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

Opportunities and challenges in the therapeutic exploitation of histamine and histamine receptor pharmacology in inflammation-driven disorders

Inflammation-driven diseases encompass a wide array of pathological conditions characterised by immune system dysregulation leading to tissue damage and dysfunction. Among the myriad of mediators involved in the regulation of inflammation, histamine has emerged as a key modulatory player. Histamine elicits its actions through four rhodopsin-like G-protein-coupled receptors (GPCRs), named chronologically in order of discovery as histamine H1, H2, H3 and H4 receptors (H1-4R). The relatively low affinity H1R and H2R play pivotal roles in mediating allergic inflammation and gastric acid secretion, respectively, whereas the high affinity H3R and H4R are primarily linked to neurotransmission and immunomodulation, respectively. Importantly, however, besides the H4R, both H1R and H2R are also crucial in driving immune responses, the H2R tending to promote yet ill-defined and unexploited suppressive, protective and/or resolving processes. The modulatory action of histamine via its receptors on inflammatory cells is described in detail. The potential therapeutic value of the most recently discovered H4R in inflammatory disorders is illustrated via a selection of preclinical models. The clinical trials with antagonists of this receptor are discussed and possible reasons for their lack of success described.

Pharmacokinetics, pharmacodynamics, and safety of izuforant, an H4R inhibitor, in healthy subjects: A phase I single and multiple ascending dose study

Izuforant is a selective, and potent histamine H4 receptor (H4R) antagonist developed to treat atopic dermatitis (AD). There is an unmet medical need for therapeutic agents to control inflammation and pruritus. Izuforant is a strong candidate for this task based on the findings of non-clinical studies showing that inhibition of the histamine-mediated signaling pathway via H4R by izuforant results in decreased pruritus and inflammation. This study aimed to evaluate the clinical pharmacokinetic (PK) and pharmacodynamic (PD) profiles of izuforant. Dose-block-randomized, double-blind, placebo-controlled, single- and multiple ascending dose studies were conducted in 64 healthy volunteers. For the single ascending dose (SAD) study, 10-600 mg izuforant was administered to the designated groups. For the multiple ascending dose (MAD) study, 100-400 mg izuforant was administered to three groups. The clinical pharmacokinetic (PK) profile of izuforant was evaluated using plasma and urine concentrations. Blood sampling for the PD assay, which measured imetit-induced eosinophil shape changes (ESC), was also conducted. A one-compartment PK model described the distribution and elimination profiles of izuforant. An imetit-induced ESC inhibition test was established and validated for PD evaluation as a measure of the H4R antagonistic effect. ESC inhibition was observed even at doses as low as 10 mg; however, this inhibition became stronger and lasted longer as the dose increased. All izuforant doses were well tolerated, and no discontinuations due to adverse events (AE) or deaths were reported.

AllergoOncology: Biomarkers and refined classification for research in the allergy and glioma nexus-A joint EAACI-EANO position paper

Epidemiological studies have explored the relationship between allergic diseases and cancer risk or prognosis in AllergoOncology. Some studies suggest an inverse association, but uncertainties remain, including in IgE-mediated diseases and glioma. Allergic disease stems from a Th2-biased immune response to allergens in predisposed atopic individuals. Allergic disorders vary in phenotype, genotype and endotype, affecting their pathophysiology. Beyond clinical manifestation and commonly used clinical markers, there is ongoing research to identify novel biomarkers for allergy diagnosis, monitoring, severity assessment and treatment. Gliomas, the most common and diverse brain tumours, have in parallel undergone changes in classification over time, with specific molecular biomarkers defining glioma subtypes. Gliomas exhibit a complex tumour-immune interphase and distinct immune microenvironment features. Immunotherapy and targeted therapy hold promise for primary brain tumour treatment, but require more specific and effective approaches. Animal studies indicate allergic airway inflammation may delay glioma progression. This collaborative European Academy of Allergy and Clinical Immunology (EAACI) and European Association of Neuro-Oncology (EANO) Position Paper summarizes recent advances and emerging biomarkers for refined allergy and adult-type diffuse glioma classification to inform future epidemiological and clinical studies. Future research is needed to enhance our understanding of immune-glioma interactions to ultimately improve patient prognosis and survival.

Histamine H4 Receptor Antagonist Ameliorates the Progression of Experimental Autoimmune Encephalomyelitis via Regulation of T-Cell Imbalance

Multiple sclerosis (MS) is a degenerative condition characterized by immune-mediated attacks on the central nervous system (CNS), resulting in demyelination and recurring T-cell responses. The histamine H4 receptor (H4R) is mainly expressed in cellular populations and plays a vital role in inflammation and immunological responses. The role of H4R in neurons of the CNS has recently been revealed. However, the precise role of H4R in neuronal function remains inadequately understood. The objective of this work was to investigate the impact of JNJ 10191584 (JNJ), a highly effective and specific H4R antagonist, on the development of experimental autoimmune encephalomyelitis (EAE) and to gain insight into the underlying mechanism involved. In this study, we examined the potential impact of JNJ therapy on the course of EAE in SJL/J mice. EAE mice were administered an oral dose of JNJ at a concentration of 6 mg/kg once a day, starting from day 10 and continuing until day 42. Afterward, the mice's clinical scores were assessed. In this study, we conducted additional research to examine the impact of JNJ on several types of immune cells, specifically Th1 (IFN-γ and T-bet), Th9 (IL-9 and IRF4), Th17 (IL-17A and RORγt), and regulatory T (Tregs; Foxp3 and TGF-β1) cells in the spleen. In this study, we further investigated the impact of JNJ on the mRNA expression levels of IFN-γ, T-bet, IL-9, IRF4, IL-17A, RORγt, Foxp3, and TGF-β1 in the brain. Daily treatment of JNJ effectively reduced the development of EAE in mice. The percentages of CD4+IFN-γ+, CD4+T-bet+, CD4+IL-9+, CD4+IRF4+, CD4+IL-17A+, and CD4+RORγt+ cells were shown to decrease, whereas the percentages of CD4+TGF-β1+ and CD4+Foxp3+ cells were observed to increase in EAE mice treated with JNJ. Therefore, the HR4 antagonist positively affected the course of EAE by modulating the signaling of transcription factors. The identified results include possible ramifications in the context of MS treatment.

Frenemies in the Microenvironment: Harnessing Mast Cells for Cancer Immunotherapy

Tumor development, progression, and resistance to therapies are influenced by the interactions between tumor cells and the surrounding microenvironment, comprising fibroblasts, immune cells, and extracellular matrix proteins. In this context, mast cells (MCs) have recently emerged as important players. Yet, their role is still controversial, as MCs can exert pro- or anti-tumor functions in different tumor types depending on their location within or around the tumor mass and their interaction with other components of the tumor microenvironment. In this review, we describe the main aspects of MC biology and the different contribution of MCs in promoting or inhibiting cancer growth. We then discuss possible therapeutic strategies aimed at targeting MCs for cancer immunotherapy, which include: (1) targeting c-Kit signaling; (2) stabilizing MC degranulation; (3) triggering activating/inhibiting receptors; (4) modulating MC recruitment; (5) harnessing MC mediators; (6) adoptive transferring of MCs. Such strategies should aim to either restrain or sustain MC activity according to specific contexts. Further investigation would allow us to better dissect the multifaceted roles of MCs in cancer and tailor novel approaches for an "MC-guided" personalized medicine to be used in combination with conventional anti-cancer therapies.

