Histamine enhances TGF-beta1-mediated suppression of Th2 responses

H2 antihistamines: May be useful for combination therapies in cancer?

Cancer morbimortality is still a great concern despite advances in research and therapies. Histamine and its receptors' ligands can modulate different biological responses according to the cell type and the receptor subtype involved. Besides the wide variety of histamine functions in normal tissues, diverse roles in the acquisition of hallmarks of cancer such as sustained proliferative signaling, resistance to cell death, angiogenesis, metastasis, altered immunity and modified microenvironment have been described. This review summarizes the present knowledge of the various roles of histamine H2 receptor (H2R) ligands in neoplasias. A bioinformatic analysis of human tumors showed dissimilar results in the expression of the H2R gene according to tumor type when comparing malignant versus normal tissues. As well, the relationship between patients' survival parameters and H2R gene expression levels also varied, signaling important divergences in the role of H2R in neoplastic progression in different cancer types. Revised experimental evidence showed multiple effects of H2R antihistamines on several of the cited hallmarks of cancer. Interventional and retrospective clinical studies evaluated different H2R antihistamines in cancer patients with two main adjuvant uses: improving antitumor efficacy (which includes regulation of immune response) and preventing toxic adverse effects produced by chemo or radiotherapy. While there is a long path to go, research on H2R antihistamines may provide new opportunities for developing more refined combination therapeutic strategies for certain cancer types to improve patients' survival and health-related quality of life.

The mRNA expression and secretion of granzyme B are up-regulated via the histamine H2 receptor in human CD4+ T cells

INTRODUCTION

Granzyme B (GZMB), a serine protease with cytotoxic and immunomodulatory functions, shows elevated levels in blood plasma of patients with atopic dermatitis (AD). It has been observed that GZMB expression in CD4+ and CD8+ T cells is higher in lesional skin in AD than in healthy skin. Since histamine is present in high concentration in the skin of AD patients, we investigated the regulation of GZMB in human CD4+ T cells by histamine.

METHODS

Naïve CD4+ T cells polarized into Th2 cells, total CD4+ T cells treated with IL-4 for 72 h and CD4+ T cells isolated from healthy donors and AD patients were investigated. The cells were stimulated with histamine or with different histamine-receptor agonists. Gene expression was evaluated by RNA-Seq. GZMB mRNA expression was detected by quantitative real time PCR, whereas GZMB secretion was measured by ELISpot and ELISA. T cell degranulation was evaluated by flow cytometry using CD107a surface expression as a degranulation marker.

RESULTS

By RNA-Seq, we identified the up-regulation of various genes of the cytotoxic pathway, in particular of GZMB, by histamine in Th2-polarized CD4+ T cells. In Th2-polarized CD4+ T cells and in CD4+ T cells activated by IL-4 the mRNA expression of GZMB was significantly up-regulated by histamine and by histamine H2 receptor (H2R) agonists. The induction of GZMB secretion by histamine was significantly higher in CD4+ T cells from AD patients than in those from healthy donors. CD107a surface expression was up-regulated by trend in response to histamine in Th2-polarized CD4+ T cells.

CONCLUSION

Our findings may help to elucidate novel mechanisms of the H2R and to achieve a better understanding of the role of GZMB in the pathogenesis of AD.

SARA suppresses myofibroblast precursor transdifferentiation in fibrogenesis in a mouse model of scleroderma

We previously reported that Smad anchor for receptor activation (SARA) plays a critical role in maintaining epithelial cell phenotype. Here, we show that SARA suppressed myofibroblast precursor transdifferentiation in a mouse model of scleroderma. Mice overexpressing SARA specifically in PDGFR-β+ pericytes and pan-leukocytes (SARATg) developed significantly less skin fibrosis in response to bleomycin injection compared with wild-type littermates (SARAWT). Single-cell RNA-Seq analysis of skin PDGFR-β+ cells implicated pericyte subsets assuming myofibroblast characteristics under fibrotic stimuli, and SARA overexpression blocked the transition. In addition, a cluster that expresses molecules associated with Th2 cells and macrophage activation was enriched in SARAWT mice, but not in SARATg mice, after bleomycin treatment. Th2-specific Il-31 expression was increased in skin of the bleomycin-treated SARAWT mice and patients with scleroderma (or systemic sclerosis, SSc). Receptor-ligand analyses indicated that lymphocytes mediated pericyte transdifferentiation in SARAWT mice, while with SARA overexpression the myofibroblast activity of pericytes was suppressed. Together, these data suggest a potentially novel crosstalk between myofibroblast precursors and immune cells in the pathogenesis of SSc, in which SARA plays a critical role.

Agomelatine Changed the Expression and Methylation Status of Inflammatory Genes in Blood and Brain Structures of Male Wistar Rats after Chronic Mild Stress Procedure

The preclinical research conducted so far suggest that depression development may be influenced by the inflammatory pathways both at the periphery and within the central nervous system. Furthermore, inflammation is considered to be strongly connected with antidepressant treatment resistance. Thus, this study explores whether the chronic mild stress (CMS) procedure and agomelatine treatment induce changes in TGFA, TGFB, IRF1, PTGS2 and IKBKB expression and methylation status in peripheral blood mononuclear cells (PBMCs) and in the brain structures of rats. Adult male Wistar rats were subjected to the CMS and further divided into matched subgroups to receive vehicle or agomelatine. TaqMan gene expression assay and methylation-sensitive high-resolution melting (MS-HRM) were used to evaluate the expression of the genes and the methylation status of their promoters, respectively. Our findings confirm that both CMS and antidepressant agomelatine treatment influenced the expression level and methylation status of the promoter region of investigated genes in PBMCs and the brain. What is more, the present study showed that response to either stress stimuli or agomelatine differed between brain structures. Concluding, our results indicate that TGFA, TGFB, PTGS2, IRF1 and IKBKB could be associated with depression and its treatment.

Chronic Mild Stress and Venlafaxine Treatment Were Associated with Altered Expression Level and Methylation Status of New Candidate Inflammatory Genes in PBMCs and Brain Structures of Wistar Rats

Preclinical studies conducted to date suggest that depression could be elicited by the elevated expression of proinflammatory molecules: these play a key role in the mediation of neurochemical, neuroendocrine and behavioral changes. Thus, this study investigates the effect of chronic mild stress (CMS) and administration of venlafaxine (SSRI) on the expression and methylation status of new target inflammatory genes: TGFA, TGFB, IRF1, PTGS2 and IKBKB, in peripheral blood mononuclear cells (PMBCs) and in selected brain structures of rats. Adult male Wistar rats were subjected to the CMS and further divided into matched subgroups to receive vehicle or venlafaxine. TaqMan gene expression assay and methylation-sensitive high-resolution melting (MS-HRM) were used to evaluate the expression of the genes and the methylation status of their promoters, respectively. Our results indicate that both CMS and chronic treatment with venlafaxine were associated with changes in expression of the studied genes and their promoter methylation status in PMBCs and the brain. Moreover, the effect of antidepressant administration clearly differed between brain structures. Summarizing, our results confirm at least a partial association between TGFA, TGFB, IRF1, PTGS2 and IKBKB and depressive disorders.

