Macrophage inflammatory protein-1beta (MIP-1beta) produced endogenously in brain during E. coli fever in rats

Altered expression of inflammation-associated molecules in striatum: an implication for sensitivity to heavy ion radiations

Background and objective

Heavy ion radiation is one of the major hazards astronauts face during space expeditions, adversely affecting the central nervous system. Radiation causes severe damage to sensitive brain regions, especially the striatum, resulting in cognitive impairment and other physiological issues in astronauts. However, the intensity of brain damage and associated underlying molecular pathological mechanisms mediated by heavy ion radiation are still unknown. The present study is aimed to identify the damaging effect of heavy ion radiation on the striatum and associated underlying pathological mechanisms.

Materials and methods

Two parallel cohorts of rats were exposed to radiation in multiple doses and times. Cohort I was exposed to 15 Gy of 12C6+ ions radiation, whereas cohort II was exposed to 3.4 Gy and 8 Gy with 56Fe26+ ions irradiation. Physiological and behavioural tests were performed, followed by 18F-FDG-PET scans, transcriptomics analysis of the striatum, and in-vitro studies to verify the interconnection between immune cells and neurons.

Results

Both cohorts revealed more persistent striatum dysfunction than other brain regions under heavy ion radiation at multiple doses and time, exposed by physiological, behavioural, and 18F-FDG-PET scans. Transcriptomic analysis revealed that striatum dysfunction is linked with an abnormal immune system. In vitro studies demonstrated that radiation mediated diversified effects on different immune cells and sustained monocyte viability but inhibited its differentiation and migration, leading to chronic neuroinflammation in the striatum and might affect other associated brain regions.

Conclusion

Our findings suggest that striatum dysfunction under heavy ion radiation activates abnormal immune systems, leading to chronic neuroinflammation and neuronal injury.

Prior viral illness increases heat stroke severity in mice

NEW FINDINGS

What is the central question of this study? We hypothesized that prior illness would increase the susceptibility to and severity of heat stroke (HS). What is the main finding and its importance? We provide the first experimental evidence, using a mouse model of HS, that recent viral illness increases the severity of HS. Our data indicate that this effect is not attributable to the exacerbation of hyperthermia but is a consequence of ongoing coagulation and systemic inflammatory reactions. Our data suggest that measurement of platelets, cytokines and chemokines before heat exposure might be indicative of susceptibility to HS, with coagulation and inflammation being potential targets for intervention that could improve recovery.

ABSTRACT

It is hypothesized that prior illness exacerbates heat stroke (HS) in otherwise healthy organisms by augmenting hyperthermia during heat exposure or deactivating cellular pathways that protect against organ injury. To test these hypotheses, we injected telemetered male C57BL/6J mice with lipopolysaccharide (LPS; 50 µg kg-1 i.p.) or polyinosinic:polycytidylic acid (PIC; 100 µg i.p.) as a bacterial or a viral mimic, respectively, with saline (SAL; equivalent volume) as a control. Mice recovered for 48 or 72 h before HS (maximal core temperature = 42.4°C). Platelet counts, cytokines, chemokines and organ injury were determined 48 or 72 h after injection (without heating) or at maximal core temperature and at 1 day of recovery from HS. In the absence of heat, PIC induced more robust signs of sickness and increased cytokines and chemokines (TNF-α, RANTES, IP-10 and MIP-1β) at 48 h, which was not observed with LPS (P < 0.05). Responses of both groups recovered by 72 h, although low platelet counts persisted after PIC (P < 0.05). Heat-induced hyperthermia was similar among mice injected with SAL, LPS and PIC; however, PIC-injected mice displayed more severe responses during recovery from HS, with reduced survival (48 h, 70 versus 100%; P < 0.05), deeper and longer post-HS hypothermia, greater reductions in platelets, elevated RANTES, IP-10, IL-6 and TNF-α and greater duodenal injury (P < 0.05). By 72 h, survival from HS was no longer reduced in PIC-injected mice, although hypothermia, the reduction in platelets and elevated cytokines persisted. Our data indicate that prior illness exacerbates the severity of HS in the absence of signs of illness at the time of heat exposure and suggest that this is attributable to persistent coagulation and inflammatory reactions that might be targets for intervention to improve recovery.