Trisubstituted 1,3,5-Triazines as Histamine H4 Receptor Antagonists with Promising Activity In Vivo

Pain is a very unpleasant experience that makes life extremely uncomfortable. The histamine H₄ receptor (H₄R) is a promising target for the treatment of inflammatory and immune diseases, as well as pain. H₄R ligands have demonstrated analgesic effects in a variety of pain models, including inflammatory pain. Continuing the search for active H₄R ligands among the alkyl derivatives of 1,3,5-triazine, we obtained 19 new compounds in two series: acyclic (I) and aliphatic (II). In vitro pharmacological evaluation showed their variable affinity for H₄R. The majority of compounds showed a moderate affinity for this receptor (K_i > 100 nM), while all compounds tested in ß-arrestin and cAMP assays showed antagonistic activity. The most promising, compound 6, (4-(cyclopentylmethyl)-6-(4-methylpiperazin-1-yl)-1,3,5-triazin-2-amine; K_i = 63 nM) was selected for further in vitro evaluation: blood-brain barrier permeability (PAMPA assay; P_e = 12.26 × 10^-6 cm/s) and toxicity tests (HepG2 and SH-5YSY cells; no toxicity up to 50 µM). Next, compound 6 tested in vivo in a carrageenan-induced inflammatory pain model showed anti-inflammatory and analgesic effects (strongest at 50 mg/kg i.p.). Furthermore, in a histamine- and chloroquine-induced pruritus model, compound 6 at a dose of 25 mg/kg i.p. and 50 mg/kg i.p., respectively, reduced the number of scratch bouts. Thus, compound 6 is a promising ligand for further studies.

Efficacy and safety of probiotics in Parkinson's constipation: A systematic review and meta-analysis

Background: Parkinson's disease (PD) is the most common neurodegenerative disease closely related to the immune system, among whose prodromes constipation is a representative symptom. Recent Randomized Controlled Trials (RCTs) have proved that probiotics can be used to effectively treat PD constipation, but the results are inconsistent. We performed a meta-analysis to assess the efficacy and safety of probiotic therapy on Parkinson's constipation. Methods: Questions about the research focus were constructed based on the Participants, Intervention, Comparison and Outcomes (PICO) Criteria. We searched electronic databases such as PubMed, Web of Science, EMBASE, Scopus, EBSCO, Cochrane and Google Scholar until March 2022 for eligible literatures. Our primary endpoints were stool frequency, stool consistency, the number of laxatives uses, UPDRS-III scores and adverse events. Results: 12 eligible studies (n = 818 patients) met the inclusion and endpoint criteria. Meta-analysis results showed that constipation symptoms were improved after probiotic treatment, including an increased stool frequency (WMD = 0.94, 95% CI:0.53 to 1.34; OR = 3.22, 95% CI:1.97-5.29), an improved stool consistency (WMD = 1.46, 95% CI:0.54-2.37), a reduced use of laxatives (WMD = -0.72, 95%CI: -1.04 to-0.41), and also a reduced Parkinson's UPDRS-III score (WMD = -6.58, 95%CI: -12.02 to -1.14); there was no significant difference in total adverse events (OR = 0.82, 95%CI:0.39-1.72). Conclusion: Our analysis suggests that probiotics can be used to improve the constipation and motor symptoms for patients with Parkinson's constipation, possibly by reducing the inflammatory response and improving gut-brain axis neuron function, whose safety also proved to be good.

Manipulation of the diet-microbiota-brain axis in Alzheimer's disease

Several studies investigating the pathogenesis of Alzheimer's disease have identified various interdependent constituents contributing to the exacerbation of the disease, including Aβ plaque formation, tau protein hyperphosphorylation, neurofibrillary tangle accumulation, glial inflammation, and the eventual loss of proper neural plasticity. Recently, using various models and human patients, another key factor has been established as an influential determinant in brain homeostasis: the gut-brain axis. The implications of a rapidly aging population and the absence of a definitive cure for Alzheimer's disease have prompted a search for non-pharmaceutical tools, of which gut-modulatory therapies targeting the gut-brain axis have shown promise. Yet multiple recent studies examining changes in human gut flora in response to various probiotics and environmental factors are limited and difficult to generalize; whether the state of the gut microbiota in Alzheimer's disease is a cause of the disease, a result of the disease, or both through numerous feedback loops in the gut-brain axis, remains unclear. However, preliminary findings of longitudinal studies conducted over the past decades have highlighted dietary interventions, especially Mediterranean diets, as preventative measures for Alzheimer's disease by reversing neuroinflammation, modifying the intestinal and blood-brain barrier (BBB), and addressing gut dysbiosis. Conversely, the consumption of Western diets intensifies the progression of Alzheimer's disease through genetic alterations, impaired barrier function, and chronic inflammation. This review aims to support the growing body of experimental and clinical data highlighting specific probiotic strains and particular dietary components in preventing Alzheimer's disease via the gut-brain axis.

Mast Cell Interaction with Foxp3+ Regulatory T Cells Occur in the Dermis after Initiation of IgE-Mediated Cutaneous Anaphylaxis

Mast cells (MCs) are well-known for their role in IgE-mediated cutaneous anaphylactic responses, but their regulatory functions in the skin are still under intense scrutiny. Using a Red MC and Basophil reporter (RMB) mouse allowing red fluorescent detection and diphtheria toxin mediated depletion of MCs, we investigated the interaction of MCs, Foxp3+ regulatory T lymphocytes (Tregs) and Langerhans cells (LCs) during passive cutaneous anaphylaxis (PCA) responses. Using intravital imaging we show that MCs are sessile at homeostasis and during PCA. Breeding RMB mice with Langerin-eGFP mice revealed that dermal MCs do not interact with epidermal-localized LCs, the latter showing constant sprouting of their dendrites at homeostasis and during PCA. When bred with Foxp3-eGFP mice, we found that, although a few Foxp3+ Tregs are present at homeostasis, many Tregs transiently infiltrated the skin during PCA. While their velocity during PCA was not altered, Tregs increased the duration of their contact time with MCs compared to PCA-control mice. Antibody-mediated depletion of Tregs had no effect on the intensity of PCA. Hence, the observed increase in Treg numbers and contact time with MCs, regardless of an effect on the intensity of PCA responses, suggests an anti-inflammatory role dedicated to prevent further MC activation.

Emerging Roles of Platelets in Allergic Asthma

Allergic asthma is a complex chronic inflammatory disease of the airways, driven by Th2 immune responses and characterized by eosinophilic pulmonary inflammation, airway hyperresponsiveness, excessive mucus production, and airway remodeling. Overwhelming evidence from studies in animal models and allergic asthmatic patients suggests that platelets are aberrantly activated and recruited to the lungs. It has been established that platelets can interact with other immune cells and secrete various biochemical mediators to promote allergic sensitization and airway inflammatory response, and platelet deficiency may alleviate the pathological features and symptoms of allergic asthma. However, the comprehensive roles of platelets in allergic asthma have not been fully clarified, leaving attempts to treat allergic asthma with antiplatelet agents questionable. In this review, we summarize the role of platelet activation and pulmonary accumulation in allergic asthma; emphasis is placed on the different interactions between platelets with crucial immune cell types and the contribution of platelet-derived mediators in this context. Furthermore, clinical antiplatelet approaches to treat allergic asthma are discussed. This review provides a clearer understanding of the roles of platelets in the pathogenesis of allergic asthma and could be informative in the development of novel strategies for the treatment of allergic asthma.

The Histamine H4 Receptor Participates in the Anti-Neuropathic Effect of the Adenosine A3 Receptor Agonist IB-MECA: Role of CD4+ T Cells

A₃ adenosine receptor (A₃AR) agonists have emerged as potent relievers of neuropathic pain by a T cell-mediated production of IL-10. The H₄ histamine receptor (H₄R), also implicated in pain modulation, is expressed on T cells playing a preeminent role in its activation and release of IL-10. To improve the therapeutic opportunities, this study aimed to verify the hypothesis of a possible cross-talk between A₃AR and H₄R in the resolution of neuropathic pain. In the mouse model of Chronic Constriction Injury (CCI), the acute intraperitoneal co-administration of the A₃AR agonist IB-MECA (0.5 mg/kg) and the H₄R agonist VUF 8430 (10 mg/kg), were additive in counteracting mechano-allodynia increasing IL-10 plasma levels. In H₄R^−/− mice, IB-MECA activity was reduced, lower pain relief and lower modulation of plasma IL-1β, TNF-α, IL-6 and IL-10 were shown. The complete anti-allodynia effect of IB-MECA in H₄R^−/− mice was restored after intravenous administration of CD4⁺ T cells obtained from naïve wild type mice. In conclusion, a role of the histaminergic system in the mechanism of A₃AR-mediated neuropathic pain relief was suggested highlighting the driving force evoked by CD4⁺ T cells throughout IL-10 up-regulation.

