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Tumor necrosis factor-alpha triggers antitoxoplasmal activity of IFN-gamma primed macrophages
L D Sibley1, L B Adams, Y Fukutomi
1Immunology Department, G. W. L. Hansen's Disease Center, Carville, LA 70721.
Abstract:
IFN-gamma is an important mediator of cellular resistance against microbial pathogens and tumor cells due in part to its potent capacity to activate macrophages for enhanced cytotoxicity. The present study demonstrates that TNF-alpha regulates the expression of enhanced antimicrobial activity by triggering IFN-gamma primed macrophages to kill or inhibit intracellular Toxoplasma gondii. Resident mouse macrophages stimulated with rIFN-gamma at levels up to 2500 U/ml failed to display enhanced antitoxoplasmal activity when cultured in vitro under low endotoxin conditions (less than 10 pg/ml), but were triggered by addition of small amounts of LPS (0.1 ng/ml). A similar requirement for LPS as a second signal necessary to trigger antitoxoplasmal activity was observed when IFN-gamma was administered to mice in vivo. The essential nature of this triggering step allowed us to explore the role of cytokines that act as endogenous regulators of macrophage activation. rTNF-alpha, although unable to confer antitoxoplasmal activity when used alone to treat macrophages, was capable of triggering IFN-gamma-primed macrophages cultured under low endotoxin conditions. The ability of TNF-alpha to trigger IFN-gamma-primed macrophages was blocked by rabbit anti-TNF-alpha polyclonal antisera but was not affected by polymyxin B indicating that TNF-alpha triggering was not due to contamination with LPS. Collectively, these findings demonstrate that TNF-alpha performs an important regulatory role in the expression of enhanced anti-microbial activity by IFN-gamma-primed macrophages.
Insights
Tumor necrosis factor-alpha (TNF-alpha) triggers macrophages primed by interferon-gamma (IFN-gamma) to fight intracellular pathogens like Toxoplasma gondii. This study reveals TNF-alpha
Area of Science:
- Immunology
- Cellular Biology
- Microbiology
Background:
- Interferon-gamma (IFN-gamma) activates macrophages for enhanced cytotoxicity against pathogens and tumor cells.
- Macrophage activation often requires multiple signals, including priming and triggering.
- Toxoplasma gondii is an intracellular pathogen that infects macrophages.
Purpose of the Study:
- To investigate the role of TNF-alpha in regulating antimicrobial activity of IFN-gamma-primed macrophages.
- To determine if TNF-alpha can act as a triggering signal for IFN-gamma-primed macrophages against intracellular pathogens.
- To elucidate the mechanism by which TNF-alpha regulates macrophage-mediated antimicrobial activity.
Main Methods:
- In vitro culture of resident mouse macrophages.
- Stimulation of macrophages with recombinant IFN-gamma and/or TNF-alpha.
- Assessment of antitoxoplasmal activity under low endotoxin conditions.
- Use of LPS, anti-TNF-alpha antisera, and polymyxin B to investigate signaling pathways.
Main Results:
- IFN-gamma-primed macrophages required a second signal, such as LPS, to exhibit enhanced antimicrobial activity in vitro.
- TNF-alpha acted as a potent trigger for IFN-gamma-primed macrophages, conferring antimicrobial activity against Toxoplasma gondii.
- TNF-alpha-mediated triggering was specific and not due to LPS contamination, as shown by antibody blocking and polymyxin B treatment.
Conclusions:
- TNF-alpha plays a crucial regulatory role in activating IFN-gamma-primed macrophages for enhanced antimicrobial defense.
- TNF-alpha can serve as an endogenous trigger for macrophage-mediated killing of intracellular pathogens.
- Understanding this cytokine interaction is vital for developing novel immunotherapies against infectious diseases.