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In polymicrobial sepsis, the extracellular histones, mainly released from activated neutrophils, significantly contribute to cardiac dysfunction (septic cardiomyopathy), as demonstrated in our previous studies using Echo-Doppler measurements. This study aims to elucidate the roles of extracellular histones and their interactions with Toll-like receptors (TLRs) in cardiac dysfunction. Through ex vivo assessments of ECG, left ventricle (LV) function parameters, and in vivo Echo-Doppler studies in mice perfused with extracellular histones, we aim to provide comprehensive insights into the mechanisms underlying sepsis-induced cardiac dysfunction. Langendorff-perfused hearts from both wild-type and TLR2, TLR3, or TLR4 knockout (KO) mice were examined. Paced mouse hearts were perfused with histones to assess contractility and relaxation. Echo-Doppler studies evaluated cardiac dysfunction after intravenous histone injection. Histone perfusion caused defects in contractility and relaxation, with TLR2 and TLR3 KO mice being partially protected. Specifically, TLR2 KO mice exhibited the greatest reduction in Echo-Doppler abnormalities, while TLR4 KO exacerbated cardiac dysfunction. Among individual histones, H1 induced the most pronounced abnormalities in cardiac function, apoptosis of cardiomyocytes, and LDH release. Our data highlight significant interactions between histones and TLRs, providing insights into histones especially H1 as potential therapeutic targets for septic cardiomyopathy. Further studies are needed to explore specific histone–TLR interactions and their mechanisms. [ABSTRACT FROM AUTHOR]

It is becoming increasingly clear that the autonomic nervous system and the immune system demonstrate cross-talk during inflammation by means of sympathetic and parasympathetic pathways (1,2). Weinvestigated whether phagocytes are [...]

Author(s): Markus Huber-Lang [1, 6]; J Vidya Sarma [2, 6]; Firas S Zetoune [2, 6]; Daniel Rittirsch [2]; Thomas A Neff [2]; Stephanie R McGuire [2]; John D Lambris [3]; [...]

We determined the roles of TLR3 and TLR9 in adverse events of polymicrobial sepsis, with a focus on development of septic cardiomyopathy, progression of which we have recently shown to be complement- and histones-dependent. So Wt, TLR3-knocked out (K.O.), and TLR9-K.O. mice were subjected to polymicrobial sepsis following cecal ligation and puncture (CLP). In the absence of either TLR3 or TLR9, the intensity of echocardiogram (Echo)-Doppler dysfunction during development of cardiomyopathy was substantially reduced in the K.O. mice. Based on our prior studies emphasizing the adverse effects of plasma C5a and histones in the cardiomyopathy of sepsis, in TLR3- and TLR9-K.O. mice, there were striking reductions in plasma levels of C5a and histones as well as reduced levels of cytokines in plasma and heart tissue after CLP. Since we know that histones cause cardiac dysfunction, rat cardiomyocytes (CMs) were exposed in vitro to the histones (purified from calf thymus), which caused bleb formation on the surfaces of CMs, suggesting histones may perturb the cell membrane of CMs. In vitro, exposure of CMs to the histones for 3 hours caused lactate dehydrogenase release from CMs. These data indicate that sepsis-induced cardiac dysfunction requires presence of TLR3 and TLR9 and may be linked to histone-induced damage of CMs. [ABSTRACT FROM AUTHOR]