Histamine receptors and COVID-19

OBJECTIVE

Reports that the over-the-counter histamine H2 receptor antagonist famotidine could help treat the novel coronavirus disease (COVID-19) appeared from April 2020. We, therefore, examined reports on interactions between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and histamine receptor antagonists.

METHODS

A systematic literature search was performed by 19 September 2020, and updated on 28 October 2020, in PubMed, Scopus, Cochrane Library and Google Scholar using (COVID-19 OR coronavirus OR SARS-CoV-2) AND (histamine antagonist OR famotidine OR cimetidine). ClinicalTrials.gov was searched for COVID-19 and (famotidine or histamine).

RESULTS

Famotidine may be a useful addition in COVID-19 treatment, but the results from prospective randomized trials are as yet awaited. Bioinformatics/drug repurposing studies indicated that, among several medicines, H1 and H2 receptor antagonists may interact with key viral enzymes. However, in vitro studies have to date failed to show a direct inhibition of famotidine on SARS-CoV-2 replication.

CONCLUSIONS

Clinical research into the potential benefits of H2 receptor antagonists in managing COVID-19 inflammation began from a simple observation and now is being tested in multi-centre clinical trials. The positive effects of famotidine may be due to H2 receptor-mediated immunomodulatory actions on mast cell histamine-cytokine cross-talk, rather than a direct action on SARS-CoV-2.

Tolerance mechanisms in allergen immunotherapy

PURPOSE OF REVIEW

Allergen immunotherapy is the only treatment modality which alters the natural course of allergic diseases by restoring immune tolerance against allergens. Deeper understanding of tolerance mechanisms will lead to the development of new vaccines, which target immune responses and promote tolerance.

RECENT FINDINGS

Successful allergen immunotherapy (AIT) induces allergen-specific peripheral tolerance, characterized mainly by the generation of allergen-specific Treg cells and reduction of Th2 cells. At the early phase, AIT leads to a decrease in the activity and degranulation of mast cells and basophils and a decrease in inflammatory responses of eosinophils in inflamed tissues. Treg cells show their effects by secreting inhibitory cytokines including interleukin (IL)-10, transforming growth factor-β, interfering with cellular metabolisms, suppressing antigen presenting cells and innate lymphoid cells (ILCs) and by cytolysis. AIT induces the development of regulatory B cells producing IL-10 and B cells expressing allergen-specific IgG4. Recent investigations have demonstrated that AIT is also associated with the formation of ILC2reg and DCreg cells which contribute to tolerance induction.

SUMMARY

Research done so far, has shown that multiple molecular and cellular factors are dysregulated in allergic diseases and modified by AIT. Studies should now focus on finding the best target and ideal biomarkers to identify ideal candidates for AIT.

Novel association between TGFA, TGFB1, IRF1, PTGS2 and IKBKB single-nucleotide polymorphisms and occurrence, severity and treatment response of major depressive disorder

Background

Activation of the immune system might affect the severity of depressive episodes as well as response to the antidepressant treatment. The purpose of this study was to investigate whether the occurrence of variant alleles of analyzed SNPs are involved in prevalence and progression of depression. Moreover, selected genes and SNPs have not been investigated in context of the disease severity and treatment. Therefore, six polymorphisms were selected: g.41354391A>G-TGFB1 (rs1800469), g.132484229C>A-IRF (rs2070729), g.186643058A>G-PTGS2 (rs5275), g.186640617C>T-PTGS2 (rs4648308), g.70677994G>A-TGFA (rs2166975) and g.42140549G>T-IKBKB (rs5029748).

Methods

A total of 360 (180 patients and 180 controls) DNA samples were genotyped using TaqMan probes.

Results

We observed that A/G of the rs2166975 TGFA, A/C of rs2070729 IRF1 and G/T of rs5029748 IKBKB were associated with an increased risk of depression development while the T/T of rs5029748 IKBKB, T/T of rs4648308 PTGS2 and G/G of rs2166975 TGFA reduced this risk. We also stratified the study group according to gender and found that genotype A/G and allele G of the rs2166975 TGFA, G/T of rs5029748 IKBKB as well as C allele of rs4648308 PTGS2, homozygote A/A and allele A of rs5275 PTGS2 were associated with increased risk of depression development in men while homozygote G/G of rs5275 PTGS2 decreased this risk. Moreover, C/T of rs4648308 PTGS2 and A/G of rs5275 PTGS2 was positively correlated with the risk of the disease occurrence in women. Furthermore, a gene-gene analysis revealed a link between studied polymorphisms and depression. In addition, A/A of rs1800469 TGFB1 was associated with earlier age of onset of the disease while G/G of this SNP increased severity of the depressive episode. Interestingly, A/C of rs2070729 IRF1 and T/T of rs5029748 IKBKB may modulate the effectiveness of selective serotonin reuptake inhibitors therapy. In conclusion, studied SNPs may modulate the risk of occurrence, age of onset, severity of the disease and response to the antidepressant treatment.

Bacterial secretion of histamine within the gut influences immune responses within the lung

BACKGROUND

Histamine is an important immunomodulator influencing both the innate and adaptive immune system. Certain host cells express the histidine decarboxylase enzyme (HDC), which is responsible for catalysing the decarboxylation of histidine to histamine. We and others have shown that bacterial strains can also express HDC and secrete histamine; however, the influence of bacterial-derived histamine on the host immune responses distant to the gut is unclear.

METHODS

The Escherichia coli BL21 (E coli BL21) strain was genetically modified to express the Morganella morganii (M morganii)-derived HDC gene (E coli BL21_HTW). E coli BL21 and E coli BL21_HTW were gavaged to ovalbumin (OVA) sensitized and challenged mice to investigate the effect of bacterial-derived histamine on lung inflammatory responses.

RESULTS

Oral administration of E coli BL21_HTW, which is able to secrete histamine, to wild-type mice reduced lung eosinophilia and suppressed ex vivo OVA-stimulated cytokine secretion from lung cells in the OVA respiratory inflammation mouse model. In histamine receptor 2 (H2R)-deficient mice, administration of histamine-secreting bacteria also reduced inflammatory cell numbers in bronchoalveolar lavage (BAL). However, the suppressive effect of bacterial-derived histamine on BAL inflammation was lost in HDC-deficient mice. This loss of activity was associated with increased expression of histamine degrading enzymes and reduced histamine receptor expression.

