Biological Clocks and Immune Function

Abstract

Circadian rhythms are internal manifestations of the 24-h solar day that allow synchronization of biological and behavioral processes to the external temporal environment. In mammals, circadian rhythms are generated and sustained by the hypothalamic master clock, or suprachiasmatic nucleus (SCN). Within the SCN, a highly coupled network of rhythmically active neuronal and glial oscillators function to maintain rhythms of approximately 24 h. These circadian rhythms are set to precisely 24 h by exposure to the light-dark cycle or other external synchronizers (zeitgebers). Virtually all aspects of physiology display circadian variation, including immune function. This chapter provides a brief review of the circadian system. We detail the neuroendocrine and autonomic nervous mechanisms by which circadian clocks communicate time of day signals to the immune system and how the immune system can feedback to alter circadian clocks. Next, we describe daily rhythms in immune function and circadian regulation of immune cell trafficking. We illustrate the functional relevance of circadian regulation of immune function via the effects of circadian disruption on disease. Finally, potential pitfalls and future directions in the field are discussed.