C5a is an inflammatory mediator generated by complement activation that positively regulates various arms of immune defense, including Toll-like receptor 4 (TLR4) signaling. The NOD-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome is activated by pathogen products and cellular/tissue damage products and is a major contributor of IL-1β. In this study, we investigate whether C5a modulates lipopolysaccharide- (LPS-) induced NLRP3 inflammasome activation in myeloid cells. Appearance of plasma IL-1β during endotoxemia was reduced in C5aR1-/- mice when compared to wild-type mice. In vitro, C5a significantly enhanced LPS-induced production of IL-1β in bone marrow Ly6C-high inflammatory monocytes, accompanied by augmented intracellular pro-IL-1β expression. This effect was abolished during p38 blockade by SB 203580 and in the absence of C5aR1. Conversely, C5a suppressed LPS-induced macrophage production of IL-1β, which was accompanied by attenuated levels of pro-IL-1β, NLRP3, and caspase-1 expression. C5a’s suppressive effects were negated during phosphoinositide 3-kinase (PI3K) inhibition by wortmannin but were largely preserved in the absence of C5aR1. Thus, C5a bidirectionally amplifies TLR4-mediated NLRP3 inflammasome activation in monocytes while suppressing this pathway in macrophages. However, as C5aR1 deficiency attenuates the IL-1β response to LPS challenge in vivo, our results suggest overall that C5a augments physiologic inflammasome responses. [ABSTRACT FROM AUTHOR]

The purpose of this study was to define the relationship in polymicrobial sepsis (in adult maleC57BL/ 6 mice) between heart dysfunction and the appearance in plasma of extracellular histones. Procedures included induction of sepsis by cecal ligation and puncture and measurement of heart function using echocardiogram/ Doppler parameters.We assessed the ability of histones to cause disequilibrium in the redox status and intracellular [Ca2+]I levels in cardiomyocytes (CMs) (from mice and rats). We also studied the ability of histones to disturb both functional and electrical responses of hearts perfused with histones. Main findings revealed that extracellular histones appearing in septic plasma required C5a receptors, polymorphonuclear leukocytes (PMNs), and the Nacht-, LRR-, and PYD-domains--containing protein 3 (NLRP3) inflammasome. In vitro exposure of CMs to histones caused loss of homeostasis of the redox systemand in [Ca2+]i, aswell as defects inmitochondrial function. Perfusion of hearts with histones caused electrical and functional dysfunction. Finally, in vivo neutralization of histones in septic mice markedly reduced the parameters of heart dysfunction. Histones caused dysfunction in hearts during polymicrobial sepsis. These events could be attenuated by histone neutralization, suggesting that histones may be targets in the setting of sepsis to reduce cardiac dysfunction. [ABSTRACT FROM AUTHOR]

We investigated how complement activation promotes tissue injury and organ dysfunction during acute inflammation. Three models of acute lung injury (ALI) induced by LPS, IgG immune complexes, or C5a were used in C57BL/6 mice, all models requiring availability of both C5a receptors (C5aR and C5L2) for full development of ALI. Ligation of C5aR and C5L2 with C5a triggered the appearance of histones (H3 and H4) in bronchoalveolar lavage fluid (BALF). BALF from humans with ALI contained H4 histone. Histones were absent in control BALF from healthy volunteers. In mice with ALI, in vivo neutralization of H4 with IgG antibody reduced the intensity of ALI. Neutro-phil depletion in mice with ALI markedly reduced H4 presence in BALF and was highly protective. The direct lung damaging effects of extracellular histones were demonstrated by airway administration of histones into mice and rats (Sprague-Dawley), which resulted in ALI that was C5a receptor-independent, and associated with intense inflammation, PMN accumulation, damage/destruction of alveolar epithelial cells, together with release into lung of cytokines/chemokines. High-resolution magnetic resonance imaging demonstrated lung damage, edema and consolidation in histone-injured lungs. These studies confirm the destructive C5a-dependent effects in lung linked to appearance of extracellular histones. [ABSTRACT FROM AUTHOR]

