Role of acute-phase proteins in interleukin-1-induced nonspecific resistance to bacterial infections in mice

Responses of selected biomarkers, female reproductive hormones and tissue changes in non-pregnant does challenged with Mannheimia haemolytica serotype A2 and its outer membrane protein (OMP) immunogen

BACKGROUND

Mannheimia haemolytica causative agent of pneumonic mannheimiosis, a common respiratory disease of goat and sheep, which cause huge economic losses to farmers worldwide. Pneumonic mannheimiosis caused by M. haemolytica serotype A2 has been reported among small ruminants in Malaysia. The lipopolysaccharide (LPS) and outer membrane protein (OMP) are major virulence determinants for M. haemolytica serotype A2. Although pneumonic mannheimiosis is known to cause poor reproductive performance in small ruminants under field conditions, there is a dearth of published information on the specific effects of M. haemolytica serotype A2 infection on the female reproductive physiology. In this experiment, we explored the impact of M. haemolytica serotype A2 and its OMP immunogen on selected pro-inflammatory cytokines, acute phase proteins, female reproductive hormones, and cellular changes in visceral and female reproductive organs of non-pregnant does.

METHODOLOGY

Twelve healthy, non-pregnant, Boer crossbreds does were divided equally into three groups (n = 4); Group 1 served as the negative control and was challenged with 2 ml of sterile PBS intranasally. Group 2 served as the positive control and was challenged with 2 ml of 10⁹ colonies forming unit (CFU) of M. haemolytica serotype A2 suspension intranasally. Group 3 was challenged with 2 ml of OMP extracted from 10⁹ CFU of M. haemolytica A2 intramuscularly. The experimental does were monitored for clinical signs and responses periodically. Blood samples were collected at 0, 1, 2, 4, 6, 12 and 24 h and 3, 7, 21, 35 and 56 days post treatment for serological analyses. All does were euthanised using the halal slaughter method on day 60 post challenge/treatment. Tissues from the uterus, liver, lung and associated bronchial lymph nodes were collected and fixed in 10% formalin for 14 days for histopathological study.

RESULTS

Compared to the control group, the challenged/treated groups showed significant (p < 0.05) increase in the rectal temperature, respiratory rate, heart rate, and rumen motility. Serum analyses revealed that the concentrations of progesterone and estrogen hormones were significantly (p < 0.05) decreased in groups 2 & 3. In contrast, the concentrations of pro-inflammatory cytokines (IL-1β and IL-6) and acute phase proteins (Hp and SAA) were significantly increased (p < 0.05) in the challenged/treated groups compared to the control group. Histopathological lesion scoring revealed mild to moderate cellular changes characterised by congestion, haemorrhage, degeneration, leucocytic cellular infiltration, and cellular necrosis in the tissues of does from the OMP treatment and bacterial challenge groups compared to the control group.

CONCLUSION

The findings from this study suggests that M. haemolytica serotype A2 and its OMP immunogen induced mild to moderate inflammatory and degenerative changes which may potentially interfere with fertilization through hormonal imbalances and cause temporary loss of fertility in infected does.

Interleukin-18 does not modulate the acute-phase response

IL-18 is a pro-inflammatory cytokine of the IL-1 family and it induces IL-1, TNF, and IL-6, all of which are endogenous pyrogens. The pyrogenic properties of recombinant IL-18 were studied in a rabbit model of fever. rIL-18 did not cause fever when injected intravenously into rabbits. Furthermore, the ability of rIL-18 to modulate other components of the acute-phase response was assessed. rIL-18 did not induce leukocytosis, or changes of circulating concentrations of lipoproteins and corticosterone in mice. In conclusion, rIL-18 is not able to induce a febrile response in rabbits and does not modulate the acute-phase response in mice.

