Regulation of scatter factor production via a soluble inducing factor.

Scatter factor (SF) (also known as hepatocyte growth factor [HGF]) is a fibroblast-derived cytokine that stimulates motility, proliferation, and morphogenesis of epithelia. SF may play major roles in development, repair, and carcinogenesis. However, the physiologic signals that regulate its production are not well delineated. We found that various human tumor cell lines that do not produce SF secrete factors that stimulate SF production by fibroblasts, suggesting a paracrine mechanism for regulation of SF production. Conditioned medium from these cell lines contained two distinct scatter factor-inducing factor SF-IF activities: a high molecular weight (> 30 kD), heat sensitive activity and a low molecular weight (< 30 kD) heat stable activity. Further studies revealed that SF-producing fibroblasts also secrete factors that stimulate their own SF production. We characterized the < 30-kD SF-IF activity from ras-3T3 (clone D4), a mouse cell line that overproduces both SF and SF-IF. The < 30-kD filtrate from ras-3T3 conditioned medium induced four- to sixfold increases in expression of SF biologic activity, immunoreactive protein, and mRNA by multiple SF-producing fibroblast lines. Ras-3T3 SF-IF activity was stable to boiling, extremes of pH, and reductive alkylation, but was destroyed by proteases. We purified ras-3T3 SF-IF about 10,000-fold from serum-free conditioned medium by a combination of ultrafiltration, cation exchange chromatography, and reverse phase chromatography. The purified protein exhibited electrophoretic mobility of about 12 kD (reduced) and 14 kD (nonreduced) by SDS-PAGE. The identity of the protein was verified by elution of biologic activity from gel slices. Purified SF-IF stimulated SF production in a physiologic concentration range (about 20-400 pM). Its properties and activities were distinct from those of IL-1 and TNF, two known inducers of SF production. We suggest that SF-IF is a physiologic regulator of SF production.

Fever: effect of drug-induced antipyresis on survival.

To determine whether the prevention of fever affects the survival of an animal infected with pathogenic bacteria, lizards (Dipsosaurus dorsalis) were infected with live Aeromonas hydrophila and received varying doses of sodium salicylate, an antipyretic drug. Twelve lizards received identical injections of bacteria along with a nontoxic dose of sodium salicylate; five animals increased their mean body temperature at least 0.6 degrees C and survived the week, whereas seven did not develop a fever and died within 3 days. These data indicate that in these lizards the prevention of fever by use of an antipyretic drug such as sodium salicylate increases the mortality rate from bacterial infection.

Endogenous pyrogen activity in human plasma after exercise.

Plasma obtained from human subjects after exercise and injected intraperitoneally into rats elevated rat rectal temperature and depressed plasma iron and zinc concentrations. The pyrogenic component was heat-denaturable and had an apparent molecular weight of 14,000 daltons. Human mononuclear leukocytes obtained after exercise and incubated in vitro released a factor into the medium that also elevated body temperature in rats and reduced trace metal concentrations. These results suggest that endogenous pyrogen, a protein mediator of fever and trace metal metabolism during infection, is released during exercise.

Fever and reduced iron: their interaction as a host defense response to bacterial infection.

When rabbits are infected with Pasteurella multocida, the concentration of iron in their plasma decreases and their rectal temperature rises. To determine whether the rise in body temperature (fever) and the fall in plasma iron may be a coordinated host defense response, Pasteurella multocida were grown in vitro at various temperatures and iron concentrations. At afebrile temperatures the bacteria grew equally well at low or high concentrations of iron. However, when the temperature of the bath was raised to a febrile temperature the growth of the bacteria was inhibited by the low, but not the high, iron concentrations. These data support the hypothesis that one of the mechanisms behind the adaptive (or beneficial) role of fever is the reduced ability of pathogenic bacteria to grow well at elevated temperatures in an iron-poor medium.

Fever and survival.

The significance of fever in response to a bacterial infection has been investigated using the lizard Dipsosaurus dorsalis as an animal model. These lizards develop a fever of about 2 degrees C after injection with the bacterium Aeromonas hydrophila. To determine whether this elevation in body temperature increases the resistance of the host to this infection, as measured by survival, lizards were infected with the live bacteria and placed in a neutral (38 degrees C), low (34 degrees or 36 degrees C), or high (40 degrees or 42 degrees C) ambient temperature. An elevation in temperature following experimental bacterial infection results in a significant increase in host survival.

Protein deficiency: its effects on body temperature in health and disease states.

