Studies on the origin of human leukocytic pyrogen

Review: Infection, fever, and exogenous and endogenous pyrogens: some concepts have changed

For many years, it was thought that bacterial products caused fever via the intermediate production of a host-derived, fever-producing molecule, called endogenous pyrogen (EP). Bacterial products and other fever-producing substances were termed exogenous pyrogens. It was considered highly unlikely that exogenous pyrogens caused fever by acting directly on the hypothalamic thermoregulatory center since there were countless fever-producing microbial products, mostly large molecules, with no common physical structure. In vivo and in vitro, lipopolysaccharides (LPSs) and other microbial products induced EP, subsequently shown to be interleukin-1 (IL-1). The concept of the `endogenous pyrogen' cause of fever gained considerable support when pure, recombinant IL-1 produced fever in humans and in animals at subnanomolar concentrations. Subsequently, recombinant tumor necrosis factor-α (TNF-α), IL-6 and other cytokines were also shown to cause fever and EPs are now termed pyrogenic cytokines. However, the concept was challenged when specific blockade of either IL-1 or TNF activity did not diminish the febrile response to LPS, to other microbial products or to natural infections in animals and in humans. During infection, fever could occur independently of IL-1 or TNF activity. The cytokine-like property of Toll-like receptor (TLR) signal transduction provides an explanation by which any microbial product can cause fever by engaging its specific TLR on the vascular network supplying the thermoregulatory center in the anterior hypothalamus. Since fever induced by IL-1, TNF-α, IL-6 or TLR ligands requires cyclooxygenase-2, production of prostaglandin E2 (PGE 2) and activation of hypothalamic PGE2 receptors provides a unifying mechanism for fever by endogenous and exogenous pyrogens. Thus, fever is the result of either cytokine receptor or TLR triggering; in autoimmune diseases, fever is mostly cytokine mediated whereas both cytokine and TLR account for fever during infection.

Interleukin 1: the first interleukin

The name 'interleukin' and the designation of interleukin 1 (IL-1) derived from the Second International Lymphokine Workshop held in Switzerland in 1979. Since then interest in the original interleukin (IL-1) has increased exponentially as measured by the numbers of publications and meetings. The main reasons for this can be seen in the accompanying centrefold. The perception of IL-1 as a biological mediator in every organ system has attracted scientists from widely different backgrounds into this area and a steady succession of important and often surprising insights into IL-1 biology has ensured that interest has been sustained at a high level. This overview of the biology of IL-1 on the tenth anniversary of its turbulent life has been compiled by Franco di Giovine and Gordon Duff. It is of necessity selective and biased towards human IL-1 and begins with some general points (mainly cautionary) as a backdrop to the centrefold.

Heat-shock protein synthesis by human polymorphonuclear cells

Mature human neutrophils from peripheral blood are known to be capable of limited protein biosynthetic activity. We now show that these cells are inducible for heat-shock protein synthesis when placed in short-term culture. Synthesis of hsp70 and hsp85 as well as the response to various temperatures and the time course of induction were typical for mammalian cell systems. This heat-shock response was blocked by actinomycin D added before heat exposure. This demonstration that hsp genes can be activated by heat exposure of terminally differentiated neutrophils supports the hypothesis that gene activation can serve a physiological role in these cells and opens up the possibility that synthesis of other gene products is similarly inducible.

Fever and aging

The pathogenesis and clinical relevance of fever is reviewed. The interrelationship between fever and other biologic responses to infection is summarized. A blunted or absent fever response to infections observed in some elderly patients may be due to defects in thermoregulation. These abnormalities in thermoregulation may include impairment of both behavioral and physiologic responses.

Studies on the production of endogenous pyrogen by rabbit monocytes: the role of calcium and cyclic nucleotides

Rabbit monocytes stimulated with endotoxin produced endogenous pyrogen, even under conditions of high or low extracellular calcium concentrations. Maximal production occurred when the concentration was in the near-physiological range. Prolonged incubation of cells with a calcium chelator prevented subsequent activation with endotoxin, an effect which was rapidly reversible by re-addition of calcium but not other cations. Addition of small amounts of lanthanum, which acts as a calcium channel blocker, prevented the restoration of pyrogen production, indicating that entry of the added calcium into the monocyte was required. Incorporation of a calcium ionophore into the cell membrane did not stimulate pyrogen production, and no measurable influx or efflux of calcium occurred during stimulation with endotoxin. These observations suggest that a slowly exchangeable calcium pool is necessary for the production of endogenous pyrogen, but that a rise in intracellular calcium is not by itself a necessary or sufficient stimulus. This stands in contrast to other biological systems in which Ca2+ directly couples stimulus and hormone secretion. Incubation of cells with agents shown to increase cyclic 3',5' AMP or cyclic 3',5' GMP levels in monocytes similarly did not stimulate pyrogen production or modulate its production by endotoxin stimulation. Thus, cyclic nucleotides also did not play a detectable role as intracellular messengers in this system. Future work is required to define more clearly the mechanism for the production of endogenous pyrogen, given its marked effects on the immune system through lymphocyte activation and temperature regulation.

