Structural and biosvnthetic features of the Mo5 human myelGd differentiation antigen

This report describes the basic structural and biosynthetic features of Mo5, a novel plasma membrane differentiation antigen (Ag) of the human myeloid lineage. As defined by the binding of antiMo5 monoclonal antibody (mAb), this Ag is expressed by virtually all myeloperoxidase-positive myeloid precursors beyond the CFU-GM in human bone marrow and is retained by circulating monocytes and polymorphonuclear neutrophils (PMNs) (1). Other hematopoietic elements of blood and bone marrow are Mo5-negative (1). Among myeloid cell lines, the monocytoid U-937 (2) and THP-I (3) lines are Mo5-positive, while HL-60 (4) and KG-I (5) are essentially negative (1). Mo5 expression by these myeloid lines (either positive or negative) exhibits no significant change as a result of their exposure to soluble stimuli inducing monocytic differentiation, which is in contrast to the acquired expression of Mol (CDI lbICDI8) under the same conditions (1). Among leukemic cells of myeloid and lymphoid origin, Mo5 expression is restricted to acute myelogenous leukemia (FAB grp. M4, M5 > M1-3), providing an additional laboratory feature to distinguish the malignant cells of this lineage (6).