Mübeccel Akdis

Role of interleukin 10 in specific immunotherapy.

The induction of allergen-specific anergy in peripheral T cells represents a key step in specific immunotherapy (SIT). Here we demonstrate that the anergic state results from increased IL-10 production. In bee venom (BV)-SIT the specific proliferative and cytokine responses against the main allergen, the phospholipase A2 (PLA), and T cell epitope-containing PLA peptides were significantly suppressed after 7 d of treatment. Simultaneously, the production of IL-10 increased during BV-SIT. After 28 d of BV-SIT the anergic state was established. Intracytoplasmic cytokine staining of PBMC combined with surface marker detection revealed that IL-10 was produced initially by activated CD4(+)CD25(+), allergen-specific T cells, and followed by B cells and monocytes. Neutralization of IL-10 in PBMC fully reconstituted the specific proliferative and cytokine responses. A similar state of IL-10-associated T cell anergy, as induced in BV-SIT, was found in hyperimmune individuals who recently had received multiple bee stings. The addition of IL-10 to soluble CD40 ligand IL-4-stimulated PBMC or purified B cells inhibited the PLA-specific and total IgE and enhanced the IgG4 formation. Accordingly, increased IL-10 production by SIT causes specific anergy in peripheral T cells, and regulates specific IgE and IgG4 production toward normal IgG4-related immunity.

IL‐10 and TGF‐β cooperate in the regulatory T cell response to mucosal allergens in normal immunity and specific immunotherapy

The regulation of normal and allergic immune responses to airborne allergens in the mucosa is still poorly understood, and the mechanism of specific immunotherapy (SIT) in normalizing the allergic response to such allergens is currently not clear. Accordingly, we have investigated the immunoregulatory mechanism of both normal and allergic responses to the major house‐dust mite (HDM) and birch pollen allergens — Dermatophagoides pteroynyssinus (Der p)1 and Bet v 1, respectively — as well as the immunologic basis of SIT to HDM in rhinitis and asthma patients. In normal immunity to HDM and birch pollen, an allergen‐specific peripheral T cell suppression to Der p 1 and Bet v 1 was observed. The deviated immune response was characterized by suppressed proliferative T celland Th1 (IFN‐γ) and Th2 (IL‐5, IL‐13) cytokine responses, and increased IL‐10 and TGF‐β secretion by allergen‐specific T cells. Neutralization of cytokine activity showed that T cell suppression was induced by IL‐10 and TGF‐β during SIT and in normal immunity to the mucosal allergens. In addition, SIT induced an antigen‐specific suppressive activity in CD4+ CD25+ T cells of allergic individuals. Together, these results demonstrate a deviation towards a regulatory/suppressor T cell response during SIT and in normal immunity as a key event for the healthy immune response to mucosal antigens.

Diagnosis and treatment of atopic dermatitis in children and adults: European Academy of Allergology and Clinical Immunology/American Academy of Allergy, Asthma and Immunology/PRACTALL Consensus Report

There are remarkable differences in the diagnostic and therapeutic management of atopic dermatitis practiced by dermatologists and pediatricians in different countries. Therefore, the European Academy of Allergy and Clinical Immunology and the American Academy of Allergy, Asthma and Immunology nominated expert teams who were given the task of finding a consensus to serve as a guideline for clinical practice in Europe as well as in North America. The consensus report is part of the PRACTALL initiative, which is endorsed by both academies.

Histamine regulates T-cell and antibody responses by differential expression of H1 and H2 receptors

Many pathological processes, including those causing allergies and autoimmune diseases, are associated with the presence of specialized subsets of T helper cells (TH1 and TH2) at the site of inflammation. The diversity of TH1 and TH2 function is not predetermined but depends on signals that drive the cells towards either subset. Histamine, released from effector cells (mast cells and basophils) during inflammatory reactions can influence immune response. Here we report that histamine enhances TH1-type responses by triggering the histamine receptor type 1 (H1R), whereas both TH1- and TH2-type responses are negatively regulated by H2R through the activation of different biochemical intracellular signals. In mice, deletion of H1R results in suppression of interferon (IFN)-γ and dominant secretion of TH2 cytokines (interleukin (IL)-4 and IL-13). Mutant mice lacking H2R showed upregulation of both TH1 and TH2 cytokines. Relevant to T-cell cytokine profiles, mice lacking H1R displayed increased specific antibody response with increased immunoglobulin-ε (IgE) and IgG1, IgG2b and IgG3 compared with mice lacking H2R. These findings account for an important regulatory mechanism in the control of inflammatory functions through effector-cell-derived histamine.

