Repeated Stress Down-Regulates β<Subscript>2</Subscript>- and α<Subscript>2C</Subscript>-Adrenergic Receptors and Up-Regulates Gene Expression of IL-6 in the Rat Spleen

Catecholamines are among first compounds released during stress, and they regulate many functions of the organism, including immune system, via adrenergic receptors (ARs). Spleen, as an immune organ with high number of macrophages, possesses various ARs, from which β₂-ARs are considered to be the most important for the modulation of immune functions. Nevertheless, little is known about the regulation and involvement of ARs in the splenic function by stress. Therefore, the aim of this work was to measure the gene expression of ARs and several cytokines in the spleen of rats exposed to a single and repeated (14×) immobilization stress (IMO). We have found a significant increase in β₂-AR mRNA after a single IMO, but a significant decrease in β₂-AR mRNA and protein level after repeated (14×) IMO. The most prominent decrease was detected in the gene expression of the α_2A- and α_2C-AR after repeated IMO. However, changes in mRNA were translated into protein levels only for the α_2C-subtype. Other types of ARs remained unchanged during the stress situation. Since we proposed that these ARs might affect production of cytokines, we measured gene expression of pro-inflammatory (TNF-α, IL-1β, IL-6 and IL-18) and anti-inflammatory (IL-10 and TGF-β1) cytokines. We detected changes only in IL-6 and IL-10 mRNA levels. While IL-6 mRNA was increased, IL-10 mRNA dropped after repeated IMO. According to these results we suggest that changes of β₂- and α_2C-ARs participate in IL-6-mediated processes in the spleen, especially during chronic stress situations.     

Effects of β-glucan extracted from Saccharomyces cerevisiae on humoral and cellular immunity in weaned piglets

Abstract

Twenty-four barrows were used to investigate the effects of β-glucan on immune function in weaned piglets. Pigs (8.09 ± 0.20 kg, 28 d of age) were fed a diet without or with supplemented β-glucan (50 mg/kg feed). All pigs were injected with ovalbumin (OVA) on day 14 to investigate their humoral immune response. On day 28, lymphocytes were isolated from all pigs to determine the effects of β-glucan on cellular immunity of pigs in vitro. Lymphocytes from six pigs of each group were incubated with 16 μg lipopolysaccharide (LPS) per ml culture medium, the remainder with an equivalent volume of culture medium alone. Samples were collected at 0, 3, 6, 12, 18, 24, and 48 h after LPS addition for determination of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interleukin-10 (IL-10). On day 31, six pigs of each group were injected with either LPS (25 μg/kg BW) or an equivalent amount of sterile saline. Blood samples were collected at 3 h after LPS injection for analysis of IL-6, TNF-α, and IL-10 in plasma. The results indicated that dietary β-glucan enhanced pig antibody response to OVA only in the first week after injection. In vitro, the increases of IL-6 and TNF-α in culture medium were partially dampened in pigs supplemented with β-glucan when their lymphocytes were incubated with LPS, whereas the increase of IL-10 was potentiated. In vivo, dietary β-glucan attenuated the increase of plasma IL-6 and TNF-α, and enhanced the increase of plasma IL-10 when pigs were challenged with LPS. These results demonstrate that β-glucan can improve the humoral immunity of pigs and modulate cellular immunity of pigs by mitigating the elevation of pro-inflammatory cytokines and enhancing the increase of anti-inflammatory cytokines after an immunological challenge.     

Effect of immunological stress to neuroendocrine and gene expression in different swine breeds

