Dynamics of myeloid cell populations during relapse-preventive immunotherapy in acute myeloid leukemia.

Relapse of leukemia in the postchemotherapy phase contributes to the poor prognosis and survival in patients with acute myeloid leukemia (AML). In an international phase IV trial (ClinicalTrials.gov; NCT01347996), 84 patients with AML in first complete remission who had not undergone transplantation received immunotherapy with histamine dihydrochloride (HDC) and low-dose IL-2 with the aim of preventing relapse. The dynamics of myeloid cell counts and expression of activation markers was assessed before and after cycles of immunotherapy and correlated with clinical outcome in terms of relapse risk and survival. During cycles, a pronounced increase in blood eosinophil counts was observed along with a reduction in monocyte and neutrophil counts. A strong reduction of blood monocyte counts during the first HDC/IL-2 treatment cycle predicted leukemia-free survival. The HDC component of the immunotherapy exerts agonist activity at histamine type 2 receptors (H2Rs) that are expressed by myeloid cells. It was observed that the density of H2 R expression in blood monocytes increased during cycles of immunotherapy and that high monocyte H2R expression implied reduced relapse risk and improved overall survival. Several other activation markers, including HLA-DR, CD86, and CD40, were induced in monocytes and dendritic cells during immunotherapy but did not predict clinical outcome. In addition, expression of HLA-ABC increased in all myeloid populations during therapy. A low expression of HLA-ABC was associated with reduced relapse risk. These results suggest that aspects of myeloid cell biology may impact clinical benefit of relapse-preventive immunotherapy in AML.

Histamine Receptor Expression in the Gastrointestinal Tract of Dogs.

Histamine is an important mediator of many physiological processes including gastrointestinal function that acts via four different histamine receptors (H1R to H4R). Elevated histamine levels and increased HR messenger ribonucleic acid (mRNA) have been shown in humans with gastrointestinal disorders such as irritable bowel syndrome or allergic intestinal diseases. As there is limited knowledge concerning the distribution of histamine receptors (HR) in dogs, one aim of this study was to investigate the expression of histamine 1 receptor (H1R), histamine 2 receptor (H2R) and histamine 4 receptor (H4R) in the canine gastrointestinal tract at protein level using immunohistochemistry. Histamine 1 receptor, H2R and H4R were widely expressed throughout the canine gastrointestinal tract including epithelial, mesenchymal, neuronal and immune cells. In addition, in situ hybridisation was established for detecting canine H4R mRNA. Results showed H4R mRNA to be present in enterocytes, lamina propria immune cells and submucosal plexus in the duodenum and colon of nearly all investigated animals. The results elucidate the importance of HR in the canine gut and represent the basis for investigating their possible impact on canine inflammatory gastrointestinal disorders.

Histamine receptors of cones and horizontal cells in Old World monkey retinas.

In primates the retina receives input from histaminergic neurons in the posterior hypothalamus that are active during the day. In order to understand how this input contributes to information processing in Old World monkey retinas, we have been localizing histamine receptors (HR) and studying the effects of histamine on the neurons that express them. Previously, we localized HR3 to the tips of ON bipolar cell dendrites and showed that histamine hyperpolarizes the cells via this receptor. We raised antisera against synthetic peptides corresponding to an extracellular domain of HR1 between the 4th and 5th transmembrane domains and to an intracellular domain near the carboxyl terminus of HR2. Using these, we localized HR1 to horizontal cells and a small number of amacrine cells and localized HR2 to puncta closely associated with synaptic ribbons inside cone pedicles. Consistent with this, HR1 mRNA was detected in horizontal cell perikarya and primary dendrites and HR2 mRNA was found in cone inner segments. We studied the effect of 5 µM exogenous histamine on primate cones in macaque retinal slices. Histamine reduced I(h) at moderately hyperpolarized potentials, but not the maximal current. This would be expected to increase the operating range of cones and conserve ATP in bright, ambient light. Thus, all three major targets of histamine are in the outer plexiform layer, but the retinopetal axons containing histamine terminate in the inner plexiform layer. Taken together, the findings in these three studies suggest that histamine acts primarily via volume transmission in primate retina.

