Single-cell sequencing datasets of IPF (GSE213017) [29], COVID-19 (GSE227136 + GSE149878) [30, 31], radiation-induced PF in mice (GSE211713) [32] and BLM-induced PF in mice (GSE210341) [33] revealed high levels of SDC4 mRNA in fibroblast cells (Supplementary Figure S2A–D). Here, SDC4 is linked to COVID-19.