Background: Pineal melatonin (MLT) is a neuroendocrine hormone that possesses a wide variety of biological effects. MLT regulation of the immune system has been studied in recent years. But very little is known about MLT interaction with neonatal cord blood mononuclear cells (CBMCs) and the lymphocyte immune system in neonates. This study was designed to investigate the proliferative effects of MLT on CBMCs and peripheral blood mononuclear cells (PBMCs).
Methods: Cord blood samples were collected from 10 normal full-term infants at the Guangzhou Maternal and Infant Hospital, China. Ten samples of adult peripheral blood were also collected from healthy volunteers. (3)H-thymidine ((3)H-TdR) incorporation was used to analyze the influence of MLT on proliferation of CBMCs. The effects of MLT on proliferation of CBMCs and PBMCs were compared.
Results: (3)H-TdR incorporation increased in a dose-dependent manner with varying MLT concentrations (50 pg/ml-50 ng/ml), but peaked at 5 ng/ml. After incubation with MLT (5 ng/ml), interleukin-2 (IL-2, 50 ng/ml), MLT+phytohemagglutinin (PHA, 5 microg/ml), and MLT+IL-2, respectively in CBMCs media, (3)H-TdR incorporation rates were 114 327+/-52 863, 16 087+/-9006, 118 360+/-59 207, and 17 682+/-7391. Compared to the control cell suspension (14 133+/-8688), (3)H-TdR incorporation rates of the MLT and MLT+PHA groups were significantly increased (t=5.9143, P<0.001; t=5.5078, P<0.001). (3)H-TdR incorporation was not different between the IL-2 and MLT+IL-2 groups (t=0.4983, P>0.05; t=0.9839, P>0.05). PHA treatment (110 397+/- 48 663) presented no difference in (3)H-TdR incorporation compared to the MLT or MLT+PHA groups (t=0.1730, P>0.05; t=0.3286, P>0.05). (3)H-TdR incorporation was significantly greater in CBMCs than in PBMCs cultures after addition of various stimulators to the culture media.
Conclusions: MLT promoted proliferation of PBMCs and also enhanced proliferation of CBMCs. The proliferative effects of MLT were greater on CBMCs than on PBMCs.