Richard S. Hotchkiss

The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)

IMPORTANCE Definitions of sepsis and septic shock were last revised in 2001. Considerable advances have since been made into the pathobiology (changes in organ function, morphology, cell biology, biochemistry, immunology, and circulation), management, and epidemiology of sepsis, suggesting the need for reexamination. OBJECTIVE To evaluate and, as needed, update definitions for sepsis and septic shock. PROCESS A task force (n = 19) with expertise in sepsis pathobiology, clinical trials, and epidemiology was convened by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine. Definitions and clinical criteria were generated through meetings, Delphi processes, analysis of electronic health record databases, and voting, followed by circulation to international professional societies, requesting peer review and endorsement (by 31 societies listed in the Acknowledgment). KEY FINDINGS FROM EVIDENCE SYNTHESIS Limitations of previous definitions included an excessive focus on inflammation, the misleading model that sepsis follows a continuum through severe sepsis to shock, and inadequate specificity and sensitivity of the systemic inflammatory response syndrome (SIRS) criteria. Multiple definitions and terminologies are currently in use for sepsis, septic shock, and organ dysfunction, leading to discrepancies in reported incidence and observed mortality. The task force concluded the term severe sepsis was redundant. RECOMMENDATIONS Sepsis should be defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. For clinical operationalization, organ dysfunction can be represented by an increase in the Sequential [Sepsis-related] Organ Failure Assessment (SOFA) score of 2 points or more, which is associated with an in-hospital mortality greater than 10%. Septic shock should be defined as a subset of sepsis in which particularly profound circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than with sepsis alone. Patients with septic shock can be clinically identified by a vasopressor requirement to maintain a mean arterial pressure of 65 mm Hg or greater and serum lactate level greater than 2 mmol/L (>18 mg/dL) in the absence of hypovolemia. This combination is associated with hospital mortality rates greater than 40%. In out-of-hospital, emergency department, or general hospital ward settings, adult patients with suspected infection can be rapidly identified as being more likely to have poor outcomes typical of sepsis if they have at least 2 of the following clinical criteria that together constitute a new bedside clinical score termed quickSOFA (qSOFA): respiratory rate of 22/min or greater, altered mentation, or systolic blood pressure of 100 mm Hg or less. CONCLUSIONS AND RELEVANCE These updated definitions and clinical criteria should replace previous definitions, offer greater consistency for epidemiologic studies and clinical trials, and facilitate earlier recognition and more timely management of patients with sepsis or at risk of developing sepsis.

Sepsis-Induced Apoptosis Causes Progressive Profound Depletion of B and CD4+ T Lymphocytes in Humans

Patients with sepsis have impaired host defenses that contribute to the lethality of the disorder. Recent work implicates lymphocyte apoptosis as a potential factor in the immunosuppression of sepsis. If lymphocyte apoptosis is an important mechanism, specific subsets of lymphocytes may be more vulnerable. A prospective study of lymphocyte cell typing and apoptosis was conducted in spleens from 27 patients with sepsis and 25 patients with trauma. Spleens from 16 critically ill nonseptic (3 prospective and 13 retrospective) patients were also evaluated. Immunohistochemical staining showed a caspase-9-mediated profound progressive loss of B and CD4 T helper cells in sepsis. Interestingly, sepsis did not decrease CD8 T or NK cells. Although there was no overall effect on lymphocytes from critically ill nonseptic patients (considered as a group), certain individual patients did exhibit significant loss of B and CD4 T cells. The loss of B and CD4 T cells in sepsis is especially significant because it occurs during life-threatening infection, a state in which massive lymphocyte clonal expansion should exist. Mitochondria-dependent lymphocyte apoptosis may contribute to the immunosuppression in sepsis by decreasing the number of immune effector cells. Similar loss of lymphocytes may be occurring in critically ill patients with other disorders.

Sepsis-induced immunosuppression: from cellular dysfunctions to immunotherapy

Sepsis — which is a severe life-threatening infection with organ dysfunction — initiates a complex interplay of host pro-inflammatory and anti-inflammatory processes. Sepsis can be considered a race to the death between the pathogens and the host immune system, and it is the proper balance between the often competing pro- and anti-inflammatory pathways that determines the fate of the individual. Although the field of sepsis research has witnessed the failure of many highly touted clinical trials, a better understanding of the pathophysiological basis of the disorder and the mechanisms responsible for the associated pro- and anti-inflammatory responses provides a novel approach for treating this highly lethal condition. Biomarker-guided immunotherapy that is administered to patients at the proper immune phase of sepsis is potentially a major advance in the treatment of sepsis and in the field of infectious disease.

