Michiko Iwase

Antigen-Specific T Cell Sensitization Is Impaired in IL-17-Deficient Mice, Causing Suppression of Allergic Cellular and Humoral Responses

Interleukin-17 (IL-17) is a proinflammatory cytokine produced by T cells. The involvement of IL-17 in human diseases has been suspected because of its detection in sera from asthmatic patients and synovial fluids from arthritic patients. In this study, we generated IL-17-deficient mice and investigated the role of IL-17 in various disease models. We found that contact, delayed-type, and airway hypersensitivity responses, as well as T-dependent antibody production, were significantly reduced in the mutant mice, while IL-17 deficiency of donor T cells did not affect acute graft-versus-host reaction. The results suggest that impaired responses were caused by the defects of allergen-specific T cell activation. Our findings indicate that IL-17 plays an important role in activating T cells in allergen-specific T cell-mediated immune responses.

Autoregulation of histamine release in medulla oblongata via H3-receptors in rabbits.

The release of histamine (HA) from the rostral ventrolateral medulla (RVL), the raphe nuclei (nR), and the solitary nucleus (nTS) was investigated in anesthetized rabbits using microdialysis and high-performance liquid chromatography. HA release upon electrical stimulation of the posterior hypothalamus (PH), where histaminergic cell bodies are located, was increased to 168% of the baseline level in the RVL (n = 6), 139% of the baseline level in the nR (n = 5), and 166% of the baseline level in the nTS (n = 4). Upon perfusion of thioperamide, an H3-receptor antagonist, via a microdialysis probe, HA release from the RVL, nR and nTS increased. The increase in HA release from the RVL, nR and nTS following thioperamide perfusion was suppressed by co-perfusion of thioperamide and an H3-receptor agonist, imetit. We found that HA is released from the RVL, nR and nTS, that the HA release from all three areas is increased upon stimulation of the PH, and that the HA release is locally influenced in opposite directions by thioperamide and imetit. These results suggest that HA release in the medulla oblongata is controlled by the PH and that H3-receptors participate in the autoregulation of HA release by providing negative feedback locally. Autoregulation of HA release via H3-receptors may be important for maintaining tonic output to the sympathetic nervous system.

Impaired ventilation and metabolism response to hypoxia in histamine H1 receptor-knockout mice.

The role of central histamine in the hypoxic ventilatory response was examined in conscious wild-type (WT) and histamine type1 receptor-knockout (H1RKO) mice. Hypoxic gas (7% O(2) and 3% CO(2) in N(2)) exposure initially increased and then decreased ventilation, referred to as hypoxic ventilatory decline (HVD). The initial increase in ventilation did not differ between genotypes. However, H1RKO mice showed a blunted HVD, in which mean inspiratory flow was greater than that in WT mice. O(2) consumption (V(O2)) and CO(2) excretion were reduced 10min after hypoxic gas exposure in both genotypes, but (V(O2)) was greater in H1RKO mice than in WT mice. The ratio of minute ventilation to (V(O2)) during HVD did not differ between genotypes, indicating that ventilation is adequately controlled according to metabolic demand in both mice. Peripheral chemoreceptor sensitivity did not differ between genotypes. We conclude that central histamine contributes via the H1 receptor to changes in metabolic rate during hypoxia to increase HVD in conscious mice.

Central histamine contributes to the inspiratory off-switch mechanism via H1 receptors in mice

Central histaminergic neurons are distributed in areas of the medulla and pons concerned with respiratory rhythm generation, but their effects on breathing pattern are unknown. We examined breathing pattern during hypercapnic responses in wild type (WT) and H1 receptor knockout (H1RKO) mice at 9-10 weeks of age before and after vagotomy. Minute ventilation increased with PaCO(2) increase equally in both genotypes; respiratory rate response was lower and tidal volume (V(T)) response higher in H1RKO mice than in WT mice. The V(T)-inspiratory time (T(I)) relation during hypercapnia was hyperbolic in both groups, with the curve in H1RKO mice shifted right-upward. After vagotomy, the V(T)-T(I) relation was a vertical line, which shifted right in H1RKO mice. We conclude that alterations of inspiratory off-switch and respiratory rhythm generation change breathing pattern without affecting central chemosensitivity in H1RKO. Histamine might affect breathing pattern centrally via H1 receptors.

