Enhanced T-cell apoptosis in human septic shock is associated with alteration of the costimulatory pathway

Identification of Potential Biomarkers of Septic Shock Based on Pathway and Transcriptome Analyses of Immune-Related Genes

Immunoregulation is crucial to septic shock (SS) but has not been clearly explained. Our aim was to explore potential biomarkers for SS by pathway and transcriptional analyses of immune-related genes to improve early detection. GSE57065 and GSE95233 microarray data were used to screen differentially expressed genes (DEGs) in SS. Gene Ontology and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analyses of DEGs were performed, and correlations between immune cell and pathway enrichment scores were analyzed. The predictive value of candidate genes was evaluated by receiver operating characteristic (ROC) curves. GSE66099, GSE4607, and GSE13904 datasets were used for external validation. Blood samples from six patients and six controls were collected for validation by qRT-PCR and western blotting. In total, 550 DEGs in SS were identified; these genes were involved in the immune response, inflammation, and infection. Immune-related pathways and levels of infiltration of CD4 + TCM, CD8 + T cells, and preadipocytes differed between SS cases and controls. Seventeen genes were identified as potential biomarkers of SS (areas under ROC curves >0.9). The downregulation of CD8A, CD247, CD3G, LCK, and HLA-DRA in SS was experimentally confirmed. We identified several immune-related biomarkers in SS that may improve early identification of disease risk.

Highlighting the Relevance of CD8+ T Cells in Filarial Infections

The T cell immune responses in filarial infections are primarily mediated by CD4+ T cells and type 2-associated cytokines. Emerging evidence indicates that CD8+ T cell responses are important for anti-filarial immunity, however, could be suppressed in co-infections. This review summarizes what we know so far about the activities of CD8+ T cell responses in filarial infections, co-infections, and the associations with the development of filarial pathologies.

Circulating BiP/Grp78 is a novel prognostic marker for sepsis-mediated immune cell death

Sepsis remains to be a major contributor to mortality in ICUs, and immune suppression caused by immune cell apoptosis determines the overall patient survival. However, diagnosis of sepsis-induced lymphopenia remains problematic with no accurate prognostic techniques or biomarkers for cell death available. Developing reliable prognostic tools for sepsis-mediated cell death is not only important for identifying patients at increased risk of immune suppression but also to monitor treatment progress of currently trialed immunotherapy strategies. We have previously shown an important role for endoplasmic reticulum stress (ER stress) in inducing sepsis-mediated cell death and here report on the identification of a secreted form of the ER chaperone BiP (immunoglobulin binding protein) as a novel circulating prognostic biomarker for immune cell death and ER stress during sepsis. Using biochemical purification and mass spectrometry coupled with an established in vitro sepsis cell death assay, we identified BiP/Grp78 as a factor secreted by lipopolysaccharide-activated macrophages that is capable of inducing cell death in target cells. Quantitative ELISA analysis showed significantly elevated levels of circulating BiP in mice undergoing polymicrobial sepsis, which was absent in Bim^-/- mice that are protected from sepsis-induced lymphopenia. Using blood serum from human sepsis patients, we could detect a significant difference in levels of secreted BiP in sepsis patients compared to nonseptic controls, suggesting that secreted circulating BiP could indeed be used as a prognostic marker that is directly correlative to immune cell death during sepsis.

Inhibitory Immune Checkpoint Molecule Expression in Clinical Sepsis Studies: A Systematic Review

OBJECTIVES

Checkpoint inhibitors have been proposed for sepsis following reports of increased checkpoint molecule expression in septic patients. To determine whether clinical studies investigating checkpoint molecule expression provide strong evidence supporting trials of checkpoint inhibitors for sepsis.

DATA SOURCES

PubMed, EMBASE, Scopus, Web of Science, inception through October 2019.

STUDY SELECTION

Studies comparing checkpoint molecule expression in septic patients versus healthy controls or critically ill nonseptic patients or in sepsis nonsurvivors versus survivors.

