Fas-Ligand Mediated Apoptosis in Severe Sepsis and Shock

Altered DNA methylation underlies monocyte dysregulation and immune exhaustion memory in sepsis

Monocytes can develop an exhausted memory state characterized by reduced differentiation, pathogenic inflammation, and immune suppression that drives immune dysregulation during sepsis. Chromatin alterations, notably via histone modifications, underlie innate immune memory, but the contribution of DNA methylation remains poorly understood. Using an ex vivo sepsis model, we show altered DNA methylation throughout the genome of exhausted monocytes, including genes implicated in immune dysregulation during sepsis and COVID-19 infection (e.g., Plac8). These changes are recapitulated in septic mice induced by cecal slurry injection. Methylation profiles developed in septic mice are maintained during ex vivo culture, supporting the involvement of DNA methylation in stable monocyte exhaustion memory. Methylome reprogramming is driven in part by Wnt signaling inhibition in exhausted monocytes and can be reversed with DNA methyltransferase inhibitors, Wnt agonists, or immune training molecules. Our study demonstrates the significance of altered DNA methylation in the maintenance of stable monocyte exhaustion memory.

A novel anoikis-related gene signature predicts prognosis in patients with sepsis and reveals immune infiltration

Sepsis is a common acute and severe medical condition with a high mortality rate. Anoikis, an emerging form of cell death, plays a significant role in various diseases. However, the role of anoikis in sepsis remains poorly understood. Based on the datasets from Gene Expression Omnibus and anoikis-related genes from GeneCards, the differentially expressed anoikis-related genes (DEARGs) were identified. Based on hub genes of DEARGs, a novel prognostic risk model was constructed, and the pattern of immune infiltration was investigated by CIBERSORT algorithm. And small molecule compounds targeting anoikis in sepsis were analyzed using Autodock. Of 23 DEARGs, CXCL8, CFLAR, FASLG and TP53 were significantly associated with the prognosis of sepsis (P < 0.05). Based on the prognostic risk model constructed with these four genes, high-risk population of septic patients had significant lower survival probability than low-risk population (HR = 3.30, P < 0.001). And the level of CFLAR was significantly correlated with the number of neutrophils in septic patients (r = 0.54, P < 0.001). Moreover, tozasertib had low binding energy with CXCL8, CFLAR, FASLG and TP53, and would be a potential compound for sepsis. Conclusively, our results identified a new prognostic model and potential therapeutic molecular for sepsis, providing new insights on mechanism and treatment of sepsis.

Neutrophil-to-lymphocyte ratio as a promising non-invasive biomarker for symptom assessment and diagnosis of interstitial cystitis/bladder pain syndrome

BACKGROUND

Our study aims to investigate the association between the serum neutrophil-to-lymphocyte ratio (NLR) and interstitial cystitis (IC), as well as to explore whether NLR can serve as a diagnostic marker to distinguish IC from overactive bladder (OAB). We postulate that elevated NLR levels are intricately linked to the onset and clinical presentation of IC, and that the NLR profiles in OAB patients exhibit discernible disparities from those of IC patients.

METHODS

In a retrospective analysis, we scrutinized the medical records of 70 women diagnosed with IC/BPS, 20 women diagnosed with OAB, and a randomly selected cohort of 150 healthy women who underwent physical examinations during the same temporal frame. A comprehensive panel of blood tests was administered to all participants, and NLR was determined through the calculation of the neutrophil-to-lymphocyte proportion. Additionally, symptom assessment questionnaires and urination diaries were collected from IC/BPS patients.

RESULTS

NLR levels exhibited significant distinctions among the IC/BPS, Normal, and OAB groups (P < 0.001). Within the IC/BPS group, Hunner type interstitial cystitis (HIC) demonstrated notably divergent NLR levels in comparison to non-Hunner type interstitial cystitis (NHIC) (p = 0.001). Additionally, we observed positive correlations between NLR and Nighttime voids (r = 0.268, p = 0.029), ICPI (r = 0.327, p = 0.007), ICSI (r = 0.369, p = 0.002), PUF Symptom Scale (r = 0.263, p = 0.032), and PUF (r = 0.297, p = 0.015). The receiver operating characteristic (ROC) analysis yielded an area under the curve (AUC) of 0.765 for NLR in distinguishing IC/BPS from the Normal group, and an AUC of 0.707 in discerning IC from OAB. Furthermore, the AUC of NLR was 0.723 for identifying HIC and NHIC patients.

