Induction of stress proteins in a panel of mouse tissues by fever-range whole body hyperthermia

Effect of Different Ambient Temperatures on Reproductive Outcome and Stress Level of Lactating Females in Two Mouse Strains

Simple Summary

The optimal temperature for laboratory mice has been under discussion for some time. Current standard temperature is 20 °C–24 °C but it has been suggested to elevate the standard to 30 °C, which is the thermoneutral zone for mice. In this study, the effect of different cage temperatures (20 °C, 25 °C, 30 °C) on reproduction and stress hormone metabolite excretion was evaluated in lactating females of two commonly used mouse strains. Pup loss was higher, and weights of mothers and pups were reduced at 30 °C compared to the lower temperatures. In addition, pups showed increased tail length at weaning under the high temperature (30 °C). There was no difference in stress hormone metabolite excretion in mice between temperature groups. We could not show any detrimental effects of the lower or higher cage temperature on stress hormone metabolite excretion, but found decreased reproductive outcome under the higher temperature.

Abstract

Ambient temperature is an important non-biotic environmental factor influencing immunological and oncological parameters in laboratory mice. It is under discussion which temperature is more appropriate and whether the commonly used room temperature in rodent facilities of about 21 °C represents a chronic cold stress or the 30 °C of the thermoneutral zone constitutes heat stress for the animals. In this study, we selected the physiological challenging period of lactation to investigate the influence of a cage temperature of 20 °C, 25 °C, and 30 °C, respectively, on reproductive performance and stress hormone levels in two frequently used mouse strains. We found that B6D2F1 hybrid mothers weaned more pups compared to C57BL/6N mothers, and that the number of weaned pups was reduced when mothers of both strains were kept at 30 °C. Furthermore, at 30 °C, mothers and pups showed reduced body weight at weaning and offspring had longer tails. Despite pronounced temperature effects on reproductive parameters, we did not find any temperature effects on adrenocortical activity in breeding and control mice. Independent of the ambient temperature, however, we found that females raising pups showed elevated levels of faecal corticosterone metabolites (FCMs) compared to controls. Peak levels of stress hormone metabolites were measured around birth and during the third week of lactation. Our results provide no evidence of an advantage for keeping lactating mice in ambient temperatures near the thermoneutral zone. In contrast, we found that a 30 °C cage temperature during lactation reduced body mass in females and their offspring and declined female reproductive performance.

A unifying model to estimate the effect of heat stress in the human innate immunity during physical activities

Public health is threatened by climate change and extreme temperature events worldwide. Differences in health predispositions, access to cooling infrastructure and occupation raises an issue of heat-related health inequality in those vulnerable and disadvantaged demographic groups. To address these issues, a comprehensive understanding of the effect of elevated body temperatures on human biological systems and overall health is urgently needed. In this paper we look at the inner workings of the human innate immunity under exposure to heat stress induced through exposure to environment and physical exertion. We couple two experimentally validated computational models: the innate immune system and thermal regulation of the human body. We first study the dynamics of critical indicators of innate immunity as a function of human core temperature. Next, we identify environmental and physical activity regimes that lead to core temperature levels that can potentially compromise the performance of the human innate immunity. Finally, to take into account the response of innate immunity to various intensities of physical activities, we utilise the dynamic core temperatures generated by a thermal regulation model. We compare the dynamics of all key players of the innate immunity for a variety of stresses like running a marathon, doing construction work, and leisure walking at speed of 4 km/h, all in the setting of a hot and humid tropical climate such as present in Singapore. We find that exposure to moderate heat stress leading to core temperatures within the mild febrile range (37, 38][Formula: see text], nudges the innate immune system into activation and improves the efficiency of its response. Overheating corresponding to core temperatures beyond 38[Formula: see text], however, has detrimental effects on the performance of the innate immune system, as it further induces inflammation, which causes a series of reactions that may lead to the non-resolution of the ongoing inflammation. Among the three physical activities considered in our simulated scenarios (marathon, construction work, and walking), marathon induces the highest level of inflammation that challenges the innate immune response with its resolution. Our study advances the current state of research towards understanding the implications of heat exposure for such an essential physiological system as the innate immunity. Although we find that among considered physical activities, a marathon of 2 h and 46 min induces the highest level of inflammation, it must be noted that construction work done on a daily basis under the hot and humid tropical climate, can produce a continuous level of inflammation triggering moieties stretched at a longer timeline beating the negative effects of running a marathon. Our study demonstrates that the performance of the innate immune system can be severely compromised by the exposure to heat stress and physical exertion. This poses significant risks to health especially to those with limited access to cooling infrastructures. This is due in part to having low income, or having to work on outdoor settings, which is the case for construction workers. These risks to public health should be addressed through individual and population-level measures via behavioural adaptation and provision of the cooling infrastructure in outdoor environments.

Oxidative stress in response to heat stress in wild caught Namaqua rock mice, Micaelamys namaquensis

Modelling of anthropogenic induced climate suggests more frequent and severe heatwaves in the future, which are likely to result in the mass die-off of several species of organisms. Oxidative stress induced by severe heat stress has previously been associated with a reduction in animal cognitive performance, depressed reproduction and lower life expectancy. Little is known about the non-lethal consequences of species should they survive extreme heat exposure. We investigated the oxidative stress experienced by the Namaqua rock mouse, a nocturnal rodent, using two experimental heat stress protocols, a 6 hour acute heat stress protocol without access to water and a 3-day heatwave simulation with ad libitum water. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers of oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defence. Incubator heat stress (heat and dehydration stress) was brought about by increasing the body temperatures of animals to 39-40.8 °C for 6 hours. Following incubator heat stress, significantly higher levels of MDA were observed in the liver. Dehydration did not explain the variation in oxidative markers and is likely a combined effect of thermal and dehydration stress. Individual body mass was significantly negatively correlated to kidney SOD and lipid peroxidation. A heatwave was simulated using a temperature cycle that would naturally occur during a heatwave in the species' local habitat, with a maximal ambient temperature of 38 °C. Following the simulated heatwave, SOD activity of the kidney demonstrated significantly lowered activity suggesting oxidative stress. Current heat waves in this species have the potential of causing oxidative stress. Heat and dehydration stress following exacerbated temperatures are likely to incur significant oxidative stress in multiple tissues demonstrating the importance of water availability to allow for rehydration to prevent oxidative stress.

