Mice depleted of alphabeta but not gammadelta T cells are resistant to mortality caused by cecal ligation and puncture

Therapeutic Strategies to Reduce Burn Wound Conversion

Burn wound conversion refers to the phenomenon whereby superficial burns that appear to retain the ability to spontaneously heal, convert later into deeper wounds in need of excision. While no current treatment can definitively stop burn wound conversion, attempts to slow tissue damage remain unsatisfactory, justifying the need for new therapeutic interventions. To attenuate burn wound conversion, various studies have targeted at least one of the molecular mechanisms underlying burn wound conversion, including ischemia, inflammation, apoptosis, autophagy, generation of reactive oxygen species, hypothermia, and wound rehydration. However, therapeutic strategies that can target various mechanisms involved in burn wound conversion are still lacking. This review highlights the pathophysiology of burn wound conversion and focuses on recent studies that have turned to the novel use of biologics such as mesenchymal stem cells, biomaterials, and immune regulators to mitigate wound conversion. Future research should investigate mechanistic pathways, side effects, safety, and efficacy of these different treatments before translation into clinical studies.

Neuronal-Activated ILC2s Promote IL-17A Production in Lung γδ T Cells During Sepsis

Background

Studies have revealed important roles for IL-17A in the development of acute lung injury (ALI) following sepsis. However, the mechanism underlying the regulation of lung IL-17A remains to be fully addressed. Recent studies suggested the effect of neuromedin U (NMU) on immune cell activation and the role of group 2 innate lymphoid cells (ILC2s) in the modulation of IL-17A production. We aimed to gain in-depth insight into the mechanism underlying sepsis-induced lung IL-17A production, particularly, the role of NMU in mediating neuronal regulation of ILC2s and IL-17A-producing γδ T cells activation in sepsis.

Methods

Wild type mice were subjected to cecal ligation and puncture (CLP) to induce sepsis with or without intraperitoneal injection of NMU. The levels of ILC2s, γδ T cells, IL-17A, NMU and NMU receptor 1 (NMUR1) in the lung were then measured. In order to determine the role of NMU signaling in ILC2 activation and the role of ILC2-released IL-9 in ILC2-γδ T cell interaction, ILC2s were sorted, and the genes of nmur1 and il9 in the ILC2s were knocked down using CRISPR/Cas9. The genetically manipulated ILC2s were then co-cultured with lung γδ T cells, and the levels of IL-17A from co-culture systems were measured.

Results

In septic mice, the levels of NMU, IL-17A, ILC2s, and IL-17A-producing γδ T cells in the lung are significantly increased, and the expression of NMUR1 in ILC2s is increased as well. Exogenous NMU further augments these increases. The main source of IL-17A in response to CLP is γδ T cells, and lung nmur1 is specifically expressed in ILC2s. In vitro co-culture of ILC2s and γδ T cells leads to increased number of γδ T cells and higher production of IL-17A from γδ T cells, and these alterations are further augmented by septic treatment and exogenous NMU. Genetic knockdown of nmur1 or il9 in ILC2s attenuated the upregulation of γδ T cells and IL-17A production.

Conclusion

In sepsis, NMU acting through NMUR1 in lung ILC2s initiates the ILC2 activation, which, in turn, promote IL-17A-producing γδ T cell expansion and secretion of IL-17A. ILC2-derived IL-9 plays an important role in mediating γδ T cell expansion and IL-17A production. This study explores a new mechanism underlying neuronal regulation of innate immunity in sepsis.

