T Helper Cell Type 2 Cytokines Coordinately Regulate Immunoglobulin E–Dependent Cysteinyl Leukotriene Production by Human Cord Blood–Derived Mast Cells

Abstract

Human mast cells (hMCs) derived in vitro from cord blood mononuclear cells exhibit stem cell factor (SCF)-dependent comitogenic responses to T helper cell type 2 (Th2) cytokines. As cysteinyl leukotriene (cys-LT) biosynthesis is a characteristic of immunoglobulin (Ig)E-activated mucosal hMCs, we speculated that Th2 cytokines might regulate eicosanoid generation by hMCs. After passive sensitization for 5 d with IgE in the presence of SCF, anti-IgE–stimulated hMCs elaborated minimal cys-LT (0.1 ± 0.1 ng/106 hMCs) and abundant prostaglandin (PG)D2 (16.2 ± 10.3 ng/106 hMCs). Priming of hMCs by interleukin (IL)-4 with SCF during passive sensitization enhanced their anti-IgE–dependent histamine exocytosis and increased their generation of both cys-LT (by 27-fold) and PGD2 (by 2.5-fold). Although priming with IL-3 or IL-5 alone for 5 d with SCF minimally enhanced anti-IgE–mediated cys-LT generation, these cytokines induced further six- and fourfold increases, respectively, in IgE-dependent cys-LT generation when provided with IL-4 and SCF; this occurred without changes in PGD2 generation or histamine exocytosis relative to hMCs primed with IL-4 alone. None of these cytokines, either alone or in combination, substantially altered the levels of cytosolic phospholipase A2 (cPLA2), 5-lipoxygenase (5-LO), or 5-LO activating protein (FLAP) protein expression by hMCs. In contrast, IL-4 priming dramatically induced the steady-state expression of leukotriene C4 synthase (LTC4S) mRNA within 6 h, and increased the expression of LTC4S protein and functional activity in a dose- and time-dependent manner, with plateaus at 10 ng/ml and 5 d, respectively. Priming by either IL-3 or IL-5, with or without IL-4, supported the localization of 5-LO to the nucleus of hMCs. Thus, different Th2-derived cytokines target distinct steps in the 5-LO/LTC4S biosynthetic pathway (induction of LTC4S expression and nuclear import of 5-LO, respectively), each of which is necessary for a full integrated functional response to IgE-dependent activation, thus modulating the effector phenotype of mature hMCs.