The intracellular localization of the 8OHG/8OHdG staining both in the nucleus and in the cytoplasm suggests that both DNA and RNA could be oxidized. To investigate whether DNA, RNA, or both are oxidized, we performed pretreatments with DNase-free RNase, RNase-free DNase, or both before 8OHG/8OHdG immunostaining. Compared to untreated serial sections of lung tissue (Fig 6, top left, A), RNase strongly decreased 8OHG/8OHdG staining (Fig 6, top middle left, B), whereas DNase had less effects (Fig 6, top middle right, C). Higher magnification analysis clearly demonstrated that 8OHG/8OHdG staining was mainly cytoplasmic in alveolar wall cells (Fig 6, center left, E), but some cells exhibited both nuclear and cytoplasmic staining (Fig 6, bottom left, I). RNase pretreatment dramatically decreased 8OHG/8OHdG immunostaining (Fig 6, center middle left, F), but some alveolar wall cells exhibited nuclear staining (Fig 6, bottom middle left, J), suggesting that some cells exhibit not only RNA, but also DNA oxidation. DNase pretreatment showed a prominent cytoplasmic localization of 8OHG/8OHdG immunostaining (Fig 6, center middle right, G, and bottom middle right, K), suggesting strong RNA oxidation in these cells. RNase and DNase combined induced complete inhibition of 8OHG/8OHdG staining, showing the selectivity of the staining for nucleic acids (Fig 6, top right, D, center right, H, and bottom right, L). Together, these data suggest that RNA oxidation is a prominent feature of alveolar wall cells in emphysema but that DNA oxidation also occurs in some alveolar wall cells. Similar results were obtained in CE and AATD lungs.