Augmentation of the proliferative response of thymocytes to phytohemagglutinin by the muramyl dipeptide1.

A synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine or muramyl dipeptide (MDP) and adjuvant-active analogs, but not lipopolysaccharide (LPS), exhibited the augmenting effect on the proliferative response of thymocytes to phytohemagglutinin (PHA). MDP also had a comitogenic effect on PHA-stimulated T lymphocytes. It was shown that the thymocyte-stimulating effect of MDP is not through the production of the monikines by MDP-stimulated macrophages and that MDP has a direct action on lymphocytes.