Histamine stimulates interleukin-6 production through histamine H1 receptors in human amnion cells.

BACKGROUND/AIMS: Previous studies have stated that maternal allergic diseases are associated with increased risk of preterm labor/delivery, but the underlying mechanisms remain unclear. This study tested the hypothesis that histamine induces interleukin (IL)-6 production in amnion cells. METHODS: Using cultured human amnion cells, we examined expression of histamine receptors and effects of histamine on IL-6 production. RESULTS: Reverse transcription-polymerase chain reaction and Western blotting revealed expression of histamine H1 receptor (H1R) and H2 receptor (H2R) in human amnion. Histamine stimulation significantly increased concentrations of IL-6 in conditioned medium, as did tumor necrosis factor-alpha and IL-1beta in positive controls. In addition, the H1R antagonist olopatadine significantly blocked histamine-induced production of IL-6, whereas the H2R antagonist ranitidine did not. CONCLUSION: Histamine appears to induce IL-6 production through H1R in human amnion cells.

Decrease in expression of histamine H2 receptors by human amniotic epithelial cells during differentiation into pancreatic beta-like cells.

OBJECTIVE AND DESIGN: Considering the role of histaminergic pathway in the differentiation of stem cells, we compared expression patterns of H(1) and H(2) receptors in the human amniotic epithelial cells (HAEC) culture at different stages of nicotinamide-induced differentiation into PBLC with the control HAEC. MATERIAL AND METHODS: HAEC isolated after term pregnancies (N = 12) were cultured in vitro. Altogether, 72 cultures were established. The culture medium in the studied group was supplemented on Day 5 with nicotinamide (10 mM). C-peptide concentration in the medium collected every 3 days for 15 days was determined immunoenzymatically as a marker of differentiation. At the same intervals the cultures were formalin-fixed and paraffinembedded for H(1) and H(2) receptors immunostaining. Quantitative immunohistochemistry was applied for evaluation of H(1) and H(2) expression. RESULTS: C-peptide was detected on Day 6 and the levels were kept gradually increased until Day 12, then stayed at almost the same level, 3.7-fold higher than initially. Expression of H(2) was unchanged until Day 9 after nicotinamide addition, then was significantly (p < 0.05) decreased and amounted (mean % value for the measurements performed on Day 12 and Day 15, +/-SEM) 49.73 +/- 11.03 of the reference value obtained in control HAEC. CONCLUSION: Variable expression of H(2) during nicotinamide-induced differentiation of HAEC into PBLC may define a time-point, indicating involvement of histamine at the earlier stages.

Expression of histamine receptors (H(1), H(2), and H(3)) in the rabbit endolymphatic sac: an immunohistochemical study.

OBJECTIVE: The endolymphatic sac (ES) is part of the membranous labyrinth of the inner ear. Its central role in immunologic activity within the inner ear has been confirmed by numerous studies. The aim of this study was to investigate the expression of histamine receptors (H(1), H(2), H(3)) in the rabbit ES. METHODS: A total of 10 healthy male New Zealand white rabbits weighing 2 to 3 kg were used in the experiments. For immunohistochemical studies, immunostaining was performed according to the avidin-biotin-peroxidase complex technique. RESULTS: Serial sections of the ES of rabbits revealed the presence of H(1), H(2), and H(3) receptor immunoreactivity. Immunoreactive cells for all H(1), H(2), and H(3) were found in the epithelial and subepithelial layers of the duct and the proximal ES. In conclusion, this study showed the immunohistochemical localization of H(1), H(2), and H(3) receptors in the ES of rabbits. These receptors may be important in the homeostasis of the inner ear. In addition, they may be target receptors in the medical treatment of inner ear disorders such as endolymphatic hydrops.

Histamine improves antigen uptake and cross-presentation by dendritic cells.

