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Activation of mouse peritoneal macrophages by monoclonal antibodies to Mac-1 (complement receptor type 3)
Abstract:
Several features of activation of mouse peritoneal macrophages were elicited by 1-2-d exposure to submicrogram concentrations of anti-Mac-1 (M1/70), a rat monoclonal antibody that reacts with the alpha chain of complement receptor type 3 (Mac-1). The changes induced included enhanced capacity to secrete H2O2 when triggered with PMA, decreased secretion of proteins, increased expression of Ia antigen and decreased phagocytosis of particles. These changes closely resembled those induced by rIFN-gamma in type, extent, and time course. The concentration of M1/70 IgG resulting in 50% of the maximal activation of macrophage H2O2-releasing capacity averaged 0.18 +/- 0.03 micrograms/ml. This activation was not blocked by anti-FcR mAb, and could be reproduced with M18/2, a mAb against beta chain of Mac-1, suggesting that a direct ligation of Mac-1 with mAb was responsible for the activation. Neither depletion of T cells nor addition of neutralizing Abs to IFN-gamma or TNF-alpha prevented M1/70-mediated macrophage activation. Moreover, F(ab')2 of M1/70, or plating of macrophages on C3bi-coated surfaces, inhibited the activation of macrophages by rIFN-gamma. These findings suggest that Mac-1 (CR3) may play an important role in macrophage activation.
Insights
Antibody binding to Mac-1 activates mouse macrophages, enhancing H2O2 secretion and altering protein and Ia antigen expression. This suggests Mac-1 plays a key role in macrophage activation pathways.
Area of Science:
- Immunology
- Cell Biology
- Macrophage Biology
Background:
- Mouse peritoneal macrophages exhibit specific activation features.
- Complement receptor type 3 (Mac-1) is a key cell surface receptor on macrophages.
- Monoclonal antibodies can modulate immune cell functions.
Purpose of the Study:
- To investigate the effects of anti-Mac-1 antibody (M1/70) on macrophage activation.
- To determine the role of Mac-1 in mediating changes in macrophage function.
- To compare M1/70-induced activation with interferon-gamma (IFN-gamma) effects.
Main Methods:
- Exposure of mouse peritoneal macrophages to submicrogram concentrations of anti-Mac-1 (M1/70) antibody for 1-2 days.
- Assay of hydrogen peroxide (H2O2) secretion upon phorbol 12-myristate 13-acetate (PMA) stimulation.
- Measurement of protein secretion, Ia antigen expression, and particle phagocytosis.
- Testing the effects of anti-FcR mAb, anti-beta chain mAb (M18/2), T cell depletion, and neutralizing antibodies to IFN-gamma and TNF-alpha.
- Evaluation of F(ab')2 fragments of M1/70 and macrophage plating on C3bi-coated surfaces.
Main Results:
- Anti-Mac-1 antibody (M1/70) induced enhanced H2O2 secretion, decreased protein secretion, increased Ia antigen expression, and reduced phagocytosis.
- These changes mirrored those induced by recombinant IFN-gamma (rIFN-gamma).
- Activation was concentration-dependent, specific to Mac-1 ligation (not FcR-mediated), and independent of T cells, IFN-gamma, or TNF-alpha.
- M1/70 F(ab')2 fragments and plating on C3bi inhibited rIFN-gamma-mediated activation.
Conclusions:
- Direct ligation of Mac-1 by anti-Mac-1 antibodies can activate macrophages.
- Mac-1-mediated activation shares functional similarities with IFN-gamma-induced activation.
- Mac-1 may play a significant role in regulating macrophage activation processes.