Endogenous pyrogen-like substance produced by reptiles

Behavioral responses during sickness in amphibians and reptiles: Concepts, experimental design, and implications for field studies

In ectothermic vertebrates, behavioral fever, where an individual actively seeks warmer areas, seems to be a primary response to pathogens. This is considered a broad and evolutionarily conserved response among vertebrates. Recent population declines in amphibians are associated with an increase of infectious disease driven largely by climate change, habitat degradation, and pollution. Immediate action through research is required to better understand and inform conservation efforts. The literature available, does not provide unifying concepts that can guide adequate experimental protocols and interpretation of data, especially when studying animals in the field. The aim of this review is to promote common understanding of terminology and facilitating improved comprehension and application of key concepts about the occurrence of both sickness behavior or behavioral fever in ectothermic vertebrates. We start with a conceptual synthesis of sickness behavior and behavioral fever, with examples in different taxa. Through this discussion we present possible paths to standardize terminology, starting from original use in endothermic tetrapods which was expanded to ectothermic vertebrates, particularly amphibians and reptiles. This conceptual expansion from humans (endothermic vertebrates) and then to ectothermic counterparts, gravitates around the concept of 'normality'. Thus, following this discussion, we highlight caveats with experimental protocols and state the need of a reference value considered normal (RVCN), which is different from experimental control and make recommendations regarding experimental procedures and stress the value of detailed documentation of behavioral responses. We also propose some future directions that could enhance interaction among disciplines, emphasizing relationships at different levels of biological organization. This is crucial given the increasing convergence of fields such as thermal physiology, immunology, and animal behavior due to emerging diseases and other global crises impacting biodiversity.

DNA Methylation and Counterdirectional Pigmentation Change following Immune Challenge in a Small Ectotherm

AbstractBy allowing for increased absorption or reflectance of solar radiation, changes in pigmentation may assist ectotherms in responding to immune challenges by enabling a more precise regulation of behavioral fever or hypothermia. Variation in epigenetic characteristics may also assist in regulating immune-induced pigmentation changes and managing the body's energetic reserves following infection. Here, we explore how dorsal pigmentation, metabolic rate, and DNA methylation in the Florida scrub lizard (Sceloporus woodi) respond to two levels of immune challenge across two habitat types. We found changes in pigmentation that are suggestive of efforts to assist in behavioral fever and hypothermia depending on the intensity of immune challenge. We also found correlations between DNA methylation in liver tissue and pigmentation change along the dorsum, indicating that color transitions may be part of a multifaceted immune response across tissue types. The relationship between immune response and metabolic rate supports the idea that energetic reserves may be conserved for the costs associated with behavioral fever when immune challenge is low and the immune functions when immune challenge is high. While immune response appeared to be unaffected by habitat type, we found differences in metabolic activity between habitats, suggesting differences in the energetic costs associated with each. To our knowledge, these results present the first potential evidence of pigmentation change in ectotherms in association with immune response. The relationship between immune response, DNA methylation, and pigmentation change also highlights the importance of epigenetic mechanisms in organism physiology.

Behavioral fever in ectothermic vertebrates

Fever is an evolutionary conserved defense mechanism which is present in both endothermic and ectothermic vertebrates. Ectotherms in response to infection can increase their body temperature by moving to warmer places. This process is known as behavioral fever. In this review, we summarize the current knowledge on the mechanisms of induction of fever in mammals. We further discuss the evolutionary conserved mechanisms existing between fever of mammals and behavioral fever of ectothermic vertebrates. Finally, the experimental evidences supporting an adaptive value of behavioral fever expressed by ectothermic vertebrates are summarized.

Effects of lipopolysaccharide and acclimation temperature on induced behavioral fever in juvenile Iguana iguana

We examined the effects of acclimation temperature and two doses (2.5 and 25mgkg(-1)) of a pyrogen (lipopolysaccharide, LPS) on behavioral thermoregulation in juvenile green iguanas. Overall means of body temperatures for the three-day trial periods were compared among three groups of animals acclimated at 15, 25, and 34 degrees C. The responses of each group of animals to the two dosages of LPS and a control saline injection were examined. Within each treatment block, animals either chose high body temperatures characteristic of a fever response or chose low body temperatures characteristic of a hypothermic response. Thermoregulation was influenced by interaction effects between and among, and independent effects of, acclimation temperature, dose of LPS, and day. In some treatment blocks, individual lizard mass positively correlated with mean individual body temperature. Mean mass of lizards that chose higher body temperatures within a treatment block was higher than the mean mass of lizards that chose lower body temperatures. From these results, we concluded that LPS may induce two different behavioral thermoregulatory responses: fever or hypothermia. The actual amplitude and direction of body temperature change appears to be affected by acclimation temperature and possibly by mass or energy reserves of the animal. If the energy reserves are not sufficient to sustain the higher rate of metabolism associated with the higher body temperatures of a hyperthermic or feverish state, the animal may resort to hypothermia.

