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Complement and the recruitment of mononuclear osteoclasts
D C Mangham1, D J Scoones, M T Drayson
1Department of Pathology, Medical School, University of Birmingham, Edgbaston.
Journal of Clinical Pathology
|June 1, 1993
Summary
Complement deposition on bone surfaces attracts mononuclear osteoclast precursors. These cells lose complement receptor expression as they mature into multinucleate osteoclasts, suggesting a role for complement in bone remodeling.
Area of Science:
- Immunology
- Bone Biology
- Cell Biology
Background:
- The complement system plays a crucial role in innate immunity.
- Osteoclasts are essential for bone resorption and remodeling.
- The mechanisms of osteoclast precursor recruitment to bone surfaces are not fully understood.
Purpose of the Study:
- To investigate if complement mediates the recruitment of mononuclear osteoclast precursors to mineralized bone surfaces.
- To explore the expression of complement receptors on osteoclasts.
Main Methods:
- In vitro incubation of synthetic hydroxyapatite with human serum.
- Assays for complement components and C3d generation.
- Immunohistochemical localization of C3 deposition and complement receptors (CR1, CR2, CR3, CR4) on bone and osteoclasts.
Main Results:
- Complement components bind to hydroxyapatite, generating C3d.
- C3 deposition was observed on newly formed bone trabecular surfaces.
- Mononuclear osteoclasts expressing CR3 and CR4 were found in close apposition to C3-deposited bone surfaces.
Conclusions:
- C3 deposition on mineralized bone surfaces likely mediates the recruitment of mononuclear osteoclasts.
- Mononuclear osteoclasts express complement receptors CR3 and CR4.
- Complement receptor expression is downregulated upon fusion into multinucleate osteoclasts.