DATA EXTRACTION

Two investigators extracted data and evaluated study quality.

DATA SYNTHESIS

Thirty-six studies were retrieved. Across 26 studies, compared with healthy controls, septic patients had significantly (p ≤ 0.05) increased CD4+ lymphocyte programmed death-1 and monocyte programmed death-ligand-1 expression in most studies. Other checkpoint molecule expressions were variable and studied less frequently. Across 11 studies, compared with critically ill nonseptic, septic patients had significantly increased checkpoint molecule expression in three or fewer studies. Septic patients had higher severity of illness scores, comorbidities, and mortality in three studies providing analysis. Across 12 studies, compared with septic survivors, nonsurvivors had significantly increased expression of any checkpoint molecule on any cell type in five or fewer studies. Of all 36 studies, none adjusted for nonseptic covariates reported to increase checkpoint molecule expression.

CONCLUSIONS

Although sepsis may increase some checkpoint molecule expression compared with healthy controls, the data are limited and inconsistent. Further, data from the more informative patient comparisons are potentially confounded by severity of illness. These clinical checkpoint molecule expression studies do not yet provide a strong rationale for trials of checkpoint inhibitor therapy for sepsis.

The Multifaceted Function of Granzymes in Sepsis: Some Facts and a Lot to Discover

Sepsis is a serious global health problem. In addition to a high incidence, this syndrome has a high mortality and is responsible for huge health expenditure. The pathophysiology of sepsis is very complex and it is not well-understood yet. However, it is widely accepted that the initial phase of sepsis is characterized by a hyperinflammatory response while the late phase is characterized by immunosuppression and immune anergy, increasing the risk of secondary infections. Granzymes (Gzms) are a family of serine proteases classified according to their cleavage specificity. Traditionally, it was assumed that all Gzms acted as cytotoxic proteases. However, recent evidence suggests that GzmB is the one with the greatest cytotoxic capacity, while the cytotoxicity of others such as GzmA and GzmK is not clear. Recent studies have found that GzmA, GzmB, GzmK, and GzmM act as pro-inflammatory mediators. Specially, solid evidences show that GzmA and GzmK function as extracellular proteases that regulate the inflammatory response irrespectively of its ability to induce cell death. Indeed, studies in animal models indicate that GzmA is involved in the cytokine release syndrome characteristic of sepsis. Moreover, the GZM family also could regulate other biological processes involved in sepsis pathophysiology like the coagulation cascade, platelet function, endothelial barrier permeability, and, in addition, could be involved in the immunosuppressive stage of sepsis. In this review, we provide a comprehensive overview on the contribution of these novel functions of Gzms to sepsis and the new therapeutic opportunities emerging from targeting these proteases for the treatment of this serious health problem.

Sepsis Triggers a Late Expansion of Functionally Impaired Tissue-Vascular Inflammatory Monocytes During Clinical Recovery

Sepsis is characterized by a systemic inflammation that can cause an immune dysfunction, for which the underlying mechanisms are unclear. We investigated the impact of cecal ligature and puncture (CLP)-mediated polymicrobial sepsis on monocyte (Mo) mobilization and functions. Our results show that CLP led to two consecutive phases of Mo deployment. The first one occurred within the first 3 days after the induction of the peritonitis, while the second phase was of a larger amplitude and extended up to a month after apparent clinical recovery. The latter was associated with the expansion of Mo in the tissue reservoirs (bone marrow and spleen), their release in the blood and their accumulation in the vasculature of peripheral non-lymphoid tissues. It occurred even after antibiotic treatment but relied on inflammatory-dependent pathways and inversely correlated with increased susceptibility and severity to a secondary infection. The intravascular lung Mo displayed limited activation capacity, impaired phagocytic functions and failed to transfer efficient protection against a secondary infection into monocytopenic CCR2-deficient mice. In conclusion, our work unveiled key dysfunctions of intravascular inflammatory Mo during the recovery phase of sepsis and provided new insights to improve patient protection against secondary infections.

