Mécanismes immunologiques de l'immunothérapie sublinguale spécifique des allergènes

Sublingual specific immunotherapy has been proven to be efficacious in treating type I allergies. It decreases the ratio of allergen-specific IgE/IgG4 antibody responses and reduces the recruitment and activation of proinflammatory cells (mast cells, basophils, eosinophils) within target organs. The impact on T cell polarization remains to be further documented but is consistent with a decrease in Th2 responses (with lower IL13 production) and a stimulation of IFN-γ or IL10 producing T lymphocytes. Allergens administered under the tongue are captured by dendritic cells (Langerhans cells) expressing IgE receptors (FcεRI and CD23), which subsequently, migrate to cervical/submaxillary lymph nodes. Langerhans cells in the sublingual mucosa produce TGFβ and IL10 and thus could potentially elicit regulatory T cells inhibiting effectors mechanisms of allergic inflammation. A better understanding of immune mechanisms involved in sublingual immunotherapy will allow designing second-generation vaccines based on recombinant allergens presented in a native configuration to the immune system, in association with adjuvants and/or mucoadhesive formulations.     

Les aéroallergènes chez le sujet non allergique : quels mécanismes ?

Non-allergic individuals are in contact with the same allergens as allergic individuals but their immune response to these allergens is one of tolerance, the mechanisms of which must be understood in oder to develop effective immunotherapy. Recent experimental reports have described several subpopulations of regulatory T cells (Tr1, Th3, Treg) that play an important role in peripheral tolerance. The mechanism of this tolerance depends on the effects of IL-10 and TGF-β, as well as on the inhibitory effect of membrane molecules such as ICOS and CTLA4. It has been demonstrated in non-allergic individuals that CD4+CD25+ T regulatory cells can inhibit both T cell proliferation and IL-5 production, whereas this T cell subpopulation is deficient in allergic individuals.     

Axes de recherche en allergologie alimentaire : hypoallergénicité et vaccins

The frequency of food allergy in the pediatric population (8%), as well as the worrying increase of prevalence of severe anaphylaxis boost the research for means of prevention and for therapeutics alternative to the sole eviction of foods. Oral desensitization and sublingual immunotherapy, being the main part of the present clinical research are not in the scope of this review. Future trends of research focus on hypoallergenicity and vaccines. The definition of hypoallergenicity is limited to a lesser reactivity because of a lesser binding of specific IgE to modified food allergens, since the conditions of the immunogenicity leading to sensitization remain unknown. Different ways for patients, alimentary industry and agronomical research are detailed: heating and cooking, enzymatic and chemical treatment of natural foods, physical treatments (texturization, ultrafiltration,…), screening of natural varieties in order to characterize some of them with a lower level or an absence of major allergens. Bioengineering of plants with a reduced level of major allergens, and site-directed mutagenesis on B epitopes could be helpful for a safer nutrition and vaccines. Possible molecular forms aimed at vaccines are considered: recombinant natural allergens, modified recombinant allergens by dimerisation, site-directed mutagenesis, fusion with other molecules, long peptides,… Associated considerations are the choice of adjuvants promoting a Th1 response, as well as vectors for the expression of recombinant food allergens: bacteria, probiotic ones, or poorly allergenic plants. Mucosal vaccines could be especially interesting for food allergens in order to add specific mechanisms of tolerance arising in the intestinal mucosa to the reorientation towards a Th1 and TREG response. Plasmidic DNA vaccines and anti-IgE vaccines are an object of research without any application in the near future. Therapeutic vaccines for food allergens might be substituted to oral desensitization and could be applied first to peanut allergy and to cross allergy between pollens and fruit or vegetable linked to panallergens. Prophylactic vaccines might be a second step for atopic infants, insofar as more knowledge could be obtained of mechanisms and enhancing factors of oral tolerance to food allergens and the “opportunity window” for the establishment of oral tolerance.     

