Circadian changes of T lymphocyte subsets in human peripheral blood

The circadian variations in circulating T cell subsets defined by monoclonal antibodies in eight healthy male volunteers were evaluated in whole blood using a flow cytometry. In all subjects, the number of lymphocytes showed a clear rhythmicity with high values at night and low values during the day. This circadian variation in circulating lymphocytes appeared to reflect largely a change in the number of T cells rather than B cells. The percentage of OKT3+ and OKT11+ cells showed a similar fluctuation with a peak at night and a depression during the day. It was found that the percentage of OKT4+ cells varied in parallel with that of T cells, particularly of OKT3+ cells, but the OKT8+ subset was not appreciably altered over a 24 h period. Thus, a circadian variation of T cells could be largely accounted for by a circadian change of OKT4+ cells. Plasma cortisol levels showed an expected circadian variation. It was also shown that there might be an intimate relationship between these circadian changes of T cell subsets and plasma cortisol levels.