Inhibition of mitogen-induced polyclonal activation by by a synthetic adjuvant, muramyl dipeptide (MDP).

A synthetic adjuvant, N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP), was previously shown to enhance polyclonal antibody response in murine spleen cell cultures. When MDP was added to the culture together with a potent murine B cell mitogen (such as bacterial lipopolysaccharide (LPS)), it inhibited completely the LPS-induced polyclonal activation without affecting either the 3H-thymidine incorporation or the number of blast cells in cultures. Strong suppression of mitogen-induced polyclonal activation by MDP was obtained by using a large range of cell concentrations in cultures and over various dosage levels of the stimulating mitogens (LPS and NWSM). An inhibition could be obtained even when MDP was added 24 hr after the addition of the mitogen, and highly significant suppression was observed in the absence of cell division in the cultures.