Interaction of melatonin with human lymphocytes: Evidence for binding sites coupled to potentiation of cyclic AMP stimulated by vasoactive intestinal peptide and activation of cyclic GMP

Abstract

Melatonin binding sites were characterized in human blood lymphocytes. The specific binding 2-[125I]iodo-melatonin ([125I]MEL) to human lymphocytes was dependent on time and temperature, stability, saturation, and reversibility. Moreover, guanine nucleotides decreased the specific binding of [125I]MEL to crude membranes of human lymphocytes, suggesting the coupling of these binding sites to a guanosine nucleotide binding regulatory protein(s). In competition studies, the specific binding of [125I]MEL to lymphocytes was inhibited by increasing concentrations of native melatonin. Scatchard analysis showed that data were compatible with the existence of two classes of binding sites: a high-affinity site with a Kd of 5.20 +/- 0.79 nM and a binding capacity of 50.6 +/- 11.0 fmol/10(7) cells, and a low-affinity site with a Kd of 208.5 +/- 50.2 nM and a binding capacity of 2691 +/- 265 fmol/10(7) cells. However, concentration-dependent binding of [125I]MEL to lymphocytes was saturable and resulted in a linear Scatchard plot, suggesting binding to a single class of binding sites. The Kd for the single site was 1.02 +/- 0.34 nM with a binding capacity of 10.1 +/- 1.6 fmol/10(7) cells. Their affinities closely correlated with the production of cyclic nucleotides, suggesting a physiological role for the melatonin binding sites. Thus, melatonin potentiated the effect of vasoactive intestinal peptide (VIP) on cyclic AMP production (ED50 = 1.9 nM) and stimulated cyclic GMP accumulation (ED50 = 125 nM). Results demonstrate the existence of two binding sites for [125I]MEL in human blood lymphocytes, with a high-affinity binding site coupled to the potentiation of the effect of VIP on cyclic AMP production and a low-affinity binding site coupled to activation of cyclic GMP production.

Melatonin improves inflammatory cytokine profiles in lung inflammation associated with sleep deprivation

“…Our results are consistent with other reports demonstrating that the lymphocyte number was decreased by melatonin treatment (19). Human lymphocytes are a target for melatonin via binding sites in the regulation of immune function (20).…”

Melatonin Involvement in Immunity and Cancer

“…Lopez-Gonzales et al [56,57], using 2[ 125 I]melatonin as ligand, characterized high-affinity melatonin binding sites in human blood lymphocytes, and low-affinity melatonin binding sites were found in human granulocytes [58]. Binding of labeled melatonin to peripheral blood T cells was markedly higher (10-fold) than that observed in B lymphocytes [59].…”

Melatonin Receptor Subtype MT2 (Mel 1b) and Not mt1 (Mel 1a) Is Associated with Melatonin-Induced Enhancement of Cell-Mediated and Humoral Immunity

“…High affinity melatonin receptors have been localized on circulating lymphocytes from rodents, chickens, and humans [16, 17], and on thymocytes and splenocytes in humans and several rodent and bird species [18, 19, 20]. In vitro melatonin administration enhances the proliferative ability of splenocytes from both female and male prairie voles (Microtus ochogaster) [21, 22], and enhances the mitogenic response of peripheral blood T lymphocytes from chickens [23].…”