Effect of protein synthesis inhibitors on leukocytic pyrogen-induced in vitro hypothalamic prostaglandin production

In order to study the antipyretic effect of inhibitors of protein synthesis, hypothalamic tissue was incubated in vitro under controlled conditions and the amount of prostaglandin E2 (PGE2) measured in the supernatant medium. Rabbit anterior hypothalamic tissue was incubated with purified human leukocytic pyrogen (LP) and after 60 minutes the supernatant fluid was assayed for PGE2 by radioimmunoassay. Control tissue incubated with Eagle's medium (MEM) released elevated levels of PGE2; however, the addition of polymyxin B (PmxB), a cationic antibiotic which blocks the activities of bacterial endotoxins, significantly reduced PGE2. In addition, endotoxin added to MEM induced from the brain tissue PGE2 production which could be reduced by the addition of PmxB. Thus, commercial culture media such as MEM may contain sufficient amounts of endotoxin to stimulate brain PGE2 production in vitro. Purified human LP incubated with hypothalamic tissue in the presence of PmxB induced PGE2 production in a dose-dependent fashion. This release could be reduced (p less than 0.001) by the presence of either cycloheximide or puromycin during incubation with LP. The addition of these inhibitors to unstimulated hypothalamic tissue incubations did not reduce background levels of PGE2. It is concluded that the antipyretic effect of protein synthesis inhibitors results in a specific decrease in LP-induced levels of PGE2.

Goals of nutritional support in acute infections

Defense mechanisms employed by the host to fight infection are highly dependent on adequate protein synthesis to support phagocytic and lymphoid cell activity as well as immunoglobulin production. Interleukin I is a small, not yet fully characterized protein produced by macrophages which appears to initiate most of the nonspecific metabolic changes observed during infection. These alterations include: increase in the synthesis of visceral proteins, white blood cells, and acute phase globulins; enhanced somatic protein breakdown; sequestering of serum iron and zinc in the liver; and induction of fever. The ability of leukocytes to produce interleukin I is impaired in patients with visceral protein depletion or kwashiorkor-like, hypoalbuminemic malnutrition and can be restored in the healthy unstressed patient within approximately three to five days by feeding. Similarly, in the stressed patient, adequate protein and caloric intake improves the ability to produce interleukin I, which may improve survival. Other defects in host defense in advanced stages of protein malnutrition include lymphopenia, impaired phagocytosis, and deficiencies in fibronectin, immunoglobulins, and complement levels. Thus, the goal of nutritional support is to maintain sufficient amounts of amino acids for visceral protein synthesis required for adequate host defense.

The influence of lipoxygenase inhibitors on the in vitro production of human leukocytic pyrogen and lymphocyte activating factor (interleukin-1)

Leukocytic pyrogen (LP), the endogenous mediator of fever, is synthesized and released from mononuclear phagocytes following activation by several microbial and immunologically-derived substances. Purified fractions of LP also stimulate thymocyte proliferation and LP seems to be indistinguishable from lymphocyte activating factor (LAF) otherwise known as interleukin-1 (IL-1). In the present investigation, we have examined the effect on IL-1 production of drugs inhibiting both cyclooxygenase- and lipoxygenase-mediated transformations of arachidonic acid (ETYA, 5,8,11,14-eicosatetraynoic acid and compound BW755C, 3-amino-1-3-trifluoromethylphenyl-2-pyrazoline). Ibuprofen inhibited the production of PGE2 from stimulated human monocytes but had no effect on LP and LAF release. ETYA prevented LP production from human monocytes when added to the incubation fluid prior to activation by Staphylococcus albus. When added after cell activation, ETYA was ineffective. Similar results were obtained using BW755C. Prostaglandin E2 (PGE2) levels in cell supernates were markedly decreased in the presence of either drug when compared to supernates from untreated, stimulated cells. Low PGE2 levels were also demonstrated in supernates of cells in which either ETYA or BW755C were added 1 hour after stimulation. Pretreatment with BW755C also resulted in decreased LAF activity in the supernates of mononuclear cells stimulated with staphylococci, endotoxin, or muramyl dipeptide. Other experiments demonstrated that crude or purified human LP retains its activity following treatment with soybean lipoxidase. These findings indicate that a product of arachidonate lipoxygenase is important in the sequence of events underlying cell activation for the production of human LP/LAF/IL-1. The possibility that LP might be an eicosanoid-peptide conjugate structurally resembling the leukotrienes was ruled out.