Heat and dehydration induced oxidative damage and antioxidant defenses following incubator heat stress and a simulated heat wave in wild caught four-striped field mice Rhabdomys dilectus

Heat waves are known for their disastrous mass die-off effects due to dehydration and cell damage, but little is known about the non-lethal consequences of surviving severe heat exposure. Severe heat exposure can cause oxidative stress which can have negative consequences on animal cognition, reproduction and life expectancy. We investigated the current oxidative stress experienced by a mesic mouse species, the four striped field mouse, Rhabdomys dilectus through a heat wave simulation with ad lib water and a more severe temperature exposure with minimal water. Wild four striped field mice were caught between 2017 and 2019. We predicted that wild four striped field mice in the heat wave simulation would show less susceptibility to oxidative stress as compared to a more severe heat stress which is likely to occur in the future. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers for oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defense. Incubator heat stress was brought about by increasing the body temperatures of animals to 39-40.8°C for 6 hours. A heat wave (one hot day, followed by a 3-day heatwave) was simulated by using temperature cycle that wild four striped field mice would experience in their local habitat (determined through weather station data using temperature and humidity), with maximal ambient temperature of 39°C. The liver and kidney demonstrated no changes in the simulated heat wave, but the liver had significantly higher SOD activity and the kidney had significantly higher lipid peroxidation in the incubator experiment. Dehydration significantly contributed to the increase of these markers, as is evident from the decrease in body mass after the experiment. The brain only showed significantly higher lipid peroxidation following the simulated heat wave with no significant changes following the incubator experiment. The significant increase in lipid peroxidation was not correlated to body mass after the experiment. The magnitude and duration of heat stress, in conjunction with dehydration, played a critical role in the oxidative stress experienced by each tissue, with the results demonstrating the importance of measuring multiple tissues to determine the physiological state of an animal. Current heat waves in this species have the potential of causing oxidative stress in the brain with future heat waves to possibly stress the kidney and liver depending on the hydration state of animals.

A Futile Battle? Protein Quality Control and the Stress of Aging

There exists a phenomenon in aging research whereby early life stress can have positive impacts on longevity. The mechanisms underlying these observations suggest a robust, long-lasting induction of cellular defense mechanisms. These include the various unfolded protein responses of the endoplasmic reticulum (ER), cytosol, and mitochondria. Indeed, ectopic induction of these pathways, in the absence of stress, is sufficient to increase lifespan in organisms as diverse as yeast, worms, and flies. Here, we provide an overview of the protein quality control mechanisms that operate in the cytosol, mitochondria, and ER and discuss how they affect cellular health and viability during stress and aging.

Autophagy--A free meal in sickness-associated anorexia

Activation of the immune system is metabolically costly, yet a hallmark of an infection is a reduction in appetite with a subsequent reduction in metabolite provision. What is the functional value of decreasing nutrient intake when an infection imposes large demands on metabolic parameters? Here, we propose that sickness-associated anorexia (SAA) upregulates the ancient process of autophagy systemically, thereby profoundly controlling not only immune- but also nonimmune-competent cells. This allows an advanced impact on the resolution of an infection through direct pathogen killing, enhancement of epitope presentation and the contribution toward the clearance of noxious factors. By rendering a 'free meal,' autophagy is thus most fundamentally harnessed during an anorexic response in order to promote both host tolerance and resistance. These findings strongly suggest a reassessment of numerous SAA-related clinical applications and a re-evaluation of current efforts in patient care.

Self-harm to preferentially harm the pathogens within: non-specific stressors in innate immunity

Therapies with increasing specificity against pathogens follow the immune system's evolutionary course in maximizing host defence while minimizing self-harm. Nevertheless, even completely non-specific stressors, such as reactive molecular species, heat, nutrient and oxygen deprivation, and acidity can be used to preferentially harm pathogens. Strategic use of non-specific stressors requires exploiting differences in stress vulnerability between pathogens and hosts. Two basic vulnerabilities of pathogens are: (i) the inherent vulnerability to stress of growth and replication (more immediately crucial for pathogens than for host cells) and (ii) the degree of pathogen localization, permitting the host's use of locally and regionally intense stress. Each of the various types of non-specific stressors is present during severe infections at all levels of localization: (i) ultra-locally within phagolysosomes, (ii) locally at the infected site, (iii) regionally around the infected site and (iv) systemically as part of the acute-phase response. We propose that hosts strategically use a coordinated system of non-specific stressors at local, regional and systemic levels to preferentially harm the pathogens within. With the rising concern over emergence of resistance to specific therapies, we suggest more scrutiny of strategies using less specific therapies in pathogen control. Hosts' active use of multiple non-specific stressors is likely an evolutionarily basic defence whose retention underlies and supplements the well-recognized immune defences that directly target pathogens.

The antioxidant transcription factor Nrf2 contributes to the protective effect of mild thermotolerance (40°C) against heat shock-induced apoptosis

The exposure of cells to low doses of stress induces adaptive survival responses that protect cells against subsequent exposure to toxic stress. The ability of cells to resist subsequent toxic stress following exposure to low dose heat stress at 40°C is known as mild thermotolerance. Mild thermotolerance involves increased expression of heat shock proteins and antioxidants, but the initiating factors in this response are not understood. This study aims to understand the role of the Nrf2 antioxidant pathway in acquisition of mild thermotolerance at 40°C, and secondly, whether the Nrf2 pathway could be involved in the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis. During cell preconditioning at 40°C, protein expression of the Nrf2 transcription factor increased after 15-60min. In addition, levels of the Nrf2 targets MnSOD, catalase, heme oxygenase-1, glutamate cysteine ligase and Hsp70 increased at 40°C. Levels of these Nrf2 targets were enhanced by Nrf2 activator oltipraz and decreased by shRNA targeting Nrf2. Levels of pro-oxidants increased after 30-60min at 40°C. Pro-oxidant levels were decreased by oltipraz and increased by knockdown of Nrf2. Increased Nrf2 expression and catalase activity at 40°C were inhibited by the antioxidant PEG-catalase and by p53 inhibitor pifithrin-α. These results suggest that mild thermotolerance (40°C) increases cellular pro-oxidant levels, which in turn activate Nrf2 and its target genes. Moreover, Nrf2 contributes to the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis, because Nrf2 activation by oltipraz enhanced thermotolerance, whereas Nrf2 knockdown partly reversed thermotolerance. Improved knowledge about the different protective mechanisms that mild thermotolerance can activate is crucial for the potential use of this adaptive survival response to treat stress-related diseases.

Sickness-Associated Anorexia: Mother Nature's Idea of Immunonutrition?

During an infection, expansion of immune cells, assembly of antibodies, and the induction of a febrile response collectively place continual metabolic strain on the host. These considerations also provide a rationale for nutritional support in critically ill patients. Yet, results from clinical and preclinical studies indicate that aggressive nutritional support does not always benefit patients and may occasionally be detrimental. Moreover, both vertebrates and invertebrates exhibit a decrease in appetite during an infection, indicating that such sickness-associated anorexia (SAA) is evolutionarily conserved. It also suggests that SAA performs a vital function during an infection. We review evidence signifying that SAA may present a mechanism by which autophagic flux is upregulated systemically. A decrease in serum amino acids during an infection promotes autophagy not only in immune cells, but also in nonimmune cells. Similarly, bile acids reabsorbed postprandially inhibit hepatic autophagy by binding to farnesoid X receptors, indicating that SAA may be an attempt to conserve autophagy. In addition, augmented autophagic responses may play a critical role in clearing pathogens (xenophagy), in the presentation of epitopes in nonprovisional antigen presenting cells and the removal of damaged proteins and organelles. Collectively, these observations suggest that some patients might benefit from permissive underfeeding.

