Related Experiment Videos
Phagocytosis enhances murine macrophage activation by interferon-gamma and tumor necrosis factor-alpha
S B Corradin1, Y Buchmüller-Rouiller, J Mauël
1Institute of Biochemistry, Epalinges, Switzerland.
Abstract:
Previously, we reported that exposure of bone marrow-derived macrophages (M phi) to a phagocytic stimulus in the simultaneous presence of interferon-gamma (IFN-gamma) induced these cells to generate nitrite (NO2-). This effect was achieved using both living (i.e. promastigotes of the protozoan parasite Leishmania enriettii) and inert (latex beads) particles. When the phagocytic stimulus was Leishmania, enhanced intracellular killing accompanied elevated NO2- secretion. As shown here, the capacity of phagocytosis to elicit NO2- production by IFN-gamma-treated M phi was inhibited by antibody to murine recombinant tumor necrosis factor-alpha (rTNF-alpha), suggesting that phagocytosis enabled IFN-gamma to activate M phi via the induction of TNF-alpha as an autocrine second signal. M phi NO2- production in response to rIFN-gamma and either exogenous TNF-alpha or Leishmania was strongly enhanced by prostaglandin E2, consistent with such a mechanism. However, addition of either Leishmania promastigotes or latex beads to M phi cultures simultaneously exposed to both IFN-gamma and exogenous murine or human rTNF-alpha further potentiated activation as measured by NO2- release. Furthermore, anti-TNF antibody failed to inhibit M phi responses to rIFN-gamma and bacterial lipopolysaccharide (LPS) in the presence or absence of Leishmania; also exogenous rTNF-alpha did not significantly affect NO2- production by IFN-gamma/LPS cultures despite a strong enhancement by Leishmania. These results suggest that phagocytosis enhances M phi responses by a process more complex than the sole induction of TNF-alpha. Phagocytosis also increased M phi NO2- production elicited by IFN-gamma plus TNF-alpha in L-arginine-deficient media. These results indicate that phagocytosis may be an important mechanism of up-regulating M phi microbicidal activity, and could be particularly relevant upon arginine depletion which occurs during an inflammatory response.
Insights
Phagocytosis enhances macrophage nitrite production, a key antimicrobial mechanism, potentially via tumor necrosis factor-alpha. This process is more complex than initially thought and crucial during inflammation.
Area of Science:
- Immunology
- Cellular Biology
- Microbiology
Background:
- Macrophages (M phi) exposed to interferon-gamma (IFN-gamma) and phagocytic stimuli produce nitrite (NO2-).
- This NO2- production is linked to enhanced intracellular killing of pathogens like Leishmania.
- Tumor necrosis factor-alpha (TNF-alpha) was previously suggested as an autocrine mediator in this process.
Purpose of the Study:
- To investigate the role of TNF-alpha in mediating phagocytosis-induced NO2- production by IFN-gamma-activated macrophages.
- To explore additional mechanisms by which phagocytosis enhances macrophage activation beyond TNF-alpha induction.
- To assess the relevance of these findings in conditions like arginine depletion during inflammation.
Main Methods:
- Bone marrow-derived macrophages were treated with IFN-gamma and various stimuli (Leishmania, latex beads, lipopolysaccharide).
- Nitrite production was measured as an indicator of macrophage activation.
- Antibodies against TNF-alpha and exogenous TNF-alpha were used to probe the signaling pathways.
Main Results:
- Antibody to TNF-alpha partially inhibited NO2- production, suggesting TNF-alpha's involvement but not exclusive role.
- Phagocytosis further potentiated NO2- release when macrophages were simultaneously exposed to IFN-gamma and exogenous TNF-alpha.
- Macrophage responses to IFN-gamma and LPS were not inhibited by anti-TNF antibody, indicating alternative activation pathways.
Conclusions:
- Phagocytosis enhances macrophage microbicidal activity through mechanisms more complex than solely inducing TNF-alpha.
- Phagocytosis-mediated NO2- production is increased in arginine-deficient conditions, relevant during inflammation.
- These findings highlight phagocytosis as a critical regulator of macrophage antimicrobial function, especially under inflammatory stress.