Here the authors use a pre-clinical model of chronic experimental asthma to show that corticosteroids suppress endogenous PGD2 and IFN-γ production, necessary for the beneficial effects of DP2 antagonism, and hence dual therapy with corticosteroids was less effective than DP2 antagonism alone at resolving airway inflammation and airway remodelling. Here, HPGDS is linked to asthma.