Histamine acting on a histamine type 1 (H1) receptor increases beta-glucuronidase release from human lung macrophages

H1-receptors: localization and role in airway physiology and in immune functions

Histamine H(1)-receptors are involved in the pathologic processes of allergy. Clinical trials of H(1)-receptor antagonists have demonstrated the efficacy of these agents in reducing the sneezing, pruritus, and rhinorrhea associated with allergic rhinitis. In the lung, H(1)-receptors mediate the bronchoconstrictive effects of histamine and increase vascular permeability, which lead to plasma exudation. H(1)-receptors are present on T cells, B cells, monocytes, and lymphocytes, and stimulation of these receptors induces pro-inflammatory effects. It has been suggested that a signal from the H(1)-receptor contributes to the antigen receptor-mediated signaling pathways that induce proliferative responses and lead to the production of cytokines and antibodies by T cells and B cells, respectively. It would appear, therefore, that the H(1)-receptor has a wider role in inflammatory processes than simply mediating the actions of histamine.

The histamine-cytokine network in allergic inflammation

Histamine is synthesized and released by human basophils, mast cells, and neurons. Its pleiotropic effects are mediated by the activation of 4 receptors: H(1), H(2), H(3), and H(4). With the advent of selective antagonists (the antihistamines widely used to treat allergic disorders), the H(1)-receptor was the first member of the receptor family to be pharmacologically defined. Increasing evidence indicates that, in addition to exerting immediate vascular and bronchial responses, histamine might modulate the immune reaction by interacting with T cells, macrophages, basophils, eosinophils, and monocytes. We have shown that, in vitro, histamine induces a concentration-dependent release of IL-6 and beta-glucuronidase from macrophages isolated from the human lung parenchyma. These effects are inhibited by fexofenadine, an H(1)-receptor antagonist, but not by ranitidine, an H(2)-receptor antagonist. This observation raises the possibility that long-term treatment with fexofenadine might have beneficial effects on immune dysregulation and tissue damage/remodeling associated with histamine-mediated macrophage activation.

Histamine induces exocytosis and IL-6 production from human lung macrophages through interaction with H1 receptors

Increasing evidence suggests that a continuous release of histamine from mast cells occurs in the airways of asthmatic patients and that histamine may modulate functions of other inflammatory cells such as macrophages. In the present study histamine (10(-9)-10(-6) M) increased in a concentration-dependent fashion the basal release of beta-glucuronidase (EC(50) = 8.2 +/- 3.5 x 10(-9) M) and IL-6 (EC(50) = 9.3 +/- 2.9 x 10(-8) M) from human lung macrophages. Enhancement of beta-glucuronidase release induced by histamine was evident after 30 min and peaked at 90 min, whereas that of IL-6 required 2-6 h of incubation. These effects were reproduced by the H(1) agonist (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)heptane carboxamide but not by the H(2) agonist dimaprit. Furthermore, histamine induced a concentration-dependent increase of intracellular Ca(2+) concentrations ([Ca(2+)](i)) that followed three types of response, one characterized by a rapid increase, a second in which [Ca(2+)](i) displays a slow but progressive increase, and a third characterized by an oscillatory pattern. Histamine-induced beta-glucuronidase and IL-6 release and [Ca(2+)](i) elevation were inhibited by the selective H(1) antagonist fexofenadine (10(-7)-10(-4) M), but not by the H(2) antagonist ranitidine. Inhibition of histamine-induced beta-glucuronidase and IL-6 release by fexofenadine was concentration dependent and displayed the characteristics of a competitive antagonism (K(d) = 89 nM). These data demonstrate that histamine induces exocytosis and IL-6 production from human macrophages by activating H(1) receptor and by increasing [Ca(2+)](i) and they suggest that histamine may play a relevant role in the long-term sustainment of allergic inflammation in the airways.

Activation by histamine of bronchial epithelial cells from nonasthmatic subjects

Histamine is a major mediator of the mast cells that are present between epithelial cells in asthma. In asthma, there is an increased expression of ICAM-1 and HLA-DR and an increased spontaneous release of fibronectin. The effect of histamine was tested on bronchial epithelial cells obtained by bronchial brushing from 22 nonasthmatic subjects. The activation of epithelial cells was assessed by immunocytochemical analysis of the expression of membrane markers (ICAM-1 and HLA-DR) using the alkaline phosphatase-anti-alkaline phosphatase method and the release of fibronectin (enzyme immunoassay). Time-response (three experiments) and dose-response (six experiments) curves showed that the maximal effect was obtained after an incubation time of 24 h and a dose of 1 microM of histamine. For this time course and concentration, there was a highly significant increase in the number of cells expressing ICAM-1 (before histamine: 10 +/- 11%; after histamine: 32 +/- 20%; P < 0.001) and HLA-DR (before histamine: 8 +/- 7%; after histamine: 23 +/- 20%; P < 0.001) and in the release of fibronectin (before histamine: 30 +/- 20 ng/10(5) viable cells; after histamine: 61 +/- 35 ng/10(5) viable cells; P < 0.003). Cycloheximide blocked these effects, suggesting that histamine requires protein synthesis for its action. Pyrilamine (H1-blocker) and ranitidine (H2-blocker) at a concentration of 10 microM decreased the effect of histamine. However, there was no additive effect when both antagonists were added. This study suggests that mast cells present in the airways have a role in the activation of epithelial cells.