GDF15 and idiopathic pulmonary fibrosis: Another study also described aberrant basaloid cells in IPF and systemic sclerosis-related ILDs, whereby those cells expressed senescence markers, CDKN2A (gene for p16), CDKN1A (gene for p21), and GDF15 [86], and that cellular senescence was one of the profibrotic regulatory pathways identified in these cells.