Consequences of Vitamin A Deficiency: Immunoglobulin Dysregulation, Squamous Cell Metaplasia, Infectious Disease, and Death

Vitamin A is an important regulator of immune protection, but it is often overlooked in studies of infectious disease. Vitamin A binds an array of nuclear receptors (e.g., retinoic acid receptor, peroxisome proliferator-activated receptor, retinoid X receptor) and influences the barrier and immune cells responsible for pathogen control. Children and adults in developed and developing countries are often vitamin A-deficient or insufficient, characteristics associated with poor health outcomes. To gain a better understanding of the protective mechanisms influenced by vitamin A, we examined immune factors and epithelial barriers in vitamin A deficient (VAD) mice, vitamin D deficient (VDD) mice, double deficient (VAD+VDD) mice, and mice on a vitamin-replete diet (controls). Some mice received insults, including intraperitoneal injections with complete and incomplete Freund’s adjuvant (emulsified with PBS alone or with DNA + Fus-1 peptide) or intranasal inoculations with Sendai virus (SeV). Both before and after insults, the VAD and VAD+VDD mice exhibited abnormal serum immunoglobulin isotypes (e.g., elevated IgG2b levels, particularly in males) and cytokine/chemokine patterns (e.g., elevated eotaxin). Even without insult, when the VAD and VAD+VDD mice reached 3–6 months of age, they frequently exhibited opportunistic ascending bacterial urinary tract infections. There were high frequencies of nephropathy (squamous cell hyperplasia of the renal urothelium, renal scarring, and ascending pyelonephritis) and death in the VAD and VAD+VDD mice. When younger VAD mice were infected with SeV, the predominant lesion was squamous cell metaplasia of respiratory epithelium in lungs and bronchioles. Results highlight a critical role for vitamin A in the maintenance of healthy immune responses, epithelial cell integrity, and pathogen control.

Neuroprotective dobutamine treatment upregulates superoxide dismutase 3, anti-oxidant and survival genes and attenuates genes mediating inflammation

Background

Labor subjects the fetus to an hypoxic episode and concomitant adrenomodullary catecholamine surge that may provide protection against the hypoxic insult. The beta1-adrenergic agonist dobutamine protects against hypoxia/aglycemia induced neuronal damage. We aimed to identify the associated protective biological processes involved.

Results

Hippocampal slices from 6 days old mice showed significant changes of gene expression comparing slices with or without dobutamine (50 mM) in the following two experimental paradigms: (1) control conditions versus lipopolysacharide (LPS) stimulation and (2) oxygen–glucose deprivation (OGD), versus combined LPS/OGD. Dobutamine depressed the inflammatory response by modifying the toll-like receptor-4 signalling pathways, including interferon regulatory factors and nuclear factor κ B activation in experimental paradigm 1. The anti-oxidant defense genes superoxide dismutase 3 showed an upregulation in the OGD paradigm while thioredoxin reductase was upregulated in LPS paradigm. The survival genes Bag-3, Tinf2, and TMBIM-1, were up-regulated in paradigm 1. Moreover, increased levels of SOD3 were verified on the protein level 24 h after OGD and control stimulation in cultures with or without preconditioning with LPS and dobutamine, respectively.

Conclusions

Neuroprotective treatment with dobutamine depresses expression of inflammatory mediators and promotes the defense against oxidative stress and depresses apoptotic genes in a model of neonatal brain hypoxia/ischemia interpreted as pharmacological preconditioning. We conclude that beta1-adrenoceptor activation might be an efficient strategy for identifying novel pharmacological targets for protection of the neonatal brain.

Electronic supplementary material

The online version of this article (10.1186/s12868-018-0415-2) contains supplementary material, which is available to authorized users.

