The acute phase of sepsis is characterized by a strong inflammatory reaction. At later stages in some patients, immunoparalysis may be encountered, which is associated with a poor outcome. By transcriptional and metabolic profiling of human patients with sepsis, we found that a shift from oxidative phosphorylation to aerobic glycolysis was an important component of initial activation of host defense. Blocking metabolic pathways with metformin diminished cytokine production and increased mortality in systemic fungal infection in mice. In contrast, in leukocytes rendered tolerant by exposure to lipopolysaccharide or after isolation from patients with sepsis and immunoparalysis, a generalized metabolic defect at the level of both glycolysis and oxidative metabolism was apparent, which was restored after recovery of the patients. Finally, the immunometabolic defects in humans were partially restored by therapy with recombinant interferon-γ, which suggested that metabolic processes might represent a therapeutic target in sepsis.

BCG vaccination prior to influenza vaccination results in a more pronounced increase and accelerated induction of functional antibody responses against the 2009 pandemic influenza A(H1N1) vaccine strain. These results may have implications for the design of vaccination strategies and could lead to improvement of vaccination efficacy.

During systemic inflammation different neutrophil subsets are mobilized to the peripheral blood. These neutrophil subsets can be distinguished from normal circulating neutrophils (CD16bright/CD62Lbright), based on either an immature CD16dim/CD62Lbright or a CD16bright/CD62Ldim phenotype. Interestingly, the latter neutrophil subset is known to suppress lymphocyte proliferation ex vivo, but how neutrophils become suppressive is unknown. We performed transcriptome analysis on the different neutrophil subsets to identify changes in mRNA expression that are relevant for their functions. Neutrophil subsets were isolated by fluorescence-activated cell sorting from blood of healthy volunteers that were administered a single dose of lipopolysaccharide (2 ng/kg i.v.) and the transcriptome was determined by microarray analysis. Interestingly, the CD16bright/CD62Ldim suppressive neutrophils showed an interferon-induced transcriptome profile. More importantly, IFN-γ, but not IFN-α or IFN-β stimulated neutrophils, acquired the capacity to suppress lymphocyte proliferation through the expression of programmed death ligand 1 (PD-L1). These data demonstrate that IFN-γ-induced expression of PD-L1 on neutrophils enables suppression of lymphocyte proliferation. Specific stimulation of neutrophils present at the inflammatory sites might therefore have a pivotal role in regulating lymphocyte-mediated inflammation and autoimmune disease.

No abstract

Sepsis is the leading cause of death in the intensive care unit and ranks in the top 10 causes of death in general worldwide. Proinflammatory mediators are related to symptoms observed early in patients with sepsis, such as fever and hemodynamic instability. However, in recent years it has become clear that most septic patients do not die from an overwhelming proinflammatory immune response but in an immunosuppressive state, which can last for days or even weeks, and that results in increased susceptibility to secondary (opportunistic) infections. Although infection control and supportive therapies will remain the cornerstone of treatment, especially in the early phase of sepsis, the identification of this so-called "immunoparalysis" is currently causing a paradigm shift in the adjunctive treatment of sepsis from therapies that suppress the immune system toward immunostimulation. In this Critical Care Perspective we give an overview of the pathophysiology of sepsis, with a focus on immunosuppressive mechanisms that play an important role in outcome. In addition, we present an appraisal of the recent advances in immunotherapy as an adjunctive treatment for sepsis.