Macrophage Activation by Cord Factor (trehalose 6,6'-dimycolate): Enhanced Association with and Intracellular Killing of Trypanosoma Cruzi

Cord factor (trehalose 6,6'-dimycolate[TDM] ), a mixture of 6,6'-diesters of alpha, alpha-D-trehalose with natural mycolic acids, has been described as having immunoregulatory and antitumor activities in vivo, although the relevant mechanisms of action remain unelucidated. In this work, we measured the effects of TDM on both mouse macrophage association with (i.e., the combined result of surface binding and uptake) and subsequent intracellular killing of Trypanosoma cruzi, the causative agent of Chagas' disease. Pretreatment of macrophage cultures with TDM for 16 h markedly increased both the ability of these cells to associate with T. cruzi and the rate of killing of parasites. The results obtained with macrophages treated with TDM after exposure to the parasites did not differ from those obtained with untreated macrophages, indicating that macrophage activation did not occur immediately after TDM treatment and was time dependent. The TDM effect was reversible since the extents of macrophage-parasite association and intracellular killing returned to normal levels 4 h after TDM treatment. Neither catalase, which scavenges hydrogen peroxide, nor sodium azide or potassium cyanide, which are inhibitors of peroxidase activity, significantly reduced the level of trypanosome killing by TDM-treated macrophages. TDM also increased the uptake of glutaraldehyde-killed T. cruzi and latex particles, suggesting that TDM could act mostly by enhancing phagocytosis and that increased cell association with the living trypanosomes did not necessarily depend on the macrophages becoming more susceptible to parasite invasion. These results indicate that TDM modulates macrophage function by augmenting both internalization and intracellular destruction. Hydrogen peroxide and peroxidase activity, postulated to be involved in phagocytic killing of T. cruzi, did not appear to be an absolute requirement for the killing of T. cruzi in TDM-treated macrophages.