Activation of NK cells in subjects exposed to mild hyper- or hypothermic load

Links between thermoregulation and aging in endotherms and ectotherms

While the link between thermoregulation and aging is generally accepted, much further research, reflection, and debate is required to elucidate the physiological and molecular pathways that generate the observed thermal-induced changes in lifespan. Our aim in this review is to present, discuss, and scrutinize the thermoregulatory mechanisms that are implicated in the aging process in endotherms and ectotherms. Our analysis demonstrates that low body temperature benefits lifespan in both endothermic and ectothermic organisms. Research in endotherms has delved deeper into the physiological and molecular mechanisms linking body temperature and longevity. While research in ectotherms has been steadily increasing during the past decades, further mechanistic work is required in order to fully elucidate the underlying phenomena. What is abundantly clear is that both endotherms and ectotherms have a specific temperature zone at which they function optimally. This zone is defended through both physiological and behavioral means and plays a major role on organismal senescence. That low body temperature may be beneficial for lifespan is contrary to conventional medical theory where reduced body temperature is usually considered as a sign of underlying pathology. Regardless, this phenomenon has been targeted by scientists with the expectation that advancements may compress morbidity, as well as lower disease and mortality risk. The available evidence suggests that lowered body temperature may prolong life span, yet finding the key to temperature regulation remains the problem. While we are still far from a complete understanding of the mechanisms linking body temperature and longevity, we are getting closer.

Coping in an intermittent swim stress paradigm compromises natural killer cell activity in rats

The effects of intermittent swim stress and stressor controllability on natural killer cell activity (NKCA) was examined. Significant decreases in splenic NKCA were observed immediately post-stress, but only when the stress was controllable. Although decreased NKCA was also observed in yoked rats subjected to the same stressor, it failed to attain statistical significance. Previous results suggest these effects are not due to corticosterone. The results suggest a cost of coping on the acute, in vitro immune measure of NKCA.

Caloric restriction and longevity: effects of reduced body temperature

Caloric restriction (CR) causes a reduction in body temperature (T(b)) which is suggested to contribute to changes that increase lifespan. Moreover, low T(b) has been shown to improve health and longevity independent of CR. In this review we examine the connections between CR, T(b) and mechanisms that influence longevity and ageing. Recent findings regarding the overlapping mechanisms of CR and T(b) that benefit longevity are discussed, including changes in body composition, hormone regulation, and gene expression, as well as reductions in low-level inflammation and reactive oxygen species-induced molecular damage. This information is summarized in a model describing how CR and low T(b), both synergistically and independently, increase lifespan. Moreover, the nascent notion that the rate of ageing may be pre-programmed in response to environmental influences at critical periods of early development is also considered. Based on current evidence, it is concluded that low T(b) plays an integral role in mediating the effects of CR on health and longevity, and that low T(b) may exert independent biological changes that increase lifespan. Our understanding of the overlap between CR- and T(b)-mediated longevity remains incomplete and should be explored in future research.

Hypothermia-enhanced splenic cytokine gene expression is independent of the sympathetic nervous system

Splenic nerve denervation abrogates enhanced splenic cytokine gene expression responses to acute heating, demonstrating that hyperthermia-induced activation of splenic sympathetic nerve discharge (SND) increases splenic cytokine gene expression. Hypothermia alters SND responses; however, the role of the sympathetic nervous system in mediating splenic cytokine gene expression responses to hypothermia is not known. The purpose of the present study was to determine the effect of hypothermia on the relationship between the sympathetic nervous system and splenic cytokine gene expression in anesthetized F344 rats. Gene expression analysis was performed using a microarray containing 112 genes, representing inflammatory cytokines, chemokines, cytokine/chemokine receptors and housekeeping genes. A subset of differentially expressed genes was verified by real-time RT-PCR analysis. Splenic SND was decreased significantly during cooling (core temperature decreased from 38 to 30 degrees C) in splenic-intact rats but remained unchanged in sham-cooled splenic-intact rats (core temperature maintained at 38 degrees C). Hypothermia upregulated the transcripts of several genes, including, chemokine ligands CCL2, CXCL2, CXCL10, and CCL20, and interleukins IL-1alpha, IL-1beta, and IL-6. Gene expression responses to hypothermia were similar for the majority of cytokine genes in splenic-intact and splenic-denervated rats. These results suggest that hypothermia-enhanced splenic cytokine gene expression is independent of splenic SND.

