KRT18 and Histiocytosis: K18 hACE2 transgenic mice developed interstitial pneumonia (Fig. 5e, f) associated with alveolar histiocytosis admixed neutrophils and lymphocytes (Fig. 5f, asterisks), mild type II pneumocyte hyperplasia (Fig. 5f, arrowhead), bronchiolar syncytia (Fig. 5f, arrow), endothelial cell hyperplasia and vasculitis (Fig. 5f, bracket) by 2 DPI.