Abstract
Variability in bacterial sterilization is a key feature of Mycobacterium tuberculosis (Mtb) disease. In a population of human macrophages, there are macrophages that restrict Mtb growth and those that do not. However, the sources of heterogeneity in macrophage state during Mtb infection are poorly understood. Here, we perform RNAseq on restrictive and permissive macrophages and reveal that the expression of genes involved in GM-CSF signaling discriminates between the two subpopulations. We demonstrate that blocking GM-CSF makes macrophages more permissive of Mtb growth while addition of GM-CSF increases bacterial control. In parallel, we find that the loss of bacterial control that occurs in HIV-Mtb coinfected macrophages correlates with reduced GM-CSF secretion. Treatment of coinfected cells with GM-CSF restores bacterial control. Thus, we leverage the natural variation in macrophage control of Mtb to identify a critical cytokine response for regulating Mtb survival and identify components of the antimicrobial response induced by GM-CSF.
Highlights
Variability in bacterial sterilization is a key feature of Mycobacterium tuberculosis (Mtb) disease
We show that human immunodeficiency virus (HIV) coinfection makes macrophages more permissive of Mtb growth, which correlates with reduced granulocyte macrophage colonystimulating factor (GM-CSF) production, and that treatment with GM-CSF, but not other canonical activators such as vitamin
In primary human monocyte-derived macrophages (MDMs) the total Mtb burden increases slowly over time, which has historically been interpreted as evidence that in the absence of sufficient activation of the vitamin D pathway, primary human MDMs slow Mtb growth but cannot kill the bacteria[3,7]
Summary
Variability in bacterial sterilization is a key feature of Mycobacterium tuberculosis (Mtb) disease. Using a bacterial live-dead reporter strain to assess macrophage antimicrobial capacity at a single cell level, we find that these macrophages display significant cell-to-cell variability in antibacterial capacity We leveraged this natural variation in antimicrobial function to define the features of the antimicrobial pathways engaged in macrophages that naturally kill the infecting bacteria. Through global transcriptional profiling and transcriptional pathway analysis of isolated macrophage subpopulations, we find that differential expression of genes implicated in the GM-CSF signaling pathway most strongly discriminates macrophages that have successfully controlled Mtb (restrictive macrophages) from macrophages that permit bacterial survival (permissive macrophages) and that addition of exogenous GMCSF further increases bacterial killing. GM-CSF mediated bacterial killing correlates with increased phagolysosomal maturation but not increased CAMP expression or reactive nitrogen species production, suggesting that it activates a different antimicrobial pathway than that activated by vitamin D and IFN-γ. We show that human immunodeficiency virus (HIV) coinfection makes macrophages more permissive of Mtb growth, which correlates with reduced GM-CSF production, and that treatment with GM-CSF, but not other canonical activators such as vitamin
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