Effects of Corticosteroid on the Expression of Thymus and Activation-Regulated Chemokine in a Murine Model of Allergic Asthma

Background: Thymus and activation-regulated chemokine (TARC; CCL17) is a lymphocyte-directed CC chemokine that specifically attracts T-helper (Th) 2 cells positive for the CC chemokine receptor 4 (CCR4+). Corticosteroids reduce airway inflammation, as reflected by reduced numbers of eosinophils and T cells and reduced expression of cytokines. We investigated TARC production and the inhibitory effects of corticosteroids on TARC expression in a murine model of allergic asthma. Methods: BALB/c mice were sensitized by intraperitoneal injection of ovalbumin (OVA) with alum. Once daily for 1 week, mice received injections of dexamethasone or 0.2 ml saline (control), then 1 h later inhaled aerosolized 1% OVA for 30 min. Mice were killed 24 h after OVA challenge for bronchoalveolar lavage and lung tissue examination. Results: TARC was expressed mainly in the bronchial epithelial cells. Dexamethasone attenuated OVA-induced airway eosinophilia, lymphocyte infiltration, and airway hyperresponsiveness. Dexamethasone also decreased TARC production in the bronchoalveolar lavage fluid and decreased expression of TARC mRNA and TARC protein in lung tissue. Conclusions: The corticosteroid dexamethasone inhibits TARC production in a murine model of allergic asthma in vivo. The beneficial effect of corticosteroids in bronchial asthma is due in part to their direct inhibitory effects on TARC production.

Posterior hypothalamic control of rabbit tracheal tension and involvement of central histaminergic neurons

The hypothalamus is involved in the control of the cardiovascular system, but airway tone is less well defined. In the posterior hypothalamus, histaminergic neuronal cell bodies are located. Effects of electrical stimulation in the posterior hypothalamus on tracheal tension and the cardiovascular system were examined in anesthetized, paralyzed and artificially ventilated rabbits. Tracheal tension was determined from pressure exerted on a balloon inserted in the trachea and measured by a pressure transducer. Electrical stimulation of the posterior hypothalamus caused tracheal tension to decrease, arterial blood pressure to increase, and mild tachycardia followed by bradycardia. The tracheal tension decrease induced by posterior hypothalamic stimulation was not affected by atropine nor by transection of either the superior laryngeal nerve or the vagus nerve, but was depressed by adrenoceptor blockade. Tracheal tension decrease was also reduced by pyrilamine, a histamine H1-receptor antagonist, administered into the fourth ventricle, but was not affected by cimetidine, a histamine H2-receptor antagonist. The stimulation sites where these effects were evoked were interspersed among the loci of histamine immunoreactive cell bodies previously reported. Results suggest that posterior hypothalamic neurons decrease tracheal tension through the sympathetic nervous system, and involve the histaminergic neurons in this route.

Vasopressin Neuron Activation and Fos Expression by Stimulation of the Caudal Ventrolateral Medulla

The present study demonstrates that projections ascending from the caudal ventrolateral medulla have direct effects on the expression of the immediate early gene c-fos and of the arginine-vasopressin gene in neurosecretory cells of the hypothalamic supraoptic nucleus. Intense Fos-like immunoreactivity (Fos-LI) was observed in many magnocellular neurons of the supraoptic nucleus after electrical stimulation of the caudal ventrolateral medulla. In sham-operated rats, Fos-LI was absent or present in very few magnocellular neurons in the supraoptic nucleus. Fos-LI was visible in neurons expressing arginine-vasopressin, and was seen rarely in oxytocin neurons by double-immunostaining method. This study showed that 76% of all Fos-positive cells were arginine-vasopressin immunoreactive, whereas only 4% of them showed oxytocin immunoreactivity in the supraoptic nucleus. With in situ hybridization, a high level of arginine-vasopressin mRNA was noted in the supraoptic nucleus 3 h after stimulation of the caudal ventrolateral medulla; the expression was highest 6 h after the stimulation compared with the same region in sham-operated animals. These findings suggest that noradrenaline, released from the axon terminals originating from the caudal ventrolateral medulla, may participate in the regulation of gene transcription of arginine-vasopressin in response to physiological stimuli.