Review: Evidence against the hypothesis that antibodies to the inner core of lipopolysaccharides in antisera raised by immunization with enterobacterial deep-rough mutants confer broad-spectrum protection during Gram-negative bacterial sepsis

Antisera to rough enterobacterial mutants of chemotypes Ra, Rc, and Re have been reported to confer broad-spectrum protection against wild-type smooth strains. It has been hypothesized that binding and neutralization of lipopolysaccharides (LPS) by antibodies to common core epitopes underlies such protection. This review summarizes experiments by our laboratory and others that do not confirm this concept and proposes reasons for the divergent results. Studies indicating broad-spectrum protection by rough-mutant antisera often had defects in experimental design or methodology. These include the failure: (i) to use matched pre- and postimmune sera from the same donors to control for variable protective activity of normal sera; (ii) to exclude the role of natural and polyclonally stimulated antibodies with proven protective activity against the infecting bacterial strain (e.g. O-specific, capsular, Pseudomonas exotoxin A); (iii) to exclude protective effects of acute-phase serum factors; (iv) to exclude protective effects of endotoxin contamination after adsorption or fractionation of antibody preparations; (v) to use non-boiled bacteria and LPS not subjected to acid-hydrolysis or gel-fractionation, and to exclude nonspecific adsorption, to demonstrate physiologically meaningful binding of rough-mutant antibodies to smooth enterobacteria and their LPS.

Identification of OprF as a complement component C3 binding acceptor molecule on the surface of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a versatile opportunistic pathogen that can cause devastating persistent infections. Complement is a highly conserved pathway of the innate immune system, and its role in the first line of defense against pathogens is widely appreciated. One of the earliest events in the complement cascade is the conversion of C3 to C3a and C3b, the latter typically binds to one or more acceptor molecules on the pathogen surface. We previously demonstrated that complement C3b binding acceptors exist on the P. aeruginosa surface. In the current study, we utilized either C3 polyclonal or C3b monoclonal antibodies in a far-Western technique followed by mass spectroscopy to identify the C3b acceptor molecule(s) on the P. aeruginosa surface. Our data provide evidence that OprF (an outer membrane porin, highly conserved in the Pseudomonadaceae) binds C3b. An oprF-deficient P. aeruginosa strain exhibits reduced C3 deposition compared to the wild type. We observed reduced internalization of oprF-deficient bacteria by neutrophils after opsonization compared with wild-type P. aeruginosa. Heterologous expression of OprF significantly enhanced C3b binding and increased serum-mediated bactericidal effects in complement-susceptible Escherichia coli. Furthermore, the predicted secondary structure of the C-terminal, surface-exposed region of OprF has high structural identity to the OmpA domain of several other Gram-negative bacteria, one of which is known to bind C3b. Therefore, these findings provide new insights into the biology of complement interactions with P. aeruginosa and other Gram-negative bacteria.

Temporal changes in concentrations of serum amyloid-A and haptoglobin and their associations with weight gain in neonatal reindeer calves

Age-related changes in serum concentrations of two acute phase proteins (APPs), haptoglobin (Hp) and serum amyloid-A (SAA) were investigated in newborn reindeer calves. Repeated blood samples were obtained from 51 reindeer calves at ages 0-32 days (2-4 samples from each calf). An increase of SAA concentrations was observed during the first 2 weeks of life. However, by the end of the observation period, SAA concentrations had decreased to levels below those of the first week. Serum Hp concentrations increased throughout the observation period. SAA concentrations in the second week had a negative association with weight gain during the entire study period (4 months). These time-related changes in APP concentrations suggest that these proteins have a role in the defence and adaptation mechanisms of newborn reindeer calves. Possible reasons for these changes include the presence of APP mediators in the colostrum, exposure to environmental pathogens after birth and age-related changes in hepatic synthesis of APP.

Comparative aspects of blood coagulation

Blood coagulation is a basic physiological defense mechanism that occurs in all vertebrates to prevent blood loss following vascular injury. In all species the basic mechanism of clot formation is similar; when endothelium is damaged a complex sequence of enzymatic reactions occurs that is localized to the site of trauma and involves both activated cells and plasma proteins. The reaction sequence is initiated by the expression of tissue factor on the surface of activated cells and results in the generation of thrombin, the most important enzyme in blood clot formation. Thrombin converts soluble fibrinogen, via soluble fibrin monomers, into the insoluble fibrin that forms the matrix of a blood clot as well as exerting positive-feedback regulation that effectively promotes additional thrombin generation that facilitates the rapid development of a thrombus. Both spontaneous and trauma-induced haemorrhagic episodes can develop in all mammals with inherited or acquired abnormalities in one or more of the coagulant proteins. Experimental studies with plasma from a wide range of species have led to the conclusion that there are extensive differences in the rates of thrombin generation and fibrin formation among species. However, current evidence suggests that at least some of these quantitative differences are likely due to the use of non-species specific laboratory reagents. Although the individual proteins involved in the procoagulant pathways exhibit similar functions in all animals, differences in amino acid sequence cause incomplete homology and varying degrees of immunological cross-reactivity for the same protein across species.