Interleukins, from 1 to 37, and interferon-γ: Receptors, functions, and roles in diseases

Advancing our understanding of mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumor development, organ transplantation, and chronic infections could lead to effective and targeted therapies. Subsets of immune and inflammatory cells interact via ILs and IFNs; reciprocal regulation and counter balance among T(h) and regulatory T cells, as well as subsets of B cells, offer opportunities for immune interventions. Here, we review current knowledge about ILs 1 to 37 and IFN-γ. Our understanding of the effects of ILs has greatly increased since the discoveries of monocyte IL (called IL-1) and lymphocyte IL (called IL-2); more than 40 cytokines are now designated as ILs. Studies of transgenic or knockout mice with altered expression of these cytokines or their receptors and analyses of mutations and polymorphisms in human genes that encode these products have provided important information about IL and IFN functions. We discuss their signaling pathways, cellular sources, targets, roles in immune regulation and cellular networks, roles in allergy and asthma, and roles in defense against infections.

Mechanisms of immune suppression by interleukin-10 and transforming growth factor-β: the role of T regulatory cells

Specific immune suppression and induction of tolerance are essential processes in the regulation and circumvention of immune defence. The balance between allergen‐specific type 1 regulatory (Tr1) cells and T helper (Th) 2 cells appears to be decisive in the development of allergy. Tr1 cells consistently represent the dominant subset specific for common environmental allergens in healthy individuals. In contrast, there is a high frequency of allergen‐specific interleukin‐4 (IL‐4)‐secreting T cells in allergic individuals. Allergen‐specific immunotherapy can induce specific Tr1 cells that abolish allergen‐induced proliferation of Th1 and Th2 cells, as well as their cytokine production. Tr1 cells utilize multiple suppressor mechanisms, such as IL‐10 and transforming growth factor‐β (TGF‐β) as secreted cytokines and various surface molecules, such as cytotoxic T‐lymphocyte antigen 4 and programmed death‐1. IL‐10 only inhibits T cells stimulated by low numbers of triggered T‐cell receptors, which depend on CD28 costimulation. IL‐10 inhibits CD28 tyrosine phosphorylation, preventing the binding of phosphatidylinositol 3‐kinase p85 and consequently inhibiting the CD28 signalling pathway. In addition, IL‐10 and TGF‐β secreted by Tr1 cells skew the antibody production from immunoglobulin E (IgE) towards the non‐inflammatory isotypes IgG4 and IgA, respectively. Induction of antigen‐specific Tr1 cells can thus re‐direct an inappropriate immune response against allergens or auto‐antigens using a broad range of suppressor mechanisms.

T cell–mediated Fas-induced keratinocyte apoptosis plays a key pathogenetic role in eczematous dermatitis

Clinical and histologic similarities between various eczematous disorders point to a common efferent pathway. We demonstrate here that activated T cells infiltrating the skin in atopic dermatitis (AD) and allergic contact dermatitis (ACD) induce keratinocyte (KC) apoptosis. KCs normally express low levels of Fas receptor (FasR) that can be substantially enhanced by the presence of IFN-gamma. KCs are rendered susceptible to apoptosis by IFN-gamma when FasR numbers reach a threshold of approximately 40,000 per KC. Subsequently, KCs undergo apoptosis induced by anti-FasR mAbs, soluble Fas ligand, supernatants from activated T cells, or direct contact between T cells and KCs. Apoptotic KCs show typical DNA fragmentation and membrane phosphatidylserine expression. KC apoptosis was demonstrated in situ in lesional skin affected by AD, ACD, and patch tests. Using numerous cytokines and anti-cytokine neutralizing mAbs, we found no evidence that cytokines other than IFN-gamma participate in this process. In addition, apoptosis-inducing pathways other than FasR triggering were ruled out by blocking T cell-induced KC apoptosis by caspase inhibitors and soluble Fas-Fc protein. Responses of normal human skin and cultured skin equivalents to activated T cells demonstrated that KC apoptosis caused by skin-infiltrating T cells is a key event in the pathogenesis of eczematous dermatitis.

In vivo switch to IL-10-secreting T regulatory cells in high dose allergen exposure.