The complement activation product, C5a, is a key factor for regulation of inflammatory responses. C5a and C5adesArg bind to their receptors, C5a R and C5 L2, but the functional roles of C5 L2 remain controversial. We screened the patterns of 23 inflammatory mediators in cultures of LPS-activated mouse peritoneal elicited macrophages ( PEMs) in the presence or absence of recombinant mouse C5a. Production of most mediators studied was suppressed by C5a, whereas G- CSF production was enhanced. G- CSF gene expression and secretion from PEMs was amplified two- to threefold by C5a in a dose- and time-dependent fashion. The degradation product C5adesArg promoted lower levels of G- CSF. The effects of C5a on G- CSF were associated with activation of PI3 K/ Akt and MEK1/2 signaling pathways. C5a did not enhance G- CSF production in cultures of PEMs from either C5a R- or C5 L2-deficient mice, indicating that both C5a receptors are indispensable for mediating the effects of C5a in the production of G- CSF. Finally, G- CSF levels in plasma during polymicrobial sepsis after cecal ligation and puncture were substantially lower in C5a R- or C5 L2-deficient mice as compared with that in C57 BL/6 J WT mice. These findings elucidate the functional characteristics of the C5 L2 receptor during the acute inflammatory response. [ABSTRACT FROM AUTHOR]

Zonulin is a protein involved in the regulation of tight junctions (TJ) in epithelial or endothelial cells. Zonulin is known to affect TJ in gut epithelial cells, but little is known about its influences in other organs. Prehaptoglobin2 has been identified as zonulin and is related to serine proteases (MASPs, C1qrs) that activate the complement system. The current study focused on the role of zonulin in development of acute lung injury (ALI) in C57BL/6 male mice following intrapulmonary deposition of IgG immune complexes. A zonulin antagonist (AT- 1001) and a related peptide with permeability agonist activities (AT-1002) were employed and given intratracheally or intravenously. Also, zonulin was blocked in lung with a neutralizing antibody. In a dose-dependent manner, AT-1001 or zonulin neutralizing antibody attenuated the intensity of ALI (as quantitated by albumin leak, neutrophil accumulation, and proinflammatory cytokines). A similar pattern was found using the bacterial lipopolysaccharide model of ALI. Using confocal microscopy on sections of injured lungs, staining patterns for TJ proteins were discontinuous, reduced, and fragmented. As expected, the leak of blood products into the alveolar space confirmed the passage of 3 and 20 kDa dextran, and albumin. In contrast to AT-1001, application of the zonulin agonist AT-1002 intensified ALI. Zonulin both in vitro and in vivo induced generation of complement C3a and C5a. Collectively, these data suggest that zonulin facilitates development of ALI both by enhancing albumin leak and complement activation as well as increased buildup of neutrophils and cytokines during development of ALI. [ABSTRACT FROM AUTHOR]

These studies were undertaken to extend emerging evidence that β2 adrenergic receptor (β2AR) agonists, in addition to their bronchorelaxing effects, may have broad anti-inflammatory effects in the lung following onset of experimental acute lung injury (ALI). Young male C57BL/6 mice (25 g) developed ALI following airway deposition of bacterial LPS or IgG immune complexes in the absence or presence of appropriate stereo-isomers (enantiomers) of β2AR agonists, albuterol or formoterol. Endpoints included albumin leak into lung and buildup of polymorphonuclear neutrophils and cytokines/chemokines in bronchoalveolar fluids. Both β2AR agonists suppressed lung inflammatory parameters (IC50 = 10-7 M). Similar effects of β2AR agonists on mediator release were found when mouse macrophages were stimulated in vitro with LPS. The protective effects were associated with reduced activation (phosphorylation) of JNK but not of other signaling proteins. Collectively, these data suggest that2AR agonists have broad anti-inflammatory effects in the setting of ALI. While β2AR agonists suppress JNK activation, the extent to which this can explain the blunted lung inflammatory responses in the ALI models remains to be determined. [ABSTRACT FROM AUTHOR]