Endogenous leukemia inhibitory factor attenuates endotoxin response

Leukemia inhibitory factor (LIF) is induced in inflammation and likely plays a regulatory role. Using LIF-deficient mice (LIF-/-), we report here that endogenous LIF has a protective role in endotoxic shock and host defence. LIF-/- mice have heightened sensitivity to LPS in a LPS/D-galactosamine (D-Gal) sensitization model compared to wild-type mice (LIF+/+), enhanced thrombocytopenia and leukopenia, with increased hepatic necrosis, neutrophil sequestration in the lung and accelerated mortality. These findings correlated with 10-fold higher tumour necrosis factor-alpha (TNFalpha) and interleukin-6 (IL-6) serum levels and reduced IL-10 production in LIF-/- mice in response to LPS. Therefore, endogenous LIF attenuates the endotoxic shock response, enhances the expression of basal acute phase proteins and IL-10 production, which downregulates TNFalpha synthesis and release and thereby confers partial protection to endotoxemia.

Dose Dependency and Individual Variability of the Lipopolysaccharide-Induced Bovine Acute Phase Protein Response

In order to investigate the dose dependency and the individual variability of the lipopolysaccharide (LPS)-induced acute phase protein response in cattle, 8 nonlactating, nonpregnant Danish Holstein cows were challenged 3 times each by intravenous injection of increasing doses (10, 100, and 1000 ng/kg, consecutively) of Escherichia coli LPS with 3-wk intervals. All 3 LPS doses resulted in a rapid increase in serum concentrations of haptoglobin and serum amyloid A (SAA) and a decrease in serum concentrations of albumin in all 8 cows. Serum concentrations of acute phase proteins (APP) remained altered for several days after each LPS injection, and their increase or decrease was significantly related to LPS dose. In addition to dose dependency, the response was also dependent on the individual, as APP concentrations differed significantly among cows. To compare APP production in 2 consecutive challenges, individual APP levels after the challenge with 100 ng LPS/kg were correlated to levels attained after the challenge with 1000 ng LPS/kg. Serum amyloid A concentrations correlated between the 2 challenges, whereas haptoglobin concentrations tended to correlate; no correlation could be demonstrated between SAA and haptoglobin concentrations in either of the challenges, which suggests that the synthesis of haptoglobin and SAA are regulated in different ways. In conclusion, cattle are highly susceptible to LPS, as very low doses of LPS elicited acute phase albumin, SAA, and haptoglobin responses. Concentrations of APP not only reflect the magnitude of LPS exposure but are also influenced by the ability of the individual cow to mount an acute phase response. The ability to produce SAA and haptoglobin may be an innate characteristic of the individual, as responses in consecutive challenges were quantitatively similar.

Proinflammatory Cytokines in the Treatment of Bacterial and Fungal Infections

Mortality due to severe bacterial infections has not been markedly effected by the introduction of new antimicrobial drugs over the last 30-40 years. This has emphasized the need for development of new therapeutic strategies to combat sepsis. The outcome of an infection depends on two factors: the growth of the microorganisms (including the effect of antibacterial drugs), and the host's defensive response to the invading organism. It is known that injection of bacterial products into experimental animals leads to enhanced nonspecific resistance to a variety of microorganisms. The discovery of the specific mediators responsible for modulation of host defense has created new possibilities for the development of alternative treatment strategies. Molecules such as interleukins, interferons, tumor necrosis factors and hematopoietic growth factors have become available in recombinant form, and their therapeutic potential in various infectious diseases has been tested in various experimental models of infections. Initial data in various patient groups indicate that adjunctive therapy with recombinant proinflammatory cytokines may have beneficial effects in the treatment of bacterial and fungal infections.