High dose bee venom exposure in beekeepers by natural bee stings represents a model to understand mechanisms of T cell tolerance to allergens in healthy individuals. Continuous exposure of nonallergic beekeepers to high doses of bee venom antigens induces diminished T cell–related cutaneous late-phase swelling to bee stings in parallel with suppressed allergen-specific T cell proliferation and T helper type 1 (Th1) and Th2 cytokine secretion. After multiple bee stings, venom antigen–specific Th1 and Th2 cells show a switch toward interleukin (IL) 10–secreting type 1 T regulatory (Tr1) cells. T cell regulation continues as long as antigen exposure persists and returns to initial levels within 2 to 3 mo after bee stings. Histamine receptor 2 up-regulated on specific Th2 cells displays a dual effect by directly suppressing allergen-stimulated T cells and increasing IL-10 production. In addition, cytotoxic T lymphocyte–associated antigen 4 and programmed death 1 play roles in allergen-specific T cell suppression. In contrast to its role in mucosal allergen tolerance, transforming growth factor β does not seem to be an essential player in skin-related allergen tolerance. Thus, rapid switch and expansion of IL-10–producing Tr1 cells and the use of multiple suppressive factors represent essential mechanisms in immune tolerance to a high dose of allergens in nonallergic individuals.

Mechanisms and treatment of allergic disease in the big picture of regulatory T cells

Various populations of regulatory T (Treg) cells have been shown to play a central role in the maintenance of peripheral homeostasis and the establishment of controlled immune responses. Their identification as key regulators of immunologic processes in peripheral tolerance to allergens has opened an important era in the prevention and treatment of allergic diseases. Both naturally occurring CD4+CD25+ Treg cells and inducible populations of allergen-specific, IL-10-secreting Treg type 1 (T(R)1) cells inhibit allergen-specific effector cells in experimental models. Skewing of allergen-specific effector T cells to a regulatory phenotype appears to be a key event in the development of healthy immune response to allergens and successful outcome in allergen-specific immunotherapy. Forkhead box protein 3-positive CD4+CD25+ Treg cells and T(R)1 cells contribute to the control of allergen-specific immune responses in several major ways, which can be summarized as suppression of dendritic cells that support the generation of effector T cells; suppression of effector T(H)1, T(H)2, and T(H)17 cells; suppression of allergen-specific IgE and induction of IgG4; suppression of mast cells, basophils, and eosinophils; interaction with resident tissue cells and remodeling; and suppression of effector T-cell migration to tissues. Current strategies for drug development and allergen-specific immunotherapy exploit these observations, with the potential for preventive therapies and cure for allergic diseases.

Epitope-specific T cell tolerance to phospholipase A2 in bee venom immunotherapy and recovery by IL-2 and IL-15 in vitro.

Bee venom phospholipase A2 (PLA) is the major allergen in bee sting allergy. It displays three peptide and a glycopeptide T cell epitopes, which are recognized by both allergic and non-allergic bee venom sensitized subjects. In this study PLA- and PLA epitope-specific T cell and cytokine responses in PBMC of bee sting allergic patients were investigated before and after 2 mo of rush immunotherapy with whole bee venom. After successful immunotherapy, PLA and T cell epitope peptide-specific T cell proliferation was suppressed. In addition the PLA- and peptide-induced secretion of type 2 (IL-4, IL-5, and IL-13), as well as type 1 (IL-2 and IFN-gamma) cytokines were abolished, whereas tetanus toxoid-induced cytokine production and proliferation remained unchanged. By culturing PBMC with Ag in the presence of IL-2 or IL-15 the specifically tolerized T cell response could be restored with respect to specific proliferation and secretion of the type 1 T cell cytokines, IL-2 and IFN-gamma. In contrast, IL-4, IL-5, and IL-13 remained suppressed. Treatment of tolerized T cells with IL-4 only partially restored proliferation and induced formation of distinct type 2 cytokine pattern. In spite of the allergen-specific tolerance in T cells, in vitro produced anti-PLA IgE and IgG4 Ab and their corresponding serum levels slightly increased during immunotherapy, while the PLA-specific IgE/IgG4 ratio changed in favor of IgG4. These findings indicate that bee venom immunotherapy induces a state of peripheral tolerance in allergen-specific T cells, but not in specific B cells. The state of T cell tolerance and cytokine pattern can be in vitro modulated by the cytokines IL-2, IL-4, and IL-15, suggesting the importance of microenvironmental cytokines leading to success or failure in immunotherapy.