Entrainment of different light regimens on the circadian rhythm of peripheral blood immune cells in mice

Abstract

Objective To explore the entrainment effect of different light regimens on the circadian rhythms of peripheral blood immune cells in mice. Methods One hundred and forty-four male C57BL/6 mice were kept under the 12 h-light and 12 h-dark cycle for 4 weeks. Then, the animals were randomly divided into 3 groups. The 24 animals in group 1 were treated with the former light regimen, the 60 animals in group 2 were kept in the light regimen of phase advance 12 hours, simulating eastward flight, and another 60 animals in group 3 were kept in the light regimen of phase delay 12 hours, simulating westward flight. Peripheral blood samples of the animals in group 1 were collected respectively one day before and 21 days after changes of light regimens, and blood samples of the animals in group 2 and 3 were collected on different days (i.e. day 2, 4, 7, 14 and 21) after changes of light regimens. Peripheral blood samples were taken at 4 different timepoints in 24 hours (i.e. 9∶00, 15∶00, 21∶00 and 3∶00). Detections were made in immune cells, including the numbers of leukocytes, the percentage of lymphocytes, the percentage of CD4+ lymphocytes, the percentage of CD8+ lymphocytes, as well as monocyte and granulocyte counts. Finally, the circadian rhythms of different immune cells were evaluated in the animals of different groups. Results The immune cells in the C57BL/6 mice displayed different circadian rhythms under the 12 h-light and 12 h-dark cycle for 4 weeks. Under the new light regimens, the circadian rhythms of immune cells were entrained. It took 2 weeks for the animals of the simulated westward flight phase delay group to entrain the circadian rhythm, while the rate of entrainment for the animals of the simulated eastward flight phase delay group was 3 weeks. Conclusions Under the 12 h-light and 12 h-dark cycle, immune cells in the peripheral blood displayed a rise and fall circadian rhythm, which might facilitate the balance of the immune system. However, under the new light regimens, the circadian rhythms of different immune cells in the peripheral blood were entrained, with the entrainment rate of immune cells in the phase delay group being faster than that of the phase advance group. Key words: Circadian rhythm; Entrainment; Mouse; Peripheral blood; Immune cell