Previous studies have shown that histamine is able to modulate the function of dendritic cells (DCs). Histamine seems to be required for the normal differentiation of DCs. Moreover, it is capable of stimulating the chemotaxis of immature DCs and of promoting the differentiation of T CD4+ cells into a Th2 profile. In this study, we analyzed whether histamine was able to modulate endocytosis and cross-presentation mediated by immature DCs. Our results show that both functions are stimulated by histamine. Endocytosis of soluble HRP and FITC-OVA and cross-presentation of soluble OVA were markedly increased by histamine. Interestingly, stimulation of endocytosis and cross-presentation appeared to be mediated through different histamine receptors. In fact, the enhancement of endocytosis was prevented by the histamine2 receptor (H2R) antagonist cimetidine, whereas the stimulation of cross-presentation was prevented by the H3R/H4R antagonist thioperamide. Of note, contrasting with the observations made with soluble Ags, we found that histamine did not increase either the uptake of OVA-attached to latex beads, or the cross-presentation of OVA immobilized on latex beads. This suggests that the ability of histamine to increase endocytosis and cross-presentation is dependent on the Ag form and/or the mechanisms through which the Ag is internalized by DCs. Our results support that histamine may favor cross-presentation of soluble allergens by DCs enabling the activation of allergen-specific T CD8+ cells, which appears to play an important role in the development of allergic responses in the airway.

Histamine H2 receptor overexpression induces U937 cell differentiation despite triggered mechanisms to attenuate cAMP signalling.

Knowing that cell-surface receptors that recognize and respond to extracellular stimuli are key components for the regular communication between individual cells required for the survival of any living organism, the aim of the present work was to investigate the effect of H2R overexpression on the U937 signal transduction pathway and its consequences on cell proliferation and differentiation. The overexpression of H2R led to an increase in cAMP basal levels, a leftward shift of agonist concentration-response curves, and similar maximal response to agonist treatment, suggesting that overexpressed H2Rs act as functional spare receptors. In this system cells triggered several mechanisms tending to restore cAMP basal levels to those of the naïve cells. H2R overexpression induced PDE activity stimulation and GRK2 overexpression. In spite of the onset of these regulatory mechanisms, H2 agonist and rolipram treatments induced the terminal differentiation of the H2R overexpressed clone, conversely to the naïve cells. Present findings show that stably H2R overexpression alters cAMP signalling as the result of not only the amounts of second messenger generated but also the activation or upregulation of various components of signalling cascade, leading to an adapted biologically unique system. This adaptation may represent an advantage or a disadvantage, depending on the biological system, but in any case, the existence of compensatory mechanisms should be considered when a clinical treatment is designed.

Histamine H1 and H2 receptors but not H4 receptors are upregulated during bone marrow regeneration.

The role of histamine receptors in radiation-induced bone marrow (BM) regeneration was investigated with aspects of functional genomics. H1R and H2R mRNA expression increased during regeneration in both histidine decarboxylase knockout (HDC-/-) and wild type (HDC+/+) mice, though to a lesser extent in HDC-/- mice. H4R mRNA expression was downregulated in both groups. Mainly CD34+ cells were responsible for the elevation of intracellular histamine and HDC content in HDC+/+ BM cell populations. The differential changes in the expression of its receptors, and also its elevated levels in hematopoietic progenitors support the regulatory role of histamine in BM regeneration, that could be further explored by future gene expression studies.

Alteration of intracellular histamine H2 receptor cycling precedes antagonist-induced upregulation.

Long-term administration of a histamine H2 receptor (H2R) antagonist (inverse agonist) induces upregulation of H2R in parietal cells, which may be relevant to the rebound hypersecretion of gastric acid that occurs after withdrawal of treatment. The mechanisms underlying this effect are unknown. We hypothesized that the H2R upregulation could be related to receptor trafficking and used H2R-green fluorescent protein (H2R-GFP) to test the hypothesis. Human H2R-GFP was generated and functionally expressed in HEK-293 cells. Binding of the H2R antagonist [3H]tiotidine was performed to quantify H2R expression, and H2R-GFP was imaged in living cells by confocal and evanescent wave microscopy. The binding affinity of [3H]tiotidine was not significantly different between H2R-GFP- and wild-type H2R-expressing HEK-293 cells, both of which had constitutive activity of adenylate cyclase. Visualization of H2R-GFP revealed that the agonist-induced H2R internalization and the antagonist-induced recycling of the internalized H2R from the recycling endosome within 2 h. Long exposure to the antagonist increased GFP fluorescence in the plasma membrane and also induced upregulation of H2R-GFP estimated by the binding assay, whereas long exposure to the agonist enhanced degradative trafficking of H2R-GFP. We examined whether the upregulation reflected an increase in receptor synthesis. Treatment with antagonist did not augment H2R mRNA, and subsequent inhibition of protein synthesis by cycloheximide had no effect on H2R upregulation. These findings suggested that upon exposure to an antagonist (inverse agonist), the equilibrium between receptor endocytosis and recycling is altered before H2R upregulation, probably via suppressing H2R degradation.