There is growing evidence that the complement activation product C5a positively or negatively regulates inflammatory functions. The studies presented here report that C5a exerts anti-inflammatory effects by altering production of the cytokines IL-17A and IL-23 during endotoxic shock in young adult male C57BL/6J mice and has similar effects on macrophages from the same mice. IL-17A and IL-23 both appeared in plasma during endotoxemia, and their neutralization improved survival. The relevant sources of IL-17A during endotoxemia were not CD4+ cells, γδ T cells, or NK cells but CD11b+F4/80+ macrophages. The addition in vitro of C5a to lipopolysaccharide-activated peritoneal macrophages dose dependently antagonized the production of IL-17A (IC50, 50-100 nM C5a) and IL-23 (IC50, 10 nM C5a). This suppression required the receptor C5aR, but was independent of the second C5a receptor, C5L2. Genetic absence of C5aR was associated with much higher levels of IL-17A and IL-23 during endotoxic shock. Mechanistically, C5a mediated its effects on the IL-17A/IL-23 axis in a 2-step process. C5a caused activation of the PI3K-Akt and MEK1/2-ERK1/2 pathways, resulting in induction of IL-10, which powerfully inhibited production of IL-17A and IL-23. These data identify previously unknown mechanisms by which the anaphylatoxin C5a limits acute inflammation and antagonizes the IL-17A/IL-23 axis. [ABSTRACT FROM AUTHOR]

The interleukin-17 (ID17) family of cytokines plays important roles in innate immune defenses against bacterial and fungal pathogens. While much is known about IL-17A, much less information is available about the IL-17F isoform. Here, we investigated gene expression and release of IL-17F and its regulation by the complement system. IL-17F was produced in mouse peritoneal elicited macrophages after TLR4 activation by LPS, peaking after 12 h. This effect was completely dependent on the presence of the adaptor protein MyD88. The copresence of the complement activation product, C5a (EC50 = 10 nM), amplified IL-17F production via the receptor C5aR. In vitro signaling studies indicated that LPS or C5a, or the combination, caused phosphorylation of Akt occurring at threonine 308 but not at serine 473. Treatment of macrophages with pharmacologic inhibitors of PI3K-Akt greatly reduced production of IL-17F as well as mRNA for IL-17F. In endotoxemia, C5a levels peaked at 6 h, while IL-17F levels peaked between 6-12 h. Full in vivo production of IL-17F during endotoxemia required C5a. A similar result was found in the cecal ligation and puncture sepsis model. These data suggest that maximal production of IL-17F requires complement activation and presence of C5a. [ABSTRACT FROM AUTHOR]

We have recently shown that antibody-induced blockade of C5a, C5a receptors, or IL-17A greatly reduced the harmful outcomes of sepsis. In the current study, normal cardiomyocytes from young (300 g) male Sprague-Dawley rats responded in vitro to C5a (ED50=55 nM) with release of IL-6 and TNFα, peaking between 2 to 8 h. Neutralizing antibodies to mouse C5a or IL-17A (ED50=40 µg for each, based on improved survival) reduced spontaneous in vitro release of cardiosuppressive cytokines and chemokines in cardiomyocytes obtained from mice with polymicrobial sepsis. A non-neutralizing C5a antibody had no such effects. Cardiomyocytes from septic mice (C57Bl/6) showed increased mRNA for TNFR1, IL-6 (gp80), and C5aR at 6 h after sepsis. Cardiomyocytes from septic C5aR-/- or C5L2-/- mice did not show spontaneous in vitro release of cytokines and chemokines. These data suggest that cardiomyocytes from septic mice release suppressive cytokines in a C5a-, C5aR-, and IL-17A-dependent manner, followed by mediator reactivity with receptors on cardiomyocytes, resulting in defective contractility and relaxation. These data may be relevant to a strategy for the treatment of heart dysfunction developing during sepsis. [ABSTRACT FROM AUTHOR]

