Mycobacterium indicus pranii and Mycobacterium bovis BCG lead to differential macrophage activation in Toll-like receptor-dependent manner

Immunology. 2014 Oct;143(2):258-68. doi: 10.1111/imm.12306.


Mycobacterium indicus pranii (MIP) is an atypical mycobacterial species possessing strong immunomodulatory properties. It is a potent vaccine candidate against tuberculosis, promotes Th1 immune response and protects mice from tumours. In previous studies, we demonstrated higher protective efficacy of MIP against experimental tuberculosis as compared with bacillus Calmette-Guérin (BCG). Since macrophages play an important role in the pathology of mycobacterial diseases and cancer, in the present study, we evaluated the MIP in live and killed form for macrophage activation potential, compared it with BCG and investigated the underlying mechanisms. High levels of tumour necrosis factor-α, interleukin-12p40 (IL-12p40), IL-6 and nitric oxide were produced by MIP-stimulated macrophages as compared with BCG-stimulated macrophages. Prominent up-regulation of co-stimulatory molecules CD40, CD80 and CD86 was also observed in response to MIP. Loss of response in MyD88-deficient macrophages showed that both MIP and BCG activate the macrophages in a MyD88-dependent manner. MyD88 signalling pathway culminates in nuclear factor-κB/activator protein-1 (NF-κB/AP-1) activation and higher activation of NF-κB/AP-1 was observed in response to MIP. With the help of pharmacological inhibitors and Toll-like receptor (TLR) -deficient macrophages, we observed the role of TLR2, TLR4 and intracellular TLRs in MIP-mediated macrophage activation. Stimulation of HEK293 cells expressing TLR2 in homodimeric or heterodimeric form showed that MIP has a distinctly higher level of TLR2 agonist activity compared with BCG. Further experiments suggested that TLR2 ligands are well exposed in MIP whereas they are obscured in BCG. Our findings establish the higher macrophage activation potential of MIP compared with BCG and delineate the underlying mechanism.

Keywords: Toll-like receptors; bacterial; cytokines.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • HEK293 Cells
  • Humans
  • Inflammation Mediators / metabolism
  • Interleukin-10 / genetics
  • Interleukin-10 / metabolism
  • Interleukin-12 Subunit p40 / metabolism
  • Interleukin-6 / metabolism
  • Macrophage Activation*
  • Macrophages, Peritoneal / immunology*
  • Macrophages, Peritoneal / metabolism
  • Macrophages, Peritoneal / microbiology*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mycobacterium bovis / immunology*
  • Myeloid Differentiation Factor 88 / genetics
  • Myeloid Differentiation Factor 88 / metabolism
  • NF-kappa B / metabolism
  • Nitric Oxide / metabolism
  • Nontuberculous Mycobacteria / immunology*
  • Signal Transduction
  • Time Factors
  • Toll-Like Receptor 2 / deficiency
  • Toll-Like Receptor 2 / genetics
  • Toll-Like Receptor 2 / metabolism*
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism
  • Transcription Factor AP-1 / metabolism
  • Tumor Necrosis Factor-alpha / metabolism


  • IL10 protein, mouse
  • Inflammation Mediators
  • Interleukin-12 Subunit p40
  • Interleukin-6
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • NF-kappa B
  • Tlr2 protein, mouse
  • Tlr4 protein, mouse
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • Transcription Factor AP-1
  • Tumor Necrosis Factor-alpha
  • interleukin-6, mouse
  • Interleukin-10
  • Nitric Oxide