Histamine and TH2 cytokines regulate the biosynthesis of cysteinyl-leukotrienes and expression of their receptors in human mast cells.

Introduction: In skin lesions of atopic dermatitis (AD), a chronic inflammatory skin disease, mast cells beyond other immune cells are present in increasing numbers. Upon activation, mast cells release a plethora of mediators, in particular histamine and leukotrienes, as well as chemokines and cytokines, which modulate the immune response of cells in their microenvironment and may influence mast cells in an autocrine loop. This study investigated the effects of histamine and TH2 cytokines on the biosynthesis of cysteinyl leukotrienes (CysLTs) as well as CysLT receptor expression on human mast cells from healthy volunteers and patients with AD.

Methods: Human mast cells were generated from CD34+ progenitor cells from peripheral blood. The cultured mast cells were stimulated with IL-4, IL-13, histamine and different histamine receptor selective ligands. Expression of enzymes in the biosynthesis of leukotrienes and expression of CysLT receptors were quantified by real-time PCR. The release of CysLTs was measured by ELISA.

Results: Mast cells from AD patients showed higher expression of 5-Lipoxygenase (5-LO) and 5-Lipoxygenase activating protein (FLAP) compared to mast cells from healthy volunteers at baseline and in presence of histamine and TH2 cytokines. Expression of leukotriene C4 synthase (LTC4S), the biosynthesis of CysLTs, and mRNA expression of both CysLT receptors were induced by histamine and TH2 cytokines in mast cells from healthy volunteers and AD patients.

Conclusion: We provide evidence that in an acute allergic situation histamine and TH2 cytokines may activate the biosynthesis of pro-allergic cysteinyl leukotrienes and up-regulation of CysLT receptor expression in human mast cells. This suggests a novel mechanism for sustaining mast cell activation through a possible autocrine signalling loop under these conditions.