimal epithelial cells secrete TGF-beta and other factors that synergize to suppress lymphocyte proliferation and regulate DC maturation. Interlobular duct epithelial cells in rabbit lacrimal glands may express similar functions.

Mucosal dendritic cells

The internal surfaces of the human body are covered by distinct types of epithelial cells and mucus-secreting cells. The mucosal surfaces serve many vital functions, such as respiration (nasal passage and lung), absorption (gastrointestinal tract), excretion (lung, urinary tract, large intestine), and reproduction (reproductive tract). In performing these functions, the host is inevitably exposed to environmental antigens, food particles, commensal flora, and pathogens. Mucosal surfaces contain specialized dendritic cells (DCs) capable of sensing these external stimuli and mounting appropriate local responses depending on the nature of the elements they encounter. In the absence of pathogens, mucosal DCs either ignore the antigen or induce regulatory responses. Upon recognition of microorganisms that invade the mucosal barrier, mucosal DCs mount robust protective immunity. This review highlights progress in our understanding of how mucosal DCs process external information and direct appropriate responses by mobilizing various cells of the innate and adaptive immune systems to achieve homeostasis and protection.

Immunomodulation: the future cure for allergic diseases

Allergies are the result of aberrant immune reactivity against common innocuous environmental proteins (allergens). A pivotal component of allergic pathogenesis is the generation of allergen-specific Th cells with an effector phenotype. These Th cells activate a complex immune cascade that triggers the release of potent mediators and enhances the mobilization of several inflammatory cells types, which in turn elicit the acute allergic reactions and promote the development of chronic inflammation. The current therapies for allergic diseases focus primarily on pharmacological control of symptoms and suppression of inflammation. This approach is beneficial, but not curative, since the underlying immune pathology is not inhibited. In an attempt to develop more effective therapeutic strategies, the scientific interest has been directed toward methods down-modulating the immune mechanisms that initiate and maintain the allergic cascade. Today, the only widely used disease-modifying form of allergy treatment is the specific immunotherapy with allergen extracts. More recently the use of anti-IgE has been approved for patients with allergic asthma. Other immunomodulatory methods being currently explored are the administration of microbial adjuvants that inhibit Th2 reactivity and the design of molecules that interrupt the activity of key allergic cytokines, chemokines, or other Th2 effector mediators.

Microbial content of drinking water in Finnish and Russian Karelia - implications for atopy prevalence

BACKGROUND AND AIM

The influence of microbial quality of drinking water from different sources on the occurrence of atopy has been poorly examined. This study was undertaken to clarify the association between the overall microbial content in drinking water and the occurrence of atopy among schoolchildren from two neighbouring areas with profound differences in living conditions and lifestyles.

METHODS

Drinking water samples were obtained from kitchens of nine schools in North Karelia, Finland and of nine schools from Pitkäranta, the Republic of Karelia, Russia. The pupils of these schools were participants of the Karelian Allergy Study. Occurrence of atopy, determined by skin prick test positivity (one or more) to 14 common airborne and food allergens, was measured in all 563 children, aged 7-16 years, from these 18 schools. Water samples were analysed using standard methods for drinking water analyses including viable counts for Escherichia coli, intestinal enterococci, coliform bacteria and heterotrophic bacteria. In addition, total cell counts including both viable and nonviable bacteria, algae and protozoans were assessed using epifluorescence microscope with 4'-6-diamidino-2-phenylindole (DAPI) staining.

RESULTS

In Finland, 29% of the children were sensitized to birch when compared with 2% of the Russian children (P < 0.0001). Overall, sensitization rates for any of the pollens were 39% and 8% (P < 0.0001), and for any of the allergens 48% and 16%, respectively (P < 0.0001). Because of substantial differences in raw water sources and treatment practices, the total numbers of microbial cells in drinking water were many-fold higher in Russia than in Finland. A dose-response relationship was found for occurrence of atopy and the DAPI value indicative of microbial cell content in the water (P < 0.0001). Further, multivariate logistic regression analysis revealed that high (>10(6) cells/ml) and intermediate (10(5)-10(6) cells/ml) DAPI values were associated with reduced risk of atopy (odds ratio 0.34, 95% confidence interval 0.20-0.57 and 0.39, 0.23-0.69, respectively), independently from other factors.

CONCLUSION

High overall content of micro-organisms in drinking water may be associated with reduced risk of atopy, independently from other determinants.

