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TLR9-dependent and independent pathways drive activation of the immune system by Propionibacterium acnes

Sandrine Tchaptchet1, Marina Gumenscheimer, Christoph Kalis

  • 1Department of Developmental Immunology, Max Planck Institute of Immunbiology und Epigenetics, Freiburg, Germany.

Plos One
|June 30, 2012
PubMed

Insights

Propionibacterium acnes can trigger a delayed immune response in mice, distinct from its known early effects. This alternative pathway, dependent on interferon-gamma and MyD88, involves toll-like receptors 2 and 4.

Area of Science:

  • Immunology
  • Microbiology
  • Infectious Diseases

Background:

  • Propionibacterium acnes is a commensal bacterium implicated in inflammatory diseases.
  • P. acnes induces immunomodulatory effects in mice, including splenomegaly and granuloma formation, typically requiring interferon-gamma (IFN-γ) and toll-like receptor 9 (TLR9).

Purpose of the Study:

  • To investigate alternative immunomodulatory responses to P. acnes beyond the well-characterized early, TLR9-dependent pathway.
  • To elucidate the mechanisms underlying a delayed, TLR9-independent immune response to P. acnes.

Main Methods:

  • Mice were primed with P. acnes to assess delayed immunomodulatory effects.
  • Experiments involved evaluating responses in the absence of TLR9 and assessing the roles of IFN-γ, MyD88, TLR2, and TLR4.

Main Results:

  • A delayed (1-2 weeks) immunomodulatory response to P. acnes was identified, distinct from the early TLR9-dependent response.
  • This alternative response was IFN-γ dependent and required a functional MyD88 signaling pathway.
  • While known MyD88-dependent receptors were excluded, TLR2 and TLR4 activation were found to be crucial for this delayed response.

Conclusions:

  • P. acnes can induce a delayed, IFN-γ-dependent immune sensitization mechanism.
  • This alternative pathway relies on MyD88 signaling, partly through TLR2 and/or TLR4, offering insights into innate immune responses.
  • Findings suggest a potential role in both infectious and sterile inflammatory conditions.

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