Immunological stress is the status of animal in active immune when they are challenged by bacterial, virus and endocrine. It is associated with immunological, neurological, and endocrinological response. An immunological stress model was established in this study using Chinese indigenous breed (Laiwu), crossbred (Lulai), and exotic breed (Yorkshire), to explore the capacity of immunological stress resistance among different breeds. The study was also to reveal the effect of chromium yeast to immunological stress. 48 post-weaning piglets were taken from three breeds, 16 piglets of each breed from Laiwu, Lulai and Yorkshire. The experiment was designed as 2 × 2 factors, immunological stress (Saline, LPS) and Chromium (with Cr, without Cr). There were four treatments: control, LPS, Cr, and Cr+LPS. Blood parameters related to immunological stress, such as IL-1β, TNF-α, GH, and cortisol, were examined after blood sample were taken at 0, 2, 5, and 7 h of post-injection. The results showed that IL-1β, TNF-α, and cortisol increased in group of LPS treatment while GH declined at 2 h of post-injection in comparison to the control (p < 0.01). However, IL-1β, TNF-α, and cortisol in group of Cr+LPS were lower than that in group of LPS while GH were higher (p < 0.05). Total RNA was extractedfrom blood lymphocytes separation samples at 2 h of post-injection. Q-PCR was applied to determine the gene expression of IL-1β, IL-6 and TNF-α. The results showed that LPS injection increased the gene expression of IL-1β, IL-6 and TNF-α. Among three breeds, the expression of IL-1β, IL-6 and TNF-α in Yorkshire were significantly higher than in Laiwu and Lulai (p < 0.05), but there was no difference between Laiwu and Lulai. Among four treatments, the expression of three genes in group of LPS was the highest, compared to the group of Cr+LPS (p < 0.05) and control (p < 0.01). This study concluded that Laiwu had stronger capacity of immunological stress resistance and next was Lulai among three breeds. Chromium yeast helped piglets relieve immunological stress.     

Stress-induced effects, which inhibit host defenses, alter leukocyte trafficking

Acute cold restraint stress (ACRS) has been reported to suppress host defenses against Listeria monocytogenes, and this suppression was mediated by beta1-adrenoceptors (β1-ARs). Although ACRS appears to inhibit mainly early innate immune defenses, interference with leukocyte chemotaxis and the involvement of β1-AR (or β2-AR) signaling had not been assessed. Thus, the link between sympathetic nerve stimulation, release of neurotransmitters, and changes in blood leukocyte profiles, including oxidative changes, following ACRS was evaluated. The numbers of leukocyte subsets in the blood were differentially affected by β1-ARs and β2-ARs following ACRS; CD3⁺ (CD4 and CD8) T-cells were shown to be decreased following ACRS, and the T cell lymphopenia was mediated mainly through a β2-AR mechanism, while the decrease in CD19⁺ B-cells was influenced through both β1- and β2-ARs, as assessed by pharmacological and genetic manipulations. In contrast to the ACRS-induced loss of circulating lymphocytes, the number of circulating neutrophils was increased (i.e., neutrophilia), and this neutrophilia was mediated through β1-ARs. The increase in circulating neutrophils was not due to an increase in serum chemokines promoting neutrophil emigration from the bone marrow; rather it was due to neutrophil release from the bone marrow through activation of a β1-AR pathway. There was no loss of glutathione in any of the leukocyte subsets suggesting that there was minimal oxidative stress; however, there was early production of nitric oxide and generation of some protein radicals. Premature egress of neutrophils from bone marrow is suggested to be due to norepinephrine induction of nitric oxide, which affects the early release of neutrophils from bone marrow and lessens host defenses.     

Aging-related hyperinflammation in endotoxemia is mediated by the α2A-adrenoceptor and CD14/TLR4 pathways

AimsSepsis is a major cause of morbidity and mortality in the elderly population. In prior studies, we have shown that in vivo, the inflammatory response in aged animals is exaggerated as compared to young animals and that this response likely accounts for the increased morbidity and mortality. Part of this uncontrolled inflammatory response in sepsis is due to the innate immune response. However, recent studies have shown that the pathogenesis of sepsis is much more complex. The adrenergic autonomic nervous system is now thought to play a key role in modulating the inflammatory response in sepsis. In this study, we hypothesize that not only is the innate immune response enhanced in response to lipopolysaccharide (LPS) in aged animals, but that the adrenergic nervous system also plays a role in the release of excess inflammatory cytokines.Main methodsMale Fischer-344 rats (young: 3 months; aged: 24 months) were used. Endotoxemia was induced by intravenous injection of lipopolysaccharide (LPS, 15 mg/kg BW). Splenic tissues were harvested and mRNA and protein were extracted. The protein expression of CD14 and TLR4, key mediators of LPS in the innate response, as well as alpha-2A adrenergic receptor (α_2A-AR) and phosphodiesterase 4D (PDE4D), as the means by which the autonomic nervous system exerts its effects were analyzed.Key findingsSplenic tissue concentrations of α_2A-AR, PDE4D, CD14, and TLR4 were significantly increased in septic aged rats as compared to aged sham rats and septic young rats. The increased expression of α_2A-AR in septic aged rats was further confirmed by immunohistochemical staining of splenic tissues.SignificanceThese data support the hypothesis that not only is the innate immune response increased in aged animals during sepsis, but that there is also an upregulated response of the adrenergic autonomic nervous system that contributes to excess proinflammatory cytokine release.     