Acute lung injury (ALI) in mouse lung occurs after distal airway deposition of IgG immune complexes (IgGICs), resulting in a breakdown of the vascular-airway barrier, causing intrapulmonary edema, hemorrhage, and accumulation of neutrophils [polymorphonuclear leukocytes (PMNs)] in the alveolar compartment, these changes being complement (C5a) and C5a receptor (C5aR) dependent. In this ALI model, C5aR expression (protein) was found to occur on upper (bronchial) and lower (alveolar) airway epithelial cells. An adenovirus construct (siRNA) was used to silence mRNA for C5aR in the lung. Under such conditions, C5aR protein was markedly reduced on lung epithelial cells, resulting in much reduced leakage of albumin into the lung, diminished buildup of PMNs, and lower levels of proinflammatory mediators in bronchoalveolar lavage fluids. These studies indicate that bronchial and alveolar epithelial cell CSaR is up-regulated and greatly contributes to inflammation and injury in the lung. The use of siRNA administered into the airways avoids systemic suppression of C5aR, which might compromise innate immunity. It is possible that such an intervention might be employed in humans with ALI or acute respiratory distress syndrome as well as in upper-airway inflammatory diseases, such as chronic obstructive pulmonary disease and asthma, where there is evidence for complement activation and buildup of PMNs. [ABSTRACT FROM AUTHOR]

Pathogen-pattern-recognition by Toll-like receptors (TLRs) and pathogen clearance after immune complex formation via engagement with Fc receptors (FcRs) represent central mechanisms that trigger the immune and inflammatory responses. In the present study, a linkage between TLR4 and FcγR was evaluated in vitro and in vivo. Most strikingly, in vitro activation of phagocytes by IgG immune complexes (IgGIC) resulted in an association of TLR4 with FcγRIII (CD16) based on coimmunoprecipitation analyses. Neutrophils and macrophages from TLR4 mutant (mut) mice were unresponsive to either lipopolysaccharide (LPS) or IgGIC in vitro, as determined by cytokine production. This phenomenon was accompanied by the inability to phosphorylate tyrosine residues within immunoreceptor tyrosine-based activation motifs (ITAMs) of the FcRγ-subunit. To transfer these findings in vivo, two different models of acute lung injury (ALI) induced by intratracheal administration of either LPS or IgGIC were employed. As expected, LPS-induced ALI was abolished in TLR4 mut and TLR4-/- mice. Unexpectedly, TLR4 mut and TLR4-/- mice were also resistant to development of ALI following IgGIC deposition in the lungs. In conclusion, our findings suggest that TLR4 and FcγRIII pathways are structurally and functionally connected at the receptor level and that TLR4 is indispensable for FccRIII signaling via FcRγ-subunit activation. [ABSTRACT FROM AUTHOR]

Activation of the complement system is a key event in the pathogenesis of sepsis. Nevertheless, the exact mechanisms remain inadequately understood. In the current study, we examined the role of complement C3 and C5 in sepsis in wild-type and C3- or C5-deficient mice induced by cecal ligation and puncture. When compared to wild-type mice, C5-/- showed identical survival, and C3-/- presented significantly reduced survival. Interestingly, this was associated with significant decreases in plasma levels of proinflammatory mediators. Moreover, although septic C3-/- animals displayed a 10-fold increase of blood-borne bacteria, C5-/- animals exhibited a 400-fold increase in bacteremia when compared to wild-type mice. These effects were linked to the inability of C5-/- mice to assemble the terminal membrane attack complex (MAC), as determined by complement hemolytic activity (CH-50). Surprisingly, although negative control C3-/- mice failed to generate the MAC, significant increases of MAC formation was found in septic C3-/- mice. In conclusion, our data corroborate that hemolytic complement activity is essential for control of bacteremia in septic mice. Thus, during sepsis, blockade of C5a or its receptors (rather than C5) seems a more promising strategy, because C5a-blockade still allows for MAC formation while the adverse effects of C5a are prevented. [ABSTRACT FROM AUTHOR]

