Presence of histaminase in fetal calf sera

Histamine H3 receptor in primary mouse microglia inhibits chemotaxis, phagocytosis, and cytokine secretion

Histamine is a physiological amine which initiates a multitude of physiological responses by binding to four known G-protein coupled histamine receptor subtypes as follows: histamine H1 receptor (H1 R), H2 R, H3 R, and H4 R. Brain histamine elicits neuronal excitation and regulates a variety of physiological processes such as learning and memory, sleep-awake cycle and appetite regulation. Microglia, the resident macrophages in the brain, express histamine receptors; however, the effects of histamine on critical microglial functions such as chemotaxis, phagocytosis, and cytokine secretion have not been examined in primary cells. We demonstrated that mouse primary microglia express H2 R, H3 R, histidine decarboxylase, a histamine synthase, and histamine N-methyltransferase, a histamine metabolizing enzyme. Both forskolin-induced cAMP accumulation and ATP-induced intracellular Ca(2+) transients were reduced by the H3 R agonist imetit but not the H2 R agonist amthamine. H3 R activation on two ubiquitous second messenger signalling pathways suggests that H3 R can regulate various microglial functions. In fact, histamine and imetit dose-dependently inhibited microglial chemotaxis, phagocytosis, and lipopolysaccharide (LPS)-induced cytokine production. Furthermore, we confirmed that microglia produced histamine in the presence of LPS, suggesting that H3 R activation regulate microglial function by autocrine and/or paracrine signalling. In conclusion, we demonstrate the involvement of histamine in primary microglial functions, providing the novel insight into physiological roles of brain histamine.

The expression and function of histamine H₃ receptors in pancreatic beta cells

BACKGROUND AND PURPOSE

Histamine and its receptors in the CNS play important roles in energy homeostasis. Here, we have investigated the expression and role of histamine receptors in pancreatic beta cells, which secrete insulin.

EXPERIMENTAL APPROACH

The expression of histamine receptors in pancreatic beta cells was examined by RT-PCR, Western blotting and immunostaining. Insulin secretion assay, ATP measurement and calcium imaging studies were performed to determine the function and signalling pathway of histamine H₃ receptors in glucose-induced insulin secretion (GIIS) from MIN6 cells, a mouse pancreatic beta cell line. The function and signalling pathway of H₃ receptors in MIN6 cell proliferation were examined using pharmacological assay and Western blotting.

KEY RESULTS

Histamine H₃ receptors were expressed in pancreatic beta cells. A selective H₃ receptor agonist, imetit, and a selective inverse H₃ receptor agonist, JNJ-5207852, had inhibitory and facilitatory effects, respectively, on GIIS in MIN6 cells. Neither imetit nor JNJ-5207852 altered intracellular ATP concentration, or intracellular calcium concentration stimulated by glucose and KCl, indicating that GIIS signalling was affected by H3 receptor signalling downstream of the increase in intracellular calcium concentration. Moreover, imetit attenuated bromodeoxyuridine incorporation in MIN6 cells. The phosphorylation of cAMP response element-binding protein (CREB), which facilitated beta cell proliferation, was inhibited, though not significantly, by imetit, indicating that activated H₃ receptors inhibited MIN6 cell proliferation, possibly by decreasing CREB phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Histamine H₃ receptors were expressed in mouse beta cells and could play a role in insulin secretion and, possibly, beta cell proliferation.

Activation of basophils by the double-stranded RNA poly(A:U) exacerbates allergic inflammation

BACKGROUND

It is commonly acknowledged that asthma is exacerbated by viral infections. On the other hand, basophil infiltration of lung tissues has been evidenced postmortem in cases of fatal disease, raising the question of a possible link between these two observations.

OBJECTIVES

Herein, we addressed the relationship between asthma exacerbation by viral infection and basophil activation and expansion by investigating how stimulation with the dsRNA polyadenylic/polyuridylic acid [poly(A:U)] affected basophil activities and recruitment in an allergic airway inflammation model.

METHODS

The effect of dsRNA on basophils was assessed by measuring the cytokine levels produced upon stimulation. We used an OVA-induced experimental model of allergic asthma. Airway hyperreactivity, recruitment of infiltrating cells, and cytokine production were determined in the lung of mice having received poly(A:U), as compared with untreated controls. The exacerbating effect of basophils was assessed both by adoptive transfer of poly(A:U)-treated basophils and by their in vivo depletion with Ba103 antibody.

