Abstract The normal variations in the number of lymphocytes and the percentages of T and B cells over a 24-hr period were studied in mice housed in cages controlled at 25°C ± 1 °C and lighted from 08:00 to 20:00. A clear circadian rhythm in the number of peripheral blood and spleen lymphocytes was demonstrated. The circadian cycle is the reverse of those in human peripheral blood lymphocytes: low during the light phase, which is the least active period in this nocturnal animal, and high at night. Cosiner analysis of individual experiments revealed that the acrophase, which means the timing of the highest point in a rhythm, was at around 12:00 in the light phase. The percentages of T and B lymphocytes varied in parallel during 1 day, being correlated with the total lymphocyte counts. This fact indicates that the circadian rhythm of murine lymphocytes, as well as that of human peripheral lymphocytes, consists of T and B cell co-variations. In the mice conditioned under the reversed lighting (lighted from 20:00 to 08:00), as was the case for normal lighting, a circadian rhythm of lymphocyte counts with a peak in the light phase was observed. In mice conditioned under both normal and reversed lighting, the lymphocyte counts started to decrease with the increase of plasma corticosterone levels in the early dark phase and reached a low in the dark phase, which is known to be a period of high corticosterone levels. A clear circadian rhythm in the number of lymphocytes was lost in adrenalectomized mice. An injection of prednisolone at physiologic concentrations to the adrenalectomized mice produces a reversible depression of circulating lymphocytes appearing early after drug administration. These results suggest that the lymphocyte circadian rhythm is caused by the plasma corticosterone rhythm.

Kawate, T., Abo, T., Hinuma, S., & Kumagai, K. (1981). Studies of the bioperiodicity of the immune response. II. Co-variations of murine T and B cells and a role of corticosteroid. The Journal of Immunology, 126(4), 1364–1367.