IMR Press / FBL / Volume 10 / Issue 2 / DOI: 10.2741/1690

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.

Open Access Article
Fever and hypothermia in systemic inflammation: recent discoveries and revisions
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1 Systemic Inflammation Laboratory, Trauma Research, St. Joseph's Hospital and Medical Center, 350 West Thomas Road, Phoenix, AZ 85013, USA
2 Division of Infectious Diseases, Department of Internal Medicine, University of Michigan Health System, 1500 West Medical Center Drive, Ann Arbor, MI 48109, USA
3 Department of Pathology and Laboratory Medicine, Emory University, Atlanta, GA 30322, USA
4 Laboratoire de Neurobiologie Integrative, Centre National de la Recherche Scientifique FRE 2723/Institut National de la Recherche Agronomique UR 1244, Institut Francois Magendie, 33077 Bordeaux, France
5 Department of Behavioral Neuroscience, Oregon Health and Science University, 3181 South West Sam Jackson Park Road, Portland, OR 97239, USA

Academic Editor: Andrej Romanovsky

Front. Biosci. (Landmark Ed) 2005, 10(2), 2193–2216; https://doi.org/10.2741/1690
Published: 1 September 2005
(This article belongs to the Special Issue Fever and hypothermia in systemic Inflammation)
Abstract

Systemic inflammation is accompanied by changes in body temperature, either fever or hypothermia. Over the past decade, the rat and mouse have become the predominant animal models, and new species-specific tools (recombinant antibodies and other proteins) and genetic manipulations have been applied to study fever and hypothermia. Remarkable progress has been achieved. It has been established that the same inflammatory agent can induce either fever or hypothermia, depending on several factors. It has also been established that experimental fevers are generally polyphasic, and that different mechanisms underlie different febrile phases. Signaling mechanisms of the most common pyrogen used, bacterial lipopolysaccharide (LPS), have been found to involve the Toll-like receptor 4. The roles of cytokines (such as interleukins-1beta and 6 and tumor necrosis factor-alpha) have been further detailed, and new early mediators (e.g., complement factor 5a and platelet-activating factor) have been proposed. Our understanding of how peripheral inflammatory messengers cross the blood-brain barrier (BBB) has changed. The view that the organum vasculosum of the lamina terminalis is the major port of entry for pyrogenic cytokines has lost its dominant position. The vagal theory has emerged and then fallen. Consensus has been reached that the BBB is not a divider preventing signal transduction, but rather the transducer itself. In the endothelial and perivascular cells of the BBB, upstream signaling molecules (e.g., pro-inflammatory cytokines) are switched to a downstream mediator, prostaglandin (PG) E2. An indispensable role of PGE2 in the febrile response to LPS has been demonstrated in studies with targeted disruption of genes encoding either PGE2-synthesizing enzymes or PGE2 receptors. The PGE2-synthesizing enzymes include numerous phospholipases (PL) A2, cyclooxygenases (COX)-1 and 2, and several newly discovered terminal PGE synthases (PGES). It has been realized that the "physiological," low-scale production of PGE2 and the accelerated synthesis of PGE2 in inflammation are catalyzed by different sets of these enzymes. The "inflammatory" set includes several isoforms of PLA2 and inducible isoforms of COX (COX-2) and microsomal (m) PGES (mPGES-1). The PGE2 receptors are multiple; one of them, EP3 is likely to be a primary "fever receptor." The effector pathways of fever start from EP3-bearing preoptic neurons. These neurons have been found to project to the raphe pallidus, where premotor sympathetic neurons driving thermogenesis in the brown fat and skin vaso-constriction are located. The rapid progress in our understanding of how thermoeffectors are controlled has revealed the inadequacy of set point-based definitions of thermoregulatory responses. New definitions (offered in this review) are based on the idea of balance of active and passive processes and use the term balance point. Inflammatory signaling and thermoeffector pathways involved in fever and hypothermia are modulated by neuropeptides and peptide hormones. Roles for several "new" peptides (e.g., leptin and orexins) have been proposed. Roles for several "old" peptides (e.g., arginine vasopressin, angiotensin II, and cholecystokinin) have been detailed or revised. New pharmacological tools to treat fevers (i.e., selective inhibitors of COX-2) have been rapidly introduced into clinical practice, but have not become magic bullets and appeared to have severe side effects. Several new targets for antipyretic therapy, including mPGES-1, have been identified.

Keywords
Body temperature
Thermoregulation
Set point
Balance point
Fever
Febrile response
Hypothermic response
Anapyrexia
Leptin
Lipopolysaccharide
LPS
Toll-like receptors
Cytokines
IL-1beta
IL-6
TNF-alpha
Prostaglandins
PGE2
Blood-brain barrier
Organum vasculosum laminae terminalis
OVLT
Vagus Nerve
PGE2- synthesizing enzymes
Phospholipases
PLA2
Fever and hypothermia in systemic inflammation 2216 Cyclooxygenases
COX-1
COX-2
Prostaglandin synthases
PGES
EP3 receptor
Thermoeffectors
Skin vasoconstriction
Thermogenesis
Brown adipose tissue
Neuropeptides
Orexins
Neuropeptide Y
Arginine vasopressin
Angiotensin II
Cholecystokinin
AlphaMSH
Corticotropin-releasing factor
Urocortins
Selective COX-2 inhibitors
Antipyretic therapy
Review
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