PGE2 acts on four receptor subtypes, being PTGER1 to PTGER4,whereas PGI2 acts primarily on PTGIR.We assessed their expression in human lung tissue of healthy smokers andpatients with COPD (GSE76925) and found maintained expression of all receptorsin disease with some small differences in expression, most notably a reducedexpression of PTGER2 and increased expression ofPTGIR (Fig.3A). The gene discussed is PTGER4; the disease is chronic obstructive pulmonary disease.