Exercising in Environmental Extremes

Athletes, military personnel, fire fighters, mountaineers and astronauts may be required to perform in environmental extremes (e.g. heat, cold, high altitude and microgravity). Exercising in hot versus thermoneutral conditions (where core temperature is > or = 1 degrees C higher in hot conditions) augments circulating stress hormones, catecholamines and cytokines with associated increases in circulating leukocytes. Studies that have clamped the rise in core temperature during exercise (by exercising in cool water) demonstrate a large contribution of the rise in core temperature in the leukocytosis and cytokinaemia of exercise. However, with the exception of lowered stimulated lymphocyte responses after exercise in the heat, and in exertional heat illness patients (core temperature > 40 degrees C), recent laboratory studies show a limited effect of exercise in the heat on neutrophil function, monocyte function, natural killer cell activity and mucosal immunity. Therefore, most of the available evidence does not support the contention that exercising in the heat poses a greater threat to immune function (vs thermoneutral conditions). From a critical standpoint, due to ethical committee restrictions, most laboratory studies have evoked modest core temperature responses (< 39 degrees C). Given that core temperature during exercise in the field often exceeds levels associated with fever and hyperthermia (approximately 39.5 degrees C) field studies may provide an opportunity to determine the effects of severe heat stress on immunity. Field studies may also provide insight into the possible involvement of immune modulation in the aetiology of exertional heat stroke (core temperature > 40.6 degrees C) and identify the effects of acclimatisation on neuroendocrine and immune responses to exercise-heat stress. Laboratory studies can provide useful information by, for example, applying the thermal clamp model to examine the involvement of the rise in core temperature in the functional immune modifications associated with prolonged exercise. Studies investigating the effects of cold, high altitude and microgravity on immunity and infection incidence are often hindered by extraneous stressors (e.g. isolation). Nevertheless, the available evidence does not support the popular belief that short- or long-term cold exposure, with or without exercise, suppresses immunity and increases infection incidence. In fact, controlled laboratory studies indicate immuno-stimulatory effects of cold exposure. Although some evidence shows that ascent to high altitude increases infection incidence, clear conclusions are difficult to make because of some overlap with the symptoms of acute mountain sickness. Studies have reported suppressed cell-mediated immunity in mountaineers at high altitude and in astronauts after re-entering the normal gravity environment; however, the impact of this finding on resistance to infection remains unclear.

The effects of restraint stress on the neuropathogenesis of Theiler's virus infection II: NK cell function and cytokine levels in acute disease

Psychological stress is thought to play an important role in multiple sclerosis. We have been investigating the role of restraint stress in Theiler's virus infection in mice as a model for multiple sclerosis. We have previously determined that restraint stressed CBA mice had higher levels of mortality following infection with Theiler's virus. We proposed that this was due to high levels of stress-induced corticosterone, which resulted in decreased numbers of circulating lymphocytes, decreased inflammatory cell infiltrates into the brain and consequently decreased viral clearance from the central nervous system (CNS). The effect of restraint stress on the innate immune response to Theiler's virus is further investigated in the current study. Restraint stressed mice developed clinical signs of encephalitis, thymic atrophy, and adrenal hypertrophy. Decreased numbers of circulating lymphocytes and increased numbers of neutrophils were observed in the stressed mice. Stressed mice also had lower numbers of spleen cells which correlated with the decreased numbers of lymphocytes in circulation. Restraint stress caused elevations in serum tumor necrosis alpha (TNF-alpha). Virus-induced natural killer cell (NK) cytotoxic activity was significantly reduced in restrained mice at one day post infection which may account for the reduced viral clearance from the CNS. These data suggest that stress-induced immunosuppression of cytolytic NK cell activity may account in part for the reduced ability to clear virus from the CNS and increased mortality observed in this model.

TH1-biased immunity induced by exposure to Antarctic winter

BACKGROUND

Certain immune functions are known to be impaired in human beings exposed to Antarctic winter; in particular, decreased amounts of serum proinflammatory cytokines, such as TNF-alpha and IL-1, were noted. It is not known, however, whether this exposure has any effect on T-cell-mediated acquired immune functions.

OBJECTIVES

This study aims to investigate whether exposure to Antarctic winter has any effect on T cell-dependent immune functions.

METHODS

We assessed changes in various immunologic indicators, including serum levels of various cytokines, peripheral blood Valpha24Vbeta11 natural killer T cell numbers, and T(H)1/T(H)2 ratios of 40 Japanese personnel exposed to an Antarctic winter. Also, a 2-month inland traverse was executed during the isolation, and the effect on the above indicators was assessed.

