Protective effects of anti-C5a in sepsis-induced thymocyte apoptosis

Protective effects of IL-6 blockade in sepsis are linked to reduced C5a receptor expression

IL-6 is known to be an important pro- and anti-inflammatory cytokine, which is up-regulated during sepsis. Our previous work has suggested a role for IL-6 in the up-regulation of C5aR in sepsis. We reported earlier that interception of C5a or C5aR results in improved outcomes in experimental sepsis. Using the cecal ligation/puncture (CLP) model in mice, we now demonstrate that treatment with anti-IL-6 Ab (anti-IL-6) results in significantly improved survival, dependent on the amount of Ab infused. CLP animals showed significantly increased binding of 125I-labeled anti-C5aR to organs when compared to either control mice at 0 h or CLP animals infused with normal rabbit 125I-labeled IgG. Binding of 125I-labeled anti-C5aR to lung, liver, kidney, and heart was significantly decreased in anti-IL-6-treated animals 6 h after CLP. RT-PCR experiments with mRNA isolated from various organs obtained 3, 6, and 12 h after CLP demonstrated increased C5aR mRNA expression during the onset of sepsis, which was greatly suppressed in CLP mice treated with anti-IL-6. These data suggest that IL-6 plays an important role in the increased expression of C5aR in lung, liver, kidney, and heart during the development of sepsis in mice and that interception of IL-6 leads to reduced expression of C5aR and improved survival.

Therapeutic potential of targeting the complement cascade in critical care medicine

Caring for the critical care patient involves many different areas of clinical expertise and serves a diverse patient population. Novel therapeutics for the critically ill must be approached with caution, because the underlying molecular mechanisms of the disease process for several commonly seen types of patients (i.e., sepsis, shock, ischemia/reperfusion) are not fully understood. A potentially new and advancing area of therapeutics that may hold promise for the critically ill is inhibition of the complement system. Various novel complement inhibitors are being developed and several are in clinical trials. The advancement of this novel area of therapeutics may one day aid the clinician by providing several different complement inhibitors/antagonists for controlling complement activation or its biologically active mediators.

Induction of cell death by sera from patients with acute brain injury as a mechanism of production of autoantibodies

OBJECTIVE

To investigate the capacity of blood draining from the central nervous system of patients with acute brain injury to induce cell death, and to determine whether this phenomenon could be a way to induce the production of autoantibodies.

METHODS

The induction of cell death of several human leukemia cell lines cultured in vitro in the presence of serum collected from the brain or the systemic circulation of patients with acute brain injury was analyzed by flow cytometry after staining with annexin V and propidium iodide. The percentages of apoptotic lymphocytes derived directly from the patients were also quantified. To investigate the mechanisms responsible for the induction of cell death, the expression of apoptosis-related molecules, as well as the effect of addition of several molecules known to interfere with apoptosis, was evaluated in the cell cultures. The presence of serum autoantibodies at the time of injury and 6 months later was studied.

RESULTS

Systemic serum and, especially, serum draining from the brain lesions induced the in vitro death of the leukemia cell lines used. Moreover, there were higher percentages of ex vivo dead lymphocytes in regional blood than in systemic blood 48 hours after injury. These effects seemed to be induced by an exogenous and/or endogenous opioid, since they were blocked by the opioid antagonist, naloxone. Furthermore, such effects were mediated by an increased expression of Bax. Importantly, apoptotic Jurkat cells were bound to autoantibodies, and patients with acute brain injury produced serum autoantibodies some months after the injury. However, they did not develop a full autoimmune disease at that time.

CONCLUSION

Serum factors from acute brain injuries induce cell death, both in vivo and in vitro. Apoptotic cells and, even more so, necrotic cells in acute brain injury are potential sources for autoantigen presentation that may stimulate autoimmune responses.

Early circulating lymphocyte apoptosis in human septic shock is associated with poor outcome

