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Antihistoplasma effect of activated mouse splenic macrophages involves production of reactive nitrogen intermediates
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:
The mechanism by which recombinant murine gamma interferon (rMuIFN-gamma) and bacterial lipopolysaccharide (LPS) activate mouse resident splenic macrophages to inhibit the intracellular growth of the fungus Histoplasma capsulatum was examined. Growth inhibition depended on L-arginine metabolism. The growth inhibitory state normally induced by rMuIFN-gamma and LPS in resident splenic macrophages did not occur when the macrophages were cultured in the presence of NG-monomethyl-L-arginine, a competitive inhibitor of L-arginine metabolism. Resident splenic macrophages treated with rMuIFN-gamma and LPS produced nitrite (NO2-), an end product of L-arginine metabolism. When macrophages were cultured in the presence of NG-monomethyl-L-arginine together with rMuIFN-gamma and LPS, only baseline levels of NO2- were detected. Spleen cells from H. capsulatum-infected mice produced high levels of NO2- in culture. The production of NO2- correlated with in vitro inhibition of the intracellular growth of H. capsulatum. Anti-tumor necrosis factor alpha antibody did not block NO2- production by the immigrant splenic macrophages and did not abolish the antihistoplasma activity.
Insights
Recombinant murine gamma interferon (rMuIFN-gamma) and lipopolysaccharide (LPS) activate macrophages to inhibit Histoplasma capsulatum growth via L-arginine metabolism and nitrite production. This pathway is crucial for the antifungal immune response.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Macrophages play a key role in innate immunity against fungal pathogens.
- Histoplasma capsulatum is an opportunistic fungal pathogen causing systemic infections.
- Interferon-gamma and lipopolysaccharide are known activators of macrophages.
Purpose of the Study:
- To elucidate the mechanism of macrophage-mediated inhibition of intracellular Histoplasma capsulatum growth.
- To investigate the role of L-arginine metabolism in this inhibitory process.
- To determine the involvement of nitrite production in the antifungal activity.
Main Methods:
- Primary mouse resident splenic macrophages were cultured with recombinant murine gamma interferon (rMuIFN-gamma) and bacterial lipopolysaccharide (LPS).
- The effect of NG-monomethyl-L-arginine, an L-arginine metabolism inhibitor, on macrophage activation and fungal growth was assessed.
- Nitrite (NO2-) production by macrophages was measured as an indicator of L-arginine metabolism.
- In vitro inhibition of intracellular H. capsulatum growth was quantified.
- The role of tumor necrosis factor alpha was investigated using an anti-TNF-alpha antibody.
Main Results:
- Macrophage-mediated inhibition of intracellular H. capsulatum growth was dependent on L-arginine metabolism.
- NG-monomethyl-L-arginine blocked the growth inhibitory state induced by rMuIFN-gamma and LPS.
- Macrophages treated with rMuIFN-gamma and LPS produced significant levels of nitrite (NO2-).
- Nitrite production was suppressed in the presence of NG-monomethyl-L-arginine.
- Nitrite production correlated with the inhibition of H. capsulatum growth.
- Anti-tumor necrosis factor alpha antibody did not affect nitrite production or antifungal activity.
Conclusions:
- L-arginine metabolism and subsequent nitrite production are critical for the activation of mouse splenic macrophages against Histoplasma capsulatum.
- The observed antifungal activity is mediated by the L-arginine-nitrite pathway, independent of tumor necrosis factor alpha.