Further similarities of endogenous pyrogen and leukocytic endogenous mediator

Glucocorticoid independent mediation of interleukin-1 induced changes in serum zinc and liver metallothionein levels

Interleukin-1 (IL-1) causes changes in zinc metabolism which have been attributed to mediation, at least in part, by glucocorticoids. However, IL-1 was found to actually lower serum corticosterone levels in rats. In addition, adrenalectomy only partially inhibited the ability of IL-1 to depress serum zinc levels and increase the amount of zinc associated with hepatic metallothionein. Furthermore, IL-1 increased total liver metallothionein protein to similar levels in both adrenalectomized and normal rats. Administering the synthetic glucocorticoid dexamethasone with IL-1 to adrenalectomized rats produced additive, but not synergistic effects on serum zinc and metallothionein concentrations. Studies with actinomycin D suggested that IL-1 induction of metallothionein might involve glucagon.

Comparative observations of fever and associated clinical hematological and blood biochemical changes after intravenous administration of staphylococcal enterotoxins B and F (toxic shock syndrome toxin-1) in goats

The present investigation was undertaken to examine the characteristics of purified toxic shock syndrome toxin-1 (staphylococcal enterotoxin F) given intravenously to dwarf goats (dose, 0.02 to 20 micrograms kg-1). Rectal temperature, heart rate, rumen motility, plasma zinc and iron concentrations, and certain other blood biochemical and hematological values were studied and compared with the changes seen after intravenous administration of staphylococcal enterotoxin B (dose, 0.02 to 0.5 micrograms kg-1). Similar changes such as fever, tachycardia, inhibition of rumen contractions, drop in plasma zinc and iron concentrations, lymphopenia, and a decrease in serum alkaline phosphatase activity were observed. In contrast to the effects of toxic shock syndrome toxin-1, staphylococcal enterotoxin B induced colic, watery diarrhea with pseudomembranes, hemoconcentration, and a more pronounced increase in blood urea nitrogen. The results obtained demonstrate that (i) in the goat staphylococcal enterotoxin B is much more potent than toxic shock syndrome toxin-1 and (ii) the goat is a useful model to study the gastro-intestinal effects caused by staphylococcal enterotoxin B. The present finding that no clear relationship could be found between the temperature response and the alterations in zinc and iron levels in plasma support the theory that the febrile reactions and the changes in plasma trace metals are mediated by different polypeptides released by activated macrophages.

Fever and changes in plasma zinc and iron concentrations in the goat: the role of leukocytic pyrogen

In goats with trypanosomiasis (T. vivax or T. congolense) no marked fall in plasma zinc concentration was seen despite high temperature peaks, whereas plasma concentrations of iron tended to undergo some decline. In goats infected with Ehrlichia phagocytophila, there was a marked decline in plasma zinc and iron to low values on the 3rd and 4th day, respectively. Circulating endogenous pyrogen (EP) or leukocytic endogenous mediator (LEM) could not be detected in plasma from febrile goats with tick-borne fever. The intravenous injection of leukocytic pyrogen (LP) in kids caused characteristic monophasic febrile reactions, whereas no significant changes in plasma trace metals were found. So, previous evidence purporting to show that LP is similar to or may be identical with LEM is demonstrably inconclusive. Intravenous injection of E. coli lipopolysaccharide (LPS) or staphylococcal enterotoxin B (SEB) induced fever and lowering of plasma zinc and iron concentrations. The decrease in those trace metal values was more persistent in goats given SEB than in those given E. coli LPS. After intramammary infusion of SEB or E. coli LPS, fever and significant decreases in plasma zinc and iron concentrations were observed but no clear relationship was found between the temperature responses and the alterations in plasma trace metal concentrations. Furthermore, the decrease in plasma iron concentration developed more rapidly in goats given SEB than in those given E. coli LPS, whereas the decrease in plasma zinc concentrations in the former was more delayed. These data support the theory that the concentrations of zinc and iron in plasma are regulated by different mechanisms, whereas febrile reactions are mediated by another type of endogenous protein.

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.

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.

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.

Acute phase proteins with special reference to C-reactive protein and related proteins (pentaxins) and serum amyloid A protein

The acute phase response among plasma proteins is a normal response to tissue injury and is therefore a fundamental aspect of many diverse disease processes. It probably usually has a beneficial net function in limiting damage and promoting repair but in some circumstances it may have pathological consequences. Sustained high levels of acute phase proteins and especially SAA are associated with the development of amyloidosis in some individuals. Increased concentrations of CRP may, by activating the complement system, contribute to inflammation and enhance tissue damage. Failure of the normal or appropriate CRP response may also possibly have deleterious effects. SAA is a polymorphic protein which is normally present only in trace amounts but which, during the acute phase response, becomes one of the major apolipoproteins associated with high-density lipoprotein particles. The function of apoSAA is not known but it must have considerable physiological significance apart from its role as the putative precursor of amyloid A protein fibrils. CRP and SAP have been very stably conserved throughout vertebrate evolution and homologous proteins are apparently present even in vertebrates. This strongly suggests that they have important functions although these have not yet been precisely delineated. The main role of CRP may be to provide for enhanced clearance of inappropriate materials from the plasma whether these are of extrinsic origin, such as microorganisms and their products, or the autologous products of cell damage and death. The interaction between aggregated CRP and plasma low-density lipoprotein may play a significant part in the normal function of CRP and may also have a role in lipoprotein metabolism, clearance, and deposition. SAP is a normal tissue protein as well as being a plasma protein. Aggregated SAP selectively binds fibronectin and this may represent an aspect of the normal function of SAP. The deposition of SAP in amyloid is evidently not a normal function but it is not known whether this deposition is involved in the pathogenesis of amyloid or whether it is merely an epiphenomenon. In any case immunohistochemical staining for SAP is useful in the diagnosis of amyloid, in investigation of glomerulonephritis, and in studying disorders of elastic tissue. Regardless of its physiological or pathophysiological functions, the assay of serum CRP is a valuable aid to clinical management in a number of different situations and in different diseases provided results are interpreted in the light of full clinical information.(ABSTRACT TRUNCATED AT 400 WORDS)

