ITGB2 and acute promyelocytic leukemia: However, the Mac-1 expression level of ATRA-treated HL60 cells was much less than that of neutrophils (Figure 2F, Supplementary Figure S1), despite the fact that Mac-1, as an important biomarker of APL differentiation, was usually used to reflect the differentiation level of ATRA-treated HL60 cells (26).