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Cytokine interactions in experimental cutaneous leishmaniasis
W Solbach1, M Röllinghoff, S Stenger
1Institute of Clinical Microbiology, University Erlangen-Nürnberg, Germany.
Insights
Interferon-gamma (IFN-gamma) alone activates macrophages to kill Leishmania parasites. Interleukin-4 (IL-4) and Tumor Necrosis Factor-alpha (TNF-alpha) synergize with low IFN-gamma levels for potent antiparasitic activity.
Area of Science:
- Immunology
- Parasitology
- Cell Biology
Background:
- Macrophages are crucial for eliminating intracellular Leishmania major amastigotes.
- Cytokines like IL-4, TNF-alpha, and IFN-gamma play key roles in macrophage activation.
Purpose of the Study:
- To investigate the individual and combined roles of IL-4, TNF-alpha, and IFN-gamma in activating macrophages against Leishmania.
- To elucidate the mechanisms underlying cytokine-mediated macrophage activation.
Main Methods:
- Peritoneal exudate macrophages were cultured with varying concentrations of IL-4, TNF-alpha, and IFN-gamma.
- Macrophage antileishmanial activity was assessed by measuring amastigote elimination.
- The involvement of the L-arginine pathway was tested using NG-monomethyl-L-arginine (L-NMMA).
Main Results:
- IFN-gamma alone induced significant amastigote elimination.
- IL-4 and TNF-alpha alone did not activate macrophages for parasite killing.
- IL-4 and TNF-alpha synergized with sub-optimal IFN-gamma concentrations to enhance antiparasitic activity.
- Endogenous TNF-alpha production was implicated in the IL-4 and IFN-gamma synergy.
- Inhibition of the L-arginine pathway with L-NMMA blocked parasite killing, indicating the role of nitrogen oxides.
Conclusions:
- Macrophage activation against Leishmania is regulated by a complex cytokine network.
- IL-4 and TNF-alpha significantly potentiate the activity of low-dose IFN-gamma.
- The L-arginine-dependent pathway producing nitrogen oxides is essential for parasite killing during synergistic activation.
Abstract:
Destruction of intracellularly living Leishmania major amastigotes is achieved by activated macrophages. In this report, we have investigated the contribution of IL-4, TNF-alpha and IFN-gamma to the induction of antileishmanial macrophage activation. It was found that as single lymphokine only IFN-gamma led to amastigote elimination by peritoneal exudate macrophages. Neither IL-4 nor TNF-alpha or the combination of both cytokines led to antimicrobial activation. When the macrophages were incubated with concentrations of IFN-gamma that by themselves were insufficient for maximum cell activation, it was found that both IL-4 and TNF-alpha very effectively synergized with IFN-gamma for induction of antiparasitic activity. The activation which was achieved when IFN-gamma was combined with IL-4 could be blocked not only with antibodies to either of the lymphokines, but also with an antiserum specific for TNF-alpha, suggesting the involvement of endogenously generated TNF-alpha in this synergism. Any of the synergistic activities observed presumably lead to the activation of the L-arginine dependent pathway used by the cell for the production of nitrogen oxides as effector molecules for parasite killing since NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of this pathway, completely blocked the killing of intracellular parasites. We conclude that macrophage activation for antiparasitic activity is directed by a complex network of cytokine-interactions, in which IL-4 and TNF-alpha very effectively synergize positively with low levels of IFN-gamma.