Extended Data Figure 10: Transduction of mouse lungs demonstrating expression of GFP or protein-VII–GFP.

a, Sections of mouse lungs transduced to express protein-VII–GFP or GFP co-stained for HMGB1. GFP signal shows multiple cell types transduced in both cases. Protein-VII–GFP has a more distinct nuclear signal than GFP, which also appears cytoplasmic. Two sections for each condition are shown to indicate transduction efficiency. b, Same as a but co-stained for prosurfactant-C to mark type II pneumocytes. Some cells are positive for both, confirming that multiple cell types were transduced. c, Zoomed images of individual epithelial cells from mouse lungs showing the characteristic protein-VII–GFP pattern colocalizing with DAPI in the nucleus. GFP only is mostly cytoplasmic. d, Schematic summarizing function of protein VII during infection. Newly synthesized protein VII late during infection can be post-translationally modified and binds to HMGB1, sequestering it on the cellular chromatin and preventing its release. Unmodified protein VII is packaged in viral progeny.