Peculiarities of leukocyte apoptosis modulation in children with pyelonephritis

One of the leading places among inflammatory diseases of the urinary tract of children belongs to pyelonephritis, the course of which presents in most cases as a severe infectious disease threatening the patient’s life, which is the main reason for development of chronic kidney failure. This study was conducted to compare apoptosis stages in peripheral blood of children of different age categories with pyelonephritis depending on etiological factor and complications. The problem of mechanisms underlying immune system misregulation, especially functional activity of leukocytes in children with pyelonephritis, have not been explored in recent years. Assessment of leukocytes (neutrophils) apoptosis stages in peripheral blood of children of different age categories with pyelonephritis depending on complications and etiological factor was the aim of present study. The children's peripheral blood samples were analysed and assessed using a flow cytofluorimeter. The present study demonstrates an increase of the level of apoptotic cells at an early stage of apoptosis in children of all age categories with chronic pyelonephritis, which can be explained by associations of a wide range of pathogens and the presence of sequelae. An increase in the number of apoptotic cells in the late stage of apoptosis is observed in children aged 1 month – 8 years, in children 8–18 years, the amount of apoptotic cells is reduced by 1.5 times. The study of apoptosis stages allows complete characterization of the dynamics of the apoptotic process and supplementation of the pathogenesis of pyelonephritis in children. Such studies will make it possible to affect apoptosis modulation to regulate or correct it and encourage the finding of innovative solutions in the treatment related to influence on the immune response. We conclude that enhancement of peripheral blood leukocyte apoptosis in chronic form of pyelonephritis especially in young children is due to the polyetiology of this form of pyelonephritis and the development of complications.

Genetic association between cluster of differentiation 86 variations and sepsis risk: A case-control study

The aim of this study was to investigate the correlation between cluster of differentiation 86 (CD86) gene rs1129055 and rs2715267 single nucleotide polymorphisms and sepsis susceptibility.One hundred twenty-five sepsis patients and 120 healthy controls were enrolled in this case-control study. CD86 polymorphisms rs1129055 and rs2715267 were genotyped through polymerase chain reaction-restriction fragment length polymorphism approach. Chi-square test was used to analyze differences in genotype and allele frequencies of the 2 polymorphisms between case and control groups. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to present the association strength of the polymorphisms with sepsis susceptibility.AA genotype and A allele frequencies of CD86 rs1129055 were significantly lower in sepsis patients than in healthy controls (P < .05), revealing their significant associations with decreased disease susceptibility (OR = 0.351, 95% CI = 0.169-0.728; OR = 0.593, 95% CI = 0.415-0.847). Nevertheless, rs2715267 had no significant association with sepsis susceptibility (P > .05).AA genotype and A allele of CD86 polymorphism rs1129055 might be correlated with decreased sepsis susceptibility in Chinese Han population, but not rs2715267. Further study should be performed to verify our findings.

Increased Expression of Cytotoxic T-Lymphocyte-Associated Protein 4 by T Cells, Induced by B7 in Sera, Reduces Adaptive Immunity in Patients With Acute Liver Failure

BACKGROUND & AIMS

Patients with acute liver failure (ALF) have defects in innate immune responses to microbes (immune paresis) and are susceptible to sepsis. Cytotoxic T-lymphocyte-associated protein 4 (CTLA4), which interacts with the membrane receptor B7 (also called CD80 and CD86), is a negative regulator of T-cell activation. We collected T cells from patients with ALF and investigated whether inhibitory signals down-regulate adaptive immune responses in patients with ALF.

METHODS

We collected peripheral blood mononuclear cells from patients with ALF and controls from September 2013 through September 2015 (45 patients with ALF, 20 patients with acute-on-chronic liver failure, 15 patients with cirrhosis with no evidence of acute decompensation, 20 patients with septic shock but no cirrhosis or liver disease, and 20 healthy individuals). Circulating CD4⁺ T cells were isolated and analyzed by flow cytometry. CD4⁺ T cells were incubated with antigen, or agonist to CD3 and dendritic cells, with or without antibody against CTLA4; T-cell proliferation and protein expression were quantified. We measured levels of soluble B7 molecules in supernatants of isolated primary hepatocytes, hepatic sinusoidal endothelial cells, and biliary epithelial cells from healthy or diseased liver tissues. We also measured levels of soluble B7 serum samples from patients and controls, and mice with acetaminophen-induced liver injury using enzyme-linked immunosorbent assays.