Heat shock proteins in the retina: Focus on HSP70 and alpha crystallins in ganglion cell survival

Heat shock proteins (HSPs) belong to a superfamily of stress proteins that are critical constituents of a complex defense mechanism that enhances cell survival under adverse environmental conditions. Cell protective roles of HSPs are related to their chaperone functions, antiapoptotic and antinecrotic effects. HSPs' anti-apoptotic and cytoprotective characteristics, their ability to protect cells from a variety of stressful stimuli, and the possibility of their pharmacological induction in cells under pathological stress make these proteins an attractive therapeutic target for various neurodegenerative diseases; these include Alzheimer's, Parkinson's, Huntington's, prion disease, and others. This review discusses the possible roles of HSPs, particularly HSP70 and small HSPs (alpha A and alpha B crystallins) in enhancing the survival of retinal ganglion cells (RGCs) in optic neuropathies such as glaucoma, which is characterized by progressive loss of vision caused by degeneration of RGCs and their axons in the optic nerve. Studies in animal models of RGC degeneration induced by ocular hypertension, optic nerve crush and axotomy show that upregulation of HSP70 expression by hyperthermia, zinc, geranyl-geranyl acetone, 17-AAG (a HSP90 inhibitor), or through transfection of retinal cells with AAV2-HSP70 effectively supports the survival of injured RGCs. RGCs survival was also stimulated by overexpression of alpha A and alpha B crystallins. These findings provide support for translating the HSP70- and alpha crystallin-based cell survival strategy into therapy to protect and rescue injured RGCs from degeneration associated with glaucomatous and other optic neuropathies.

Unfolding the Role of Large Heat Shock Proteins: New Insights and Therapeutic Implications

Heat shock proteins (HSPs) of eukaryotes are evolutionarily conserved molecules present in all the major intracellular organelles. They mainly function as molecular chaperones and participate in maintenance of protein homeostasis in physiological state and under stressful conditions. Despite their relative abundance, the large HSPs, i.e., Hsp110 and glucose-regulated protein 170 (Grp170), have received less attention compared to other conventional HSPs. These proteins are distantly related to the Hsp70 and belong to Hsp70 superfamily. Increased sizes of Hsp110 and Grp170, due to the presence of a loop structure, result in their exceptional capability in binding to polypeptide substrates or non-protein ligands, such as pathogen-associated molecules. These interactions that occur in the extracellular environment during tissue injury or microbial infection may lead to amplification of an immune response engaging both innate and adaptive immune components. Here, we review the current advances in understanding these large HSPs as molecular chaperones in proteostasis control and immune modulation as well as their therapeutic implications in treatment of cancer and neurodegeneration. Given their unique immunoregulatory activities, we also discuss the emerging evidence of their potential involvement in inflammatory and immune-related diseases.

Housing temperature influences the pattern of heat shock protein induction in mice following mild whole body hyperthermia

PURPOSE

Researchers studying the murine response to stress generally use mice housed under standard, nationally mandated conditions as controls. Few investigators are concerned whether basic physical aspects of mouse housing could be an additional source of stress, capable of influencing the subsequent impact of an experimentally applied stressor. We have recently become aware of the potential for housing conditions to impact important physiological and immunological properties in mice.

MATERIALS AND METHODS

Here we sought to determine whether housing mice at standard temperature (ST; 22 °C) vs. thermoneutral temperature (TT; 30 °C) influences baseline expression of heat shock proteins (HSPs) and their typical induction following a whole body heating.

RESULTS

There were no significant differences in baseline expression of HSPs at ST and TT. However, in several cases, the induction of Hsp70, Hsp110 and Hsp90 in tissues of mice maintained at ST was greater than at TT following 6 h of heating (which elevated core body temperature to 39.5 °C). This loss of HSP induction was also seen when mice housed at ST were treated with propranolol, a β-adrenergic receptor antagonist, used clinically to treat hypertension and stress.

CONCLUSIONS

Taken together, these data show that housing temperature significantly influences the expression of HSPs in mice after whole body heating and thus should be considered when stress responses are studied in mice.

Fever and the thermal regulation of immunity: the immune system feels the heat

Fever is a cardinal response to infection that has been conserved in warm-blooded and cold-blooded vertebrates for more than 600 million years of evolution. The fever response is executed by integrated physiological and neuronal circuitry and confers a survival benefit during infection. In this Review, we discuss our current understanding of how the inflammatory cues delivered by the thermal element of fever stimulate innate and adaptive immune responses. We further highlight the unexpected multiplicity of roles of the pyrogenic cytokine interleukin-6 (IL-6), both during fever induction and during the mobilization of lymphocytes to the lymphoid organs that are the staging ground for immune defence. We also discuss the emerging evidence suggesting that the adrenergic signalling pathways associated with thermogenesis shape immune cell function.

Fever, immunity, and molecular adaptations

The heat shock response (HSR) is an ancient and highly conserved process that is essential for coping with environmental stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms temporarily subject themselves to thermal stress in the face of infections. We review the phylogenetically conserved mechanisms that regulate fever and discuss the effects that febrile-range temperatures have on multiple biological processes involved in host defense and cell death and survival, including the HSR and its implications for patients with severe sepsis, trauma, and other acute systemic inflammatory states. Heat shock factor-1, a heat-induced transcriptional enhancer is not only the central regulator of the HSR but also regulates expression of pivotal cytokines and early response genes. Febrile-range temperatures exert additional immunomodulatory effects by activating mitogen-activated protein kinase cascades and accelerating apoptosis in some cell types. This results in accelerated pathogen clearance, but increased collateral tissue injury, thus the net effect of exposure to febrile range temperature depends in part on the site and nature of the pathologic process and the specific treatment provided.

AAV-mediated and pharmacological induction of Hsp70 expression stimulates survival of retinal ganglion cells following axonal injury

We evaluated the effect of AAV2- and 17-AAG (17-N -allylamino-17-demethoxygeldanamycin)-mediated upregulation of Hsp70 expression on the survival of retinal ganglion cells (RGCs) injured by optic nerve crush (ONC). AAV2-Hsp70 expression in the retina was primarily observed in the ganglion cell layer. Approximately 75% of all transfected cells were RGCs. RGC survival in AAV2-Hsp70 injected animals was increased by an average of 110% 2 weeks after the axonal injury compared to the control. The increase in cell numbers was not even across the retinas with a maximum effect of approximately 306% observed in the inferior quadrant. 17-AAG-mediated expression of Hsp70 has been associated with cell protection in various models of neurodegenerative diseases. We show here that a single intravitreal injection of 17-AAG (0.2 ug/ul) results in an increased survival of ONC injured RGCs by approximately 49% compared to the vehicle-treated animals. Expression of Hsp70 in retinas of 17-AAG-treated animals was upregulated approximately by 2-fold compared to control animals. Our data support the idea that the upregulation of Hsp70 has a beneficial effect on the survival of injured RGCs, and the induction of this protein could be viewed as a potential neuroprotective strategy for optic neuropathies.

