Circadian variations of autologous mixed lymphocyte reactions and endogenous cortisol

The degree of proliferation of human T cells stimulated with autologous PHA-T cells and with autologous non-T cells displays circadian variations. The highest proliferation occurs with cells isolated from blood drawn at 8 a.m. in mixed lymphocyte reactions (MLR) with autologous PHA-T cells and from blood drawn at 8 p.m. in MLR with autologous non-T cells. The circadian variations of autologous MLRs appear to reflect changes in the proliferative response of T cells. In autologous MLRs with non-T cells as stimulators the extent of proliferation was inversely correlated with the level of endogenous cortisol. The circadian variations of autologous MLRs do not reflect non-specific changes in the proliferative and stimulatory properties of T and non-T cells, since circadian variations were not observed in the proliferative response of T cells to mitogens and in allogeneic MLRs. Circadian variations of autologous MLRs must be taken into account when analyzing abnormalities of these reactions in pathological conditions.