Site specific therapy: an integrative approach to treating melanoma.

There have been many proposed theories for effectively treating melanoma, especially through the regulation of histamine. Histamine has been proven to be a major regulator of the immune system's T-helper cell subset balance and major shifts in this balance towards TH2 cytokines have contributed to diseases such as asthma, lupus and cancer. Histamine also causes suppression of interferon-induced proteins needed for anti-tumor response and activates T-suppressor cell function in cancers such as squamous cell carcinoma and melanoma. Scientific evidence has suggested the possibility of an anthistamine approach as treatment to these diseases and for melanoma, there has been great promise. This is due to the fact that melanotic cells have been elucidated to express histamine receptors and as a result, regulation of histamine could occur specifically at the site of these epidermal growths. Another factor to consider is how effective an inflammatory response can be when combined with regulation of histamine. Inflammation is a very powerful tool against pathogenic environments by causing cytokine recruitment and migration of dendritic cells to infected sites. Adequate stimulation of an inflammatory response at the specific site of any cancerous region would greatly weaken its evasive mechanisms. However, there are no reports showing high efficacy utilizing the benefits of regulating inflammation and histamine that could cause TH1 subset levels to predominate, down-regulate T-suppressor cells, up-regulate interferon-induced proteins and properly sustain migration of dendritic cells concurrently. These benefits have been proven in separate instances for a range of diseases but have not been assessed as a combined modality for melanoma therapy. Therefore successful melanoma treatment should integrate these principles involving: the use of H2 antagonists for preventing the negative effects of histamine, monoclonal antibodies to ensure an effective dendritic cell response, and routine pro-inflammatory induction at the specific site of the melanotic tissue to ensure recognition of the cancer that has evaded immunity.

Granulocyte macrophage-colony stimulating factor increases the expression of histamine and histamine receptors in monocytes/macrophages in relation to arteriosclerosis.

OBJECTIVE: To study the effect of granulocyte macrophage-colony-stimulating factor (GM-CSF) on histamine metabolism in arteriosclerosis, the expression of histidine decarboxylase (HDC; histamine-producing enzyme), histamine receptors 1 and 2 (HH1R and HH2R), and GM-CSF was investigated in human and mouse arteriosclerotic carotid arteries. Furthermore, the molecular mechanisms of GM-CSF-induced HDC and HH1R expression in monocytic U937 cells were investigated. METHODS AND RESULTS: Immunohistochemistry showed that atherosclerotic human coronary and mouse ligated carotid arteries contained HDC-expressing macrophages. Gene expression of HDC, HH1R, HH2R, and GM-CSF was also detected in the lesions. In U937 cells, GM-CSF enhanced histamine secretion and gene expression of HDC and HH1R. A promoter assay showed that GM-CSF enhanced gene transcription of HDC and HH1R but not HH2R. CONCLUSIONS: The present results indicate that HDC and HHR are expressed in arteriosclerotic lesion, and that GM-CSF induces HDC and HH1R expression in monocytes. Locally produced histamine might participate in atherogenesis by affecting the expression of atherosclerosis-related genes in monocytes and smooth muscle cells. The presence of histamine-producing macrophages and gene expression of histamine receptors and GM-CSF was demonstrated in arteriosclerotic lesions. In monocytic U937 cells, GM-CSF upregulated the expression of histamine and HH1R. Coordinated expression of histamine and its receptors by GM-CSF would participate in atherogenesis by affecting monocytic and SMC gene expression.