CONCLUSIONS

Our study unveils the prospective utility of serum NLR as a promising biomarker for both diagnostic and symptom evaluation purposes in IC/BPS patients. It effectively demarcates this condition from OAB, which presents with similar clinical features. Consequently, NLR demonstrates potential as a non-invasive diagnostic instrument to distinguish between the subtypes of IC, particularly HIC and NHIC, which manifest similar symptoms within the IC/BPS spectrum.

Altered DNA methylation underlies monocyte dysregulation and innate exhaustion memory in sepsis

Innate immune memory is the process by which pathogen exposure elicits cell-intrinsic states to alter the strength of future immune challenges. Such altered memory states drive monocyte dysregulation during sepsis, promoting pathogenic behavior characterized by pro-inflammatory, immunosuppressive gene expression in concert with emergency hematopoiesis. Epigenetic changes, notably in the form of histone modifications, have been shown to underlie innate immune memory, but the contribution of DNA methylation to this process remains poorly understood. Using an ex vivo sepsis model, we discovered broad changes in DNA methylation throughout the genome of exhausted monocytes, including at several genes previously implicated as major drivers of immune dysregulation during sepsis and Covid-19 infection (e.g. Plac8 ). Methylome alterations are driven in part by Wnt signaling inhibition in exhausted monocytes, and can be reversed through treatment with DNA methyltransferase inhibitors, Wnt agonists, or immune training molecules. Importantly, these changes are recapitulated in septic mice following cecal slurry injection, resulting in stable changes at critical immune genes that support the involvement of DNA methylation in acute and long-term monocyte dysregulation during sepsis.

Correlation between neutrophil to lymphocyte ratio and overactive bladder in South Korean women: a community-based, cross-sectional study

OBJECTIVE

Many women with overactive bladder (OAB) do not seek medical care despite urinary symptoms. As the diagnosis and treatment of OAB are often late, there is a need to identify undiagnosed OAB patients and start effective treatment. Furthermore, an objective and appropriate screening biomarker for OAB is needed. This study aimed to investigate the relationship between serum neutrophil-to-lymphocyte ratio (NLR) and OAB in South Korean women.

DESIGN

Cross-sectional, retrospective study.

SETTING

Jeju National University Hospital.

PARTICIPANTS

This study included a total of 4394 women (mean age=48.6 years) who underwent self-referred health screenings.

INTERVENTIONS

Blood tests were conducted and the NLR was calculated by dividing the number of neutrophils by the number of lymphocytes.

OUTCOME MEASURES

The severity of OAB was evaluated using the OAB Symptom Score (OABSS).

RESULTS

Approximately 9.8% of participants (n=432) were diagnosed with OAB. The association pattern between the NLR and urinary tract symptoms was variable; however, NLR was associated with OAB, by the OABSS and OAB severity (p<0.001). The NLR had a significant relationship with OAB after age, body mass index, homoeostatic model assessment for insulin resistance, 25-hydroxyvitamin D, stress status, and medication for hypertension (OR 1.19, 95% CI 1.06 to 1.32) were adjusted.

CONCLUSIONS

Elevated NLR is associated with OAB; hence, NLR may be a cost-effective and readily available biomarker of OAB in women.

Evaluation of molecular changes of distal organs after small bowel transplantation

The ischemia and reperfusion of a jejunal graft during transplantation triggers the stress of endoplasmic reticulum thus inducing the synthesis of pro-inflammatory cytokines. Spreading of these signals stimulate immunological reactions in distal tissues, i.e. lung, liver and spleen. The aim of this study was to detect the molecular changes in liver and spleen induced by transplanted jejunal graft with one or six hours of reperfusion (group Tx1 and Tx6). Analysis of gene expression changes of inflammatory mediators (TNF-alpha, IL-10) and specific chaperones (Gadd153, Grp78) derived from endoplasmic reticulum (ER) was done and compared to control group. The qRT-PCR method was used for amplification of the specific genes. The levels of corresponding proteins were detected by Western blot with immunodetection. Protein TNF-alpha was in liver tissue significantly overexpressed in the experimental group Tx1 by 48 % (p<0.001). In the group Tx6 we found decreased levels of the same protein to the level of controls. However, the protein concentrations of TNF-alpha in spleen showed increased levels in group Tx1 by 31 % (p<0.001) but even higher levels in the group Tx6 by 115 % (p<0.001) in comparing to controls. Our data demonstrated that the spleen is more sensitive to post-transplantation inflammation than liver, with consequent stress of ER potentially inducing apoptosis and failure of basic functions of lymphoid tissue.