Behavioral rise in body temperature and tachycardia by handling of a turtle (Clemmys insculpta)

Three turtles, Clemmys insculpta, were kept together in a terrarium in a climatic chamber at 18 degrees C, with lights on at 07:00 h and off at 19:00 h. In one corner of the terrarium an infrared lamp produced an operative temperature of 42.5 degrees C, thereby allowing behavioral temperature regulation during the light period. When the turtles were handled only once a day for the purpose of taking cloacal temperature, their body temperature held stable at about 22-23 degrees C. Immediately after being handled the turtles sought the radiant heat and regulated their body temperature at about 4 degrees C higher than before the handling. When repeatedly handled every 15 min for 2 h the turtles maintained a high body temperature by their behavior. When not repeatedly handled the turtles returned to their initial preferred body temperature ca 22-23 degrees C within 2 h. It is hypothesized that handling causes in turtles a fever similar to that observed in stressed mammals. The turtles were equipped with an electrocardiogram radio transmitter and their heart rate was recorded at a distance. Heart rate in undisturbed turtles was 28.3+/-0.6 bt/min. During a 1-min handling, their heart rate rose to 40.2+/-0.8 bt/min. This tachycardia persisted several minutes, then their heart rate returned to the baseline value in ca. 10 min. Stress fever and tachycardia are taken as signs of emotion in turtles.

The adaptive value of fever

There is overwhelming evidence in favor of fever being an adaptive host response to infection that has persisted throughout the animal kingdom for hundreds of millions of years. As such, it is probable that the use of antipyretic/anti-inflammatory/analgesic drugs, when they lead to suppression of fever, results in increased morbidity and mortality during most infections; this morbidity and mortality may not be apparent to most health care workers because fever is only one of dozens of host defense responses. Furthermore, most infections are not life-threatening and subtle changes in morbidity are not easily detected.

Cytokines in the viviparous reproduction of squamate reptiles: interleukin-1 alpha (IL-1 alpha) and IL-1 beta in placental structures of a skink

Placental viviparity is known in many species of squamate reptiles. Among these, some scincids have developed an epithelio-chorial chorio-allantoic placenta which in the structure of its central ridged zone is similar to those of certain therian mammalian species. A broad range of immunoregulatory peptides, cytokines, has been identified at the maternofetal interface of several species of mammals, either with invasive or non-invasive types of placenta. Thus we began to study whether interleukin-1, which is considered to play a crucial role in mammalian pregnancy, might also be involved in the viviparity of reptilian species. Placentae of Chalcides chalcides L. were processed by immunohistochemistry and incubated in a culture medium for different times. A very strong immunoreactivity for interleukin-1 alpha (IL-1 alpha) and for interleukin-1 beta (IL-1 beta) was present in the chorial epiblast and in uterine epithelial cells, with varying degree and localization in different periods of pregnancy. IL-1 beta was also released into the medium at different amounts during incubation. In light of the mammalian data, our results suggest that the role of cytokines in pregnancy may represent a significant event in the evolution of placental viviparity.

Human tumor necrosis factor alpha influences rainbow trout Oncorhynchus mykiss leucocyte responses

Human recombinant tumor necrosis factor alpha (rTNF alpha) and rainbow trout macrophage activating factor (postulated gamma-interferon (gamma-IFN) analogue) synergised to elevate the respiratory burst activity of trout macrophages. This elevated response may parallel phenomena described in mammals where TNF alpha and gamma-IFN commonly synergise. Human rTNF alpha also synergised with mitogenic stimuli to heighten proliferation responses of trout head kidney leucocytes. These data are indicative of a conserved TNF alpha receptor on trout leucocytes (and possibly the TNF alpha molecule itself) and support the notion of an interactive cytokine network regulating immune responses in fish.

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

Fever in snails, reflection on a negative result

1. Groups of aquatic snails (Limnaea auricularia) were placed in a temperature gradient and their thermopreferendum measured. 2. Injected with various amounts of killed Escherichia coli, bacterial endotoxin, human interleukin, and prostaglandin E1, E2 and F2 alpha, they did not develop a fever. 3. High doses of prostaglandins were toxic. 4. These results suggest that fever appeared in the course of evolution after the emergence of molluscs and before that of arthropods.

Genomic sequence for human prointerleukin 1 beta: possible evolution from a reverse transcribed prointerleukin 1 alpha gene

We have isolated the human prointerleukin 1 (proIL-1) beta gene from leukocyte and fetal liver libraries. The nucleotide sequence and its gene organization reveals that the proIL-1 beta gene is composed of seven exons with a primary transcription product length of 7,008 nucleotides. The exon sequence agrees well with that of the human proIL-1 beta cDNA. Features of interest within the transcriptional unit include positioned TATA, CAT, and poly-adenylation signals for gene regulation, as well as the signatures of gene duplication via retrotransposition in the form of flanking direct repeats and a genomic poly A tail. The genomic organization of the proIL-1 beta gene with respect to the number and position of exon boundaries is strikingly similar to that of the recently reported human proIL-1 alpha gene. Therefore, we hypothesize that the proIL-1 beta may have arisen by a reverse transcriptase mediated duplication of the related alpha gene.