Involvement of PGE2and RANTES inStaphylococcus aureus-induced fever in rats

This study investigated the involvement of prostaglandins and regulated on activation, normal T cell expressed and secreted (RANTES), in fever induced by live Staphylococcus aureus (no. 25923, American Type Culture Collection) injection in rats. S. aureus was injected intraperitoneally at 109, 1010, and 2 × 1010colony-forming units (CFU)/cavity, and body temperature (Tb) was measured by radiotelemetry. The lowest dose of S. aureus induced a modest transient increase in Tb, whereas the two higher doses promoted similar long-lasting and sustained Tbincreases. Thus, the 1010CFU/cavity dose was chosen for the remaining experiments. The Tbincrease induced by S. aureus was accompanied by significant decreases in tail skin temperature and increases in PGE2levels in the cerebrospinal fluid (CSF) and hypothalamus but not in the venous plasma. Celecoxib (selective cyclooxygenase-2 inhibitor, 2.5 mg/kg po) inhibited the fever and the increases in PGE2concentration in the CSF and hypothalamus induced by S. aureus. Dipyrone (120 mg/kg ip) reduced the fever from 2.5 to 4 h and the PGE2increase in the CSF but not in the hypothalamus. S. aureus increased RANTES in the peritoneal exudate but not in the CSF or hypothalamus. Met-RANTES (100 μg/kg iv), a chemokine (C-C motif) receptor (CCR)1/CCR5 antagonist, reduced the first 6 h of fever induced by S. aureus. This study suggests that peripheral (local) RANTES and central PGE2production are key events in the febrile response to live S. aureus injection. As dipyrone does not reduce PGE2synthesis in the hypothalamus, it is plausible that S. aureus induces fever, in part, via a dipyrone-sensitive PGE2-independent pathway.

Neuropeptide FF receptor antagonist, RF9, attenuates the fever induced by central injection of LPS in mice

The endogenous opioid system has been found to be involved in the fever caused by lipopolysaccharide (LPS). Neuropeptide FF (NPFF, FLFQPQRF-NH(2)) is an endogenous peptide known to modulate opioid activity, mainly in the central nervous system. Therefore, those data suggested a link between LPS-induced fever and NPFF systems. Using a model of acute neuroinflammation, we sought to determine the effects of NPFF systems on the fever induced by i.c.v. injection of LPS. Coinjected with different doses of NPFF (10 and 30 nmol), the fever of LPS (125 ng) was not modified. Interestingly, the selective NPFF receptors antagonist RF9 (30 nmol) injected into the third ventricle failed to induce significant effect, but it decreased the fever of LPS (125 ng) after cerebral administration in mice. These results suggest that NPFF receptors activation is required for LPS to produce fever. This interaction is the first evidence that NPFF systems participate in the control of acute neuroinflammation in conscious animals.

Intrahypothalamic injection of the HIV-1 envelope glycoprotein induces fever via interaction with the chemokine system

Wasting syndrome is a common complication of HIV infection and is marked by progressive weight loss and weakness, often associated with fever. The mechanisms involved in the pathogenesis of these syndromes are not well defined, and neither are the brain areas involved. The present study tests a new hypothesis: that the preoptic anterior hypothalamus (POAH), the main brain area for thermoregulation and fever, has a role in the pathogenesis of fever induced by glycoprotein 120 (gp120), the surface envelope protein used by the HIV to gain access into immune cells, and that the CXC chemokine receptors (CXCR4) that serve as a coreceptor for HIV entry mediate the effect. A sterilized stainless steel C313G cannula guide was implanted into the POAH, and a biotelemetry system was used to monitor the body temperature (Tb) changes. The administration of gp120 into the POAH induced fever in a dose-dependent manner. To demonstrate possible links between the gp120 and CXCR4 in generating the fever, we pretreated the rats with 1,1'-[1,4-phenylenebis(methylene)]bis[1,4,8,11-tetraazacyclotetradecane] octohydrobromide dihydrate (AMD 3100), an antagonist of stromal cell-derived growth factor (SDF)-1alpha/CXCL12, acting at its receptor, CXCR4, 30 min before administration of gp120. AMD 3100 significantly reduced the gp120-induced fever. The present studies show that the presence of HIV-1 envelope glycoprotein gp120 in the POAH provokes fever via interaction CXCR4 pathway.

CCR1 and CCR5 chemokine receptors are involved in fever induced by LPS (E. coli) and RANTES in rats