Identification and Validation of Potential miRNAs, as Biomarkers for Sepsis and Associated Lung Injury: A Network-Based Approach

Sepsis is a dysregulated immune response disease affecting millions worldwide. Delayed diagnosis, poor prognosis, and disease heterogeneity make its treatment ineffective. miRNAs are imposingly involved in personalized medicine such as therapeutics, due to their high sensitivity and accuracy. Our study aimed to reveal the biomarkers that may be involved in the dysregulated immune response in sepsis and lung injury using a computational approach and in vivo validation studies. A sepsis miRNA Gene Expression Omnibus (GEO) dataset based on the former analysis of blood samples was used to identify differentially expressed miRNAs (DEMs) and associated hub genes. Sepsis-associated genes from the Comparative Toxicogenomics Database (CTD) that overlapped with identified DEM targets were utilized for network construction. In total, 317 genes were found to be regulated by 10 DEMs (three upregulated, namely miR-4634, miR-4638-5p, and miR-4769-5p, and seven downregulated, namely miR-4299, miR-451a, miR181a-2-3p, miR-16-5p, miR-5704, miR-144-3p, and miR-1290). Overall hub genes (HIP1, GJC1, MDM4, IL6R, and ERC1) and for miR-16-5p (SYNRG, TNRC6B, and LAMTOR3) were identified based on centrality measures (degree, betweenness, and closeness). In vivo validation of miRNAs in lung tissue showed significantly downregulated expression of miR-16-5p corroborating with our computational findings, whereas expression of miR-181a-2-3p and miR-451a were found to be upregulated in contrast to the computational approach. In conclusion, the differential expression pattern of miRNAs and hub genes reported in this study may help to unravel many unexplored regulatory pathways, leading to the identification of critical molecular targets for increased prognosis, diagnosis, and drug efficacy in sepsis and associated organ injuries.

γδT cells but not αβT cells contribute to sepsis-induced white matter injury and motor abnormalities in mice

BACKGROUND

Infection and sepsis are associated with brain white matter injury in preterm infants and the subsequent development of cerebral palsy.

METHODS

In the present study, we used a neonatal mouse sepsis-induced white matter injury model to determine the contribution of different T cell subsets (αβT cells and γδT cells) to white matter injury and consequent behavioral changes. C57BL/6J wild-type (WT), T cell receptor (TCR) δ-deficient (Tcrd ^-/-, lacking γδT cells), and TCRα-deficient (Tcra ^-/-, lacking αβT cells) mice were administered with lipopolysaccharide (LPS) at postnatal day (PND) 2. Brain myelination was examined at PNDs 12, 26, and 60. Motor function and anxiety-like behavior were evaluated at PND 26 or 30 using DigiGait analysis and an elevated plus maze.

RESULTS

White matter development was normal in Tcrd ^-/- and Tcrα ^-/- compared to WT mice. LPS exposure induced reductions in white matter tissue volume in WT and Tcrα ^-/- mice, but not in the Tcrd ^-/- mice, compared with the saline-treated groups. Neither LPS administration nor the T cell deficiency affected anxiety behavior in these mice as determined with the elevated plus maze. DigiGait analysis revealed motor function deficiency after LPS-induced sepsis in both WT and Tcrα ^-/- mice, but no such effect was observed in Tcrd ^-/- mice.

CONCLUSIONS

Our results suggest that γδT cells but not αβT cells contribute to sepsis-induced white matter injury and subsequent motor function abnormalities in early life. Modulating the activity of γδT cells in the early stages of preterm white matter injury might represent a novel therapeutic strategy for the treatment of perinatal brain injury.