Little is known about the effects of protein malnutrition on the ability to regulate body temperature during health and disease. To investigate this area, we placed young rabbits on a low-protein diet and recorded their body temperatures. There were no differences between the protein-deprived and control animals concerning their abilities to maintain constant body temperatures during exposure to low (5 C, 10 C) and thermoneutral ambient temperature (20 C). In a warm ambient temperature (30 C) the protein-deprived animals were actually better able to maintain a lower body temperature. Injections with heat killed bacteria led to little or no fever in the protein-deprived group. However, intravenous injections of endogenous pyrogen, a protein mediator of fever, resulted in fevers virtually identical to that attained in control animals. These data indicate that the attenuated febrile response to bacterial injection during protein deprivation may be due to a diminished production of endogenous pyrogen, and not to some alteration in the central nervous system sensitivity to pyrogens.

The role of fever in appetite suppression after endotoxin administration.

In order to test the hypothesis that fever, and not some other aspect of the acute phase response, decreases food intake after administration of endotoxin, food intake of rats was studied under conditions of 1) fever, 2) antipyresis, and 3) endotoxin tolerance. Injection of endotoxin resulted in a significant elevation in rectal temperature and a significant reduction in food intake. Administration of the antipyretic drug sodium salicylate to endotoxin-injected animals lowered rectal temperatures to control levels, but food intake was still suppressed. When rats were made tolerant to endotoxin by repeated injections, an attenuated fever was observed, and food intake was not significantly different from that of control animals. We conclude that the effects of endotoxin on body temperature can be dissociated from its effects on food intake. We speculate that the failure of endotoxin to suppress food intake in endotoxin-tolerant rats may be due to a decreased production of endogenous pyrogen.

Suppression of food intake during infection: is interleukin-1 involved?

Loss of food appetite is a common manifestation of acute infectious illness and is believed to contribute to the negative nitrogen balance and loss of body weight that is seen during infection. The frequency with which anorexia occurs with infection suggests that it may be part of the acute phase response. In the present experiments, food intake of fasted rats was suppressed following injection of interleukin-1, a polypeptide that mediates many host responses to infection. We conclude that infection-induced anorexia is, in part, due to the release of interleukin-1.

Fever and malnutrition: endogenous pyrogen/interleukin-1 in malnourished patients.

The effect of protein-calorie malnutrition on the release of endogenous pyrogen/interleukin-1 (EP/IL-1), the protein responsible for the induction of fever, was investigated in 18 hospitalized patients with chronic malnutrition. Monocytes from the 18 patients and from 19 healthy controls were cultured overnight after stimulation with Staphylococcus epidermidis. The presence of EP/IL-1 was tested by injecting culture supernatants into rabbits and measuring the maximum febrile response (delta Tmax). Malnourished patients produced significantly less EP/IL-1 than controls (delta Tmax = 0.27 +/- 0.04 degrees C for patients vs 0.49 +/- 0.03 degrees C for controls, p less than 0.001). The poor febrile response in the malnourished patients was related to low serum albumin and retinol-binding protein, but not to thyroxine-binding albumin or lymphocyte number. This abnormality may help explain the poor febrile response often noted in hospitalized debilitated patients.

Polymyxin B use does not ensure endotoxin-free solution.

Polymyxin B is often added to in vitro samples to 'ensure' that endotoxin activity is removed. We present data, from the standard rabbit pyrogen test and the Limulus amebocyte lysate assay, that polymyxin B bound to a gel support will bind some, but not all, endotoxin. These data, in conjunction with previously published data by Morrison and Curry (1979), indicate that those studies that have relied on polymyxin B to inactivate endotoxin must be re-evaluated.

Fever.

Fever, the regulation of body temperature at an elevated level, is a common response to infection throughout the vertebrates. Mammals and birds rely on both physiologic and behavioral mechanisms to raise their body temperatures to this elevated thermoregulatory "set-point" during infection. Lower vertebrates such as fishes and reptiles primarily rely on behavior to elevate their body temperatures. For example, the febrile lizard will spend greater lengths of time near a heat source, and as a result its body temperature rises. A fever appears to be induced by a variety of substances such as bacteria, viruses, and fungi. These inducers of fever result in various types of phagocytes producing a heat-labile protein(s?), endogenous pyrogen. It is this endogenous pyrogen that is thought to result, ultimately, in the thermoregulatory set-point being raised. Within the past several years considerable evidence has accumulated that moderate elevations in body temperature are beneficial to the infected host. Studies with bacterial and viral infected animals have shown that moderate fevers increase survival rate. Many components of the nonspecific host defense response to infection such as leukocyte mobility, lymphocyte transformation, and effects of interferon, appear to be enhanced by elevations in temperature that simulate moderate fevers. In addition, some evidence indicates that a fever in conjunction with the changes in plasma iron levels known to occur during infection is a synergistic host defense response. More research needs to be done to determine for specific diseases whether moderate fevers are beneficial, neutral, or harmful to the infected host.