Histamine in cancer immunology and immunotherapy. Current status and new perspectives

Cancer is the second leading cause of death globally and its incidence and mortality are rapidly increasing worldwide. The dynamic interaction of immune cells and tumor cells determines the clinical outcome of cancer. Immunotherapy comes to the forefront of cancer treatments, resulting in impressive and durable responses but only in a fraction of patients. Thus, understanding the characteristics and profiles of immune cells in the tumor microenvironment (TME) is a necessary step to move forward in the design of new immunomodulatory strategies that can boost the immune system to fight cancer. Histamine produces a complex and fine-tuned regulation of the phenotype and functions of the different immune cells, participating in multiple regulatory responses of the innate and adaptive immunity. Considering the important actions of histamine-producing immune cells in the TME, in this review we first address the most important immunomodulatory roles of histamine and histamine receptors in the context of cancer development and progression. In addition, this review highlights the current progress and foundational developments in the field of cancer immunotherapy in combination with histamine and pharmacological compounds targeting histamine receptors.

The Function of the Histamine H4 Receptor in Inflammatory and Inflammation-Associated Diseases of the Gut

Histamine is a pleiotropic mediator involved in a broad spectrum of (patho)-physiological processes, one of which is the regulation of inflammation. Compounds acting on three out of the four known histamine receptors are approved for clinical use. These approved compounds comprise histamine H1-receptor (H₁R) antagonists, which are used to control allergic inflammation, antagonists at H₂R, which therapeutically decrease gastric acid release, and an antagonist at H₃R, which is indicated to treat narcolepsy. Ligands at H₄R are still being tested pre-clinically and in clinical trials of inflammatory diseases, including rheumatoid arthritis, asthma, dermatitis, and psoriasis. These trials, however, documented only moderate beneficial effects of H₄R ligands so far. Nevertheless, pre-clinically, H₄R still is subject of ongoing research, analyzing various inflammatory, allergic, and autoimmune diseases. During inflammatory reactions in gut tissues, histamine concentrations rise in affected areas, indicating its possible biological effect. Indeed, in histamine-deficient mice experimentally induced inflammation of the gut is reduced in comparison to that in histamine-competent mice. However, antagonists at H₁R, H₂R, and H₃R do not provide an effect on inflammation, supporting the idea that H₄R is responsible for the histamine effects. In the present review, we discuss the involvement of histamine and H₄R in inflammatory and inflammation-associated diseases of the gut.

Impact of histamine H4 receptor deficiency on the modulation of T cells in a murine breast cancer model

BACKGROUND

The histamine H4 receptor (H4R) is preferentially expressed in immune cells and is a potential therapeutic target for inflammatory and autoimmune diseases. This study aimed at further exploring the role of H4R in the immunobiology of breast cancer.

METHODS

We used wild type (WT) and H4R deficient mice (KO) to evaluate whether H4R genotypes show a different distribution of T cell subsets in spleens, tumours and tumour draining lymph nodes (TDLN) in a syngeneic ErbB2-positive breast cancer model developed orthotopically with LM3 cells and its impact on tumour growth.

RESULTS

The presence of tumours had a differential impact on the distribution of T cells in TDLN from KO mice compared to WT ones. At day 21 post-inoculation (p.i.) of cells, despite no significant changes in the tumour weight, TDLN from KO mice showed a significantly increased proportion of CD8⁺ T cells compared to WT mice. At day 38 p.i. of cells a reduced tumour weight was evident in KO mice. This was accompanied by a decreased proportion of CD4⁺CD25⁺FoxP3⁺ regulatory T cells in TDLN of KO compared to WT mice. Tumour-bearing KO mice showed a better survival compared to WT mice.

CONCLUSIONS

H4R-mediated mechanisms may modulate the immune tumour microenvironment, promoting an immunosuppressive milieu. Results suggest that H4R could be explored as an immunotherapeutic target with potential benefit in combination with immunotherapy. Further preclinical and clinical studies are necessary to confirm this hypothesis.

Stimulation of histamine H4 receptor participates in cold-induced browning of subcutaneous white adipose tissue

Although many studies have shown that histamine and its signaling regulate energy homeostasis through the central nervous system, their roles in adipose tissues remain poorly understood. Here, we identified that the histamine H4 receptor (HrH4) was highly expressed in adipocytes at a level higher than that of the other three receptors (i.e., HrH1, HrH2, and HrH3). The HrH4 expression in adipocytes responded to cold through thermogenesis and lipolysis, supported by results from both mouse and cell models. When HrH4 expression was knocked down in the subcutaneous white adipose tissue (scWAT), browning and lipolysis effects triggered by cold were ablated, and the oxygen consumption was also lowered both at the normal and cold conditions. Moreover, mice exhibited browned scWAT, accelerated metabolic rates, and tolerance to hypothermia when 4-methylhistamine (4MH), a selective HrH4 agonist, was adjacently injected to the scWAT. Consistent with these findings, 4MH also triggered the browning and lipolytic effects in cultured C3H10T1/2 adipocytes. Mechanically, we demonstrated that p38/MAPK and ERK/MAPK pathways were involved in these processes. In conclusion, our findings have uncovered an effective role of HrH4 in adipose tissue browning.

The histamine-4 receptor antagonist JNJ7777120 prevents immune abnormalities by inhibiting RORγt/T-bet transcription factor signaling pathways in BTBR T+ Itpr3tf/J mice exposed to gamma rays

Autism is a neurodevelopmental disorder characterized by deficits and qualitative impairments in communication and implicit skill learning. Its prevalence is higher than previous estimates, and treatments have limited efficacy and are costly. Here, we assessed the therapeutic potential of JNJ77777120 (JNJ), a histamine-4 receptor (H4R) antagonist, using BTBR T⁺ Itpr3^tf/J (BTBR) mice, a confirmed model of autism, and C57BL/6J (C57) mice, a commonly chosen reference strain. We first examined the effects of JNJ treatment on BTBR mice exposed to gamma-rays (irradiation-exposed) using a three-chambered apparatus. We further investigated the possible molecular mechanisms through which JNJ administration modulates IL-17A-, RORγT-, IL-22-, T-bet-, STAT3-, ICOS-, and Foxp3-producing CD8⁺ T cells in the spleens of irradiation-exposed BTBR mice. The effects of JNJ administration on the mRNA and protein expression of IL-17A, RORγT, IL-22, T-bet, STAT-3, pSTAT3, IL-10, and Foxp3 in brain tissue were also explored. Results showed that JNJ treatment with irradiation exposure increased social interactions in BTBR mice compared to that in irradiation-exposed BTBR mice. Additionally, JNJ-treated and irradiation-exposed BTBR mice exhibited decreases in IL-17A-, RORγT-, IL-22-, T-bet-, and STAT3-producing CD8⁺ T cells and increases in ICOS- and Foxp3-producing CD8⁺ T cells. Moreover, JNJ treatment and irradiation exposure in BTBR mice regulated the mRNA and protein expression levels of IL-17A, RORγT, IL-22, T-bet, STAT3, pSTAT-3, IL-10, and Foxp3 in the brain tissue. These results suggest that JNJ is useful for the treatment of autism, as this H4R antagonist could block inflammatory cytokine production and transcription factor signaling.