Arid5a exacerbates IFN-γ-mediated septic shock by stabilizing T-bet mRNA

Adenine-thymine (AT)-rich interactive domain containing protein 5a (Arid5a) is an RNA-binding protein that has been shown to play an important immune regulatory function via the stabilization of IL-6 and STAT3 mRNA. However, the role of Arid5a in the overwhelming and uncontrolled immune response that leads to septic shock is unknown. Here, we report that Arid5a-deficient mice are highly resistant to lipopolysaccharide (LPS)-induced endotoxic shock and secrete lower levels of major proinflammatory cytokines, including IFN-γ, IL-6, and TNF-α, than WT mice in response to LPS. Arid5a deficiency resulted in decreased levels of IFN-γ under Th1 cell conditions, in which T-box expressed in T cells (T-bet) mRNA expression was inhibited. Arid5a bound to the conserved stem loop structure of the 3'UTR of T-bet and stabilized its mRNA. Arid5a-deficient mice were also resistant to Propionibacterium acnes-primed LPS injection, which is considered to be a T-cell-mediated IFN-γ dependent endotoxic shock mouse model. Thus, regulation of IFN-γ by Arid5a via the stabilization of T-bet mRNA in Th1 cells contributes to the development of septic shock in mice. In addition, our previous study suggests that Arid5a control the IL-6 level in vivo in response to LPS by stabilization of IL-6 mRNA. We also observed that neutralization of IFN-γ and IL-6 significantly recovered the mice from endotoxic shock. Taken together, we conclude that Arid5a regulates the augmentation of IL-6 and IFN-γ in response to LPS, which possibly works synergistically for amplification of various other cytokines that ultimately cause the development of septic shock in mice.

Role of cellular events in the pathophysiology of sepsis

INTRODUCTION

Sepsis is a dysregulated host immune response due to an uncontrolled infection. It is a leading cause of mortality in adult intensive care units globally. When the host immune response induced against a local infection fails to contain it locally, it progresses to sepsis, severe sepsis, septic shock and death.

METHOD

Literature survey was performed on the roles of different innate and adaptive immune cells in the development and progression of sepsis. Additionally, the effects of septic changes on reprogramming of different immune cells were also summarized to prepare the manuscript.

FINDINGS

Scientific evidences to date suggest that the loss of balance between inflammatory and anti-inflammatory responses results in reprogramming of immune cell activities that lead to irreversible tissue damaging events and multi-organ failure during sepsis. Many surface receptors expressed on immune cells at various stages of sepsis have been suggested as biomarkers for sepsis diagnosis. Various immunomodulatory therapeutics, which could improve the functions of immune cells during sepsis, were shown to restore immunological homeostasis and improve survival in animal models of sepsis.

CONCLUSION

In-depth and comprehensive knowledge on the immune cell activities and their correlation with severity of sepsis will help clinicians and scientists to design effective immunomodulatory therapeutics for treating sepsis.

Full activation of CD4+ T cells early during sepsis requires specific antigen

Supplemental digital content is available in the text.

During sepsis, CD4⁺ T cells express activation markers within the first 24 h. In the present study, the mechanisms of T-cell activation and its consequences were addressed in an acute peritonitis model in mice. The response of CD4⁺ T cells to sepsis induction was compared between OTII mice, characterized by ovalbumin-specific T-cell receptor–transgenic T cells, and C57BL/6 controls (wild type [WT] mice). Because ovalbumin was absent during peritonitis, the OTII CD4⁺ T cells could not be activated by canonical antigen recognition. In both OTII and WT control mice, CD4⁺ T effector cells and CD4⁺ Foxp3⁺ regulatory T cells (Tregs) expressed the activation marker CD69 early after sepsis onset. However, full activation with upregulation of CD25 and proliferation took place only in the presence of the antigen. Besides this, the fraction of Tregs was lower in OTII than that in WT mice. Sepsis mortality was increased in OTII mice. Our data show that, in sepsis, partial activation of CD4⁺ T cells is induced by a T-cell receptor–independent pathway, whereas full stimulation and proliferation require a specific antigen. Antigen-dependent T-cell effector functions as well as Treg activity may contribute to sepsis survival.

Murine IL-17+ Vγ4 T lymphocytes accumulate in the lungs and play a protective role during severe sepsis

Background

Lung inflammation is a major consequence of the systemic inflammatory response caused by severe sepsis. Increased migration of γδ T lymphocytes into the lungs has been previously demonstrated during experimental sepsis; however, the involvement of the γδ T cell subtype Vγ4 has not been previously described.

Methods

Severe sepsis was induced by cecal ligation and puncture (CLP; 9 punctures, 21G needle) in male C57BL/6 mice. γδ and Vγ4 T lymphocyte depletion was performed by 3A10 and UC3-10A6 mAb i.p. administration, respectively. Lung infiltrating T lymphocytes, IL-17 production and mortality rate were evaluated.