Should a new tuberculosis vaccine be administered intranasally?

Most of the world's population is vaccinated with the only available vaccine against tuberculosis (TB), the Bacillus Calmette-Guérin (BCG) vaccine that was developed almost a century ago. Despite the wide coverage of the BCG vaccine, there are great variations in protective efficacy among different study populations. BCG vaccination protects against childhood forms of TB, but this immunity wanes with age, resulting in none, or insufficient, protection against adult pulmonary TB (PTB). PTB is the major disease manifestation of TB in adults and it causes death at the most productive age, further adding to poverty in already impoverished countries. Therefore, new more effective vaccines and novel immunisation strategies are urgently needed. The most common route of TB is by inhalation of tubercle bacilli leading to the establishment of a primary infection in the lung. Immunising through the nasal mucosal surface should therefore have advantage over other routes, as such vaccine administration elicits protective immune responses also in the lung, i.e. at the site of primary infection. Several new TB-vaccine candidates have been evaluated for their protective efficacy in animal models using the mucosal route of immunisation. In formulating such vaccines, the adjuvants and delivery systems are crucially important.

New aspects on inflammation in allergic diseases

BACKGROUND

Allergic disease has currently reached epidemic proportions, with a high percentage of individuals in the developed world exhibiting an allergic response after exposure to some common environmental factors. Although new strategies for the treatment and management of allergic diseases have decreased the mortality rate, a high percentage of affected persons still require frequent hospitalization and experience decreased quality of life.

METHODS

An internet-based literature search was performed for recent contributions on the underlying mechanisms provoking an allergic response and their potential for therapeutic approaches.

RESULTS

Novel concepts on allergic responses have emerged: allergic disease may result from an imbalance between allergen activation of regulatory T cells and effector T helper 2 cells (Th2), a process in which dendritic cells are key players. Cytokines such as interleukin (IL)-6, IL-21, IL-25, and human thymic stromal lymphopoietin (TSLP) seem to be important contributors in allergic processes. New data on IgE effector responses and on the IgE-independent mechanisms involved in allergic reactions have resolved some unanswered questions about these reactions.

CONCLUSIONS

These new findings on allergic diseases have important implications for diagnosis and management, with potential improvements in prevention and treatment, which could provide a cure in the future.

Disconnection of man and the soil: reason for the asthma and atopy epidemic?

Intense search has been going on to find factors responsible for the asthma and atopy epidemic in Western societies. Attention has increasingly been devoted to environmental saprophytes, which, in addition to gut commensals, might be the major players in the development and fine tuning of immunologic homeostasis. This review outlines current evidence for the role of environmental saprophytes in the development of atopic disease and considers the consequences of urbanization in reducing contacts with soil microorganisms. The major microbial components that have been shown to possess immunomodulatory capacity and their respective Toll-like receptors are also discussed, as are the possible mechanisms underlying the ability of saprophytes to confer protection against atopic disease.

Role and regulation of lung collectins in allergic airway sensitization

Inhalation of allergens in atopic patients results in a characteristic inflammatory response while in normal, healthy individuals it elicits no symptoms. The mechanisms by which the pulmonary immune system accomplishes elimination of inhaled particles and suppression of the ensuing inflammatory response are poorly understood. Based on their structural uniqueness, specific localization and functional versatility the hydrophilic surfactant proteins [surfactant protein (SP)-A and SP-D] are important candidate regulators of these processes. Recent studies in our laboratory and others indicated significant changes in levels of these molecules during the asthmatic response in animal models as well as in asthmatic patients. Because of their capability to directly inhibit T-cell activation and T-cell-dependent allergic inflammatory events, SP-A and SP-D may be significant contributors to the local control of T-helper (Th)2-type inflammation in the airways. This review will discuss their relevant structural-functional features and recent evidence supporting the hypothesis that SP-A and SP-D have a role in regulation of allergic airway sensitization.

