Increased susceptibility to Candida infection following cecal ligation and puncture

Relationship between SARS-CoV-2 infection and ICU-acquired candidemia in critically ill medical patients: a multicenter prospective cohort study

BACKGROUND

While SARS-CoV2 infection has been shown to be a significant risk-factor for several secondary bacterial, viral and Aspergillus infections, its impact on intensive care unit (ICU)-acquired candidemia (ICAC) remains poorly explored.

METHOD

Using the REA-REZO network (French surveillance network of ICU-acquired infections), we included all adult patients hospitalized for a medical reason of admission in participating ICUs for at least 48 h from January 2020 to January 2023. To account for confounders, a non-parsimonious propensity score matching was performed. Rates of ICAC according to SARS-CoV2 status were compared in matched patients. Factors associated with ICAC in COVID-19 patients were also assessed using a Fine-Gray model.

RESULTS

A total of 55,268 patients hospitalized at least 48 h for a medical reason in 101 ICUs were included along the study period. Of those, 13,472 were tested positive for a SARS-CoV2 infection while 284 patients developed an ICAC. ICAC rate was higher in COVID-19 patients in both the overall population and the matched patients' cohort (0.8% (107/13,472) versus 0.4% (173/41,796); p < 0.001 and 0.8% (93/12,241) versus 0.5% (57/12,241); p = 0.004, respectively). ICAC incidence rate was also higher in those patients (incidence rate 0.51 per 1000 patients-days in COVID-19 patients versus 0.32 per 1000 patients-days; incidence rate ratio: 1.58 [95% CI:1.08-2.35]; p = 0.018). Finally, patients with ICAC had a higher ICU mortality rate (49.6% versus 20.2%; p < 0.001).

CONCLUSION

In this large multicenter cohort of ICU patients, although remaining low, the rate of ICAC was higher among COVID-19 patients.

Association between selective digestive decontamination and decreased rate of acquired candidemia in mechanically ventilated ICU patients: a multicenter nationwide study

BACKGROUND

Candidemia is a high-risk complication among intensive care unit (ICU) patients. While selective digestive decontamination (SDD) has been shown to be effective in preventing ICU-acquired bacterial secondary infection, its effects on ICU-acquired candidemia (ICAC) remain poorly explored. Therefore, we sought to assess the effects of SDD on ICAC.

METHOD

Using the REA-REZO network, we included adult patients receiving mechanical ventilation for at least 48 h from January 2017 to January 2023. Non-parsimonious propensity score matching with a 1:1 ratio was performed to investigate the association between SDD and the rate of ICAC.

RESULTS

A total of 94 437 patients receiving at least 48 h of mechanical ventilation were included throughout the study period. Of those, 3 001 were treated with SDD and 651 patients developed ICAC. The propensity score matching included 2 931 patients in the SDD group and in the standard care group. In the matched cohort analysis as well as in the overall population, the rate of ICAC was lower in patients receiving SDD (0.8% versus 0.3%; p = 0.012 and 0.7% versus 0.3%; p = 0.006, respectively). Patients with ICAC had higher mortality rate (48.4% versus 29.8%; p < 0.001). Finally, mortality rates as well as ICU length of stay in the matched populations did not differ according to SDD (31.0% versus 31.1%; p = 0.910 and 9 days [5-18] versus 9 days [5-17]; p = 0.513, respectively).

CONCLUSION

In this study with a low prevalence of ICAC, SDD was associated with a lower rate of ICAC that did not translate to higher survival.