Results

Severe sepsis induced by CLP in C57BL/6 mice led to an intense lung inflammatory response, marked by the accumulation of γδ T lymphocytes (comprising the Vγ4 subtype). γδ T lymphocytes present in the lungs of CLP mice were likely to be originated from peripheral lymphoid organs and migrated towards CCL2, CCL3 and CCL5, which were highly produced in response to CLP-induced sepsis. Increased expression of CD25 by Vγ4 T lymphocytes was observed in spleen earlier than that by αβ T cells, suggesting the early activation of Vγ4 T cells. The Vγ4 T lymphocyte subset predominated among the IL-17⁺ cell populations present in the lungs of CLP mice (unlike Vγ1 and αβ T lymphocytes) and was strongly biased toward IL-17 rather than toward IFN-γ production. Accordingly, the in vivo administration of anti-Vγ4 mAb abrogated CLP-induced IL-17 production in mouse lungs. Furthermore, anti-Vγ4 mAb treatment accelerated mortality rate in severe septic mice, demonstrating that Vγ4 T lymphocyte play a beneficial role in host defense.

Conclusions

Overall, our findings provide evidence that early-activated Vγ4 T lymphocytes are the main responsible cells for IL-17 production in inflamed lungs during the course of sepsis and delay mortality of septic mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-015-0098-8) contains supplementary material, which is available to authorized users.

Immunosuppression after sepsis: systemic inflammation and sepsis induce a loss of naïve T-cells but no enduring cell-autonomous defects in T-cell function

Sepsis describes the life-threatening systemic inflammatory response (SIRS) of an organism to an infection and is the leading cause of mortality on intensive care units (ICU) worldwide. An acute episode of sepsis is characterized by the extensive release of cytokines and other mediators resulting in a dysregulated immune response leading to organ damage and/or death. This initial pro-inflammatory burst often transits into a state of immune suppression characterised by loss of immune cells and T-cell dysfunction at later disease stages in sepsis survivors. However, despite these appreciations, the precise nature of the evoked defect in T-cell immunity in post-acute phases of SIRS remains unknown. Here we present an in-depth functional analysis of T-cell function in post-acute SIRS/sepsis. We document that T-cell function is not compromised on a per cell basis in experimental rodent models of infection-free SIRS (LPS or CpG) or septic peritonitis. Transgenic antigen-specific T-cells feature an unaltered cytokine response if challenged in vivo and ex vivo with cognate antigens. Isolated CD4(+)/CD8(+) T-cells from post-acute septic animals do not exhibit defects in T-cell receptor-mediated activation at the the level of receptor-proximal signalling, activation marker upregulation or expansion. However, SIRS/sepsis induced transient lymphopenia and gave rise to an environment of immune attenuation at post acute disease stages. Thus, systemic inflammation has an acute impact on T-cell numbers and adaptive immunity, but does not cause major cell-autonomous enduring functional defects in T-cells.

Toll-like receptor 4 stimulation before or after Streptococcus pneumoniae induced sepsis improves survival and is dependent on T-cells

Introduction

Endotoxin tolerance improves outcomes from gram negative sepsis but the underlying mechanism is not known. We determined if endotoxin tolerance before or after pneumococcal sepsis improved survival and the role of lymphocytes in this protection.

Methods

Mice received lipopolysaccharide (LPS) or vehicle before or after a lethal dose of Streptococcus pneumoniae. Survival, quantitative bacteriology, liver function, and cytokine concentrations were measured. We confirmed the necessity of Toll-like receptor 4 (TLR4) for endotoxin tolerance using C3H/HeN (TLR4 replete) and C3H/HeJ (TLR4 deficient) mice. The role of complement was investigated through A/J mice deficient in C5 complement. CBA/CaHN-Btk^xid//J mice with dysfunctional B cells and Rag-1 knockout (KO) mice deficient in T and B cells delineated the role of lymphocytes.

