The CD68 antibody antigen is a 110 kDa highly glycosylated transmembrane protein which is mainly located in lysosomes. CD68 is commonly regarded as a marker for monocytes and macrophages in many human tissues as well as fibroblasts, endothelial cells and tumor cells. Studies have shown that the CD68 antibody stains blast cells in a large percentage of acute myelogenous leukemia but none in acute lymphoblastic leukemia. Another study showed that [KP1] stained normal/reactive and neoplastic mast cells in lymph node and mastocytosis. The intensity of CD68 staining in individual cell types was found to depend on the fixation technique.