Mechanisms of allergen-specific immunotherapy

Allergen-specific immunotherapy has been used for 100 years as a desensitizing therapy for allergic diseases and represents the potentially curative and specific method of treatment. The mechanisms of action of allergen-specific immunotherapy include the very early desensitization effects, modulation of T-and B-cell responses and related antibody isotypes, and migration of eosinophils, basophils, and mast cells to tissues, as well as release of their mediators. Regulatory T (Treg) cells have been identified as key regulators of immunologic processes in peripheral tolerance to allergens. Skewing of allergen-specific effector T cells to a regulatory phenotype appears as a key event in the development of healthy immune response to allergens and successful outcome in patients undergoing allergen-specific immunotherapy. Naturally occurring forkhead box protein 3-positive CD4(+)CD25(+) Treg cells and inducible 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; and suppression of effector T-cell migration to tissues. New strategies for immune intervention will likely include targeting of the molecular mechanisms of allergen tolerance and reciprocal regulation of effector and Treg cell subsets.     

Induction of IL-10-producing type 2 innate lymphoid cells by allergen immunotherapy is associated with clinical response

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Flt3-ligand plasmid prevents the development of pathophysiological features of chronic asthma in a mouse model

Airway inflammation and remodeling are primary characteristics of long-standing asthma. A balance between the T_H1/T_H2 cytokines regulates the accumulation and activation of inflammatory cells, including mast cells and eosinophils. Recently, we demonstrated that pUMVC3-hFLex, an active plasmid, mammalian expression vector for the secretion of Flt3-L, reversed established airway hyperresponsiveness (AHR) in a murine model of acute allergic airway inflammation. The present experiments were undertaken to examine the effect of pUMVC3-hFLex in a chronic model of allergic airway inflammation that was established in Balb/c mice by sensitization and challenge with ovalbumin (OVA). pUMVC3-hFLex or the control plasmid, pUMVC3, were administered by injection into the muscle interior tibialis. Treatment with pUMVC3-hFLex completely reversed established AHR (p<0.05), and this effect continued even after several exposures to the allergen (p<0.05). pUMVC3-hFLex treatment prevented the development of goblet cell hyperplasia and subepithelial fibrosis, and significantly reduced serum levels of IL-4 and IL-5, and increased serum IL-10 levels (p<0.05) with no effect on serum IL-13. Serum IgE or serum total and anti-OVA IgG1 and IgG2a levels did not change. Total BALF cellularity and BALF IL-5 levels were reduced (p<0.05), but there was no significant effect on BALF IL-10 and IL-13. These results suggest that pUMVC3-hFLex treatment can prevent the development of airway remodeling and maintain airway protection in chronic experimental asthma model, and might provide a novel approach for treating chronic asthma.     

Current immunological approaches for management of allergic rhinitis and bronchial asthma

A large population world over is affected with allergic diseases and asthma. Pharmacotherapy for allergic diseases and asthma is effective in controlling symptoms but on discontinuation of medication, symptoms reoccur. In contrast, immunotherapy modifies and corrects the underlying pathological immune responses in an antigen-specific manner. Immunotherapy shows an increase in IgG (blocking antibody) that competes with IgE for allergen, inhibiting the release of inflammatory mediators. Recent studies suggest that immunotherapy acts by modifying CD4+ T-cell responses either by immune deviation, T-cell anergy and/or both. Current immunological approaches for management of allergies and asthma involve immunization with native allergen, modified allergen, peptides/cDNA of allergen, anti-IgE, adjuvants coupled allergen, including immunostimulatory DNA sequences, cytokines, and bacterial products. These approaches modulate the immune response and are intended to give long-term benefit.     

