Histamine Induces Exocytosis and IL-6 Production from Human Lung Macrophages Through Interaction with H1 Receptors

Abstract

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 β-glucuronidase (EC50 = 8.2 ± 3.5 × 10−9 M) and IL-6 (EC50 = 9.3 ± 2.9 × 10−8 M) from human lung macrophages. Enhancement of β-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 H1 agonist (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)heptane carboxamide but not by the H2 agonist dimaprit. Furthermore, histamine induced a concentration-dependent increase of intracellular Ca2+ concentrations ([Ca2+]i) that followed three types of response, one characterized by a rapid increase, a second in which [Ca2+]i displays a slow but progressive increase, and a third characterized by an oscillatory pattern. Histamine-induced β-glucuronidase and IL-6 release and [Ca2+]i elevation were inhibited by the selective H1 antagonist fexofenadine (10−7–10−4 M), but not by the H2 antagonist ranitidine. Inhibition of histamine-induced β-glucuronidase and IL-6 release by fexofenadine was concentration dependent and displayed the characteristics of a competitive antagonism (Kd = 89 nM). These data demonstrate that histamine induces exocytosis and IL-6 production from human macrophages by activating H1 receptor and by increasing [Ca2+]i and they suggest that histamine may play a relevant role in the long-term sustainment of allergic inflammation in the airways.

Expression and function of Na+/Ca2+ exchangers 1 and 3 in human macrophages and monocytes

“…Rapid activation of NCX activity seems sufficient to induce this response since brief exposure of macrophages to Na 1 -free medium (10 min) was just as effective as prolonged incubation (4 h) in inducing TNF-a release. Ca 21 is involved in the production of TNF-a and other cytokines in macrophages [42,45] and many stimuli that activate cytokine production also generate Ca 21 signals [44,[55][56][57]. However, these stimuli raise cytoplasmic Ca 21 concentrations by energy-dependent mechanisms related to intracellular intermediates.…”

“…Histamine induces a Ca 21 signal in human macrophages by activating the H 1 receptor, which is coupled with the phospholipase C-pathway [41,42]. To evaluate whether NCX can operate in the forward mode contributing to restore Ca 21 gradients after a receptor-mediated Ca 21 -spike event, we preincubated HLM Effects of Na 1 -free medium on exocytosis and cytokine/chemokine production in HLM Macrophages and monocytes rely on Ca 21 signaling to activate cell functions relevant to inflammation and immune regulation.…”

“…To evaluate whether NCX can operate in the forward mode contributing to restore Ca 21 gradients after a receptor-mediated Ca 21 -spike event, we preincubated HLM Effects of Na 1 -free medium on exocytosis and cytokine/chemokine production in HLM Macrophages and monocytes rely on Ca 21 signaling to activate cell functions relevant to inflammation and immune regulation. These include the release of preformed granule proteins (exocytosis) [26,42] and the production of proinflammatory cytokines and chemokines [42][43][44][45]. Therefore, we evaluated the effects of Na 1 -free medium on the release of b-glucuronidase -a lysosomal enzyme used as a marker of exocytosis [42,46] -from HLM.…”

“…Histamine induces a Ca 21 signal in human macrophages by activating the H 1 receptor, which is coupled with the phospholipase C-pathway [41,42]. To evaluate whether NCX can operate in the forward mode contributing to restore Ca 21 gradients after a receptor-mediated Ca 21 -spike event, we preincubated HLM with CB-DMB before stimulation with histamine (1 mM).…”

“…These include the release of preformed granule proteins (exocytosis) [26,42] and the production of proinflammatory cytokines and chemokines [42][43][44][45]. Therefore, we evaluated the effects of Na 1 -free medium on the release of b-glucuronidase -a lysosomal enzyme used as a marker of exocytosis [42,46] -from HLM. Figure 7 shows that incubation of HLM with the Na 1 -free medium for 4 h did not influence the basal release of b-glucuronidase, whereas a secretory phospholipase A 2 (sPLA 2 ), used as a positive control [46], induced its release from HLM.…”