The protective role of human ghrelin in sepsis: Restoration of CD4 T cell proliferation

Decrease of CD4 T cell numbers causes immunosuppression in sepsis. We previously showed the beneficial role of ghrelin in sepsis. We hypothesize that the protective outcome of ghrelin in sepsis is mediated partially through the restoration of CD4 T cells’ proliferation. Sepsis was induced in mice by cecal ligation and puncture (CLP). The percentage of CD4 T cells in spleen was assessed by flow cytometry and their proliferation was determined by carboxyfluorescein succinimidyl ester (CSFE). Compared to sham mice, the percentages of splenic CD4 T cells were reduced by 20%, 21%, and 29% at day 1, 2 and 3 after CLP, respectively. Human ghrelin was given to 3 day septic mice by s.c. injection at 5 and 24 h after CLP. Treatment with ghrelin restored the loss of CD4 T cells by increasing their proliferation in septic mice. The expression of cyclin D1 and B1 was significantly increased, while the expression of p57 was decreased in ghrelin-treated mice compared to vehicle-treated mice in sepsis. Treatment with human ghrelin significantly increased the p-AKT levels in the spleen compared to vehicle-treated septic mice. Human ghrelin plays an important role in reestablishing the proliferation of CD4 T cells and serves as a promising therapeutic agent in sepsis.

Apoptotic Diminution of Immature Single and Double Positive Thymocyte Subpopulations Contributes to Thymus Involution During Murine Polymicrobial Sepsis

To generate and maintain functional T-cell receptor diversity, thymocyte development is tightly organized. Errors in this process may have dramatic consequences, provoking, for example, autoimmune diseases. Probably for this reason, the thymus reacts to septic stress with involution, decreasing the numbers of thymocytes. Because it is still unclear which thymocyte subpopulation contributes to thymus involution and whether thymocyte emigration is altered, we were interested to clarify this question in detail. Here, we show, using the cecal ligation and puncture (CLP) mouse model of polymicrobial sepsis, that predominantly immature thymocytes are reduced. The number of immature single positive thymocytes was most marked diminished (CLP: 6.54 × 10 ± 3.79 × 10 vs. sham: 4.54 × 10 ± 7.66 × 10 cells/thymus [24 h], CLP: 2.60 × 10 ± 2.14 × 10 vs. sham: 2.17 × 10 ± 1.90 × 10 cells/thymus [48 h]), and was consequently associated with the highest rate of apoptosis (8.4 [CLP] vs. 2.2% [sham]), the reduction in double positive thymocytes being associated with a smaller apoptotic response (number, CLP: 2.33 × 10 ± 1.38 × 10 vs. sham: 1.07 × 10 ± 2.72 × 10 cells/thymus [24 h], CLP: 2.34 × 10 ± 9.08 × 10 vs. sham: 3.5 × 10 ± 9.62 × 10 cells/thymus [48 h]; apoptosis: 2.5% [CLP] vs. 0.7% [sham]). Analysis of T-cell receptor excision circles revealed that the emigration of mature thymocytes was not inhibited. Real-time qPCR analysis revealed upregulation of pro-apoptotic Bim expression and suggested interference between Notch receptor expression on thymocytes and the respective ligands on thymic stromal cells during CLP-dependent sepsis, which might be responsible for the altered thymocyte viability in CLP-dependent sepsis.

Usefulness of neutrophil-lymphocyte ratio in young children with febrile urinary tract infection

PURPOSE

Acute pyelonephritis (APN) is a serious bacterial infection that can cause renal scarring in children. Early identification of APN is critical to improve treatment outcomes. The neutrophil-lymphocyte ratio (NLR) is a prognostic marker of many diseases, but it has not yet been established in urinary tract infection (UTI). The aim of this study was to determine whether NLR is a useful marker to predict APN or vesicoureteral reflux (VUR).

METHODS

We retrospectively evaluated 298 pediatric patients (age≤36 months) with febrile UTI from January 2010 to December 2014. Conventional infection markers (white blood cell [WBC] count, erythrocyte sedimentation rate [ESR], C-reactive protein [CRP]), and NLR were measured.