Physiological Roles of Mast Cells: Collegium Internationale Allergologicum Update 2019

Mast cells are immune cells which have a widespread distribution in nearly all tissues. These cells and their mediators are canonically viewed as primary effector cells in allergic disorders. However, in the last years, mast cells have gained recognition for their involvement in several physiological and pathological conditions. They are highly heterogeneous immune cells displaying a constellation of surface receptors and producing a wide spectrum of inflammatory and immunomodulatory mediators. These features enable the cells to act as sentinels in harmful situations as well as respond to metabolic and immune changes in their microenvironment. Moreover, they communicate with many immune and nonimmune cells implicated in several immunological responses. Although mast cells contribute to host responses in experimental infections, there is no satisfactory model to study how they contribute to infection outcome in humans. Mast cells modulate physiological and pathological angiogenesis and lymphangiogenesis, but their role in tumor initiation and development is still controversial. Cardiac mast cells store and release several mediators that can exert multiple effects in the homeostatic control of different cardiometabolic functions. Although mast cells and their mediators have been simplistically associated with detrimental roles in allergic disorders, there is increasing evidence that they can also have homeostatic or protective roles in several pathophysiological processes. These findings may reflect the functional heterogeneity of different subsets of mast cells.

Stimulation of histamine H4 receptors increases the production of IL-9 in Th9 polarized cells

BACKGROUND AND PURPOSE

Th9 cells represent a recently defined subset of CD4⁺ T-helper cells, characterized by a high production of IL-9. They are found at increased frequency in lesions of atopic dermatitis, where IL-9 is also elevated. As histamine is up-regulated in lesions of inflammatory skin diseases, we investigated the expression profile of histamine receptors and their functional role on Th9 cells.

EXPERIMENTAL APPROACH

Naïve CD4⁺ T-cells were purified from human peripheral blood mononuclear cells, using magnetic beads and further differentiated into Th9 cells. During differentiation, cells were additionally stimulated with histamine receptor agonists or left untreated. Histamine receptor expression as well as IL-9 production was measured.

KEY RESULTS

As proof of a successful differentiation, IL-9 production was measured at mRNA and protein level. Expression of mRNA for histamine H₁ , H₂ and H₄ receptors were up-regulated in differentiated Th9 cells compared to Th0 cells, while no mRNA for the H₃ receptor was detectable. Stimulation of Th9 cells with histamine significantly up-regulated expression of mRNA and protein for IL-9 . Experiments with specific histamine receptor agonists and antagonists revealed that this up-regulation was mediated by H₄ receptors.

CONCLUSIONS AND IMPLICATIONS

In summary, our study demonstrates a functional role for histamine H₄ receptors on Th9 cells, which might amplify the pro-inflammatory potency of these cells. Together with earlier studies on Th2 and Th17 cells, this study underlines the promising approach for the use of H₄ receptor antagonists in inflammatory and allergic diseases such as atopic dermatitis.

LINKED ARTICLES

This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Immunomodulatory role of histamine H4 receptor in breast cancer

BACKGROUND

Although the role of histamine H4 receptor (H4R) in immune cells is being extensively investigated, its immunomodulatory function in cancer is completely unknown. This study aimed to investigate the role of H4R in antitumour immunity in a model of triple-negative breast cancer.

METHODS

We evaluated growth parameters, histological characteristics and the composition of tumour, splenic and tumour draining lymph node (TDLN) immune subsets, in a syngeneic model, developed orthotopically with 4T1 cells in H4R knockout (H4R-KO) and wild-type mice.

RESULTS

Mice lacking H4R show reduced tumour size and weight, decreased number of lung metastases and percentage of CD4+ tumour-infiltrating T cells, while exhibiting increased infiltration of NK cells and CD19+ lymphocytes. Likewise, TDLN of H4R-KO mice show decreased CD4+ T cells and T regulatory cells (CD4+CD25+FoxP3+), and increased percentages of NK cells. Finally, H4R-deficient mice show decreased Tregs in spleens and non-draining lymph nodes, and a negative correlation between tumour weight and the percentages of CD4+, CD19+ and NK splenic cells, suggesting that H4R also regulates antitumour immunity at a systemic level.

CONCLUSIONS

This is the first report that demonstrates the participation of H4R in antitumour immunity, suggesting that H4R could be a target for cancer treatment.

Glia-immune interactions post-ischemic stroke and potential therapies

IMPACT STATEMENT

This article reviews glial cell interactions with the immune system post-ischemic stroke. Research has shown that glial cells in the brain play a role in altering phenotypes of other glial cells and have downstream immune cell targets ultimately regulating a neuroinflammatory response. These interactions may play a deleterious as well as beneficial role in stroke recovery. Furthermore, they may provide a novel way to approach potential therapies, since current stroke drug therapy is limited to only one Food and Drug Administration-approved drug complicated by a narrow therapeutic window. Until this point, most research has emphasized neuroimmune interactions, but little focus has been on bidirectional communication of glial-immune interactions in the ischemic brain. By expanding our understanding of these interactions through a compilation of glial cell effects, we may be able to pinpoint major modulating factors in brain homeostasis to maintain or discover ways to suppress irreversible ischemic damage and improve brain repair.

H4 Receptor Inhibits Lipopolysaccharide-induced NF-κB Activation by Interacting with Tumor Necrosis Factor Receptor-Associated Factor 6

Microglia, the resident immune cells of the central nervous system (CNS), are activated at the beginning of the inflammatory response and induce detrimental neuroinflammation by producing excessive pro-inflammatory cytokines. Nuclear factor kappa B (NF-κB) signaling facilitates the onset of microglia activation. However, the molecular mechanisms underlying the negative regulation of NF-κB remain to be fully elucidated. In the present study, our results indicated that H4R expression increased in a rat model of lipopolysaccharide (LPS)-induced CNS inflammation. Knockdown of H4R in microglia HAPI cells enhanced the production of cytokines following LPS stimulation. Co-immunoprecipitation experiments further revealed an interaction between H4R and tumor necrosis factor receptor-associated factor 6 (TRAF6) in microglia, which was verified both in vivo and in vitro. Our experimental results support our hypothesis that H4R interacts with TRAF6 to inhibit the release of inflammatory cytokines in LPS-induced microglia cells by decreasing TRAF6-mediated ubiquitination of K63. These findings provide theoretical and experimental evidence regarding the role of H4R in the microglia inflammatory response, which may aid in the development of novel treatments for inflammation.

The Role of Histamine and Histamine Receptors in Mast Cell-Mediated Allergy and Inflammation: The Hunt for New Therapeutic Targets

Histamine and its receptors (H1R–H4R) play a crucial and significant role in the development of various allergic diseases. Mast cells are multifunctional bone marrow-derived tissue-dwelling cells that are the major producer of histamine in the body. H1R are expressed in many cells, including mast cells, and are involved in Type 1 hypersensitivity reactions. H2R are involved in Th1 lymphocyte cytokine production. H3R are mainly involved in blood–brain barrier function. H4R are highly expressed on mast cells where their stimulation exacerbates histamine and cytokine generation. Both H1R and H4R have important roles in the progression and modulation of histamine-mediated allergic diseases. Antihistamines that target H1R alone are not entirely effective in the treatment of acute pruritus, atopic dermatitis, allergic asthma, and other allergic diseases. However, antagonists that target H4R have shown promising effects in preclinical and clinical studies in the treatment of several allergic diseases. In the present review, we examine the accumulating evidence suggesting novel therapeutic approaches that explore both H1R and H4R as therapeutic targets for histamine-mediated allergic diseases.