CONCLUSION

Histamine secretion from bacteria within the gut can have immunological consequences at distant mucosal sites, such as within the lung. These effects are influenced by host histamine receptor expression and the expression of histamine degrading enzymes.

Immunomodulatory properties of cimetidine: Its therapeutic potentials for treatment of immune-related diseases

Histamine exerts potent modulatory impacts on the cells of innate- [including neutrophils, monocytes, macrophages, dendritic cells (DCs), natural killer (NK) cells and NKT cells] and adaptive immunity (such as Th1-, Th2-, Th17-, regulatory T-, CD8⁺ cytotoxic T cells, and B cells) through binding to histamine receptor 2 (H2R). Cimetidine, as an H2R antagonist, reverses the histamine-mediated immunosuppression, as it has powerful stimulatory effects on the effector functions of neutrophils, monocytes, macrophages, DCs, NK cells, NKT cells, Th1-, Th2-, Th17-, and CD8⁺ cytotoxic T cells. However, cimetidine reduces the regulatory/suppressor T cell-mediated immunosuppression. Experimentally, cimetidine potentiate some immunologic activities in vitro and in vivo. The therapeutic potentials of cimetidine as an immunomodulatory agent were also investigated in a number of human diseases (such as cancers, viral warts, allergic disorders, burn, and bone resorption) and vaccination. This review aimed to provide a concise summary regarding the impacts of cimetidine on the immune system and highlight the cellular mechanisms of action and the immunomodulatory effects of this drug in various diseases to give novel insights regarding the therapeutic potentials of this drug for treatment of immune-related disorders. The review encourages more investigations to consider the immunomodulatory characteristic of cimetidine for managing of immune-related disorders.

Expression and function of histamine and its receptors in atopic dermatitis

Background

Atopic dermatitis constitutes a most burdensome chronic inflammatory skin disease. Standard treatment is cumbersome and often targets its main symptom, pruritus, only insufficiently.

Findings

Recent advances in our understanding of the role of histamine and its four receptors suggest new approaches which target the histamine receptors alone or as combination therapies to more efficiently combat pruritus and inflammation in atopic dermatitis.

Conclusions

With this review, we provide an overview on histamine and the expression of its four receptors on skin resident and nonresident cells. Furthermore, we summarize recent studies which suggest anti-histamine therapy to efficiently combat pruritus and inflammation in atopic dermatitis and discuss possible approaches to incorporate these findings into more effective treatment strategies for atopic dermatitis in childhood.

Nerve-sparing abdominal radical trachelectomy: a novel concept to preserve uterine branches of pelvic nerves

OBJECTIVES

Nerve-sparing techniques to avoid bladder dysfunction in abdominal radical hysterectomy have been established during the past two decades, and they have been applied to radical trachelectomy. Although trachelectomy retains the uterine corpus, no report mentions the preservation of uterine branches of pelvic nerves. The aim of the present study was to introduce and discuss our unique concept for preserving them.

STUDY DESIGN AND RESULTS

Four cases with FIGO stage Ia2-Ib1 cervical cancer, in which preservation of uterine branches of the pelvic nerves was attempted, are presented. Operative procedures basically followed the previously reported standard approaches for nerve-sparing radical hysterectomy or trachelectomy, except for some points. Before resection of the sacrouterine ligament, the hypogastric nerve was first identified and translocated laterally. Subsequently, the uterine branches of the pelvic nerve were identified as a continuation of the hypogastric nerve and could be scooped with forceps by detachment of the surrounding connective tissues. Further detachment toward the uterine corpus enabled them to be completely separated from the cervix. This separation was extended up to the level of the junction of the upper and lower branches of the uterine artery. Thereafter, standard resection of the parametrium and paracolpium was performed, followed by cervical resection when it was confirmed that the isolated uterine branches of the pelvic nerves were safely translocated and preserved. There were no recurrences of cancer in these patients.

CONCLUSIONS

Uterine branches of autonomic nerves can be safely preserved, and the procedure may be considered one of the nerve-sparing techniques for radical abdominal trachelectomy, which may hopefully improve the reproductive outcomes of this operation, although it needs to be evaluated with more patients.

Immune regulation by intralymphatic immunotherapy with modular allergen translocation MAT vaccine

BACKGROUND

Allergen-specific immunotherapy (SIT) faces problems related to side effects and limited efficacy. Direct administration of allergen extracts into lymph nodes induces increased specific IgG production and T-cell responses using significantly lower allergen doses.

METHODS

In this study, mechanisms of immune regulation by MAT vaccines in vitro and in allergen-SIT of cat-allergic rhinitis patients, who received 3 inguinal intra-lymph node injections of MAT-Fel d 1 vaccine, were investigated in PBMC and cell cultures for specific T-cell proliferation, Fel d 1-tetramer-specific responses, and multiple immune regulatory molecules.

RESULTS

MAT-Fel d 1 vaccine was efficiently internalized by antigen-presenting cells. This was followed by precaspase 1 cleavage to caspase 1 and secretion of IL-1β, indicating inflammasome activation. Mat-Fel d 1 induced specific T-cell proliferation and an IL-10- and IFN-γ-dominated T-cell responses with decreased Th2 cytokines at 100 times lower doses than Fel d 1. Induction of immune tolerance by MAT-Fel d 1-ILIT involved multiple mechanisms of immune suppression. Early Fel d 1-specific T-cell activation was followed by full T-cell unresponsiveness to allergen after 1 year in the MAT-Fel d 1 group, characterized by increased allergen-specific T regulatory cells, decreased circulating Fel d 1 tetramer-positive cells, increased IL-10 and FOXP3 expression, and change in the HR2/HR1 ratio toward HR2.

CONCLUSIONS

This study demonstrates the induction of allergen tolerance after 3 intra-lymph node injections of MAT-Fel d 1 vaccine, mediated by increased cellular internalization of the allergen, activation of inflammasome, and generation of allergen-specific peripheral T-cell tolerance.

