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TNF-alpha activates human monocytes for Paracoccidioides brasiliensis killing by an H2O2-dependent mechanism

J P M Carmo1, L A Dias-Melicio, S A Calvi

  • 1Department of Microbiology and Immunology, São Paulo State University (UNESP), Botucatu, SP, Brazil.

Medical Mycology
|June 15, 2006
PubMed

Insights

Tumor necrosis factor alpha (TNF-alpha) activates human monocytes to kill Paracoccidioides brasiliensis yeast. Hydrogen peroxide (H2O2) produced by these cells is key to this fungicidal activity.

Area of Science:

  • Immunology
  • Mycology
  • Biochemistry

Background:

  • Paracoccidioides brasiliensis is a highly virulent fungal pathogen.
  • Human monocytes play a crucial role in innate immunity against fungal infections.
  • Tumor necrosis factor alpha (TNF-alpha) is a key cytokine in immune responses.

Purpose of the Study:

  • To investigate the mechanism by which TNF-alpha-activated human monocytes kill P. brasiliensis.
  • To determine the role of reactive oxygen species (ROS) and nitric oxide (NO) in this fungicidal process.

Main Methods:

  • Human monocytes were activated with recombinant TNF-alpha.
  • Fungicidal activity against P. brasiliensis yeast was assessed.
  • The effects of catalase (CAT), superoxide dismutase (SOD), and NG-monomethyl-L-arginine (NG-MMLA) on fungicidal activity were evaluated.
  • Hydrogen peroxide (H2O2) production by activated monocytes was measured.

Main Results:

  • TNF-alpha-activated monocytes exhibited significant fungicidal activity against P. brasiliensis.
  • This activity was inhibited by CAT, indicating a role for H2O2.
  • SOD and NG-MMLA did not inhibit the fungicidal activity, ruling out superoxide anion and nitric oxide as primary mediators.
  • A direct correlation was observed between intracellular H2O2 production and fungal killing.

Conclusions:

  • Hydrogen peroxide (H2O2) is a critical mediator in the killing of highly virulent P. brasiliensis by TNF-alpha-activated human monocytes.
  • This finding elucidates a specific host-pathogen interaction mechanism in paracoccidioidomycosis.

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