RESULTS

We found that in vitro treatment with poly(A:U) increased basophil functions by inducing TH 2-type cytokine and histamine production, whereas in vivo treatment increased peripheral basophil recruitment. Furthermore, we provide the first demonstration for increased infiltration of basophils in the lung of mice suffering from airway inflammation. In this model, disease symptoms were clearly exacerbated upon adoptive transfer of basophils exposed to poly(A:U), relative to their unstimulated counterpart. Conversely, in vivo basophil depletion alleviated disease syndromes, thus validating the transfer data.

CONCLUSIONS

Our findings provide the first evidence for airway inflammation exacerbation by basophils following dsRNA stimulation.

Histamine-cytokine connection in immunity and hematopoiesis

A number of recent studies have led to a reappraisal of the functional capacities of histamine in immunity and hematopoiesis. This change of perspective was provided by the following findings: (1) the evidence for multiple cellular sources of histamine, differing from mature basophils and mast cells by their ability to newly synthesize and liberate the mediator without prior storage, (2) the discovery of a novel histamine receptor (H4R), preferentially expressed on hematopoietic and immunocompetent cells, (3) the potential intracellular activity of histamine through cytochrome P450 and (4) the demonstration of a histamine-cytokine cross-talk. Indeed, cytokines not only modulate the degranulation process of histamine but also control its neosynthesis by the histamine-forming enzyme, histidine decarboxylase (HDC), at transcriptional and post-transcriptional levels. In turn, histamine intervenes in the intricate cytokine network, regulating cytokine production by immune cells through distinct receptors signaling distinct biological effects. This type of regulation is particularly relevant in the context of TH1/TH2 differentiation, autoimmunity and tumor immunotherapy.

Thrombopoietin induces histidine decarboxylase gene expression in c-mpl transfected UT7 cells

The leukemic cell line UT7 is endowed with both megakaryocyte and basophil differentiation potential, as judged by its capacity to respond to PMA by displaying megakaryocytic and basophilic markers and to produce histamine by neosynthesis. Herein, we addressed the question whether the biological activities characteristic of basophil differentiation were still induced when c-mpl-transfected UT7 cells received a specific megakaryocytic differentiation signal delivered by thrombopoietin (TPO). Surprisingly, we found that histamine synthesis did effectively occur in response to the growth factor. This activity was not associated with megakaryopoiesis since it was not detected in megakaryocytes generated from CD34(+) cells cultured in the presence of TPO. Comparing different c-mpl-transfected cell lines, we found that the amount of histamine generated in response to TPO correlated with their responsiveness to PMA, but not with their level of c-mpl expression, thus revealing an intrinsic basophil differentiation potential. Both PMA- and TPO-induced histamine synthesis was reduced by PKC and MEKs inhibitors, indicating that the induction occurred through a common signalling pathway.

Modulation of histidine decarboxylase activity and cytokine synthesis in human leukemic cell lines: relationship with basophilic and/or megakaryocytic differentiation

In the present study, we show that UT7D1 cells, derived from the pluripotent cell line UT7, express high levels of histidine decarboxylase (HDC) mRNA spontaneously. These cells conserve the ability to differentiate into megakaryocytes upon stimulation with PMA, while greatly increasing their HDC activity. We provide evidence that enhanced HDC activity reflects the basophil rather than the megakaryocytic differentiation potential of UT7DI cells. Indeed, in addition to HDC mRNA, they express spontaneously several other mRNA coding for molecules present in basophils (FcepsilonRI, CCR3, IL-4Ralpha, IL-5Ralpha). Furthermore, the basophil antigen Bsp-1 is displayed on the surface of some UT7D1 cells in response to PMA concomitantly with increased histamine synthesis and mRNA expression of typical basophil-derived cytokines (IL-6, IL-4, and IL-13). Nevertheless, PMA cannot sustain the differentiation of this lineage, because mRNAs for basophil markers gradually diminish during long-term culture, whereas molecules associated with the megakaryocytic lineage remain prominent. In support of the notion that HDC activity is not related with megakaryopoiesis, we show that PMA-induced CD41 expression and PDGF transcription occurs in the K562 cells, though neither HDC mRNA nor any known basophil marker are expressed in these conditions. In contrast, all these markers are expressed in the basophilic leukemia cell line KU812F. Interestingly, the megakaryocytic cell line HEL produces also substantial amounts of histamine and expresses FcepsilonRI, thus revealing its basophil differentiation potential. HEL as well as KU812F need not be stimulated with PMA to react with Bsp-1 mAb, suggesting that they are more engaged into the basophil differentiation scheme than UT7D1. Other leukemic cell lines unrelated to the megakaryocyte or basophil lineage, like HL60 and U937 do neither synthesize histamine nor express basophil markers before or after PMA stimulation. To our knowledge, this is the first evidence for a factor-dependent cell line with megakaryocyte/basophil bipotentiality with which early stages of basophil commitment can be analyzed.

