Melatonin can produce immunoenhancement in Japanese quail ( Coturnix coturnix japonica) without prior immunosuppression

Abstract

In recent years, it has been determined that melatonin has important immunostimulatory properties in mammalian and avian species. Typically, this immunoenhancement has only been examined in immunosuppressed animals. The effect of melatonin on normal (unsuppressed) immune systems is yet to be evaluated in avian species. An experiment was performed to determine if transient and/or continuous melatonin treatments could enhance immune functions in Japanese quail without prior immunosuppression. All quail were kept on a short photoperiod (8:16LD) throughout the study. In this experiment, 50.0 μg/ ml melatonin was provided ad libitum to adult Japanese quail in the drinking water either continuously or for 3 h per day. Control birds received diluent continuously throughout the experiment. Both the cellular and humoral immune responses were determined immediately after 3 weeks treatment. A cutaneous basophil hypersensitivity reaction to phytohemagglutinin (PHA-P) was measured to evaluate the cellular immune response. To evaluate the humoral immune response, primary antibody titers were calculated 7 days post-intravenous injection with a Chukar red blood cell (CRBC) suspension. The cellular and humoral immune responses were significantly elevated in the transient (3 h) and continuous (24 h) melatonin treatment groups as compared to the control group (0 h). As compared to the control group, the cellular immune response was increased 25% and 38% for the 3 and 24 h melatonin treatments, respectively. The humoral immune response was increased 26% and 32% for the 3 and 24 h melatonin treatments, respectively. Furthermore, continuous (24 h) melatonin availability significantly increased the cellular, but not humoral immune responses as compared to the transient (3 h) group, given melatonin for 3 h prior to the scotophase (13:00–16:00 h). From these data, it was clear that transient and continuous administration of melatonin increased the cellular and humoral immune responses of Japanese quail without prior immunosuppression. These data suggest that the immunoenhancing effect of melatonin is not limited to reconstitution of weakened immune systems, but can be observed in normal, immunologically unsuppressed birds.