SDC4 and infection: Interestingly, many transcription factors that maintain alveolar structure and integrity, such as NKX2-1, SFTP families, IRX2, NPNT, SDC4, SHROOM3, TGFBR2, and TMED2 [13], were significantly downregulated after infection (Fig. 2D, E), particularly these results from the hematoxylin-eosin (HE) staining also demonstrated that alveolar cells and structures of the two dead patients were obviously damaged compared with the age-matched control group (Fig. 2F, G).