Cytokine-induced endogenous production of prostaglandin D 2 is essential for human group 2 innate lymphoid cell activation

Group 2 innate lymphoid cells (ILC2s) play a key role in the initiation and maintenance of type 2 immune responses. The prostaglandin (PG) D -chemoattractant receptor-homologous molecule expressed on T 2 cells (CRTH2) receptor axis potently induces cytokine production and ILC2 migration. We set out to examine PG production in human ILC2s and the implications of such endogenous production on ILC2 function. The effects of the COX-1/2 inhibitor flurbiprofen, the hematopoietic prostaglandin D synthase (HPGDS) inhibitor KMN698, and the CRTH2 antagonist CAY10471 on human ILC2s were determined by assessing receptor and transcription factor expression, cytokine production, and gene expression with flow cytometry, ELISA, and quantitative RT-PCR, respectively. Concentrations of lipid mediators were measured by using liquid chromatography-tandem mass spectrometry and ELISA. We show that ILC2s constitutively express HPGDS and upregulate COX-2 upon IL-2, IL-25, and IL-33 plus thymic stromal lymphopoietin stimulation. Consequently, PGD and its metabolites can be detected in ILC2 supernatants. We reveal that endogenously produced PGD is essential in cytokine-induced ILC2 activation because blocking of the COX-1/2 or HPGDS enzymes or the CRTH2 receptor abolishes ILC2 responses. PGD produced by ILC2s is, in a paracrine/autocrine manner, essential in cytokine-induced ILC2 activation. Hence we provide the detailed mechanism behind how CRTH2 antagonists represent promising therapeutic tools for allergic diseases by controlling ILC2 function.