Phylogenetic studies on lymphokines. Fish lymphocytes respond to human IL-1 and epithelial cells produce an IL-1 like factor

The results obtained indicate, that catfish peripheral blood lymphocytes recognize and respond to human IL-1. The second part of this report is dealing with a substance produced by carp epidermal cells with functional similarities to mammalian IL-1.

Is fever beneficial?

Fever, the regulation of body temperature at an elevated level, is a common response to infection throughout the vertebrates, as well as in many species of invertebrate animals. It is probable that fever evolved as an adaptive response to infection hundreds of millions of years ago. Many components of the nonspecific and specific host response to infection are enhanced by small elevations in temperature. Perhaps more important, studies of bacterial- and viral-infected animals have shown that, in general, moderate fevers decrease morbidity and increase survival rate.

Molecular basis of fever in humans

This review presents several areas of research on the pathogenesis of fever in humans and updates new information concerning the role of fever in host defense mechanisms. Fever is mediated by a polypeptide of phagocytic cell origin called leukocytic pyrogen. Several agents and disease processes are associated with the synthesis and release of leukocytic pyrogen. Although the original studies on leukocytic pyrogen suggested that the neutrophil was the primary source, recent experiments indicate the mononuclear phagocyte to be the major producer of leukocytic pyrogen. The mechanism by which human monocytes are stimulated to produce leukocytic pyrogen is discussed, including the effects of corticosteroids, estrogens and antipyretics on the synthesis of leukocytic pyrogen in vitro. The ability of leukocytic pyrogen to alter the hypothalamic thermoregulatory center by increasing arachidonic acid metabolite levels is the most likely mechanism by which leukocytic pyrogen initiates fever. Antipyretics prevent the synthesis of certain cyclooxygenase metabolites, which accounts for their ability to reduce fever. Studies on the chemical and physical properties of human leukocytic pyrogen are reviewed and form the basis for current experiments on the similarities between leukocytic pyrogen and lymphocyte activating factor. These studies suggest that leukocytic pyrogen, in addition to producing fever, also stimulates non-hypothalamic cells involved in aspects of the acute-phase response. In this regard, leukocytic pyrogen may be an important mechanism for host defenses. Hyperthermia may also be beneficial to the host but is distinct from fever; the role of leukocytic pyrogen as well as hyperthermia as a defense mechanism is discussed.

Studies on the active site of human leukocytic pyrogen

Leukocytic pyrogen, a polypeptide produced by phagocytic mononuclear cells, is thought to be the endogenous mediator of fever. In addition to its effects on thermoregulation, leukocytic pyrogen has been shown to induce synthesis of acute-phase proteins, increase lymphocyte blastogenesis to mitogens, and cause release of neutrophil-specific granule contents. Despite its important role in biologic responses, little is known concerning the structure-function relationship of the molecule. In the present studies several protein-modifying conditions were used in order to examine specific amino acid participation at the active site. Because the state of purity of leukocytic pyrogen may be critical during certain reaction conditions, highly purified preparations were used. Experiments suggest that the active site requires the gamma-carboxyl group of glutamic acid and that blocking arginine reduces both the pyrogenic and neutrophil releasing properties of the molecule. Other studies demonstrate that the pyrogenicity of human leukocytic pyrogen is not due to serine esterase or carboxypeptidase B activity and that the 15,000-dalton molecule may be a glycoprotein. These experiments provide further evidence that the lymphocyte-activating and neutrophil-granule-releasing properties of human leukocytic pyrogen require the same active site which produces fever.

Fever and survival: the role of serum iron

1. The effects of bacterial infection and temperature on serum iron levels were investigated in the lizard Dipsosaurus dorsalis. 2. Changes in body temperature from normal (38 degrees C) to febrile (41 degrees C) did not alter serum iron levels. Injection with Aeromonas hydrophila led to a significant reduction in serum iron levels, comparable to that found in mammals. This reduction in serum iron level was independent of the lizard's body temperature. 3. When grown in vitro, A. hydrophila grew equally well at afebrile (38 degrees C) and febrile (41 degrees C) temperatures. When the iron levels of the growth medium were reduced, the bacterial growth was diminished at the febrile temperature but was not significantly affected at the afebrile temperature. 4. The addition of iron supplements to bacterially infected lizards led to an increase in the percent mortality. 5. These results indicate that one of the mechanisms behind the beneficial, or adaptive value of fever in D. dorsalis is the decrease in iron available to the pathogenic micro-organisms.