Histamine-producing cell-stimulating activity. A biological activity shared by interleukin 3 and granulocyte-macrophage colony-stimulating factor

The histamine-producing cell-stimulating factor (HCSF) was first described as a lymphokine which is produced during secondary mixed leukocyte culture and which induces increased histamine synthesis by murine hematopoietic cells. It has been shown that it is different from interleukin 3 (IL 3), despite the fact that pure IL 3 expresses HCSF activity. Our results provide evidence that this factor (constitutively produced by the P388 D1 cell line) is identical with granulocyte-macrophage colony-stimulating factor (GM-CSF) i.e.: (a) physiochemical properties of HCSF and GM-CSF, such as molecular weight, isoelectric charge, hydrophobicity and behavior during affinity chromatography, are indistinguishable and both activities coelute during all biochemical purification procedures; (b) increased bone marrow cell histamine synthesis induced by P388 D1-derived HCSF is inhibited by anti-GM-CSF antiserum; (c) the GM-CSF cDNA probe hybridizes with a poly(A)+RNA from P388 D1 cells while no hybridizing signal was obtained with poly(A)+RNA from WEHI-3 and from P815 cells. On the other hand, the IL 3 cDNA probe hybridizes with a 1.0-kb poly(A)+RNA from WEHI-3 but not with those from P388 D1 and P815. Moreover, well known sources of GM-CSF, such as lung conditioned medium and semi-purified GM-CSF from phytohemagglutinin-induced supernatant of the murine T lymphoma LBRM-33-5 A4 (preparation devoid of IL 3), as well as recombinant murine GM-CSF, induce increased histamine synthesis by hematopoietic cells. All these results demonstrate that, in our culture conditions, the P388 D1 cell line spontaneously produces GM-CSF which is responsible for the P388 D1-induced HCS activity. Consequently, the latter is a property shared by the two distinct hematopoietic growth factors acting on the less committed cells, i.e. IL 3 and GM-CSF, whereas M-CSF or G-CSF are unable to induce histamine production. Interestingly, IL-4 which is known to support established mast cell line proliferation cannot induce HCS activity. In addition, none of the other cytokines tested, such as IL 1, IL 2, interferons or tumor necrosis factor can express HCS activity. This expression seems to be a specific property of IL 3 and GM-CSF.

Cellular immune functions in patients with primary hyperparathyroidism: effects of histamine and cimetidine

The possibility of a link between parathyroid hyperfunction and cellular immune functions was studied in primary hyperparathyroid (1 degree HP) patients. The effect of cimetidine on lymphocyte functions in 1 degree HP patients and control subjects was also investigated. Histamine-induced suppressor activity of lymphocytes from 1 degree HP patients was significantly greater than that of controls. Cimetidine addition to both normal and 1 degree HP lymphocyte cultures abolished histamine-induced suppression. In vivo administration of cimetidine, while ineffective towards normal lymphocytes, depressed phytohemagglutinin stimulation of 1 degree HP lymphocytes, indicating possible immunological damage caused by this drug, which is frequently used in the treatment of patients with 1 degree HP.

A high-sampling-rate automated continuous-flow fluorometric technique for the analysis of nanogram levels of histamine in biological samples

An automated continuous-flow technique of the modified fluorometric method of Shore was devised to obtain a high sampling rate (60/h) and a sensitive measurement of the histamine content of biological samples. The volumes of samples range from 50 to 500 microliter. A linear relationship is obtained from 0 to 5 micrograms/ml (histamine base) with a good specificity. The limit of detection is 25 pg (actual amount). The coefficient of variation is less than or equal to +/- 5% for concentrations of less than 2 ng/ml and from +/- 0.2 to +/- 2% for higher concentrations. With this technique more sensitive, more specific, and twice as fast as similar ones, histamine content in 350-400 unknowns can be measured routinely in a working day. It has been used for more than 4 years and has proven to be a reliable and useful tool for the numerous research studies in which histamine is involved: immunology, allergy, pharmacology, dermatology, cancer, nutrition.