T helper cell type 2 cytokines coordinately regulate immunoglobulin E-dependent cysteinyl leukotriene production by human cord blood-derived mast cells: Profound induction of leukotriene C-4 synthase expression by interleukin 4

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 spe culated that Th2 cytokines might regulate eicosanoid generation by hMCs. Af ter 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/10(6) hMCs) and abundant prostaglandin (PG)D-2 (16.2 +/- 10.3 ng/10(6) hMCs). Priming of hM Cs by interleukin (IL)-4 with SCF during passive sensitization enhanced the ir anti-IgE-dependent histamine exocytosis and increased their generation o f both cys-LT (by 27-fold) and PGD(2) (by 2.5-fold). Although priming; with IL-3 or IL-5 alone for 5 d with SCF minimally enhanced anti-IgE-mediated c ys-LT generation, these cytokines induced further six- and fourfold increas es, respectively, in IgE-dependent cys-LT generation when provided with IL- 3 and SCF; this occurred without changes in PGD(2) 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 cytos olic phospholipase A(2) (cPLA(2)), 5-lipoxygenase (5-LO), or 5-LO activatin g protein (FLAP) protein expression by hMCs. In contrast, IL-4 priming dram atically induced the steady-state expression of leukotriene C-4 synthase (L TC4S) mRNA within 6 h, and increased the expression of LTC4S protein and fu nctional 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 witho ut IL-4, supported the localization of 5-LO to the nucleus of hMCs. Thus, d ifferent Th2-derived cytokines target distinct steps in the 5-LO/LTC4S bios ynthetic 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 phenoty pe of mature hMCs.