Thyrotropin-releasing hormone-like immunoreactive neurons in rabbit medulla oblongata

Thyrotropin-releasing hormone-like immunoreactive (TRH-LI) neuronal cell bodies and processes were identified by using the peroxidase-antiperoxidase method in the medullar oblongata of rabbits. TRH-LI cell bodies were mainly distributed in the ventral medulla (paraolivary and parapyramidal regions), and caudal raphe nuclei (nucleus raphe obscurus and nucleus raphe pallidus). TRH-LI processes with varicosities were densely distributed in the solitary nucleus, dorsal motor nucleus of the vagus nerve and area postrema. TRH-LI processes appeared to be in contact with unlabelled cell bodies in the dorsal motor nucleus of the vagus nerve.

Histamine type 1 receptor deficiency reduces airway inflammation in a murine asthma model.

Background: Histamine plays an important role in immediate and late immune responses. The histamine type 1 (H1) receptor is expressed on several immune cell populations, but its role in a murine model of asthma remains unclear. The present study evaluated the role of histamine H1 receptors in airway allergic inflammation by comparing the development of bronchial asthma in histamine H1 receptor gene knockout (H1RKO) and wild-type mice. Methods: H1RKO and wild-type mice were sensitized by intraperitoneal injection of ovalbumin (OVA) or saline, and then challenged with aerosolized OVA or saline. Ventilatory timing in response to inhaled methacholine was measured, and samples of blood, bronchoalveolar lavage, and lung tissues were taken 24 h after the last OVA challenge. Results: OVA-treatedwild-type mice showed significantly increased airway eosinophilic infiltration, and airway response to methacholine compared to OVA-treated H1RKO mice. The serum level of immunoglobulin E and levels of interleukin (IL)-4, IL-5, IL-13, and TGF-β1 in bronchoalveolar lavage fluid were lower in OVA-treated H1RKO mice than in OVA-treated wild-type mice, but there was no significant difference in interferon-γ expression. Overall, deletion of histamine H1 receptors reduced allergic responses in a murine model of bronchial asthma. Conclusion: Histamine plays an important role via H1 receptors in the development of T helper type 2 responses to enhance airway inflammation.

Central histaminergic neurons regulate rabbit tracheal tension through the cervical sympathetic nerve.

We previously showed that stimulation of the posterior hypothalamus decreases tracheal tension and involves central histaminergic neurons. In the present study, we reveal that central histaminergic neurons project to the rostral ventrolateral medulla and affect cervical sympathetic nervous activity in rabbits. Administration of histamine into the fourth ventricle increased cervical sympathetic nervous activity and decreased tracheal tension. These effects were inhibited by administration of a histamine H receptor antagonist, pyrilamine, into the fourth ventricle. Unilateral injection of DL-homocysteic acid into the tuberomammillary nucleus increased cervical sympathetic nervous activity, an effect was antagonized by bilateral injection of pyrilamine into the rostral ventrolateral medulla. The pulse correlogram between the stimulation pulse applied to the tuberomammillary nucleus and the cervical sympathetic nerve activity showed a mode at 150 to 200 ms, which was reduced by pyrilamine administration into the fourth ventricle. Fibers anterogradely labeled by Phaseolus vulgaris leucoagglutinin (PHA-L) injected into the tuberomammillary nucleus were distributed in the A1, A2, C1, and C2 areas which are determined by tyrosine hydroxylase-immunohistochemistry. PHA-L positive neurons were in close contact with tyrosine hydroxylase-immunoreactive neurons in these four areas. Cell bodies in the tuberomammillary nucleus retrogradely labeled with fluorogold from the rostral ventrolateral medulla were immunoreactive with histamine. These results suggest that an excitatory efferent pathway projects from the tuberomammillary nucleus to the cervical sympathetic nerve and that the histaminergic neurons of this pathway influence tracheal tension through the rostral ventrolateral medulla.