Les modèles expérimentaux d’eczéma de contact

Knowledge of the pathophysiology of Allergic Contact Dermatitis (ACD) derives chiefly from the murine experimental model of Contact Hypersensitivity referred to as the Mouse Ear Swelling Test (MEST). ACD is mediated by activation of CD8+ cytotoxic T cells specific for haptens in contact with the skin, and down-regulated by CD4+ T cells which limit the magnitude of the skin inflammation and participate to its resolution. Although the MEST is a major tool in the fields of immunodermatology and fundamental immunology, it is not sensitive enough to detect the sensitizing properties of common weak allergens and therefore is not used anymore in immunotoxicological studies. The MEST has been replaced by the Local lymph node Assay (LLNA), which brought tangible ethical benefits, but is endowed with low sensitivity and specificity. Recently, we reported that mice deficient in CD4+ T regulatory cells, but not normal mice, could develop a typical ACD reaction to weak haptens involved in human ACD to fragrances (Hexylcinnamaldehyde, Eugenol, Hydroxycitronellal). From this in vivo results, we developed an in vitro assay, referred to as the Weak Hapten Interferon Secreting T LymphocytE test (Whistle), able to detect the sensitizing properties of chemicals in contact with the skin.     

SLIT Improves Cedar Pollinosis by Restoring IL-10 Production from Tr1 and Monocytes~IL-10 Productivity Is Critical for Becoming Allergic ~

BackgroundAllergen-specific immunotherapy (SIT) is currently used for several allergic disorders and IL-10- producing regulatory T cells (Tr1) induced by SIT suppress allergic reactions. We investigated the relation between IL-10 production and acquiring allergy.MethodsA prospective study was undertaken to evaluate the effect of SIT on IL-10 production in T cells and other cell fractions in children with pollinosis. In addition, blood samples were collected from non-allergic healthy controls and patients with pollinosis to compare the levels of IL-10 production. PBMC were cultured with pollen peptides or control allergens, and the IL-10 production from monocyte and CD4 T cell was analyzed.ResultsMonocytes and CD4 T cells from SIT group of patients produced high levels of IL-10, suggesting that the induction of IL-10 is essential for inducing T cell tolerance. IL-10 production from monocytes and T cells was significantly increased in non-allergic controls compared to patients with pollinosis. This high IL-10 production was observed even when PBMC were stimulated with antigens other than pollen peptides.ConclusionsIL-10 is critical for induction of specific T cell tolerance, and increased production of IL-10 by monocytes and T cells during inflammatory responses or after SIT may influence effector cells in allergy. Present data implicates that the low productivity of IL-10 by monocytes and T cells is closely related with sensitivity to multiple allergens, and resistance to allergic diseases. Augmentation of constitutive IL-10 production from immune system is a potential therapeutic approach for allergic disorders.     

Lymphocytes T et allergie alimentaire

The pathogenesis of food allergy was, in the past, focused on atopy, IgE and auxiliary lymphocytes responsible for class switching. Nevertheless, some allergic reactions induced by foods do not involve IgE. Mechanisms of breaking tolerance and cell mechanisms at the level of the gut mucosa are now better understood. This analysis of the involvement of lymphocytes in food allergy will begin with comments on presentation of antigens in Peyer's patches, followed by comments on a recognition mechanism involving surface receptors and regulation by chemokines. In association with intestinal immunity, regulatory T cells have a central role in the induction of immunization or tolerance to foods.     

Caractéristiques non allergéniques des allergènes

Allergens are capable of inducing specific IgE production and are recognized by IgE-receptor bearing cells, more particularly mast cells and basophils expressing Fc?RI, the high affinity IgE receptor. However, they are also capable of directly stimulating certain cells of the bronchial mucosa, especially in a protease-dependent way. For example, many allergens such as those from house dust mites (Dermatophagoides pteronyssinus et Dermatophagoides farinae) have protease activity which is involved in the activation of bronchial epithelial cells, dendritic cells, T lymphocytes, B cells, eosinophils and airway smooth muscle cells. Overall, these activations amplify Th2 polarization, recruitment and activation of inflammatory cells, and airway smooth muscle cell contraction. Receptors such as the protease-activated receptor (PAR) have been involved in these functions. PAR-2, which has a role in protease-dependent activation by many allergens, is over-expressed in bronchial biopsies from asthmatic patients. Both phenomena may be involved in the development and amplification of allergic asthma.     

