In particular, we found an association between plasma proteins elevated in severe COVID-19, such as HGF, AREG, CKAP4, S100A12, NCF2, ITGB6, and a subpopulation of monocytes with lower expression of CD86 and HLA-DR, which are characteristics of myeloid-derived suppressor-like cells (Figure S8A). Here, CKAP4 is linked to COVID-19.