RESULTS

All subjects were healthy during the Antarctic isolation. The levels of serum TNF-alpha, IL-1Ra, IL-6, and IL-1beta were dramatically reduced and remained at low levels throughout the isolation. The decrease in the levels of TNF-alpha and IL-1Ra was more pronounced during the inland traverse than during the rest of the isolation. The percentage of Valpha24Vbeta11 natural killer T cells was significantly increased at the midpoint of the isolation. Most interestingly, T(H)1/T(H)2 ratio was increased significantly, and this T(H)1 bias was most prominent at the late point of the isolation.

CONCLUSIONS

Exposure to an Antarctic winter appeared to induce T(H)1-skewed immunity in human beings.

Cytokine and hormone profiles in mice subjected to handling combined with rectal temperature measurement stress and handling only stress

Stress is known to either up or down regulate immunity. In this study, mice were subjected to handling combined with rectal temperature measurement (RTM) stress or handling only stress. We investigated whether there were any significant differences in the effect of handling combined with RTM and handling only on NK cell activity, serum cytokine (IL-1beta, IL-6, and TNF-alpha) and ACTH and beta-endorphin levels, and splenic cytokine (IL-1beta, IL-6, TNF-alpha, IFN-alpha, and IFN-beta) levels. Circulating cytokines and hormones and splenic cytokine mRNA levels were measured in individual mice. NK cell activity was significantly increased in both stress groups when compared to the control group. Handling combined with RTM produced significantly increased serum levels of IL-1beta, IL-6, and beta-endorphin. Serum IL-1beta, ACTH, and beta-endorphin were elevated significantly in the handling only group. Splenic TNFalpha mRNA in both of the stress groups and IL-6 mRNA in handling only group decreased significantly. Our observations are supported by existing literature demonstrating that various stressors have differential effects on immune functions and the neuroendocrine hormones and cytokines, which regulate them.

Cold exposure: human immune responses and intracellular cytokine expression

It is commonly believed that exposure to cold environmental temperatures depresses immune function and increases the risk for infection. This review paper will 1) present an overview of human physiological responses to cold exposure, 2) present the human studies examining the effects of cold exposure on immune responses, and 3) summarize recent experiments from our laboratories examining the effects of exercise and fatigue on immune responses during subsequent cold exposure. Based on the review of the literature, there is no support for the concept that cold exposure depresses immune function.

Immune changes in humans during cold exposure: effects of prior heating and exercise

This study examined the immunological responses to cold exposure together with the effects of pretreatment with either passive heating or exercise (with and without a thermal clamp). On four separate occasions, seven healthy men [mean age 24.0 +/- 1.9 (SE) yr, peak oxygen consumption = 45.7 +/- 2.0 ml. kg(-1). min(-1)] sat for 2 h in a climatic chamber maintained at 5 degrees C. Before exposure, subjects participated in one of four pretreatment conditions. For the thermoneutral control condition, subjects remained seated for 1 h in a water bath at 35 degrees C. In another pretreatment, subjects were passively heated in a warm (38 degrees C) water bath for 1 h. In two other pretreatments, subjects exercised for 1 h at 55% peak oxygen consumption (once immersed in 18 degrees C water and once in 35 degrees C water). Core temperature rose by 1 degrees C during passive heating and during exercise in 35 degrees C water and remained stable during exercise in 18 degrees C water (thermal clamping). Subsequent cold exposure induced a leukocytosis and granulocytosis, an increase in natural killer cell count and activity, and a rise in circulating levels of interleukin-6. Pretreatment with exercise in 18 degrees C water augmented the leukocyte, granulocyte, and monocyte response. These results indicate that acute cold exposure has immunostimulating effects and that, with thermal clamping, pretreatment with physical exercise can enhance this response. Increases in levels of circulating norepinephrine may account for the changes observed during cold exposure and their modification by changes in initial status.

Tumor cell apoptosis, lymphocyte recruitment and tumor vascular changes are induced by low temperature, long duration (fever-like) whole body hyperthermia

