Histamine-induced activation of human lung macrophages

Background: Histamine plays a central role in the pathogenesis of allergic and inflammatory diseases by modulating vascular and airway responses. Increasing evidence suggests that histamine also regulates the function of inflammatory and immune cells. Macrophages are primarily involved in inflammatory diseases of the lung. We explored the ability of low concentrations of histamine to induce the release of proinflammatory mediators from human lung macrophages.

Methods: Macrophages purified (> 95%) from lung parenchyma by Percoll density gradients and adherence to polystyrene dishes were incubated (37 degrees C, 2-24 h) with histamine (10(-9)-10(-6) M). At the end of incubation, the release of beta-glucuronidase and IL-6 was determined.

Results: Histamine induced a concentration-dependent release of beta-glucuronidase and IL-6 with a maximum release after 2 and 6 h of incubation, respectively. Exocytosis induced by histamine was noncytotoxic and was Ca(2+)- and temperature-dependent. The effect of histamine was inhibited by the H(1) receptor antagonist fexofenadine but not by the H(2) antagonist ranitidine.

Conclusions: These data indicate that histamine is an effective stimulus for exocytosis and cytokine production from human lung macrophages. These effects are inhibited by pharmacological concentrations of fexofenadine. Our results suggest that histamine may contribute to the long-term evolution of lung inflammation and tissue remodelling in allergic diseases by modulating the production of proinflammatory and immunoregulatory mediators by macrophages.