Regulation of neutrophil interleukin 8 gene expression and protein secretion by LPS,TNF-α, and IL-1β

Neutrophils are possibly involved in the pathogenesis of various lung diseases through the release of numerous mediators. In the present study, we studied the regulation of IL-8 gene induction and protein secretion in human blood neutrophils. Northern blot analysis revealed that LPS increased IL-8 mRNA levels in neutrophils, with a maximal fivefold increase by 2 h. IL-8 mRNA levels returned to baseline value within 12 h. In contrast, LPS-stimulated monocytes demonstrated a sustained increase of IL-8 mRNA levels for more than 24 h. TNF-α, IL-1β, and phorbol myristate acetate also increased IL-8 mRNA levels in neutrophils. Immunohistochemical analysis confirmed that IL-8 was localized within stimulated neutrophils. IL-8 secretion by neutrophils and monocytes was quantified using a specific ELISA for IL-8. Resting neutrophils secreted minimal IL-8 activity. However when cells were stimualted with LPS, TNF-α, or IL-1bT, neutrophils secreted IL-8. IL-8 secretion was most marked during the first 2 h after stimulation and decreased thereafter. In contrast, monocytes maintained a high rate of IL-8 secretion over 12 h. Although a single monocyte secreted 70-fold more IL-8 than did a single neutrophil after 4 h of incubation, the high abundance of neutrophils in peripheral blood made the neutrophil-secreted IL-8 more significant. During the first 2 h, neutrophils secreted ～40% of the IL-8 released by monocytes in the same volume of blood. This ratio decreased to 9% after 12 h. Neutrophil-secreted IL-8 may play an autocrine or paracrine role during the initial stage of inflammation. © 1993 Wiley-Liss, Inc.     

Effects of Norepinephrine on Immune Functions of Cultured Splenic Lymphocytes Exposed to Aluminum Trichloride

The aim of this study was to investigate the effect of norepinephrine (NE) on spleen lymphocytes exposed to aluminum trichloride (AlCl₃). In this experiment, lymphocytes were isolated from spleens of healthy Wistar rats weighing about 130 g and cultured with RPMI-1640 medium containing the final concentration of 0.552 mmol/L AlCl₃. NE was added to the cultured cells at the final concentrations of 0 (control group), 0.1 (low-dose group), 1 (mid-dose group), and 10 (high-dose group)?nmol/L. No addition of both AlCl₃ and NE serviced as blank (BG). The T lymphocyte proliferation; the contents of IL-2, TNF-α, and T lymphocyte subsets; immunoglobulin G (IgG) and intracellular cyclic adenosine monophosphate (cAMP) concentrations; and β₂-adrenergic receptor (β₂-AR) density were measured at the end of the culture. The result showed that NE decreased T lymphocyte proliferation and the contents of IL-2, TNF-α, and T lymphocyte subsets whereas increased the concentrations of IgG and intracellular cAMP and β₂-AR density of the lymphocyte exposed to AlCl₃. AlCl₃ exposure without adding NE showed the similar impacts on these measures compared with BG. The results suggested that NE aggravated AlCl₃ immunotoxicity on the lymphocytes and disordered the immune functions of the lymphocyte through the β₂-AR-cAMP signal pathway.     