A single treatment of low-temperature, long-duration, whole-body hyperthermia of either severe combined immunodeficient (SCID) mice bearing human breast tumor xenografts or Balb/c mice bearing syngeneic tumors for 6-8 hr can cause a temporary reduction of tumor volume and/or a growth delay. In both animal model systems, this inhibition is correlated with the appearance of large numbers of apoptotic tumor cells. Because this type of mild heat exposure, comparable to a common fever, is not itself directly cytotoxic, other explanations for the observed tumor cell death were considered. Our data support the hypothesis that this hyperthermia protocol stimulates some component(s) of the immune response, which results in increased antitumor activity. In support of this hypothesis, increased numbers of lymphocyte-like cells, macrophages, and granulocytes are observed in the tumor vasculature and in the tumor stroma immediately following this mild hyperthermia exposure. In Balb/c mice, an infiltrate persists in the tumor for at least 2 weeks. Using the SCID mouse/human tumor system, we found that both host natural killer (NK) cells and injected human NK cells were increased at the site of tumor following hyperthermia treatment. Experiments using anti-asialo-GM1 antibodies indicate that the tumor cell apoptosis seen in the SCID mouse appears to be due largely to the activity of NK cells, although additional roles for other immunoeffector cells and cytokines appear likely in the immunologically complete Balb/c model. Another interrelated hypothesis is that immunoeffector cells may have greater access to the interior of the tumor because we have observed that this treatment causes an obvious expansion in the diameter of blood vessels within the tumor and an increase in nucleated blood cells within the vessels, which persists as long as 2 weeks after treatment. Further study of the mechanisms by which mild hyperthermia exerts antitumor activity could result in this treatment protocol being used as an effective, nontoxic adjuvant to immunotherapy and/or other cancer therapies.

Impact of heat exposure and moderate, intermittent exercise on cytolytic cells

This study examined the impact of heat exposure and moderate, intermittent exercise on the CD16+ and CD56+ cell counts and cytolytic activity. Eleven healthy male subjects [mean (SD): age = 27.1 (3.0) years, peak oxygen intake, VO2peak = 47.6 (6.2) ml. kg-1. min-1] were assigned to each of four different experimental conditions according to a randomized-block design. While in a climatic chamber maintained at a comfortable temperature (23 degrees C) or heated (40 degrees C, 30% relative humidity, r.h.), subjects performed either two 30-min bouts of cycle-ergometer exercise at approximately 50% VO2peak (separated by a 45-min recovery interval), or remained seated for 3 h. Blood samples were analyzed for CD16+ and CD56+ cell counts, cytolytic activity and the concentrations of various exercise stress hormones (norepinephrine, epinephrine and cortisol). Heat exposure alone had no significant effect on cytolytic cells. The (CD16+ and CD56+) cell count increased significantly (P < 0.0001) during each exercise bout under both environmental conditions, but returned to baseline levels 15-45 min following each exercise bout. Total cytolytic activity (determined by a standard 51Cr release assay using K562 cells) followed a similar pattern, but cytolytic activity per CD16+ or CD56+ cell was not significantly modified by exercise. Our findings show a strong association between hemodynamic factors and recruitment of cytolytic cells into the peripheral circulation. Alterations in cytolytic activity of the whole blood during and following moderate exercise seem to be the result of changes in CD16+ and CD56+ cell counts.

Central stimulation of hormone release and the proliferative response of lymphocytes in humans

The central nervous system (CNS) may communicate with the immune system by direct innervation of lymphoid organs and/or by neurotransmitters and changes in neuroendocrine functioning and hormone release. The consequences of selective transient changes in circulating hormones on immune functioning in humans have not yet been studied. To address this problem, the authors evaluated the lymphoproliferative responses to optimal and suboptimal concentrations of phytohemagglutinin (PHA) and pokeweek mitogen (PWM) under selective enhancement of circulating growth hormone, prolactin, or norepinephrine. The authors failed to demonstrate any effect of elevated growth hormone levels after clonidine challenge on the lymphoproliferative response to mitogens. Similarly, the results did not show any effect of elevated prolactin concentrations induced by domperidone administration on the immune test. Exposure of volunteers to cold resulted in elevation of plasma norepinephrine levels without changes in growth hormone, epinephrine, or cortisol secretion. Cold exposure induced elevation of plasma norepinephrine and reduction of the lymphoproliferative response to the suboptimal dosage of PHA. The reduction was significant 180 and 240 min after exposure. These results are indicative of a relationship between norepinephrine and immunity.

Suppression of murine melanoma growth with a combination of microwave hyperthermia and local injection of interleukin 2

Local microwave hyperthermia in combination with local injections of interleukin 2 (IL-2) was found to exert a remarkable suppressive effect on murine melanoma growth. Both of these therapeutic modalities caused marked tumour infiltration with natural killer cells. After microwave hyperthermia or IL-2 injection alone there was minimal T-cell infiltration, but T cells were more in evidence following combination therapy.

