Low zone tolerance induced by systemic application of allergens inhibits Tc1-mediated skin inflammation

Regulation of immune response genes in the skin of allergic and clinically tolerant individuals exposed to p-phenylenediamine

BACKGROUND

p-Phenylenediamine (PPD) is a potent contact allergen found in many hair colour products. However, not all individuals develop allergic contact dermatitis (ACD) although they are regularly exposed to PPD. It is unclear whether these asymptomatic individuals are true non-responders to PPD or whether they mount a response to PPD without showing any symptoms.

METHODS

Skin biopsies were collected from 11 asymptomatic hairdressers regularly exposed to PPD and from 10 individuals with known ACD on day 4 after patch testing with 1% PPD in petrolatum and petrolatum exclusively as control. RNA sequencing and confocal microscopy were performed.

RESULTS

T cell activation, inflammation and apoptosis pathways were up-regulated by PPD in both asymptomatic and allergic individuals. Compared to asymptomatic individuals with a negative patch test, individuals with a strong reaction to PPD strongly up-regulated both pro- and anti-inflammatory cytokines genes. Interestingly, PPD treatment induced significant up-regulation of several genes for chemokines, classical type 2 dendritic cell markers and regulatory T cell markers in both asymptomatic and allergic individuals. In addition, apoptosis signalling pathway was activated in both non-responders and allergic individuals.

CONCLUSION

This study demonstrates that there are no true non-responders to PPD but that the immune response elicited by PPD differs between individuals and can lead to either tolerance, subclinical inflammation or allergy.

Antigen-Specific Treatment Modalities in MS: The Past, the Present, and the Future

Antigen-specific therapy for multiple sclerosis may lead to a more effective therapy by induction of tolerance to a wide range of myelin-derived antigens without hampering the normal surveillance and effector function of the immune system. Numerous attempts to restore tolerance toward myelin-derived antigens have been made over the past decades, both in animal models of multiple sclerosis and in clinical trials for multiple sclerosis patients. In this review, we will give an overview of the current approaches for antigen-specific therapy that are in clinical development for multiple sclerosis as well provide an insight into the challenges for future antigen-specific treatment strategies for multiple sclerosis.

Analysis of allergic immune responses in humanized mice

Nowadays, more than 25% of the population in industrial countries are affected by IgE-mediated (atopic) allergic diseases such as allergic rhinitis, asthma and atopic eczema. Due to intensive research on basis of in vitro studies with human immune cells and different murine in vivo models of allergy fundamental mechanisms of allergic immune responses have been elucidated during the last years. However, human studies are restricted and the immune system of mice differs from the human immune system in several aspects so that the transferability of experimental results from mice to men is limited. Humanized mice represent a new tool to analyze the interaction of human immune cells under physiological conditions as far as possible, particularly to test novel therapeutic strategies. This review summarizes the impact of humanized mouse models for the investigation and treatment of allergic diseases.

Dose-response relationship of specific allergen exposure-induced immunological tolerance: a mouse model

BACKGROUND

It is believed that adequate allergen preimmunization exposure could induce immunologic tolerance. The purpose of this study was to investigate the dose-dependent mechanisms related to antigen-specific tolerance induction in a mouse model.

METHODS

Mice were assigned to 5 groups: the control (Cont) group received phosphate-buffered saline (PBS) preimmunization exposure and PBS sham immunization; the other 4 groups were exposed preimmunization to PBS (PBS group) or ovalbumin (OVA) (first mucosal doses: 1.25%, 2.5%, or 5% wt/vol aerosol from days -3 to -1) prior to OVA immunization. The OVA-immunized mice received intraperitoneal doses of 20 μg OVA (on days 1, 7, and 14), and then a second set of mucosal doses with 0.5% wt/vol OVA aerosol (on days 18 to 20). After assessment of airway hyperresponsiveness (AHR), the mice were euthanized and their blood, bronchoalveolar lavage fluids (BALFs), and lung tissues were collected for further analyses.

RESULTS

OVA-immunized mice exposed to OVA preimmunization had reduced AHR and immunoglobulin E production when compared to the PBS group. OVA preimmunization exposure inhibited eosinophilic inflammation in lung tissues. The proportions of BALF eosinophil counts from the groups exposed to OVA preimmunization were significantly decreased when compared with those exposed to PBS preimmunization. The balance of T helper 2 (Th2) and T regulatory (Treg) cytokines in BALFs were additionally observed in this mouse model.