The role of regulatory T cells in the regulation of upper airway inflammation

Allergic rhinitis (AR) and chronic rhinosinusitis with nasal polyps (CRSwNP) are inflammatory diseases of the upper airway, with a similar immunologic profile, characterized by aberrant and persistent type 2 inflammation. One cell population that has been identified as altered in both disease types is regulatory T cell (Treg). Tregs have the capacity to modulate T-effector function and suppress inflammatory cytokine production in a broad range of cell types. Given the ability of Tregs to control inflammation, the role of Tregs in respiratory diseases has attracted much attention. As discussed in this article, alterations in the Treg numbers and function, or both, have been identified in AR and CRSwNP, although much of the data is conflicting. Here, we explored what is known and, in many cases, unknown about the mechanisms by which Tregs differentiate and function, and how these functions can be controlled in the mucosal microenvironment. By gaining a greater understanding of these processes, it may be possible to harness the natural immunosuppressive activity of Tregs to ameliorate the chronic inflammation associated with AR and CRSwNP.

Platelet-Activating Factor-Induced Reduction in Contact Hypersensitivity Responses Is Mediated by Mast Cells via Cyclooxygenase-2-Dependent Mechanisms

Platelet-activating factor (PAF) stimulates numerous cell types via activation of the G protein-coupled PAF receptor (PAFR). PAFR activation not only induces acute proinflammatory responses, but it also induces delayed systemic immunosuppressive effects by modulating host immunity. Although enzymatic synthesis and degradation of PAF are tightly regulated, oxidative stressors, such as UVB, chemotherapy, and cigarette smoke, can generate PAF and PAF-like molecules in an unregulated fashion via the oxidation of membrane phospholipids. Recent studies have demonstrated the relevance of the mast cell (MC) PAFR in PAFR-induced systemic immunosuppression. The current study was designed to determine the exact mechanisms and mediators involved in MC PAFR-mediated systemic immunosuppression. By using a contact hypersensitivity model, the MC PAFR was not only found to be necessary, but also sufficient to mediate the immunosuppressive effects of systemic PAF. Furthermore, activation of the MC PAFR induces MC-derived histamine and PGE₂ release. Importantly, PAFR-mediated systemic immunosuppression was defective in mice that lacked MCs, or in MC-deficient mice transplanted with histidine decarboxylase- or cyclooxygenase-2-deficient MCs. Lastly, it was found that PGs could modulate MC migration to draining lymph nodes. These results support the hypothesis that MC PAFR activation promotes the immunosuppressive effects of PAF in part through histamine- and PGE₂-dependent mechanisms.

Histamine Release from Mast Cells and Basophils

Mast cells and basophils represent the most relevant source of histamine in the immune system. Histamine is stored in cytoplasmic granules along with other amines (e.g., serotonin), proteases, proteoglycans, cytokines/chemokines, and angiogenic factors and rapidly released upon triggering with a variety of stimuli. Moreover, mast cell and basophil histamine release is regulated by several activating and inhibitory receptors. The engagement of different receptors can trigger different modalities of histamine release and degranulation. Histamine released from mast cells and basophils exerts its biological activities by activating four G protein-coupled receptors, namely H1R, H2R, H3R (expressed mainly in the brain), and the recently identified H4R. While H1R and H2R activation accounts mainly for some mast cell- and basophil-mediated allergic disorders, the selective expression of H4R on immune cells is uncovering new roles for histamine (possibly derived from mast cells and basophils) in allergic, inflammatory, and autoimmune disorders. Thus, the in-depth knowledge of mast cell and basophil histamine release and its biologic effects is poised to uncover new therapeutic avenues for a wide spectrum of disorders.

Microbiome, probiotics and neurodegenerative diseases: deciphering the gut brain axis

The gut microbiota is essential to health and has recently become a target for live bacterial cell biotherapies for various chronic diseases including metabolic syndrome, diabetes, obesity and neurodegenerative disease. Probiotic biotherapies are known to create a healthy gut environment by balancing bacterial populations and promoting their favorable metabolic action. The microbiota and its respective metabolites communicate to the host through a series of biochemical and functional links thereby affecting host homeostasis and health. In particular, the gastrointestinal tract communicates with the central nervous system through the gut-brain axis to support neuronal development and maintenance while gut dysbiosis manifests in neurological disease. There are three basic mechanisms that mediate the communication between the gut and the brain: direct neuronal communication, endocrine signaling mediators and the immune system. Together, these systems create a highly integrated molecular communication network that link systemic imbalances with the development of neurodegeneration including insulin regulation, fat metabolism, oxidative markers and immune signaling. Age is a common factor in the development of neurodegenerative disease and probiotics prevent many harmful effects of aging such as decreased neurotransmitter levels, chronic inflammation, oxidative stress and apoptosis-all factors that are proven aggravators of neurodegenerative disease. Indeed patients with Parkinson's and Alzheimer's diseases have a high rate of gastrointestinal comorbidities and it has be proposed by some the management of the gut microbiota may prevent or alleviate the symptoms of these chronic diseases.

Preliminary study of histamine H4 receptor expressed on human CD4+ T cells and its immunomodulatory potency in the IL-17 pathway of psoriasis

BACKGROUND

Previous studies have shown the expression of histamine H₄ receptor (H4R) on CD4⁺ T cells, especially human CD4⁺ T_h2-polarized T cells.

OBJECTIVE

This study aimed to investigate the role of H4R on these effector T cells in psoriasis.

METHODS

We enrolled three patients each with active psoriasis, inactive psoriasis, scalp seborrheic dermatitis, and three normal controls, and compared the basal expression of H4R mRNA in their peripheral blood CD4⁺ T cells. Then, we identified H4R expression in dermal CD4⁺ T cells. Furthermore, we investigated H4R expression after stimulating separated peripheral blood CD4⁺ T cells with several inflammatory cytokines.

RESULTS

The results showed higher H4R expression in the active psoriasis group compared to the inactive psoriasis group. It was interesting that interleukin (IL)-23, which is a representative cytokine contributing to T_h17 cell differentiation, stimulated H4R expression significantly. After adding a selective H4R antagonist (JNJ-7777120) while the CD4⁺ T cells were polarized into T_h17 cells, we observed a tendency toward suppressed IL-17 secretion.

CONCLUSIONS

Histamine stimulation influences the IL-17 pathway in psoriasis via the fourth histamine receptor subtype, H4R, on CD4⁺ T cells. The immunomodulatory roles of H4R suggest its potency as a new therapeutic target for obstinate psoriasis.

Pharmacological targeting of allergen-specific T lymphocytes

Allergic disorders are the result of a complex pathophysiology, involving major cellular lineages and a multitude of humoral factors of the innate and adaptive immune system, and have the tendency to involve multiple organs. Consequently, even standard pharmacological treatment of allergies is rarely specific but usually targets more than one pathway/cellular system at a time. Accordingly, many of the classic anti-allergic drugs have a critical impact also on T helper cells, which are pivotal not only during the sensitization but also the maintenance phase of allergic diseases. Recent years have seen a dramatic increase of novel drugs with the potency to interfere, more or less specifically, with T lymphocyte function, which might, possibly together with classic anti-allergic drugs, help harnessing one of the central cellular players in allergic responses. A major theme in the years to come will be a thoughtful combination of previously established with recently developed treatment modalities.