Allergènes recombinants et immunothérapie

The development of new immunotherapy techniques using products produced by molecular biology requires that their efficacy be controlled by appropriate clinical trials. An outline of the principal molecules derived through fundamental research during the past few years will include recombinant allergens corresponding to natural allergens that are pertinent because of their high prevalence of sensitivity, hypoallergenic derivatives of recombinant allergens (polymers, fragments, molecules with mutations or amino acid deletions), hybrid molecules, T-cell epitopes, B-cell epitopes, and molecules conjugated with CpG or other co-stimulants. The biological activity of a large number of these molecules has been demonstrated in vivo. The selection of candidate molecules for immunotherapy will depend first of all on the results of preliminary open studies on a limited number of patients. Here, we report the results of five double blind immunotherapy studies, in which the control group received placebo, and in two studies another group was treated with natural extract. The most statistically significant clinical results were observed with unmodified recombinant allergens, without occurrence of severe systemic reactions. In these five studies, there was a significant increase in the level of specific IgG with the natural allergen and with the recombinant allergens. Decrease in skin test responses in the treated groups relative to the placebo group was significant in two of the three studies. Studies including a greater number of patients are now needed to meet the demands of regulatory requirements for clinical development of recombinant allergens.     

皮下注射变应原特异性免疫治疗作用机制

变应原特异性免疫治疗(allergen-specific immunotherapy,ASIT)是给予IgE介导的变态反应性疾病患者逐渐增加剂量的变应原产物以改善其所导致的临床症状的治疗方法。ASIT的主要机制是通过改变辅助性T细胞和调节性T细胞的平衡以诱导外周T细胞耐受,从而减少变应原特异性效应T细胞产生的炎性细胞因子,增加抑制性细胞因子产生,使B细胞分泌的抗体IgE同型转化为IgG4。本文旨在就目前所知的ASIT作用机制进行阐述。     

Immunité innée et allergie : les cellules dendritiques

The innate immune system provides a quick response to infection, notably by using sensor receptors such as Toll-like receptors (TLR), but it also informs and directs the adaptive immune response through dendritic cells (DC). In the allergic reaction, DC play a fundamental role by transporting allergen to lymph nodes and by inducing allergen-specific T cell responses. The polarized Th2 response induced in allergic patients by DC can be modified by the participation of certain TLR, thereby inhibiting the development of the allergic reaction. Therapeutic approaches using allergens combined with TLR ligands are being evaluated to increase the efficacy of specific immunotherapy.     

Adjuvants et formulations de l’immunothérapie spécifique par voie sublinguale

Sublingual immunotherapy (SLIT) is a non-invasive and efficacious treatment for type I respiratory allergies. To identify candidate adjuvants and galenic formulations capable of inducing tolerance by the sublingual route, an initial screening was carried out using in vitro cocultures of human monocyte-derived dendritic cells and naïve CD4⁺ T cells. Selected molecules were subsequently tested in a murine asthma model of sublingual immunotherapy in BALB/c mice sensitized to ovalbumin. In this model, we evaluated bronchial hyperreactivity (measured by whole-body plethysmography), pulmonary inflammation (evaluated histologically), and type 2 humoral and cellular immune responses monitored by Elisa and Elispot techniques in mice sensitized with either soluble or with adjuvant-formulated ovalbumin. Four categories of adjuvant known to increase IL-10 +/− IFNγ production by naïve CD4⁺ T cells (Treg/Th1) were found to enhance SLIT efficacy in vivo in these mice. These adjuvants were: vitamin D3/dexamethasone, Lactobacillus plantarum, the TLR2 agonist Pam3CSK4, and the TLR4 synthetic ligand OM-294-BA-MP. In addition, sublingual administration of ovalbumin combined with mucoadhesive maize-derived maltodextrin increased sublingual tolerance induction by targeting oral dendritic cells and ovalbumin-specific T cells in cervical and submaxillary lymph nodes. In conclusion, better understanding of specific immune responses to allergen at the level of the sublingual mucosa may lead to the development of new sublingual vaccines. In the future, such vaccines would incorporate Th1/Treg adjuvants, as well as mucoadhesive galenic formulations that target dendritic cells in the sublingual mucosa.     

