Effects of photoperiod and melatonin on lymphocyte activities in male broiler chickens

Understanding the role of the pineal gland in regulating the immune respons e and the role of photoperiod in influencing pineal gland secretions are be coming increasingly important. The purposes of the present experiments were to investigate the effects of different photoperiod regimens on T- and B-l ymphocyte activities in broiler chickens. Next, the influence of different photoperiod regimens on the responsiveness of lymphocytes to melatonin in v itro was examined. The effect of melatonin in vitro on lymphocyte activitie s was also studied, regardless of the photoperiod received. Finally, the ef fects of photoperiod on the profiles of different splenocyte cell types wer e investigated. To study the effect of photoperiod on lymphocyte activities , different photoperiod regimens were used. These were: constant lighting, 23 h light:1 h darkness; intermediate lighting, 12 h light:12 h darkness; a nd intermittent lighting, 1 h light:3 h darkness. Peripheral blood and sple nic lymphocyte activities were tested at 3 and 6 wk of age by performing a mitogen cell-proliferation assay with a polyclonal T-cell mitogen, concanav alin A (Con A), and T-dependent B-cell mitogen, pokeweed mitogen (PWM). To study the effect of photoperiod on the responsiveness of lymphocytes to mel atonin in vitro or the effect of melatonin in vitro on lymphocyte activitie s regardless of photoperiod received, lymphocytes from the chickens that we re exposed to the different photoperiod regimens were incubated with mitoge n and different concentrations of melatonin. To study the effect of photope riod on profiles of different cell types, the percentages of splenocyte sub populations from birds exposed to different photoperiods were determined us ing flow cytometry with CD4(+), CD8(+), CD3(+), and B-cell markers. The res ults of these studies indicate that splenic T and B lymphocytes from 6-wk-o ld chickens grown in intermittent Lighting had higher activities than those from chickens grown in constant lighting. Peripheral blood and splenic lym phocytes from chickens raised under constant lighting were more responsive to melatonin in vitro than those from chickens raised under intermittent li ghting. This difference in response may be due to lower levels of melatonin in birds receiving constant lighting, making them more sensitive to melato nin in vitro. Melatonin in vitro enhanced the mitogenic response of periphe ral blood T lymphocytes from 6-wk-old chickens, splenic T lymphocytes from 3-wk-old chickens, and splenic T and possibly B lymphocytes from B-wk-old c hickens. Finally, intermittent lighting increased the percentages of spleni c CD4(+), CD8(+), and CD3(+) cells but not B-cell subpopulations at 6 wk of age, presumably because of increased levels of melatonin in birds receivin g intermittent lighting. Our results re-emphasize the importance of melaton in in regulating host immune response; this regulation could be accomplishe d through exposing broiler chicks to intermittent lighting.