MPO and COVID-19: While non-classical monocyte numbers were diminished in COVID-19, HLA-DRhiCD11chi inflammatory monocytes with an ISG signature were elevated in mild COVID-19 and monocytes in severe COVID-19 featured strongly reduced HLA-DR expression, high expression levels of genes with anti-inflammatory and immature properties, including SELL (CD62L), CD163, MPO and PLAC8, as well as increased expression of S100A family members, e.g. S100A12 (42).