Schisandrin B attenuates acetaminophen-induced hepatic injury through heat-shock protein 27 and 70 in mice

BACKGROUND AND AIM

Schisandrin B is an active component isolated from Schisandra chinensis (TurcZ.) Baill. that is widely used as an antihepatotoxic agent. Schisandrin B has significant hepatoprotective effect against chemical and immunological liver injury. This study aimed to investigate the effect of Schisandrin B on the expression of 27- and 70-kDa heat-shock protein (HSP) and its role in protection against acetaminophen-induced liver injury in mice.

METHODS

After the mice were pretreated, Western blot and real-time quantitative polymerase chain reaction were used to detect the protein and gene expression of HSP27 and HSP70, respectively; the liver tissues were subjected to histological evaluation, and alanine aminotransferase and aspartate aminotransferase activities in the serum were measured.

RESULTS

Oral administration of Schisandrin B increased the expression of HSP27 and HSP70 in a time- and dose-dependent manner. The inducing effect of Schisandrin B on HSP27 and HSP70 was also confirmed by real-time quantitative polymerase chain reaction. In the acetaminophen-induced liver injury mouse model, the prior oral administration of Schisandrin B (200 mg/kg) three times in 24 h markedly alleviated liver injury as indicated by the amelioration of histopathological hepatic necrosis and the reduction of alanine aminotransferase and aspartate aminotransferase activities in the serum. However, the earlier actions of Schisandrin B were all suppressed significantly by Quercetin, a known HSP inhibitor.

CONCLUSION

The hepatic cytoprotective action of Schisandrin B against acetaminophen-induced liver injury is mediated, at least in part, by the induction of HSP27 and HSP70 in mice.

Broad MICA/B expression in the small bowel mucosa: a link between cellular stress and celiac disease

The MICA/B genes (MHC class I chain related genes A and B) encode for non conventional class I HLA molecules which have no role in antigen presentation. MICA/B are up-regulated by different stress conditions such as heat-shock, oxidative stress, neoplasic transformation and viral infection. Particularly, MICA/B are expressed in enterocytes where they can mediate enterocyte apoptosis when recognised by the activating NKG2D receptor present on intraepithelial lymphocytes. This mechanism was suggested to play a major pathogenic role in active celiac disease (CD). Due to the importance of MICA/B in CD pathogenesis we studied their expression in duodenal tissue from CD patients. By immunofluorescence confocal microscopy and flow cytometry we established that MICA/B was mainly intracellularly located in enterocytes. In addition, we identified MICA/B⁺ T cells in both the intraepithelial and lamina propria compartments. We also found MICA/B⁺ B cells, plasma cells and some macrophages in the lamina propria. The pattern of MICA/B staining in mucosal tissue in severe enteropathy was similar to that found in in vitro models of cellular stress. In such models, MICA/B were located in stress granules that are associated to the oxidative and ER stress response observed in active CD enteropathy. Our results suggest that expression of MICA/B in the intestinal mucosa of CD patients is linked to disregulation of mucosa homeostasis in which the stress response plays an active role.

The heat-shock protein-70-induced renoprotective effect is partially mediated by CD4+ CD25+ Foxp3 + regulatory T cells in ischemia/reperfusion-induced acute kidney injury

Recent reports suggest the presence of heat-shock protein (HSP)-reactive T cells with a regulatory phenotype in various inflammatory diseases. To test whether HSP exerts renoprotective effects through regulatory T cells (Tregs), ischemia/reperfusion injury was done with or without heat preconditioning in mice. Splenocytes from heat-preconditioned mice had Treg expansion and a reduced proliferative response upon mitogenic stimulus. T cells from heat-preconditioned mice failed to reconstitute postischemic injury when adoptively transferred to T cell-deficient nu/nu mice in contrast to those from control mice. Tregs were also increased in heat-preconditioned ischemic kidneys. Depleting Tregs before heat preconditioning abolished the renoprotective effect, while adoptive transfer of these cells back into Treg-depleted mice partially restored the beneficial effect of heat preconditioning. Inhibition of HSP70 by quercetin suppressed Treg expansion, as well as renoprotective effects. Transferring Tregs in quercetin-treated heat-preconditioned mice partially restored the beneficial effect of heat preconditioning. The specificity of immune cell HSP70 in renoprotection was confirmed by partial restoration of kidney injury when T cells from HSP70-deficient heat preconditioned mice were adoptively transferred to nu/nu mice. Thus, the renoprotective effect of HSP70 may be partially mediated by a direct immunomodulatory effect through Tregs. Better understanding of immunomodulatory mechanisms of various stress proteins might facilitate discovery of new preventive strategies in acute kidney injury.

Fever, hyperthermia and the heat shock response

The heat shock response is a highly conserved primitive response that is essential for survival against a wide range of stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms raise their core body temperature and temporarily subject themselves to thermal stress in the face of infections. The present review documents studies showing the potential overlap between the febrile response and the heat shock response and how both activate the same common transcriptional programme (although with different magnitudes) including the stress-activated transcription factor, heat shock factor-1, to modify host defences in the context of infection, inflammation and injury. The review focuses primarily on how hyperthermia within the febrile range that often accompanies infections and inflammation acts as a biological response modifier and modifies innate immune responses. The characteristic 2-3 °C increase in core body temperature during fever activates and utilises elements of the heat shock response pathway to modify cytokine and chemokine gene expression, cellular signalling and immune cell mobilisation to sites of inflammation, infection and injury. Interestingly, typical proinflammatory agonists such as Toll-like receptor agonists modify the heat shock-induced transcriptional programme and expression of HSP genes following co-exposure to febrile range hyperthermia or heat shock, suggesting a complex reciprocal regulation between the inflammatory pathway and the heat shock response pathway.

Turning up the heat: immune brinksmanship in the acute-phase response

The acutephase response (APR) is a systemic response to severe trauma, infection, and cancer, although many of the numerous cytokine-mediated components of the APR are incompletely understood. Some of these components, such as fever, reduced availability of iron and zinc, and nutritional restriction due to anorexia, appear to be stressors capable of causing harm to both the pathogen and the host. We review how the host benefits from differences in susceptibility to stress between pathogens and the host. Pathogens, infected host cells, and neoplastic cells are generally more stressed or vulnerable to additional stress than the host because: (a) targeted local inflammation works in synergy with APR stressors; (b) proliferation/growth increases vulnerability to stress; (c) altered pathogen physiology results in pathogen stress or vulnerability; and (d) protective heat shock responses are partially abrogated in pathogens since their responses are utilized by the host to enhance immune responses. Therefore, the host utilizes a coordinated system of endogenous stressors to provide additional levels of defense against pathogens. This model of immune brinksmanship can explain the evolutionary basis for the mutually stressful components of the APR.