CONCLUSION

Our results suggest that preimmunization exposure to an appropriate dose of a specific antigen could suppress allergic airway inflammation by induction of immunological tolerance.

Immunoregulation in cutaneous allergy: prevention and control

PURPOSE OF REVIEW

The cutaneous surface is exposed to a myriad of encounters with chemicals, allergens and microbes. Nevertheless, it withstands these environmental assaults without overt inflammation. We will discuss the role of T regulatory cells in a situation where this tissue homeostasis fails - cutaneous allergy, in particular contact hypersensitivity.

RECENT FINDINGS

Immune regulation is a complex process that is mediated by many cellular players. T regulatory cells have risen to particular prominence as potent immunosuppressors because their absence results in inflammation including skin allergy. Recent findings revealed that T regulatory cells comprise a heterogeneous group of subpopulations with specialized homing capabilities and suppressor functions. The stability of the T regulatory cell subset in proinflammatory microenvironments is controversially discussed. In addition, it has recently been shown that mechanisms by which T regulatory cells exert their immunosuppressive functions can be adopted by pathogenic effector T cells in certain situations.

SUMMARY

In cutaneous allergy, immunoregulatory mechanisms are dysfunctional. The cellular players comprise classical T regulatory cells as well as effector T cells with regulatory activities. Understanding their role in skin homeostasis and the mechanisms by which their regulatory functions are abrogated will yield novel therapeutic targets for the treatment of cutaneous allergies.

Crosstalk of regulatory T cells and tolerogenic dendritic cells prevents contact allergy in subjects with low zone tolerance

BACKGROUND

Allergic contact dermatitis is one of the most common occupational diseases. A main protective mechanism in those who do not develop allergic contact dermatitis is tolerance induction by repeated exposure to low doses of contact allergen, which is termed low zone tolerance (LZT). The mechanisms that determine the tolerance induction in subjects with LZT are still elusive.

OBJECTIVE

We performed analysis of the role of CD4(+)CD25(+) forkhead box protein 3 (FOXP3)-positive regulatory T (Treg) cells and dendritic cells (DCs) in mice with LZT.

METHODS

Mechanisms of tolerance induction were analyzed in a murine model of LZT by using FOXP3 and IL-10 reporter mice, as well as mice that allow the selective depletion of Treg cells or DCs.

RESULTS

Depletion of CD4(+)CD25(+)FOXP3(+) Treg cells during tolerance induction completely abolishes the development of LZT, resulting in a pronounced contact hypersensitivity response. Adoptive transfer experiments, depletion studies, and use of cell type-specific deficient mice revealed that IL-10 production is critical for the suppressor function of Treg cells in mice with LZT and that tolerogenic CD8(+)CD11c(+) DCs located in the skin-draining lymph nodes are essential for LZT. In the absence of Treg cells, DCs did not develop tolerogenic functions, indicating that activated IL-10(+) Treg cells might imprint the tolerogenic DC phenotype. Cell communication analysis revealed that the education of tolerogenic DCs might involve a direct interaction with Treg cells mediated by gap junctions. Subsequently, induction of tolerogenic CD11c(+) DCs leads to the generation of hapten-specific CD8(+) Treg cells, which protect against contact hypersensitivity.

CONCLUSIONS

Our data demonstrate critical interactions between CD4(+)CD25(+)FOXP3(+) Treg cells and tolerogenic CD8(+)CD11c(+) DCs during the induction of LZT.

Mechanisms of chemical-induced innate immunity in allergic contact dermatitis

Allergic contact dermatitis (ACD) is one of the most prevalent occupational skin diseases and causes severe and long-lasting health problems in the case of chronification. It is initiated by an innate inflammatory immune response to skin contact with low molecular weight chemicals that results in the priming of chemical-specific, skin-homing CD8(+) Tc1/Tc17 and CD4(+) Th1/Th17 cells. Following this sensitization step, T lymphocytes infiltrate the inflamed skin upon challenge with the same chemical. The T cells then exert cytotoxic function and secrete inflammatory mediators to produce an eczematous skin reaction. The recent characterization of the mechanisms underlying the innate inflammatory response has revealed that contact allergens activate innate effector mechanisms and signalling pathways that are also involved in anti-infectious immunity. This emerging analogy implies infection as a potential trigger or amplifier of the sensitization to contact allergens. Moreover, new mechanistic insights into the induction of ACD identify potential targets for preventive and therapeutic intervention. We summarize here the latest findings in this area of research.

