Therefore, PASC-PF is characterized by the sustained loss of functional alveolar epithelial cells, and the persistence of metaplastic Krt5+ cells, Krt8hi transitional cells, and Krt5−Krt17+ aberrant basaloid cells, which is histologically akin to other fibrotic lung diseases such as idiopathic pulmonary fibrosis (IPF) (Extended data Fig. 2b,c) (30, 31). This evidence concerns the gene KRT5 and pemphigus foliaceus.