Mucosal Immunity and Self-Tolerance in the Ocular Surface System

This paper articulates a new working hypothesis that explains many of the pathophysiological conditions described under the common rubric "dry eye" as altered states of mucosal immune regulation. A central principle of mucosal immune physiology is that the parenchymal tissues at the effector sites, i.e., the sites at which secretory antibodies are produced, maintain local signaling milieus that support differentiation of IgA+ plasmablasts and survival of IgA+ plasmacytes. These local signaling milieus also support robust regulatory networks that maintain tolerance to commensual microbes, benign antigens, and parenchymal autoantigens. The regulatory networks are mediated by cycles of interactions between successive generations of dendritic cells, which normally mature with tolerogenic functions, and regulatory T cells, which normally reinforce the system's ability to generate new tolerogenic dendritic cells. The systemic endocrine environment controls expression of the local signaling milieu in the mammary gland and in the prostate and male urethral glands. Emerging evidence indicates that the local signaling milieu in the lacrimal gland also is determined, in part, by the systemic endocrine environment. This working hypothesis suggests explanations for the excess incidence of Sjogren syndrome among women and for the mechanisms of several different immunophysiological states in addition to Sjogren syndrome that, like Sjogren syndrome, are associated with the classical symptoms and signs of dry eye. It also comprises a promising rationale for specific new approaches to therapy.

Intragastric administration of Mycobacterium vaccae inhibits severe pulmonary allergic inflammation in a mouse model

BACKGROUND

Coexistence with harmless microorganisms such as lactobacilli, saprophytic mycobacteria and some helminths, throughout evolution, may have shaped the host immune system. Exposure to such organisms may have therapeutic benefits by triggering immunoregulatory mechanisms that control inappropriate immune responses to self, gut contents or allergens.

OBJECTIVE

We determined whether treatment with Mycobacterium vaccae by gavage influences the host immune response both locally and systemically. We also investigated whether delivery by this route prevents severe symptoms of disease in a murine model of pulmonary allergic inflammation.

RESULTS

A single intragastric administration of M. vaccae induced a transient increase in the production of IL-10 and IFN-gamma by mesenteric lymph nodes cells and splenocytes. In addition, in a mouse model of pulmonary allergic inflammation, a single treatment with M. vaccae by gavage not only diminished the total cellular infiltrate and the eosinophilic component induced by subsequent intratracheal allergen challenge, but also biased local and systemic cytokine production towards IL-10. Delivery of M. vaccae by gavage was as effective as subcutaneous treatment.

CONCLUSION

This is the first report to suggest that heat-killed mycobacteria can down-regulate symptoms of allergic inflammation by the intragastric route. These data suggest an alternative route of treatment with M. vaccae for patients with allergic conditions.

Regulation of allergy and autoimmunity in helminth infection

Parasitic infections are a major theme in the "hygiene hypothesis", as allergies and autoimmune diseases are less prevalent in countries with higher burdens of helminths and other parasitic organisms. Helminths"-the grouping of multicellular worm parasites including nematodes, cestodes and trematodes-tend to establish long-lived, chronic infections indicating successful down-modulation of the host immune system. In this review, we describe the intricate immunology of host-helminth interactions and how parasites manipulate immune responses to enhance their survival. In so doing, they often minimise immunopathology and, it is suggested, reduce host susceptibility to, and severity of allergic and autoimmune diseases. Studies on helminth-infected communities and individuals support the hypothesis that an immuno-regulatory network promoted by parasites extends its influence to limiting allergies. Experimental models are now probing more deeply into the area of immune modulation by helminths, and we discuss the likely mechanisms by which helminths could be establishing a strongly regulatory environment. Understanding and harnessing the modulatory capacity of helminths may uncover novel therapeutic interventions, mimicking and exploiting their evolution for our benefit. Parasitic infections are a major theme in the "hygiene hypothesis", as allergies and autoimmune diseases are less prevalent in countries with higher burdens of helminths and other parasitic organisms. Helminths"-the grouping of multicellular worm parasites including nematodes, cestodes and trematodes-tend to establish long-lived, chronic infections indicating successful down-modulation of the host immune system. In this review, we describe the intricate immunology of host-helminth interactions and how parasites manipulate immune responses to enhance their survival. In so doing, they often minimise immunopathology and, it is suggested, reduce host susceptibility to, and severity of allergic and autoimmune diseases. Studies on helminth-infected communities and individuals support the hypothesis that an immuno-regulatory network promoted by parasites extends its influence to limiting allergies. Experimental models are now probing more deeply into the area of immune modulation by helminths, and we discuss the likely mechanisms by which helminths could be establishing a strongly regulatory environment. Understanding and harnessing the modulatory capacity of helminths may uncover novel therapeutic interventions, mimicking and exploiting their evolution for our benefit.