T cell killing by tolerogenic dendritic cells protects mice from allergy

It is well established that allergy development can be prevented by repeated low-dose exposure to contact allergens. Exactly which immune mechanisms are responsible for this so-called low zone tolerance (LZT) is not clear, although CD8⁺ suppressor T cells are known to have a role. Here, we show that TNF released by tolerogenic CD11⁺CD8⁺ DCs located in skin-draining lymph nodes is required and sufficient for development of tolerance to contact allergens in mice. DC-derived TNF protected mice from contact allergy by inducing apoptosis in allergen-specific effector CD8⁺ T cells via TNF receptor 2 but did not contribute to the generation and function of the regulatory T cells associated with LZT. The TNF-mediated killing mechanism was induced in an allergen-specific manner. Activation of tolerogenic DCs by LZT CD8⁺ suppressor T cells and enhanced TNF receptor 2 expression on contact allergen-specific CD8⁺ effector T cells were required for LZT. Our findings may explain how tolerance protects from allergic diseases, which could allow for the development of new strategies for allergy prevention.

Imunopatologia da dermatite de contato alérgica

A dermatite de contato alérgica é consequência de uma reação imune mediada por células T contra químicos de baixo peso molecular, denominados haptenos. É uma condição frequente que ocorre em todas as raças e faixas etárias e afeta a qualidade de vida de seus portadores. O mecanismo imunológico desta doença vem sendo revisto nas últimas décadas com significativo avanço no seu entendimento. A metabolização e o caminho dos haptenos, bem como a formação e o mecanismo de ação das células responsáveis tanto pela reação quanto pelo seu término, são discutidos neste artigo

Prevention of diabetes in NOD mice by repeated exposures to a contact allergen inducing a sub-clinical dermatitis

BACKGROUND

Type 1 diabetes is an autoimmune disease, while allergic contact dermatitis although immune mediated, is considered an exposure driven disease that develops due to epicutaneous contact with reactive low-molecular chemicals. The objective of the present study was to experimentally study the effect of contact allergens on the development of diabetes in NOD mice. As the link between contact allergy and diabetes is yet unexplained we also examined the effect of provocation with allergens on Natural Killer T (NKT) cells, since involvement of NKT cells could suggest an innate connection between the two diseases.

METHOD

NOD mice 4 weeks of age were exposed, on the ears, to two allergens, p-phenylenediamine and 2,4-dinitrochlorobenzene respectively, to investigate the diabetes development. The mice were followed for a maximum of 32 weeks, and they were either repeatedly exposed to the allergens or only sensitized a week after arrival. The stimulation of NKT cells by the two allergens were additionally studied in C57BL/6 mice. The mice were sensitized and two weeks later provocated with the allergens. The mice were subsequently euthanized at different time points after the provocation.

RESULTS

It was found that repeated application of p-phenylenediamine reduced the incidence of diabetes compared to application with water (47% vs. 93%, P = 0.004). Moreover it was shown that in C57BL/6 mice both allergens resulted in a slight increment in the quantity of NKT cells in the liver. Application of the allergens at the same time resulted in an increased number of NKT cells in the draining auricular lymph node, and the increase appeared to be somewhat allergen specific as the accumulation was stronger for p-phenylenediamine.

CONCLUSION

The study showed that repeated topical application on the ears with a contact allergen could prevent the development of diabetes in NOD mice. The contact allergens gave a non-visible, sub-clinical dermatitis on the application site. The preventive effect on diabetes may be due to stimulation of peripheral NKT cells, as shown for provocation with p-phenylenediamine in the C57BL/6 mouse. This epicutaneous procedure may lead to new strategies in prevention of type 1 diabetes in humans.

Transfer of tolerance to collagen type V suppresses T-helper-cell-17 lymphocyte-mediated acute lung transplant rejection

BACKGROUND

Rat lung allograft rejection is mediated by collagen type V (col(V)) specific T-helper-cell 17 (Th17) cells. Adoptive transfer of these cells is sufficient to induce rejection pathology in isografts, whereas tolerance to col(V) suppresses allograft rejection. Therefore, we tested whether regulatory T cells from tolerant rats could suppress the Th17-mediated rejection in the syngeneic model of lung transplantation.

METHODS

Rats were subjected to syngeneic left lung transplantation, and acute rejection was induced by adoptive transfer of lymph node cells from col(V)-immunized rats. Tolerance was induced by intravenous injection of col(V), and spleen lymphocytes were used for adoptive transfer. CD4+ T cells were depleted using magnetic beads. Lung isografts were analyzed using micro-positron emission tomography imaging and histochemistry. The transvivo delayed type hypersensitivity assay was used to analyze the Th17 response.

