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Regulation of macrophage Fc receptor expression and phagocytosis by histidine-rich glycoprotein
N S Chang1, R W Leu, J A Rummage
1Guthrie Research Institute, Laboratory of Molecular Immunology, Guthrie Medical Center, Sayre, Pennsylvania 18840.
Abstract:
Regulation of macrophage Fc receptor (Fc gamma R)-mediated phagocytic function by histidine-rich glycoprotein (HRG) was investigated. Pretreatment of oil-elicited inflammatory mouse peritoneal macrophages with HRG for 1-3 hr increased their Fc gamma R-mediated binding and phagocytosis of IgG-opsonized sheep erythrocyte conjugates (EA). A significant reduction of Fc gamma R-dependent EA binding and phagocytosis occurred after pretreatment of macrophages with HRG for more than 8 hr. These results indicate that HRG is capable of modulating Fc gamma R expression in a biphasic fashion, which directly affects the overall efficiency of phagocytosis. HRG differentially regulated the functions of Fc gamma R subclasses. For example, HRG reduced the efficiency of Fc gamma RII (Fc gamma 2b/gamma 1R)-dependent phagocytosis of erythrocytes conjugated with monoclonal IgG2b or IgG1 by macrophages pretreated with HRG for 24 hr. However, when similar studies were performed using erythrocytes coated with monoclonal IgG2a, HRG was less effective in inhibiting Fc gamma RI (Fc gamma 2aR)-dependent phagocytosis. As an HRG-binding glycosaminoglycan, heparin failed to block the regulatory function of HRG on macrophages. Similarly, interferon-gamma (IFN-gamma) was not capable of blocking the functional activity of HRG. These studies suggest that HRG regulates macrophage function via a novel pathway different from that of heparin or IFN-gamma.
Insights
Histidine-rich glycoprotein (HRG) regulates macrophage phagocytosis in a biphasic manner, initially enhancing and then reducing Fc gamma receptor-mediated functions. HRG differentially affects Fc gamma receptor subclasses, suggesting a novel regulatory pathway.
Area of Science:
- Immunology
- Cell Biology
- Glycoprotein Research
Background:
- Macrophage phagocytosis is crucial for immune responses.
- Fc gamma receptors (Fc gamma R) mediate phagocytosis of IgG-opsonized particles.
- Histidine-rich glycoprotein (HRG) is a plasma protein with known biological functions.
Purpose of the Study:
- To investigate the role of histidine-rich glycoprotein (HRG) in regulating macrophage Fc gamma receptor (Fc gamma R)-mediated phagocytosis.
- To determine the effect of HRG on Fc gamma R expression and function.
- To explore the pathway through which HRG modulates macrophage activity.
Main Methods:
- Incubation of mouse peritoneal macrophages with HRG for varying durations (1-3 hr and >8 hr).
- Assessment of Fc gamma R-mediated binding and phagocytosis of IgG-opsonized sheep erythrocytes (EA).
- Differential analysis of Fc gamma R subclass (Fc gamma RI and Fc gamma RII) function using specific IgG subclasses.
Main Results:
- HRG pretreatment for 1-3 hr enhanced Fc gamma R-mediated phagocytosis of EA.
- HRG pretreatment for >8 hr significantly reduced Fc gamma R-dependent EA binding and phagocytosis.
- HRG differentially modulated Fc gamma R subclasses, reducing Fc gamma RII-dependent phagocytosis more than Fc gamma RI-dependent phagocytosis.
- Heparin and interferon-gamma (IFN-gamma) did not block HRG's regulatory function.
Conclusions:
- HRG exhibits a biphasic regulation of macrophage Fc gamma R-mediated phagocytosis.
- HRG differentially affects Fc gamma R subclasses, impacting phagocytic efficiency.
- HRG appears to regulate macrophage function through a novel pathway distinct from heparin or IFN-gamma.