Lymphocytes T régulateurs et maladies auto-immunes systémiques : lupus érythémateux systémique,polyarthrite rhumatoïde et syndrome de Gougerot-Sjögren primaire

Regulatory/suppressor T cells (Tregs) maintain immunologic homeostasis and prevent autoimmunity. They are the guardians of dominant tolerance. Recent research reveals quantitative and/or functional defect of Tregs in systemic autoimmune diseases. In this article, past and recent studies of Tregs in human systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and primary Sjögren's syndrome (pGSS) are reviewed. Most studies report that Tregs are decreased in peripheral blood of subjects with active SLE. A population of CD4+CD25−Foxp3+ is specifically described in SLE. Tregs functions are still discussed. Tregs counts in peripheral blood of RA patients vary across studies. Enrichment of synovial fluid in Tregs contrasts with inflammation. Tregs suppressive effects are altered in vivo in RA secondary to proinflammatory cytokines environment and resistance of effector T cells to Tregs. In pGSS, the conflicting place of Tregs in the balance prevention of autoimmunity/antitumor immunity is unspecified. Immunosuppressive treatments, like corticosteroids and anti-TNF, modulate Tregs cells population. There is increasing interest in the use of Tregs as a biological therapy to preserve and restore tolerance to self-antigen. However, difficulties to characterize these lymphocytes and controversies in the results of studies refrain their use in current clinical practice.     

调节性T细胞与过敏性支气管哮喘

这篇综述主要围绕调节性T细胞(regulatory T cells,Treg)在过敏性支气管哮喘(简称哮喘)免疫发病机制中所承担的角色以及以其为靶点的过敏性哮喘的免疫治疗.研究者认为Treg是机体免疫反应程序中关键的调节因素,它能够通过各种机制诱导机体对自身抗原和过敏原产生免疫耐受,从而维持机体免疫系统的稳定.近年来,随着对Treg的研究不断深入,越来越多类型的Treg得以区分.研究发现其中主要是CD4+Treg抑制机体对过敏原的免疫反应,而控制过敏性疾病(过敏性哮喘)的发生和发展.因此,这有力的证实了恢复和诱导过敏性哮喘患者体内Treg的功能是一种有效的潜在的治疗方法.     

Donor-specific transplantation tolerance: the paradoxical behavior of CD4+CD25+ T cells

To investigate the antigen specificity of regulatory T cells capable of preventing transplant rejection, we have developed two different strategies to achieve tolerance to fully mismatched skin grafts in euthymic mice. A combination of nondepleting Abs targeting CD4, CD8, and CD154 (CD40 ligand) induces dominant transplantation tolerance to fully mismatched skin allografts. Such tolerance is antigen-specific, mediated by regulatory T cells, and can be extended through linked suppression to na?ve lymphocytes. The same protocol, when combined with allogeneic bone marrow, enables the development of mixed hematopoietic chimerism and deletional tolerance. Although we cannot exclude that some regulatory T cells may persist in chimeric mice, these cells are insufficient to mediate linked suppression. CD4(+)CD25(+) T cells, whether taken from na?ve mice or from mice tolerized through either treatment protocol, were always able to prevent rejection of skin grafts by na?ve CD4(+) T cells, and did so with no demonstrable specificity for the tolerizing donor antigens. Such data question whether CD4(+)CD25(+) regulatory T cells alone can account for the antigen specificity of dominant transplantation tolerance.     

