CTSG and COVID-19: Notably, gene expression of non-primary granule proteins, including Ctsg, S100a8, and Mmp8, are reportedly also increased in human leukocytes during severe COVID-19 cases relative to mild cases, but these increases were not seen in murine bone marrow neutrophils in our mild and severe MHV-1 infection model using B6 and A/J mice (45–47).