The role of lymphocyte apoptosis in septic shock remains a controversial issue. Using Annexin V and flow cytometry analysis on freshly isolated cells, we evaluated circulating lymphocyte apoptosis in 23 septic shock, 25 sepsis without shock, 7 nonseptic critically ill, and 25 control patients. In patients with sepsis, we compared day 1 lymphocyte apoptosis (i.e., within 3 days of the onset of infection) with that observed 5-7 days after (day 6) according to shock state, mortality, and seventy factors. At day 1, patients in septic shock exhibited higher lymphocyte apoptosis than that present in controls (16.5% +/- 3.5% vs. 3% +/- 0.5%, respectively, P = 0.0001). At day 6, patients with sepsis without shock restored undamaged CD4+ T and CD8+ T lymphocyte counts, whereas patients in septic shock increased only CD4+ T cells. Similarly, survivors restored undamaged lymphocyte count at day 6 (+70%, P < 0.001), whereas nonsurvivors did not. Day 6 undamaged lymphocyte count negatively correlated with day 1 SAPS II, day 6 LOD score, mechanical ventilation, and ICU stay duration. We observed no apoptotic effect of septic shock plasma or septic shock circulating mononuclear cells on target lymphoid cell lines. We found no alteration in any death receptors Fas, TRAIL-R1, TRAIL-R2, or in their ligands on circulating blood cells. Catecholamines and interleukin 10 levels significantly increased in patients with septic shock, but did not correlate with apoptosis levels. We conclude that lymphocyte apoptosis is rapidly increased in blood of patients in septic shock and that lymphocyte apoptosis leads to a profound and persistent lymphopenia associated with poor outcome. These results suggest that lymphocyte apoptosis is one of the main components of human septic shock immune dysfunction and could be related more to microcirculatory disturbance than to circulating factors.

Increased C5a receptor expression in sepsis

Excessive production of the complement activation product C5a appears to be harmful during the development of sepsis in rodents. Little is known about the role of the C5a receptor (C5aR) and its presence in different organs during sepsis. Using the cecal ligation/puncture (CLP) model in mice, we show here that C5aR immunoreactivity was strikingly increased in lung, liver, kidney, and heart early in sepsis in both control and neutrophil-depleted mice. C5aR mRNA expression in these organs was also significantly increased during sepsis. Immunohistochemical analysis revealed patterns of increased C5aR expression in parenchymal cells in all four organs following CLP. Mice injected at the start of CLP with a blocking IgG to C5aR (alphaC5aR) showed dramatically improved survival when compared with animals receiving nonspecific IgG, as did mice injected with alphaC5a. In alphaC5aR-treated mice, serum levels of IL-6 and TNF-alpha and bacterial counts in various organs were significantly reduced during CLP when compared with control CLP animals. These studies demonstrate for the first time that C5aR is upregulated in lung, liver, kidney, and heart during the early phases of sepsis and that blockade of C5aR is highly protective from the lethal outcome of sepsis.

Altered neutrophil trafficking during sepsis

In sepsis, dysregulation of the inflammatory system is well known, as reflected in excessive inflammatory mediator production, complement activation, and appearance of defects in phagocytic cells. In the current study sepsis was induced in rats by cecal ligation/puncture. Early in sepsis the beta(1) and beta(2) integrin content on blood neutrophils increased in a nontranscriptional manner, and the increase in beta(2), but not beta(1), integrin content was C5a dependent. Similar changes could be induced in vitro on blood neutrophils following contact with phorbol ester or C5a. Direct injury of lungs of normal rats induced by deposition of IgG immune complexes (IgG-IC) caused 5-fold increases in the myeloperoxidase content that was beta(2), but not beta(1), dependent. In contrast, in cecal ligation/puncture lungs myeloperoxidase increased 10-fold after IgG immune complex deposition and was both beta(1) and beta(2) integrin dependent. These data suggest that sepsis causes enhanced neutrophil trafficking into the lung via mechanisms that are not engaged in the nonseptic state.

C5a receptor and thymocyte apoptosis in sepsis

In sepsis, apoptosis occurs in many different organs. The mediators responsible for induction of apoptosis are not clearly known, although there are some suggestions that C5a and the C5a receptor (C5aR) might be directly linked to apoptosis. In the cecal ligation/puncture (CLP) model of sepsis in rats, apoptosis occurs early in a variety of organs, especially in the thymus. We demonstrate that thymocytes from normal rats show specific, saturable, and high affinity binding of 125I-labeled recombinant rat C5a. C5a binding to thymocytes was significantly increased 3 h after CLP and also when thymocytes from normal rats were first incubated in vitro with lipopolysaccharide (LPS) or IL-6. The expression of C5aR mRNA in thymocytes was markedly increased 3, 6, and 12 h after CLP and increased similarly when normal thymocytes were first exposed to LPS or IL-6 in vitro. Thymocytes obtained 2 or 3 h after CLP and exposed in vitro to C5a, but not normal thymocytes, underwent increased apoptosis, as demonstrated by annexin-V binding, coinciding with increased activation of caspases 3, 6, and 8. These data provide the first direct evidence that in the early onset of sepsis, increased expression of C5aR occurs in thymocytes, which increases their susceptibility to C5a-induced apoptosis.