Mechanisms of allergen-specific immunotherapy: multiple suppressor factors at work in immune tolerance to allergens

Allergen-specific immunotherapy (AIT) has been used for more than 100 years as a desensitizing therapy for IgE-mediated allergic diseases and represents a potentially curative way of treatment. The mechanisms of action of AIT include the induction of very early desensitization of mast cells and basophils; generation of regulatory T and regulatory B (Breg) cell responses; regulation of IgE and IgG4; decreases in numbers and activity of eosinophils and mast cells in mucosal allergic tissues; and decreases in the activity of basophils in circulation. Skewing of allergen-specific effector T and effector B cells to a regulatory phenotype appears as a key event in the course of AIT and normal immune response to allergens. Recently, inducible IL-10-secreting Breg cells were also demonstrated to contribute to allergen tolerance through suppression of effector T cells and selective induction of IgG4 isotype antibodies. Allergen-specific regulatory T and Breg cells orchestrate a general immunoregulatory activity, which can be summarized as suppression of cytokines from inflammatory dendritic cells; suppression of effector TH1, TH2, and TH17 cells; suppression of allergen-specific IgE and induction of IgG4; and suppression of migration of mast cells, basophils, eosinophils, and effector T cells to tissues. A detailed knowledge of the mechanisms of AIT is not only important in designing the prevention and treatment of allergic diseases but might also find applications in the treatment of autoimmune diseases, organ transplantation, chronic infection, and cancer.

Activation of histamine H4 receptors decreases epithelial-to-mesenchymal transition progress by inhibiting transforming growth factor-β1 signalling pathway in non-small cell lung cancer

Previous investigations found that epithelial-to-mesenchymal transition (EMT) was an important character of non-small cell lung cancer (NSCLC) and it was also suggested that histamine H4 receptors may have a role in preventing EMT progress in certain kind of tumours. However, the effect of H4 receptor activation on EMT progress of NSCLC and its potential mechanisms remain unclear. Therefore, we performed both in vitro and in vivo experiments to explore the effects of specific H4 receptor agonist 4-methylhistamine and antagonist JNJ7777120 on EMT progress. We showed the expression of H4 receptors in NSCLC and found that 4-methylhistamine increased the expression of the epithelial marker E-cadherin and decreased the expression of Vimentin, the mesenchymal marker, in both NSCLC cell lines and xenograft NSCLC tumours. Pretreatment with JNJ7777120 or H4 receptor gene silencing decreased while overexpression of H4 receptors facilitated this effect of 4-methylhistamine. Furthermore, we showed that down-regulation of cyclic adenosine monophosphate (cAMP) was the secondary signalling after H4 receptor activation, which in turn resulted in inactivation of transforming growth factor-β1 (TGF-β1) pathway and down-regulation of several important EMT inducing factors such as ZEB1, Snail and Slug. In conclusion, these findings revealed the anti-EMT effect of histamine H4 receptor activation in NSCLC, which provide novel insight into the development mechanism of NSCLC; and H4 receptors may be a new therapeutic target for NSCLC treatment.

Histamine H₂ receptor signaling × environment interactions determine susceptibility to experimental allergic encephalomyelitis

Histamine and its receptors are important in both multiple sclerosis and experimental allergic encephalomyelitis (EAE). C57BL/6J (B6) mice deficient for the histamine H2 receptor (H2RKO) are less susceptible to EAE and exhibit blunted Th1 responses. However, whether decreased antigen-specific T-cell effector responses in H2RKO mice were due to a lack of H2R signaling in CD4(+) T cells or antigen-presenting cells has remained unclear. We generated transgenic mice expressing H2R specifically in T cells on the H2RKO background, and, using wild-type B6 and H2RKO mice as controls, induced EAE either in the presence or absence of the ancillary adjuvant pertussis toxin (PTX), which models the effects of infectious inflammatory stimuli on autoimmune disease. We monitored the mice for clinical signs of EAE and neuropathology, as well as effector T-cell responses using flow cytometry. EAE severity and neuropathology in H2RKO mice expressing H2R exclusively in T cells become equal to those in wild-type B6 mice only when PTX is used to elicit disease. EAE complementation was associated with frequencies of CD4(+)IFN-γ(+) and CD4(+)IL-17(+) cells that are equal to or greater than those in wild-type B6, respectively. Thus, the regulation of encephalitogenic T-cell responses and EAE susceptibility by H2R signaling in CD4(+) T cells is dependent on gene × environment interactions.

Targeted disruption of organic cation transporter 3 (Oct3) ameliorates ischemic brain damage through modulating histamine and regulatory T cells

The organic cation transporters OCT1, 2, and 3 (SLC22A1-3) have been implicated in the elimination of biogenic amines such as histamine. Among them, OCT3 was identified as an uptake-2 transporter, responsible for clearance of histamine. Because increasing evidence suggests the involvement of histamine in cerebral ischemia, we investigated the effects of targeted disruption of organic cation transporter-3 (Oct3) on the severity of ischemic brain damage. Transient focal ischemia for 1 hour was induced by occlusion of the middle cerebral artery (MCA) of homozygous Oct3-deficient mice and their wild-type (Wt) littermates. Although targeted disruption of Oct3 did not affect physiological parameters after MCA occlusion, this disruption significantly increased histamine content in the ischemic cortex and significantly reduced the infarct volume after cerebral ischemia. Furthermore, targeted disruption of Oct3 prevented the reduction of regulatory T-cell proportion after cerebral ischemia while this disruption did not affect Th1 and Th2 cells proportions after ischemia. Since repeated administration of L-histidine (a precursor of histamine) to Wt mice also showed the same effects, our observations suggested that OCT3 is the molecule responsible for clearance of ischemia-induced histamine in the brain and targeted disruption of Oct3 ameliorated ischemic brain damage through an increase in regulatory T cells.

Early suppression of basophil activation during allergen-specific immunotherapy by histamine receptor 2

BACKGROUND

Early desensitization of FcεRI-bearing mast cells and basophils has been demonstrated in allergen-specific immunotherapy and drug desensitization. However, its mechanisms have not been elucidated in detail. Histamine is one of the main mediators released on FcεRI triggering of basophils and mast cells, and it exerts its functions through histamine receptors (HRs).

OBJECTIVES

We sought to investigate HR expression on basophils of patients undergoing venom immunotherapy (VIT) and its effect on allergen, IgE, and FcεRI cross-linking-mediated basophil function and mediator release.

METHODS

Basophils were purified from the peripheral blood of patients undergoing VIT and control subjects and were studied functionally by using real-time PCR, flow cytometry and ELISA assays.

RESULTS

Rapid upregulation of H2R within the first 6 hours of the build-up phase of VIT was observed. H2R strongly suppressed FcεRI-induced activation and mediator release of basophils, including histamine and sulfidoleukotrienes, as well as cytokine production in vitro.

CONCLUSION

Immunosilencing of FcεRI-activated basophils by means of selective suppression mediated by H2R might be highly relevant for the very early induction of allergen tolerance and the so-called desensitization effect of VIT.

