Microfold Cells Actively Translocate Mycobacterium tuberculosis to Initiate Infection

• Mtb translocates across model M cells in vitro in an active, transcellular process
• Depletion of airway M cells in mice reduces Mtb dissemination via NALT
• M cells contribute to Mtb dissemination from the airway mucosa
• Airway M cell depletion in mice prior to aerosol Mtb infection improves survival

SummaryThe prevailing paradigm is that tuberculosis infection is initiated when patrolling alveolar macrophages and dendritic cells within the terminal alveolus ingest inhaled Mycobacterium tuberculosis (Mtb). However, definitive data for this model are lacking. Among the epithelial cells of the upper airway, a specialized epithelial cell known as a microfold cell (M cell) overlies various components of mucosa-associated lymphatic tissue. Here, using multiple mouse models, we show that Mtb invades via M cells to initiate infection. Intranasal Mtb infection in mice lacking M cells either genetically or by antibody depletion resulted in reduced invasion and dissemination to draining lymph nodes. M cell-depleted mice infected via aerosol also had delayed dissemination to lymph nodes and reduced mortality. Translocation of Mtb across two M cell transwell models was rapid and transcellular. Thus, M cell translocation is a vital entry mechanism that contributes to the pathogenesis of Mtb.

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