TH17 and TH22 cells: a confusion of antimicrobial response with tissue inflammation versus protection

Substantial progress in understanding mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumors, organ transplantation, chronic infections, and pregnancy is in an exciting developmental phase that might lead to a variety of targeted therapeutic approaches. Recent progress in the interaction between immune/inflammatory cell subsets through cytokines, particularly the extension of the knowledge on reciprocal regulation and counterbalance between subsets of T(H)1, T(H)2, T(H)9, T(H)17, T(H)22, T follicular helper cells and different subsets of regulatory T cells, as well as corresponding and co-orchestrating B-cell, natural killer cell, dendritic cell, and innate lymphoid cell subsets, offers new possibilities for immune intervention. Studies on new subsets confirm the important role of T cells in the instruction of tissue cells and also demonstrate the important role of feedback regulation for the polarization toward distinct T-cell subsets. T(H)17 and T(H)22 cells are 2 emerging T(H) cell subsets that link the immune response to tissue inflammation; IL-17A and IL-17F and IL-22 are their respective prototype cytokines. Although both cytokines play roles in immune defense to extracellular bacteria, IL-17 augments inflammation, whereas IL-22 plays a tissue-protective role. This review focuses on current knowledge on T(H)17 and T(H)22 cells and their role in inflammation, with special focus on the mechanisms of their generation and driving and effector cytokines, as well as their role in host defense, autoimmunity, and allergic diseases.     

Anti-T-cell Ig and mucin domain-containing protein 1 antibody decreases TH2 airway inflammation in a mouse model of asthma

BACKGROUND: The T-cell Ig and mucin domain-containing (TIM) gene locus has been linked to differences in T(H)2 responsiveness and asthma susceptibility in mice. The homologous locus in human subjects harbors the gene for TIM-1, which encodes a receptor for hepatitis A virus and has been linked with decreased susceptibility to atopic disease in hepatitis A virus-seropositive individuals. OBJECTIVE: We investigated the effects of administering antibodies against TIM-1 in a mouse model of allergic asthma to determine whether the treatment could downregulate T(H)2 cytokines and reduce pulmonary inflammation. METHODS: BALB/c mice were sensitized and challenged with ovalbumin to induce airway inflammation. Before the ovalbumin challenge, mice were treated with anti-TIM-1 mAb or a control antibody. RESULTS: Administration of anti-TIM-1 antibody to mice after ovalbumin sensitization and before ovalbumin challenge results in a significant decrease in inflammatory cells in bronchoalveolar lavage fluid compared with administration of a control antibody. The decrease is accompanied by significantly lower antigen-specific production of the T(H)2 cytokines IL-10 and IL-13 by cells from the draining lymph nodes. The T(H)1 cytokine IFN-gamma appears to be unaffected. Analysis of the lungs shows that goblet cell hyperplasia and mucus production and the expression of IL-10 are markedly decreased in anti-TIM-1-treated mice. CONCLUSION: The results indicate that anti-TIM-1 might offer a novel approach to treating asthma.     

Oligoclonal Expansion of CD45RO+ T Lymphocytes in Omenn Syndrome

Omenn syndrome comprises a rare form of combined immunodeficiency with T_H2-type features of eosinophilia and elevated IgE. Previous studies have led to reports of restricted heterogeneity in the T lymphocyte repertoire, and in vitro cloned T lymphocytes have been shown to produce IL-4 and IL-5. We hypothesized that (1) T cell receptor V(D)J DNA sequence analysis would confirm and further define the putative restricted heterogeneity, and (2) increased production of IL-4 and IL-5 should be found in nonstimulated T lymphocytes, if the molecular pathogenesis of Omenn syndrome is an uncontrolled T_H2 state. We report the results of molecular analyses of T lymphocytes from an untreated 3-month-old patient. Oligoclonal T cell receptor variable gene usage was found. Sequence analysis revealed sets of identical V(D)J sequences, each in-frame, with apparently normal N-diversification and no obvious antigen combining site motif. From fresh, nonstimulated lymphocytes, proinflammatory T_H1 cytokines could be detected, but T_H2 cytokines could not, so that a simple T_H1/T_H2 paradigm cannot explain the eosinophilia and elevated IgE in Omenn syndrome. Our studies fully document for the first time at the molecular level that clonally expanded populations of T lymphocytes are present in Omenn syndrome.     