RESULTS

Adoptive cotransfer of col(V)-specific effector cells with cells from col(V)-tolerized rats suppressed severe vasculitis and bronchiolitis with parenchymal inflammation, and the expression of interleukin (IL)-17 transcripts in mediastinal lymph nodes induced by effector cells alone. Analysis by transvivo delayed type hypersensitivity showed that the reactivity to col(V) was dependent on the presence of tumor necrosis factor-alpha and IL-17 but not interferon-gamma. Depletion of CD4+ T cells from the suppressor cell population abrogated the col(V)-specific protection.

CONCLUSION

Th17-mediated acute rejection after lung transplantation is ameliorated by CD4+ col(V)-specific regulatory T cells. The mechanism for this Th17 suppression is consistent with tolerance induction to col(V). The goal of transplantation treatment, therefore, should target Th17 development and not suppression of T-cell activation by suppressing IL-2.

Low zone tolerance requires ICAM-1 expression to limit contact hypersensitivity elicitation

Painting subsensitizing doses of contact sensitizers on skin (low-dose tolerization) induces antigen (Ag)-specific tolerance, known as low zone tolerance (LZT), which has been experimentally demonstrated by the inhibition of contact hypersensitivity (CHS). Although LZT resulted from the inhibition of the sensitization phase, the effects on the effector/elicitation phase remain unknown. L-selectin and ICAM-1 regulate leukocyte influx into inflamed tissues during the elicitation phase of CHS. LZT was investigated in mice lacking either L-selectin or ICAM-1 to evaluate the roles these leukocyte receptors play in LZT during the elicitation phase. Low-dose tolerization effectively suppressed CHS in wild-type and L-selectin-deficient mice, but not in ICAM-1-deficient mice. Low-dose-tolerized ICAM-1-deficient splenocytes effectively suppressed the elicitation phase in naive wild-type recipients. Sensitized ICAM-1-deficient splenocytes showed normal proliferative responses to the sensitizing Ag and generated normal CHS in wild-type recipients. Thus, ICAM-1 deficiency did not affect sensitization. LZT was associated with a lack of ICAM-1 upregulation after elicitation, suggesting a potentially mechanistic role for ICAM-1. The blockade of IL-10, a possible mediator of LZT, produced by hapten-specific suppressor cells, abrogated LZT and restored ICAM-1 upregulation. These results indicate that low-dose tolerization controls CHS by abrogating ICAM-1 upregulation during the elicitation phase.

T regulatory cells in contact hypersensitivity

PURPOSE OF REVIEW

The review summarizes the recent investigations focused on T regulatory cells in hapten diseases.

RECENT FINDINGS

Multiple mechanisms ensure tolerance to small chemicals penetrating the skin. Among these, specific T regulatory cells play a major role in controlling harmful immune responses to environmental antigens. Most of the T regulatory cells involved in this process belongs to the CD4 subset and suppress hapten-specific immune response through the release of IL-10 and through direct interaction with effector T cells, blocking their function.

SUMMARY

Methods for in-vitro and in-vivo expansion of specific T regulatory cells may represent an innovative approach for the cure of contact hypersensitivity.

From innate to adaptive immune responses in contact hypersensitivity

PURPOSE OF REVIEW

To summarize recent findings that highlight the importance of the innate inflammatory immune responses in contact dermatitis and their role for the adaptive T-cell response to contact allergens. Implications for anti-inflammatory therapy based on recent reports are discussed.

RECENT FINDINGS

Allergic contact dermatitis is studied widely in the mouse model. Recent work has identified an important role of innate pattern recognition receptors and innate immune cells in contact hypersensitivity. The role of skin dendritic cells has been studied with novel approaches for in-vivo depletion. New findings were made in the field of anti-inflammatory therapy either by uncovering new aspects of pathomechanisms or by the use of drugs that target different elements of the inflammatory cascade.

SUMMARY

Inflammation is a pivotal element of allergic contact dermatitis. Studies in the mouse contact hypersensitivity model are beginning to shed light on the still largely unknown molecular mechanisms that enable contact allergens such as chemicals, metal ions and plant compounds to initiate the inflammatory innate immune response. This is a prerequisite for the adaptive immune response to occur. The recent progress in research points out the great potential of anti-inflammatory therapy covering a wide range of molecular targets.

