1Gamal El-Saeid Eid and 2Fahad J Al-Shammary.
1Microbiology and Immunology Unit, 2Clinical Biochemistry Unit, Department of Clinical Laboratory Sciences, College of Applied Medical Science, King Saud University, Riyadh.
Peripheral blood samples were obtained from male and female volunteers of different ages. Mononuclear immune cells were separated and stimulated in vitro with phytohemagglutonin (PHA) at different concentrations (0, 2.5, 5.0 and 10 mg/ml). The effect of melatonin on PHA-stimulated cells was studied at various concentrations (0, 10-7, 10-6, 10-5, 10-4 and 10-3 M) through measurement of lymphocyte proliferation using colorimetric tetrazolium reduction assay, from which the stimulation index (SI) was calculated. Melatonin, at concentrations of 10-7 to 10-5 M, activated PHA-treated and non-treated cells as evidenced by the slight elevation of SI of these cells. However, the highest SI was detected at 10-7 M concentration of melatonin, especially with cells isolated from young males and young females as compared to old groups. The activity of melatonin on PHA-treated cells was reduced by increasing its concentration, where the highest concentration of melatonin (10-3 M) induced significant inhibition of cell proliferation. The results indicated that the effect of melatonin on PHA-stimulated cells is dose dependent as well as age dependent. Finally, our recommended physiological concentration range of melatonin is 10-7 to 10-6 M which induce the highest SI expressed by PHA-treated and non-treated immune cells. Our results support the suggestion that melatonin may be involved in the regulation of human immune system functions by modulating the proliferative response and physiological activities.