Molecular mechanisms in endotoxin fever

Two important concepts are presented in this review. First, endotoxin fever, like all fevers, is mediated by a host product, leukocytic pyrogen (LP). The mechanism by which LP production is initiated by endotoxin is discussed and evidence is provided which clearly distinguishes the biological and physical differences between LP and endotoxins. The second concept is that many of the molecular and neurochemical mechanisms by which LP causes fever by its action on the hypothalamic thermoregulatory center are also observed when endotoxins are introduced into the central nervous system. Thus, there may be experimental and clinical situations in which endotoxins can directly affect the hypothalamus and initiate fever. Although this bi-modal effect of endotoxin on the production of fever can occur, the importance of LP in mediating endotoxin and other fevers cannot be overstated.

Pathophysiology of bacteremia

Despite the frequency and importance of both nosocomial and "community-acquired" bacteremia, definitive information concerning crucial pathophysiologic events in human bacteremia remains sparse. An extensive variety of clinical manifestations, such as fever, rigors, shock, altered circulatory dynamics, cutaneous manifestations changes in the coagulation, complement, and other mediator systems, and effects on the lungs, heart, kidney, liver, and other end organs, have been described, but it is difficult to determine the relative frequency of these events in bacteremia caused by different species. The extensive number of bacterial species capable of producing bacteremia and variations in the type of presentation, such as acute, asymptomatic, and chronic, even when bacteremia is produced by the same species, undoubtedly contribute to this difficulty and suggest that a variety of pathophysiologic mechanisms occur in various bacteremias. In contrast, the relative frequency of various manifestations and some pathophysiologic mechanisms have been better delineated in Gram-negative bacteremia. The development of bacteremia enhances the lethality of most types of localized infection and several studies have demonstrated a relation between the magnitude of bacteremia and the outcome of the disease. Among various pathophysiologic alterations, mechanisms involved in the production of fever have been delineated most clearly. Fever appears to reflect a "common pathway" with almost all infectious agents and results from release of endogenous pyrogen from phagocytic cells. Endogenous pyrogen regulates the thermostatic setting of the body through its effect on the anterior hypothalamus. Endogenous pyrogen seems identical with Interleukin 1 and exerts a variety of other biologic activities. An extensive number of bacterial components have been proposed as "effectors" and an equally large number of endogenous substances proposed as "mediators" of the pathophysiologic events in bacteremia. The importance of many of these effectors and mediators has been postulated largely on the basis of in vitro and animal studies. The lack of critical clinical studies hampers extrapolation of these experimental studies to human bacteremia. The development of more effective therapy for the complications of bacteremia, such as shock, will continue to be hampered until the mechanisms involved in the production of those pathophysiologic events that are crucial determinants of outcome have been delineated more precisely in human disease.

Production of fever and its effects on the host

Leukocytic pyrogen (LP) is a polypeptide that is released from phagocytic leukocytes and mediates fever, by direct action on the thermoregulatory centers in the hypothalamus. During the mediation a complex series of biochemical events occurs in the hypothalamus, including increases in prostaglandin synthesis. The production of LP by phagocytic leukocytes (predominantly monocyte/macrophage) requires synthesis of protein and new messenger-RNA. Recently, it has been discovered that LP has other direct effects on the host. Amongst these effects are: increases in acute phase reactants, including serum amyloid A protein (SAA); release of specific granule contents from neutrophils in vitro; a similarity (if not identity) to human lymphocyte activating factor (LAF) which is a monokine. Thus, LP may have a much broader role to play in the inflammatory response than just mediating fever.

Molecular basis of fever in humans

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

Studies on the active site of human leukocytic pyrogen

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

Fever: its history, cause, and function

Concepts of fever from Hippocrates to the present are briefly outlined and compared with current ideas of the pathogenesis of fever. Evidence is presented that endogenous pyrogen, the hormone that elevates body temperature, is identical with lymphocyte-activating factor, a monokine that stimulates lymphocyte proliferation and function.It now appears that inflammation and fever are closely interrelated phenomena that are modulated by a single hormone and that have been selected by evolution to protect the host against infection.