Excessive increase of serum interleukin 6 jeopardizes host defense against multi-bacterial infection

Serum interleukin 6 (IL-6) is elevated among patients who have undergone surgery, trauma, and thermal injury. It is well known that the greater the increase of serum IL-6, the higher the incidence of post-injury morbidity and mortality is. However, it has not been determined whether the physiological effects of IL-6 increase the rate of morbidity and mortality or if IL-6 is just a bystander that only indicates the severity of the injury. To elucidate this, we planned to investigate the effect of IL-6 on a multi-bacterial infection, one of the most frequent post-injury complications. CDF1 male mice were administered recombinant human IL-6 (hIL-6) continuously at a dose of 0, 1, or 10 microg/day. The mice then underwent cecal ligation without puncture that induced slow multi-bacterial infection. The survival rate of mice receiving 10 microg/day of hIL-6 was significantly lower (38.5%) than the rate of those receiving 0 (83.3%) or 1 (92.3%) microg/day of hIL-6. The result of this study showed that only excessive increases in serum IL-6, to levels that were observed among patients who underwent severe injury or extensive surgery with high incidence of post-injury infection, jeopardize the host's defense against bacterial infection.

Production of granulocyte colony-stimulating factor in the nonspecific acute phase response enhances host resistance to bacterial infection

Mice mounting an acute phase response, induced by sterile inflammation after a single s.c. injection of casein 24 h beforehand, were remarkably protected against lethal infection with Gram-positive or Gram-negative bacteria. This was associated with enhanced early clearance of bacteremia, greater phagocytosis and oxidative burst responses by neutrophils, and enhanced recruitment of neutrophils into tissues compared with control, nonacute phase mice. Casein-induced inflammation was also associated with increased concentrations of G-CSF in serum, and administration of neutralizing Ab to this cytokine completely abrogated protection against Escherichia coli infection after casein pretreatment. Injection of recombinant murine G-CSF between 3 and 24 h before infection conferred the same protection as casein injection. In contrast, the casein-induced acute phase response affected neither serum values of TNF-alpha, IL-1 beta, or IL-6 after E. coli infection nor susceptibility to LPS toxicity. Furthermore, protection against infection was unaffected in IL-1R knockout mice, which have deficient acute phase plasma protein responses, or after nonspecific inhibition of acute phase protein synthesis by D-galactosamine or specific depletion of complement C3 by cobra venom factor. Increased production of G-CSF in the acute phase response is thus a key physiological component of host defense, and pretreatment with G-CSF to prevent bacterial infection in at-risk patients now merits further study, especially in view of increasing bacterial resistance to antibiotics.

Development of a clinical syndrome resembling haemorrhagic septicaemia in the buffalo following intravenous inoculation of Pasteurella multocida serotype B:2 endotoxin and the role of tumour necrosis factor-alpha

Clinical changes and acute phase responses, including tumour necrosis factor-alpha (tnfalpha), in six buffalo calves were examined following intravenous inoculation of a bolus of endotoxin (1 microg kg(-1) bodyweight in 10 ml of phosphate-buffered saline [ pbs ]) extracted from Pasteurella multocida serotype B:2, the bacterium responsible for haemorrhagic septicaemia (hs) in Asia. Endotoxin injection caused a rapid onset of clinical signs characterised by dullness, sternal recumbency, elevated rectal temperatures, excessive salivation and dyspnoea that lasted for up to 12 hours post-inoculation (p.i.). Serum concentrations of tnfalpha rose within 1 hour p.i. to reach peak values ranging between 8 and 140 ng ml(-1) at 1-2 hours p.i. and then declined rapidly to baseline levels 3-5 hours p.i. Endotoxin injection induced other acute phase changes, including a rapid leucopenia and reductions in the serum concentrations of iron and zinc and a delayed but prolonged increase in haptoglobin from 12 hours p.i. that reached a plateau from about 60 hours p.i. Three control calves injected with 10 ml pbs showed no clinical or blood compositional changes. By reproducing key signs of hs the work confirms a pivotal role of endotoxin in the pathogenesis of hs and emphasises the exquisite sensitivity of the buffalo to P multocida endotoxin.