Leukocytic pyrogen: a major mediator of the acute phase reaction

The acute phase reaction is initiated and regulated by leukocytic pyrogen which is released by activated host phagocytes at inflammatory sites during inflammatory reactions of any etiology. The physiological alterations which follow include, in addition to the characteristic acute phase protein changes, fever, granulocytosis, fall in serum iron and zinc, metabolic stimulation of blood granulocytes, activation of T-cell function and doubtless other effects as yet unrecognized. These responses are mediated by free or by protein-bound LP molecules and reflect both direct receptor coupled effects and more indirect mechanisms such as release of secondary mediators from cells or body fluids and involvement of neural or neurohumoral pathways. This unitarian hypothesis implies a functional interrelationship between the component parts, and allows a model for critical examination and new hypothesis testing. The wider availability of pure preparations of LP and of possible subtypes of LP and of a sensitive immunoassay would help us to prove or to expand this hypothesis and to advance our understanding of this important phase of acute inflammation. Earlier in this conference we heard that the mediator derepresses a message: I'd like to put forward the idea that in the acute phase reaction the mediator is the message.

The effects of adrenal hormones, endotoxin and turpentine on serum components of the plaice (Pleuronectes platessa L.)

1. Within 24 hr of injection into plaice, cortisol, deoxycorticosterone, adrenalin or endotoxin cause an increase (P less than 0.001) in circulating C-reactive protein (CRP). Turpentine and soluble dexamethasone have no effect. 2. The increase in CRP with endotoxin is not enhanced with adrenalin or deoxycorticosterone, and in conjunction with cortisol the increase is additive. 3. Changes in CRP are independent of the amounts of serum amyloid P-component or total protein. 4. Turpentine, cortisol and adrenalin cause a rapid increase in circulating glucose. 5. It is concluded that some adrenal hormones stimulate the CRP acute phase response in plaice, without an apparent provoking agent.

An in vitro bioassay for leukocytic endogenous mediator(s) using cultured rat hepatocytes

Primary cultures of adult rat hepatocytes were used to assay for the presence of leukocytic mediator(s) (LEM), a neutrophil derived protein(s) capable of stimulating the synthesis of acute-phase plasma proteins when injected into rats. In the presence of physiological concentrations of dexamethasone (40 mM), the hepatocytes secreted a variety of plasma proteins as demonstrated by crossed immunoelectrophoresis. The addition of LEM to hepatocytes increased the secretion of several acute-phase related plasma proteins, including fibrinogen and hepatoglobin, and decreased albumin secretion. These results mimic the acute-phase response observed in the intact animal. Fibrinogen secretion was used as a quantitative marker for determining LEM activity. The rate of fibrinogen secretion depended upon both the concentration of dexamethasone and LEM present during a given 24-h assay period. One unit of LEM activity is defined as that concentration of LEM capable of producing a 50% maximal stimulation of fibrinogen secretion.

Fever and trace metal changes in endotoxin-challenged neonates

During infections, plasma Fe and Zn generally fall, while body temperature and plasma Cu rise. However, infected neonates usually do not develop fever during the first week of postnatal life. While fever could not be evoked in neonatal guinea pigs by 2 micrograms/kg of S. enteritidis endotoxin until they were 8 days old, their plasma levels of Fe and Zn were lowered significantly from birth; plasma Cu tended to increase from 2 days postnatally. These results indicate that, contrary to the refractoriness to endotoxin of the fibrific system, the ability to alter trace metal levels exists from birth. Thus, fever and trace metal levels are not necessarily coupled for host defense during infection.

Role of the central nervous system in acute-phase responses to leukocytic pyrogen

Intracerebroventricular injection of rabbit leukocytic pyrogen (LP) into conscious, healthy cannulated rabbits produced markedly enhanced febrile and acute-phase responses as compared with equivalent-dose, single bolus intravenous injection. The increased effectiveness in inducing granulocytosis and hypoferremia on intracerebroventricular injection was matched by changing the method of administration of intravenous LP from a single initial bolus to multiple fractional doses over a 2-h period. This suggested that augmentation for these parameters may have reflected only a "reservoir" function of the cerebral ventricles which prevented rapid clearance of LP from the blood. The ability of LP to induce hepatic synthesis of haptoglobin and C-reactive protein was so markedly enhanced by intracerebroventricular injection, however, that a role of the central nervous system in mediating or in modifying in an important way a non-neural mechanism for this mediation must be postulated.