T lymphocytes as a target of histamine action

Histamine is one of the most important biogenic amines in medicine and biology but its role in allergy, autoimmune and neoplastic diseases has not yet been fully defined. The last few years have brought many discoveries concerning important modulatory effects of histamine and its receptors on basic mechanisms of the immunological processes. The role of histamine H1 and H2 receptors in immunomodulation has been established. The immunomodulatory function of a newly described histamine H4 receptor has been revealed. One of the most important modulatory effects of histamine currently studied is its influence on T lymphocyte differentiation and function. Our present knowledge suggests that histamine may have a wider influence on various immunological processes than is now accepted; therefore, we need further studies to fully clarify the role of histamine and its receptors. This knowledge can bring new therapeutic solutions in allergies, autoimmune diseases and malignancies.

Immunological approaches for tolerance induction in allergy

Allergy is the consequence of an inappropriate inflammatory immune response generated against harmless environmental antigens. In allergic disorders such as asthma and rhinitis, the Th2 mediated phenotype is a result of loss of peripheral tolerance mechanisms. In cases such as these, approaches such as immunotherapy attempt to treat the underlying cause of allergic disease by restoring tolerance. Immunotherapy initiates many complex mechanisms within the immune system that result in initiation of innate immunity, activation of both cellular and humoral B cell immunity, as well as triggering T regulatory subsets which are major players in the establishment of peripheral tolerance. Though studies clearly demonstrate immunotherapy to be efficacious, research to improve this treatment is ongoing. Investigation of allergenicity versus immunogenicity, native versus modified allergens, and the use of adjuvant and modality of dosing are all current strategies for immunotherapy advancement that will be reviewed in this article.

Elevated macrophage migration inhibitory factor and decreased transforming growth factor-beta levels in major depression--no influence of celecoxib treatment

OBJECTIVES

The involvement of an immune process in the pathophysiology of major depression disorder (MDD) was substantiated by studies demonstrating elevated levels of proinflammatory cytokines and prostaglandin E(2) (PGE(2)). Cyclooxygenase-2 (COX-2) inhibitors lead to a reduced production of PGE(2) and have been shown to improve depressive symptoms. We investigated the three immune parameters macrophage migration inhibitory factor (MIF), transforming growth factor-β (TGF-β) and soluble CD14 (sCD14) in a randomized, placebo-controlled trial of the COX-2 inhibitor celecoxib as add-on therapy in patients with MDD treated with reboxetine.

METHODS

Thirty-two patients with depression and 20 healthy controls participated in the study. The patients were treated with reboxetine and celecoxib or placebo. Immune parameters were measured from serum at baseline, after three and five weeks using ELISA.

RESULTS

Celecoxib as add-on strategy resulted in a significant reduction of Hamilton Depression Scale scores compared to placebo. Depressed patients showed significantly elevated MIF (p < 0.001) and reduced TGF-β (p = 0.006) concentrations at baseline. There was no difference in sCD14-concentrations. There was no difference between the placebo and the celecoxib group and no change over time.

LIMITATIONS

Limitations of the study are the relatively small sample size and lack of functional assessment of HPA axis in parallel.

CONCLUSIONS

MIF is a promising new candidate in the neuro-immune interplay that may link depressive symptoms, altered immune state and HPA-axis dysregulation. Reduced levels of TGF-β replicate previous findings and support the importance of this regulatory cytokine in major depressive disorder.

Regulation of the immune response and inflammation by histamine and histamine receptors

Histamine is a biogenic amine with extensive effects on many cell types, including important immunologic cells, such as antigen-presenting cells, natural killer cells, epithelial cells, and T and B lymphocytes. Histamine and its 4 receptors represent a complex system of immunoregulation with distinct effects dependent on receptor subtypes and their differential expression. These are influenced by the stage of cell differentiation, as well as microenvironmental influences, leading to the selective recruitment of effector cells into tissue sites accompanied by effects on cellular maturation, activation, polarization, and effector functions, which lead to tolerogenic or proinflammatory responses. In this review we discuss the regulation of histamine secretion, receptor expression, and differential activation of cells within both the innate and adaptive immune responses. It is clear that the effects of histamine on immune homeostasis are dependent on the expression and activity of the 4 currently known histamine receptors, and we also recognize that 100 years after the original identification of this biogenic amine, we still do not fully understand the complex regulatory interactions between histamine and the host immune response to everyday microbial and environmental challenges.

The role of histamine in asthma

Histamine is a ubiquitous inflammatory mediator intimately associated with the pathology of allergy. Traditional antihistamines, targeting the histamine H1 receptor, have failed to demonstrate a significant role for histamine in asthma. Novel immunomodulatory roles for histamine and the discovery of a novel histamine receptor, the histamine H4 receptor, have resulted in a reassessment of its importance in asthma.

Specific immunotherapy and turning off the T cell: how does it work?

OBJECTIVE

To examine T-regulatory (Treg) cell functions in allergic immune responses and their roles during allergen specific immunotherapy based on recent developments and current understanding of immune regulation.

DATA SOURCES

PubMed search of English-language articles regarding Treg cells and allergen specific immunotherapy.

STUDY SELECTION

Articles on the subject matter were selected and reviewed.

RESULTS

Allergen specific immunotherapy is the ultimate treatment modality targeting the immunopathogenic mechanisms of allergic disorders. A diminished allergen-specific T-cell proliferation and suppressed secretion of T(H)1- and T(H)2-type cytokines are the characteristic hallmarks. In addition, Treg cells inhibit the development of allergen-specific T(H)2 and T(H)1 cell responses and therefore exert key roles in healthy immune response to allergens. Treg cells potently suppress IgE production and directly or indirectly control the activity of effector cells of allergic inflammation, such as eosinophils, basophils, and mast cells.

CONCLUSION

As advancements in the field of allergen specific immunotherapy ensue, they may provide novel progression of more rational and safer approaches for the prevention and treatment of allergic disorders. Currently, the Treg cell field is an open research area to increase our understanding in mechanisms of peripheral tolerance to allergens.

Immunological mechanisms of allergen-specific immunotherapy

The studies on the mechanisms of specific immunotherapy (SIT) point out its targets that decide on the efficacy of SIT and hence might be used for its further improvement. Several mechanisms have been proposed to explain the beneficial effects of immunotherapy. The knowledge of the mechanisms underlying allergic diseases and curative treatment possibilities has experienced exciting advances over the last three decades. Studies in several clinical trials in allergen-SIT have demonstrated that the induction of a tolerant state against allergens in many ways represents a key step in the development of a healthy immune response against allergens. Several cellular and molecular mechanisms have been demonstrated: allergen-specific suppressive capacities of both inducible subsets of CD4(+) CD25(+) forkhead box P3(+) T-regulatory and IL-10-secreting type 1 T-regulatory cells increase in peripheral blood; suppression of eosinophils, mast cells, and basophils; Ab isotype change from IgE to IgG4. This review aims at the better understanding of the observed immunological changes associated with allergen SIT.