Retinoic acid enhances histamine content and H1 receptor expression in human neuroblastoma cell line Paju.

BACKGROUND: A human neuroblastoma cell line (Paju) was induced by retinoic acid (RA) to differentiate into neuron-like cells. MATERIALS AND METHODS: We studied the expression and the possible role of histamine receptors H1 and H2 in retinoic-acid mediated differentiation by semiquantitative RT-PCR. We studied the effect of exogeneously added RA on the morphological change of the human neuroblastoma cell line and the differentiation was followed by vimentine, glial fibrillary acidic protein (GFAP) and neurofilament (NF) immunostaining. We monitored the change of the histidine decarboxylase (HDC) expression and the histamine content during the RA treatment by immunoblot and flow cytometry methods. RESULTS: Our data showed that H1 and H2 histamine receptors are present on Paju cells. Ten nM RA markedly increased the H1 receptor expression of these cells, while the H2 expression was unchanged. CONCLUSION: In the RA-treated Paju cells, the histamine content increased compared to the untreated cells, suggesting that neuroblastoma-derived histamine is involved in the regulation of RA-induced in vitro differentiation by H1 receptors.

Polyclonal anti-histamine H2 receptor antibodies detect differential expression of H2 receptor protein in primary vascular cell types.

OBJECTIVE AND DESIGN: One of the factors defining cellular response might be the distribution and density of receptor subtypes on cell membranes. It was our aim to quantify and compare histamine H2 receptor expression in primary vascular cell types. We have therefore generated antibodies directed against the second extra-cellular loop of the H2 receptor. METHODS: The specificity of polyclonal anti-H2 receptor antibodies designed for this purpose was examined by Western blot analysis and immunohistochemistry. H2 receptor expression was quantified by ELISA. Regulation of H2 receptor gene expression was analyzed by competitive RT-PCR. RESULTS: Our results indicate that the polyclonal antibodies specifically interact with the histamine H2 receptor. Furthermore, utilizing these antibodies we were able to show significant differences in H2 receptor levels in human umbilical arterial and vein endothelial cells as well as smooth muscle cells. CONCLUSIONS: We conclude that the antibodies generated against the extra-cellular domain of the H2 receptor are specific and can be utilized to detect and quantify H2 receptor expression. Furthermore, the significant differences in H2 receptor expression in different vascular cell types might play a critical role in defining histamine induced cellular responses during physiological or pathophysiological processes.

Localisation of mRNAs for diamine oxidase and histamine receptors H1 and H2, at the feto-maternal interface of human pregnancy.

OBJECTIVE AND DESIGN: To localise mRNAs for the histamine receptors H1, H2 and H3, and for diamine oxidase, in the placenta and decidua of the human feto-maternal interface. MATERIALS AND METHODS: Complementary DNA for each mRNA of interest was amplified by polymerase chain reaction. Sub-cloned sequences were used to prepare probes for in situ hybridisation, and these were employed to localise the expression of mRNAs for histamine receptors H1 and H2, and for diamine oxidase. RESULTS: mRNA for histamine receptors H1 and H2, and for diamine oxidase could be detected at the feto-maternal interface of human pregnancy, and localised to both decidual and placental cells. CONCLUSION: The co-expression of these receptors and DAO is consistent with a role for histamine at the feto-maternal interface of human pregnancy.

Expression of receptors regulating gastric acidity in the developing sheep stomach.

Acid secretion first appears in the stomach during the later stages of fetal development. Gastric acid secretion is regulated by the stimulatory effects of gastrin, histamine, acetylcholine and the inhibitory actions of somatostatin on their respective receptors. A semi-quantitative reverse transcriptase-polymerase chain reaction method for the determination of changes in mRNA expression for these receptors was developed and correlated with known changes in gastric acidity. Glyceraldehyde-3-phosphate dehydrogenase (GAP-DH) was used as a reference and an internal standard. The antrum and fundus from four age groups were assayed: 80 days of gestation, 110 days of gestation, term (145 days) and adult animals. The CCK B/gastrin and the histamine (H(2)) receptor mRNA were significantly lower in samples from the fundus of fetuses, from 80 and 110 days of gestation when compared with the adult fundus. Histamine receptor mRNA in the antrum was also significantly lower in the 80 and 110 days of gestation samples relative to the term fetal antrum. Somatostatin II receptor mRNA levels in the antrum decreased with increasing age with no change in the fundus. These findings suggest that changes in receptor gene expression, may be responsible for the diminished gastric acidity and responsiveness observed in the fetal stomach.