Role of the hepatic function in the development of the pyrogenic tolerance to muramyl dipeptide

We have demonstrated that the hepatic function may have an important role in the development of tolerance to the pyrogenic effect induced by endotoxin. To further investigate if the role of the hepatic function in the development of tolerance also extends to that induced by other pyrogenic stimuli, we investigated the effect of galactosamine, a specific inhibitor of the hepatic protein synthesis, on the development of tolerance to the pyrogenic effect induced by muramyl dipeptide (MDP) in rats. Pyrogenic tolerance was observed after the second intravenous or intraperitoneal injection of MDP (500 microgram/kg), 24 h after the first injection, similar to what was observed with endotoxin. Pyrogenic tolerance was abolished when galactosamine (300 mg/kg ip) was injected simultaneously with MDP (500 microgram/kg iv) on the first day. When uridine (600 mg/kg ip) was administered simultaneously with galactosamine (300 mg/kg ip) and the first injection of MDP (500 microgram/kg ip), pyrogenic tolerance was again observed after the second injection of the peptidoglycan. In conclusion, the hepatic function may not be important only for the development of tolerance to endotoxin, but also to a totally different pyrogenic stimulus such as MDP.

Mechanism of high susceptibility of iron-overloaded mouse to Vibrio vulnificus infection

Vibrio vulnificus produces fulminant septicemia in humans with underlying conditions, particularly those with diseases that elevate the iron level. The effect of a high iron level on the virulence of V. vulnificus was therefore investigated in mice treated with iron dextran. The mice loaded with iron became highly susceptible to V. vulnificus infection, the LD50 (50% lethal dose) decreased five logs when infected per peritoneum. However, when infected via the oral route, the LD50 was affected little unless the mouse was treated with an additional drug such as cyclophosphamide or D-galactosamine. Mice with or without iron-overloading died when the bacterial concentration in the blood reached 10(5) cfu/ml or above. Iron increased the growth rate of the bacteria, both inside and outside of the animal, quickly reaching a lethal concentration in the iron-overloaded mouse. V. vulnificus, grown with or without the addition of iron, showed strong cytotoxicity on the isolated cells or within the animal at high bacterial concentration. Iron overload stimulated the production of tumor necrosis factor alpha (TNF-alpha), a major factor of septic shock, in mice upon infection with the bacteria, probably caused by the endotoxin; however, the neutrophils, whose migration is effected by TNF-alpha, appeared to be less active. Taken together, the major virulence factor of V. vulnificus appeared to be the accelerated growth of bacteria to quickly reach the lethal level and the lower activity of immune cells including neutrophil as a result of iron-overloading. These two effects manifest other virulence factors, the host's as well as bacterial. Such factors, other than TNF-alpha stimulated by the endotoxin, enhanced cytotoxicity, which kills the host cells including the host's immune cells.

Effect of heat stress on LPS-induced febrile response in D-galactosamine-sensitized rats

We have previously reported that heat conditioning augments lipopolysaccharide (LPS)-induced fever in rats, which is accompanied by an accumulation of heat shock protein (HSP) in the liver and the reduction of the plasma level of tumor necrosis factor (TNF-alpha) (Kluger MJ, Rudolph K, Soszynski D, Conn CA, Leon LR, Kozak W, Wallen ES, and Moseley PL. Am J Physiol Regulatory Integrative Comp Physiol 273: R858-R863, 1997). In the present study we have tested whether inhibition of protein synthesis in the liver can reduce the effect of this heat conditioning on the LPS-induced febrile response in the rat. D-galactosamine (D-gal) was used to selectively inhibit liver protein synthesis. D-gal (500 mg/kg) or PBS as control was administered intraperitoneally 1 h before heat stress. LPS (50 microg/kg ip) was injected 24 h post-heat exposure. Treatment with D-gal blunted the febrile response to LPS. Moreover, heat-conditioned rats treated first with D-gal and subsequently with LPS demonstrated a profound fall in core temperature 10--18 h post-LPS. A significant increase of serum TNF-alpha accompanied this effect of D-gal on fever. Heat-conditioned animals receiving D-gal showed an inhibition in inducible HSP-70 in the liver. These data support the role of hepatic function in modulating the febrile response to LPS.