Exposure of adult mice to environmental tobacco smoke fails to enhance the immune response to inhaled antigen

Epidemiologic evidence supports a role for environmental tobacco smoke (ETS) in the occurrence and severity of allergies/asthma. However, neither the precise combination of ETS and allergen exposure nor the mechanism (or mechanisms) by which these factors interact and contribute to asthma induction is known. Animal model studies have failed to establish a convincing relationship between ETS exposure and asthma induction, perhaps because of methodological inadequacies. Here, we tested the hypothesis that ETS inhalation would provoke an asthmatic response by overcoming normal airway tolerance to inhaled antigens. Our protocol combined daily ETS exposure with nose-only sensitization to ovalbumin. Three strains of mice were tested, each with a different level of susceptibility to airway hypersensitivity. Immunological responses were assessed by immunoglobulin production. Airway inflammation was assessed by bronchoalveolar lavage differentials and lung histopathology. Airway hyperresponsiveness was determined by methacholine challenge. The mice produced ovalbumin-specific antibodies following ovalbumin exposure in a strain-dependent manner. Only the A/J mice produced detectable levels of ovalbumin-specific immunoglobulin (Ig) E. Both A/J and BALB/c mice produced ovalbumin-specific IgG1 antibodies. The C57Bl/6 mice did not produce detectable levels of antibodies. The A/J mice also exhibited airway inflammation following ovalbumin exposure. Neither the C57Bl/6 nor the BALB/c mice exhibited signs of airway inflammation. Exposure to ETS failed to enhance ovalbumin-specific antibody production, airway inflammation, or hyperresponsiveness. Together these results indicate that ETS exposure accompanied by nose-only allergen sensitization fails to overcome aerosol tolerance in adult mice.

Characterization of a B220+Lymphoid Cell Subpopulation with Immune Modulatory Functions in Nasal-Associated Lymphoid Tissues

Complex mechanisms operate on mucosal tissues to regulate immune responsiveness and tolerance. When the lymphocyte subpopulations from murine nasal-associated lymphoid tissues (NALT) were characterized, we observed an accumulation of B220(low)CD3(low)CD4(-)CD8(-)CD19(-)c-Kit(+) cells. TCR transgenic mice and athymic mice were used for monitoring T cell lineage and the presence of extrathymic T cell precursors. The majority of cells from NALT exhibited a T cell precursor phenotype (CD4(-)CD8(-)CD19(-)c-Kit(+)). Fas-independent apoptosis was their main mechanism of cell death. We also demonstrated that B220(low)CD4(-)CD8(-)CD19(-) cells from NALT exhibited the potential to down-regulate the activation of mature T cells. However, the innate immunity receptor TLR2 was also highly expressed by this cell subpopulation. Moreover, nasal stimulation with a TLR2/6 agonist resulted in a partial activation of the double-negative cells. These results suggest that the immune responses in NALT may be in part modulated by a cell subpopulation that maintains a tolerogenic milieu by its proapoptotic status and suppressive activity, which can be reverted through stimulation of a TLR signaling cascade.

The Mycoplasma-derived macrophage-activating 2-kilodalton lipopeptide triggers global immune activation on nasal mucosa-associated lymphoid tissues

A better knowledge on how immune responses are initiated in mucosal tissues would facilitate the design of new mucosal vaccines, as well as improve our understanding on host defense against infection. We investigated the mechanisms of adjuvanticity of the Mycoplasma-derived macrophage-activating 2-kDa lipopeptide (MALP-2), which binds to the heterodimer formed by the Toll-like receptors 2 and 6 (TLR2 and -6), at the level of the murine nasal mucosa-associated lymphoid tissues (NALT). TLR2 expression analysis demonstrated that several cell types from the nasal cavity were able to overexpress this receptor, either constitutively (such as B cells) or after stimulation (i.e., T cells). MALP-2 stimulated a strong B-cell activation. In addition, the antigen presentation capacity of dendritic cells was improved after in vivo loading with antigen in the presence of MALP-2. We also observed an up-regulated expression of activation markers and adhesion molecules on T cells, suggesting that they have enhanced responsiveness and interaction potential. Quantitative reverse transcription-PCR analysis showed that MALP-2 administration resulted in the stimulation of a proinflammatory cascade. We observed an early up-regulated expression of IP-10, MCP-1, MCP-3, MIP-1alpha, MIP-2, and CCR-2 which was reversed within 36 h. The obtained results demonstrated that MALP-2 creates a reversible local microenvironment which promotes effective priming of T and B cells in the NALT.

