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Inhibition of macrophage tumoricidal activity by immune complexes and altered erythrocytes
Abstract:
Engagement of the macrophage membrane by biologic particles including insoluble immune complexes inhibited the development of lymphokine-mediated nonspecific tumoricidal activity by murine macrophages. The degree of inhibition was dependent on the dose of particles and the lymphokine concentration. Inhibition was not due to macrophage cell death or to diminution of cell adherence after ingestion of the immune complexes. Soluble immune complexes were not inhibitory, although approximately 10% of the complexes became cell-associated. Monomeric or heat-aggregated IgG was also not inhibitory. IgG-opsonized erythrocytes (EA) were inhibitory and inhibition was dependent on the degree of opsonization. In contrast, nonopsonized erythrocytes (E), which did not bind to macrophages, were not inhibitory. Phagocytosis of glutaraldehyde-treated E or E carrying IgM antibody and complement (EAC) also led to a reduction of tumorilytic activity. Insoluble immune complexes were inhibitory when added either before or after lymphokine. Phagocytosis was neither sufficient nor necessary to cause inhibition because 1) ingestion of polystyrene latex beads did not diminish tumoricidal activity, and 2) macrophages plated on IgG-coated surfaces were inhibited with respect to the tumoricidal function. Inhibition was not affected when indomethacin (10(-6) M) was included in the assay, which indicated that prostaglandins were not involved in the process. Thus, macrophage tumoricidal responsiveness may be compromised by interaction of biologic substances with macrophage plasma membranes. This process may thereby inactivate an important host defense mechanism against neoplastic cells.
Insights
Macrophage interaction with certain particles, like immune complexes, impairs their tumor-killing ability. This immune suppression, crucial for fighting cancer, can be triggered by various biologic substances binding to macrophage membranes.
Area of Science:
- Immunology
- Cell Biology
- Cancer Research
Background:
- Macrophages are critical immune cells involved in tumor surveillance and destruction.
- Lymphokines activate macrophages to develop tumoricidal (tumor-killing) activity.
- The interaction of macrophages with biologic particles can modulate their immune functions.
Purpose of the Study:
- To investigate how engagement of the macrophage membrane by biologic particles affects lymphokine-induced tumoricidal activity.
- To determine the mechanisms underlying this inhibition, distinguishing between particle binding and phagocytosis.
Main Methods:
- Murine macrophages were treated with various particles including insoluble immune complexes, soluble immune complexes, IgG-coated erythrocytes (EA), non-opsonized erythrocytes (E), and erythrocytes with IgM antibody and complement (EAC).
- Polystyrene latex beads and macrophages plated on IgG-coated surfaces were used to differentiate between phagocytosis and membrane engagement.
- Macrophage tumoricidal activity was assessed after lymphokine activation and particle treatment, with and without indomethacin to evaluate prostaglandin involvement.
Main Results:
- Insoluble immune complexes and IgG-opsonized erythrocytes significantly inhibited lymphokine-mediated macrophage tumoricidal activity in a dose-dependent manner.
- Inhibition occurred regardless of whether particles were added before or after lymphokine, and was not due to cell death or reduced adherence.
- Phagocytosis of inert particles (latex beads) did not inhibit tumoricidal activity, and macrophages on IgG-coated surfaces were inhibited, indicating membrane engagement, not just ingestion, is key.
Conclusions:
- Engagement of the macrophage plasma membrane by biologic substances, particularly insoluble immune complexes and opsonized particles, compromises their tumoricidal function.
- This inhibition mechanism, independent of phagocytosis and prostaglandins, highlights a potential way the host defense against cancer can be inactivated.
- Understanding these interactions is crucial for developing strategies to enhance anti-tumor immunity.