In the context of IPF, a greater proportion of AEC1, AEC2, and club cells expressed GDF15. However, given the decreased abundance of cells expressing markers of AEC1 and AEC2 in IPF, club, ciliated, and basal cells are likely the most significant source of GDF15 (Fig. 3D) (43). The gene discussed is GDF15; the disease is idiopathic pulmonary fibrosis.