Use of mouse models of allergic rhinitis to study the upper and lower airway link

PURPOSE OF REVIEW

Allergic rhinitis and asthma are examples of a continuum of airway diseases with diverse clinical manifestations. This review examines the most recent work in mouse models studying upper and lower airway links and interactions.

RECENT FINDINGS

The concept of united airways has been supported by investigative and epidemiological studies. Studies using mouse models of asthma and models of allergic rhinitis have demonstrated that analogous pathways lead to inflammation and airway hyperresponsiveness. Th2-type T cells and IL-13 play important immunopathologic roles. Recent studies have examined upper airway mucosal immune responses and development of both allergic and tolerant phenotypes. In a model of allergic airways disease, there is evidence of lower airway inflammation and airways hyperresponsiveness following application of allergen only to the nares, suggesting local stimulation can activate distal allergic responses. Immunomodulatory properties of the airway mucosa have also been explored. Allergen-specific tolerance can be induced by appropriate stimulation of airway mucosa and is associated with activation of IL-10-producing T cells. This effect is mediated by antigen presenting cells, especially dendritic cells.

SUMMARY

Immune stimulation of the airway mucosa, both in the upper and lower airways, results in active T-cell-mediated immune responses leading toward tolerance or asthma and allergic rhinitis. Regulation of these T-cell responses is currently under investigation. It is clear from these studies that antigenic stimulation of any part of the respiratory mucosa can have ripple effects along the entire airway and supports the concept of united airways.

Toll-like receptor control of the adaptive immune responses

Recognition of microbial infection and initiation of host defense responses is controlled by multiple mechanisms. Toll-like receptors (TLRs) have recently emerged as a key component of the innate immune system that detect microbial infection and trigger antimicrobial host defense responses. TLRs activate multiple steps in the inflammatory reactions that help to eliminate the invading pathogens and coordinate systemic defenses. In addition, TLRs control multiple dendritic cell functions and activate signals that are critically involved in the initiation of adaptive immune responses. Recent studies have provided important clues about the mechanisms of TLR-mediated control of adaptive immunity orchestrated by dendritic cell populations in distinct anatomical locations.

Airway peptidoglycan and immunostimulatory DNA exposures have divergent effects on the development of airway allergen hypersensitivities

BACKGROUND

Environmental exposures to toll-like receptor (TLR) ligands have been suggested to provide immunologic protection against allergic diseases. However, some TLRs use unique intracellular signaling pathways, suggesting that ambient TLR ligand exposures might induce a range of host responses.

OBJECTIVE

These investigations compared peptidoglycan (PGN; TLR2)-induced and immunostimulatory sequence DNA oligodeoxynucleotide (ISS-ODN; TLR9)-induced innate responses and determined how airway exposures to these TLR ligands affect adaptive immunity and the asthmatic phenotype.

METHODS

In in vitro and in vivo studies innate responses to PGN and ISS-ODN were compared. Alternatively, mice were intranasally immunized with ovalbumin (OVA) alone or OVA plus PGN or ISS-ODN, and adaptive immune profiles and responses to airway OVA challenge were assessed.

RESULTS

PGN and ISS-ODN induced divergent innate responses predictive of their having TH2- and TH1-biasing adjuvant potential, respectively. Consistent with these findings, mice intranasally immunized with OVA alone had relatively weak adaptive responses, whereas intranasal OVA/PGN- and OVA/ISS-ODN-coimmunized mice had much stronger humoral and cellular responses that were TH2 and TH1 biased, respectively. Finally, on airway allergen challenge, mice intranasally immunized with OVA alone had modest TH2-biased airway hypersensitivity responses, whereas airway responses were greatly exaggerated for intranasal OVA/PGN-immunized mice. In contrast, intranasal OVA/ISS-ODN-immunized mice had little evidence of airway hypersensitivity after airway allergen challenge.

CONCLUSIONS

Considered in a larger context, these results suggest that inspired air is likely to contain TLR ligands capable of both preventing and precipitating the asthmatic phenotype.