Diverse immune mechanisms may contribute to the survival benefit seen in cancer patients receiving hyperthermia

There is increasing documentation of significant survival benefits achieved in cancer patients treated with hyperthermia in combination with radiation and/or chemotherapy. Most evidence collected regarding the mechanisms by which hyperthermia positively influences tumor control has centered on in vitro data showing the ability of heat shock temperatures (usually above 42 degrees C) to result in radio- or chemosensitization. However, these high temperatures are difficult to achieve in vivo, and new thermometry data in patients reveal that much of the tumor and surrounding region is only heated to 40-41 degrees C or less as a result of vascular drainage from the target zone of the heated tumor. Thus, there is now a growing appreciation of a role for mild hyperthermia in the stimulation of various arms of the immune system in contributing to long term protection from tumor growth. Indeed, a review of recent literature suggests the existence of an array of thermally sensitive functions which may exist naturally to help the organism to establish a new "set point" of immune responsiveness during fever. This review summarizes recent literature identifying complex effects of temperature on immune cells and potential cellular mechanisms by which increased temperature may enhance immune surveillance.

Modulating expression of brain heat shock proteins by estrogen in ovariectomized mice model of aging

Heat shock proteins (HSPs) serve as molecular chaperones and endogenous cytoprotective factors. Two of the well-studied HSPs, HSP70, and HSP27 can be significantly induced in many areas of brain by a variety of stressors. A decrease in expression of brain HSPs has been documented in aged brain. Estrogen is well known as a neuroprotective hormone, and it has been reported that estrogen can regulate HSP70 and HSP27 expression in neuronal cells. In this study, the relationship between estrogen and heat stress-induced brain HSPs expression in young and aged ovariectomized (OVX) mice was investigated. Our results show that heat stress-induced levels of HSP70 proteins and mRNA transcripts was significantly lower in brain of aged (12 month) OVX mice, compared with young (2 month) OVX mice group. Estrogen supplementation (17beta-estradiol 0.5mg/kg for 7 days) restored heat stress-induced brain HSP70 expression and attenuated heat stress-induced brain DNA fragmentation, caspase 3 activation and mitochondrial leakage of cytochrome c and AIF in OVX mice. These results suggest that estrogen deficiency during aging down-regulates heat stress-induced brain HSP70 expression, which reveals a previously unknown link between estrogen deficiency and stress response elements.

Hyperthermia in the febrile range induces HSP72 expression proportional to exposure temperature but not to HSF-1 DNA-binding activity in human lung epithelial A549 cells

Expression of heat shock proteins (HSPs) is classically activated at temperatures above the physiologic range (>or=42 degrees C) via activation of the stress-activated transcription factor, heat shock factor-1 (HSF-1). Several studies suggest that less extreme hyperthermia, especially within the febrile range, as occurs during fever and exertional/environmental hyperthemia, can also activate HSF-1 and enhance HSP expression. We compared HSP72 protein and mRNA expression in human A549 lung epithelial cells continuously exposed to 38.5 degrees C, 39.5 degrees C, or 41 degrees C or exposed to a classic heat shock (42 degrees C for 2 h). We found that expression of HSP72 protein and mRNA increased linearly as incubation temperature was increased from 37 degrees C to 41 degrees C, but increased abruptly when the incubation temperature was raised to 42 degrees C. A similar response in luciferase activity was observed using A549 cells stably transfected with an HSF-1-responsive luciferase reporter plasmid. However, activation of intranuclear HSF-1 DNA-binding activity was comparable at 38.5 degrees C, 39.5 degrees C, and 41 degrees C and only modestly greater at 42 degrees C but the mobility of HSF1 protein on a denaturing gel was altered with increasing exposure temperature and was distinctly different at 42 degrees C. These findings indicate that the proportional changes in HSF-1-dependent HSP72 expression at febrile-range temperatures are dependent upon exposure time and temperature but not on the degree of HSF-1 DNA-binding activity. Instead, HSF-1-mediated HSP expression following hyperthermia and heat shock appears to be mediated, in addition to HSF-1 activation, by posttranslational modifications of HSF-1 protein.

Thermotolerance induced at a fever temperature of 40 °C protects cells against hyperthermia-induced apoptosis mediated by death receptor signalling

Mild temperatures such as 40 °C are physiological and occur during fevers. This study determines whether mild thermotolerance induced at 40 °C can protect HeLa cells against activation of the death receptor pathway of apoptosis by lethal hyperthermia (42–45 °C). Protein expression of heat shock proteins (Hsps) 27, 32, 60, 72, 90, and 110 was increased in thermotolerant cells (3 h, 40°C). Lethal hyperthermia (42–43 °C)  caused cell death by apoptosis, but at 45 °C there was a switch to necrosis. Mild thermotolerance protected cells against heat-induced apoptosis (Annexin V labelling). Hyperthermia induced apoptosis through generation of reactive oxygen species (ROS) and death receptor signalling. The antioxidant polyethylene glycol-catalase abrogated increased expression of Fas death ligand and caspase-8 activation in response to lethal hyperthermia (42–43 °C). Mild thermotolerance attenuated the heat induction of ROS and FasL, which were initiating events in death receptor activation and signalling. Mild thermotolerance inhibited early events in hyperthermia-induced death receptor apoptosis such as Fas-associated death domain (FADD) translocation to membranes, caspase-8 activation, and tBid translocation to mitochondria. Downstream events in apoptosis such as caspase-3 activation, cleavage of PARP and ICAD, and chromatin condensation were also diminished in thermotolerant cells. It is important to improve knowledge about adaptive responses induced by exposure to mild stresses, such as fever temperatures, which can protect cells against subsequent exposure to lethal stress.

Fever-range whole body hyperthermia increases the number of perfused tumor blood vessels and therapeutic efficacy of liposomally encapsulated doxorubicin

PURPOSE

Two major questions were addressed: (1) Can fever-range whole body hyperthermia (FR-WBH) affect the number of perfused tumor blood vessels? (2) Can pre-treatment with FR-WBH improve accumulation or anti-tumor efficacy of doxorubicin or DOXIL (liposomal doxorubicin)?

MATERIALS AND METHODS

Perfused blood vessels were visualized by intravenous injection of the fluorescent dye (DiOC7(3)) and the number of labeled vessels in tumors and normal organs of unheated mice and those previously heated to 39.5 degrees C for 6 hours were compared. Using three animal tumor models (one syngeneic murine model and two human tumor xenografts in SCID mice) we also compared tumor growth and amount of intratumoral doxorubicin (given as free drug or as DOXIL) in control mice or those given pre-treatment with FR-WBH.

RESULTS

FR-WBH had no effect on the number of CD-31 labeled blood vessels. However, in tumors, but not in normal organs of the same animals, FR-WBH resulted in a significant increase in those blood vessels which could take up dye over a prolonged period of time after heating. There was also an increase in DOXIL uptake in the tumors of mice given FR-WBH prior to drug injection as well as enhanced therapeutic efficacy in all three tumor models.

