MDP and LPS act synergistically to induce arginine-dependent cytostatic activity in rat alveolar macrophages.

Rat alveolar macrophages can be activated in vitro for cytostatic activity against tumor cells by MDP and LPS acting in synergy. MDP can be substituted for by analogs active as adjuvants. Macrophage activation correlates with an increased production of nitrite and citrulline. NG-monomethyl-L-arginine, a specific inhibitor of the L-arginine metabolism having nitrite and citrulline as end products, abolishes the cytostatic activity. We therefore conclude that, in this model, the main effector mechanism of the cytostatic activity is mediated by molecules derived from L-arginine through the newly described NOo-generating pathway.