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Muramyl peptides and serotonin interact at specific binding sites on macrophages and enhance superoxide release
Abstract:
Serotonin at low micromolar concentrations inhibited binding of two [125I]-labeled muramyl peptides to resident mouse peritoneal cells and to a macrophage-derived cell line, PU5-1.8-F7. Binding of [3H]serotonin was inhibited in parallel fashion. Overnight incubation with serotonin or muramyl peptide enhanced the release of superoxide by both types of cells when later stimulated with phorbol myristate acetate. Serotonin antagonists decreased binding of muramyl peptide and serotonin and diminished the subsequent enhancement of superoxide release. A cell line variant lacking detectable binding sites for muramyl peptide was far less responsive (superoxide release) than the parent line, to either drug. The data are consistent with sharing of a common set of receptors on the macrophage by muramyl peptide and serotonin and with involvement of these receptors in enhancing superoxide release.
Insights
Serotonin and muramyl peptides share macrophage receptors, influencing cell responses. This interaction affects superoxide release, suggesting a common signaling pathway for these molecules in immune cells.
Area of Science:
- Immunology
- Neuroscience
- Cell Biology
Background:
- Macrophages play a crucial role in innate immunity.
- Muramyl peptides are components of bacterial cell walls with immunomodulatory effects.
- Serotonin, a neurotransmitter, also exhibits immunomodulatory properties.
Purpose of the Study:
- To investigate the potential interaction between serotonin and muramyl peptides at the receptor level on macrophages.
- To determine if this interaction influences macrophage functional responses, such as superoxide release.
Main Methods:
- Utilized [125I]-labeled muramyl peptides and [3H]-serotonin to assess binding to mouse peritoneal cells and a macrophage cell line (PU5-1.8-F7).
- Measured superoxide release from cells after incubation with serotonin or muramyl peptides and subsequent stimulation with phorbol myristate acetate.
- Employed serotonin antagonists and a cell line variant lacking muramyl peptide binding sites to further elucidate receptor involvement.
Main Results:
- Low micromolar concentrations of serotonin inhibited the binding of muramyl peptides and serotonin to macrophages.
- Overnight incubation with either serotonin or muramyl peptide enhanced superoxide release upon stimulation.
- Serotonin antagonists reduced binding and superoxide release, and a cell line variant deficient in muramyl peptide binding showed diminished responsiveness.
Conclusions:
- Data suggest that macrophages possess a common receptor for both muramyl peptides and serotonin.
- These shared receptors are involved in modulating macrophage superoxide release, indicating a crosstalk between neurochemical and immunological signaling pathways.
- This finding opens new avenues for understanding immune regulation and potential therapeutic interventions targeting macrophage function.