Cell Death in Disease: Mechanisms and Emerging Therapeutic Concepts

One of the abiding mysteries of all multi-cellular organisms is the requirement for controlled death —apoptosis — of unwanted cells. It has been estimated that without apoptosis an 80 year old person would have two tons of bone marrow and lymph nodes and an intestine 16 kilometers long.1 Progress in defining pathways of apoptosis has revealed complex interconnections between various cell death programs that may affect the treatment of a wide range of diseases.2–10 This article reviews advances in our understanding of mechanisms of cell death and highlights current and potential therapies based upon these concepts. Perhaps the most widely used classification of mammalian cell death consists of two types: apoptosis and necrosis.3,4,11 Autophagy, which has recently been proposed as a third distinct mode of cell death, is a process by which cells generate energy and metabolites by digesting organelles or macromolecules.12–15. Normally, autophagy allows a starving cell, or a cell deprived of growth factors to survive.12–15 Ultimately, however, cells deprived of nutrients for extended periods will digest all available substrates and die an ‘autophagy-associated cell death’. Distinctions between apoptosis, necrosis, and autophagy entail differences in mode-specific or selective morphologic, biochemical, and molecular attributes (Fig. 1).3,4,11 Figure 1 Schematic diagram showing 3 possible pathways of cell death An important concept embodied in part by these attributes is “programmed” cell death. Cell death is “programmed” if it is genetically controlled. The two fundamental types of programmed cell death are apoptosis and autophagy-associated cell death.3,12 The recognition that cell death can occur by genetically controlled processes has enabled advances in unraveling the mechanisms of many diseases. As a result, we now have improved knowledge of the initiation of cell death programs and the relevant signaling pathways. This information has facilitated development of pharmacologic agents that initiate or inhibit programmed cell death.6–8,16 Moreover, there is now evidence that necrosis, traditionally considered an accidental form of cell death, can, in certain instances, be initiated or modulated under programmed control mechanisms.17–21

Immunosuppression in sepsis: a novel understanding of the disorder and a new therapeutic approach.

Failures of highly touted trials have caused experts to call for re-evaluation of the current approach toward sepsis. New research has revealed key pathogenic mechanisms; autopsy results have shown that most patients admitted to intensive care units for treatment of sepsis had unresolved septic foci at post mortem, suggesting that patients were unable to eradicate invading pathogens and were more susceptible to nosocomial organisms, or both. These results suggest that therapies that improve host immunity might increase survival. Additional work showed that cytokine production by splenocytes taken post mortem from patients who died of sepsis is profoundly suppressed, possibly because of so-called T-cell exhaustion-a newly recognised immunosuppressive mechanism that occurs with chronic antigenic stimulation. Results from two clinical trials of biomarker-guided therapeutic drugs that boosted immunity showed promising findings in sepsis. Collectively, these studies emphasise the degree of immunosuppression that occurs in sepsis, and explain why many previous sepsis trials which were directed at blocking inflammatory mediators or pathogen recognition signalling pathways failed. Finally, highly encouraging results from use of the new immunomodulatory molecules interleukin 7 and anti-programmed cell death 1 in infectious disease point the way for possible use in sepsis. We hypothesise that immunoadjuvant therapy represents the next major advance in sepsis.

Caspase inhibitors improve survival in sepsis: a critical role of thelymphocyte

Sepsis induces lymphocyte apoptosis and prevention of lymphocyte death may improve the chances of surviving this disorder. We compared the efficacy of a selective caspase-3 inhibitor to a polycaspase inhibitor and to caspase-3−/− mice. Both inhibitors prevented lymphocyte apoptosis and improved survival. Caspase-3−/− mice shared a decreased, but not total, block of apoptosis. The polycaspase inhibitor caused a very substantial decrease in bacteremia. Caspase inhibitors did not benefit RAG-1−/− mice, which had a >tenfold increase in bacteremia compared to controls. Adoptive transfer of T cells that overexpressed the anti-apoptotic protein Bcl-2 increased survival. T cells stimulated with anti-CD3 and anti-CD28 produced increased interleukin 2 and interferon γ by 6 h. Thus, caspase inhibitors enhance immunity by preventing lymphocyte apoptosis and lymphocytes act rapidly, within 24 h, to control infection.

The sepsis seesaw: tilting toward immunosuppression

The immune response goes haywire during sepsis, a deadly condition triggered by infection. Richard S. Hotchkiss and his colleagues take the focus off of the prevailing view that the key aspect of this response is an exuberant inflammatory reaction. They assess recent human studies bolstering the notion that immunosuppression is also a major contributor to the disease. Many people with sepsis succumb to cardiac dysfunction, a process examined by Peter Ward. He showcases the factors that cause cardiomyocyte contractility to wane during the disease.