Mechanisms of endotoxin tolerance in human intestinal microvascular endothelial cells

Lipopolysaccharide (endotoxin) tolerance is well described in monocytes and macrophages, but is less well characterized in endothelial cells. Because intestinal microvascular endothelial cells exhibit a strong immune response to LPS challenge and play a critical regulatory role in gut inflammation, we sought to characterize the activation response of these cells to repeated LPS exposure. Primary cultures of human intestinal microvascular endothelial cells (HIMEC) were stimulated with LPS over 6-60 h and activation was assessed using U937 leukocyte adhesion, expression of E-selectin, ICAM-1, VCAM-1, IL-6, IL-8, manganese superoxide dismutase, HLA-DR, and CD86. Effect of repeat LPS stimulation on HIMEC NF-kappaB and mitogen-activated protein kinase (MAPK) activation, generation of superoxide anion, and Toll-like receptor 4 expression was characterized. LPS pretreatment of HIMEC for 24-48 h significantly decreased leukocyte adhesion after subsequent LPS stimulation. LPS pretreatment inhibited expression of E-selectin, VCAM-1, IL-6, and CD86, while ICAM-1, IL-8, and HLA-DR were not altered. Manganese superoxide dismutase expression increased with repeated LPS stimulation, with a reduction in intracellular superoxide. NF-kappaB activation was transiently inhibited by LPS pretreatment for 6 h, but not at later time points. In contrast, p44/42 MAPK, p38 MAPK, and c-Jun N-terminal kinase activation demonstrated inhibition by LPS pretreatment 24 or 48 h prior. Toll-like receptor 4 expression on HIMEC was not altered by LPS. HIMEC exhibit endotoxin tolerance after repeat LPS exposure in vitro, characterized by diminished activation and intracellular superoxide anion concentration, and reduced leukocyte adhesion. HIMEC possess specific mechanisms of immunoregulatory hyporesponsiveness to repeated LPS exposure.     

Effects of single or repeated administrations of methamphetamine on immune response in mice.

The present study aimed to clarify the connection between immune responses and the administration frequency of methamphetamine (MAP) in male and female mice. Male and female ddY mice were given single or multiple (repeated for 10 days) intraperitoneal injections of MAP (5.0 mg/kg/day). The following immune parameters were examined; the number of leukocytes in peripheral blood and the proliferative activity (phytohemagglutinin;PHA, lipopolysaccharide; LPS response) and natural killer (NK) cell activity in splenic lymphocytes. Further, the differences in metabolic function in the spleen in response to MAP (and its metabolite amphetamine) in male and female mice were measured by gas chromatography. The results of the present study were that; 1) single and repeated MAP injections reduced leukocytes; 2) single MAP injection increased the proliferative response of splenic lymphocytes to PHA stimulation in only male mice, but the response to LPS stimulation was slightly increased in both male and female mice; 3) single and repeated MAP injections reduced NK cell activity of splenic lymphocytes, and especially in female mice with 5 injections of MAP; 4) with 10 MAP injections the NK cell activity and leukocytes recovered to the level of controls; and 5) the metabolic activity of MAP was reduced in female mice treated acutely with MAP in comparison to male mice. These results appear to indicate that immune responses to MAP were involved in the different results shown for administration frequency, sex difference and metabolic process of MAP.     

LILRA2 selectively modulates LPS-mediated cytokine production and inhibits phagocytosis by monocytes

The activating immunoglobulin-like receptor, subfamily A, member 2 (LILRA2) is primarily expressed on the surface of cells of the innate immunity including monocytes, macrophages, neutrophils, basophils and eosinophils but not on lymphocytes and NK cells. LILRA2 cross-linking on monocytes induces pro-inflammatory cytokines while inhibiting dendritic cell differentiation and antigen presentation. A similar activating receptor, LILRA4, has been shown to modulate functions of TLR7/9 in dendritic cells. These suggest a selective immune regulatory role for LILRAs during innate immune responses. However, whether LILRA2 has functions distinct from other receptors of the innate immunity including Toll-like receptor (TLR) 4 and FcγRI remains unknown. Moreover, the effects of LILRA2 on TLR4 and FcγRI-mediated monocyte functions are not elucidated. Here, we show activation of monocytes via LILRA2 cross-linking selectively increased GM-CSF production but failed to induce IL-12 and MCP-1 production that were strongly up-regulated by LPS, suggesting functions distinct from TLR4. Interestingly, LILRA2 cross-linking on monocytes induced similar amounts of IL-6, IL-8, G-CSF and MIP-1α but lower levels of TNFα, IL-1β, IL-10 and IFNγ compared to those stimulated with LPS. Furthermore, cross-linking of LILRA2 on monocytes significantly decreased phagocytosis of IgG-coated micro-beads and serum opsonized Escherichia coli but had limited effect on phagocytosis of non-opsonized bacteria. Simultaneous co-stimulation of monocytes through LILRA2 and LPS or sequential activation of monocytes through LILRA2 followed by LPS led lower levels of TNFα, IL-1β and IL-12 production compared to LPS alone, but had additive effect on levels of IL-10 and IFNγ but not on IL-6. Interestingly, LILRA2 cross-linking on monocytes caused significant inhibition of TLR4 mRNA and protein, suggesting LILRA2-mediated suppression of LPS responses might be partly via regulation of this receptor. Taken together, we provide evidence that LILRA2-mediated activation of monocytes is significantly different to LPS and that LILRA2 selectively modulates LPS-mediated monocyte activation and FcγRI-dependent phagocytosis.     