RESULTS

Peripheral blood samples from patients with ALF had a higher proportion of CD4⁺ CTLA4⁺ T cells than controls; patients with infections had the highest proportions. CD4⁺ T cells from patients with ALF had a reduced proliferative response to antigen or CD3 stimulation compared to cells from controls; incubation of CD4⁺ T cells from patients with ALF with an antibody against CTLA4 increased their proliferative response to antigen and to CD3 stimulation, to the same levels as cells from controls. CD4⁺ T cells from controls up-regulated expression of CTLA4 after 24-48 hours culture with sera from patients with ALF; these sera were found to have increased concentrations of soluble B7 compared to sera from controls. Necrotic human primary hepatocytes exposed to acetaminophen, but not hepatic sinusoidal endothelial cells and biliary epithelial cells from patients with ALF, secreted high levels of soluble B7. Sera from mice with acetaminophen-induced liver injury contained high levels of soluble B7 compared to sera from mice without liver injury. Plasma exchange reduced circulating levels of soluble B7 in patients with ALF and expression of CTLA4 on T cells.

CONCLUSIONS

Peripheral CD4⁺ T cells from patients with ALF have increased expression of CTLA4 compared to individuals without ALF; these cells have a reduced response to antigen and CD3 stimulation. We found sera of patients with ALF and from mice with liver injury to have high concentrations of soluble B7, which up-regulates CTLA4 expression by T cells and reduces their response to antigen. Plasma exchange reduces levels of B7 in sera from patients with ALF and might be used to restore antimicrobial responses to patients.

Lymphocyte depression as a predictor of postoperative intraabdominal abscess after appendectomy in children

BACKGROUND

This study evaluated the efficacy of lymphopenia to predict postappendectomy intraabdominal abscess (IAA) in pediatric complex appendicitis.

METHODS

This single-center retrospective cohort study included appendectomy patients with complex appendicitis from 4/2012 to 10/2014. IAA was diagnosed based on imaging or undergoing a drainage procedure. Labs were used from the closest day prior to abscess diagnosis or day of discharge from index admission. Lymphocyte percentage was categorized based on age-specific cutoffs with lymphopenia defined as a low percentage. Comparisons were made using chi-square or Fisher exact tests for categorical variables and Mann-Whitney U-tests for continuous variables.

RESULTS

Of 611 appendectomy patients with complicated appendicitis, 551 had WBC and differential. IAA was identified in 79 (12.9%) patients. There were no significant differences in demographics between IAA and non-IAA groups. Patients with IAA had higher rates of leukocytosis (44.3% versus 12.3%, p<0.001) and higher rates of age-based lymphopenia (84% vs. 46%, p<0.001). IAA was independently associated with leukocytosis (OR 3.65, p<0.001) and lymphopenia (OR 4.46, p<0.001). Patients with leukocytosis and lymphopenia had the highest abscess rate (36%), and those with normal labs had the lowest (3%, p<0.001).

CONCLUSIONS

Lymphocyte depression is a useful adjunct to predict postoperative IAA in patients with complicated appendicitis.

LEVEL OF EVIDENCE

III.

Altered T Lymphocyte Proliferation upon Lipopolysaccharide Challenge Ex Vivo

Context

Sepsis is characterized by the development of adaptive immune cell alterations, which intensity and duration are associated with increased risk of health-care associated infections and mortality. However, pathophysiological mechanisms leading to such lymphocyte dysfunctions are not completely understood, although both intrinsic lymphocyte alterations and antigen-presenting cells (APCs) dysfunctions are most likely involved.