RNA and protein synthesis in human peripheral blood polymorphonuclear leukocytes

Polymorphonuclear leukocytes purified from human peripheral blood synthesized RNA and proteins when placed in cell culture. Autoradiography of the cultured cells revealed that a majority of mature PMNs were engaged in macromolecule synthesis, and an analysis of newly synthesized proteins by SDS-polyacrylamide gel electrophoresis showed that many different polypeptide chains were synthesized by these cells. The rate of [3H]uridine incorporation and the pattern of newly synthesized proteins were modulated by Con A and glucocorticoids. These results suggest that in spite of their short lifetime and a large performed enzymatic apparatus, mature PMNs retain a substantial capacity for RNA and protein synthesis; and, further, that modulation of macromolecule synthesis forms part of the mechanism by which PMNs respond to inflammatory and anti-flammatory stimuli.

Secretion of plasminogen activator by human polymorphonuclear leukocytes. Modulation by glucocorticoids and other effectors

Purified human PMNs secrete plasminogen activator. This secretion is stimulated by Con A and low concentrations of PMA, and is inhibited by low concentrations of glucocorticoids, and by cAMP, actinomycin D, and cycloheximide. In contrast, the release of granule-bound enzymes, such as elastase, is achieved only at higher concentrations of PMA, and is not affected by any of the inhibitors that block plasminogen activator production. These results show that the production of plasminogen activatory by PMNs is controlled by agents that affect inflammations, and that this control is not shared by other lytic enzymes known to be associated with these cells. This suggests a particular role for plasminogen activator in the response pattern of PMNs and also supports the concept, previously developed for macrophages, that the secretion of this enzyme is correlated with cell migration in vivo.

Human leukocytic pyrogen: purification and development of a radioimmunoassay

Leukocytic pyrogen is a small endogenous protein that mediates fever. Because of the limitations of bioassays, circulating leukocytic pyrogen has not been demonstrated during fever in humans. The pyrogen was produced in vitro after phagocytosis of staphylococci by blood monocytes. Antibody against the pyrogen was obtained from rabbits immunized with leukocytic pyrogen and the antiserum was purified by solid-phase immunoadsorbants. Purified antibody to the pyrogen was attached to activated Sepharose 4B and used in conjunction with gel filtration to purify the pyrogen. The pyrogen was labeled with 125I and further purified by gel filtration and ion-exchange chromatography. The final preparation of 125I-labeled pyrogen demonstrated a homogeneous band during isoelectric focusing and other separation procedures. With antibody to pyrogen attached to Sepharose, less than 0.1 of a rabbit pyrogenic dose of human leukocytic pyrogen inhibited the binding of 125I-labeled pyrogen to this immunoadsorbant, and this inhibition was not affected by the presence of human serum. Thus, a radioimmunoassay for human leukocytic pyrogen has been developed that may be used to detect circulating pyrogen during fever in humans.

The production of antibody against human leukocytic pyrogen

Human peripheral blood leukocytes were stimulated with killed staphylococci in vitro to release leukocytic pyrogen (LP). Supernates from these stimulated leukocytes were concentrated, emulsified in Freund's complete adjuvant, and injected intradermally into rabbits. After seven monthly booster injections, rabbit antiserum destroyed the pyrogenic activity of human LP, and the titer of this neutralizing ability increased in the subsequent 7 mo. The pyrogen-neutralizing capacity of the rabbit antiserum was recovered in the globulin fraction, the IgG and IgM peaks of Sephadex G-200, and the acid-eluted fraction of a goat anti-rabbit IgG immunoadsorbant. The neutralizing antibody was specific for human LP inasmuch as it had no effect on rabbit, guinea pig, or monkey LP. When coupled to Sepharose, this antibody bound human LP; after acid elution from this immunoadsorbant, LP was recovered without loss of biologic or chemical characteristics. The antiserum was also absorbed with stimulated leukocyte supernates which did not contain LP, and this had no effect on the titer of anti-LP. Crude human LP, eluted from immunoadsorbant columns prepared from absorbed antiserum, contained significantly reduced contaminating protein when evaluated by polyacrylamide gel electrophoresis. These studies have established that specific antibody to human leukocytic pyrogen can be produced. This antibody is useful in the further study and purification of leukocytic pyrogen and its role in the pathogenesis of human fever.