Dendritic cells and atopic eczema/dermatitis syndrome

PURPOSE OF REVIEW

The manifestation of atopic eczema/dermatitis syndrome is believed to result from a complex interrelationship of environmental factors, pharmacological abnormalities, skin barrier defects, and immunological phenomena. Although we are only beginning to understand the molecular basis of this disease, much progress has been made in defining key events leading to the manifestation of allergic inflammation. Here, we review recent findings that underscore the importance of dendritic cells as being central to shape these proinflammatory responses.

RECENT FINDINGS

Evidence for a differential regulation of the high affinity receptor for IgE, Fc epsilon RI, on the surface of atopic dendritic cells compared with non-atopic dendritic cells became apparent. In atopic donors, in contrast to non-atopic donors, the intracellular expression of the gamma-chains of Fc epsilon RI is sufficient, thus leading to the assembly with the alpha-chain and surface expression of the receptor. This finding is of considerable interest for an understanding of the pathophysiology of IgE-mediated dendritic cell functions in atopic eczema/dermatitis syndrome. In addition, it has been shown that keratinocytes from the epidermal skin of individuals with atopic eczema/dermatitis syndrome express human thymic stromal lymphopoietin, which activates dendritic cells to attract T helper type 2 cells into the skin. Furthermore, these activated dendritic cells prime naïve T cells into T helper type 2 cells.

SUMMARY

The past few years have seen a remarkable process of refocusing in atopy. Dendritic cells in particular have been at the centre of this process. It has become unequivocally clear that these cells have the power of shaping the allergic response.

Mycobacterium vaccae induces a population of pulmonary CD11c+ cells with regulatory potential in allergic mice

The hygiene hypothesis proposes that common, harmless microorganisms, present throughout our evolutionary history, have helped to develop immunoregulatory mechanisms that prevent inappropriate immune responses by the host. Using a mouse model of allergic pulmonary inflammation, we report that treatment with an ubiquitous saprophytic mycobacterium, Mycobacterium vaccae, significantly reduces allergic inflammation by decreasing type 2 responses such as eosinophilia and IL-4 expression. Rather than observing an increase in type-1 cytokine expression, we found elevated production of IL-10 in the lungs suggesting a role for regulatory T cells. Since induction of these cells may be dependent on APC, we investigated the effects of M. vaccae treatment on pulmonary CD11c+ cells. Increased levels of IL-10, TGF-beta and IFN-alpha mRNA were detected in CD11c+ cells from M. vaccae-treated allergic mice. We propose that M. vaccae-induced CD11c+ cells have a potential regulatory role at the site of inflammation through their secretion of immunomodulatory cytokines.

Runx3 regulates mouse TGF-beta-mediated dendritic cell function and its absence results in airway inflammation

Runx3 transcription factor regulates cell lineage decisions in thymopoiesis and neurogenesis. Here we report that Runx3 knockout (KO) mice develop spontaneous eosinophilic lung inflammation associated with airway remodeling and mucus hypersecretion. Runx3 is specifically expressed in mature dendritic cells (DC) and mediates their response to TGF-beta. In the absence of Runx3, DC become insensitive to TGF-beta-induced maturation inhibition, and TGF-beta-dependent Langerhans cell development is impaired. Maturation of Runx3 KO DC is accelerated and accompanied by increased efficacy to stimulate T cells and aberrant expression of beta2-integrins. Lung alveoli of Runx3 KO mice accumulate DC characteristic of allergic airway inflammation. Taken together, abnormalities in DC function and subset distribution may constitute the primary immune system defect, which leads to the eosinophilic lung inflammation in Runx3 KO mice. These data may help elucidate the molecular mechanisms underlying the pathogenesis of allergic airway inflammation in humans.

The role of regulatory T cells in allergy

Atopic diseases are characterized by Th2 and IgE responses to common environmental and food antigens. In vivo, IgE production depends on interactions between allergen-specific B lymphocytes and Th2 lymphocytes. IgE levels are extremely low in normal individuals, suggesting that IgE production is under strong regulation. One of the reasons behind the lack of atopy in healthy individuals is the activity of regulatory T cells, which prevent naïve T helper cell precursors from acquiring a differentiated Th2 phenotype. In addition to naturally occurring regulatory T cells, atopy can be prevented by allergen-specific tolerant/regulatory cells induced through mucosal stimulation, and by mechanisms that directly suppress Iepsilon sterile transcript production on activated B lymphocytes. This article reviews the recent progress on thymic-derived as well as peripherally induced regulatory T cells as they relate to atopy. The latter discussion also includes regulatory T cells that arise through immunotherapy.