Involvement of the acute phase protein alpha 1-acid glycoprotein in nonspecific resistance to a lethal gram-negative infection

Resistance to gram-negative infection can be induced by pretreating animals with several agents such as turpentine and interleukin (IL)-1. Because these agents are powerful inducers of acute phase proteins, we wondered whether these proteins, more particularly alpha(1)-acid glycoprotein (alpha(1)-AGP), are involved in nonspecific resistance to infection. Turpentine and IL-1 protect completely against a lethal challenge of Klebsiella pneumoniae when given 48 and 12-48 h before the challenge, respectively. alpha(1)-AGP induction in the serum reached peak values 48 h after turpentine and 12-48 h after IL-1 injection. Administration of alpha(1)-AGP, 2 h before a challenge of K. pneumoniae, significantly increased the survival. Numbers of bacteria cultured from blood and organs were significantly lower in mice pretreated with a protective dose of turpentine, IL-1, or alpha(1)-AGP. These data suggest that alpha(1)-AGP is a possible mediator in turpentine- or IL-1-induced protection because time points of maximal induction of alpha(1)-AGP by turpentine or IL-1 and of optimal protection by alpha(1)-AGP coincide. Transgenic overexpression of rat alpha(1)-AGP protected mice from a K. pneumoniae infection. Bacterial counts in blood and organs were significantly lower in transgenic mice, and only in control mice were large necrotic areas, apoptosis, and blood clots observed in the spleen. Our data suggest that alpha(1)-AGP prevents gram-negative infections and may be an essential component in nonspecific resistance to infection.

Intracerebroventricular injection of anti-Fas activates the hypothalamus-pituitary-adrenal axis and induces peripheral interleukin-6 and serum amyloid A in mice: comparison with other ligands of the tumor necrosis factor/nerve growth factor receptor superfamily

Fas is a receptor of the tumor necrosis factor (TNF)/ nerve growth factor (NGF) receptor superfamily that mediates apoptosis and some inflammatory changes. As the central administration of TNF is known to activate the hypothalamus-pituitary-adrenal axis (HPAA) and to induce peripheral responses including induction of serum interleukin (IL)-6 and serum amyloid A (SAA), we investigated the effects of intracerebroventricular (i.c.v.) administration of agonist anti-Fas monoclonal antibody Jo2. Centrally administered anti-Fas (1 microg/mouse, i.c.v.) induced elevated levels of corticosterone, IL-6, and SAA comparable to those observed after i.c.v. administration of recombinant murine TNF. On the other hand, administration of murine NGF did not elevate serum corticosterone or IL-6, but induced SAA. Thus, Fas can trigger a centrally mediated anti-inflammatory response (HPAA activation) and induce a peripheral acute-phase response comparable to that induced with TNF, whereas NGF induces only acute-phase proteins.

Proinflammatory cytokines and treatment of disease

Bacterial infections in the immunocompromised host cause considerable mortality, and even recently developed antimicrobial strategies often fail to cure these infections, especially in granulocytopenic patients. Cytokines and hematopoietic growth factors have been shown to stimulate host defense mechanisms in vitro and in vivo. The possible role of the proinflammatory cytokines interleukin (IL)-1, tumor necrosis factor-alpha, IL-6, and IL-8 as modulators of host resistance to bacterial infections is discussed. Interleukin-1 has been effective in various animal models of potentially lethal bacterial infection, even during severe granulocytopenia. The protective mechanism of IL-1 may be mediated by downregulation of cytokine receptors and cytokine production and induction of acute phase proteins. Moreover, in subacute and chronic infections IL-1 interferes with microbial outgrowth via mechanisms that have only been partly elucidated.