Study

The aim of the current study was to evaluate whether lipopolysaccharide (LPS, mimicking initial Gram negative bacterial challenge) could directly impact lymphocyte function after sepsis. Therefore, we explored ex-vivo the effect of LPS priming on human T lymphocyte proliferation induced by different stimuli.

Results

We showed that LPS priming of PBMCs reduced T cell proliferative response and altered IFNγ secretion after stimulation with OKT3 but not with phytohaemagglutinin or anti-CD2/CD3/CD28-coated beads stimulations. Interestingly only LPS priming of monocytes led to decreased T cell proliferative response as opposed to LPS priming of lymphocytes. Importantly, LPS priming was associated with reduced expression of HLA-DR, CD86 and CD64 on monocytes but not with the modification of CD3, CTLA4, PD-1 and CD28 expressions on lymphocytes. Finally, IFNγ stimulation restored monocytes accessory functions and T cell proliferative response to OKT3.

Conclusion

We conclude that LPS priming does not directly impact lymphocyte functions but reduces APC’s capacity to activate T cells. This recapitulates ex vivo indirect mechanisms participating in sepsis-induced lymphocyte alterations and suggests that monocyte-targeting immunoadjuvant therapies in sepsis may also help to improve adaptive immune dysfunctions. Direct mechanisms impacting lymphocytes being also at play during sepsis, the respective parts of direct versus indirect sepsis-induced lymphocyte alterations remain to be evaluated in clinic.

Functional polymorphisms in CD86 gene are associated with susceptibility to pneumonia-induced sepsis

Sepsis is an illness in which the body has a severe response to bacteria or other germs. A bacterial infection in the body such as lungs may set off the response that leads to the disease. CD86 (B7-2) is expressed on various immune cells and plays critical roles in immune responses. Genetic polymorphisms in CD86 gene may affect the development of several diseases. Here, we evaluated the association between two CD86 polymorphisms (rs1915087C/T and rs2332096T/G) and susceptibility to pneumonia-induced sepsis. CD86 rs1915087C/T and rs2332096T/G were identified in 186 pneumonia-induced septic patients and 196 healthy controls in the Chinese population. Results revealed that subjects with rs1915087CT and TT genotypes had significantly lower risk of pneumonia-induced sepsis than those with CC genotype [odds ratio (OR) = 0.58, 95% confidence interval (CI), 0.37-0.91, p = 0.017, and OR = 0.40, 95%CI, 0.21-0.76, p = 0.005]. However, prevalence of rs2332096GG genotype and G allele were significantly increased in patients than in healthy controls (OR = 2.75, 95%CI, 1.46-5.16, p = 0.001, and OR = 1.65, 95%CI, 1.21-2.24, p = 0.001]. We further investigated functions of these two polymorphisms by assessing gene expression in peripheral blood mononuclear cells and in monocytes. Data showed subjects carrying rs2332096GG genotype had significantly decreased level of CD86 in monocytes than those carrying rs2332096TT genotype. These results indicate that CD86 polymorphisms are associated with susceptibility to pneumonia-induced sepsis and may affect gene expression in monocytes.

Escherichia coli-induced immune paralysis is not exacerbated during chronic filarial infection

