FUT4 and COVID-19: PMN-MDSC is most often described as CD11b + CD33dim HLA-DR− CD14− CD15 + CD66b+, whereas M-MDSC is mainly defined as CD11b + CD33hi HLA-DR− CD14+ CD15−.[29] However, the phenotype of immature neutrophils in severe COVID-19 is also changed during the pathological process.