Induction of anaphylatoxin C5a receptors in rat hepatocytes by lipopolysaccharide in vivo: mediation by interleukin-6 from Kupffer cells

BACKGROUND & AIMS

In normal rat liver, anaphylatoxin C5a induces glucose output from hepatocytes indirectly via prostanoids released from Kupffer cells. Correspondingly, it was found that hepatocytes, in contrast to Kupffer cells, did not express C5a receptors. Lipopolysaccharide (LPS) has been reported to enhance C5a receptor expression in murine livers. This might be the result of de novo expression in hepatocytes.

METHODS

C5a receptor expression was investigated in hepatocytes after in vivo treatment of rats with LPS and in vitro stimulation of isolated cells with LPS and proinflammatory cytokines on messenger RNA (mRNA) and protein level, and functionally in isolated hepatocytes and perfused liver.

RESULTS

In vivo treatment of rats with LPS induced C5a receptor mRNA and protein in hepatocytes with a maximum after 8-10 hours. At this time-point, C5a directly activated glycogen phosphorylase in isolated hepatocytes and enhanced glucose output in perfused livers without the involvement of prostanoids. LPS failed to induce C5a receptors in cultured hepatocytes in vitro, whereas interleukin (IL) 6 and IL-1beta, which are known to be released from Kupffer cells on stimulation with LPS, did so. In cocultures of hepatocytes with Kupffer cells, LPS induced C5a receptors in hepatocytes in an IL-6-dependent manner.

CONCLUSIONS

Thus, IL-6 from Kupffer cells appears to be the main mediator of LPS-induced de novo expression of C5a receptors in hepatocytes.

Molecular signatures of sepsis: multiorgan gene expression profiles of systemic inflammation

During sepsis the host's system-wide response to microbial invasion seems dysregulated. Here we explore the diverse multiorgan transcriptional programs activated during systemic inflammation in a cecal ligation/puncture model of sepsis in rats. Using DNA microarrays representing 7398 genes, we examined the temporal sequence of sepsis-induced gene expression patterns in major organ systems including lung, liver, kidney, thymus, spleen, and brain. Although genes known to be associated with systemic inflammation were identified by our global transcript analysis, many genes and expressed sequence tags not previously linked to the septic response were also elucidated. Taken together, our results suggest activation of a highly complex transcriptional response in individual organs of the septic animal. Several overlying themes emerged from our genome-scale analysis that includes 1) the sepsis response elicited gene expression profiles that were either organ-specific, common to more than one organ, or distinctly opposite in some organs; 2) the brain is protected from sepsis-induced gene activation relative to other organs; 3) the thymus and spleen have an interesting cohort of genes with opposing gene expression patterns; 4) genes with proinflammatory effects were often balanced by genes with anti-inflammatory effects (eg, interleukin-1beta/decoy receptor, xanthine oxidase/superoxide dismutase, Ca2+-dependent PLA2/Ca2+-independent PLA2); and 5) differential gene expression was observed in proteins responsible for preventing tissue injury and promoting homeostasis including anti-proteases (TIMP-1, Cpi-26), oxidant neutralizing enzymes (metallothionein), cytokine decoy receptors (interleukin-1RII), and tissue/vascular permeability factors (aquaporin 5, vascular endothelial growth factor). This global perspective of the sepsis response should provide a molecular framework for future research into the pathophysiology of systemic inflammation. Understanding, on a genome scale, how an organism responds to infection, may facilitate the development of enhanced detection and treatment modalities for sepsis.

Anaphylatoxins and infectious and non-infectious inflammatory diseases

In recent years a plethora of data has accumulated directing toward an important role of polypeptides C3a and C5a and its degradation product C5adesArg, summarized as anaphylatoxins (ATs), in microbial host defense and immune regulation. The ATs exert their various biologic functions by interacting with specific C3a- and C5a-receptors present on cells of myeloid origin, epithelial cells, smooth muscle cells as well as on activated B- and T-cells. Activation of AT receptors mediates signal transduction pathways triggering a variety of proinflammatory events. However, by interacting with the cytokine- and chemokine network C3a and C5a exhibit also anti-inflammatory properties. In this review the focus is on the pathogenetic role of the ATs in sepsis, immune complex disease, delayed type hypersensitivity and asthma. Discussed are data from animal models in which the ATs are blocked by specific C3a or C5a inhibitors or from mice with genetic deletions of the specific receptors of either C3a or C5a/C5adesArg.