Of mice and men: Laboratory murine models for recapitulating the immunosuppression of human sepsis

Prolonged immunosuppression is increasingly recognized as the major cause of late phase and long-term mortality in sepsis. Numerous murine models with different paradigms, such as lipopolysaccharide injection, bacterial inoculation, and barrier disruption, have been used to explore the pathogenesis of immunosuppression in sepsis or to test the efficacy of potential therapeutic agents. Nonetheless, the reproducibility and translational value of such models are often questioned, owing to a highly heterogeneric, complex, and dynamic nature of immunopathology in human sepsis, which cannot be consistently and stably recapitulated in mice. Despite of the inherent discrepancies that exist between mice and humans, we can increase the feasibility of murine models by minimizing inconsistency and increasing their clinical relevance. In this mini review, we summarize the current knowledge of murine models that are most commonly used to investigate sepsis-induced immunopathology, highlighting their strengths and limitations in mimicking the dysregulated immune response encountered in human sepsis. We also propose potential directions for refining murine sepsis models, such as reducing experimental inconsistencies, increasing the clinical relevance, and enhancing immunological similarities between mice and humans; such modifications may optimize the value of murine models in meeting research and translational demands when applied in studies of sepsis-induced immunosuppression.

Recurrent Sepsis Exacerbates CD4+ T Cell Exhaustion and Decreases Antiviral Immune Responses

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to an infection. It is a disease with a high incidence, mortality, and recurrence rate and frequently results in its survivors requiring readmission into hospitals. The readmission is mainly due to recurrent sepsis. Patients with recurrent sepsis are more susceptible to secondary infections partly due to immune dysfunction, leading to a higher mortality in the long term. However, there remains a gap in the understanding of immunological characteristics and underlying mechanisms of recurrent sepsis. In this study, we used mouse models of acute and recurrent sepsis to investigate their different immunological characteristics. And then we subjected the two mouse models to a secondary influenza A virus (H1N1) infection and characterized the different immune responses. Here, we demonstrated that CD4⁺ T cells present an exacerbated exhaustion phenotype in response to recurrent sepsis as illustrated by the decreased frequency of CD4⁺ T cells, reduced co-stimulatory CD28 and increased inhibitory PD-1 and Tim-3 expression on CD4⁺ T cells, increased frequency of regulatory T cells, and reduced MHC-II expression on antigen-presenting cells. Moreover, we showed that antiviral immune responses decrease in the recurrent sepsis mouse model subjected to a secondary infection as illustrated by the reduced pathogen clearance and inflammatory response. This may be a consequence of the exacerbated CD4⁺ T cell exhaustion. In summary, recurrent sepsis exacerbates CD4⁺ T cell exhaustion and decreases antiviral immune responses, contributing to significant morbidity, increased late mortality, and increased health care burden in recurrent sepsis patients.

Fungal-Bacterial Interactions in Health and Disease

Fungi and bacteria encounter each other in various niches of the human body. There, they interact directly with one another or indirectly via the host response. In both cases, interactions can affect host health and disease. In the present review, we summarized current knowledge on fungal-bacterial interactions during their commensal and pathogenic lifestyle. We focus on distinct mucosal niches: the oral cavity, lung, gut, and vagina. In addition, we describe interactions during bloodstream and wound infections and the possible consequences for the human host.

Sepsis induces long-lasting impairments in CD4+ T-cell responses despite rapid numerical recovery of T-lymphocyte populations

Massive apoptosis of lymphocytes is a hallmark of sepsis. The resulting immunosuppression is associated with secondary infections, which are often lethal. Moreover, sepsis-survivors are burdened with increased morbidity and mortality for several years after the sepsis episode. The duration and clinical consequences of sepsis induced-immunosuppression are currently unknown. We have used the mouse model of peritoneal contamination and infection (PCI) to investigate the quantitative and qualitative recovery of T lymphocytes for 3.5 months after sepsis with or without IL-7 treatment. Thymic output and the numbers of naive and effector/memory CD4⁺ and CD8⁺ lymphocytes quickly recovered after sepsis. IL-7 treatment resulted in an accelerated recovery of CD8⁺ lymphocytes. Next generation sequencing revealed no significant narrowing of the T cell receptor repertoire 3.5 months after sepsis. In contrast, detailed functional analyses of T helper (Th)-cell responses towards a fungal antigen revealed a significant loss of Th cells. Whereas cytokine production was not impaired at the single cell level, the absolute number of Th cells specific for the fungal antigen was reduced. Our data indicate a clinically relevant loss of pathogen-specific T cell clones after sepsis. Given the small number of naive T lymphocytes specific for a given antigen, this decrement of T cell clones remains undetected even by sensitive methods such as deep sequencing. Taken together, our data are compatible with long lasting impairments in CD4⁺ T-cell responses after sepsis despite rapid recovery of T lymphocyte populations.