This study, besides examining the involvement of CCR1 and CCR5 receptors in the LPS-induced fever (lipopolysaccharide, Escherichia coli) in male Wistar rats, evaluated if RANTES (regulated on activation, normal T cells expressed and secreted) injected into the preoptic area of the anterior hypothalamus (AH/POA) would promote an integrated febrile response via these receptors. Moreover, the effects of selective and non-selective cyclooxygenase blockers on both fever and the level of prostaglandin (PG)E(2) in the cerebrospinal fluid (CSF) after injection of RANTES into the AH/POA were also investigated. Met-RANTES, CCR1 and CCR5 receptor antagonist, reduced LPS-evoked fever dose dependently. RANTES microinjected into the AH/POA increased the rectal temperature of rats dose dependently and caused a significant decrease in the tail skin temperature and an increase (at 2.5 and 5 h) of the levels of PGE(2) in the CSF. Met-RANTES prevented the fever induced by RANTES. Ibuprofen abolished the fever caused by RANTES between 60 min and 2.5 h, and it reduced the temperature until the end of observation period. Celecoxib blocked the RANTES-induced fever, while indomethacin reduced it in the last 60 min of the experimental period. At 2.5 and 5 h all antipyretics brought the CSF PGE(2) level near to the control. These results indicate that CCR1 and CCR5 receptors are involved in the fever induced by systemic LPS and intrahypothalamic RANTES. RANTES promotes an integrated febrile response accompanied by an increase of CSF PGE(2). The inhibitory effects of celecoxib and ibuprofen suggest that PGE(2) was generated via COX-2. As indomethacin dissociates fever and the decrease of PGE(2) level during the RANTES-induced fever, an alternative COX-2-independent pathway or other mechanisms of action of celecoxib and ibuprofen might be considered.

Endotoxin fever in granulocytopenic rats: evidence that brain cyclooxygenase-2 is more important than circulating prostaglandin E2

PGE(2) is a recognized mediator of many fevers, and cyclooxygenase (COX) is the major therapeutic target for antipyretic therapy. The source, as well as the site of action of PGE(2), as an endogenous pyrogen, is widely accepted as being central, but PGE(2) in the circulation, possibly from leukocytes, may also contribute to the development of fever. However, bacterial infections are important causes of high fever in patients receiving myelosuppressive chemotherapy, and such fevers persist despite the use of COX inhibitors. In the study reported here, the febrile response to bacterial LPS was measured in rats made leukopenic by cyclophosphamide. A striking increase in LPS fever occurred in these granulocytopenic rats when compared with febrile responses in normal animals. Unlike LPS fever in normal rats, fever in granulocytopenic rats was neither accompanied by an increase in blood PGE(2) nor inhibited by ibuprofen. Both leukopenic and normal rats showed LPS-induced COX-2-immunoreactivity in cells associated with brain blood vessels. Furthermore, LPS induced an increase of PGE(2) in cerebrospinal fluid. Induction of COX-2-expression and PGE(2) production was inhibited by ibuprofen in normal but not in leukopenic rats. Although the results presented are, in part, confirmatory, they add new information to this field and open a number of important questions as yet unresolved. Overall, the present results indicate that, in contrast to immunocompetent rats, leukocytes and/or other mechanisms other than PGE(2) are implicated in the mechanisms restricting and reducing the enhanced febrile response to endotoxin in immunosuppressed hosts.

CCL3/Macrophage inflammatory protein-1α induces fever and increases prostaglandin E2 in cerebrospinal fluid of rats: Effect of antipyretic drugs

The aim of this study was to investigate whether the increase in body temperature caused by intracerebroventricular (i.c.v.) injection of recombinant mouse CCL3/MIP1alpha [C-C (two adjacent conserved cysteines) ligand 3/macrophage inflammatory protein-1alpha] constitutes solely a hyperthermic response or a true integrated fever. Additionally, we examined the effects of systemic administration of different antipyretic drugs including the glucocorticoid dexamethasone, on cerebrospinal fluid (CSF) concentration of prostaglandin (PG) E2 and on febrile response induced by CCL3/MIP1alpha. I.c.v. administration of CCL3/MIP1alpha evokes an integrated fever accompanied by a reduction in tail skin temperature and an increase in PGE2 concentration in the CSF. Dexamethasone and indomethacin markedly reduced the fever and the elevation of CSF PGE2 concentration induced by lipopolysaccharide (LPS) whereas both response evoked by i.c.v. CCL3/MIP1alpha were insensitive to this steroid. Indomethacin only blocked the PGE2 increase in the CSF whereas ibuprofen and celecoxib each blocked the fever and the elevation of CSF PGE2. In this study, we have demonstrated for the first time that CCL3/MIP1alpha evokes an integrated febrile response accompanied by an increase of PGE2 levels in the CSF. These events are dissociated, especially in animals treated with indomethacin. If PGE2 does not participate in the febrile response evoked by CCL3/MIP1alpha, the inhibition of this response by celecoxib and ibuprofen indicates additional mechanisms to the well-known inhibition of COX enzymes by these drugs. Such mechanisms do not seem to depend on cytokine synthesis and subsequent COX-2 induction.

