Methods: We studied mice genetically deficient in M-cells (SpiB-/-) or wild type mice depleted of M-cells via anti-RANKL antibody treatment. We established a novel mouse intranasal infection model to initiate Mtb infection via M-cells. We used an in vitro M-cell mediated translocation assay, a Mtb eccD1mutant lacking its Type VII secretion system, and a fluorescent bead translocation assay.
Results: Intranasal Mtb infection in SpiB-/- mice resulted in reduced invasion and dissemination to draining lymph nodes. Transient depletion of M-cells also reduced mycobacterial dissemination in both intranasal and low-dose aerosol infection models. Using in vitro assays we found that translocation across M-cells was rapid, temperature-dependent and required eccD1. Mtb translocation across NALT required the Type VII secretion system, and its secreted effector ESAT-6 was sufficient to mediate translocation of inert beads across M-cells in vitro. Finally, M-cell depletion immediately prior to Mtb aerosol infection significantly delayed mortality in mice.
Conclusion: We conclude that M-cells are a vital portal of entry for Mtb. We propose a revised paradigm for Mtb infection that incorporates M-cell mediated entry to facilitate dissemination to lymph nodes. M-cell entry may therefore account for scrofula and other lymphatic forms of disease that together represent more than 10% of all tuberculosis cases annually.
V. Zacharia, None
D. K. Marciano, None
Y. Wu, None
H. Yagita, None
B. Levine, None
M. U. Shiloh, None