CONCLUSIONS

FR-WBH increases the number of perfused blood vessels in tumors over a prolonged period following FR-WBH and thus may be useful for improving tumor targeting of cancer therapeutics. We discuss these data in relation to long-conserved thermoregulatory features in normal vasculature, which may be deficient in tumor vasculature.

Dehydroepiandrosterone: a modulator of cellular immunity and heat shock protein 70 production during polymicrobial sepsis

OBJECTIVE

DHEA is an immunomodulatory steroid hormone that improves survival during systemic inflammation. A DHEA-induced modulation of heat shock protein response may be an alternative mechanism contributing to the beneficial effects of this hormone. We investigated the effect of DHEA administration on survival, cellular immune functions, and HSP-70 production in septic mice.

DESIGN AND SETTING

Randomized animal study, level I trauma center, university research laboratory.

SUBJECTS

Male NMRI mice.

INTERVENTIONS

Mice were subjected to sham operation (laparotomy, LAP) or sepsis (cecal ligation and puncture, CLP) with or without administration of either saline 0.9% (LAP, CLP) or 20 mg/kg DHEA subcutaneously (LAP/DHEA, CLP/DHEA). Survival was monitored over a 48-h period. Splenocyte apoptosis rate (AnnexinV binding), splenocyte proliferation ([3H]thymidine incorporation), TNF-alpha plasma concentration (ELISA), and HSP-70 concentration (ELISA) in tissue extracts from liver, lung, and spleen were monitored 48 h after onset of sepsis.

RESULTS

DHEA administration improved the survival of septic mice (78% vs. 50%). This effect was paralleled by increased splenocyte proliferation, decreased cellular apoptosis rate of splenocytes, and attenuation of TNF-alpha release. Furthermore, an increased HSP-70 concentration was observed in lungs and spleens of DHEA-treated septic animals.

CONCLUSIONS

DHEA-treatment decreased the mortality rate of septic mice. This was accompanied by improved cellular immune functions and an augmented heat shock response (HSP-70) of lungs and spleens. Further studies are required to demonstrate a direct relationship between the improved survival and the observed alterations in the immune system in DHEA-treated animals.

Cell stress induced HSP are targets of regulatory T cells: A role for HSP inducing compounds as anti-inflammatory immuno-modulators?

T cell responses to heat shock proteins (HSP) have disease suppressive activities through production of anti-inflammatory cytokines in patients and in models of inflammatory diseases. There is evidence that the anti-inflammatory activity of HSP-specific T cells depends on their recognition of endogenous HSP epitopes as expressed by stressed cells at sites of inflammation. Previously, we have demonstrated that such T cells can be induced by conserved sequences of microbial HSP. Now we propose that drug induced up-regulation of endogenous HSP can contribute to anti-inflammatory T cell regulation.

CXC chemokines: a new family of heat-shock proteins?

The heat shock (HS) response is a generalized stress response that is characterized by the induced synthesis of a family of proteins referred to as heat shock proteins (HSPs). These proteins protect cells from a myriad of stressful insults in part by functioning as chaperones for denatured proteins. Increasing evidence suggests that the stress response is not limited to the HSP family of genes, but includes numerous other genes that are regulated by HS through the activation of the stress-activated transcription factor, heat shock factor-1 (HSF-1). Based on observations from our own in vivo hyperthermia models, we hypothesized that the CXC chemokine family of neutrophil activators and chemoattractants might be a previously unrecognized class of HS-responsive genes. Analysis of the promoters of the CXC family of chemokines in both human and mouse showed that they share a common promoter organization in which multiple copies of the HSF-1 binding sequence (heat shock response element, HRE) are present in the 5'-upstream flanking region of each of these genes. We have reviewed previous work from our own laboratory and others demonstrating a strong correlation between activation of HSPs and generation of CXC chemokines. Although rigorous experimental evidence is still required to support this hypothesis, this strong and consistent correlation between expression of HSPs and CXC chemokines in vivo and in vitro model systems suggests that the putative HREs present in the CXC chemokine genes are functionally active. We speculate that the activation of the HS response during febrile range hyperthermia, inflammation, infection and injury directly enhances expression of the CXC chemokines, thereby augmenting neutrophil delivery to sites of infection and injury during febrile illnesses.

Comparison of the anti-tumor effects of various whole-body hyperthermia protocols: correlation with HSP 70 expression and composition of splenic lymphocytes

Whole-body hyperthermia (WBH) has been used as an adjunct approach to radio-/ chemotherapy for tumor therapy for many years. However, the molecular mechanism underlying the enhancement of tumor control is not clearly understood. It has been hypothesized that WBH might activate immune system by inducing the expression of heat shock proteins (HSPs), which are thought to facilitate the presentation of tumor-specific antigens. In the present work, we examined the effects of various thermal doses of WBH on tumor growth delay and HSP70 levels in tumors on C57BL/6 mice, as well as on splenic lymphocyte subpopulations. The maximal WBH effect (about 40% decrease in tumor weight) was achieved by a 2-hour WBH treatment everyday at 40.0 degrees C. By using this treatment schedule, the populations of CD3+/CD4+ T cells and CD3+/CD8+ T cells increased by 4 and 3 times, respectively, at the end of WBH treatment period. When the length of day-by-day WBH treatment was longer than 2 hours or the frequency of WBH treatment was lower than once a day, the effect of tumor growth delay and the population of CD3+ T lymphocyte in spleen increase were discounted. On the other hand, the HSP70 levels in tumor nodules rose continuously as the WBH treating time increased, but the populations of NK cells in spleen did not change significantly. The results suggest that an increased CD3+ T lymphocyte population is closely related to the anti-tumor effect of WBH, which might be a useful marker for effectiveness of hyperthermia. However, neither the levels of HSP70 nor the NK cell populations in spleen appear to correlate to tumor control.

Impact of fever-range thermal stress on lymphocyte-endothelial adhesion and lymphocyte trafficking

The evolutionarily conserved febrile response has been associated with improved survival during infection in endothermic and ectothermic species although its protective mechanism of action is not fully understood. Temperatures within the range of physiologic fever influence multiple parameters of the immune response including lymphocyte proliferation and cytotoxic activity, neutrophil and dendritic cell migration, and production or bioactivity of proinflammatory cytokines. This review focuses on the emerging role of fever-range thermal stress in promoting lymphocyte trafficking to secondary lymphoid organs that are major sites for launching effective immune responses during infection or inflammation. Specific emphasis will be on the molecular basis of thermal control of lymphocyte-endothelial adhesion, a critical checkpoint controlling lymphocyte extravasation, as well as the contribution of interleukin-6 (IL-6) trans-signaling to thermal activities. New results are presented indicating that thermal stimulation of lymphocyte homing potential is evident in evolutionarily distant endothermic vertebrate species. These observations support the view that the evolutionarily conserved febrile response contributes to immune protection and host survival by amplifying lymphocyte access to peripheral lymphoid organs.