Adrenergic Receptors and Fat Cells: Differential Recruitment by Physiological Amines and Homologous Regulation

The control of fat cell lipolysis by the catecholamines involves at least four different adrenoceptor subtypes; three β (β1-, β2-, and β3-ARs) and one α2-adrenoceptor(α2-AR). The physiological importance of the β- and α2A-ARs varies according to the species, the sex, the age, the anatomical location of fat deposits and the degree of obesity in humans and animals. The physiological amines operate through differential recruitment of these sites on the basis of their relative affinities. This point has been assessed by in vitro studies and has partly been confirmed in in vivo experiments using selected a/β-AR antagonists and in situ microdialysis. The affinity of the β3-AR for catecholamines is less than that of the classical β1- and β2-ARs in the various species investigated. Conversely, it is the α2-AR which exhibit the highest affinity for the physiological amines in all fat cells. The relative order of affinity of the various fat cell ARs for the physiological amines defined in binding studies and in vitro ass ays is α2 > β1 > β2 > β3 for norepinephrine and α2 >β2 > β1> β3 for epinephrine. When considering differential β-AR recruitment by catecholamines, it is the β1-AR which is always activated at the lowest norepinephrine levels, whatever the species, while the activation of the β3-AR requires higher norepinephrine levels. In addition to the differential recruitment, differential regulation by hormones could also occur for each fat cell AR subtype. The α2-and β3-ARs are less prone to desensitization and down-regulation by comparison with the β1- and β2-AR.     

Desipramine administered chronically inhibits lipopolysaccharide-stimulated production of IL-1β in the brain and plasma of rats

Nowadays, it is assumed that therapeutic efficacy of antidepressants depends, at least partly, on their anti-inflammatory properties. The present study investigated for the first time the effect of 21-day oral administration of desipramine on the lipopolysaccharide (LPS)-stimulated IL-1β concentration in the olfactory bulb, hypothalamus, frontal cortex, hippocampus and plasma of rats, and on the LPS-induced IL-1β mRNA level in the olfactory bulb. Desipramine (15 mg/kg/day) reduced significantly the LPS (250 μg/kg i.p.)-induced IL-1β concentration in the olfactory bulb, hypothalamus and in plasma, and diminished the LPS effect on IL-1β mRNA in the olfactory bulb. Plasma concentration of desipramine was comparable to its therapeutic range. By using the α1/α2-adrenoceptor antagonist prazosin and the unspecific β-adrenoceptor antagonist propranolol given prior to LPS, we found that the effect of desipramine on LPS-induced IL-1β production was partially mediated by both adrenoceptors in the olfactory bulb and plasma, and that β-adrenoceptors contributed also to its effect on the stimulated IL-1β concentration in the hypothalamus. The effect of LPS on the cerebral IL-1β levels was, in part, mediated by β-adrenoceptors and, in a region-specific manner, by α1/α2-adrenoceptors. The findings provide evidence for central and peripheral anti-inflammatory activity of desipramine and confirm the impact of the noradrenergic system on IL-1β production induced by an immunostimulatory challenge.     