RESULTS

WBC, CRP, ESR, and NLR were higher in APN than in lower UTI (P<0.001). Multiple logistic regression analyses showed that NLR was a predictive factor for positive dimercaptosuccinic acid (DMSA) defects (P<0.001). The area under the receiver operating characteristic (ROC) curve was high for NLR (P<0.001) as well as CRP (P<0.001) for prediction of DMSA defects. NLR showed the highest area under the ROC curve for diagnosis of VUR (P<0.001).

CONCLUSION

NLR can be used as a diagnostic marker of APN with DMSA defect, showing better results than those of conventional markers for VUR prediction.

Overexpression of Fas and FasL is associated with infectious complications and severity of experimental severe acute pancreatitis by promoting apoptosis of lymphocytes

This study investigated the relationship of Fas and Fas ligand (FasL) expression and apoptosis of lymphocytes in relation to the pathogenic immune response and infectious complications observed in experimental severe acute pancreatitis in mice. Forty male Balb/c mice were randomly divided into control, mild (MAP), and severe acute pancreatitis (SAP) groups. Overexpression of Fas/FasL messenger ribonucleic acid (mRNA) and protein was observed in spleen-derived lymphocytes in SAP (p < 0.01). Apoptosis of these resulted in a depletion of circulating lymphocytes in this group (p < 0.05). A further significant change in the SAP group with infectious complications was observed. A positive relationship was found between the Fas/FasL expression and lymphocyte apoptosis, and negative relationships were observed between Fas/FasL expression and CD4⁺ and CD19⁺ lymphocytes and the CD4⁺/CD8⁺ ratio in SAP mice (p < 0.01). The results suggest that the overexpression of Fas/FasL is associated with infectious complications and severity of experimental severe acute pancreatitis by promoting apoptosis of lymphocytes.

Progression of apoptic signaling from mesenteric ischemia-reperfusion injury to lungs: correlation in the level of ER chaperones expression

Multiple organ dysfunction syndrome (MODS) is characterized by the development of probably reversible, progressive dysfunction of vital systems in two or more organs, directly undamaged by surgery or other trauma. The organs which have the most common potential dysfunction are lungs, liver, kidneys, heart and gastrointestinal tract. The small intestine is the source of production of proinflammatory mediators leading and contributing to multiorgan failure. The endoplasmic reticulum (ER), after ischemia and post-ischemic reperfusion, is significantly involved in the activation of enterocyte apoptosis. The purpose of this study was to determine the stage of apoptosis in the lungs, initiated through inflammatory response from the small intestine. We analyzed changes in mRNA levels of pro-apoptotic genes Gadd153 (Chop) and anti-apoptotic genes Grp78 (Bip) in the small intestine wall and lung parenchyma. During experimental procedure the rats underwent 60 min of ischemia, caused by complete occlusion of the mesenteric arteria cranialis, with subsequent reperfusion and evaluation after 1 h, 24 h and 30 days (from R1, R24 to R30, respectively, each group n = 8). The gene expression levels were measured using RT-PCR followed by electrophoresis and visualization under UV. In the lungs we detected significantly lower level of expression Grp78 by 45 ± 6.9%. This suggests that ischemic attack and subsequent reperfusion did not promote ER stress in the lungs through induction of Gadd153 expression in the small intestine. There is still no effective approach to the treatment of affected ischemic intestine tissue, to stop the processes with could eventually lead to MODS. Therefore it is necessary to study changes in the damaged tissue at the molecular level and try to suggest possible therapeutic defined routes to the protection of tissue.

Sepsis-induced apoptosis leads to active suppression of delayed-type hypersensitivity by CD8+ regulatory T cells through a TRAIL-dependent mechanism

Patients who survive severe sepsis often display severely compromised immune function. One hallmark of such immune suppression in septic patients is an impaired delayed-type hypersensitivity (DTH) response, manifested by a loss of skin testing to recall Ags. Because sepsis induces significant apoptosis in lymphoid and myeloid cells, and apoptotic cells are themselves tolerogenic, we tested the hypothesis that suppression of DTH is mediated by tolerogenic properties of the apoptotic cells generated during sepsis. Mice subjected to cecal ligation and puncture demonstrated a loss of DTH for the 7 d following cecal ligation and puncture; however, the immune response returned to normal by day 10. Blocking sepsis-induced apoptosis via Bcl-2 overexpression or Bim deficiency prevented the loss of DTH. Importantly, injection of apoptotic cells into Bim-/- mice prevented an effective DTH response, thereby suggesting a causal link between apoptotic cells and immune suppression. Surprisingly, when TRAIL null mice were examined, we found that these animals had significant apoptosis but retained their DTH responses. Further studies revealed that apoptotic cells generated during sepsis induced a CD8+ regulatory T cell that suppressed DTH by TRAIL production. These results establish a link between apoptotic cells and immune suppression during sepsis and suggest TRAIL may be a viable therapeutic target for boosting the adaptive immune response following sepsis.

