title: Clock mutation affects circadian regulation of circulating blood cells.
abstract: BACKGROUND
  Although the number of circulating immune cells is subject to high-amplitude circadian rhythms, the underlying mechanisms are not fully understood.
  
  
  METHODS
  To determine whether intact CLOCK protein is required for the circadian changes in peripheral blood cells, we examined circulating white (WBC) and red (RBC) blood cells in homozygous Clock mutant mice.
  
  
  RESULTS
  Daytime increases in total WBC and lymphocytes were suppressed and slightly phase-delayed along with plasma corticosterone levels in Clock mutant mice. The peak RBC rhythm was significantly reduced and phase-advanced in the Clock mutants. Anatomical examination revealed hemoglobin-rich, swollen red spleens in Clock mutant mice, suggesting RBC accumulation.
  
  
  CONCLUSIONS
  Our results suggest that endogenous clock-regulated circadian corticosterone secretion from the adrenal gland is involved in the effect of a Clock mutation on daily profiles of circulating WBC. However, intact CLOCK seems unnecessary for generating the rhythm of corticosterone secretion in mice. Our results also suggest that CLOCK is involved in discharge of RBC from the spleen.
authors.affiliation: Clock Cell Biology Research Group, Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan. k-ooishi@aist.go.jp
authors.forename: Katsutaka
authors.initials: K
authors.lastname: Oishi
authors.forename: Naoki
authors.initials: N
authors.lastname: Ohkura
authors.forename: Koji
authors.initials: K
authors.lastname: Kadota
authors.forename: Manami
authors.initials: M
authors.lastname: Kasamatsu
authors.forename: Kentaro
authors.initials: K
authors.lastname: Shibusawa
authors.forename: Juzo
authors.initials: J
authors.lastname: Matsuda
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Machida
authors.forename: Shuichi
authors.initials: S
authors.lastname: Horie
authors.forename: Norio
authors.initials: N
authors.lastname: Ishida