Boron Affects Immune Function Through Modulation of Splenic T Lymphocyte Subsets,Cytokine Secretion,and Lymphocyte Proliferation and Apoptosis in Rats

This study demonstrated the mechanisms of boron effects in a rat model and provided a scientific basis for the rational of boron use. These findings were achieved by investigating the effects of boron (10, 20, 40, 80, 160, 320, and 640 mg/L in drinking water or 1.5, 3, 6, 12, 24, 48, and 96 mg/kg BW) on rat serum immunoglobulins (IgGs), splenic cytokines, lymphocyte subsets, as well as on lymphocyte proliferation and apoptosis. Addition of 20 (3) and 40 (6) mg/L (mg/kg BW) of boron to drinking water significantly increased rat serum IgG concentrations, splenic IFN-γ and IL-4 expression as well as the number of splenic CD3⁺, CD4⁺ and proliferating cell nuclear antigen (PCNA)⁺ cells. Supplementation of drinking water with 40 mg/L (6 mg/kg BW) boron also markedly increased splenic IL-2 expression and the CD4⁺/CD8⁺ cell ratio and reduced splenic CD8⁺ cell number. Supplementation with 80 mg/L (12 mg/kg BW) boron significantly increased CD3⁺ and PCNA⁺ cell numbers (P < 0.05) and decreased the IL-10 expression in the spleen. Addition of 320 (48) and 640 (96) mg/L (mg/kg BW) boron markedly reduced the serum IgG concentrations; splenic IL-2 and IL-10 expression; the number of CD3⁺, CD4⁺ and PCNA⁺ cells; and increased the number of splenic CD8⁺ and caspase-3⁺ cells and promoted caspase-3 expression in CD3⁺ cells. In conclusion, these findings suggest that the supplementation of rat drinking water with 20(3) and 40(6) mg/L (mg/kg BW) boron can markedly enhance humoral and cellular immune functions, while boron concentrations above 320 mg/L (48 mg/kg BW) can have an inhibitory effect or even toxicity on immune functions. These results exhibit a U-shaped response characteristic of low and high doses of boron supplementation on immune function and imply that proper boron supplementation in food for humans and animals could be used as an immunity regulator.     

Stress triggered changes in expression of genes for neurosecretory granules in adrenal medulla

With acute stress, the release of adrenomedullary catecholamines is important for handling the emergency situation. However, when chronic or repeated, stress alters the allostatic load and leads to a hyperadrenergic state, resulting in the development or worsening of a wide range of diseases. To help elucidate the mechanism, we examined the effects of single and repeated immobilization stress on gene expression of components of neurosecretory vesicles in the adrenal medulla. Male Sprague-Dawley rats were exposed to immobilization stress once for 2?h (1× IMO) or daily for six consecutive days (6× IMO). Compared to unstressed controls, 1× IMO elevated gene expression of vesicular monoamine transporter 2 (VMAT2). In response to 6× IMO, not only was VMAT2 mRNA still elevated, but chromogranin A (CgA) and chromogranin B (CgB) mRNAs were also increased two to three-fold above basal levels. To investigate the possible role of the hypothalamic-pituitary-adrenal axis in the induction of VMAT2, PC12 cells were treated with the synthetic glucocorticoid dexamethasone, which was found to elevate VMAT2 mRNA expression. The findings suggest that following repeated stress, elevations of various components of neurosecretory vesicles in the adrenal can facilitate more efficient utilization of the well-characterized heightened catecholamine levels.     

Effect of exercise intensity and AICAR on isoform-specific expressions of murine skeletal muscle PGC-1α mRNA: a role of β₂-adrenergic receptor activation

