Circadian variations in antigen-specific proliferation of human T lymphocytes and correlation to cortisol production.

Cortisol is a well-known immunosuppressant when used therapeutically. The present investigation was set out to study if diurnal variations in endogenous cortisol production are reflected by changes in proliferative responses of human lymphocytes to either a mitogen (phytohemagglutinin-A, PHA) or an antigen (tetanus toxoid, TT) stimulus. The study included eight healthy volunteers. Blood was withdrawn at 0200, 0600, 1000, and 1800h for preparation of lymphocytes and determination of cortisol in plasma. Isolated cells were incubated without (baseline activity) or with inclusion of either 1 micrograms PHA or 10 micrograms TT. Proliferation was measured by labelling with 3H-thymidine for 16 h o…