Inhibitory Effect of Imiquimod-Induced Psoriasis-Like Skin Inflammation in Mice by Histamine H4 Receptor Agonist 4-Methylhistamine

Psoriasis is a chronic inflammatory immune-mediated autoimmune skin disorder. The histamine H4 receptor (H4R) agonist 4-methylhistamine (4-MH) plays an important role in immunomodulation of inflammatory responses associated with allergic inflammatory diseases. In this study, we investigated the effects of H4R agonist 4-MH on the development of imiquimod (IMQ)-induced psoriasis-like skin inflammation in mice and explored the immunoregulatory mechanism involved. The total clinical severity scores were significantly ameliorated by treatment with 4-MH (20 mg/kg) and 4-MH (40 mg/kg). Histological analysis of the skin revealed that 4-MH (20 mg/kg) and 4-MH (40 mg/kg) significantly attenuated the psoriatic phenotypes, including epidermal hyperplasis, hyperkeratosis and lymphocytes infiltration. Treatment with 4-MH (20 mg/kg) and 4-MH (40 mg/kg) led to reductions in the levels of Th1 cytokines (TNF-α, IFN-α, and IL-27) in the serum and dorsal skin, whereas Th17 cytokines levels (IL-17A and IL-23) did not change in response to treatment with 4-MH (20 mg/kg) and 4-MH (40 mg/kg). Furthermore, the number of CD4(+) CD25(+) FoxP3(+) regulatory T (Treg) cells was significantly increased by treatment with 4-MH (40 mg/kg). Taken together, these results imply that H4R agonist 4-MH might be an effective immunomodulatory approach for treatment of patients with psoriasis and the effects may be related to inhibited epidermal alteration, selectively reduced Th1 pro-inflammatory cytokines, and recruited CD4(+) CD25(+) FoxP3(+) Treg cells.

Cellular analysis of the histamine H4 receptor in human myeloid cells

The human histamine H4 receptor (H4R) is a Gαi/o-coupled receptor which is mainly expressed on hematopoietic cells. Accordingly, the receptor is implicated in the pathology of various diseases such as autoimmune disorders, bronchial asthma and pruritus. Due to complicated receptor pharmacology, the lack of a reliable antibody and limited availability of primary cells expressing the receptor the physiology of this receptor is still poorly understood. Therefore, we aimed to assess absolute receptor mRNA expression and functionality (intracellular Ca(2+) release) in various human myeloid cell types such as granulocytes, monocytes, macrophages and dendritic cells (DCs). This was put into context with the expression of the H1R and H2R. In addition, the influence of various inflammatory stimuli on H4R expression was investigated in macrophages and monocyte-derived DCs. We found that classically activated macrophages treated with pro-inflammatory stimuli down-regulated histamine receptor mRNA expression as did LPS and zymosan A matured monocyte-derived DCs. In contrast, alternatively activated macrophages (IL-4 or IL-13) upregulated H2R and H4R expression compared to controls. Consistent with existing literature, we found eosinophils to be the major source of the H4R. Since availability of primary eosinophils is limited, we developed a cell model based on the differentiated eosinophilic cell line EOL-1, in which H4R pharmacology and physiology may be studied.

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.

c-kit plays a critical role in induction of intravenous tolerance in experimental autoimmune encephalomyelitis

c-kit (CD117) is a tyrosine kinase receptor found in various types of immune cells. It has been shown that c-kit plays a role in the pathogenesis of multiple sclerosis, an inflammatory demyelinating disorder of the CNS. Recent data have suggested an immunoregulatory effect of c-kit. We therefore examined the role of c-kit in autoantigen-induced i.v. tolerance in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Our results show that induction of intravenous tolerance against EAE in B6 mice is characterized by increased numbers of CD117(+) cells and altered mast cell-associated molecules in the periphery and in the CNS. W(-sh) (c-kit-deficient) mice were resistant to i.v autoantigen-induced tolerance, with increased proinflammatory cytokine production in the periphery. I.v. autoantigen in WT mice suppressed the production of proinflammatory cytokines IFN-γ and IL-6 and up-regulated the expression of FoxP3, a transcription factor of Tregs; however, in W(-sh) mice, IFN-γ and IL-6 were increased with a failure of FoxP3 induction upon i.v. autoantigen injection and is thus a mechanism for resistance to i.v. tolerance induction in these mice. We conclude that c-kit signaling has a regulatory role in i.v. tolerance and could be a target for potential immunotherapy in autoimmune disorders.

Histamine 4 receptor promotes expression of costimulatory B7.1/B7.2 molecules, CD28 signaling and cytokine production in stress-induced immune responses

Recently, the expression of histamine 4 receptor (H4R) on neurons was reported, however its function in cells within the central nervous system (CNS) remains poorly understood. To this end, we used the H4R agonist, 4-methylhistamine (4-MeH), and the H4R antagonist, JNJ77777120 (JNJ), to investigate the function of H4R signaling in immune cells in a murine model of chronic stress. Treatment of stressed mice with 4-MeH resulted in an increase in the proportion of lymphocyte subsets (CD3(+), CD8(+), CD28(+), and CD4(+)CD28(+)) and cells expressing the co-stimulatory molecules CD80(+) (B7.1) and CD86(+) (B7.2) in heparinized blood as compared to normal control (NC) and stressed control (SC) groups. We also observed that as compared to NC and SC mice, 4-MeH-treated mice showed greater production of IL-2(+), IL-6(+), IL-9(+), IL-21(+), and IL-27(+) cytokines in the spleen and by splenic CD4(+) T cells. Furthermore, 4-MeH treatment of stressed mice led to an increase in the levels of serum Th1/Th17 cytokines and corticosterone, and a decrease in Th2 cytokines. Treatment of chronically-stressed mice with 4-MeH also augmented expression of IL-6, IL-21, NF-κB p65, and STAT3 mRNA. Moreover, Western blot analyses confirmed increased protein expression of NF-κB, iNOS, and STAT3 expression following 4-MeH treatment of chronically-stressed mice as compared to controls. These proteins provide a novel relevant targets for the manipulation of chronic stress induced immune regulation. In striking contrast, treatment of stressed mice with the H4R antagonist, JNJ, resulted in a substantial reduction in all of the aforementioned effects upon immune cell percentages and cytokine production.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.

Histamine and Skin Barrier: Are Histamine Antagonists Useful for the Prevention or Treatment of Atopic Dermatitis?

Atopic Dermatitis (AD), the most common chronic inflammatory skin disease, is characterized by an overactive immune response to a host of environmental allergens and dry, itchy skin. Over the past decade important discoveries have demonstrated that AD develops in part from genetic and/or acquired defects in the skin barrier. Histamine is an aminergic neurotransmitter involved in physiologic and pathologic processes such as pruritus, inflammation, and vascular leak. Enhanced histamine release has been observed in the skin of patients with AD and antihistamines are often prescribed for their sedating and anti-itch properties. Recent evidence suggests that histamine also inhibits the terminal differentiation of keratinocytes and impairs the skin barrier, raising the question whether histamine might play a role in AD barrier impairment. This, coupled with the notion that histamine’s effects mediated through the recently identified histamine receptor H4R, may be important in allergic inflammation, has renewed interest in this mediator in allergic diseases. In this paper we summarize the current knowledge on histamine and histamine receptor antagonists in AD and skin barrier function.

Histamine type 2 receptor expression on peripheral blood regulatory lymphocytes in patients with allergic rhinitis treated with specific immunotherapy

BACKGROUND

Both histamine H1- and H2-receptors (H2R) were found on regulatory T (Treg) cells; however, there is a paucity of information regarding the role of H2R in Treg function. This study aimed to investigate the effects of natural allergen stimulation and specific immunotherapy (SIT) on H2R expression in Treg cells in patients with allergic rhinitis (AR).

METHODS

In this prospective, double-blind, placebo-controlled study 41 patients with AR were screened for 1 year and treated with SIT (n = 21) or placebo (n = 20) for the next 2 years. Fifteen healthy subjects were included as a control. Subsets of Treg cells that expressed H2R were assessed annually in the blood by flow cytometry: before, at the height of the pollen season, and after, at the end of the pollen season. In addition, total nasal symptom score, the use of rescue medication, and nasal eosinophilia were evaluated.

RESULTS

Treg cells of AR patients slightly up-regulate H2R out of the pollen season. Natural allergen stimulation results in prompt up-regulation of H2R within these cells. SIT significantly decreased the number of Treg cells with increased expression of H2R in the blood exclusively at the height of pollen season, which, however, had no impact on the expression of H2R in Treg cells. SIT improved significantly the symptom score, rescue medication use, and decreased nasal eosinophilia.

