Cysteinyl leukotriene E(4) activates human group 2 innate lymphoid cells and enhances the effect of prostaglandin D(2) and epithelial cytokines

BACKGROUND: Group 2 innate lymphoid cells (ILC2s) are a potential innate source of type 2 cytokines in the pathogenesis of allergic conditions. Epithelial cytokines (IL-33, IL-25, and thymic stromal lymphopoietin [TSLP]) and mast cell mediators (prostaglandin D(2) [PGD(2)]) are critical activators of ILC2s. Cysteinyl leukotrienes (cysLTs), including leukotriene (LT) C(4), LTD(4), and LTE(4), are metabolites of arachidonic acid and mediate inflammatory responses. Their role in human ILC2s is still poorly understood. OBJECTIVES: We sought to determine the role of cysLTs and their relationship with other ILC2 stimulators in the activation of human ILC2s. METHODS: For ex vivo studies, fresh blood from patients with atopic dermatitis and healthy control subjects was analyzed with flow cytometry. For in vitro studies, ILC2s were isolated and cultured. The effects of cysLTs, PGD(2), IL-33, IL-25, TSLP, and IL-2 alone or in combination on ILC2s were defined by using chemotaxis, apoptosis, ELISA, Luminex, quantitative RT-PCR, and flow cytometric assays. The effect of endogenous cysLTs was assessed by using human mast cell supernatants. RESULTS: Human ILC2s expressed the LT receptor CysLT(1), levels of which were increased in atopic subjects. CysLTs, particularly LTE(4), induced migration, reduced apoptosis, and promoted cytokine production in human ILC2s in vitro. LTE(4) enhanced the effect of PGD(2), IL-25, IL-33, and TSLP, resulting in increased production of type 2 and other proinflammatory cytokines. The effect of LTE(4) was inhibited by montelukast, a CysLT(1) antagonist. Interestingly, addition of IL-2 to LTE(4) and epithelial cytokines significantly amplified ILC2 activation and upregulated expression of the receptors for IL-33 and IL-25. CONCLUSION: CysLTs, particularly LTE(4), are important contributors to the triggering of human ILC2s in inflammatory responses, particularly when combined with other ILC2 activators.