Results

Endotoxin tolerance improved survival from pneumococcal sepsis in mice with TLR4 that received LPS pretreatment or posttreatment. Survival was associated with reduced bacterial burden and serum cytokine concentrations. Death was associated with abnormal liver function and blood glucose concentrations. Endotoxin tolerance improved survival in A/J and CBA/CaHN-Btk^xid//J mice but not Rag-1 KO mice.

Conclusions

TLR4 stimulation before or after S. pneumoniae infection improved survival and was dependent on T-cells but did not require an intact complement cascade or functional B cells.

Regulation of lymphocyte trafficking by CXC chemokine receptor 3 during septic shock

RATIONALE

Lymphocytes have been shown to facilitate systemic inflammation and physiologic dysfunction in experimental models of severe sepsis. Our previous studies show that natural killer (NK) cells migrate into the peritoneal cavity during intraabdominal sepsis, but the trafficking of NKT and T lymphocytes has not been determined. The factors that regulate lymphocyte trafficking during sepsis are currently unknown.

OBJECTIVES

To ascertain the importance of CXC chemokine receptor 3 (CXCR3) as a regulator of lymphocyte trafficking during sepsis and determine the contribution of CXCR3-mediated lymphocyte trafficking to the pathogenesis of septic shock.

METHODS

Lymphocyte trafficking was evaluated in control and CXCR3-deficient mice using flow cytometry during sepsis caused by cecal ligation and puncture (CLP). Survival, core temperature, cytokine production, and bacterial clearance were measured as pathobiological endpoints.

MEASUREMENTS AND MAIN RESULTS

This study shows that concentrations of the CXCR3 ligands CXCL9 (monokine induced by interferon γ, MIG) and CXCL10 (interferon γ-induced protein 10, IP-10) increase in plasma and the peritoneal cavity after CLP, peak at 8 hours after infection, and are higher in the peritoneal cavity than in plasma. The numbers of CXCR3(+) NK cells progressively decreased in spleen after CLP with a concomitant increase within the peritoneal cavity, a pattern that was ablated in CXCR3-deficient mice. CXCR3-dependent recruitment of T cells was also evident at 16 hours after CLP. Treatment of mice with anti-CXCR3 significantly attenuated CLP-induced hypothermia, decreased systemic cytokine production, and improved survival.

CONCLUSIONS

CXCR3 regulates NK- and T-cell trafficking during sepsis and blockade of CXCR3 attenuates the pathogenesis of septic shock.

B cells enhance early innate immune responses during bacterial sepsis

Type I interferon–responsive B cells provide early protection against bacterial sepsis.

Microbes activate pattern recognition receptors to initiate adaptive immunity. T cells affect early innate inflammatory responses to viral infection, but both activation and suppression have been demonstrated. We identify a novel role for B cells in the early innate immune response during bacterial sepsis. We demonstrate that Rag1^−/− mice display deficient early inflammatory responses and reduced survival during sepsis. Interestingly, B cell–deficient or anti-CD20 B cell–depleted mice, but not α/β T cell–deficient mice, display decreased inflammatory cytokine and chemokine production and reduced survival after sepsis. Both treatment of B cell–deficient mice with serum from wild-type (WT) mice and repletion of Rag1^−/− mice with B cells improves sepsis survival, suggesting antibody-independent and antibody-dependent roles for B cells in the outcome to sepsis. During sepsis, marginal zone and follicular B cells are activated through type I interferon (IFN-I) receptor (IFN-α/β receptor [IFNAR]), and repleting Rag1^−/− mice with WT, but not IFNAR^−/−, B cells improves IFN-I–dependent and –independent early cytokine responses. Repleting B cell–deficient mice with the IFN-I–dependent chemokine, CXCL10 was also sufficient to improve sepsis survival. This study identifies a novel role for IFN-I–activated B cells in protective early innate immune responses during bacterial sepsis.

