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Modulation of receptors for the colony-stimulating factor, CSF-1, by bacterial lipopolysaccharide and CSF-1
Abstract:
The ability of the mononuclear phagocyte-specific colony-stimulating factor, CSF-1, to down-regulate its receptor on peritoneal exudate macrophages (PEM) was examined. Because of the essentially irreversible binding of CSF-1 to its receptor at 2 degrees C, unoccupied cell surface receptors could be measured by rapidly cooling PEM to 2 degrees C and determining the amount of 125I-CSF-1 bound at this temperature. On incubation with 125I-CSF-1 at 37 degrees C more receptors were lost than could be accounted for by 125I-CSF-1 binding. This receptor loss, apparently caused by CSF-1 itself, was shown to be due in large part to the presence of contaminating lipopolysaccharide (LPS), which at 10 ng/ml was by itself able to cause complete loss of the CSF-1 receptors. LPS also induced loss of the insulin receptor by PEM. LPS did not cause apparent CSF-1 receptor loss by binding to the receptor or by stimulating the release of CSF-1 or substances which compete for the binding of 125I-CSF-1 to the receptor. However, LPS did stimulate release of factors by LPS responsive (C3H/HeN) PEM which caused CSF-1 receptor loss by LPS non-responsive (C3H/HeJ) PEM. In the absence of LPS induced effects, incubation of 125I-CSF-1 with PEM at 37 degrees C resulted in down-regulation of the CSF-1 receptors. The number of CSF-1 receptor sites down-regulated corresponded to the number of CSF-1 molecules that were cell-associated plus the number that were intracellularly degraded and released.
Insights
Colony-stimulating factor 1 (CSF-1) down-regulates its receptor on macrophages, but lipopolysaccharide (LPS) contamination significantly impacts this process. LPS alone causes receptor loss and stimulates factors that mediate this effect.
Area of Science:
- Cell biology
- Immunology
- Molecular signaling
Background:
- Colony-stimulating factor 1 (CSF-1) is crucial for mononuclear phagocyte development and function.
- CSF-1 exerts its effects by binding to its specific receptor on target cells.
- Understanding receptor regulation is key to deciphering immune cell responses.
Purpose of the Study:
- To investigate the down-regulation of the CSF-1 receptor on peritoneal exudate macrophages (PEM).
- To determine the influence of lipopolysaccharide (LPS) contamination on CSF-1 receptor regulation.
- To elucidate the mechanisms by which LPS affects CSF-1 receptor expression.
Main Methods:
- Measurement of unoccupied cell surface receptors using 125I-CSF-1 binding at 2°C.
- Incubation of PEM with 125I-CSF-1 at 37°C to assess receptor down-regulation.
- Analysis of LPS effects on CSF-1 and insulin receptor expression.
- Investigation of LPS-induced factor release and its impact on receptor loss.
Main Results:
- CSF-1 binding at 37°C led to greater receptor loss than expected, attributed to LPS contamination.
- Lipopolysaccharide (LPS) alone induced complete loss of CSF-1 receptors and insulin receptors.
- LPS stimulated the release of factors from responsive macrophages that caused CSF-1 receptor loss in non-responsive macrophages.
- In the absence of LPS, CSF-1 induced receptor down-regulation through receptor internalization and degradation.
Conclusions:
- Lipopolysaccharide (LPS) significantly confounds studies on CSF-1 receptor down-regulation.
- LPS itself directly causes CSF-1 receptor loss and also induces soluble factors that mediate this effect.
- Proper controls for LPS are essential for accurate investigation of CSF-1 receptor dynamics in macrophages.