miR‑23a downregulation modulates the inflammatory response by targeting ATG12‑mediated autophagy

Autophagy, part of the innate immune defense mechanisms, is activated during the initial phase of septic insult. Previous studies indicated that micro (mi)RNAs are additionally involved in the host response to sepsis; however, the association between miRNAs and autophagy during this process is not fully understood. To study the role of miRNA (miR)-23a in autophagy initiated by sepsis, macrophages treated with lipopolysaccharides, in addition to blood samples from patients, were evaluated for miR-23a expression levels. Cell viability, inflammatory mediators and autophagic markers were investigated following overexpression or inhibition of miR-23a. The results suggested that miR-23a was suppressed subsequent to septic insult, promoting autophagy and suppressing a hyper inflammatory response, leading to enhanced cell viability. A luciferase assay and western blot analysis confirmed ubiquitin-like protein ATG12 to be the target of miR-23a. The present study revealed that the downregulation of miR-23a regulates an inflammatory response during septic insult via autophagy promotion.

Polymicrobial sepsis and non-specific immunization induce adaptive immunosuppression to a similar degree

Sepsis is frequently complicated by a state of profound immunosuppression, in its extreme form known as immunoparalysis. We have studied the role of the adaptive immune system in the murine acute peritonitis model. To read out adaptive immunosuppression, we primed post-septic and control animals by immunization with the model antigen TNP-ovalbumin in alum, and measured the specific antibody-responses via ELISA and ELISpot assay as well as T-cell responses in a proliferation assay after restimulation. Specific antibody titers, antibody affinity and plasma cell counts in the bone marrow were reduced in post-septic animals. The antigen-induced splenic proliferation was also impaired. The adaptive immunosuppression was positively correlated with an overwhelming general antibody response to the septic insult. Remarkably, antigen “overload” by non-specific immunization induced a similar degree of adaptive immunosuppression in the absence of sepsis. In both settings, depletion of regulatory T cells before priming reversed some parameters of the immunosuppression. In conclusion, our data show that adaptive immunosuppression occurs independent of profound systemic inflammation and life-threatening illness.

Anti-PD-L1 peptide improves survival in sepsis

BACKGROUND

Sepsis remains a leading cause of death in most intensive care units. Many deaths in sepsis are due to nosocomial infections in patients who have entered the immunosuppressive phase of the disorder. One cause of immunosuppression in sepsis is T-cell exhaustion mediated by programmed cell death-1 (PD-1) interaction with its ligand (PD-L1). Studies demonstrated that blocking the interaction of PD-1 with PD-L1 with knockout mice or inhibitory antibodies reversed T-cell dysfunction and improved sepsis survival. This study assessed the efficacy of a novel short-acting peptide (compound 8) that inhibits PD-1:PD-L1 signaling in a clinically relevant second-hit fungal sepsis model.

METHODS

Mice underwent cecal ligation and puncture to induce peritonitis. Three days later, mice received intravenous injection of Candida albicans. Forty-eight hours after Candida infection, mice were treated with compound 8 or inactive peptide. The effect of Candida infection on expression of coinhibitory molecules, PD-1, and PD-L1 were quantitated by flow cytometry on CD4+ cells, CD8+ cells, natural killer (NK) cells, and natural killer T-cells (NKT). The effect of compound 8 on survival was also examined.

RESULTS

Four days after fungal infection, PD-1 and PD-L1 expressions were markedly increased on CD4+, NK, and NKT cells in septic versus sham-operated mice (%PD-1 on CD4+, 11.9% versus 2.8%; and %PD-L1 on NKT, 14.8% versus 0.5%). Compared with control, compound 8 caused a 2-fold increase in survival from 30% to 60%, P < 0.05.

CONCLUSIONS

Compound 8 significantly improved survival in a clinically relevant immunosuppressive model of sepsis. These results support immunoadjuvant therapy targeting T-cell exhaustion in this lethal disease.