Role of histamine in cardiac muscle function--an attempt at demonstrating the presence of intracellular histaminergic H2-type receptors.

BACKGROUND: Histamine is one of the biologically active substances that activate adenyl cyclase enzymatic system through H2 receptor. The aim of the study is demonstration of the presence of membranous histamine receptors in cardiomyocytes and determination of their role in function of the cardiac muscle cell. MATERIAL AND METHODS: The experiments were carried out on 20 rabbits divided into two experimental groups. Electric and mechanical activity of cardiac muscle trabecula was registered by glass microelectrodes' method in group I and by saccharose slit method in group II. RESULTS: In group I after administration of 2.5 microM x l-1 of histamine mean rhythm rate increased to 61 +/- 2.7 stimulations x min-1, contractile tone increased by 55.7 +/- 4.9% in relation to the control values, relaxation time shortened to 139.2 +/- 1.8 ms, while time to pike decreased to 229.6 +/- 2.5 ms. The following effects were observed after administration of 5 microM x l-1 of histamine: mean rhythm rate increased to 76.4 +/- 4.5 x min-1, amplitude of the potentials was unchanged, while their duration shortened to 227.7 +/- 3.2 ms, contractile tone increased by 122.4 +/- 12.9%, average. In group II contractile tone increased by mean 110%, time to pike decreased to 103 +/- 1.5 ms, while relaxation time--to 210.2 +/- 4.2 ms. Frequency of spontaneous stimulations as well as amplitude and duration of the action potential remained unchanged in all of the experiments. CONCLUSIONS: Positive chronotropic and inotropic action of histamine added to the extracellular fluid point to the presence of histaminergic receptor in rabbit's cardiac muscle. H2 histaminergic receptors are situated not only on the external surface of cellular membrane of rabbit's right heart atrium trabeculae, but also inside the cells. Experiments with histamine administration by the "cut end" method suggest that the role of intracellular H2 histaminergic receptors is associated with controlling the contractile processes of the cardiac muscle.

Histamine upregulates Th1 and downregulates Th2 responses due to different patterns of surface histamine 1 and 2 receptor expression.

Histamine, which acts via G protein-coupled receptors, is an important mediator of immediate hypersensitivity and is also able to influence the nature of T cell responses. We demonstrated that TH1 and Th2 cells express distinct surface histamine receptor patterns and that Th1-type responses are enhanced by histamine, whereas Th2-type responses are negatively regulated, due to different intracellular signals generated by histamine stimulation. These findings account for negative feedback regulation in a wide variety of pathologies.

Novel insights into histamine H2 receptor biology.

Histamine exerts multiple biological actions through one of three receptor subtypes (H1, H2, and H3). This review focuses on new developments regarding the structure and function of the H2 receptor. In addition to the important role this receptor plays in stimulating gastric acid secretion, recent studies have demonstrated that it is also involved in regulating gastrointestinal motility and intestinal secretion. The potential role of the H2 receptor in regulating cell growth and differentiation has also been added to the list of actions this biogenic amine may exert in both normal and transformed tissues. Molecular cloning of the gene indicates that it has the structural characteristics of a heptahelical G protein-linked receptor. Site-directed mutagenesis studies of this receptor reveal the presence of key amino acids within the third and fifth transmembrane domains that are critical for ligand recognition. Molecular approaches have also shed light on the structural components of the H2 receptor important in regulating desensitization and internalization. Although the H2 receptor was classically thought to couple to the adenylate cyclase pathway, recent work with the cloned receptor indicates that it can also activate the phosphoinositide signaling cascade through an independent G protein-dependent mechanism. The novel observation that histamine may stimulate c-fos gene expression lends further support to the possible role of this receptor in regulating cell growth and differentiation.