The Hibernating Immune System
Several physiological changes take place during hibernation, which are thought to allow animals to conserve energy and limit organ injury as might otherwise occur due to the physiological extremes of torpor and arousal. Significant changes occur in the immune system during torpor. The number of circulating leukocytes drops by ~90% during entrance into torpor and seems to be driven by low body temperature. Normal cell counts restore upon arousal. Recently, we demonstrated that clearance of circulating lymphocytes is due to retention in lymphoid organs caused by a reduced plasma level of sphingosine-1-phosphate (S1P). Besides its effects on leukocyte migration, hibernation affects complement function, phagocytosis capacity, cytokine production, lymphocyte proliferation, and antibody production. The reduced immune function might play a major role in the etiology of White Nose Syndrome (WNS) in hibernating bats. Further, the ability to induce a fully reversible state of immune suppression in humans might aid the treatment of several inflammatory and immune-mediated diseases. Unraveling the mechanisms underlying the reduced immune function during torpor will not only enhance fundamental knowledge about the immune system, but might also lead to the development of a strategy to limit mortality due to WNS.
KeywordsGround Squirrel Skin Allograft Febrile Response Arctic Ground Squirrel White Nose Syndrome
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