Distinct Effects of Integrins αXβ2 and αMβ2 on Leukocyte Subpopulations during Inflammation and Antimicrobial Responses

Integrins α_Mβ₂ and α_Xβ₂ are homologous adhesive receptors that are expressed on many of the same leukocyte populations and bind many of the same ligands. Although α_Mβ₂ was extensively characterized and implicated in leukocyte inflammatory and immune functions, the roles of α_Xβ₂ remain largely obscure. Here, we tested the ability of mice deficient in integrin α_Mβ₂ or α_Xβ₂ to deal with opportunistic infections and the capacity of cells derived from these animals to execute inflammatory functions. The absence of α_Mβ₂ affected the recruitment of polymorphonuclear neutrophils (PMN) to bacterial and fungal pathogens as well as to model inflammatory stimuli, and α_Mβ₂-deficient PMN displayed defective inflammatory functions. In contrast, deficiency of α_Xβ₂ abrogated intraperitoneal recruitment and adhesive functions of monocytes and macrophages (Mϕ) and the ability of these cells to kill/phagocytose Candida albicans or Escherichia coli cells both ex vivo and in vivo During systemic candidiasis, the absence of α_Xβ₂ resulted in the loss of antifungal activity by tissue Mϕ and inhibited the production of tumor necrosis factor alpha (TNF-α)/interleukin-6 (IL-6) in infected kidneys. Deficiency of α_Mβ₂ suppressed Mϕ egress from the peritoneal cavity, decreased the production of anti-inflammatory IL-10, and stimulated the secretion of IL-6. The absence of α_Xβ₂, but not of α_Mβ₂, increased survival against a septic challenge with lipopolysaccharide (LPS) by 2-fold. Together, these results suggest that α_Mβ₂ plays a primary role in PMN inflammatory functions and regulates the anti-inflammatory functions of Mϕ, whereas α_Xβ₂ is central in the regulation of inflammatory functions of recruited and tissue-resident Mϕ.

Sepsis-induced long-term immune paralysis--results of a descriptive, explorative study

Background

Long-lasting impairment of the immune system is believed to be the underlying reason for delayed deaths after surviving sepsis. We tested the hypothesis of persisting changes to the immune system in survivors of sepsis for the first time.

Methods

In our prospective, cross-sectional pilot study, eight former patients who survived catecholamine-dependent sepsis and eight control individuals matched for age, sex, diabetes and renal insufficiency were enrolled. Each participant completed a questionnaire concerning morbidities, medications and infection history. Peripheral blood was collected for determination of i) immune cell subsets (CD4⁺, CD8⁺ T cells; CD25⁺ CD127^- regulatory T cells; CD14⁺ monocytes), ii) cell surface receptor expression (PD-1, BTLA, TLR2, TLR4, TLR5, Dectin-1, PD-1 L), iii) HLA-DR expression, and iv) cytokine secretion (IL-6, IL10, TNF-α, IFN-γ) of whole blood stimulated with either α-CD3/28, LPS or zymosan.

Results

After surviving sepsis, former patients presented with increased numbers of clinical apparent infections, including those typically associated with an impaired immune system. Standard inflammatory markers indicated a low-level inflammatory situation in former sepsis patients. CD8⁺ cell surface receptor as well as monocytic HLA-DR density measurements showed no major differences between the groups, while CD4⁺ T cells tended towards two opposed mechanisms of negative immune cell regulation via PD-1 and BTLA. Moreover, the post-sepsis group showed alterations in monocyte surface expression of distinct pattern recognition receptors; most pronouncedly seen in a decrease of TLR5 expression. Cytokine secretion in response to important activators of both the innate (LPS, zymosan) and the adaptive immune system (α-CD3/28) seemed to be weakened in former septic patients.

Conclusions

Cytokine secretion as a reaction to different activators of the immune system seemed to be comprehensively impaired in survivors of sepsis. Among others, this could be based on trends in the downregulation of distinct cell surface receptors. Based on our results, the conduct of larger validation studies seems feasible, aiming to characterize alterations and to find potential therapeutic targets to engage.