Circulating inflammatory mediators during start of fever in differential diagnosis of gram-negative and gram-positive infections in leukopenic rats

Gram-negative and gram-positive infections have been considered the most important causes of morbidity and mortality in patients with leukopenia following chemotherapy. However, discrimination between bacterial infections and harmless fever episodes is difficult. Because classical inflammatory signs of infection are often absent and fever is frequently the only sign of infection, the aim of this study was to assess the significance of serum interleukin-6 (IL-6), IL-10, macrophage inflammatory protein-2 (MIP-2), procalcitonin (PCT), and C-reactive protein (CRP) patterns in identifying bacterial infections during start of fever in normal and cyclophosphamide-treated (leukopenic) rats following an injection of lipopolysaccharide (LPS) or muramyl dipeptide (MDP) as a model for gram-negative and gram-positive bacterial infections. We found that, compared to normal rats, immunosuppressed animals exhibited significantly higher fevers and lesser production of all mediators, except IL-6, after toxin challenge. Moreover, compared to rats that received MDP, both groups of animals that received an equivalent dose of LPS showed significantly higher fevers and greater increase in serum cytokine levels. Furthermore, in contrast to those in immunocompetent rats, serum levels of IL-6 and MIP-2 were not significantly changed in leukopenic animals after MDP injection. Other serum markers such as PCT and CRP failed to discriminate between bacterial stimuli in both groups of animals. These results suggest that the use of the analyzed serum markers at an early stage of fever could give useful information for the clinician for excluding gram-negative from gram-positive infections.

Unresponsiveness of mu-opioid receptor knockout mice to lipopolysaccharide-induced fever

Recently, we demonstrated that lipopolysaccharide (LPS)-induced fever could be suppressed by a selective mu-opioid receptor antagonist, indicating that the mu-opioid system is involved in the LPS fever. In the present study, to confirm the role of the mu-opioid system in the pathogenesis of LPS fever, we used mice lacking the mu-opioid receptor. In the wild type (WT), following intraperitoneal (i.p.) injection of 100 microg kg(-1) of LPS, body temperature (T(b)) increased approximately 1 degrees C and remained elevated during the 360-min recording period. In the mu-opioid receptor knockout (MOR-KO) mice, the administration of 100 microg kg(-1) i.p. of LPS did not induce fever during the recording period. Saline by itself, given i.p., did not alter the T(b), either in WT or MOR-KO. These results confirm that the mu-opioid system is involved in LPS-induced fever.

Role of endogenous macrophage inflammatory protein-2 in regulating fever induced by bacterial endotoxin in normal and immunosuppressed rats

During myelosuppressive chemotherapy, Gram-negative bacterial infection with consequent exposure to lipopolysaccharide (LPS) is one of the most important causes of persistent fever. The classical model of the pathogenesis of fever suggests that pro-inflammatory cytokines, produced by leucocytes in the bloodstream in response to exogenous pyrogens such as bacterial LPS, represent the distal mediators of the febrile response. Neutrophils are the first effectors cells and the most prominent leucocyte population involved in acute bacterial infection. Macrophage inflammatory protein (MIP)-2 plays a crucial role in influencing early cell trafficking and neutrophil activation during pathophysiological processes and serves the same chemotactic function as human interleukin-8. In the present study, we investigated the role of MIP-2 in the development of a febrile response induced by LPS in immunocompetent and leukopenic rats. Intraperitoneal injection of LPS in leukopenic rats elicited a biphasic febrile response of rapid onset, the magnitude and duration of which were significantly greater than in immunocompetent animals. The febrile responses to LPS were accompanied by a pronounced induction of serum MIP-2 levels at 1, 2 and 4 h compared with their respective controls. In both normal and leukopenic rats, neutralization of endogenous MIP-2 bioactivity by systemic administration of antirat MIP-2 antibody caused a significant attenuation of the early phase of LPS fever. However, in contrast with normal rats, the second phase of fever was unimpaired by anti-MIP-2 in leukopenic rats. These findings suggest that circulating MIP-2 is involved in the generation of the early phase of LPS fever that contributes to the maintenance of the later phase of fever in immunocompetent, but not leukopenic, rats. Our data support a regulatory role for endogenous MIP-2 in initiating the fever responses to LPS. Furthermore, these results provide evidence that different cellular and humoral mechanisms are implicated in the development of a febrile response triggered by Gram-negative bacterial infections in leukopenic hosts.