Differential modulation of endotoxin responsiveness by human caspase-12 polymorphisms

Caspases mediate essential key proteolytic events in inflammatory cascades and the apoptotic cell death pathway. Human caspases functionally segregate into two distinct subfamilies: those involved in cytokine maturation (caspase-1, -4 and -5) and those involved in cellular apoptosis (caspase-2, -3, -6, -7, -8, -9 and -10). Although caspase-12 is phylogenetically related to the cytokine maturation caspases, in mice it has been proposed as a mediator of apoptosis induced by endoplasmic reticulum stress including amyloid-β cytotoxicity, suggesting that it might contribute to the pathogenesis of Alzheimers disease. Here we show that a single nucleotide polymorphism in caspase-12 in humans results in the synthesis of either a truncated protein (Csp12-S) or a full-length caspase proenzyme (Csp12-L). The read-through single nucleotide polymorphism encoding Csp12-L is confined to populations of African descent and confers hypo-responsiveness to lipopolysaccharide-stimulated cytokine production in ex vivo whole blood, but has no significant effect on apoptotic sensitivity. In a preliminary study, we find that the frequency of the Csp12-L allele is increased in African American individuals with severe sepsis. Thus, Csp12-L attenuates the inflammatory and innate immune response to endotoxins and in doing so may constitute a risk factor for developing sepsis.

Apoptosis in lymphoid and parenchymal cells during sepsis : Findings in normal and T- and B-cell-deficient mice

OBJECTIVES To determine if apoptosis (programmed cell death) occurs systemically in lymphoid and parenchymal cells during sepsis. To examine the potential role of T and B cells in the apoptotic process using knockout mice deficient in mature T and B lymphocytes. DESIGN Prospective, randomized, controlled trial. SETTING Animal laboratory in a university medical setting. INTERVENTIONS Cecal ligation and puncture (CLP) (n = 34) or sham surgery (n = 13) was performed in female ND4 mice and, 15 to 22 hrs postoperatively, thymus, lung, heart, spleen, ileum, colon, liver, kidney, brain, and muscle were obtained and examined for apoptosis. A second group of mice (Rag-1) which are totally deficient in mature T and B cells also underwent CLP (n = 14) or sham surgery (n = 14) and had examination of tissues for apoptosis. MEASUREMENTS AND MAIN RESULTS Four methods with varying sensitivities and specificities were used to detect apoptosis, including: a) DNA agarose gel electrophoresis; b) terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL); c) electron microscopy; and d) light microscopy. In CLP mice, multiple methods demonstrated apoptosis in lymphocytes in thymus, spleen, ileum, colon, lung, and skeletal muscle. In addition to lymphocytes, parenchymal cells in ileum, colon, lung, and to a lesser extent, in skeletal muscle and kidney were apoptotic in CLP mice. There was no evidence of apoptosis by any method of detection in liver, brain, or heart. Results in Rag-1 mice which are deficient in T and B cells demonstrated extensive apoptosis in thymus, spleen, and ileum with less degrees of apoptosis in colon and lung. Both lymphoid cells and parenchymal cells were apoptotic. Rag-1 mice which underwent CLP did not die prematurely and there were no apparent observable differences in the physical response (tachypnea, piloerection, lethargy, etc), or intra-abdominal bowel inflammation/adhesions compared with CLP mice with normal T and B cells. CONCLUSIONS Apoptosis is an important mechanism of cell death in lymphocytes and parenchymal cells in sepsis and occurs systemically in many organs. Apoptosis may be an important cause of immunologic suppression in sepsis by inducing widespread lymphocyte depletion. Alternately, apoptosis may be beneficial to host survival by down-regulating the inflammatory response which accompanies sepsis. The degree to which parenchymal cell apoptosis is contributing to multiple organ failure cannot be determined from the present study. Findings in Rag-1 mice demonstrate that mature T and B cells and their secretory products are not necessary for apoptosis to occur during sepsis and that apoptotic cell death is not restricted to T or B cells. Apoptosis may be a key regulator of the balance between the pro- and anti-inflammatory process.

Depletion of Dendritic Cells, But Not Macrophages, in Patients with Sepsis

Dendritic cells (DCs) are a group of APCs that have an extraordinary capacity to interact with T and B cells and modulate their responses to invading pathogens. Although a number of defects in the immune system have been identified in sepsis, few studies have examined the effect of sepsis on DCs, which is the purpose of this study. In addition, this study investigated the effect of sepsis on macrophages, which are reported to undergo apoptosis, and MHC II expression, which has been noted to be decreased in sepsis. Spleens from 26 septic patients and 20 trauma patients were evaluated by immunohistochemical staining. Although sepsis did not decrease the number of macrophages, sepsis did cause a dramatic reduction in the percentage area of spleen occupied by FDCs, i.e., 2.9 ± 0.4 vs 0.7 ± 0.2% in trauma and septic patients, respectively. The number of MHC II-expressing cells, including interdigitating DCs, was decreased in septic, compared with trauma, patients. However, sepsis did not appear to induce a loss of MHC II expression in those B cells, macrophages, or DCs that were still present. The dramatic loss of DCs in sepsis may significantly impair B and T cell function and contribute to the immune suppression that is a hallmark of the disorder.