Body Temperature during hibernation is highly correlated with a decrease in circulating innate immune cells in the brown bear (Ursus arctos): a common feature among hibernators?

• Published in: International Journal of Medical Sciences
• Main Authors: Sahdo, Berolla, L. Evans, Alina, M. Arnemo, Jon, Fröbert, Ole, Särndahl, Eva, Blanc, Stéphane
• Other Authors: Department of Clinical Medicine, Örebro University, Department of Forestry and Wildlife Management, Hedmark University College, Section of Arctic Veterinary medicine, Norwegian School of Veterinary Science, Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences (SLU), Department of Cardiology, Département Ecologie, Physiologie et Ethologie (DEPE-IPHC), Institut Pluridisciplinaire Hubert Curien (IPHC), Université de Strasbourg (UNISTRA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2013
• Subjects: brown bear; Ursus arctos; Hibernation; Innate immunity; Leukocytes; Torpor; envir; geo; Arctic
• Online Access: https://doi.org/10.7150/ijms.4476; https://hal.archives-ouvertes.fr/hal-00805200/file/Sahdo.pdf; https://hal.archives-ouvertes.fr/hal-00805200

International audience Background: Hibernation involves periods of severely depressed metabolism (torpor) and decreases in body temperature (Tb). Small arctic mammals ( < 5kg), in which Tb generally drop drastically, display leukopenia during hibernation. This raised the question of whether the decreased leukocyte counts in mammalian hibernators is due to torpor per se or is secondary to low Tb. The present study examined immune cell counts in brown bears (Ursus arctos), where torpor is only associated with shallow decreases in Tb. The results were compared across hibernator species for which immune and Tb data were available. Methods and Results: The white blood cell counts were determined by flow cytometry in 13 bears captured in the field both during summer and winter over 2 years time. Tb dropped from 39.6±0.8 to 33.5±1.1°C during hibernation. Blood neutrophils and monocytes were lower during hibernation than during the active period (47%, p= 0.001; 43%, p=0.039, respectively), whereas no change in lymphocyte counts was detected (p=0.599). Further, combining our data and those from 10 studies on 9 hibernating species suggested that the decline in Tb explained the decrease in innate immune cells (R2=0.83, p < 0.0001). Conclusions: Bears have fewer innate immune cells in circulation during hibernation, which may represent a suppressed innate immune system. Across species comparison suggests that, both in small and large hibernators, Tb is the main driver of immune function regulation during winter dormancy. The lack of a difference in lymphocyte counts in this context requires further investigations.