Chronobiological features of the immune system.: Effect of calorie restriction

The circadian organization of living organisms is fully established being a key component the activity of the neuro-endocrin-immune system that maintains the homeostasis. Secondary lymph organs, such as submaxillary lymph nodes and spleen, have been shown to exhibit a 24 h variation in blastogenic proliferative capacity and distribution of B and T subsets, with specific achrophases depending on the parameter studied or the lymphoid organ considered. However, less is known about the thymus. The immune system has been shown to change by calorie restriction, although no information is available about possible effects in 24 h variations. Similar questions can be posed for the neuro-endocrine system. As an example, some data are shown in this article about the effects of calorie restriction on the neuro-endocrin-immune system in growing male Wistar rats. Calorie restriction blunted the circadian secretory pattern of TSH observed in the control group that was characterized by the existence of two peaks at 17:00 or 01:00 h and that explained the low basal metabolic rate of these animals under this experimental condition. Concerning the immune system, the thymus gland exhibited 24 h variations in T, B and immature cells in both control and calorie-restricted male rats, thus confirming the circadian organization of the immune system. Moreover this circadian organization was changed by calorie restriction.