CONCLUSION

Natural pollen exposure results in up-regulation of H2R in Treg cells. Immunotherapy might transiently decrease the number of Treg-H2R(+) cells in the blood, which may be associated with their migration to the peripheral tissues. This study was part of the clinical trial registered in www.clinicaltrials.gov.

The histamine H4 receptor: from orphan to the clinic

The histamine H4 receptor (H4R) was first noted as a sequence in genomic databases that had features of a class A G-protein coupled receptor. This putative receptor was found to bind histamine consistent with its homology to other histamine receptors and thus became the fourth member of the histamine receptor family. Due to the previous success of drugs that target the H1 and H2 receptors, an effort was made to understand the function of this new receptor and determine if it represented a viable drug target. Taking advantage of the vast literature on the function of histamine, a search for histamine activity that did not appear to be mediated by the other three histamine receptors was undertaken. From this asthma and pruritus emerged as areas of particular interest. Histamine has long been suspected to play a role in the pathogenesis of asthma, but antihistamines that target the H1 and H2 receptors have not been shown to be effective for this condition. The use of selective ligands in animal models of asthma has now potentially filled this gap by showing a role for the H4R in mediating lung function and inflammation. A similar story exists for chronic pruritus associated with conditions such as atopic dermatitis. Antihistamines that target the H1 receptor are effective in reducing acute pruritus, but are ineffective in pruritus experienced by patients with atopic dermatitis. As for asthma, animal models have now suggested a role for the H4R in mediating pruritic responses, with antagonists of the H4R reducing pruritus in a number of different conditions. The anti-pruritic effect of H4R antagonists has recently been shown in human clinical studies, validating the preclinical findings in the animal models. A selective H4R antagonist inhibited histamine-induced pruritus in health volunteers and reduced pruritus in patients with atopic dermatitis. The history to date of the H4R provides an excellent example of the deorphanization of a novel receptor and the translation of this into clinical efficacy in humans.

Prevention of bleomycin-induced lung inflammation and fibrosis in mice by naproxen and JNJ7777120 treatment

Pulmonary fibrosis, a progressive and lethal lung disease characterized by inflammation and accumulation of extracellular matrix components, is a major therapeutic challenge for which new therapeutic strategies are warranted. Cyclooxygenase (COX) inhibitors have been previously utilized to reduce inflammation. Histamine H4 receptor (H4R), largely expressed in hematopoietic cells, has been identified as a novel target for inflammatory and immune disorders. The aim of this study was to evaluate the effect of JNJ7777120 (1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methylpiperazine), a selective H4R antagonist, and naproxen, a well known nonsteroidal anti-inflammatory drug, and their combination in a murine model of bleomycin-induced fibrosis. Bleomycin (0.05 IU) was instilled intratracheally to C57BL/6 mice, which were then treated by micro-osmotic pump with vehicle, JNJ7777120 (40 mg/kg b.wt.), naproxen (21 mg/kg b.wt.), or a combination of both. Airway resistance to inflation, an index of lung stiffness, was assessed, and lung specimens were processed for inflammation, oxidative stress, and fibrosis markers. Both drugs alone were able to reduce the airway resistance to inflation induced by bleomycin and the inflammatory response by decreasing COX-2 and myeloperoxidase expression and activity and thiobarbituric acid-reactive substance and 8-hydroxy-2'-deoxyguanosine production. Lung fibrosis was inhibited, as demonstrated by the reduction of tissue levels of transforming growth factor-β, collagen deposition, relative goblet cell number, and smooth muscle layer thickness. Our results demonstrate that both JNJ7777120 and naproxen exert an anti-inflammatory and antifibrotic effect that is increased by their combination, which could be an effective therapeutic strategy in the treatment of pulmonary fibrosis.

Distinct signalling pathways of murine histamine H1- and H4-receptors expressed at comparable levels in HEK293 cells

Histamine (HA) is recognized by its target cells via four G-protein-coupled receptors, referred to as histamine H₁-receptor (H₁R), H₂R, H₃R, and H₄R. Both H₁R and H₄R exert pro-inflammatory functions. However, their signal transduction pathways have never been analyzed in a directly comparable manner side by side. Moreover, the analysis of pharmacological properties of the murine orthologs, representing the main targets of pre-clinical research, is very important. Therefore, we engineered recombinant HEK293 cells expressing either mouse (m)H₁R or mH₄R at similar levels and analyzed HA-induced signalling in these cells. HA induced intracellular calcium mobilization via both mH₁R and mH₄R, with the mH₁R being much more effective. Whereas cAMP accumulation was potentiated via the mH₁R, it was reduced via the mH₄R. The regulation of both second messengers via the H₄R, but not the H₁R, was sensitive to pertussis toxin (PTX). The mitogen-activated protein kinases (MAPKs) ERK 1/2 were massively activated downstream of both receptors and demonstrated a functional involvement in HA-induced EGR-1 gene expression. The p38 MAPK was moderately activated via both receptors as well, but was functionally involved in HA-induced EGR-1 gene expression only in H₄R-expressing cells. Surprisingly, in this system p38 MAPK activity reduced the HA-induced gene expression. In summary, using this system which allows a direct comparison of mH₁R- and mH₄R-induced signalling, qualitative and quantitative differences on the levels of second messenger generation and also in terms of p38 MAPK function became evident.

The Role of Mast Cells in Molding the Tumor Microenvironment

Mast cells (MCs) are granulocytic immune cells that reside in tissues exposed to the external environment. MCs are best known for their activity in allergic reactions, but they have been involved in different physiological and pathological conditions. In particular, MC infiltration has been shown in several types of human tumors and in animal cancer models. Nevertheless, the role of MCs in the tumor microenvironment is still debated because they have been associated either to good or poor prognosis depending on tumor type and tissue localization. This dichotomous role relies on MC capacity to secrete a broad spectrum of molecules with modulatory functions, which may condition the final tumor outcome also promoting angiogenesis and tissue remodeling. In this review, we analyze the multifaceted role of mast cell in tumor progression and inhibition considering their ability to interact with: i) immune cells, ii) tumor cells and iii) the extracellular matrix. Eventually, the current MC targeting strategies to treat cancer patients are discussed. Deciphering the actual role of MCs in tumor onset and progression is crucial to identify MC-targeted treatments aimed at killing cancer cells or at making the tumor vulnerable to selected anti-cancer drugs.

Antagonism of histamine H4 receptors exacerbates clinical and pathological signs of experimental autoimmune encephalomyelitis

BACKGROUND AND PURPOSE

The histamine H4 receptor has a primary role in inflammatory functions, making it an attractive target for the treatment of asthma and refractory inflammation. These observations suggested a facilitating action on autoimmune diseases. Here we have assessed the role of H4 receptors in experimental autoimmune encephalomyelitis (EAE) a model of multiple sclerosis (MS).

EXPERIMENTAL APPROACH

We induced EAE with myelin oligodendrocyte glycoprotein (MOG35-55 ) in C57BL/6 female mice as a model of MS. The histamine H4 receptor antagonist 5-chloro-2-[(4-methylpiperazin-1-yl)carbonyl]-1H-indole (JNJ7777120) was injected i.p. daily starting at day 10 post-immunization (D10 p.i.). Disease severity was monitored by clinical and histopathological evaluation of inflammatory cells infiltrating into the spinal cord, anti-MOG35-55 antibody production, assay of T-cell proliferation by [(3) H]-thymidine incorporation, mononucleate cell phenotype by flow cytometry, cytokine production by elisa assay and transcription factor quantification of mRNA expression.

KEY RESULTS

Treatment with JNJ7777120 exacerbated EAE, increased inflammation and demyelination in the spinal cord of EAE mice and increased IFN-γ expression in lymph nodes, whereas it suppressed IL-4 and IL-10, and augmented expression of the transcription factors Tbet, FOXP3 and IL-17 mRNA in lymphocytes. JNJ7777120 did not affect proliferation of anti-MOG35-55 T-cells, anti-MOG35-55 antibody production or mononucleate cell phenotype.

