Monocytic niches enable Mycobacterium Tuberculosis Persistence in Lymph Nodes

Abstract

Tuberculosis remains a leading cause of infectious mortality worldwide, in part due to the ability of Mycobacterium tuberculosis (Mtb) to persist within host tissues despite robust immune activation. While pulmonary infection has historically dominated studies of tuberculosis pathogenesis, emerging evidence suggests that lymphoid tissues play a critical role in shaping disease outcome. This dissertation investigates the lung-draining mediastinal lymph node (medLN) as a central and underappreciated site of Mtb persistence, addressing the paradox that the medLN serves as both the primary site of adaptive immune priming and a long-term bacterial reservoir.Using complementary approaches including mouse infection models, multiparameter confocal microscopy, flow cytometry, single-cell transcriptomics, and mathematical modeling, this work defines the cellular and spatial mechanisms that enable Mtb survival within the medLN. We identify conventional dendritic cells and monocytes as early carriers of Mtb from the lung to the medLN and show that, by three weeks post-infection, Mtb becomes concentrated within monocytic aggregates that support bacterial persistence. Conventional dendritic cells—particularly cDC1 and inflammatory cDC2 subsets—are required for robust TH1-skewed CD4 T cell priming due to sequential waves of IL-12 production in the medLN during the first 3 weeks of infection. However, the monocytic niche in the medLN provides a site of bacterial persistence, where overwhelming numbers of Mtb-specific TH1 effector T cells fail to reduce Mtb burden within the medLN, despite effective control in the lung. These findings reveal a state of functional immunological blindness within the medLN, in which immune activation is uncoupled from immune efficacy. Together, this work redefines lymphoid tissue involvement in tuberculosis pathogenesis, establishes the medLN as a privileged niche for Mtb persistence, and highlights the need for therapeutic and vaccine strategies that target tissue-specific immune constraints rather than immune activation alone.