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Phagocytosis of beta-1,3-D-glucan-derivatized microbeads by mouse peritoneal macrophages involves three different
Z Konopski1, L T Rasmussen, R Seljelid
1Institute of Medical Biology, University of Tromsø, Norway.
Abstract:
Intraperitoneal injection of beta-1,3-D-glucan coupled to the surface of monodisperse methacrylate microbeads improves the resistance against bacterial infections in mice, while methacrylate microbeads alone do not. The effect of the glucan-derivatized microbeads (GDM) is considered to be mediated through peritoneal macrophages. We show that both GDM and the underivatized methacrylate microbeads (UDM) treated with normal serum were rapidly bound and phagocytized by mouse peritoneal macrophages in vitro. We found that both complement and fibronectin opsonized the beads and were responsible for the uptake. Treatment of microbeads with serum lacking fibronectin and complement activity still gave some uptake of GDM, but not uptake of UDM. The uptake of GDM was similar to the uptake of untreated GDM and was inhibited by pretreatment of macrophages with soluble beta-1,3-D-glucan. Our conclusion is that GDM and UDM intraperitoneally bind fibronectin and C3 through activation of the alternative pathway of complement. This leads to their phagocytosis by macrophages through fibronectin and complement receptors. GDM are also internalized via beta-glucan receptors. We present the hypothesis that the beta-glucan receptors on peritoneal macrophages account for the protective effect of GDM in intraperitoneal bacterial infections.
Insights
Beta-1,3-D-glucan microbeads enhance resistance to bacterial infections by engaging peritoneal macrophages. This interaction is mediated by complement and fibronectin, with beta-glucan receptors playing a key role in the protective effect.
Area of Science:
- Immunology
- Biomaterials Science
Background:
- Beta-1,3-D-glucan coupled to microbeads enhances resistance to bacterial infections in mice.
- The protective mechanism is hypothesized to involve peritoneal macrophages.
Purpose of the Study:
- To investigate the mechanisms by which glucan-derivatized microbeads (GDM) and underivatized methacrylate microbeads (UDM) are recognized and phagocytized by peritoneal macrophages.
- To elucidate the role of complement and fibronectin in the opsonization and uptake of these microbeads.
- To explore the contribution of beta-glucan receptors to the phagocytosis of GDM.
Main Methods:
- In vitro phagocytosis assays using mouse peritoneal macrophages.
- Treatment of microbeads with normal serum, serum lacking fibronectin and complement, and soluble beta-1,3-D-glucan.
- Analysis of complement (C3) and fibronectin binding to microbeads.
Main Results:
- Both GDM and UDM were rapidly bound and phagocytized by macrophages when opsonized with normal serum, indicating roles for complement and fibronectin.
- Macrophage uptake of GDM was partially mediated by beta-glucan receptors, as shown by inhibition with soluble beta-1,3-D-glucan.
- UDM uptake was primarily dependent on complement and fibronectin, while GDM showed some uptake independent of these opsonins.
Conclusions:
- Glucan-derivatized microbeads and underivatized methacrylate microbeads bind fibronectin and C3 via the alternative complement pathway, leading to macrophage phagocytosis.
- Macrophages internalize microbeads through fibronectin and complement receptors, with GDM also utilizing beta-glucan receptors.
- Beta-glucan receptors on peritoneal macrophages are hypothesized to be responsible for the enhanced resistance to intraperitoneal bacterial infections conferred by GDM.