Cytokine Message and Protein Expression During Lung Granuloma Formation and Resolution Induced by the Mycobacterial Cord Factor Trehalose-6,6′-Dimycolate

Abstract

Trehalose-6,6'-dimycolate (TDM), or cord factor, is a mycobacterial cell wall component that induces granuloma formation and proinflammatory cytokine production in vivo and in vitro. The purpose of this work was to better understand the mechanisms by which TDM promotes lung granuloma formation. This was accomplished by characterizing cytokine mRNA expression during TDM-induced alveolitis culminating in cohesive granuloma development. A single intravenous injection of TDM given to C57BL/6 mice produced lung granulomas that peaked in number 5 days after challenge and were nearly resolved by 14 days. mRNA in whole lung preparations was quantitated by bioluminescent RT-PCR. Tumor necrosis factor-α (TNF-α), interleukin1β (IL-1β), and IL-6 were significantly elevated during granuloma development and decreased during granuloma resolution. There were no detectable changes in mRNA for interferon-γ (IFN-γ), IL-2, IL-4, IL-5, IL10, and IL-12(p40). The level of TNF-α protein extracted from lung minces highly correlated with morphologic indices of granulomatous inflammation, indicating that it may be an important modulator of the inflammatory intensity induced by TDM. TDM may interact specifically with macrophages in vivo, as evidenced by induction of TNF-α, IL-1β, and IL-6, but not IFN-γ, protein in bone marrow-derived macrophages from C57BL/6 mice. TDM may therefore play an important role early in macrophage activation during the host granulomatous response to mycobacteria.