IL-17A is a proinflammatory cytokine produced by a variety of cells. In the current study, we examined the role of IL-17A in sepsis induced in mice by cecal ligation and puncture (CLP). IL-17A levels, which rose time-dependently in plasma after CLP, were not affected in the absence of αβ T cells or neutrophils. In sharp contrast, γδ T cell-knockout or γδ T cell-depleted mice displayed baseline IL-17A plasma levels after CLP. Neutralization of IL-17A by two different antibodies improved sepsis (survival from ∼10% to nearly 60%). Unexpectedly, antibody treatment was protective, even when administration of anti-IL-17A was delayed for up to 12 h after CLP. These protective effects of IL-17A blockade were associated with substantially reduced levels of bacteremia together with significant reductions of systemic proinflammatory cytokines and chemokines in plasma. In vitro incubation of mouse peritoneal macrophages with lipopolysaccharide (LPS) in the copresence of IL-17A substantially increased the production of TNF-α, IL-1β, and IL-6 by these cells. These data suggest that, during experimental sepsis, γδ T cell-derived IL-17A promotes high levels of proinflammatory mediators and bacteremia, resulting in enhanced lethality. IL-17A may be a potential therapeutic target in sepsis.--Flierl, M. A., Rittirsch, D., Gao, H., Hoesel, L. M., Nadeau, B. A., Day, D. E., Zetoune, F. S., Sarma, J. V., Huber-Lang, M. S., Ferrara, J. L. M., Ward, P. A. Adverse functions of IL-17A in experimental sepsis. [ABSTRACT FROM AUTHOR]

The function of the C5a receptors, C5ar (encoded by C5ar) and C5l2 (encoded by Gpr77), especially of C5l2, which was originally termed a 'default receptor', remains a controversial topic. Here we investigated the role of each receptor in the setting of cecal ligation and puncture–induced sepsis by using antibody-induced blockade of C5a receptors and knockout mice. In 'mid-grade' sepsis (30–40% survival), blockade or absence of either C5ar or C5l2 greatly improved survival and attenuated the buildup of proinflammatory mediators in plasma. In vivo appearance or in vitro release of high mobility group box 1 protein (HMGB1) required C5l2 but not C5ar. In 'high-grade' sepsis (100% lethality), the only protective condition was the combined blockade of C5l2 and C5ar. These data suggest that C5ar and C5l2 contribute synergistically to the harmful consequences in sepsis and that C5l2 is required for the release of HMGB1. Thus, contrary to earlier speculation, C5l2 is a functional receptor rather than merely a default receptor. [ABSTRACT FROM AUTHOR]

Defective cardiac function during sepsis has been referred to as "cardiomyopathy of sepsis." It is known that sepsis leads to intensive activation of the complement system. In the current study, cardiac function and cardiomyocyte contractility have been evaluated in rats after cecal ligation and puncture (CLP). Significant reductions in left ventricular pressures occurred in vivo and in cardiomyocyte contractility in vitro. These defects were prevented in CLP rats given blocking antibody to C5a. Both mRNA and protein for the C5a receptor (C5aR) were constitutively expressed on cardiomyocytes; both increased as a function of time after CLP. In vitro addition of recombinant rat C5a induced dramatic contractile dysfunction in both sham and CLP cardiomyocytes, but to a consistently greater degree in cells from CLP animals. These data suggest that CLP induces C5aR on cardiomyocytes and that in vivo generation of C5a causes C5a-C5aR interaction, causing dysfunction of cardiomyocytes, resulting in compromise of cardiac performance. [ABSTRACT FROM AUTHOR]

Presents findings of a study which investigated the presence and regulation of the second C5a receptor on neutrophils and various organs during sepsis. Evaluation the role for C5L2 nucleotide sequence in balancing the biological responses to C5a; Comparison of 5′-RACE polymerase chain reaction, cyclic DNA cloning and sequence in the rat C5L2 receptor; Contrast between C5L2 and C5aR expression in neutrophils during sepsis; Expression of nRNA for C5L2 during sepsis; Effects of αC5aR and αC5L2 on in vitro and in vivo production of interleukin-6.