Pyrogens Enhance β-Endorphin Release in Hypothalamus and Trigger Fever That Can Be Attenuated by Buprenorphine

At first, we investigated whether both beta-endorphin release level in the hypothalamus and body temperature can be altered after intracerebroventricular (i.c.v.) injection of either lipopolysaccharide (LPS), interleukin-1beta (IL-1beta), or prostaglandin E(2) (PGE(2)) in rats. It was found that in the rat, i.c.v. administration of either LPS (0.5 microg in 10 microl), IL-1beta (10 ng in 10 microl), or PGE(2) (200 ng in 10 microl), in addition to producing fever, upregulated the immunoreactivity of beta-endorphin in the preoptic anterior hypothalamus of rat brain. Secondarily, we assessed whether the fever induced by either LPS, IL-1beta, or PGE(2) can be altered by pretreatment with buprenorphine (an opioid receptor antagonist). The results revealed that i.c.v. administration of buprenorphine (1 - 10 microg in 10 microl) alone had an insignificant effect on the body temperature. However, the fever induced by i.c.v. injection of either LPS, IL-1beta, or PGE(2) was significantly attenuated by pretreatment with i.c.v. injection of buprenorphine 1 h before the pyrogen injection in rats. The results suggest that pyrogens enhance beta-endorphin release in the hypothalamus and trigger fever which can be attenuated by buprenorphine, an opioid receptor antagonist.

Differential sensitivities of pyrogenic chemokine fevers to cyclooxygenase isozymes antibodies

It has been proposed that prostaglandin (PG)E(2) production via a process catalyzed by the inducible isoform of cyclooxygenase (COX)-2 and activation of specific PGE(2) receptor subtypes within the preoptic/anterior hypothalamus (AH/POA) is the last step and unique pathway in the induction of a fever. However, many data support the existence of a PG-independent pathway. That is, other more rapid mechanisms, which involve the constitutive COX-1 isozyme, may be more critical for a PG-dependent fever. Thus, we examined the role of both COX isoforms in the AH/POA in fevers induced by macrophage inflammatory protein (MIP)-1beta, a PG-independent pyrogen, and RANTES (regulated on activation, normal T-cells expressed and secreted), a PG-dependent pyrogen. In freely moving rats, two independent polyclonal antibodies were used which neutralize COX-1 and COX-2. The microinjection of either MIP-1beta or RANTES into the pyrogen-sensitive region of the AH/POA induced an intense fever of rapid onset. Peripheral pretreatment with an antipyretic dose of dexamethasone which prevents COX-2 expression, or the microinjections into the AH/POA of either anti-COX-1 or anti-COX-2, blocked the febrile response induced by RANTES but not that induced by MIP-1beta. These results provide strong evidence for the existence of rapid mechanisms in the AH/POA which involve both COX isozymes during the fever induced by RANTES, and further support the existence of an alternative PG-independent pathway in the febrile response.

Induced neuronal expression of class I major histocompatibility complex mRNA in acute and chronic inflammation models

Studies have demonstrated neuronal expression of class I major histocompatibility complex (MHC) mRNA and protein in normal and developing brain and in response to injury or viral infection. We report neuronal expression of class I MHC mRNA in hypothalamic paraventricular nucleus (PVN) neurons in rats following systemic infection with Trypanosoma brucei brucei parasites (chronic) and in response to intravenous 1 mg/kg lipopolysaccharide administration (acute peripheral) and in striatal neurons following intrastriatal 5 microg lipopolysaccharide injection (acute central). These results demonstrate that neurons can be a source of immune signaling molecules and establish class I MHC as part of the neuronal component of immune responses.

Fever induction pathways: evidence from responses to systemic or local cytokine formation

The immune and central nervous systems are functionally connected and interacting. The concept that the immune signaling to the brain which induces fever during infection and inflammation is mediated by circulating cytokines has been traditionally accepted. Administration of bacterial lipopolysaccharide (LPS) induces the appearance of a so-termed "cytokine cascade" in the circulation more or less concomitantly to the developing febrile response. Also, LPS-like fever can be induced by systemic administration of key cytokines (IL-1 beta, TNF-alpha, and others). However, anti-cytokine strategies against IL-1 beta or TNF-alpha along with systemic injections of LPS frequently lead to attenuation of the later stages of the febrile response but not of the initial phase of fever, indicating that cytokines are rather involved in the maintenance than in the early induction of fever. Within the last years experimental evidence has accumulated indicating the existence of neural transport pathways of immune signals to the brain. Because subdiaphragmatic vagotomy prevents or attenuates fever in response to intraperitoneal or intravenous injections of LPS, a role for vagal afferent nerve fibers in fever induction has been proposed. Also other sensory nerves may participate in the manifestation of febrile responses under certain experimental conditions. Thus, injection of a small dose of LPS into an artificial subcutaneous chamber results in fever and formation of cytokines within the inflamed tissue around the site of injection. This febrile response can be blocked in part by injection of a local anesthetic into the subcutaneous chamber, indicating a participation of cutaneous afferent nerve signals in the manifestation of fever in this model. In conclusion, humoral signals and an inflammatory stimulation of afferent sensory nerves can participate in the generation and maintenance of a febrile response.

