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Gamma interferon cooperates with lipopolysaccharide to activate mouse splenic macrophages to an antihistoplasma state
T E Lane1, B A Wu-Hsieh, D H Howard
1Department of Microbiology and Immunology, University of California, Los Angeles School of Medicine 90024.
Abstract:
Inhibition of the intracellular growth of Histoplasma capsulatum by murine resident red pulp splenic macrophages was examined. Splenic macrophages, unlike resident peritoneal macrophages, required a prolonged preincubation (18 h) with recombinant murine gamma interferon (rMuIFN-gamma) for activation. To be fully activated, the splenic macrophages required incubation with rMuIFN-gamma in combination with 0.1 microgram of lipopolysaccharide (LPS) per ml. Splenic macrophages stimulated with rMuIFN-gamma, LPS, or rMuIFN-gamma and LPS produced tumor necrosis factor alpha (TNF-alpha), but recombinant murine TNF-alpha (rMuTNF-alpha) did not activate macrophages when used alone or as a second signal with rMuIFN-gamma. Anti-TNF-alpha antibody did not block IFN-gamma-LPS activation of splenic macrophages to any significant extent. One hundred micromolar ferrous sulfate antagonized IFN-gamma-LPS activation of splenic macrophages, indicating that iron was involved in the fungistatic activity of cytokine-stimulated phagocytes. Our results indicate that (i) splenic macrophages differ significantly from peritoneal macrophages in their requirements for activation and (ii) the mechanism by which splenic macrophages exert their antifungal effects involves iron.
Insights
Murine splenic macrophages require prolonged interferon-gamma and lipopolysaccharide preincubation for activation. Antifungal activity against Histoplasma capsulatum involves iron, not tumor necrosis factor-alpha.
Area of Science:
- Immunology
- Mycology
Background:
- Resident red pulp splenic macrophages play a role in controlling intracellular pathogens.
- Understanding macrophage activation is crucial for developing antifungal therapies.
Purpose of the Study:
- To investigate the activation requirements of murine splenic macrophages for inhibiting Histoplasma capsulatum growth.
- To elucidate the role of cytokines and iron in splenic macrophage antifungal activity.
Main Methods:
- Splenic macrophages were preincubated with recombinant murine gamma interferon (rMuIFN-gamma) and/or lipopolysaccharide (LPS).
- Tumor necrosis factor alpha (TNF-alpha) production was measured.
- The effect of ferrous sulfate and anti-TNF-alpha antibody on macrophage activation was assessed.
Main Results:
- Splenic macrophages required prolonged rMuIFN-gamma preincubation and LPS for full activation, differing from peritoneal macrophages.
- Activated splenic macrophages produced TNF-alpha, but rMuTNF-alpha did not enhance activation.
- Ferrous sulfate antagonized activation, indicating iron's involvement in fungistatic activity.
Conclusions:
- Murine splenic macrophages have distinct activation requirements compared to peritoneal macrophages.
- Iron is a key component in the mechanism of splenic macrophage-mediated inhibition of Histoplasma capsulatum growth.