Interleukin-7 and anti-programmed cell death 1 antibody have differing effects to reverse sepsis-induced immunosuppression

Sepsis remains a major cause of morbidity and mortality in most intensive care units. Protracted sepsis can evolve into a state of profound immunosuppression characterized by secondary infections, frequently with opportunistic-type pathogens. Immunoadjuvant therapy is currently being evaluated as a novel treatment for patients with sepsis. Two of the most promising immunoadjuvants are interleukin-7 (IL-7) and anti-programmed cell death 1 antibody (anti-PD-1). Both IL-7 and anti-PD-1 have been reported to boost host immunity and improve outcomes in patients with viral infections and cancer. The purpose of this study was to define the immunological mechanisms of action of IL-7 and anti-PD-1 in the two-hit sepsis model of cecal ligation and puncture followed by Candida albicans. In addition, we examined whether combined treatment with IL-7 and anti-PD-1 provided any additive beneficial effects in reversing immune dysfunction. The present findings demonstrated that IL-7 and anti-PD-1 had differing effects on innate and adaptive immune functions. Compared with anti-PD-1, IL-7 increased lymphocyte proliferation; expression of lymphocyte adhesion molecules, lymphocyte function-associated antigen 1, and very late antigen-4; interferon-γ production; and CD28 expression on splenic CD8 T cells. In contrast, anti-PD-1 seemed to have a greater effect on major histocompatibility complex class II expression on splenic macrophages and dendritic cells than IL-7. Combined treatment with IL-7 and anti-PD-1 produced additive effects on CD28 expression, lymphocyte proliferation, and splenic secretion of interferon-γ. In conclusion, the present study shows differences in immunomodulatory actions between IL-7 and anti-PD-1 and provides a potential rationale for combining IL-7 and anti-PD-1 in the therapy of sepsis.

High-dose ascorbate with low-dose amphotericin B attenuates severity of disease in a model of the reappearance of candidemia during sepsis in the mouse

Amphotericin B (Ampho B) isa fungicidal drug that causes cell wall injury. Pharmacological ascorbate induces the extracellular prooxidants, which might enter the Ampho B-induced cell wall porosity and act synergistically.W e tested low-dose Ampho B with a short course of pharmacological ascorbate using a mouse model of sepsis preconditioned with an injection of Candida albicans 6 h prior to cecal ligation and puncture (CLP). In this model, candidemia reappeared as early as 6 h after CLP with a predictably high mortality rate. This characteristic mimics sepsis in the phase of immunosuppression inpatients. Using the model, at 12- and 18-h post-CLP, we administered isotonic (pH neutralized) pharmacological ascorbate intravenously with low-dose Ampho B or sodium deoxycholate, vehicle-controlled, administered IP. The survival rate of low-dose Ampho B plus ascorbate was 53%, compared with < 11% for low-dose Ampho B or high-dose Ampho B alone. In addition, a beneficial effect was demonstrated in terms of kidney damage,liver injury, spleen histopathology, and serum markers at 24 h after CLP. Kidney injury was less severe in low-dose Ampho B plus ascorbate combination therapy due to less severe sepsis. Moreover, ascorbate enhanced the effectiveness of phagocytosis against C. albicans in human phagocytic cells. Taken together, the data indicate that the new mouse model simulates sepsis-induced immunosuppression and that the combination of pharmacological ascorbate with an antifungal drug is a potentially effective treatment that may reduce nephrotoxicity, and perhaps also increase fungicidal activity in patients with systemic candidiasis caused by Candida albicans.