Differences in pyrogen production by mononuclear phagocytes and by fibroblasts or HeLa cells

Phagocytosis of bacteria stimulates "professional" phagocytes to produce and release endogenous pyrogen (EP), the protein that mediates fever. To determine whether "nonprofessional" phagocytes also have this capacity, mouse and human fibroblasts and HeLa cells were cultured after ingestion of latex or chicken erythrocytes (CE), and EP release into culture supernate measured by mouse assay. No detectable pyrogen was released by these cell types after phagocytosis, whereas both latex and CE stimulated EP production by cultured mouse macrophages. These studies support the hypothesis that only professional phagocytes of bone marrow origin synthesize EP and induce fever.

On the mechanism of pyrogenic action of ricin

The incubation of rabbit white blood cells with ricin, the toxic protein of castor oil seeds, leads to the production of endogenous pyrogens. This induction can be inhibited by the antibiotics actinomycin D or cycloheximide. The results are discussed in terms of disturbed corticosteroid- and Mg2+-levels.

Colchicine stimulation of pyrogen production by human blood leukocytes

The effect of colchicine, an anti-inflammatory agent, on endogenous pyrogen (EP) production by human blood leukocytes in vitro was examined. Colchicine not only failed to suppress EP production by human leukocytes stimulated by phagocytosis, but, in the absence of other stimuli, micromolar concentrations of the drug induced pyrogen production and release by both polymorphonuclear (PMN) and mononuclear leukocytes. The response was dose related, occurring at concentrations above 0.1 muM. Colcemid and vinblastine, other agents which bind to microtubular protein, also induced pyrogen release from human leukocytes, whereas lumicolchicine, a light-alerted derivative of colchicine without affinity for microtubules, was ineffective. Colchicine did not induce EP production by rabbit leukocytes, even at 100 muM concentration. Studies of the mechanism of PMN leukocyte activation by Colcemid indicated that although the time required for contact between drug and leukocyte was brief, pyrogen production and release did not begin for 6 or more hours. If added during this time, puromycin prevented subsequent production and release of pyrogen. These results indicated that agents which interfere with the assembly of microtubules induce EP production and secretion by human leukocytes in vitro.

Studies on the mechanism of endogenous pyrogen production. III. Human blood monocytes

The characteristics of pyrogen production and release by human blood monocytes were investigated. A dose-response assay of monocyte pyrogen in rabbits indicated a linear relationship of temperature elevation to dose of pyrogen at lower doses. Monocytes did not contain pyrogen when first obtained, nor did they release it spontaneously even after 5 days of incubation in vitro. Pyrogen production was apparent 4 h after stimulation by endotoxin or phagocytosis, and continued for 24 h or more. Puromycin, an inhibitor of protein synthesis, prevented both initiation and continuation of pyrogen production and release. Pyrogen-containing supernates retained most pyrogenic activity during overnight incubation even in the presence of activated cells. Lymphocytes appeared to play no role in either initiation or continuation of pyrogen production in these studies.

Studies on the mechanism of endogenous pyrogen production. II. Role of cell products in the regulation of pyrogen release from blood leukocytes

Some characteristics of the process by which endogenous pyrogen (EP), the mediator of fever, is released from cells were examined by using human blood leukocytes incubated in vitro. Studies were designed to examine a possible role for leukocyte products, including EP, in the induction, augmentation, or suppression of pyrogen release by blood leukocytes. Products of stimulated leukocytes, including a partially purified preparation of EP, did not induce significant activation of nonstimulated cells. Also, no evidence was obtained that stimulated cell products either augment or inhibit pyrogen production by other stimulated cells. A feedback control of EP production was thus not observed. A crude preparation of EP, containing other products of activated cells, maintained its pyrogenicity when incubated at pH 7.4 but not at pH 5.0. These studies thus provide no support for hypothesized control mechanisms regulating production of EP by blood leukocytes. By contrast, local inactivation of EP at inflammatory sites may modify the amount of EP entering the blood, and hence fever.