Immunomodulatory role of histamine H2 receptor in allergen-specific immunotherapy: a mouse model of allergic rhinitis

OBJECTIVE

The purpose of this pilot study was to investigate the effects of HR2 on allergen-specific immunotherapy in a mouse model of allergic rhinitis.

STUDY DESIGN

An in vivo study using an animal model.

SETTING

Catholic Research Institutes of Medical Science.

METHODS

Fifty mice were divided into 5 groups: control, allergic rhinitis (AR), immunotherapy (IT), immunotherapy with HR2 agonist (HI), and immunotherapy with HR2 antagonist (HB). All mice except for the control group were sensitized with ovalbumin (OVA). After 1 week, mice in the IT, HI, and HB groups underwent immunotherapy by intradermal injections of OVA. During immunotherapy, the HI group was injected with HR2 agonist, whereas the HB group was injected with HR2 antagonist. All sensitized mice were challenged with intranasal OVA. After the final challenge, allergic behavior was evaluated. Interleukin (IL)-13, interferon-γ, IL-10, and transforming growth factor (TGF)-β levels in nasal lavage fluid (NALF), as well as OVA-specific IgE levels in serum, were measured. The number of eosinophils in lamina propria was evaluated.

RESULTS

The levels of serum OVA-specific IgE and IL-13 in NALF were significantly increased in the HB group compared with the IT group (P < .05). Also, the tissue eosinophil counts were higher in the HB group than in the IT group (P < .05).

CONCLUSION

HR2 antagonist impaired OVA-specific immunotherapy in mice. Although confirmation of this preliminary result is needed, these findings suggest that HR2 receptors may have inhibitory effects on immune tolerance. The authors suggest that application of this property could enhance the efficiency of allergen-specific immunotherapy.

[Histamine as an immunomodulator]

The role of histamine as an important proinflammatory mediator has been well known for nearly 100 years. In regards to the immediate type allergic response, there is no debate about the importance of histamine. In addition, histamine has immunomodulatory functions, some of which are related to the histamine H2 receptor. However, with the discovery of the histamine H(4) receptor in the year 2000, the role of histamine as an immunomodulator became more obvious. The histamine H(4) receptor is expressed on several hematopoietic cells; along with the chemotaxis of immune cells, this recently characterized receptor modulates also the cytokine and chemokine secretion of some hematopoietic cells. Highly selective histamine H(4) receptor antagonists display promising results in animal models of allergic inflammatory diseases and also in in vitro studies on animal and human cells. These first results indicate that the histamine H(4) receptor is an interesting new pharmacological target for the treatment of allergic inflammatory disorders. This review summarizes the most important immunomodulatory functions of histamine and points to some possible indications in dermatology.

T regulatory cells and their counterparts: masters of immune regulation

The interaction of environmental and genetic factors with the immune system can lead to the development of allergic diseases. The essential step in this progress is the generation of allergen-specific CD4(+) T-helper (Th) type 2 cells that mediate several effector functions. The influence of Th2 cytokines leads to the production of allergen-specific IgE antibodies by B cells, development and recruitment of eosinophils, mucus production and bronchial hyperreactivity, as well as tissue homing of other Th2 cells and eosinophils. Meanwhile, Th1 cells may contribute to chronicity and the effector phases. T cells termed T regulatory (Treg) cells, which have immunosuppressive functions and cytokine profiles distinct from that of either Th1 or Th2 cells, have been intensely investigated during the last 13 years. Treg cell response is characterized by an abolished allergen-specific T cell proliferation and the suppressed secretion of Th1 and Th2-type cytokines. Treg cells are able to inhibit the development of allergen-specific Th2 and Th1 cell responses and therefore play an important role in a healthy immune response to allergens. In addition, Treg cells potently suppress IgE production and directly or indirectly suppress the activity of effector cells of allergic inflammation, such as eosinophils, basophils and mast cells. Currently, Treg cells represent an exciting area of research, where understanding the mechanisms of peripheral tolerance to allergens may soon lead to more rational and safer approaches for the prevention and cure of allergic diseases.

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.

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 beta 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.

T-cell tolerance to inhaled allergens: mechanisms and therapeutic approaches

BACKGROUND

Specific immune response to allergens is decisive in the development of clinically healthy or allergic states.

OBJECTIVE

Recent developments in the mechanisms of allergen-specific peripheral tolerance can be used for future treatment modalities.

METHODS

This review focuses on recent developments in allergen tolerance.

RESULTS/CONCLUSION

The balance between allergen-specific IL-10-secreting T regulatory cells (Tr1) and T helper 2 (Th2) cells appears to be decisive in the development of allergic and healthy immune response against allergens. Induction of IL-10- and TGF-beta-producing Tr1 cells, IgG4-isotype-blocking antibodies, and suppressed mast cells, basophils and eosinophils represent major components of a relatively normalized immune response after allergen-specific immunotherapy and healthy immune response to aeroallergens in sensitized individuals.

Regulation of transforming growth factor beta-induced responses by protein kinase A in pancreatic acinar cells

TGF-beta is an important regulator of growth and differentiation in the pancreas and has been implicated in pancreatic tumorigenesis. We have recently demonstrated that TGF-beta can activate protein kinase A (PKA) in mink lung epithelial cells (Zhang L, Duan C, Binkley C, Li G, Uhler M, Logsdon C, Simeone D. Mol Cell Biol 24: 2169-2180, 2004). In this study, we sought to determine whether TGF-beta activates PKA in pancreatic acinar cells, the mechanism by which PKA is activated, and PKA's role in TGF-beta-mediated growth regulatory responses. TGF-beta rapidly activated PKA in pancreatic acini while having no effect on intracellular cAMP levels. Coimmunoprecipitation experiments demonstrated a physical interaction between a Smad3/Smad4 complex and the regulatory subunits of PKA. TGF-beta also induced activation of the PKA-dependent transcription factor CREB. Both the specific PKA inhibitor H89 and PKI peptide significantly blocked TGF-beta's ability to activate PKA and CREB. TGF-beta-mediated growth inhibition and TGF-beta-induced p21 and SnoN expression in pancreatic acinar cells were blocked by H89 and PKI peptide. This study demonstrates that this novel cross talk between TGF-beta and PKA signaling pathways may play an important role in regulating TGF-beta signaling in the pancreas.

