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Serum amyloid P-component-induced enhancement of macrophage listericidal activity
Abstract:
Purified serum amyloid P component (SAP), the major acute-phase reactant of mice, augmented the in vitro listericidal activity of inflammatory (elicited) macrophages, bone marrow-derived monocytes, and macrophages from a subcutaneous site of inflammation. Monocytes and macrophages from C57BL/B6 mice, which are relatively resistant to Listeria monocytogenes, exhibited a significantly greater enhanced killing capacity for listeria than macrophages from listeria-susceptible A/J mice. SAP did not alter the extent of phagocytosis by macrophages of opsonized L. monocytogenes, nor was SAP opsonic for listeria. Mannose-derived simple sugars inhibited the binding of SAP to macrophages and consequently prevented the enhanced SAP-dependent listericidal activity. Macrophages from lipopolysaccharide-hyporesponsive mice also had increased microbicidal activity following incubation with SAP. SAP activated macrophages independently of lymphokine. Therefore, SAP may serve as a mediator of the heightened nonspecific host defense response that is associated with the acute phase of the systemic inflammatory response.
Insights
Serum amyloid P component (SAP) enhances the ability of macrophages to kill Listeria. This immune-boosting effect, mediated by mannose sugars, occurs independently of lymphokines, suggesting SAP
Area of Science:
- Immunology
- Microbiology
- Biochemistry
Background:
- Serum amyloid P component (SAP) is a major acute-phase reactant in mice.
- Host defense mechanisms are crucial for combating bacterial infections like Listeria monocytogenes.
Purpose of the Study:
- To investigate the role of SAP in modulating the listericidal activity of macrophages.
- To elucidate the mechanism by which SAP enhances macrophage-mediated killing of Listeria.
Main Methods:
- In vitro assessment of macrophage listericidal activity upon incubation with purified SAP.
- Evaluation of SAP's effect on phagocytosis and opsonization of Listeria.
- Investigation of the role of mannose-derived sugars in SAP-mediated enhancement.
- Analysis of SAP's effect on macrophages from different mouse strains and lipopolysaccharide-hyporesponsive mice.
Main Results:
- SAP significantly augmented the in vitro listericidal activity of inflammatory macrophages, monocytes, and macrophages from inflamed sites.
- Macrophages from Listeria-resistant mice (C57BL/B6) showed greater enhancement than those from susceptible mice (A/J).
- SAP did not affect phagocytosis or act as an opsonin for Listeria.
- Mannose-derived sugars inhibited SAP binding to macrophages and abolished the enhanced listericidal activity.
- SAP enhanced microbicidal activity in macrophages from lipopolysaccharide-hyporesponsive mice, independent of lymphokine activation.
Conclusions:
- SAP enhances macrophage-mediated killing of Listeria through a mechanism involving mannose-binding, independent of opsonization or lymphokines.
- SAP may act as a key mediator in the non-specific host defense during the acute phase of systemic inflammation.
- These findings highlight SAP's potential role in innate immunity and host defense against bacterial pathogens.