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Updated: Oct 13, 2026
Investigation of Macrophage Polarization Using Bone Marrow Derived Macrophages
Published on: June 23, 2013
Down-regulation of mannose receptor activity in macrophages after treatment with lipopolysaccharide and phorbol
V L Shepherd1, R Abdolrasulnia, M Garrett
1VA Medical Center, Nashville, TN 37212.
Abstract:
We have investigated the effects of LPS and PMA on the expression of functional mannose receptors in rat bone marrow-derived macrophages. After 48 h of treatment with LPS (10 ng/ml) and PMA (100 nM), mannose receptor activity was reduced by 70 to 80%. The effect of these agents on receptor activity was not reversible, and activity continued to decline after the agents were removed. Pretreatment of cells with dexamethasone was effective in blocking the LPS/PMA-induced down-regulation. Serine protease inhibitors did not block the reduction in receptor activity, suggesting that proteolysis is not involved in receptor down-regulation. LPS/PMA treatment did not increase turnover of the receptor. Ligand uptake studies showed that the total capacity of the uptake system was reduced by 80%, although the Kuptake was unaffected. Binding of 125I-mannose-BSA to intact macrophages showed a 70% decrease in surface receptor activity after treatment with LPS/PMA. LPS/PMA treatment had no effect on total receptor synthesis as quantitated by immunoprecipitation of metabolically labeled receptor. However, binding of metabolically labeled receptor to mannose-Sepharose, and binding of 125I-mannose-BSA to immunoprecipitated receptor revealed that intracellular plus surface binding sites were reduced to approximately 30% after LPS/PMA treatment. These results suggest that LPS/PMA treatment of macrophages results in an inactivation of mannose receptors with no effect on receptor turnover or biosynthesis.
Insights
Lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA) significantly reduce functional mannose receptor activity in macrophages by causing inactivation, not affecting synthesis or turnover. Dexamethasone prevents this down-regulation.
Area of Science:
- Immunology
- Cell Biology
- Macrophage Biology
Background:
- Mannose receptors are crucial for innate immunity and phagocytosis in macrophages.
- Understanding how external stimuli affect mannose receptor function is vital for immune response modulation.
Purpose of the Study:
- To investigate the impact of lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA) on functional mannose receptor expression in rat bone marrow-derived macrophages.
- To elucidate the mechanisms underlying LPS/PMA-induced changes in mannose receptor activity.
Main Methods:
- Treatment of macrophages with LPS and PMA.
- Assay of mannose receptor activity and ligand uptake.
- Analysis of receptor synthesis, turnover, and binding kinetics.
- Investigation of the role of dexamethasone and serine protease inhibitors.
Main Results:
- LPS and PMA treatment reduced mannose receptor activity by 70-80% through inactivation, not affecting receptor biosynthesis or turnover.
- Dexamethasone pretreatment blocked the LPS/PMA-induced down-regulation.
- Ligand uptake capacity decreased by 80% without altering the uptake constant (Kuptake).
- Total binding sites (intracellular and surface) were reduced to approximately 30%.
Conclusions:
- LPS/PMA treatment leads to functional inactivation of mannose receptors in macrophages.
- The down-regulation mechanism involves inactivation rather than changes in receptor synthesis or degradation.
- Dexamethasone can protect mannose receptors from LPS/PMA-induced inactivation.
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