RANTES: a new prostaglandin dependent endogenous pyrogen in the rat

Fever, a hallmark of disease, is a highly complex process initiated by the action of a number of endogenous pyrogens on the thermosensitive cells of the brain. We describe the activity of RANTES, a chemotactic cytokine, as intrinsically pyrogenic in the rat, when it is delivered directly to the thermosensitive region of the rat's anterior hypothalamic, pre-optic area (AH/POA). RANTES, microinjected into the AH/POA in a dose of 1, 5, 10, 15, 25 or 50 pg, produces an immediate and intense dose-related fever following injection. Increasing the dose to 100 pg did not result in a further increase in the febrile response. No significant change in body temperature was produced by heat-inactivated RANTES. The intrahypothalamic injection of antibodies against RANTES (2.0 microg, 15 min prior to RANTES) significantly blocked the fever induced by this chemokine. Pretreatment with ibuprofen blocked the fever induced by RANTES. In order of potency, the magnitude of the febrile response induced by RANTES was greater than that produced with equipotent doses of either macrophage inflammatory protein-1beta or interleukin-6. The results thus demonstrate that RANTES is the most potent endopyrogen discovered thus far and exerts its action directly on pyrogen-sensitive cells of the AH/POA through a prostaglandin-dependent pathway.

In vivo evidence that activation of tyrosine kinase is a trigger for lipopolysaccharide-induced fever in rats

We measured the rectal temperature of free-moving, conscious rats after intracerebroventricular (i.c.v.) injections of lipopolysaccharide (LPS) and interleukin-1beta (IL-1beta) with or without various antagonists to investigate the mechanisms involved in LPS-induced fever. LPS (3 microg) elicited significant increases in rectal temperature, which lasted from 0.5 h to more than 8 h after administration. This febrile response was inhibited by pretreatment with L-nitro-arginine (LNA), indomethacin (IND), genistein (GEN), tyrphostin 46 and anti-rat IL-1beta antibody (anti-IL-1beta Ab), but was not inhibited by pretreatment with daidzein or chelerythrine (CHE) into the ventricle. LPS (0.3 microg) following orthovanadate (i.c.v.) produced fever, although the small amount of LPS (0.3 microg) or orthovanadate alone showed no effect on rectal temperature. I.c.v. injections of IL-1beta also induced fever of approximately 4-h duration. This effect was inhibited by pretreatment with IND and anti-IL-1beta Ab, but was not inhibited by pretreatment with LNA, GEN or CHE into the ventricle. These findings demonstrate that in the central nervous system, LPS increases IL-1beta production after activation of tyrosine kinase and NO synthase, and IL-1beta promotes prostaglandin production resulting in increased rectal temperature. Activation of tyrosine kinase in the central nervous system is probably a trigger for the febrile response induced by LPS.

Localization of macrophage inflammatory protein: macrophage inflammatory protein-1 expression in rat brain after peripheral administration of lipopolysaccharide and focal cerebral ischemia

