Importance of histamine in the cytokine network in the lung through H2 and H3 receptors: stimulation of IL-10 production.

Histamine, a well-known inflammatory mediator, has been implicated in various immunoregulatory effects that are poorly understood. Thus, we tested the hypothesis that histamine inhibits the release of a proinflammatory cytokine, namely TNF, by stimulating the release of an anti-inflammatory cytokine, IL-10. Alveolar macrophages (AMs) from humans, Sprague Dawley rats, and the AM cell line, NR8383, were treated with different concentrations of histamine (10-5-10-7 M) for 2 h prior to their stimulation with suboptimal concentration of LPS (1 ng/ml) for 4 h. Histamine inhibited TNF release in a dose-dependent manner. This inhibition was mimicked by H2 and H3 receptor agonists, but not by H1 receptor agonist. Furthermore, we demonstrated the expression of H3 receptor mRNA in human AMs. Interestingly, treatment of AMs with anti-IL-10, anti-PGE2, or a NO synthase inhibitor (Nomega-nitro-l -arginine methyl ester) before the addition of histamine abrogated the inhibitory effect of the latter on TNF release. Histamine treatment (10-5 M) increased the release of IL-10 from unstimulated (2.2-fold) and LPS-stimulated (1. 7-fold) AMs. Unstimulated AMs, NR8383, express few copies of IL-10 mRNA, as tested by quantitative PCR, but expression of IL-10 was increased by 1.5-fold with histamine treatment. Moreover, the stimulation of IL-10 release by histamine was abrogated by pretreatment with anti-PGE2 or the NO synthase inhibitor, Nomega-nitro-l -arginine methyl ester. Thus, histamine increases the synthesis and release of IL-10 from AMs through PGE2 and NO production. These results suggest that histamine may play an important role in the modulation of the cytokine network.