Comparison of macrophage phenotype between decidua basalis and decidua parietalis by flow cytometry

The two regions of the maternal decidua, decidua basalis and decidua parietalis, differ in the extent of trophoblast invasion and consequently in cytokines and other biological mediators, extracellular matrix and cellular components. Our aim was to compare the phenotypic features of macrophages from the two decidual regions across a broad gestational age range. We isolated macrophages by enzymatic digestion from healthy decidua samples obtained after elective abortions, at 9-18-week and at 19-23-weeks, or after term deliveries (caesarean sections at term and spontaneous term vaginal deliveries). Macrophages were analysed by flow cytometry applying the same instrument settings to all the samples to allow semi-quantitative comparison of the expression of a particular marker between different samples. We found higher expressions of CD80, CD86 and HLA-DR, suggestive of a more activated phenotype of decidual macrophages, at early/mid pregnancy than at term. Marginal differences were found between term decidual macrophages obtained after spontaneous vaginal deliveries or caesarean sections which imply that the parturient process is not associated with decidual macrophage activation. The expressions of CD105, DC-SIGN and MMR were the strongest in decidua basalis of mid pregnancy and indicate the importance of decidual macrophages in tissue homeostasis at the uteroplacental interface.

The role of histamine H1 and H4 receptors in allergic inflammation: the search for new antihistamines

Histamine has a key role in allergic inflammatory conditions. The inflammatory responses resulting from the liberation of histamine have long been thought to be mediated by the histamine H1 receptor, and H1-receptor antagonists--commonly known as antihistamines--have been used to treat allergies for many years. However, the importance of histamine in the pathology of conditions such as asthma and chronic pruritus may have been underestimated. Here, we review accumulating evidence suggesting that histamine indeed has roles in inflammation and immune function modulation in such diseases. In particular, the discovery of a fourth histamine receptor (H4) and its expression on numerous immune and inflammatory cells has prompted a re-evaluation of the actions of histamine, suggesting a new potential for H4-receptor antagonists and a possible synergy between H1 and H4-receptor antagonists in targeting various inflammatory conditions.

Reduced incidence of insect-bite hypersensitivity in Icelandic horses is associated with a down-regulation of interleukin-4 by interleukin-10 and transforming growth factor-beta1

Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses caused by IgE-mediated reactions to bites of insects of the genus Culicoides. IBH does not occur in Iceland due to the absence of Culicoides. However, Icelandic horses exported to mainland Europe as adults (1st generation) have a > or =50% incidence of developing IBH. In contrast, their progeny (2nd generation) has a <10% incidence of IBH. Here we show that peripheral blood mononuclear cells (PBMC) from Icelandic horses born in mainland Europe and belonging either to the IBH or healthy subgroup produce less interleukin (IL)-4 after polyclonal or allergen-specific stimulation when compared with counterparts from horses born in Iceland. We examined a role of IL-10 and transforming growth factor (TGF)-beta1 in down-regulation of IL-4 in healthy 2nd generation Icelandic horses. Supernatants of PBMC from 2nd generation healthy horses down-regulated the proportion of IL-4-producing cells and IL-4 production in stimulated cultures of PBMC from 1st generation IBH. This inhibition was mimicked by a combination of IL-10 and TGF-beta1 but not by the single cytokines. Cultures of stimulated PBMC of healthy 2nd generation horses produced a low level of IL-4, but IL-4 production was increased by anti-equine IL-10 and anti-human TGF-beta1. This shows for the first time that in horses, IL-10 and TGF-beta1 combined regulate IL-4 production in vitro. It is suggested that in this naturally occurring IgE-mediated allergy, IL-10 and TGF-beta1 have a role in the down-regulation of IL-4-induced allergen-specific Th2 cells, thereby reducing the incidence of IBH.

Histamine 4 receptor activation induces recruitment of FoxP3+ T cells and inhibits allergic asthma in a murine model

Histamine has an important role in regulation of immune response which is mediated by differential expression of four distinct receptors, H1R-H4R. H1R and HR2 have previously been shown to be involved with modulation of lung inflammation. H4R is also expressed on inflammatory cells; therefore, we investigated the potential role of H4R in development of allergic asthma in a murine model. We determined that the H4R agonist 4-methylhistamine when delivered intratracheally before Ag challenge mitigated airway hyperreactivity and inflammation. This was associated with an increase in IL-10 and IFN-gamma, but not TGF-beta or IL-16, as well as a decrease in IL-13 in the bronchoalveolar lavage fluid. We also observed that H4R agonist instillation resulted in accumulation of FoxP3(+) T cells suggesting a direct effect on T regulatory cell recruitment. To investigate this further, we determined the in vitro effect of H4R stimulation on human T cell migration. The H4R agonist induced a 2- to 3-fold increase in T cell migration, similar to that seen for H1R agonists. Cells transmigrating to the H4R agonist, but not H1R, were skewed toward a CD4 cell expressing CD25 and intracellular FoxP3. H4R-responsive cells suppressed proliferation of autologous T cells, an effect that was dependent on IL-10 production. We conclude that H4R stimulation enriches for a regulatory T cell with potent suppressive activity for proliferation. These findings identify a novel function for H4R and suggest a potential therapeutic approach to attenuation of asthmatic inflammation.

Connective tissue growth factor expression is regulated by histamine in lung fibroblasts: potential role of histamine in airway remodeling

BACKGROUND

In the inflamed lung of allergic asthma, an aberrant injury-repair response is accompanied by structural changes in the airway, known as airway remodeling. TGF-beta and its downstream mediator connective tissue growth factor (CTGF) are playing a key role in these processes, resulting in irreversible airway remodelling.

OBJECTIVE

As histamine is a key mediator of allergic reactions, we investigated whether histamine is involved in airway remodeling.

METHODS

The effect of histamine and TGF-beta1 on proliferation of lung fibroblast cells IMR-90 was studied by [(3)H]-thymidine proliferation assay. The regulation of CTGF by histamine and TGF-beta1 in lung fibroblasts was analyzed by RT-PCR, real-time PCR, Western blot analysis, and promoter analysis and characterized by specific histamine-receptor antagonists.

RESULTS

Histamine and TGF-beta1 enhanced proliferation of lung fibroblast cells IMR-90. Both induced CTGF mRNA and protein expression with different time kinetics. Whereas TGF-beta1 induced maximal CTGF expression after 12 hours (347% +/- 23%), histamine-induced maximal CTGF expression was lower and delayed (maximum expression of 204% +/- 11% after 48 hours). Histamine and TGF-beta1 stimulated the CTGF promoter and the TGF-beta-response element in the CTGF promoter. The histamine-induced CTGF expression was mediated through the histamine receptor (HR1) and could be completely abolished by TNF-alpha.

