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Influence of antibody and complement components on phagocytosis and chemiluminescence of macrophages
Abstract:
Macrophages are known to release reactive oxygen species (O2-, 1O2, H2O2, OH.) in response to various membrane stimuli. However, our studies show that phagocytic stimulation of macrophages is not necessarily accompanied by a stimulation of the oxidative burst. Whereas IgG-opsonized erythrocytes were capable to induce phagocytosis and a chemiluminescence response, both being dependent on the number of IgG bound per erythrocyte, C3b-bearing erythrocytes were well ingested but failed to induce any chemiluminescence reaction. Furthermore, stimulation of macrophages, via the Fc-receptors, seems to alter their functional state in regard to the activation of a receptor, which enables them to recognize membrane lesions on the target erythrocyte. The presence of IgG and membrane lesions, e.g. the C5b-9-complex of complement, induced a marked increase in chemiluminescence compared with stimulation by IgG-bearing particles alone. The augmented response of macrophages was at least in part due to an additional release of H2O2, which was not liberated in response to IgG-bearing erythrocytes. This "lesion recognizing receptor" in the macrophage membrane could not be activated by stimulation of C3b-receptors, indicating its functional linkage to the Fc-receptors.
Insights
Macrophages can phagocytose, but not always release reactive oxygen species (ROS). Fc-receptor stimulation, combined with membrane lesions, significantly enhances macrophage chemiluminescence and hydrogen peroxide release.
Area of Science:
- Immunology
- Cellular Biology
- Biochemistry
Background:
- Macrophages are key immune cells involved in phagocytosis and releasing reactive oxygen species (ROS) like superoxide (O2-), singlet oxygen (1O2), hydrogen peroxide (H2O2), and hydroxyl radicals (OH.).
- The oxidative burst, a rapid release of ROS, is a critical component of macrophage antimicrobial activity.
Purpose of the Study:
- To investigate the relationship between phagocytic stimulation of macrophages and the oxidative burst.
- To determine if different opsonins and target cell properties influence ROS production.
- To explore the role of Fc-receptors and complement components in modulating macrophage responses.
Main Methods:
- Macrophages were stimulated with erythrocytes opsonized with either immunoglobulin G (IgG) or complement component C3b.
- Phagocytosis and chemiluminescence responses were measured to assess macrophage activation.
- The production of hydrogen peroxide (H2O2) was quantified under different stimulation conditions.
Main Results:
- IgG-opsonized erythrocytes induced both phagocytosis and a chemiluminescence response, dependent on IgG density.
- C3b-bearing erythrocytes were phagocytosed but did not elicit a chemiluminescence response.
- Stimulation via Fc-receptors, especially when combined with membrane lesions (e.g., C5b-9 complex), significantly increased chemiluminescence and H2O2 release compared to IgG alone.
- This enhanced response was linked to a specific 'lesion recognizing receptor' functionally associated with Fc-receptors, not C3b-receptors.
Conclusions:
- Phagocytic stimulation of macrophages does not invariably trigger an oxidative burst.
- Fc-receptor engagement, particularly in the presence of target cell membrane damage, primes macrophages for an augmented ROS production.
- A distinct receptor, linked to Fc-receptors, recognizes membrane lesions and mediates enhanced H2O2 release, independent of C3b receptor activation.