There are three isoforms of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) mRNA, which promotes mitochondrial biogenesis in skeletal muscles. Compared with PGC-1α-a mRNA, PGC-1α-b or PGC-1α-c mRNA is transcribed by a different exon 1 of the PGC-1α gene. In this study, effects of exercise intensity and 5-aminoimidazole-4-carboxamide-1β-d-ribofuranoside (AICAR) on isoform-specific expressions of PGC-1α were investigated. All isoforms were increased in proportion to exercise intensity of treadmill running (10-30 m/min for 30 min). Preinjection of β?-adrenergic receptor (AR) antagonist (ICI 118551) inhibited the increase in PGC-1α-b and PGC-1α-c mRNAs, but not the increase in PGC-1α-a mRNA, in response to high-intensity exercise. Although high-intensity exercise activated α2-AMP-activated protein kinase (α2-AMPK) in skeletal muscles, inactivation of α2-AMPK activity did not affect high-intensity exercise-induced mRNA expression of all PGC-1α isoforms, suggesting that activation of α2-AMPK is not mandatory for an increase in PGC-1α mRNA by high-intensity exercise. A single injection in mice of AICAR, an AMPK activator, increased mRNAs of all PGC-1α isoforms. AICAR increased blood catecholamine concentrations, and preinjection of β?-AR antagonist inhibited the increase in PGC-1α-b and PGC-1α-c mRNAs but not the increase in PGC-1α-a mRNA. Direct exposure of epitrochlearis muscle to AICAR increased PGC-1α-a but not the -b isoform. These data indicate that exercise-induced PGC-1α expression was dependent on the intensity of exercise. Exercise or AICAR injection increased PGC-1α-b and PGC-1α-c mRNAs via β?-AR activation, whereas high-intensity exercise increased PGC-1α-a expression by a multiple mechanism in which α2-AMPK is one of the signaling pathways.     

Depletion of Dendritic Cells Enhances Innate Anti-Bacterial Host Defense through Modulation of Phagocyte Homeostasis

Dendritic cells (DCs) as professional antigen-presenting cells play an important role in the initiation and modulation of the adaptive immune response. However, their role in the innate immune response against bacterial infections is not completely defined. Here we have analyzed the role of DCs and their impact on the innate anti-bacterial host defense in an experimental infection model of Yersinia enterocolitica (Ye). We used CD11c-diphtheria toxin (DT) mice to deplete DCs prior to severe infection with Ye. DC depletion significantly increased animal survival after Ye infection. The bacterial load in the spleen of DC-depleted mice was significantly lower than that of control mice throughout the infection. DC depletion was accompanied by an increase in the serum levels of CXCL1, G-CSF, IL-1α, and CCL2 and an increase in the numbers of splenic phagocytes. Functionally, splenocytes from DC-depleted mice exhibited an increased bacterial killing capacity compared to splenocytes from control mice. Cellular studies further showed that this was due to an increased production of reactive oxygen species (ROS) by neutrophils. Adoptive transfer of neutrophils from DC-depleted mice into control mice prior to Ye infection reduced the bacterial load to the level of Ye-infected DC-depleted mice, suggesting that the increased number of phagocytes with additional ROS production account for the decreased bacterial load. Furthermore, after incubation with serum from DC-depleted mice splenocytes from control mice increased their bacterial killing capacity, most likely due to enhanced ROS production by neutrophils, indicating that serum factors from DC-depleted mice account for this effect. In summary, we could show that DC depletion triggers phagocyte accumulation in the spleen and enhances their anti-bacterial killing capacity upon bacterial infection.     

Lipopolysaccharide induces rapid production of IL-10 by monocytes in the presence of apoptotic neutrophils

There is growing evidence that apoptotic neutrophils have an active role to play in the regulation and resolution of inflammation following phagocytosis by macrophages and dendritic cells. However, their influence on activated blood monocytes, freshly recruited to sites of inflammation, has not been defined. In this work, we examined the effect of apoptotic neutrophils on cytokine production by LPS-activated monocytes. Monocytes stimulated with LPS in the presence of apoptotic neutrophils for 18 h elicited an immunosuppressive cytokine response, with enhanced IL-10 and TGF-beta production and only minimal TNF-alpha and IL-1beta cytokine production. Time-kinetic studies demonstrated that IL-10 production was markedly accelerated in the presence of apoptotic neutrophils, whereas there was a sustained reduction in the production of TNF-alpha and IL-1beta. This suppression of proinflammatory production was not reversible by depletion of IL-10 or TGF-beta or by addition of exogenous IFN-gamma. It was demonstrated, using Transwell experiments, that monocyte-apoptotic cell contact was required for induction of the immunosuppressive monocyte response. The response of monocytes contrasted with that of human monocyte-derived macrophages in which there was a reduction in IL-10 production. We conclude from these data that interaction between activated monocytes and apoptotic neutrophils creates a unique response, which changes an activated monocyte from being a promoter of the inflammatory cascade into a cell primed to deactivate itself and other cells.