SERPINA1 and pulmonary emphysema: More recently, single-cell RNA sequencing data sets of adult human lung tissue have consistently demonstrated SERPINA1 transcript expression in alveolar type 2 cells (AT2s) and macrophages.12, 13, 14, 15, 16 AT2s are facultative progenitors of the distal lung, the structure primarily injured in emphysema observed in AATD.