Cecal ligation and puncture

The cecum contains a high concentration of microbes, which are a combination of Gram-negative and Gram-positive flora. These bacteria range from anaerobic to facultative aerobic to aerobic organisms. In the procedure described in this unit, the ligation of the cecum produces a source of ischemic tissue as well as polymicrobial infection. This combination of ischemic/necrotic tissue and microbial infection distinguishes this multifactorial model from a number of other bacterial sepsis models, including but not limited to: bacteremia secondary to intravenous or intraperitoneal administration; fecal administration or intraperitoneal administration of fecal or bacterial plugs; colonic stents; and bacterial abscess formation.

Recipient T lymphocytes modulate the severity of antibody-mediated transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is a serious complication of transfusion and has been ranked as one of the leading causes of transfusion-related fatalities. Nonetheless, many details of the immunopathogenesis of TRALI, particularly with respect to recipient factors are unknown. We used a murine model of antibody-mediated TRALI in an attempt to understand the role that recipient lymphocytes might play in TRALI reactions. Intravenous injection of an IgG2a antimurine major histocompatibility complex class I antibody (34-1-2s) into BALB/c mice induced moderate hypothermia and pulmonary granulocyte accumulation but no pulmonary edema nor mortality. In contrast, 34-1-2s injections into mice with severe combined immunodeficiency caused severe hypothermia, severe pulmonary edema, and approximately 40% mortality indicating a critical role for T and B lymphocytes in suppressing TRALI reactions. Adoptive transfer of purified CD8+ T lymphocytes or CD4+ T cells but not CD19+ B cells into the severe combined immunodeficiency mice alleviated the antibody-induced hypothermia, lung damage, and mortality, suggesting that T lymphocytes were responsible for the protective effect. Taken together, these results suggest that recipient T lymphocytes play a significant role in suppressing antibody-mediated TRALI reactions. They identify a potentially new recipient mechanism that controls the severity of TRALI reactions.

Interleukin-7 (IL-7) treatment accelerates neutrophil recruitment through gamma delta T-cell IL-17 production in a murine model of sepsis

The sepsis syndrome represents an improper immune response to infection and is associated with unacceptably high rates of mortality and morbidity. The interactions between T cells and the innate immune system while combating sepsis are poorly understood. In this report, we observed that treatment with the potent, antiapoptotic cytokine interleukin-7 (IL-7) accelerated neutrophil recruitment and improved bacterial clearance. We first determined that T cells were necessary for the previously observed IL-7-mediated enhanced survival. Next, IL-7 increased Bcl-2 expression in T cells isolated from septic mice as early as 3 h following treatment. This treatment resulted in increased gamma interferon (IFN-γ) and IP-10 production within the septic peritoneum together with local and systemic increases of IL-17 in IL-7-treated mice. We further demonstrate that the increase in IL-17 was largely due to increased recruitment and production by γδ T cells, which express CXCR3. Consistent with increased IL-17 production, IL-7 treatment increased CXCL1/KC production, neutrophil recruitment, and bacterial clearance. Significantly, end-organ tissue injury was not significantly different between vehicle- and IL-7-treated mice. Collectively, these data illustrate that IL-7 can mediate the cross talk between Th1 and Th17 lymphocytes during sepsis such that neutrophil recruitment and bacterial clearance is improved while early tissue injury is not increased. All together, these observations may underlay novel potential therapeutic targets to improve the host immune response to sepsis.

Sepsis, leukocytes, and nitric oxide (NO): an intricate affair

Sepsis is exceedingly burdensome for hospital intensive care unit caregivers, and its incidence, as well as sepsis-related deaths, is increasing steadily. Sepsis is characterized by a robust increase in NO production throughout the organism that is driven by iNOS. Moreover, NO is an important factor in the development of septic shock and is synthesized by NOS, an enzyme expressed by a variety of cells, including vascular endothelium, macrophages, and neutrophils. However, the effects of NO on leukocyte functions, and the underlying mechanisms, are relatively unknown. Thus, the present review focuses on the effects of NO and its derivatives on cells of the immune system. Experimental evidences discussed herein show that NO induces posttranslational modifications of key proteins in targeted processes with the potential of deterring cellular physiology. Consequently, the manipulation of NO distribution in septic patients, used in conjunction with conventional treatments aimed at restoring normal immune functions, may represent a valuable therapeutic strategy.

