FIGURE 1.

Glucocorticoids induce T cell migration into spleen from blood and enhance immune response at night by expression of IL-7R and CXCR4. Zeitgeber time (ZT) is a unit of cycle consisted of 12 h light/12 h dark phase. ZT0 is defined as the time when light on and ZT12 is defined as the time when light off. At the rest phase (ZT4) in mice, more T cells circulate in peripheral blood. At the onset of the active phase, the adrenal cortex releases glucocorticoids, which induce IL-7R and CXCR4 expression on T cells. At the active phase (ZT16), the elevated receptors trigger T cell migration into second lymphoid tissues such as spleen, lymph nodes, and Peyer’s patches. The T cell accumulation induces a stronger immune response by effector CD8 T cells and follicular helper T (Tfh) cells against bacterial infections and soluble antigens.