Stimulatory effect of N-acetyl Muramyl dipeptide in vivo: proliferation of bone marrow progenitor cells in mice.

The effects of single and multiple injections of N-acetyl muramyl dipeptide (MDP) on peripheral leukocytes, colony-forming cells (i.e., bone marrow granulocyte-macrophage progenitor cells), and the humoral immune response (to bovine serum albumin) were investigated in mice. Whereas low doses of MDP (0.1 to 1 mg/kg) provoked lymphocytosis, larger doses (10 mg/kg upward) resulted in lymphocytopenia and an increase in the number of young stab neutrophils and monocytes. MDP induced a dose-dependent increase in the number of bone-marrow macrophage progenitor cells, the maximum being reached by a dose around 10 mg/kg. A 50% increase in the maximum effect was produced by a dose around 0.1 mg/kg. The higher the dose, the longer the increase in these progenitor cells persisted. MDP mediated a dose-dependent antibody response to small amounts of bovine serum albumin, correlating with the proliferation of progenitor cells.