Sepsis initially starts with a systemic inflammatory response (SIRS phase) and is followed by a compensatory anti-inflammatory response syndrome (CARS) that causes impaired adaptive T-cell immunity, immune paralysis and an increased susceptibility to secondary infections. In contrast, parasitic filariae release thousands of microfilariae into the peripheral blood without triggering inflammation, as they induce regulatory, anti-inflammatory host responses. Hence, we investigated the impact of chronic filarial infection on adaptive T-cell responses during the SIRS and CARS phases of a systemic bacterial infection and analysed the development of T-cell paralysis following a subsequent adenovirus challenge in BALB/c mice. Chronic filarial infection impaired adenovirus-specific CD8(+) T-cell cytotoxicity and interferon-γ responses in the absence of a bacterial challenge and led to higher numbers of splenic CTLA-4(+)  CD4(+) T cells, whereas splenic T-cell expression of CD69 and CD62 ligand, serum cytokine levels and regulatory T-cell frequencies were comparable to naive controls. Irrespective of filarial infection, the SIRS phase dominated 6-24 hr after intravenous Escherichia coli challenge with increased T-cell activation and pro-inflammatory cytokine production, whereas the CARS phase occurred 6 days post E. coli challenge and correlated with high levels of transforming growth factor-β and increased CD62 ligand T-cell expression. Escherichia coli-induced impairment of adenovirus-specific CD8(+) T-cell cytotoxicity and interferon-γ production was not additionally impaired by chronic filarial infection. This suggests that filarial immunoregulation does not exacerbate E. coli-induced T-cell paralysis.

Early infectious acute respiratory distress syndrome is characterized by activation and proliferation of alveolar T-cells

Acute respiratory distress syndrome (ARDS) in humans is characterized by the infiltration of polymorphonuclears in the alveolar spaces. However, the role of T-cells in ARDS is unknown. Our aim was to characterize the T-cell phenotype in bronchoalveolar lavage (BAL) during the early phase of acute lung infection(ALI)/ARDS-infected patients in comparison to a control group (CG). BAL lymphocyte phenotypes of two ALI, 16 ARDS, and eight CG were examined by flow cytometry. ALI/ARDS showed a significant increase in CD4 and CD8 T-cell activation as compared to CG. Moreover, a significant level of proliferation was observed using the Ki67 marker in ARDS patients as compared to controls (median): 37 versus 6 % for CD4 T-cells (p = 0.022) and 34 versus 2 % for CD8 T-cells (p = 0.009). In contrast, the percentage of T-regulatory cells and apoptotic T-cells were similar in both groups. Among costimulatory molecules, we observed an overexpression of CTLA-4/CD152 on CD4 T-cells in ALI/ARDS as compared to CG: 30 versus 7 %, respectively (p = 0.063). In further characterizing T-cell subsets expressing high levels of CD152, we found the presence of IL-17 secreting CD4 T-cells in ALI/ARDS. In humans, ALI/ARDS due to infection is associated with a high level of T-cell activation and proliferation, along with the presence of Th17 cells, which are known to attract polymorphonuclears.

Sepsis: multiple abnormalities, heterogeneous responses, and evolving understanding

Sepsis represents the host's systemic inflammatory response to a severe infection. It causes substantial human morbidity resulting in hundreds of thousands of deaths each year. Despite decades of intense research, the basic mechanisms still remain elusive. In either experimental animal models of sepsis or human patients, there are substantial physiological changes, many of which may result in subsequent organ injury. Variations in age, gender, and medical comorbidities including diabetes and renal failure create additional complexity that influence the outcomes in septic patients. Specific system-based alterations, such as the coagulopathy observed in sepsis, offer both potential insight and possible therapeutic targets. Intracellular stress induces changes in the endoplasmic reticulum yielding misfolded proteins that contribute to the underlying pathophysiological changes. With these multiple changes it is difficult to precisely classify an individual's response in sepsis as proinflammatory or immunosuppressed. This heterogeneity also may explain why most therapeutic interventions have not improved survival. Given the complexity of sepsis, biomarkers and mathematical models offer potential guidance once they have been carefully validated. This review discusses each of these important factors to provide a framework for understanding the complex and current challenges of managing the septic patient. Clinical trial failures and the therapeutic interventions that have proven successful are also discussed.