Modulation of a cardiogenic shock inducible RNA by chemical stress: adapt73/PigHep3

BACKGROUND

Understanding how mammalian cells respond to stress is important in the study, detection, and therapy of stress-related disorders. We have been studying cellular stress response in hamster HA-1 cells by using an adaptive response model. HA-1 cells respond to a minimally toxic "pretreatment" dose of hydrogen peroxide by synthesizing RNAs and proteins that protect them against subsequent exposure to a higher cytotoxic concentration of peroxide. The purpose of our studies is to identify and partially characterize any mRNA whose steady state level is significantly modulated during adaptation.

METHODS

HA-1 cells were exposed to a pretreatment dose of hydrogen peroxide and RNA extracted. The differential display technique was used to identify modulated mRNAs. The effects of calcium ionophore A23187 and cis (II)-platinum on the modulation of mRNA from HA-1 cells and A23187 on the modulation of mRNAs from human IMR-90 cells were also determined.

RESULTS

One of the RNAs induced by a pretreatment concentration of hydrogen peroxide was designated adapt73. The size of the induced adapt73 RNA was determined to be 2.1 kb. Induction of adapt73 was maximal 5 hours after peroxide treatment, but elevated levels were still obvious at 10 hours. This induction was not specific to oxidative stress, because other stress agents including as (II)-platinum and especially calcium ionophore A23187 also induced adapt73 mRNA levels. Partial sequencing of adapt73 and a subsequent GenBank homology search revealed extensive homology to a novel RNA from pig, designated PigHep3, that was identified as a cardiogenic shock response gene from liver in pigs that were undergoing resuscitation after circulatory shock. Homology to a completely sequenced but uncharacterized human homolog was also found. Using a partially sequenced expressed sequence tag (EST) human clone to adapt73, we probed Northern blots containing RNA from IMR-90 human fibroblasts treated with A23187. A strongly induced human adapt73 mRNA homolog was observed, almost identical in size to its hamster homolog. In vitro transcription and translation of the human EST clone revealed a translatable Adapt73 protein product.

CONCLUSIONS

These data indicate that adapt73/PigHep3 RNA can be induced by multiple chemical stress, that these inductions occur under protective or adaptive response conditions, that there is an inducible human homolog to adapt73, and suggest that adapt73 may be an important physiologic mediator of organ and cellular shock response in mammals.

Interleukin-1 (IL-1)-induced resistance to bacterial infection: role of the type I IL-1 receptor

Pretreatment with a low dose of recombinant human interleukin-1 beta (IL-1) (3 to 30 micrograms/kg) 24 h before a lethal Pseudomonas aeruginosa infection prolongs survival in neutropenic mice. We investigated the role of the type I IL-1 receptor (IL-1RI) and IL-1RII in this IL-1-induced protection by using a specific IL-1 receptor antagonist (IL-1-Ra), which blocks effects mainly via IL-1RI. Pretreatment with IL-1Ra before IL-1 partially blocked the IL-1-induced enhanced survival, whereas pretreatment with a specific neutralizing monoclonal antibody to IL-1RI (35F5) eliminated the IL-1 induced protection. The nonapeptide fragment 163-171 of recombinant human IL-1 beta, which possesses the immunoadjuvant but not the inflammatory effect of the entire molecule via a non-receptor-mediated signal transduction process, did not reproduce the IL-1-induced protection. IL-1-induced protection was associated with reduced serum aspartate aminotransferase and alanine aminotransferase concentrations in conjunction with ameliorated histopathology of the liver. These findings may be due to reduced cytokine production and cytokine sensitivity of target cells after infection. We conclude that the IL-1-induced nonspecific resistance to infection is mediated by cells bearing IL-1RI and is associated with a reduction of liver damage.

