Lung type 2 innate lymphoid cells express cysteinyl leukotriene receptor 1, which regulates TH2 cytokine production

Background: Cysteinyl leukotrienes (CysLTs) contribute to asthma pathogenesis, in part through cysteinyl leukotriene receptor 1 (CysLT1R). Recently discovered lineage-negative type 2 innate lymphoid cells (ILC2s) potently produce IL-5 and IL-13. Objectives: We hypothesized that lung ILC2s might be activated by leukotrienes through CysLT1R. Methods: ILC2s (Thy1.2 1 lineage-negative lymphocytes) and CysLT1R were detected in the lungs of wild-type, signal transducer and activator of transcription 6-deficient (STAT6(-/-)), and recombination-activating gene 2-deficient (RAG2(-/-)) mice by means of flow cytometry. T(H)2 cytokine levels were measured in purified lung ILC2s stimulated with leukotriene D-4 (LTD4) in the presence or absence of the CysLT1R antagonist montelukast. Calcium influx was measured by using Fluo-4 intensity. Intranasal leukotriene C-4, D-4, and E-4 were administered to naive mice, and levels of ILC2 IL-5 production were determined. Finally, LTD4 was coadministered with Alternaria species repetitively to RAG2(-/-) mice (with ILC2s) and IL-7 receptor-deficient mice (lack ILC2s), and total ILC2 numbers, proliferation (Ki-67(+)), and bronchoalveolar lavage fluid eosinophil numbers were measured. Results: CysLT1R was expressed on lung ILC2s from wild-type, RAG2(-/-), and STAT6(-/-) naive and Alternaria species-challenged mice. In vitro LTD4 induced ILC2s to rapidly generate high levels of IL-5 and IL-13 within 6 hours of stimulation. Interestingly, LTD4, but not IL-33, induced high levels of IL-4 by ILC2s. LTD4 administered in vivo rapidly induced ILC2 IL-5 production that was significantly reduced by montelukast before treatment. Finally, LTD4 potentiated Alternaria species-induced eosinophilia, as well as ILC2 accumulation and proliferation. Conclusions: We present novel data that CysLT1R is expressed on ILC2s and LTD4 potently induces CysLT1R-dependent ILC2 production of IL-4, IL-5, and IL-13. Additionally, LTD4 potentiates Alternaria species-induced eosinophilia and ILC2 proliferation and accumulation.