Production of T cell-activating monokine of guinea pig macrophages induced by MDP and partial characterization of the monokine.

The production of T cell-activating factor(s) by macrophages stimulated with muramyl dipeptide (MDP) was studied. By MDP stimulation, a rapid increase in intracellular activity of the T cell-activating factor was induced, which preceded an increase of the activity in the extracellular medium. The rapid appearance of the activity in the cell and that in the medium were both inhibited by cycloheximide or puromycin. These results demonstrated that MDP stimulated rapid production of T cell-activating factors by inducing de novo synthesis of the factors, and that these newly formed factors are rapidly secreted. The activities of intracellular and extracellular secreted factors were both found in high m.w. (50,000 to 90,000) and low m.w. (10,000 to 30,000) fractions by gel filtration. The secreted high m.w. factor migrated as a single peak and did not dissociate into smaller components in SDS-PAGE analysis, indicating that the high m.w. factor is neither a complex of low m.w. factor with other proteins nor an aggregate of low m.w. factors. The properties are similar to those of our previously reported factor that helped antigenic activation of T cells for lymphokine production.