Restricted MHC-II trafficking in Mycobacterium tuberculosis-infected M2-like macrophages limits CD4+ T cell activation
Recognition of infected macrophages by CD4+ T cells is essential to immune protection against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). However, not all infected macrophage subsets successfully elicit T cell activation. We recently discovered that M2-like macrophages fail to efficiently activate memory CD4+ T cells when infected with Mtb, yet successfully elicit T cell activation when loaded with peptides, {gamma}-irradiated bacteria, or Mtb whole cell lysate. Since the mechanisms underlying CD4+ T cell evasion by infected M2 but not M1-like macrophages remain underexplored, we sought to determine the genes and pathways unique to Mtb infection of M2-like cells, including alveolar macrophages. RNA sequencing of human macrophages infected with virulent Mtb identified enrichment of IL-10 and type I interferon (IFN) signaling genes, including IL10RA and HERC5, respectively, in infected M2-like monocyte-derived and alveolar macrophages. However, genes involved in MHC-II trafficking, such as AP1M2, were higher in infected M1-like macrophages. In complementary experiments using fluorescence microscopy and flow cytometry, we observed impaired trafficking of newly synthesized MHC-II to the plasma membrane of Mtb-infected M2-like macrophages despite high total surface MHC-II levels. Neutralization of IL-10 or knockdown of HERC5 restored MHC-II trafficking to the cell surface among infected M2-like macrophages and significantly enhanced activation of memory CD4+ T cells in an MHC-II-dependent manner. These findings identify coordinated IL-10 and type I IFN signaling as key mechanisms that restrict MHC-II trafficking to the plasma membrane in Mtb-infected M2-like macrophages, thereby limiting antigen presentation and CD4+ T cell activation. We propose that host-directed therapies targeting these pathways in infected alveolar macrophages will facilitate T cell recognition for the prevention or treatment of active TB. Author SummaryRecognition of infected macrophages by CD4+ T cells is essential to immune protection against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). However, not all infected macrophage subsets successfully elicit T cell activation. We recently discovered that M2-like macrophages fail to efficiently activate memory CD4+ T cells when infected with Mtb, yet they successfully elicit T cell activation when treated with peptides, {gamma}-irradiated bacteria, or Mtb whole cell lysate. In this study, we identified genes and pathways uniquely upregulated in Mtb-infected M2-like macrophages that are linked to inefficient CD4+ T cell activation, including IL-10 signaling and type I interferon (IFN) pathways. These pathways were linked to reduced MHC-II trafficking to the plasma membrane in Mtb-infected M2-like macrophages. Neutralization of IL-10 or knockdown of HERC5 restored MHC-II trafficking and augmented memory CD4+ T cell activation. Our study demonstrates that IL-10 signaling and type I IFN pathways play detrimental roles in macrophages during Mtb infection, impairing MHC-II trafficking and CD4+ T cell activation. Since lung-resident alveolar macrophages express a dominant M2-like phenotype, these findings suggest that targeting IL-10 and type I IFN signaling may offer a strategy to enhance CD4+ T cell-mediated immunity and improve TB outcomes.