Pro-inflammatory cytokines in a ruminant model: pathophysiological, pharmacological, and therapeutic aspects

Infection evokes complex changes which are thought to be caused by production and release of pro-inflammatory cytokines such as tumour necrosis factor (TNF-alpha), interferons (INFs), and interleukins (ILs). They regulate local inflammatory reactions, but may also gain access to the circulation and induce systemic effects collectively known as the Acute Phase Response. To improve our understanding of the pathophysiology of pro-inflammatory cytokines in ruminants, studies have been performed with TNF-alpha, IL1-alpha/beta, and IFN-alpha/ gamma as well as with cytokine-inducers in dwarf goats. In relation to therapy, the following aspects may be of interest: a) Cytokine therapy given before or just after microbial challenge induces in vivo antimicrobial activity. Moreover, cytokines potentiate in vivo the antimicrobial activity of antibiotics, b) Cytokines may act as biological response modifiers for enhancing specific immunity to vaccines, and c) Cytokines may affect drug absorption, disposition, and metabolite formation in disease states. Although studies of the actions of corticosteroids, nonsteroidal anti-inflammatory and antipyretic agents, antibodies to endotoxin, TNF-alpha, or IL-1, synthetic E. coli lipid A precursors, hydrazine, isoniazid, chloroquine, polymyxin B, bicyclic imidazoles, hydroxamates, and tyrosine kinase inhibitors in endotoxaemic animals have shed further light on inflammatory processes, clinical studies in this field are urgently required to evaluate their beneficial effect.

Interleukin-1 and related pro-inflammatory cytokines in the treatment of bacterial infections in neutropenic and non-neutropenic animals

Bacterial infections in the immunocompromized host cause considerable mortality, and even the recently developed antimicrobial strategies often fail to cure these infections, especially in granulocytopenic patients. Cytokines and hematopoietic growth factors have been shown to stimulate host defense mechanisms in vitro and in vivo. We discuss the possible role of the pro-inflammatory cytokines interleukin-1, tumor necrosis factor-alpha, interleukin-6 and interleukin-8 as modulators of host resistance to bacterial infections. Interleukin-1 has been shown effective in various animal models of potentially lethal bacterial infection, even during severe granulocytopenia. The protective mechanism of interleukin-1 may be mediated via downregulation of cytokine receptors and cytokine production, and via induction of acute phase proteins. Moreover, in subacute and chronic infections interleukin-1 interferes with microbial outgrowth, via mechanisms that have only been partially elucidated.

Roles of tumor necrosis factor alpha, granulocyte-macrophage colony-stimulating factor, platelet-activating factor, and arachidonic acid metabolites in interleukin-1-induced resistance to infection in neutropenic mice

Treatment with a single low dose (80 to 800 ng) of interleukin-1 (IL-1) 24 h before a lethal bacterial challenge in granulocytopenic and in normal mice enhances nonspecific resistance. The mechanism behind this protection has only partially been elucidated. Since IL-1 induces production of tumor necrosis factor alpha (TNF-alpha), granulocyte-macrophage colony-stimulating factor (GM-CSF), platelet-activating factor (PAF), and arachidonic acid metabolites, we investigated the potential role of these substances in IL-1-induced protection. Low doses of murine TNF-alpha but not of human TNF-alpha enhanced survival, suggesting an effect via the type II TNF receptor rather than the type I TNF receptor, which has little species specificity. In line with this TNF-alpha-induced protection from infection, pretreatment with a low dose of a rat anti-murine TNF-alpha monoclonal antibody tended to inhibit IL-1-induced protection, suggesting a role of TNF-alpha as a mediator of IL-1-induced enhanced resistance to infection. Pretreatment with higher doses of anti-TNF-alpha, however, showed a dose-related protective effect per se, which could be further enhanced by a suboptimal dose of IL-1. A combination of optimal doses of anti-TNF-alpha and IL-1 produced an increase in survival similar to that produced by separate pretreatments. This lack of further enhancement of survival by combined optimal pretreatments suggests a similar mechanism of protection, most likely attenuation of deleterious effects of overproduced proinflammatory cytokines like TNF-alpha during lethal infection. Pretreatment with different doses of GM-CSF before a lethal Pseudomonas aeruginosa challenge in neutropenic mice did not enhance survival. Different doses of WEB 2170, a selective PAF receptor antagonist, of MK-886, a selective inhibitor of leukotriene biosynthesis, or of several cyclooxygenase inhibitors did not reduce the protective effect of IL-1 pretreatment. We conclude that IL-1-induced nonspecific resistance is partially mediated by induction of TNF-alpha and not by GM-CSF, PAF, and arachidonic acid metabolites. The mechanism of action of IL-1 seems to be similar to that of anti-TNF-alpha.