Effect of Synthetic Muramyl Dipeptide (MDP) on Differentiation of Myeloid Leukemic Cells

It has been reported that the M1 cell line, established from a myeloid leukemia of an SL strain mouse (9), can be induced to differentiate into mature macrophages and granulocytes by exposure to various factors (7-9, 12, 14, 17, 21, 24-26).As differentiation markers of Ml cells, various characters, such as Fc and C3 receptors, phagocytosis of latex particles, motility, lysosomal enzymes, cell morphology, and the capacity to cooperate with lymphocytes to produce antibody-forming cells ( 27), have been employed.Synthetic N-acetyl muramyl dipeptide (MDP) is known to be the minimal structure required for adjuvant activity of bacterial cell wall peptidoglycan for increasing both humoral and cell-mediated immune responses (1,4,5,10,11,22).For the mode of action of MDP, it has been suggested that the dipeptide potentiates immune responsiveness by mediation of T cells (13) or of macrophages which release factors acting on B cells through T-cell mediation (6).Moreover, adherent peritoneal macrophages can be activated in vitro by MDP and acquire cytostatic activity against tumor cells (10,23).Recently, it was also shown that MDP augments the cytolytic activity of macrophages of cultured cell lines without the participation of other cell types (22).In the present paper, we report the effect of MDP on the differentiation of M1 cells into mature macrophages.The clone of Ml cells, M1/436-7, established by Dr.