Human basophil chemotaxis and activation are regulated via the histamine H4 receptor

Abstract Background IgE‐mediated cross‐linking of Fcε RI results in the release of mediators stored in basophil granules, such as histamine and proteases, and in the de novo synthesis of sulfidoleukotrienes. Objective In this study, we investigated the role of the histamine receptors, in particular that of the histamine H4 receptor (H4R), in modulating human basophil function. Methods The mRNA expression of the histamine receptors was measured by real‐time PCR . Migration of basophils was assessed using the modified Boyden chamber technique. The expression levels of CD 63 and CD 203c on the cell surface and the sulfidoleukotriene release were determined by flow cytometry and ELISA , respectively. Results We could show that highly purified basophils express the H1R, H2R, and H4R but not the H3R mRNA . Human basophils expressed higher H4R mRNA levels as compared to the expression levels of the H1R ( P < 0.01). Histamine and the H4R agonist ST ‐1006 initiated active migration of basophils ( P < 0.001). A significant reduction in Fcε RI cross‐linking‐mediated surface expression of CD 63 and CD 203c was observed on basophils after pre‐incubation with histamine or the specific H4R agonist ST ‐1006 ( P < 0.01). The synthesis and release of sulfidoleukotrienes from basophils after activation with different stimuli, by Fcε RI cross‐linking or by stimulation with hymenoptera venom allergens, were significantly reduced by histamine or the H4R agonist ST ‐1006 ( P < 0.05–0.001). Conclusion These data imply that the H4R regulates IgE‐dependent processes in human basophils and provides a novel function of the H4R preventing an overwhelming immune reaction by engagement of a negative feedback loop.