Pyrogen release in vitro by lymphoid tissues from patients with Hodgkin's disease

The mechanism of fever in patients with Hodgkin's disease was investigated by examining endogenous pyrogen production by blood, spleen, and lymph node cells incubated in vitro. Blood leucocytes from febrile or afebrile patients with Hodgkin's disease did not produce pyrogen spontaneously. Spleen cells, however, frequently released pyrogen during initial incubations, unlike spleen cells from patients with non-malignant diseases. Pyrogen production occurred from spleens without observed pathologic infiltrates of Hodgkin's disease. Lymph nodes involved with Hodgkin's disease produced pyrogen more frequently than did nodes involved with other diseases. Pyrogen production by tissue cells was prolonged, required protein synthesis, and in some cases was due to mononuclear cells; it did not correlate with fever in the patient. These studies demonstrate spontaneous production of endogenous pyrogen in vitro by lymphoid tissue cells from patients with Hodgkin's disease.

Demonstration and characterization of two distinct human leukocytic pyrogens

Human monocytes and neutrophils were separated from buffy coats of blood obtained from normal donors. Following incubation with heat-killed staphylococci, monocyte preparations contained 20 times more pyrogenic activity in the supernatant media than did supernates from an equal number of neutrophils. During purification of these pyrogens it was discovered that these cell preparations each produced a distinct and different pyrogen. The pyrogen obtained from neutrophils had a mol wt of 15,000 following Sephadex G-75 gel filtration, an isoelectric point of 6.9, and could be precipitated and recovered from 50% ethanol at -10 degrees C. In contrast, the pyrogen derived from monocyte preparations had a mol wt of 38,000, an isoelectric point of 5.1, and was destroyed in cold ethanol. Both molecules were unaffected by viral neuraminidase but biologically destroyed at 80 degrees C for 20 min and with trypsin at pH 8.0. The febrile peak produced by partially purified neutrophil pyrogen occurred at 40 min while that from monocytes was at 60 min. In addition, monocyte pyrogen produced more sustained fevers for the same peak elevation as neutrophil pyrogen. These studies demonstrate for the first time two chemically and biologically distinctive pyrogens derived from circulating human white blood cells and have important implications for our understanding of the pathogenesis of fever in man.

Cardiovascular and metabolic effects of whole or fractionated gram-negative bacterial endotoxin in the unanesthetized Rhesus monkey

Rhesus monkeys were infused with endotoxin lipopolysaccharide (LPS) (10 mg/kg [LPS 10 ] or 2.5 mg/kg [LPS 2.5 ]) or with fractions of LPS containing 6.3% lipid (PS 1 ) or 0.5% lipid (PS 2 ) (2.5 mg/kg). Systemic and regional hemodynamics, leukocyte counts, blood gases, pH, and plasma bradykinin concentration were measured. Monkeys receiving LPS 10 , LPS 2.5 , or PS 1 became hypotensive (mean blood pressure -37 ± 10 mm Hg) and had decreased peripheral vascular resistance (-10% to -24% of the base line), compensated metabolic acidosis, and elevated plasma bradykinin concentrations (14 ± 6 ng/ml) 2 hours after infusion. Vasodilation occurred in coronary, hepatic, and splanchnic vasculature; vasoconstriction occurred in the spleen. Cardiac output was diverted from muscle to viscera. Monkeys receiving PS 2 were normotensive with elevated peripheral vascular resistance (+46%) and no measurable plasma bradykinin concentration. By 6 hours, marked elevation of peripheral vascular resistance developed in monkeys given LPS 10 (+113%) and LPS 2.5 (+57%). Monkeys receiving PS 1 returned to base-line values, but monkeys receiving PS 2 remained unchanged. Leukopenia (-50% to -65%) was persistent only in monkeys receiving LPS or PS 1 . Toxicity of LPS apparently depends on the lipid portions of the molecule. Vasodilation and bradykinin generation are correlated with persistent granulocytopenia. Late toxicity may be independent of early cardiovascular events.

Synthesis of endogenous pyrogen by rabbit leukocytes

Rabbit ieukocytes from peritoneal exudates and from blood were stimulated to form leukocyte pyrogen in the presence of radiolabeled amino acids. The stimuli used were endotoxin, phagocytosis, and tuberculin. The crude leukocyte pyrogen samples were purified; pyrogen from exudate cells was rendered homogeneous; pyrogen from blood cells was still contaminated with other proteins. All the purified pyrogens were radioactive; and for all it was shown that radioactivity and pyrogenic activity coincided on electrophoresis at pH 3.5 and pH 9 in acrylamide and on isoelectric focusing in acrylamide. Furthermore, pyrogens obtained from exudate cells stimulated in different ways, or from blood cells and exudate cells stimulated with endotoxin, appeared to be identical. These results suggest that leukocyte pyrogen was synthesized de novo from amino acid precursors and that leukocytes made the same pyrogen whatever the stimulus used to activate them.