Melatonin plays a critical role in inducing B lymphocyte proliferation of the bursa of Fabricius in broilers via monochromatic lights.

To study the role of melatonin in the monochromatic light-induced B lymphocyte proliferation of bursa, a total of 360 newly hatched broilers, including intact, sham-operated, and pinealectomized groups, were exposed to blue light (BL), green light (GL), red light (RL) and white light (WL) from a light-emitting diode system for 14d. Both in vivo and in vitro studies showed that the percentage of proliferating cell nuclear antigen (PCNA)-immunoreactive lymphocytes and the lymphocyte proliferation in response to lipopolysaccharide in the bursa of broilers in the GL intact group was the highest values among the different intact groups with altered plasma melatonin levels. Additionally, the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and total antioxidant capability (T-AOC) were the highest, whereas malondialdehyde (MDA) content and inducible nitric oxide synthase (iNOS) expression were significantly decreased in the GL intact group. After pinealectomy, the levels of SOD, GSH-Px and T-AOC decreased remarkably in the various light-treatment groups, whereas the MDA content and iNOS expression significantly increased. The administration of exogenous melatonin (250pg/mL) in vitro also significantly enhanced the bursal B lymphocyte proliferation. These findings suggest that GL illumination effectively elevates the antioxidative capacity to promote B lymphocyte proliferation of bursa in young broilers, which might depend on enhanced melatonin secretion.