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High-affinity binding of melatonin by human circulating T lymphocytes (CD4+)
M G Gonzalez-Haba1, S Garcia-Mauriño, J R Calvo
1Department of Medical Biochemistry and Molecular Biology, University of Seville School of Medicine, Spain.
Summary
Melatonin binds to human T lymphocytes, particularly CD4+ cells, but not B cells. This binding is specific and suggests T cells are a target for melatonin signaling.
Area of Science:
- Immunology
- Endocrinology
- Cell Biology
Background:
- Melatonin is a hormone with known immunomodulatory effects.
- The specific interactions between melatonin and human lymphocytes are not fully understood.
Purpose of the Study:
- To investigate the presence and characteristics of melatonin binding sites on human circulating lymphocytes.
- To determine which lymphocyte subpopulations, if any, are targeted by melatonin.
Main Methods:
- Radioligand binding assays were used to detect and characterize melatonin binding sites on human T and B lymphocytes.
- Lymphocyte subpopulations (CD4+ and CD8+ T cells) were analyzed for melatonin binding.
- Melatonin binding was assessed for its dependence on time, stability, reversibility, saturability, and specificity.
- Correlation between melatonin binding and endogenous melatonin production (via urinary 6-sulfatoxymelatonin) was examined.
Main Results:
- High-affinity binding sites for melatonin were identified on human circulating T lymphocytes, but not on B lymphocytes.
- Melatonin binding to T cells exhibited characteristics of a specific, saturable, and reversible receptor interaction.
- The affinity of these binding sites (Kd = 0.27 nM) indicates recognition of physiological melatonin concentrations.
- Melatonin binding was predominantly observed in CD4+ T cells compared to CD8+ T cells.
- Melatonin binding was inversely correlated with endogenous melatonin production.
Conclusions:
- Human circulating T lymphocytes possess high-affinity binding sites for melatonin.
- CD4+ T cells appear to be a primary target for melatonin among human circulating lymphocytes.
- These findings suggest a direct role for melatonin in modulating T cell function.