Cell number-dependent regulation of Hsp70B' expression: evidence of an extracellular regulator

Hsp70B' is a unique member of the human Hsp70 family of chaperones about which information is scarce. Unlike the major inducible Hsp72 protein, Hsp70B' is strictly inducible having little or no basal expression levels in most cells. We observed that Hsp70B' appears transiently in response to heat stress whereas Hsp72 levels persist for many days. Also, Hsp70B' is optimally induced when cell numbers are low, whereas Hsp72 levels are greatest at higher cell number. Hsp70B' promoter activation was measured by flow cytometry using an Hsp70B' promoter-driven GFP construct. In heat stressed cells, promoter activation is cell number independent over a broad range. However, when cell number increases beyond a certain population size, cells are less stress inducible for Hsp70B' and induction becomes highly cell number-dependent. Cell number differences in Hsp70 activation cannot be explained by changes in Hsf-1 DNA-binding activity or hyperphosphorylation. Cells with few or no cell matrix attachments (laminin-coated and low attachment plates, respectively) appear to be more sensitive to cell number-dependent inhibition. Medium conditioned by the low cell number (LCN) populations supports increased Hsp70B' promoter activation in high cell number (HCN) cultures. Likewise, medium conditioned in HCN culture conditions causes decreased activation of Hsp70B' promoter in LCN cultures. As HCN-conditioned medium has all the components necessary for cell growth, two possibilities for the activation of Hsp70B' gene expression exist: an inhibitory component that accumulates in culture medium at HCN, or an activator that accumulates at LCN.

The effect of induced hyperthermia on the immune system

Therapeutical hyperthermia has been considered for cancer therapy since William Coley observed tumour remission after induction of fever by bacterial toxins at the end of the 19th century. Because fever is associated with a variety of immunological reactions, it has been suspected, that therapeutical hyperthermia might also activate the immune system in a reproducible manner and thereby positively influence the course of the disease. During the last decade, new insight has been gained regarding the immunological changes taking place during therapeutic hyperthermia. In this chapter, we review the most relevant data known about the effect of hyperthermia on the immune system with special focus on alterations induced by therapeutical whole-body hyperthermia (WBH) in cancer patients.

Heat shock response and acute lung injury

All cells respond to stress through the activation of primitive, evolutionarily conserved genetic programs that maintain homeostasis and assure cell survival. Stress adaptation, which is known in the literature by a myriad of terms, including tolerance, desensitization, conditioning, and reprogramming, is a common paradigm found throughout nature, in which a primary exposure of a cell or organism to a stressful stimulus (e.g., heat) results in an adaptive response by which a second exposure to the same stimulus produces a minimal response. More interesting is the phenomenon of cross-tolerance, by which a primary exposure to a stressful stimulus results in an adaptive response whereby the cell or organism is resistant to a subsequent stress that is different from the initial stress (i.e., exposure to heat stress leading to resistance to oxidant stress). The heat shock response is one of the more commonly described examples of stress adaptation and is characterized by the rapid expression of a unique group of proteins collectively known as heat shock proteins (also commonly referred to as stress proteins). The expression of heat shock proteins is well described in both whole lungs and in specific lung cells from a variety of species and in response to a variety of stressors. More importantly, in vitro data, as well as data from various animal models of acute lung injury, demonstrate that heat shock proteins, especially Hsp27, Hsp32, Hsp60, and Hsp70 have an important cytoprotective role during lung inflammation and injury.

Heat shock protein expression in brain: a protective role spanning intrinsic thermal resistance and defense against neurotropic viruses

Heat shock proteins (HSPs) play an important role in the maintenance of cellular homeostasis, particularly in response to stressful conditions that adversely affect normal cellular structure and function, such as hyperthermia. A remarkable intrinsic resistance of brain to hyperthermia reflects protection mediated by constitutive and induced expression of HSPs in both neurons and glia. Induced expression underlies the phenomenon of hyperthermic pre-reconditioning, where transient, low-intensity heating induces HSPs that protect brain from subsequent insult, reflecting the prolonged half-life of HSPs. The expression and activity of HSPs that is characteristic of nervous tissue plays a role not just in the maintenance and defense of cellular viability, but also in the preservation of neuron-specific luxury functions, particularly those that support synaptic activity. In response to hyperthermia, HSPs mediate preservation or rapid recovery of synaptic function up to the point where damage in other organ systems becomes evident and life threatening. Given the ability of HSPs to enhance gene expression by neurotropic viruses, the constitutive and inducible HSP expression profiles would seem to place nervous tissues at risk. However, we present evidence that the virus-HSP relationship can promote viral clearance in animals capable of mounting effective virus-specific cell-mediated immune responses, potentially reflecting HSP-dependent increases in viral antigenic burden, immune adjuvant effects and cross-presentation of viral antigen. Thus, the protective functions of HSPs span the well-characterized intracellular roles as chaperones to those that may directly or indirectly promote immune function.

Heat-shock proteins: new keys to the development of cytoprotective therapies

As molecular chaperones, heat-shock proteins (HSPs) function to limit protein aggregation, facilitate protein refolding and chaperone other proteins. Under conditions of cellular stress, intracellular HSP levels increase in order to provide cellular protection and maintain homeostasis. Evidence exists that the HSP family may be secreted into the circulation via lipid raft-mediated, granule-mediated or exosome-mediated exocytosis in haematopoietic and tumour cells. Extracellular HSPs exert immunomodulatory activities and play an important role in innate immune activation against pathogen infection. Membrane-bound Hsp70 in tumour cells or released chaperone-tumour associated antigen complex represent a target structure for the cytolytic attack by natural killer cells or T lymphocytes. Cellular stresses induce stress granule formation to evade detrimental cellular effects, mediating preconditioning phenotype. Therefore, induction of cellular stress tolerance by preconditioning (e.g., heat shock) might be potential therapeutic targets.

Sexual dimorphism of the intracellular heat shock protein 72 response

The majority of previous work examining stress responses has been done in males. Recently, it has become clear that the impact of stressor exposure is modulated by sex. One stress response that may be affected by sex is the induction of intracellular heat shock protein (HSP) 72, which is a stress- responsive molecular chaperone that refolds denatured proteins and promotes cellular survival. The following study compared HSP72 in males and females and also examined whether the estrous cycle altered HSP72 induction in females. We hypothesized that females compared with males would have a constrained HSP72 response after an acute stressor and that the stress-induced HSP72 response in females would fluctuate with the estrous cycle. Male and female F344 rats were either left in their home cage or exposed to acute tail-shock stress (8–10/group). Immediately following stressor, trunk blood was collected and tissues were flash frozen. Vaginal smear and estrogen enzyme immunoassay were used to categorize the phase of estrous. Results show that female rats had a greater corticosterone response than males, that both males and females exhibit a stress-induced release of progesterone, and that males and females had equal levels of stress-induced circulating norepinephrine. Sexual dimorphism of the HSP72 (ELISA) response existed in pituitary gland, mesenteric lymph nodes, and liver such that female rats had an attenuated HSP72 response compared with males after stress. The adrenal glands, spleen, and heart did not exhibit sexual dimorphism of the HSP72 response. The estrous cycle did not have a significant effect on basal or stress-induced HSP72 in females.

