Dormant Mycobacterium tuberculosis fails to block phagosome maturation and shows unexpected capacity to stimulate specific human T lymphocytes

J Immunol. 2013 Jul 1;191(1):274-82. doi: 10.4049/jimmunol.1202900. Epub 2013 Jun 3.


Dormancy is defined as a stable but reversible nonreplicating state of Mycobacterium tuberculosis. It is currently thought that dormant M. tuberculosis (D-Mtb) is responsible for latent tuberculosis (TB) infection. Recently, D-Mtb was also shown in sputa of patients with active TB, but the capacity of D-Mtb to stimulate specific immune responses was not investigated. We observed that purified protein derivative-specific human CD4(+) T lymphocytes recognize mycobacterial Ags more efficiently when macrophages are infected with D-Mtb instead of replicating M. tuberculosis (R-Mtb). The different Ag recognition occurs even when the two forms of mycobacteria equally infect and stimulate macrophages, which secrete the same cytokine pattern and express MHC class I and II molecules at the same levels. However, D-Mtb but not R-Mtb colocalizes with mature phagolysosome marker LAMP-1 and with vacuolar proton ATPase in macrophages. D-Mtb, unlike R-Mtb, is unable to interfere with phagosome pH and does not inhibit the proteolytic efficiency of macrophages. We show that D-Mtb downmodulates the gene Rv3875 encoding for ESAT-6, which is required by R-Mtb to block phagosome maturation together with Rv3310 gene product SapM, previously shown to be downregulated in D-Mtb. Thus, our results indicate that D-Mtb cannot escape MHC class II Ag-processing pathway because it lacks the expression of genes required to block the phagosome maturation. Data suggest that switching to dormancy not only represents a mechanism of survival in latent TB infection, but also a M. tuberculosis strategy to modulate the immune response in different stages of TB.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Dendritic Cells / immunology
  • Humans
  • Immune Evasion
  • Latent Tuberculosis / immunology*
  • Latent Tuberculosis / microbiology
  • Latent Tuberculosis / pathology
  • Lymphocyte Activation / immunology*
  • Macrophages / immunology
  • Monocytes / immunology
  • Mycobacterium tuberculosis / growth & development
  • Mycobacterium tuberculosis / immunology*
  • Phagosomes* / immunology
  • Phagosomes* / microbiology
  • T-Lymphocyte Subsets / immunology*
  • T-Lymphocyte Subsets / microbiology
  • T-Lymphocyte Subsets / pathology