Simulated Night Shift Disrupts Circadian Rhythms of Immune Functions in Humans

This work delineates the normal oscillation and responsiveness of circulating monocytes and T lymphocytes in ten human volunteers over circadian time. Under normal circadian parameters, bimodal cytokine secretion was observed with the night peak caused by an increased responsiveness of monocytes, and the day peak corresponding to a higher absolute number of monocytes. T lymphocytes demonstrated an evening peak caused by both higher cell count and responsiveness. When subjected to a night shift schedule (acute circadian disruption) monocyte and T cells circulating phase was not changed but the responsiveness of both cell types was advanced (earlier expression of cytokine) after stimulation. This suggests that acute changes in sleep-wake cycles alter the cell intrinsic responsiveness to stimulation whereas parameters governing circulation may lag behind.