Early alterations of the innate and adaptive immune statuses in sepsis according to the type of underlying infection

Introduction

Although major changes of the immune system have been described in sepsis, it has never been studied whether these may differ in relation to the type of underlying infection or not. This was studied for the first time.

Methods

The statuses of the innate and adaptive immune systems were prospectively compared in 505 patients. Whole blood was sampled within less than 24 hours of advent of sepsis; white blood cells were stained with monoclonal antibodies and analyzed though a flow cytometer.

Results

Expression of HLA-DR was significantly decreased among patients with severe sepsis/shock due to acute pyelonephritis and intraabdominal infections compared with sepsis. The rate of apoptosis of natural killer (NK) cells differed significantly among patients with severe sepsis/shock due to ventilator-associated pneumonia (VAP) and hospital-acquired pneumonia (HAP) compared with sepsis. The rate of apoptosis of NKT cells differed significantly among patients with severe sepsis/shock due to acute pyelonephritis, primary bacteremia and VAP/HAP compared with sepsis. Regarding adaptive immunity, absolute counts of CD4-lymphocytes were significantly decreased among patients with severe sepsis/shock due to community-acquired pneumonia (CAP) and intraabdominal infections compared with sepsis. Absolute counts of B-lymphocytes were significantly decreased among patients with severe sepsis/shock due to CAP compared with sepsis.

Conclusions

Major differences of the early statuses of the innate and adaptive immune systems exist between sepsis and severe sepsis/shock in relation to the underlying type of infection. These results may have a major impact on therapeutics.

Impaired CD4+ T-cell proliferation and effector function correlates with repressive histone methylation events in a mouse model of severe sepsis

Immunosuppression following severe sepsis remains a significant human health concern, as long-term morbidity and mortality rates of patients who have recovered from life-threatening septic shock remain poor. Mouse models of severe sepsis indicate this immunosuppression may be partly due to alterations in myeloid cell function; however, the effect of severe sepsis on subsequent CD4(+) T-cell responses remains unclear. In the present study, CD4(+) T cells from mice subjected to an experimental model of severe sepsis (cecal ligation and puncture (CLP)) were analyzed in vitro. CD4(+)CD62L(+) T cells from CLP mice exhibited reduced proliferative capacity and altered gene expression. Additionally, CD4(+)CD62L(+) T cells from CLP mice exhibit dysregulated cytokine production after in vitro skewing with exogenous cytokines, indicating a decreased capability of these cells to commit to either the T(H)1 or T(H)2 lineage. Repressive histone methylation marks were also evident at promoter regions for the T(H)1 cytokine IFN-gamma and the T(H)2 transcription factor GATA-3 in naïve CD4(+) T cells from CLP mice. These results provide evidence that CD4(+) T-cell subsets from post-septic mice exhibit defects in activation and effector function, possibly due to chromatin remodeling proximal to genes involved in cytokine production or gene transcription.

Effect of hypertonic saline resuscitation on CD4+CD25+ regulatory T cells and gammadelta T cells after hemorrhagic shock and resuscitation in relation to apoptosis and iNOS

BACKGROUND

Hemorrhagic shock and resuscitation induce immunosuppression. CD4CD25 regulatory T cells and gammadeltaT cells may affect these immunosuppressive conditions. Hypertonic saline resuscitation reduces damage to organs and apoptosis and also restores immunosuppressive condition. We investigated how hypertonic saline resuscitation affected the induction of CD4CD25 regulatory T cells and gammadeltaT cells, and their apoptosis after hemorrhagic shock and resuscitation, and its relationship to inducible nitric oxide synthase (iNOS) (nitric oxide production).