Mechanical Ventilation Induces an Inflammatory Response in Preinjured Lungs in Late Phase of Sepsis

Mechanical ventilation (MV) may amplify the lung-specific inflammatory response in preinjured lungs by elevating cytokine release and augmenting damage to the alveolar integrity. In this study, we test the hypothesis that MV exerts different negative impacts on inflammatory response at different time points of postlung injury. Basic lung injury was induced by cecal ligation and puncture (CLP) surgery in rats. Physiological indexes including blood gases were monitored during MV and samples were assessed following each experiment. Low V_T (tidal volume) MV caused a slight increase in cytokine release and tissue damage at day 1 and day 4 after sepsis induced lung injury, while cytokine release from the lungs in the two moderately ventilated V_T groups was amplified. Interestingly, in the two groups where rats received low V_T MV, we found that infiltration of inflammatory cells was only profound at day 4 after CLP. Marked elevation of protein leakage indicated a compromise in alveolar integrity in rats that received moderate V_T MV at day 4 following CLP, correlating with architectural damage to the alveoli. Our study indicates that preinjured lungs are more sensitive to mechanical MV at later phases of sepsis, and this situation may be a result of differing immune status.

Polymicrobial Sepsis Increases Susceptibility to Chronic Viral Infection and Exacerbates CD8+ T Cell Exhaustion

Patients who survive sepsis display suppressed immune functions, often manifested as an increased susceptibility to secondary infections. Recently, using a cecal-ligation and puncture (CLP) model of sepsis, we showed that sepsis induces substantial and long-lasting changes in the available naive CD8(+) T cell repertoire affecting the capacity of the host to respond to newly encountered acute infections. However, the extent to which sepsis changes the host susceptibility to chronic infection and affects CD8(+) T cell responses is currently unknown. In this study, we demonstrate that inbred and outbred mice recovering from a septic event are more susceptible to lymphocytic choriomeningitis virus (LCMV) clone-13 infection exhibited by mortality and viral burden. Primary virus-specific CD8(+) T cells in LCMV clone-13-infected septic mice displayed exacerbated CD8(+) T cell exhaustion illustrated by increased inhibitory molecule expression (e.g., programmed cell death 1, lymphocyte-activation gene 3, and 2B4) and diminished Ag-driven cytokine production (e.g., IFN-γ, TNF-α) compared with similarly infected sham-treated mice. Importantly, therapeutic inhibitory molecule dual blockade (anti-PD-L1 and anti-lymphocyte-activation gene 3) increased the number of circulating LCMV-specific CD8(+) T cells, and improved CD8(+) T cell function and pathogen control in chronically infected septic mice. Together, these results illustrate that polymicrobial sepsis compromises the overall health of the host leading to increased vulnerability to chronic infection and exacerbated CD8(+) T cell exhaustion. Collectively, our findings suggest that septic survivors may be more susceptible and at greater risk for developing exhaustible CD8(+) T cells upon encountering a subsequent chronic infection.

Sepsis induced immunosuppression: Implications for secondary infections and complications

Sepsis is the commonest cause of admission to medical ICUs across the world. Mortality from sepsis continues to be high. Besides shock and multi-organ dysfunction occurring following the intense inflammatory reaction to sepsis, complications arising from sepsis-related immunoparalysis contribute to the morbidity and mortality from sepsis. This review explores the basis for sepsis related immune dysfunction and discusses its clinical implications for the treating intensivist. Recent trends indicate that a significant proportion of septic patients succumb to the complications of secondary infections and chronic critical care illness from the initial bout of sepsis. Therefore care-givers in the ICU need to be aware of the impediments posed by sepsis-related immune dysfunction that can impair recovery in patients with sepsis and contribute to sepsis-related mortality.

Polymicrobial sepsis alters antigen-dependent and -independent memory CD8 T cell functions

Mortality from sepsis frequently results from secondary infections, and the extent to which sepsis affects pathogen-specific memory CD8 T cell responses remains unknown. Using the cecal ligation and puncture model of polymicrobial sepsis, we observed rapid apoptosis of pre-existing memory CD8 T cells after sepsis induction that led to a loss in CD8 T cell-mediated protection. Ag sensitivity (functional avidity) and Ag-driven secondary expansion of memory CD8 T cells were decreased after sepsis, further contributing to the observed loss in CD8 T cell-mediated immunity. Moreover, Ag-independent bystander activation of memory CD8 T cells in response to heterologous infection was also significantly impaired early after sepsis induction. The reduced sensitivity of pre-existing memory CD8 T cells to sense inflammation and respond to heterologous infection by IFN-γ production was observed in inbred and outbred hosts and controlled by extrinsic (but not cell-intrinsic) factors, suggesting that sepsis-induced changes in the environment regulate innate functions of memory CD8 T cells. Taken together, the data in this study revealed a previously unappreciated role of sepsis in shaping the quantity and functionality of infection- or vaccine-induced memory CD8 T cells and will help further define the decline in T cell-mediated immunity during the sepsis-induced phase of immunosuppression.