Presents a study on the effects of C5a on lipopolysaccharide(LPS)-induced interleukin(IL)-6 generation in neutrophils in vitro and on in vivo IL-6 production in septic rodents. Effects of C5a on LPS-induced IL-6 production and gene transcription; Effects of blockade of C5a/C5a receptor activation on serum IL-6 levels during sepsis; Effects of signaling pathway inhibitors on IL-6 production in neutrophils; Conclusions of the study.

Signaling in neutrophils involving the powerful complement anaphylatoxin (C5a) and its receptor (C5aR) plays an essential role in innate immunity. We have previously shown in rodents that blockade of either C5a or C5aR dramatically improves survival rates in experimental sepsis. We have also shown that defensive functions of neutrophils are compromised during sepsis in a C5a-dependent manner. The main aim of the current study was to elucidate the mechanisms for C5aR alteration on neutrophils during sepsis and to evaluate the relationship between C5aR levels on neutrophils and survival after the onset of sepsis. [ABSTRACT FROM AUTHOR]

In human sepsis and in cecal ligation and puncture (CLP)-induced sepsis in rodents, progressive heart failure, as characterized by falling left ventricular pressures and cardiac output, occurs. Human sepsis is associated with the appearance in serum of complement activation products (anaphylatoxins C3a and C5a). In response to pathophysiological stress (such as in sepsis), signaling through the G-protein coupled receptors (such as of C3a and C5a) found on cell membranes in the heart results in the activation of intermediate signaling pathways in cardiomyocytes (CMs) including mitogen-activated protein kinases (MAPKs) and protein kinase C, which in turn modulate transcriptional factors that amplify gene expression. Studies have shown that the three major MAPKs pathways (ERK/MAPK (p42/44), SAPK/JNK (1/2) and p38) are differentially regulated during heart disease. We therefore evaluated the activation status of these pathways in isolated CMs as a function of time after the onset of CLP induced sepsis in rats by Western blotting. Peak activation (as assessed by protein phosphorylation) occurred in all three MAPK pathways in CMs between 12 and 48 hour after CLP. In addition, we found that activation of phospholamban (PLB), an important regulator of calcium homeostasis in CMs, peaked 12 hour after CLP. The relationship between activation of MAPKs and PLB to development of cardiac myopathy during sepsis remains to be determined. These data indicate that during CLP induced sepsis extensive MAPK activation occurs in CMs. [ABSTRACT FROM AUTHOR]

Over the first days of polymicrobial sepsis, there is robust activation of the innate immune system, causing the appearance of proinflammatory cytokines and chemokines, along with the appearance of extracellular histones, which are highly proinflammatory and prothrombotic. In the current study, we studied different innate immune responses in mice with knockout (KO) of complement protein 6 (C6). Polymorphonuclear neutrophils (PMNs) from these KO mice had defective innate immune responses, including defective expression of surface adhesion molecules, generation of superoxide anion, and appearance of reactive oxygen species and histone release after activation of PMNs, along with defective phagocytosis. In addition, in C62/2 mice, the NLRP3 inflammasome was defective both in PMNs and in macrophages. When these KO mice were subjected to polymicrobial sepsis, their survival was improved, associated with reduced levels in the plasma of proinflammatory cytokines and chemokines and lower levels of histones in plasma. In addition, sepsis-induced cardiac dysfunction was attenuated in these KO mice. In a model of acute lung injury induced by LPS, C62/2 mice showed reduced PMN buildup and less lung epithelial/endothelial cell dysfunction (edema and hemorrhage). These data indicate that C62/2 mice have reduced innate immune responses that result in less organ injury and improved survival after polymicrobial sepsis. [ABSTRACT FROM AUTHOR]