Twenty-Four-Hour Analysis of Lymphocyte Subpopulations and Cytokines in Healthy Subjects

Fourteen healthy male subjects were studied under resting conditions for 24 or 48 h. The 24-h variations of ACTH and Cortisol with peaks in the morning were confirmed. Interleukin-2 release was profoundly reduced at 8:00. A cosine function could be fitted to lymphocyte subpopulations including populations such as T_{helper-memory} cells (CD4+/CDw29) and HLA-DR-bearing cells displaying peak values during the night and minimal values at 9:00. Numbers of natural killer cells (CD57) were not correlated to other cell populations and no rhythm could be detected. Interleukin-1 (3 was detectable in some plasma samples only with an interleukin-1 ELISA kit (Quantakine HS^R), but neither a 24-h rhythm nor reproducible results could be obtained for day 1 and 2 of the study. We conclude that there might be a temporal relation between the parameters analyzed: Higher levels of endogenous Cortisol in the morning hours probably inhibit the cellular interleukin-2 synthesis and are responsible for an enhanced migration of lymphocytes from the blood into the tissues of the reticuloendothelial system. These results might be indicative of a circadian organization of the immune system which may play a role in both physiological and pathological functioning. (Chronobiology International, 13(6), 423–434, 1996)