Ultrastructural peroxidase cytochemistry of three established human myelogenous leukemia cell lines, HL-60, KG-1 and ML-2

We studied the ultrastructural peroxidase cytochemistry of three established human acute myelogenous leukemia cell lines (HL-60, KG-1 and ML-2) to clarify the cytochemical differences and the differences in maturation/differentiation stages. HL-60 cells contained azurophil granules which exhibited strong peroxidase reaction. The more central region of individual granules is less reactive than the outer portion of these granules. The secretory apparatus of HL-60 cells, i.e. rough endoplasmic reticulum, perinuclear cisterna and Golgi apparatus, also contained peroxidase-reactive material. ML-2 cells contained azurophil granules with peroxidase reaction; however, nuclear membranes were peroxidase-negative and thin cisternae of rough endoplasmic reticulum exhibited only a faint peroxidase reaction. KG-1 cells were peroxidase-negative. From these findings KG-1 is classified as the least mature of the cell lines studied. ML-2 cells are considered early promyelocytes and HL-60 cells as late promyelocytes.