Macrophage inflammatory protein is a member of the C-C subfamily of chemokines, which exhibits, in addition to proinflammatory activities, a potent endogenous pyrogen activity. In this study, we analysed the time-course of expression and cellular source of macrophage inflammatory protein-1alpha and macrophage inflammatory protein-1beta, in inflammation of the rat brain associated with ischemia and endotoxemia. Using in situ hybridization histochemistry, we observed that intravenously injected bacterial lipopolysaccharide induced a transient expression of macrophage inflammatory protein-1alpha and macrophage inflammatory protein-1beta messenger RNAs throughout the brain, with maximal expression 8-12 h after lipopolysaccharide treatment. We also revealed an early increase in macrophage inflammatory protein-1alpha and macrophage inflammatory protein-1beta messenger RNA levels, after permanent and transient middle cerebral artery occlusion, starting as early as 1 h after the occlusion and reaching a peak of expression 8-16 h after middle cerebral artery occlusion. The induction of macrophage inflammatory protein-1 messenger RNA was clearly stronger in the transient than in the permanent middle cerebral artery-occluded rat brains, showing that the reperfusion process influences the extent of the chemokine response after middle cerebral artery occlusion. In situ hybridization combined with immunohistochemistry for glial fibrillary acidic protein, a specific marker for astrocytes, excluded astrocytes as the cellular source of macrophage inflammatory protein-1 messenger RNAs after both middle cerebral artery ischemia and lipopolysaccharide treatment. Using immunohistochemistry, macrophage inflammatory protein-1alpha protein expression was shown to be induced in a time-dependent manner after lipopolysaccharide treatment and middle cerebral artery occlusion. Macrophage inflammatory protein-1alpha immunopositive cells co-localized with cells stained with OX-42 antibody, a microglia/macrophage marker. These results indicate that macrophage inflammatory protein-1 is implicated in the inflammatory reaction of the brain in response to ischemia or infection, and might modulate the host defence febrile response to a pathogenic stimulus.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

Lipopolysaccharide-induced expression of IP-10 mRNA in rat brain and in cultured rat astrocytes and microglia

Using mRNA differential display technique, we have found a differentially expressed band in rat brain, designated HAP2G1, which was the strongest one induced in response to peripheral administration of lipopolysaccharide (LPS). Sequence analysis showed that HAP2G1 cDNA is the rat homologue of the human alpha-chemokine IP-10. Using RT-PCR technique and in situ hybridization, we demonstrate that IP-10 mRNA was expressed only in brain tissue of rats treated with LPS and not in control brain tissue. Using semi-quantitative PCR, we found that both cultured astrocytes and microglia express IP-10 mRNA after treatment with LPS. LPS-induced IP-10 mRNA reached peak levels in rat brain and in cultured microglia at approximately 3 h after treatment with LPS. At 10 h, IP-10 mRNA was markedly decreased, and at 24 h it was low but still detectable by PCR or in situ hybridization. In contrast to unstimulated microglia, unstimulated astrocytes constitutively expressed IP-10 mRNA at a low level. Increased IP-10 expression could possibly be involved in the microglia response to inflammatory stimuli in vivo.

Antibodies to macrophage inflammatory protein-1beta in preoptic area of rats fail to suppress PGE2 hyperthermia

This study determined whether macrophage inflammatory protein-1beta (MIP-1beta) plays a role in the hyperthermia caused by prostaglandin E2 (PGE2) given intracerebroventricularly (i.c.v.) in the rat. In these experiments, anti-murine MIP-1beta antibody (anti-MIP-1beta) was micro-injected in the anterior hypothalamic, preoptic area (AH/POA) just before i.c.v. PGE2. The results showed that anti-MIP-1beta failed to alter the PGE2 hyperthermia. However, immunocytochemical studies revealed MIP-1beta immunoreactivity detectable in both the organum vasculosum laminae terminalis (OVLT) and AH/POA in the febrile rat. These data thus demonstrate that MIP-1beta is sequestered in diencephalic structures underlying thermoregulation even though it is not involved in PGE2 hyperthermia. This dissociation supports the viewpoint that at least two distinct systems exist in the brain which underlie a febrile response: MIP-1beta underlies one component whereas PGE2 comprises the other.

Role of interleukin-1 beta, interleukin-6 and macrophage inflammatory protein-1 beta in prostaglandin-E2-induced hyperthermia in rats

The purpose of this study was to investigate the role of pyrogenic cytokines, such as IL-1 beta, IL-6 and MIP-1 beta, in the mechanisms underlying the hyperthermic response of rats to central injection of PGE2. Thus, specific murine neutralizing antibodies against these cytokines were micro-injected directly into the anterior hypothalamic, preoptic area (AH/POA) of unrestrained rats just before intracerebroventricular injection of PGE2. The significant hyperthermia induced by PGE2 was markedly suppressed by micro-injection of anti-IL-6 and partially attenuated by anti-IL-1 beta. However, the micro-injection of anti-MIP-1 beta failed to alter the hyperthermic response. The results indicate that PGE2-induced hyperthermia is presumably mediated through actions of IL-6 on the thermosensitive cells of the AH/POA and confirm that distinct and alternate pathways exist in the rat brain for the induction of fever.