Seasonal Variation in Vitamin D3 Levels Is Paralleled by Changes in the Peripheral Blood Human T Cell Compartment

It is well-recognized that vitamin D3 has immune-modulatory properties and that the variation in ultraviolet (UV) exposure affects vitamin D3 status. Here, we investigated if and to what extent seasonality of vitamin D3 levels are associated with changes in T cell numbers and phenotypes. Every three months during the course of the entire year, human PBMC and whole blood from 15 healthy subjects were sampled and analyzed using flow cytometry. We observed that elevated serum 25(OH)D3 and 1,25(OH)2D3 levels in summer were associated with a higher number of peripheral CD4+ and CD8+ T cells. In addition, an increase in naïve CD4+CD45RA+ T cells with a reciprocal drop in memory CD4+CD45RO+ T cells was observed. The increase in CD4+CD45RA+ T cell count was a result of heightened proliferative capacity rather than recent thymic emigration of T cells. The percentage of Treg dropped in summer, but not the absolute Treg numbers. Notably, in the Treg population, the levels of forkhead box protein 3 (Foxp3) expression were increased in summer. Skin, gut and lymphoid tissue homing potential was increased during summer as well, exemplified by increased CCR4, CCR6, CLA, CCR9 and CCR7 levels. Also, in summer, CD4+ and CD8+ T cells revealed a reduced capacity to produce pro-inflammatory cytokines. In conclusion, seasonal variation in vitamin D3 status in vivo throughout the year is associated with changes in the human peripheral T cell compartment and may as such explain some of the seasonal variation in immune status which has been observed previously. Given that the current observations are limited to healthy adult males, larger population-based studies would be useful to validate these findings

Sleep benefits subsequent hippocampal functioning.

Sleep before learning benefits memory encoding through unknown mechanisms. We found that even a mild sleep disruption that suppressed slow-wave activity and induced shallow sleep, but did not reduce total sleep time, was sufficient to affect subsequent successful encoding-related hippocampal activation and memory performance in healthy human subjects. Implicit learning was not affected. Our results suggest that the hippocampus is particularly sensitive to shallow, but intact, sleep. © 2009 Nature America, Inc. All rights reserved

Neuroendocrine and metabolic regulation of plasma growth hormone secretory profiles

Like many other neuroendocrine hormones, growth hormone (GH; somatotropin) secretion is pulsatile with regular releasing bursts on a relatively low constitutive basal secretion. This chapter discusses current knowledge of the regulation and the function of GH pulsatile profiles, with new development of laboratory approaches and introduces knowledge about GH functions on metabolic regulation in addition to the conventional concept of a role in regulating body growth. As reported in the literature, amplitude, frequency, and regularity of GH secretion are tightly linked to metabolic conditions with clear species and gender differences. In response to negative and positive energy balances, the GH pulsatile pattern changes to mobilize or store energy in adipose, muscle, and liver in order to accommodate the changing nutritional conditions. Changes in GH pulsatility are achieved through regulating the hypothalamo–pituitary GH axis with altered levels of key stimulatory and inhibitory hormones, GH-releasing hormone (GHRH) and somatostatin (SRIF, somatotropin release inhibiting factor). The hypothalamic–pituitary GH axis is constantly under the influence of peripheral metabolic factors, such as lipid and glucose levels; peripheral metabolic regulatory hormones, such as leptin and insulin; and central metabolic regulatory neuropeptides, such as neuropeptide Y and\ua0melanocortin. Regulation of the hypothalamic–pituitary GH axis is achieved through activation of cell membrane receptors, intracellular signaling pathways, and membrane ion channels. Detailed regulatory mechanisms are discussed in this chapter in order to understand the coupling of cell electrophysiological properties and the hormone secretory process of exocytosis in hypothalamic neurons and pituitary GH-secreting somatotrophs. Technical advances in electrophysiology, cell imaging analysis, and real-time in vivo hormone analysis are discussed to deepen the understanding of physiological and pathophysiological regulation of GH secretion. Future directions are also discussed, as are unanswered questions in this field