Immature dendritic cell-derived exosomes rescue septic animals via milk fat globule epidermal growth factor-factor VIII [corrected]

Sepsis, a highly lethal systemic inflammatory syndrome, is associated with increases of proinflammatory cytokines (e.g., TNF-alpha, HMGB1) and the accumulation of apoptotic cells that have the potential to be detrimental. Depending on the timing and tissue, prevention of apoptosis in sepsis is beneficial; however, thwarting the development of secondary necrosis through the active removal of apoptotic cells by phagocytosis may offer a novel anti-sepsis therapy. Immature dendritic cells (IDCs) release exosomes that contain milk fat globule EGF factor VIII (MFGE8), a protein required to opsonize apoptotic cells for phagocytosis. In an experimental sepsis model using cecal ligation and puncture, we found that MFGE8 levels decreased in the spleen and blood, which was associated with impaired apoptotic cell clearance. Administration of IDC-derived exosomes promoted phagocytosis of apoptotic cells and significantly reduced mortality. Treatment with recombinant MFGE8 was equally protective, whereas MFGE8-deficient mice suffered from increased mortality. IDC exosomes also attenuated the release of proinflammatory cytokines in septic rats. Liberation of HMGB1, a nuclear protein that contributes to inflammation upon release from unengulfed apoptotic cells, was prevented by MFGE8-mediated phagocytosis in vitro. We conclude that IDC-derived exosomes attenuate the acute systemic inflammatory response in sepsis by enhancing apoptotic cell clearance via MFGE8.

Phagocytosis and postphagocytic reaction of cord blood and adult blood monocyte after infection with green fluorescent protein-labeled Escherichia coli and group B Streptococci

BACKGROUND

Neonatal sepsis is characterized by an excessive inflammatory response induced by immune cells (monocytes). We investigated the initial stage of monocyte-pathogen interaction, i.e. bacterial ingestion and degradation at the single-cell level, by comparing a new flow cytometric procedure with culture methods. We also examined the hypothesis that, in terms of phagocytosis-induced cell death (PICD), phenotype, or cytokine production, cord blood monocytes (CBMO) differ from monocytes derived from adults (peripheral blood monocytes, PBMO).

METHODS

Phagocytosis and intracellular degradation were assessed by means of flow cytometry and bacterial cultures of green fluorescent protein-labeled group B Streptococci (GBS) and Escherichia coli. The production of reactive oxygen species (ROS) was measured through luminol-enhanced chemiluminescence. Apoptosis, phenotype, and cytokine production were assessed through flow cytometry.

RESULTS

Flow cytometry and bacterial cultures showed no difference between phagocytosis and degradation of GBS and E. coli by PBMO and CBMO. A high correlation between both methods was observed. No difference in ROS production was evident. In comparison with PBMO, CBMO apoptosis was lower after exposure to GBS and E. coli. Similarities were found between nonapoptotic monocytes and pro-inflammatory monocytes.

CONCLUSIONS

PICD is lower in CBMO during the early stages of monocyte-pathogen interaction. Our results emphasize that monocyte apoptosis has a potential role in tailoring the immune response in neonatal sepsis.

INTESTINAL ISCHEMIA-REPERFUSION-INDUCED ACUTE LUNG INJURY AND ONCOTIC CELL DEATH IN MULTIPLE ORGANS

Most acute respiratory distress syndrome studies have been focused on the lung injury. Little is known about other organs during the development of acute respiratory distress syndrome. Herein, we investigated the injury and cell death in multiple organs after intestinal ischemia-reperfusion (IIR) in C57BL/6 mice. Terminal transferase dUTP nick end labeling staining was used as a marker of cell death. Caspase 3 and cathepsin B activation as markers of caspase-dependent and caspase-independent apoptosis, respectively, and electron microscopy for ultimate characterization of cell death were used. In comparison with control and sham-operated mice, the IIR group showed interstitial inflammatory infiltrates in the lung and significant increases of lung injury parameters and plasma lactate dehydrogenase and aspartate aminotransferase levels. Terminal transferase dUTP nick end labeling-positive cells and immunostaining for hemeoxygenase 1, an enzyme induced by inflammatory stimuli, were increased in the lung, heart, and kidney, but not in the liver. The number of hemeoxygenase 1-positive cells positively and significantly correlated to the number of terminal transferase dUTP nick end labeling-positive cells. Cell death was not associated with caspase 3 or cathepsin B activation. Electron microscopy showed morphological features compatible with oncotic rather than apoptotic cell death or necrosis, including mitochondrial swelling and cytoplasm disorganization in pulmonary and renal epithelial cells, lung and cardiac endothelial cells, and myocytes. These results indicate that, although lung injury is the most significant manifestation after IIR, oncotic cell death occurs in the lung, heart, and kidney, which may be related to ischemia and inflammation.

