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.

We hypothesized that lung ILC2s might be activated by leukotrienes through CysLT1R.

ILC2s (Thy1.2⁺ 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_H2 cytokine levels were measured in purified lung ILC2s stimulated with leukotriene D₄ (LTD₄) in the presence or absence of the CysLT1R antagonist montelukast. Calcium influx was measured by using Fluo-4 intensity. Intranasal leukotriene C₄, D₄, and E₄ 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.

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.

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.