Corticotropin releasing hormone is involved in exercise-induced elevation in core temperature.

To determine the involvement of corticotropin releasing factor (CRF) in exercise-induced elevation in core temperature of female rats, CRF antibody or vehicle was injected intracerebroventricularly (ICV) into rats that had free access to exercise wheels for 6 weeks. On the day of injection, there were no differences in body temperature or activity following these injections. However, exercising animals had a significantly attenuated daytime temperature when compared to vehicle control animals at one day postinjection with the CRF antibody. Although these animals have significantly lower body temperature than the animals that received vehicle, the injection of CRF antibody had no effect on locomotor activity. Therefore, this decrease in temperature is not due to a reduction in activity. These results suggest that CRF is involved in the exercise-induced elevation in daytime body temperature. Since this antibody also attenuates fevers caused by IL-1 beta (and presumably other cytokines), it is possible that the daytime elevation in body temperature of exercising rats is mediated by IL-1 beta or other cytokines.

Effect of nicotine on the immune system: possible regulation of immune responses by central and peripheral mechanisms.

Nicotine (NT) treatment impairs T-cell receptor (TCR)-mediated signaling, leading to the arrest of T cells in the G1 phase of the cell cycle and inhibition of the antibody plaque-forming cell (AFC) response to sheep red blood cells (SRBC). This paper summarizes some of the previous findings related to cigarette smoke/NT and the immune response, and presents preliminary evidence suggesting that mice chronically treated with NT (0.5 mg/day/kg body weight) have a depressed inflammatory response in the turpentine-induced abscess model of inflammation. This ability of nicotine to attenuate an inflammatory response may also be the cause of reduced mortality of chronically nicotine-treated mice from acute influenza A pneumonitis. Moreover, in LEW rats, decreased anti-SRBC AFC responses were also observed after intracerebroventricular (i.c.v.) administration of relatively small concentrations of NT (28 micrograms/day/kg body weight) which, when given peripherally, did not affect the AFC response. In vitro the addition of NT to T cells increased protein tyrosine kinase (PTK) activity and intracellular Ca2+ concentration [Ca2+]i. These results support the hypothesis that NT alters immune responses by directly interacting with T cells, as well as indirectly through brain-immune interactions.

Molecular mechanisms of fever and endogenous antipyresis.

This review summarizes recent studies on endogenous antipyretic mechanisms. Fever is the result of a balance between pyrogenic and cryogenic cytokines and hormones. Although there is considerable evidence that fever evolved as a host defense response, it is important that the rise in body temperature not be too high. Many endogenous cryogens or antipyretics that limit the rise in body temperature have been identified during the last 25 years. These include alpha-MSH, arginine vasopressin, glucocorticoids, TNF (under certain circumstances), and IL-10. Most recently, evidence has accumulated that cytochrome P-450 (P-450), part of the alternative pathway for arachidonic acid metabolism, plays an important role in reduction of fever and inflammation. Supporting a role for P-450 in endogenous antipyresis and antiinflammation includes evidence that (1) inducers of P-450 reduce fever, (2) inhibitors of P-450 cause a larger fever, (3) and P-450 arachidonic acid metabolites reduce fever.

Human circadian rhythms in temperature, trace metals, and blood variables.

The literature supports the concept that circadian changes in body temperature reflect changes in the thermoregulatory set point. We were interested in studying the relationship between the circadian rhythm in body temperature and 24-h variations in plasma concentrations of iron, zinc, circulating leukocyte counts, and plasma interleukin 1 (IL-1) activity. Eight healthy men were studied for two separate 48-h sessions. Rectal temperature, plasma iron and zinc concentrations, plasma IL-1 activity, circulating leukocyte counts, and several other blood variables were monitored. Circadian rhythms in temperature, trace metals, and various leukocyte populations were demonstrated. The 24-h pattern of changes in plasma concentrations of iron and zinc approximate an inverse relationship with rectal temperature. Although we were unable to detect any IL-1 activity in human plasma collected at 4-h intervals, the daily changes in plasma trace metal concentrations and the variations in leukocyte populations may provide indirect evidence for a daily variation in local (e.g., in liver) or central nervous system release of IL-1.

Effect of exercise and food restriction on selected markers of the acute phase response in hamsters.

