PDPN and infection: Cells within cluster 0, 1, 2, 3, and to a lesser extent cells within cluster 5 up-regulated genes associated with FRCs [57] in response to infection, including Pdpn, Pdgfra, Pdgrfb, Vim, and Col6a3, as well as secreted factors such as Vefga and Tnfsf13b (encoding for BAFF) (S3A Fig).