超表达Serrate1树突细胞对支气管哮喘小鼠CD4+CD25+T细胞分化的作用

2组小鼠肺组织的病理学改变.结果 与对照组相比,Serrate1组可使哮喘小鼠脾脏CD4+CD25+T细胞数量明显增多,占CD4+T细胞的百分数亦明显增高;Serrate1组CDZT细胞IL-10、CTLA-4、TGFβ1 mRNA表达明显增强,且气道炎症明显减轻.结论 超表达Serrate1 DC能抑制哮喘小鼠CD4+T细胞分化和促进CD4+T细胞分泌抑制性细胞因子,有效改善哮喘小鼠气道炎症,表明DC可通过Notchl/Serrate 1信号通路影响调节性T细胞分化、逆转哮喘免疫耐受缺陷.     

Les allergènes recombinants : leur apport à l’allergologie en 2006

Advances in molecular biology techniques have led to the production of recombinant allergens, about thirty of them now being available for measurements (DIAGNOSIS?) in vitro. These recombinant allergens correspond to a precise molecular variant of a natural allergen, and their biological activity has to be evaluated in comparison with the corresponding natural allergen. The advantages of recombinant allergens are essentially the creation of allergenic preparations having constant pharmaceutic properties, which allows determination of specific IgE directed against different molecular components of an allergenic source, for example, pollen, mites, etc. The main consequences of these biological advances are the following: evaluation of sensitivities to allergen molecules in different populations (molecular epidemiology), improvement of extracts used for diagnosis by selection of the most pertinent allergenic sources and in quantifying their major allergen content, definition of the spectrum of recognition of specific IgE vis-à-vis different molecular components (spectrotype), quantitative evaluation of IgE responses, establishing the molecular basis of cross-reactions between different inhaled allergens, between different food allergens, and between inhaled allergens and food allergens. As regards allergy practice, this new diagnostic tool can lead to better interpretation of polysensitivities, observed by skin tests and in vitro tests. Some examples of particular clinical cases associated with specific sensitivities vis-à-vis certain recombinant allergens will be presented.     

Dual function of CTLA-4 in regulatory T cells and conventional T cells to prevent multiorgan autoimmunity

Cytotoxic T lymphocyte antigen-4 (CTLA-4) is an inhibitory receptor on T cells essential for maintaining T cell homeostasis and tolerance to self. Mice lacking CTLA-4 develop an early onset, fatal breakdown in T cell tolerance. Whether this autoimmune disease occurs because of the loss of CTLA-4 function in regulatory T cells, conventional T cells, or both is unclear. We show here that lack of CTLA-4 in regulatory T cells leads to aberrant activation and expansion of conventional T cells. However, CTLA-4 expression in conventional T cells prevents aberrantly activated T cells from infiltrating and fatally damaging nonlymphoid tissues. These results demonstrate that CTLA-4 has a dual function in maintaining T cell tolerance: CTLA-4 in regulatory T cells inhibits inappropriate naïve T cell activation and CTLA-4 in conventional T cells prevents the harmful accumulation of self-reactive pathogenic T cells in vital organs.     

Donor-lymphocyte infusion induces transplantation tolerance by activating systemic and graft-infiltrating double-negative regulatory T cells

Donor-lymphocyte infusion (DLI) before transplantation can lead to specific tolerance to allografts in mice, nonhuman primates, and humans. We and others have demonstrated a role for regulatory T cells in DLI-induced, donor-specific transplantation tolerance, but it is not known how regulatory T cells are activated and where they execute their function. In this study, we observed, in both transgenic and normal mice, that DLI before transplantation is required for activation of alphabeta-T-cell-receptor-positive, CD3(+)CD4(-)CD8(-) double-negative (DN) regulatory T cells in the periphery of recipient mice. More interestingly, DLI induced DN regulatory T cells to migrate preferentially to donor-specific allogeneic skin grafts and to form a majority of graft-infiltrating T cells in accepted skin allografts. Furthermore, both recipient-derived peripheral and graft-infiltrating DN T cells were able to suppress and kill antidonor CD8(+) T cells in an antigen-specific manner. These data indicate that DLI may induce donor-specific transplantation tolerance by activating recipient DN regulatory T cells in the periphery and by promoting migration of regulatory T cells to donor-specific allogeneic skin grafts. Our results also show that DN regulatory T cells can eliminate antidonor T cells both systemically and locally, a finding suggesting that graft-infiltrating T cells can be beneficial to graft survival.