PI16 and infection: (Fig. 1A) Specific mesenchymal subpopulations were identified using previously described markers: alveolar fibroblasts (Npnt, Ces1d, and Col13a1), adventitial fibroblasts (Pi16, Dcn, and Col14a1), peribronchial fibroblasts (Hhip, Aspn), and smooth muscle cells (Acta2, Myh11) (Fig. 1B).(31, 34, 49, 50) Constitutive expression of versican was observed in all four clusters of mesenchymal cells collected from mice before infection, although variability in versican expression was noted among populations.