Augmentation by Priming with Interferon-γ of the Binding of a Muramyl Dipeptide Derivative to Macrophages Resulting in Synergistic Macrophage Activation

Abstract

Macrophage (MA) activation by recombinant murine interferon-gamma (rMuIFN-γ) and a synthetic muramyl dipeptide derivative, N^α-(N-acetylmuramyl-L-alanyl-D-isoglutaminyl)-N^ε-stearoyl-L-lysine [MDP-Lys(L18)], was examined. The cytostatic activity of MA that had been primed with rMuIFN-γ against Lewis lung adenocarcinoma cells was augmented extensively by exposure to MDP-Lys(L18) for a minimum of 15min, though such treatment in the reverse sequence interfered with the effects of rMuIFN-γ on MA. The binding assays revealed that rMuIFN-γ bound to MA with an apparent dissociation constant (Kd) of 0.93×10^-9M (16, 000 binding molecules/cell), while MDP-Lys(L18) bound nonspecifically and was endocytosed by MA at 37°. The amount of MDP-Lys(L18) bound to the rMuIFN-γ-primed MA was significantly greater than that bound to the MA without rMuIFN-γ priming. A small increase in the amount of MDP-Lys(L18) associated with MA was also observed at 4°, but the amount was one order of magnitude less than that at 37°. The binding of rMuIFN-γ to MA was significantly suppressed by priming with MDP-Lys(L18). These results indicate that the binding of rMuIFN-γ in preference to MDP-Lys(L18) to MA is of great importance in the mechanisms of MA activation.