Cell death during sepsis: integration of disintegration in the inflammatory response to overwhelming infection

Sepsis is a major health problem and a leading cause of death worldwide. In recent years, a crescendo of attention has been directed to the mechanisms of cell death that develop during this disease, since these are viewed as important contributors to the proinflammatory and anti-inflammatory responses associated with poor outcome. Here we discuss mechanisms of cell death evident severe bacterial infection and sepsis including necrosis, apoptosis, pyroptosis, and extracellular trap-associated neutrophil death, with a particular emphasis on lymphocyte apoptosis and its contribution to the immunosuppressed phenotype of late sepsis. Individual bacterial pathogens express virulence factors that modulate cell death pathways and influence the sepsis phenotype. A greater knowledge of cell death pathways in sepsis informs the potential for future therapies designed to ameliorate immune dysfunction in this syndrome

Computational Identification of Transcriptional Regulators in Human Endotoxemia

One of the great challenges in the post-genomic era is to decipher the underlying principles governing the dynamics of biological responses. As modulating gene expression levels is among the key regulatory responses of an organism to changes in its environment, identifying biologically relevant transcriptional regulators and their putative regulatory interactions with target genes is an essential step towards studying the complex dynamics of transcriptional regulation. We present an analysis that integrates various computational and biological aspects to explore the transcriptional regulation of systemic inflammatory responses through a human endotoxemia model. Given a high-dimensional transcriptional profiling dataset from human blood leukocytes, an elementary set of temporal dynamic responses which capture the essence of a pro-inflammatory phase, a counter-regulatory response and a dysregulation in leukocyte bioenergetics has been extracted. Upon identification of these expression patterns, fourteen inflammation-specific gene batteries that represent groups of hypothetically ‘coregulated’ genes are proposed. Subsequently, statistically significant cis-regulatory modules (CRMs) are identified and decomposed into a list of critical transcription factors (34) that are validated largely on primary literature. Finally, our analysis further allows for the construction of a dynamic representation of the temporal transcriptional regulatory program across the host, deciphering possible combinatorial interactions among factors under which they might be active. Although much remains to be explored, this study has computationally identified key transcription factors and proposed a putative time-dependent transcriptional regulatory program associated with critical transcriptional inflammatory responses. These results provide a solid foundation for future investigations to elucidate the underlying transcriptional regulatory mechanisms under the host inflammatory response. Also, the assumption that coexpressed genes that are functionally relevant are more likely to share some common transcriptional regulatory mechanism seems to be promising, making the proposed framework become essential in unravelling context-specific transcriptional regulatory interactions underlying diverse mammalian biological processes

Hydrodynamic delivery of siRNA in a mouse model of sepsis

The use of siRNA in vivo as well as in animal models has become more widespread in recent years, leading to further questions as to the best mode of delivery that will achieve optimal knockdown. While the exact mechanism of siRNA uptake at a cellular level has yet to be fully elucidated, various delivery techniques are being researched, including the use of viral vectors of shRNA, liposome encapsulations, and hydrodynamic delivery of naked siRNA. We describe the use of hydrodynamic administration as a technique to deliver, in vivo, naked siRNA constructs into experimental animals as a method of transient gene knockdown. This method may prove useful in situations where knockout animals do not exist, or to determine the effect of gene knockdown at specific time points during an experiment. © 2008 Humana Press

Treatment with GITR agonistic antibody corrects adaptive immune dysfunction in sepsis

Apoptosis of CD4+ T cells and TH2 polarization are hallmarks of sepsis-induced immunoparalysis. In this study, we characterized sepsis-induced adaptive immune dysfunction and examined whether improving T-cell effector function can improve outcome to sepsis. We found that septic mice produced less antigen-specific T-cell–dependent IgM and IgG2a antibodies than sham-treated mice. As early as 24 hours after sepsis, CD4+ T cells proliferated poorly to T-cell receptor stimulation, despite normal responses to phorbol myristate acetate and ionomycin, and possessed decreased levels of CD3ζ. Five days following immunization, CD4+ T cells from septic mice displayed decreased antigen-specific proliferation and production of IL-2 and IFN-γ but showed no difference in IL-4, IL-5, or IL-10 production. Treatment of mice with anti-GITR agonistic antibody restored CD4+ T-cell proliferation, increased TH1 and TH2 cytokine production, partially prevented CD3ζ down-regulation, decreased bacteremia, and increased sepsis survival. Depletion of CD4+ T cells but not CD25+ regulatory T cells eliminated the survival benefit of anti-GITR treatment. These results indicate that CD4+ T-cell dysfunction is a key component of sepsis and that improving T-cell effector function may be protective against sepsis-associated immunoparalysis