Ensuring animal welfare while meeting scientific aims using a murine pneumonia model of septic shock

With animal models, death as an intentional end point is ethically unacceptable. However, in the study of septic shock, death is still considered the only relevant end point. We defined eight humane end points into four stages of severity (from healthy to moribund) and used to design a clinically relevant scoring tool, termed "the mouse clinical assessment score for sepsis" (M-CASS). The M-CASS was used to enable a consistent approach to the assessment of disease severity. This allowed an ethical and objective assessment of disease after which euthanasia was performed, instead of worsening suffering. The M-CASS displayed a high internal consistency (Cronbach α = 0.97) with a high level of agreement and an intraclass correlation coefficient equal to 0.91. The plasma levels of cytokines and markers of oxidative stress were all associated with the M-CASS score (Kruskal-Wallis test, P < 0.05). The M-CASS allows tracking of disease progression and animal welfare requirements.

Severe sepsis facilitates intestinal colonization by extended-spectrum-β-lactamase-producing Klebsiella pneumoniae and transfer of the SHV-18 resistance gene to Escherichia coli during antimicrobial treatment

Infections caused by multidrug-resistant pathogens are frequent and life threatening in critically ill patients. To investigate whether severe sepsis affects gut colonization by resistant pathogens and genetic exchange between opportunistic pathogens, we tested the intestinal-colonization ability of an extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strain carrying the SHV-18 resistance gene and the transfer ability of the resistance gene to endogenous Escherichia coli under ceftriaxone treatment in rats with burn injury only or severe sepsis induced by burns plus endotoxin exposure. Without ceftriaxone treatment, the K. pneumoniae strain colonized the intestine in both septic and burned rats for a short time, with clearance occurring earlier in burn-only rats but never in sham burn rats. In both burned and septic rats, the colonization level of the challenge strain dropped at the beginning and then later increased during ceftriaxone treatment, after which it declined gradually. This pattern coincided with the change in resistance of K. pneumoniae to ceftriaxone during and after ceftriaxone treatment. Compared with burn-only injury, severe sepsis had a more significant effect on the change in antimicrobial resistance to ceftriaxone. Only in septic rats was the resistance gene successfully transferred from the challenge strain to endogenous E. coli during ceftriaxone treatment; the gene persisted for at least 4 weeks after ceftriaxone treatment. We concluded that severe sepsis can facilitate intestinal colonization by an exogenous resistant pathogen and the transfer of the resistance gene to a potential endogenous pathogen during antimicrobial treatment.

Lipid mediators in immune dysfunction after severe inflammation

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Aberrant LM levels contribute to immune dysfunction in CI.

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Aberrance reflects dysregulation of inflammatory resolution pathways or their failure.

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Targeted manipulation of LMs restores immune competence and outcomes in animal models.

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Stratified resolution-based immunomodulatory strategies hold therapeutic potential.

Sepsis, trauma, burns, and major surgical procedures activate common systemic inflammatory pathways. Nosocomial infection, organ failure, and mortality in this patient population are associated with a quantitatively different reprioritization of the circulating leukocyte transcriptome to the initial inflammatory insult, greater in both magnitude and duration, and secondary to multiple observed defects in innate and adaptive immune function. Dysregulation of inflammatory resolution processes and associated bioactive lipid mediators (LMs) mechanistically contribute to this phenotype. Recent data indicate the potential efficacy of therapeutic interventions that either reduce immunosuppressive prostaglandins (PGs) or increase specialized proresolving LMs. Here, we reassess the potential for pharmacological manipulation of these LMs as therapeutic approaches for the treatment of critical illness (CI).

