[Circadian variation of lymphocyte subsets in health subjects]

In our study cortisol and interleukin 2 (IL-2) levels were measured and lymphocyte sub-population analyses were performed on blood samples collected every four hours, for 24 hours from 10 healthy subjects aged 38-65 years. A clear circadian rhythm was validated for cortisol serum levels, for CD8, CD8 dim, CD16 and delta TcS1 with acrophase in the morning, and for CD2, CD4, CD/CD8 ratio, HLA-DR, CD20 and CD25 with acrophase at night. CD8 bright and TcR delta 1 presented higher levels in the morning without validation of the circadian rhythm. Changes of serum levels of IL-2 did not show circadian rhythmicity. The results show that specific lymphocyte subsets present different profiles of nyctohemeral changes and this may explain time related variations of immune responses.