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.