PTGDS and allergic disease: In the context of allergy, sPLA2-III secreted from immature mast cells is functionally coupled with lipocalin-type PGD2 synthase (L-PGDS) in neighboring fibroblasts to supply a microenvironmental pool of PGD2, which in turn acts on the PGD2 receptor DP1 on mast cells to promote their proper maturation [46].