CDKN1A and chronic obstructive pulmonary disease: However, phLF isolated from control, IPF, and COPD and cultured in cell culture had a very similar phenotype characterized by low expression of the different senescence-related markers: CDKN1A/P21, CDKN2A/P16, and TP53 gene expression, SA-β-galactosidase activity, and secretion of SASP-related components.