A combined therapeutic modality with hyperthermia and locally administered rIFN-beta inhibited the growth of B16 melanoma in association with the modulation of cellular infiltrates

Murine B16-F10 melanoma was treated with local microwave hyperthermia, local injection of murine recombinant interferon-beta (rIFN-beta) or a combination of both in order to investigate the augmentation of anti-proliferative effects with this combination treatment. Concerning the local modulation of immunological reactions of the host, local hyperthermia at 43 degrees C for 15 min on murine melanoma caused remarkable infiltration of natural killer cells and local injection of rIFN-beta led to considerable infiltration of T cells. When these two modalities were combined, the infiltration of NK cells completely disappeared and, instead, remarkable augmentation of T cell infiltration occurred. Synergistic suppressive effects on melanoma growth with occasional scar formation were seen with this combined modality. These results indicate that local hyperthermia with a combination of rIFN-beta modulates local immune reactions of the host, and probably this immune reaction is partly involved in the course of the suppression of tumor growth.

Influence of whole-body hyperthermia on natural cytotoxicity of liver blood-borne sinusoidal cells

Rat liver sinusoidal cytotoxic cells were examined after exposure to in vivo and in vitro hyperthermia at 40-41 degrees C. Whole-body hyperthermia lasting for 4 h caused a decrease in the cytotoxic activity of liver sinusoidal washout cells against YAC-1 and K562 cells. Surprisingly, the percentage of washout cells with morphology of LGL (large granular lymphocyte) increased both in the liver washout and in portal blood compared to control normothermic animals. The proportions of phenotypically characterized cell subpopulations isolated from liver sinusoids did not change. Elimination of i.v. injected 125I-labelled K562 cells was decreased during hyperthermia. In vitro incubation of liver sinusoidal cytotoxic cells for 3 h at 41 degrees C decreased their cytotoxic activity by affecting the process of effector-target cell binding. However, once the effector-target cell conjugates were formed, the cytotoxic process proceeded as in normothermic conditions. These data suggest that inhibition of liver sinusoidal cytotoxic cell activity after hyperthermia may be a result of deficient target cell recognition by the effector cell.

Effects of local prostatic hyperthermia on human NK and T cell function

Studies on lymphocyte subsets, mitogen transformation and NK cytotoxicity of blood mononuclear cells (BMNC) were performed in 30 patients who received transrectal microwave hyperthermia (TRHT) of the prostate. Of the 30 patients, 15 had advanced adenocarcinoma of the prostate (CAP) and 15 had severely symptomatic benign prostatic hyperplasia (BPH). Local TRHT was given twice a week for a total of six sessions. The treatments were administered at 2450 MHz or 434 MHz using a water-cooled rectal applicator. Each TRHT session lasted for 30 min at steady-state temperature controlled on the rectal mucosa at 45 degrees C. Studies of immune reactions were performed before TRHT, at the completion of six TRHT sessions, and at 1, 2, 4, and 6 months from therapy. Identical studies at the same time-interval were performed in 30 healthy male volunteers. In the 15 CAP patients the results of the immune studies obtained before TRHT, including CD4+/CD8+ ratio, PHA and Con-A transformation indices were significantly lower (p less than 0.01) than in the 15 BPH patients and in the 30 normal volunteers. The 15 BPH patients and the 30 normal volunteers all had immune parameters within the normal limits. Following the administration of TRHT in the 15 CAP patients, a transient significant (p less than 0.01) stimulation of the tested cell-mediated immune parameters was observed when compared with the pretreatment values. The peak effect of this stimulation was noted at 2 months with a subsequent decrease. In the 15 BPH patients a lesser degree of immune stimulation was noted. As expected there was no substantial change in the measured cell-mediated immune parameters in the 30 normal volunteers. A significant increase of NK cytotoxic activity was noted following TRHT in CAP patients when compared with the pretreatment results. This activity reached 120-130% of the individual initial values, being significant at p less than 0.01. The finding of transient stimulation of cell-mediated immune reaction, following local hyperthermia in patients with CAP, may be of some clinical relevance and of clinical importance. Additional studies are being formulated to confirm these interesting findings.

Effects of local hyperthermia on natural killer activity in mice

The effect of local hyperthermia on natural killer (NK) activity in C3H mice was investigated, because there have been reports on both the enhancing and suppressing effects of hyperthermia on NK activity. When right hind legs of mice were treated at 43 degrees C for 45 min, NK activity was first suppressed. It reached its lowest level 2 days after the treatment, then recovered, and was significantly enhanced on the 7th day. When mice were treated at a lower temperature (41 degrees C), NK activity was enhanced even 2 days after the treatment. In addition, the suppression of NK activity, which was observed 2 days after the treatment at 43 degrees C, was diminished to some extent by i.p. injection of liposomal recombinant human superoxide dismutase (L-r-hSOD). From these results it is suggested that local hyperthermia had an enhancing effect on NK activity, which plays an important role in the anti-tumour mechanism of hyperthermia, and that transient suppression of NK activity after hyperthermia at 43 degrees C was partially cancelled by the administration of L-r-hSOD.