Nickel, palladium and rhodium induced IFN-gamma and IL-10 production as assessed by in vitro ELISpot-analysis in contact dermatitis patients

BACKGROUND

Recent attempts to diminish nickel use in most industrial products have led to an increasing utilization of alternative metal compounds for destinations such as the alloys used in orthopaedics, jewellery and dentistry. The present study was undertaken with the aim to evaluate the potential for an allergic response to nickel, palladium and rhodium on the basis of antigen-specific induction of inflammatory/regulatory cytokines, and to characterize, according to the cytokine profiles, the nature of simultaneous positive patch tests elicited in vivo. Peripheral blood mononuclear cells (PBMC) from 40 patients with different patch test results were kept in short term cultures in the presence of optimized concentrations of NiSO4 x 6H2O, PdCl2 and Rh(CH3COO)2. The production of IFN-gamma and IL-10 elicited by metal compounds were analyzed by the ELISpot assay.

RESULTS

We found a specific IFN-gamma response by PBMC upon in vitro stimulation with nickel or palladium in well recognized allergic individuals. All controls with a negative patch test to a metal salt showed an in vitro IL-10 response and not IFN-gamma production when challenged with the same compound. Interestingly, all subjects with positive patch test to both nickel and palladium (group 3) showed an in vitro response characterized by the release of IFN-gamma after nickel stimulation and production of IL-10 in response to palladium.

CONCLUSION

These results strongly suggest that the different cytokine profiles elicited in vitro reflect different immune responses which may lead to the control of the allergic responses or to symptomatic allergic contact dermatitis. The development of sensitive and specific in vitro assays based on the determination of the cytokine profiles in response to contact allergens may have important diagnostic and prognostic implications and may prove extremely useful in complementing the diagnostic limits of traditional patch testing.

New aspects of the molecular basis of contact allergy

PURPOSE OF REVIEW

The aim of the review is to provide an up-to-date scenario of the mechanisms governing contact allergy, a widely diffused immune response to small chemicals (haptens) penetrating the skin.

RECENT FINDINGS

The availability of animal models for contact allergy, such as murine contact hypersensitivity, is of great importance in understanding the pathomechanisms of the allergic response, although all these findings need confirmation in humans. Contact allergy is the result of the activation of both innate and adaptive immunity in response to haptens. Both skin resident cells, such as keratinocytes and mast cells, and immigrating leucocytes, including T lymphocytes and natural killer cells, actively participate in the reaction. Different types of T-regulatory cells appear to be crucial in the prevention of contact allergy or in the early termination of the reaction. Understanding the mechanisms that regulate immune responses to haptens is critical for the development of innovative therapeutic approaches.

SUMMARY

Although contact allergy is predominantly a T-cell-mediated disease, humoral immune responses and innate immunity actively participate in the initiation and expression of the allergic disease.

Advances in basic and clinical immunology in 2006

This article reviews the progress in the field of basic and clinical immunology in 2006, focusing on the articles published in the Journal. The role of Toll-like receptors in the immune response was explored in detail in several articles. The knowledge gained in these investigations is being used to develop strategies that enhance the immunogenicity of vaccines to prevent infectious diseases and to have an immunomodulatory effect on allergic diseases. Other components of the innate immunity reported on were the recognition of allergens with lipid-derived motifs by CD1d-restricted T cells and the role of dendritic cells in the development of an allergic response. More than 120 primary immunodeficiencies were defined at a molecular level, and biological agents such as TNF-alpha antagonists and IFN-alpha were shown to have therapeutic use. New anti-HIV drugs that block cell entry were proven to be effective, thus offering alternative therapies to respond to the development of multidrug-resistant HIV strains. The modern understanding of immunologic concepts is helping to elucidate the mechanisms of defense against viruses, bacteria, and parasites; as a result, strategies to improve management and prevention continue to emerge.

Immunoregulation by targeting T cells in the treatment of allergy and asthma

T-cell responses to allergens are crucial in determining the choice between health and disease. Th2 responses drive synthesis of IgE and the recruitment, maturation, survival and effector function of accessory cells such as eosinophils, basophils and mast cells. Allergen-specific strategies for targeting T-cell responses in established allergic diseases have been employed with success for almost a century. Recently, new insight into the mechanism of action of such approaches has revealed modulation of the delicate and complex regulatory mechanisms including suppression of Th2 responses through antagonistic Th1 responses and regulation through IL-10 and TGFbeta production.