CONCLUSIONS

These findings demonstrate that histamine plays a potential role in the induction of airway remodeling mediated by the induction of lung fibroblasts proliferation and CTGF expression.

CLINICAL IMPLICATIONS

This mechanism could be important for prophylactic strategies aiming at airway remodeling and could be a new indication for antihistamine treatment.

Healthy immune response to allergens: T regulatory cells and more

The specific immune response to allergens is decisive in the development of clinically healthy or allergic states. In healthy individuals, the B-cell response varies between there being no response and the production of IgG(4)- or IgG(1)-dominating allergen-specific antibodies in the presence or absence of low amounts of IgE. If a detectable immune response is mounted, T regulatory type 1 (Tr1) cells specific for common environmental allergens consistently represent the dominant subset in healthy individuals. Exposure to high doses of allergens leads to a high concentration of specific IgG(4), detectable IgE and a Tr1 type of immune response. Induction of IL-10- and TGF-beta-producing Tr1 cells, IgG(4) isotype blocking antibodies, and suppressed mast cells, basophils and eosinophils represent major components of a relatively normalized immune response after allergen-specific immunotherapy (SIT).

The role of TGF-beta in allergic inflammation

The transforming growth factor beta (TGF-beta) plays a dual role in allergic disease. It is important in suppressing T cells and also mediates repair responses that lead to unwanted remodeling of tissues. Advances in the immunology of allergy indicate that allergens cause overreactions in the lymphocyte compartment because of the lack or decreased number of suppressive, regulatory T cells. TGF-beta was shown to induce regulatory T cells and participate directly in suppression of effector T cells. Therefore, TGF-beta may help return reactivity to allergens to normal subsymptomatic activity. Whether chronic inflammatory diseases such as asthma profit from TGF-beta-mediated suppression of specific immune responses or whether the TGF-beta-mediated tissue remodeling aggravates diseases more than it helps control immune reactions is unclear. This article addresses these issues and future strategies in this field.

Mechanisms of allergen-specific immunotherapy: T-regulatory cells and more

Activation-induced cell death, anergy, or immune response modulation by regulatory T cells (Treg cells) are essential mechanisms of peripheral T-cell tolerance. Genetic predisposition and environmental instructions tune thresholds for the activation of T cells, other inflammatory cells, and resident tissue cells in allergic diseases. Skewing allergen-specific effector T cells to a Treg-cell phenotype seems to be crucial in maintaining a healthy immune response to allergens and successful allergen-specific immunotherapy. The Treg-cell response is characterized by an abolished allergen-specific T-cell proliferation and the suppressed secretion of T-helper 1- and T-helper 2-type cytokines. Suppressed proliferative and cytokine responses against allergens are induced by multiple suppressor factors, including cytokines such as interleukin-10 (IL-10) and transforming growth factor beta (TGF-beta), and cell surface molecules such as cytotoxic T-lymphocyte antigen-4, programmed death-1, and histamine receptor 2. The increased levels of IL-10 and TGF-beta produced by Treg cells potently suppress IgE production while simultaneously increasing the production of noninflammatory isotypes IgG4 and IgA, respectively. In addition, Treg cells directly or indirectly suppress the activity of effector cells of allergic inflammation, such as mast cells, basophils, and eosinophils. In conclusion, peripheral tolerance to allergens is controlled by multiple active suppression mechanisms on T cells, regulation of antibody isotypes, and suppression of effector cells. The application of current knowledge of Treg cells and related mechanisms of peripheral tolerance may soon lead to more rational and safer approaches to the prevention and cure of allergic disease.

Histamine receptors in immune regulation and allergen-specific immunotherapy

The cells involved in the regulation of immune responses and hematopoiesis express histamine receptors and secrete histamine. Histamine acting through four types of its receptors has been shown not only to affect chronic inflammatory responses but also to regulate several essential events in the immune response. Histamine signals have a role in the mechanisms of tolerance induced during allergen-specific immunotherapy (SIT), acting mainly through its receptor (HR) type 2. It positively interferes with the peripheral antigen tolerance induced by T regulatory cells in several pathways. The rationale for the concomitant use of H1 antihistamines during SIT is diverse and includes reduction of its immediate side effects as well as enhancement of mechanisms of specific tolerance and anti-inflammatory effects of vaccination.

Mechanisms of allergen specific immunotherapy--T-cell tolerance and more

Specific immune suppression and induction of tolerance are essential processes in the regulation and circumvention of immune defence. The balance between allergen-specific T-regulatory (Treg) cells and T helper 2 cells appears to be decisive in the development of allergic and healthy immune response against allergens. Treg cells consistently represent the dominant subset specific for common environmental allergens in healthy individuals. In contrast, there is a high frequency of allergen-specific T helper 2 cells in allergic individuals. A decrease in interleukin (IL)-4, IL-5 and IL-13 production by allergen-specific CD4+ T cells due to the induction of peripheral T cell tolerance is the most essential step in allergen-specific immunotherapy (SIT). Suppressed proliferative and cytokine responses against the major allergens are induced by multiple suppressor factors, such as cytokines like IL-10 and transforming growth factor (TGF)-beta and cell surface molecules like cytotoxic T lymphocyte antigen-4, programmed death-1 and histamine receptor 2. There is considerable rationale for targeting T cells to increase efficacy of SIT. Such novel approaches include the use of modified allergens produced using recombinant DNA technology and adjuvants or additional drugs, which may increase the generation of allergen-specific peripheral tolerance. By the application of the recent knowledge in Treg cells and related mechanisms of peripheral tolerance, more rational and safer approaches are awaiting for the future of prevention and cure of allergic diseases.

T regulatory cells and the control of allergic disease

Allergic diseases are caused by the induction of T helper (Th)2 cells and IgE responses specific for common environmental antigens (allergens) in susceptible individuals. There is increasing interest in the role of both naturally occurring and induced regulatory T cell (Treg) populations in preventing these inappropriate immune responses and the underlying sensitisation to allergens. Current evidence suggests that Tregs may actively prevent Th2 responses to allergens occurring in healthy non-atopic individuals and that their function may be impaired in allergic patients. Evidence that existing therapies may act by modulating Treg function is reviewed. Future research aims to understand the mechanisms involved in the generation and function of allergen-specific Tregs. A primary aim is to promote the development of optimised therapeutic regimens with the capacity to provide long-lasting, allergen-specific, inhibitory mechanisms at the time and site of allergen challenge.