STRESS PROTEIN EXPRESSION KINETICS

In all organisms there is an elevated synthesis of a select family of "stress proteins" in response to a broad array of environmentally driven stress vectors including elevated or depressed temperature, changes in pH, treatment with many classes of chemicals, ischemia, desiccation, and UV irradiation. The presence of stress proteins, often termed heat shock proteins (HSPs), has been recognized for more than four decades, and there is an extensive literature that addresses the structure and properties of HSPs, their function in normal and injured cells and tissues, and the molecular mechanisms of HSP expression in response to stress. Owing to this substantial aggregate of research, there is a growing appreciation of the potential for manipulating the magnitude and timing of elevated HSP expression to achieve targeted therapeutic objectives. The successful realization of this potential requires an understanding of the kinetics of the HSP expression process in response to sublethal stress regimens along with the ability to model the governing events in the process to design practical protocols that could be applied in therapeutic settings. Significant progress has been made in recent years in defining and developing capabilities in these two areas.

Emerging evidence indicates that physiologically relevant thermal stress regulates dendritic cell function

Elevations in temperature that are associated with inflammation or fever have been linked to improved survival from infections, enhanced immunological functions, and increased control of tumor growth. Over the past few years, several groups have begun to explore the possible linkage among these observations and have tested the hypothesis that various immune cells are especially sensitive to thermal stimulation. However, relatively little is known regarding the effects of thermal stimulation on antigen presenting cells (APCs), such as dendritic cells (DCs). Very recently, several groups have begun to examine the ability of thermal stimuli to regulate the function of these cells which are known to play a pivotal role in the efficacy of vaccines and other immunotherapies. In this review, we summarize what has been discovered about the role of mild thermal stress in regulating various Dendritic cell (DC) activities. Excitingly, it appears that mild elevations of temperature have the potential to enhance antigen uptake, activation associated migration, maturation, cytokine expression and T cell stimulatory activity of DCs. While these studies reveal that the timing, temperature and duration of heating is important, they also set the stage for essential questions that now need to be investigated regarding the molecular mechanisms by which elevated temperatures regulate DC function. With this information, we may soon be able to maximize the strategic use of thermal therapy as an adjuvant, i.e., combining its use with cancer immunotherapies such as vaccines, which depend upon the function of DCs. Several possible strategies and timepoints involving the clinical application of hyperthermia in combination with immunotherapy are presented.

Nitric oxide production is regulated by fever-range thermal stimulation of murine macrophages

As macrophages are often called to function at times of elevated ambient temperature (e.g., during local inflammation or systemic fever), it is possible that their production of critical effector molecules, such as nitric oxide (NO) or inducible NO synthase (iNOS), is sensitive to physiological changes in temperature. To test this possibility, the threshold requirements for production of NO and iNOS in murine peritoneal macrophages maintained under normothermic conditions (37 degrees C) or following mild (fever-range) hyperthermia (39.5 degrees C) were compared. We found that hyperthermia alone had no observable effect on basal NO production or iNOS protein or message. However, although interferon (IFN)-gamma and lipopolysaccharide (LPS) were needed to induce NO at 37 degrees C, we observed that addition of only LPS was sufficient for production of NO if there were a pretreatment at 39.5 degrees C. Further, if IFN-gamma and LPS were given after thermal exposure, a substantial increase in NO and iNOS was observed over that seen using cells kept at normothermic conditions. Macrophages isolated from mice lacking heat shock factor-1 did not attenuate the ability of mild thermal stress to modulate NO production. Reverse transcriptase-polymerase chain reaction data revealed that thermal regulation of iNOS expression is not entirely at the transcriptional level, suggesting possible points of post-transcriptional thermal sensitivity. These data support the concept that altering the thermal microenvironment is an important means by which the host can manipulate macrophage responses. Increases in temperature (e.g., during fever) may function to lower the activation threshold needed for production of effector molecules in times of infection.

Febrile-range hyperthermia augments neutrophil accumulation and enhances lung injury in experimental gram-negative bacterial pneumonia

We previously demonstrated that exposure to febrile-range hyperthermia (FRH) accelerates pathogen clearance and increases survival in murine experimental Klebsiella pneumoniae peritonitis. However, FRH accelerates lethal lung injury in a mouse model of pulmonary oxygen toxicity, suggesting that the lung may be particularly susceptible to injurious effects of FRH. In the present study, we tested the hypothesis that, in contrast with the salutary effect of FRH in Gram-negative peritonitis, FRH would be detrimental in multilobar Gram-negative pneumonia. Using a conscious, temperature-clamped mouse model and intratracheal inoculation with K. pneumoniae Caroli strain, we showed that FRH tended to reduce survival despite reducing the 3 day-postinoculation pulmonary pathogen burden by 400-fold. We showed that antibiotic treatment rescued the euthermic mice, but did not reduce lethality in the FRH mice. Using an intratracheal bacterial endotoxin LPS challenge model, we found that the reduced survival in FRH-treated mice was accompanied by increased pulmonary vascular endothelial injury, enhanced pulmonary accumulation of neutrophils, increased levels of IL-1beta, MIP-2/CXCL213, GM-CSF, and KC/CXCL1 in the bronchoalveolar lavage fluid, and bronchiolar epithelial necrosis. These results suggest that FRH enhances innate host defense against infection, in part, by augmenting polymorphonuclear cell delivery to the site of infection. The ultimate effect of FRH is determined by the balance between accelerated pathogen clearance and collateral tissue injury, which is determined, in part, by the site of infection.

Febrile-range hyperthermia augments pulmonary neutrophil recruitment and amplifies pulmonary oxygen toxicity

Febrile-range hyperthermia (FRH) improves survival in experimental infections by accelerating pathogen clearance, but may also increase collateral tissue injury. We hypothesized that FRH would worsen the outcome of inflammation stimulated by a non-replicating agonist and tested this hypothesis in a murine model of pulmonary oxygen toxicity. Using a conscious, temperature-controlled mouse model, we showed that maintaining a core temperature at FRH (39 degrees C to 40 degrees C) rather than at euthermic levels (36.5 degrees C to 37 degrees C) during hyperoxia exposure accelerated lethal pulmonary vascular endothelial injury, reduced the inspired oxygen threshold for lethality, induced expression of granulocyte-colony stimulating factor, and expanded the circulating neutrophil pool. In these same mice, FRH augmented pulmonary expression of the ELR(+) CXC chemokines, KC and LPS-induced CXC chemokine, enhanced recruitment of neutrophils, and changed the histological pattern of lung injury to a neutrophilic interstitial pneumonitis. Immunoblockade of CXC receptor-2 abrogated neutrophil recruitment, reduced pulmonary vascular injury, and delayed death. These combined data demonstrate that FRH may enlist distinct mediators and effector cells to profoundly shift the host response to a defined injurious stimulus, in part by augmenting delivery of neutrophils to sites of inflammation, such as may occur in infections. In certain conditions, such as in the hyperoxic lung, this process may be deleterious.