RESUMO
The effect of time of administration of exogenous melatonin (M) at the rate of 100 microg/Kg BW of rat/day for 14 days on immunomodulation to killed Pasteurella multocida (P52 strain) vaccine (KPMV) was investigated in male albino rats during spring season with photoperiod of LL 13: DD 11 h and 25 +/- 2.5 degrees C air temperature and 70 +/- 4% relative humidity. The experiment was conducted at an altitude of 172 mts above mean sea level at latitude 28.20 degrees north, longitude 79.24 degrees east (Bareilly, U.P. India). The experimental animals were divided in-groups of 8 rats each, as KPMV + M at 4.00 h; KPMV + M at 16.00 h; KPMV and their controls M4, M16, PBS respectively. Humoral immune response was monitored at weekly intervals by an indirect ELISA and cellular immunity by leukocyte migration inhibition test (LMIT) and delayed type of hypersensitivity (DTH). As evinced by in-vitro assays and in-vivo protection studies, both humoral and cellular immune responses to KPMV were augmented in rats receiving exogenous melatonin at 4.00 h as compared to slightly reduced responses in rats treated with melatonin at 16.00 h. It was concluded that the circadian timings of melatonin administration modulate immune response in rats.