Suppression of serum IgE response and systemic anaphylaxis in a food allergy model by orally administered high-dose TGF-beta

Some epidemiological or association studies suggest that transforming growth factor-beta (TGF-beta) in breast milk may be a decisive factor in diminishing the risk of allergic diseases during infancy. The observations have prompted us to investigate whether TGF-beta, when taken orally, can affect allergic immune responses. Repeated high-dose ovalbumin peptide (OVA) feeding was previously reported to induce OVA-specific IgE production and an anaphylactic reaction after intravenous challenge of OVA in OVA-TCR transgenic mice, which might represent a model for food allergy. By using this model, we showed here that oral administration of high-dose TGF-beta simultaneously with OVA feeding significantly inhibited the OVA-specific IgE elevation and anaphylactic reaction in OVA-TCR transgenic DO11.10 mice. These effects were associated with suppression of OVA-specific IL-4 production and GATA-3 expression and with up-regulation of IFN-gamma production and T-bet expression by splenocytes. Intra-peritoneal injection of anti-TGF-beta-neutralizing antibody abolished the inhibitory effects of orally administered TGF-beta on the serum IgE response and anaphylactic reaction after OVA feeding in DO11.10 mice. Interestingly, oral administration of high-dose TGF-beta suppressed activation-induced T cell death induced by OVA feeding in DO11.10 mice. We thus conclude that TGF-beta, when taken orally at high dose, has the capacity to modulate a food allergy-related reaction, at least in part, through its systemic activity.     

Targeting IL-17 in psoriasis: From cutaneous immunobiology to clinical application

Psoriasis vulgaris is a chronic, immune-mediated inflammatory skin disease associated with complex genetic susceptibility. Although the hallmark of psoriasis is characterized by cutaneous inflammation and keratinocyte hyperproliferation, recent studies show that the pathologic features observed in psoriasis arises as a result of innate and adaptive immune activation in genetically prone individuals. Studies focused on the microenvironment in the skin of psoriasis lesions have revealed novel cellular and cytokine abnormalities of the immune system. One pathway important is the role of the T_H17/IL-17 dysregulation. The recent development of biologics that target the IL-17 cytokine pathway has confirmed the importance of T_H17 and IL-17 homeostasis in the skin and yielded potent therapies in the treatment of psoriasis, and potentially other autoimmune diseases.     

IL-10 and TGF-beta 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 cell and Th1 (IFN-gamma) and Th2 (IL-5, IL-13) cytokine responses, and increased IL-10 and TGF-beta secretion by allergen-specific T cells. Neutralization of cytokine activity showed that T cell suppression was induced by IL-10 and TGF-beta 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.     

IL-15 prevents allergic rhinitis through reactivation of antigen-specific CD8+ cells

BACKGROUND: Allergic rhinitis is one of the most common allergic inflammatory diseases characterized by a predominant TH2 response with antigen-specific IgE synthesis. IL-15 plays important roles in activation and maintenance of memory CD8+T cells capable of producing IFN-gamma, which regulates TH2 responses. OBJECTIVE: To investigate the roles of endogenous IL-15 in allergic inflammation, we examined allergic rhinitis in IL-15 knockout (KO) mice sensitized with ovalbumin followed by intranasal rechallenge with ovalbumin. METHODS: IL-15KO mice were sensitized intraperitoneally with ovalbumin/complete Freund's adjuvant on day 0 and ovalbumin/IFA on day 7, and then were intranasally challenged with ovalbumin on days 21, 22, 23, 24, and 25. Nasal symptoms and histologic changes were examined. IgE production and TH2 responses were measured by ELISA. Purified CD8+T cells or recombinant IL-15 were administered into ovalbumin-sensitized mice. RESULTS: The levels of IgE production and TH2 responses in IL-15KO mice were comparable to those in control mice after ovalbumin sensitization. However, sneezing, infiltration of eosinophils into the nasal mucosa, and TH2 cytokine production were aggravated in ovalbumin-sensitized IL-15KO mice after intranasal challenge with ovalbumin. Adoptive transfer of CD8+6 T cells from ovalbumin-sensitized mice suppressed the TH2 responses in mice but not in IL-15KO mice. Administration of IL-15 with ovalbumin significantly prevented the development of allergic rhinitis in ovalbumin-sensitized mice. CONCLUSION: We demonstrate with IL-15KO mice that endogenous IL-15 plays an important role in suppression of allergic rhinitis at effector phase. Intranasal administration of IL-15 is useful as a therapeutic approach to control allergic rhinitis. CLINICAL IMPLICATIONS: Intranasal administration of recombinant IL-15 might become new immunotherapy for allergic rhinitis.