Pathways mediating resolution of inflammation: when enough is too much

Patients with critical illness, and in particular sepsis, are now recognized to undergo unifying, pathogenic disturbances of immune function. Whilst scientific and therapeutic focus has traditionally been on understanding and modulating the initial pro-inflammatory limb, recent years have witnessed a refocusing on the development and importance of immunosuppressive 'anti-inflammatory' pathways. Several mechanisms are known to drive this phenomenon; however, no overriding conceptual framework justifies them. In this article we review the contribution of pro-resolution pathways to this phenotype, describing the observed immune alterations in terms of either a failure of resolution of inflammation or the persistence of pro-resolution processes causing inappropriate 'injurious resolution'-a novel hypothesis. The dysregulation of key processes in critical illness, including apoptosis of infiltrating neutrophils and their efferocytosis by macrophages, are discussed, along with the emerging role of specialized cell subtypes Gr1(+) CD11b(+) myeloid-derived suppressor cells and CD4(+) CD25(+) FoxP3(+) T-regulatory cells.

Sustained and incomplete recovery of naive CD8+ T cell precursors after sepsis contributes to impaired CD8+ T cell responses to infection

Patients who survive severe sepsis often display compromised immune function with impairment in innate and adaptive immune responses. These septic patients are highly susceptible to "secondary" infections with intracellular pathogens that are usually controlled by CD8(+) T cells. It is not known when and if this observed immunoparalysis of CD8(+) T cell immunity recovers, and the long-term consequences of sepsis on the ability of naive CD8(+) T cells to respond to subsequent infections are poorly understood. In this study, using the cecal-ligation and puncture mouse model of sepsis, we show that sepsis induces a rapid loss of naive CD8(+) T cells. However, IL-15-dependent numerical recovery is observed a month after initial septic insult. Numerical recovery is accompanied by IL-15-dependent phenotypic changes where a substantial proportion of naive (Ag-inexperienced) CD8(+) T cells display a "memory-like" phenotype (CD44(hi)/CD11a(hi)). Importantly, the impairment of naive CD8(+) T cells to respond to viral and bacterial infection was sustained for month(s) after sepsis induction. Incomplete recovery of naive CD8(+) T cell precursors was observed in septic mice, suggesting that the availability of naive precursors contributes to the sustained impairment in primary CD8(+) T cell responses. Thus, sepsis can result in substantial and long-lasting changes in the available CD8(+) T cell repertoire affecting the capacity of the host to respond to new infections.

TLR3 agonist improves survival to secondary pneumonia in a double injury model

BACKGROUND

Toll-like receptors (TLR) can initiate various immune responses and are therefore activated under diverse infectious states. Previous studies have focused on TLR3 primarily as an antiviral pathway. However, recent research has demonstrated its efficacy in bacterial infection. Having developed a murine double injury model of cecal ligation and puncture (CLP) followed by Pseudomonas aeruginosa (Pa), we hypothesized that targeted administration of Poly I:C, a TLR3 agonist, would protect mice against secondary pneumonia.

MATERIAL AND METHODS

B6 mice underwent CLP followed 4 d afterward by an intranasal dose of Pa. Animals were given Poly I:C or vehicle (phosphate-buffered saline) intranasally 24 h post CLP and every day thereafter for a total of 6 d. For acute studies, mice were sacrificed at two time points, 4 d post CLP and 1 d post pneumonia (Pa).

RESULTS

Poly I:C treatment led to a significant improvement in survival (69% versus 33%). Cytokine analysis from bronchioalveolar lavage displayed significant differences both immediately before and after pneumonia. Bronchioalveolar lavage cultures taken at 24 h post double injury showed significantly higher colony counts in the lungs of control animals compared with those of Poly I:C animals. Measurements of TLR3 expression showed significant increases within both the immune and lung epithelial cells of Poly I:C-treated mice. Finally, the lungs of treated animals had significant increases in lymphocytes and innate cells.

CONCLUSIONS

The prophylactic treatment applied in this clinically relevant model further illustrates the overarching hypothesis of immune dysfunction and the possibility of corrective immune modulation within the setting of sepsis.