Biomarkers of sepsis

Sepsis is an unusual systemic reaction to what is sometimes an otherwise ordinary infection, and it probably represents a pattern of response by the immune system to injury. A hyper-inflammatory response is followed by an immunosuppressive phase during which multiple organ dysfunction is present and the patient is susceptible to nosocomial infection. Biomarkers to diagnose sepsis may allow early intervention which, although primarily supportive, can reduce the risk of death. Although lactate is currently the most commonly used biomarker to identify sepsis, other biomarkers may help to enhance lactate’s effectiveness; these include markers of the hyper-inflammatory phase of sepsis, such as pro-inflammatory cytokines and chemokines; proteins such as C-reactive protein and procalcitonin which are synthesized in response to infection and inflammation; and markers of neutrophil and monocyte activation. Recently, markers of the immunosuppressive phase of sepsis, such as anti-inflammatory cytokines, and alterations of the cell surface markers of monocytes and lymphocytes have been examined. Combinations of pro- and anti-inflammatory biomarkers in a multi-marker panel may help identify patients who are developing severe sepsis before organ dysfunction has advanced too far. Combined with innovative approaches to treatment that target the immunosuppressive phase, these biomarkers may help to reduce the mortality rate associated with severe sepsis which, despite advances in supportive measures, remains high.

The early phase of human sepsis is characterized by a combination of apoptosis and proliferation of T cells

PURPOSE

T cell activation as well as unresponsiveness has been described in separate studies in sepsis. Our aim was to establish the coexistence of both T cell fate in human sepsis.

PATIENTS AND METHODS

This is a cross-sectional study of 48 patients presenting with severe sepsis or septic shock and 15 healthy controls. Cytofluorometric techniques were used to quantify T cell activation, apoptosis, proliferation, expression of costimulatory molecules, and cytokine secretion.

RESULTS

Patients with sepsis were characterized by a significant increase in the percentage of activated T cell subsets, as measured using CD69 marker, compared with healthy controls (P<.05). T cell proliferation as measured through Ki67 expression was obvious in infected patients for both CD4 and CD8 T cell subsets compared with controls (P ≤.006). T cell subset apoptosis as measured using Hoechst dye was also increased in infected patients compared with controls (P ≤.002). CD4 T cell proliferation was correlated with interleukin 2 secretion (R(2)=0.84, P<.001), whereas up-regulation of CD4 T cell apoptosis was correlated with CTLA-4 expression (R(2)=0.24, P=.001). No such similar relationship was observed for CD8(+) T cells.

CONCLUSIONS

Concomitant T cell proliferation and T cell apoptosis are observed in human sepsis, being related to a different pathway.

The pathogenesis of sepsis

Sepsis is a serious clinical condition that represents a patient's response to a severe infection and has a very high mortality rate. Normal immune and physiologic responses eradicate pathogens, and the pathophysiology of sepsis is due to the inappropriate regulation of these normal reactions. In an ideal scenario, the first pathogen contact with the inflammatory system should eliminate the microbe and quickly return the host to homeostasis. The septic response may accelerate due to continued activation of neutrophils and macrophages/monocytes. Upregulation of lymphocyte costimulatory molecules and rapid lymphocyte apoptosis, delayed apoptosis of neutrophils, and enhanced necrosis of cells/tissues also contribute to the pathogenesis of sepsis. The coagulation system is closely tied to the inflammatory response, with cross talk between the two systems driving the dysregulated response. Biomarkers may be used to help diagnose patients with sepsis, and they may also help to identify patients who would benefit from immunomodulatory therapies.

Established and novel biomarkers of sepsis

The increased incidence of sepsis, a systemic response to infection that occurs in some patients, has stimulated interest in identifying infected patients who are at risk and intervening early. When this condition progresses to severe sepsis (characterized by organ dysfunction), mortality is high. Hospitals that have implemented recommendations of the Surviving Sepsis Campaign have seen a reduction in mortality rate for hospital-acquired severe sepsis. They may reduce this further by focusing on new approaches to diagnosing sepsis, especially at an early stage. Sepsis is a complicated syndrome with many physiological derangements and many emerging laboratory markers of sepsis have been proposed as adjuncts to clinical evaluation. The list includes cytokines, acute phase proteins, neutrophil activation markers, markers of abnormal coagulation and, recently, markers of suppression of both the innate and adaptive immune response. The perfect biomarker would accurately identify patients at risk of developing severe sepsis and then guide targeted therapy.