Human CD4+CD25+ regulatory T lymphocytes inhibit lipopolysaccharide-induced monocyte survival through a Fas/Fas ligand-dependent mechanism

Although it is known that septic shock induces immunosuppression, the mechanism for this phenomenon is not well understood. Monocytes play a central role in septic shock pathophysiology, which is also characterized by an increased proportion of natural regulatory T (Treg) cells. We therefore investigated whether Treg could be involved in the decreased monocyte expression of CD14 and HLA-DR observed during septic shock. We demonstrated that human Treg inhibit LPS-induced retention of monocyte CD14. Because loss of CD14 is a hallmark of monocyte apoptosis, this suggests that Treg inhibit monocyte survival. This effect was largely mediated through the release of a soluble mediator that was not identical with either IL-10 or IL-4. The Fas/FasL pathway participated in the effect as it was blocked by anti-FasL Abs and reproduced by Fas agonist and recombinant soluble FasL. Furthermore, expression of FasL was much higher on Treg than on their CD25(-) counterparts. Collectively, these results indicate that Treg act on monocytes by inhibiting their LPS-induced survival through a proapoptotic mechanism involving the Fas/FasL pathway. This may be an important mechanism for septic shock-induced immunosuppression and may offer new perspectives for the treatment of this deadly disease.

Sepsis during pregnancy

OBJECTIVES

To provide a current review of the literature regarding the assessment and management of sepsis during pregnancy.

DESIGN

A comprehensive review of current English-language literature search was performed with Ovid MEDLINE using the Medical Subject Headings pregnancy and sepsis, with Medical Subject Headings or keywords seeking randomized controlled trials and clinical reports, and by reviewing the bibliographies of clinical practice guidelines.

RESULTS

Sepsis-related maternal morbidity and mortality is a significant and persistent problem in the modern critical care obstetric unit. The management of sepsis during pregnancy is challenging. The obstetric intensivist must simultaneously discern the effect of maternal physiologic changes on fetal vulnerability and the effect of the fetus on maternal status throughout the various phases of pregnancy. Little direct evidence exists to validate the extrapolation of some sepsis treatment modalities from other nonpregnant patient populations. Nevertheless, early detection, accurate diagnosis, and aggressive appropriate treatment strategies may significantly improve outcome. Approaches like the Surviving Sepsis Campaign guidelines are unproven but seem reasonable and practical.

CONCLUSIONS

Sepsis during pregnancy is uncommon yet potentially fatal. Diagnostic and therapeutic guidelines should predominantly pattern those currently utilized for nonpregnant patients.

Role of increased sphingomyelinase activity in apoptosis and organ failure of patients with severe sepsis

Numerous studies support the notion that an activation of sphingomyelinases and a subsequent increase of the concentration of the bioactive lipid mediator ceramide are critical in the concert of inflammatory stimuli and to the induction of apoptosis during inflammation. Here we show that patients with severe sepsis exhibit an enhanced sphingolytic activity in comparison with controls [262 pmol/(mlxh) vs. 123.6 pmol/(mlxh), P<0.005]. During the clinical course, a further increase was paralleled by the severity of illness and by fatal outcome. Moreover, we show that oxidative stress may partially account for the increased activity through posttranslational modification of the enzyme. In a murine endotoxic shock model, administration of a low molecular weight inhibitor diminished the rise in enzymatic activity and improved the survival rate. In liver specimen, inhibition of activity correlated with a reduced rate of hepato-cellular apoptosis. Our data support the concept that activation of the plasmatic isoform of sphingomyelinase may play a critical role in the development of apoptosis and organ failure in sepsis. An inhibition of the secreted isoform of sphingomyelinase should be explored further as a potential target in the complicated puzzle of sepsis.