Macrophage reprogramming by mycolic acid promotes a tolerogenic response in experimental asthma

  • Korf J
  • Pynaert G
  • Tournoy K
 et al. 
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RATIONALE: Mycolic acid (MA) constitutes a major and distinguishing cell wall biolipid from Mycobacterium tuberculosis. MA interferes with the lipid homeostasis of alveolar macrophages, inducing differentiation into foamy macrophages exhibiting increased proinflammatory function. OBJECTIVES: We verified the interference of this altered macrophage function with inhaled antigen-triggered allergic airway inflammation and underlying Th2 lymphocyte reactivity. METHODS: Using ovalbumin (OVA) as model allergen, C57BL/6 or BALB/C mice were sensitized by OVA-alum immunization. Experimental asthma, triggered subsequently by repetitive nebulized OVA inhalation, was assessed, using as readout parameters eosinophilia, peribronchial inflammation, and Th2 cytokine function. MEASUREMENTS AND MAIN RESULTS: A single intratracheal treatment of sensitized mice with MA, inserted into liposomes as carriers, prevented the onset of OVA-triggered allergic airway inflammation and promoted unresponsiveness to a secondary set of allergen exposures. The development of this tolerant condition required an 8-d lapse after MA instillation, coinciding with the appearance of foamy alveolar macrophages. MA-conditioned CD11b(+)F4/80(+) macrophages, transferred to the airways, mimicked the tolerogenic function of instilled MA; however, without the 8-d lapse requirement. Indicative of a macrophage-mediated tolerogenic antigen-presenting function, major histocompatibility complex (MHC)-mismatched donor macrophages failed to promote tolerance. Furthermore, Treg markers were strongly increased and established tolerance was lost after in situ depletion of CD25(+) Treg cells. Contrary to the interleukin-10 dependence of tolerogenic dendritic cells, IFN-gamma deficiency but not interleukin-10 deficiency abrogated the tolerogenic capacity of MA-conditioned macrophages. CONCLUSIONS: These results document an innate-driven Mycobacterium tuberculosis MA-triggered immune regulatory mechanism in control of pulmonary allergic responses by converting macrophages into IFN-gamma-dependent tolerogenic antigen-presenting cells.

Author-supplied keywords

  • Allergic airway inflammation
  • Foamy macrophages
  • Mycobacterium tuberculosis
  • Mycolic acid
  • Tolerance

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  • Johanna E. Korf

  • Gwenda Pynaert

  • Kurt Tournoy

  • Tom Boonefaes

  • Antoon Van Oosterhout

  • Daisy Ginneberge

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