High‐affinity binding of melatonin by human circulating T lymphocytes (CD4 ⁺ )

This paper shows the presence of high‐ affinity binding sites for melatonin in human circu‐lating T lymphocytes, but not in B lymphocytes. The binding of melatonin to T cells was dependent on time, stable, reversible, saturable, specific, and in‐versely correlated to the production of melatonin, expressed as the nocturnal 12 h production of its urinary metabolite 6‐sulfatoxymelatonin. The affin‐ity of these binding sites ( K d = 0.27 nM) suggests that they may recognize the physiological concentrations of melatonin in serum. Moreover, among the lymphocyte subpopulations studied, binding of melatonin was mostly found in CD4+ cells rather than in CD8+ cells. Results suggest that CD4 + cells may be the target of melatonin among the human circulating lymphocytes.—Gonzalez‐Haba, M. G., Garcia‐Mauriño, S., Calvo, J. R., Goberna, R., Guerrero, J. M. High‐affinity binding of melatonin by human circulating T lymphocytes (CD4 + ). FASEB J . 9, 1331‐1335(1995)