CONCLUSIONS AND IMPLICATIONS

H4 receptor blockade was detrimental in EAE. Given the interest in the development of H4 receptor antagonists as anti-inflammatory compounds, it is important to understand the role of H4 receptors in immune diseases to anticipate clinical benefits and also predict possible detrimental effects.

Histamine H₃ receptors, the complex interaction with dopamine and its implications for addiction

Histamine H₃ receptors are best known as presynaptic receptors inhibiting the release of histamine, as well as other neurotransmitters including acetylcholine and dopamine. However, in the dorsal and ventral striatum, the vast majority of H₃ receptors are actually located postsynaptically on medium sized spiny output neurons. These cells also contain large numbers of dopamine (D₁ and D₂) receptors and it has been shown that H₃ receptors form heterodimers with both D₁ and D₂ receptors. Thus, the anatomical localization of H₃ receptors suggests a complex interaction that could both enhance and inhibit dopaminergic neurotransmission. Dopamine, especially within the striatal complex, plays a crucial role in the development of addiction, both in the initial reinforcing effects of drugs of abuse, as well as in maintenance, relapse and reinstatement of drug taking behaviour. It is, therefore, conceivable that H₃ receptors can moderate the development and maintenance of drug addiction. In the present review, we appraise the current literature on the involvement of H₃ receptors in drug addiction and try to explain these data within a theoretical framework, as well as provide suggestions for further research.

Concomitant exposure to ovalbumin and endotoxin augments airway inflammation but not airway hyperresponsiveness in a murine model of asthma

Varying concentrations of lipopolysaccharide (LPS) in ovalbumin (OVA) may influence the airway response to allergic sensitization and challenge. We assessed the contribution of LPS to allergic airway inflammatory responses following challenge with LPS-rich and LPS-free commercial OVA. BALB/c mice were sensitized with LPS-rich OVA and alum and then underwent challenge with the same OVA (10 µg intranasally) or an LPS-free OVA. Following challenge, bronchoalveolar lavage (BAL), airway responsiveness to methacholine and the lung regulatory T cell population (Treg) were assessed. Both OVA preparations induced BAL eosinophilia but LPS-rich OVA also evoked BAL neutrophilia. LPS-free OVA increased interleukin (IL)-2, IL-4 and IL-5 whereas LPS-rich OVA additionally increased IL-1β, IL-12, IFN-γ, TNF-α and KC. Both OVA-challenged groups developed airway hyperresponsiveness. TLR4-deficient mice challenged with either OVA preparation showed eosinophilia but not neutrophilia and had increased IL-5. Only LPS-rich OVA challenged mice had increased lung Tregs and LPS-rich OVA also induced in vitro Treg differentiation. LPS-rich OVA also induced a Th1 cytokine response in human peripheral blood mononuclear cells.We conclude that LPS-rich OVA evokes mixed Th1, Th2 and innate immune responses through the TLR-4 pathway, whereas LPS-free OVA evokes only a Th2 response. Contaminating LPS is not required for induction of airway hyperresponsiveness but amplifies the Th2 inflammatory response and is a critical mediator of the neutrophil, Th1 and T regulatory cell responses to OVA.

Key mediators in the immunopathogenesis of allergic asthma

Asthma is described as a chronic inflammatory disorder of the conducting airways. It is characterized by reversible airway obstruction, eosinophil and Th2 infiltration, airway hyper-responsiveness and airway remodeling. Our findings to date have largely been dependent on work done using animal models, which have been instrumental in broadening our understanding of the mechanism of the disease. However, using animals to model a uniquely human disease is not without its drawbacks. This review aims to examine some of the key mediators and cells of allergic asthma learned from animal models and shed some light on emerging mediators in the pathogenesis allergic airway inflammation in acute and chronic asthma.

An NT4/TrkB-dependent increase in innervation links early-life allergen exposure to persistent airway hyperreactivity

Children who are exposed to environmental respiratory insults often develop asthma that persists into adulthood. In this study, we used a neonatal mouse model of ovalbumin (OVA)-induced allergic airway inflammation to understand the long-term effects of early childhood insults on airway structure and function. We showed that OVA sensitization and challenge in early life led to a 2-fold increase in airway smooth muscle (ASM) innervation (P<0.05) and persistent airway hyperreactivity (AHR). In contrast, OVA exposure in adult life elicited short-term AHR without affecting innervation levels. We found that postnatal ASM innervation required neurotrophin (NT)-4 signaling through the TrkB receptor and that early-life OVA exposure significantly elevated NT4 levels and TrkB signaling by 5- and 2-fold, respectively, to increase innervation. Notably, blockade of NT4/TrkB signaling in OVA-exposed pups prevented both acute and persistent AHR without affecting baseline airway function or inflammation. Furthermore, biophysical assays using lung slices and isolated cells demonstrated that NT4 was necessary for hyperreactivity of ASM induced by early-life OVA exposure. Together, our findings show that the NT4/TrkB-dependent increase in innervation plays a critical role in the alteration of the ASM phenotype during postnatal growth, thereby linking early-life allergen exposure to persistent airway dysfunction.

Histamine induces chemotaxis and phagocytosis in murine bone marrow-derived macrophages and RAW 264.7 macrophage-like cells via histamine H4-receptor

OBJECTIVE

Expression and function of histamine H4-receptor, an immunomodulatory receptor involved in inflammatory diseases, on murine macrophages, which are vital for immunity, were investigated.

MATERIALS AND METHODS

The expression pattern of histamine receptors on bone marrow-derived macrophages of BALB/c mice and on RAW 264.7 cells was studied at the mRNA level by reverse transcription polymerase chain reaction. The functional relevance of histamine receptors was investigated by analyzing histamine-induced chemotaxis and phagocytosis in the presence of histamine receptor antagonists mepyramine (histamine H1-receptor), famotidine (histamine H2-receptor), thioperamide (histamine H3/4-receptors) and JNJ7777120 (histamine H4-receptor).

RESULTS

Both bone marrow-derived macrophages and RAW 264.7 cells express mRNA for histamine H1-receptor and histamine H4-receptor. Residual amounts of histamine H2-receptor mRNA are found in bone marrow-derived macrophages only. In both cellular models, histamine induced chemotaxis and phagocytic activity, which was reduced by thioperamide as well as by JNJ 7777120, but not by mepyramine or famotidine.

CONCLUSION

In murine bone marrow-derived macrophages and RAW 264.7 macrophage-like cells histamine H4-receptor mediates chemotaxis and phagocytic activity.

A new approach for the study of lung smooth muscle phenotypes and its application in a murine model of allergic airway inflammation

Phenotypes of lung smooth muscle cells in health and disease are poorly characterized. This is due, in part, to a lack of methodologies that allow for the independent and direct isolation of bronchial smooth muscle cells (BSMCs) and vascular smooth muscle cells (VSMCs) from the lung. In this paper, we describe the development of a bi-fluorescent mouse that permits purification of these two cell populations by cell sorting. By subjecting this mouse to an acute allergen based-model of airway inflammation that exhibits many features of asthma, we utilized this tool to characterize the phenotype of so-called asthmatic BSMCs. First, we examined the biophysical properties of single BSMCs from allergen sensitized mice and found increases in basal tone and cell size that were sustained ex vivo. We then generated for the first time, a comprehensive characterization of the global gene expression changes in BSMCs isolated from the bi-fluorescent mice with allergic airway inflammation. Using statistical methods and pathway analysis, we identified a number of differentially expressed mRNAs in BSMCs from allergen sensitized mice that code for key candidate proteins underlying changes in matrix formation, contractility, and immune responses. Ultimately, this tool will provide direction and guidance for the logical development of new markers and approaches for studying human lung smooth muscle.