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IFN-gamma enhances sensitivity of human macrophages to extracellular ATP-mediated lysis
D K Blanchard1, S McMillen, J Y Djeu
1University of South Florida College of Medicine, Department of Medical Microbiology and Immunology, Tampa 33612.
Abstract:
In an effort to determine the mechanism by which autologous monocytes are killed by lymphokine-activated killer cells, soluble mediators were examined for their direct effect on target cells. Extracellular ATP (ATPo), but not ADP, was found to lyse human culture-derived macrophages in a 6-h 51Cr-release assay. Treatment of monocytes with human rIFN-gamma rendered those cells significantly more sensitive to ATPo compared to untreated or granulocyte-macrophage CSF-(GM-CSF) treated cells. In addition, IFN-gamma-treated macrophages released approximately 80% of 51Cr label within 15 min after the addition of ATPo, whereas GM-CSF-treated cells did not release significant levels of radiolabel until 4 to 6 h after initial stimulation with ATPo. Time course studies also demonstrated that 3 days of incubation of macrophages with IFN-gamma induced optimal sensitivity to ATPo, although some effect was noted after 4 h of incubation. Thus, IFN-gamma treatment of macrophages elicited increased sensitivity to ATPo-mediated lysis, a phenomenon characterized by rapid release of 51Cr from labeled cells and which is possibly due to induction or activation of surface ATP-binding receptors different from those present on GM-CSF-treated or untreated macrophages.
Insights
Extracellular ATP (ATPo) lyses human macrophages, with sensitivity significantly enhanced by interferon-gamma (IFN-gamma) treatment. This IFN-gamma effect involves rapid cell lysis, suggesting altered ATP-binding receptors on macrophages.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Lymphokine-activated killer (LAK) cells can induce autologous monocyte lysis.
- The soluble mediators involved in this cytotoxic mechanism require further investigation.
- Extracellular nucleotides, such as ATP, are increasingly recognized for their roles in cell signaling and immune responses.
Purpose of the Study:
- To elucidate the mechanism of autologous monocyte lysis by LAK cells.
- To investigate the direct effects of soluble mediators, specifically extracellular ATP (ATPo), on target cells.
- To determine the influence of cytokines like interferon-gamma (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF) on monocyte sensitivity to ATPo.
Main Methods:
- Utilized a 6-hour 51Cr-release assay to measure target cell lysis.
- Treated human culture-derived macrophages with recombinant human IFN-gamma or GM-CSF.
- Examined the time course of lysis induction by ATPo following cytokine treatment.
Main Results:
- Extracellular ATP (ATPo), but not ADP, directly lysed human macrophages.
- IFN-gamma treatment significantly increased macrophage sensitivity to ATPo-mediated lysis compared to untreated or GM-CSF-treated cells.
- IFN-gamma-treated macrophages exhibited rapid 51Cr release within 15 minutes of ATPo addition, while GM-CSF-treated cells showed delayed lysis (4-6 hours).
- Optimal sensitivity to ATPo was achieved after 3 days of IFN-gamma incubation.
Conclusions:
- IFN-gamma treatment enhances macrophage sensitivity to ATPo-mediated lysis.
- The rapid lysis observed suggests IFN-gamma may induce or activate specific surface ATP-binding receptors.
- These findings contribute to understanding the complex interactions between cytokines, extracellular nucleotides, and immune cell cytotoxicity.