Acute aerobic exercise has been shown to elicit physiological changes characteristic of the acute phase response (APR), a nonspecific host defense response. Regular evocation of these changes may prime the immune system to improve resistance to disease. Because food deprivation is associated with an impaired APR, food restriction may prevent these beneficial changes. We tested the hypotheses that voluntary exercise elicits an APR and that food restriction modifies this response in four groups of hamsters: ad libitum-fed sedentary, ad libitum-fed exercised, food-restricted sedentary, and food-restricted exercised. Five variables altered during an APR were examined: core temperature, serum iron, serum interleukin-6, serum amyloid A, and serum glucocorticoids measured by biotelemetry, colorimetric analysis, B-9 cell growth assay, indirect enzyme-linked immunosorbent assay, and radioimmunoassay, respectively. Blood was drawn during the hamsters' inactive period after 19-20 days of access to running wheels. Resting core temperature was elevated by exercise and depressed by food restriction (P < 0.01). Iron was depressed by food restriction (P < 0.01). Cortisol, but not corticosterone, was elevated by food restriction (P < 0.001). There were no significant differences among groups in interleukin-6 (P > 0.49) or serum amyloid A (P > 0.29). We conclude that there is little evidence that voluntary exercise or exercise combined with food restriction causes an APR in hamsters.

Effect of voluntary exercise and food restriction in response to lipopolysaccharide in hamsters.

We tested the hypothesis that voluntary running and moderate food restriction alter the acute phase response (APR), one index of nonspecific immune function. Hamsters were kept sedentary or permitted to run and were fed ad libitum or had food restricted for 20 days and were then injected intraperitoneally with saline or lipopolysaccharide (LPS). Fever and circulating interleukin-6, serum amyloid A (SAA), serum iron, and cortisol were measured by biotelemetry, B-9 cell growth assay, indirect enzyme-linked immunosorbent assay, colorimetric analysis, and radioimmunoassay, respectively. The febrile temperature; hypoferremia; and elevation of circulating interleukin-6, SAA, and cortisol after LPS injection were not altered by exercise. Because baseline temperatures were elevated in the exercised hamsters, the change in temperature in response to LPS was less than it was in the sedentary hamsters. Food restriction significantly decreased SAA and elevated cortisol after LPS injection and depressed the absolute temperature to which the core temperature rose in response to LPS in one trial but not in another. Because food restriction depressed baseline temperatures, it also affected the change in temperature after LPS injection. The hypoferremic response to LPS was inhibited in hamsters that were both food restricted and permitted to run. We conclude that exercise does not enhance the APR to a low dose of LPS, whereas food restriction and the combination of exercise and food restriction depress some portions of the APR in hamsters.

The adaptive value of fever.

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

Body temperature, motor activity, and feeding behavior of mice treated with beta-chlornaltrexamine.

The effects of an irreversible long term opioid antagonism on circadian rhythms in body temperature (Tb), locomotor activity (Act) and feeding under normal conditions and following lipopolysaccharide administration (LPS; 2.5 mg/kg) have been investigated in unrestrained mice housed at their thermoneutral zone (30 degrees C). beta-chlornaltrexamine (beta-CNA; 5 mg/kg) given intraperitoneally decreased Tb on the day of injection, depressed Act, and reduced food and water intake for several days. The drug destroyed circadian rhythm in Tb for 4 consecutive days after administration due to prevention of the night time increases in temperature, whereas mean day time Tb of mice treated with beta-CNA remained similar to controls. Between days 5-8 the day-time Tb of beta-CNA-injected mice decreased, and the mice started displaying regular daily variations albeit with smaller amplitude and at lower level than controls. The depressive effect of beta-CNA on circadian variation in activity was more prolonged than its effect on Tb suggesting that these two variables are independently regulated. beta-CNA prevented the febrile response of the mice to LPS and enhanced the hypophagic effect of LPS. We conclude that normal circadian rhythms in Tb and Act, as well as certain symptoms of sickness behavior, have an opioid component.

Endotoxin tolerance does not alter open field-induced fever in rats.

Exposure to an open field has been shown to cause a rise in the body temperature of rats. In many respects, this rise in body temperature is similar to fevers caused by endotoxin and other inflammatory stimuli. Rats repeatedly injected with endotoxin develop tolerance to the fever-inducing action of endotoxin. We hypothesized that repeated pretreatment with endotoxin would modify the fever caused by exposure to psychological stress. To test this hypothesis, we compared open field-induced fevers in rats made endotoxin tolerant to those rats not endotoxin tolerant. We found that endotoxin tolerance had no effect on open field fevers.