Supplementary Material for: Cytokines Involved in Interferon-γ Production by Human Macrophages

Interferon (IFN)-γ is important to the immune defense against intracellular pathogens and specifically the ability of macrophages to control Mycobacterium tuberculosis (MTB). Increasing evidence has accumulated to support the idea that macrophages produce IFN-γ. We describe here the cytokine interactions that determine IFN-γ expression and secretion during MTB infection of human macrophages. Detection of biologically important IFN-γ levels in culture supernatants of MTB-infected human macrophages requires the addition of interleukin (IL)-12. IL-18 augmented IFN-γ production from human macrophages in response to the combination of MTB and supplemental IL-12. Although IL-18 gene expression was generally unchanged, IL-18 protein secretion was enhanced by the combination of MTB and IL-12, and functioned primarily to stimulate IFN-γ release. Importantly, IL-27 induced by MTB infection opposed IFN-γ production by antagonizing IL-18 activity in human macrophages. Neutralization of IL-27 increased the expression of the IL-18 receptor β-chain. Additionally, IL-27 blocked NF-ĸB activation in response to IL-18. These results define the signals required for IFN-γ production by human macrophages and highlight the interactions between cytokines produced during MTB infection. Together, they identify a novel role for IL-27 in regulating macrophage function by disrupting IL-18 activity.