METHODS

Male inbred C57BL6/J mice 8-week to 12-week-old as wild type and iNOS gene knock out (iNOS-/-), weighing 20 g to 35 g, were used. Hemorrhagic shock model of +/-40 mm Hg for 60 minutes was setup. Animals were randomly assigned to the following four resuscitation group: (1) wild HS: resuscitation with hypertonic saline (4 mL/Kg of 7.5% NaCl) and shed blood (SB), (2) wild 2LR: resuscitation with lactated Ringer's solution (two times the volume of the SB) and SB, (3) iNOS knockout HS, and (4) iNOS knockout 2LR. Untreated groups for wild and iNOS knockout mice were designated as control groups. Samples of thymus and spleen were harvested at 2 hours, 6 hours, 24 hours, and 48 hours after resuscitation. CD4CD25 regulatory T cells and gammadeltaT cells were analyzed using three-color flow cytometry.

RESULTS

(1) gammadelta T cells increased earlier at 24 hours and CD4CD25 regulatory T cells increased later at 48 hours compared with controls in spleen of wild type (p < 0.01). (2) Hypertonic saline resuscitation suppressed gammadelta T cells compared with 2LR at 24 hours in iNOS knockout mice in spleen (p < 0.05). Hypertonic saline resuscitation increased apoptosis of CD4CD25 regulatory T cells at 48 hours in iNOS knockout mice in spleen (p < 0.01). (3) CD4CD25 regulatory T cells of iNOS knockout both in HS and 2LR groups at 48 hours decreased compared with wild type both in HS and 2LR groups in spleen (p < 0.01). (4) Apoptotic gammadelta T cells both in spleen and thymus in iNOS knockout mice at 48 hours increased compared with those in wild type (p < 0.05, respectively, except gammadelta T cells 2LR in spleen: p = 0.058).

CONCLUSION

gammadelta T cells increased earlier at 24 hours, whereas CD4CD25 regulatory T cells increased later at 48 hours in spleen of wild type. Hypertonic saline was effective without the presence of iNOS, i.e., decreased gammadelta T cells at 24 hours and increased apoptosis of CD4CD25 regulatory T cells at 48 hours. CD4CD25 regulatory T cells at 48 hours without iNOS decreased compared with those of wild type. gammadelta T cells at 48 hours induced apoptosis under the condition without iNOS in spleen and thymus. iNOS worked as an accelerating factor for immunosuppressive condition, affected apoptosis, and immunoenhancing effect by hypertonic saline.

Role of T cells for cytokine production and outcome in a model of acute septic peritonitis

Although it is generally accepted that early defense mechanisms are controlled by cells of the innate immune system, T cells were found to be crucial for host resistance against acute septic peritonitis. However, the mechanisms by which T cells mediate protection are not fully understood. Here, we demonstrate mice deficient for recombinase-activating gene (RAG) 1, which lack mature B and T cells, showed enhanced susceptibility and impaired bacterial clearance in a model of acute septic peritonitis. Whereas B-cell-deficient muMT mice showed no significant difference in the survival rate after peritonitis induction, T-cell-deficient Balb/c nude mice exhibited reduced survival. Importantly, analysis of cytokine production in both RAG-1-deficient and T-cell-deficient nude mice indicated strongly attenuated production of IL-12, interferon (IFN) gamma, and IL-10 during sepsis. Reduced cytokine levels were detected both in serum and in organ extracts of septic mice. Direct analysis of T cells isolated from septic mice demonstrated that T cells respond to an acute septic challenge by increased production of IFN-gamma and IL-10. Moreover, bacterial numbers in spleens of septic RAG-1-deficient mice were significantly increased as compared with controls, suggesting that T cells are engaged in the early antibacterial immune defense during sepsis, possibly via the production of IFN-gamma. In summary, these results imply that T cells contribute to protective immune responses against acute systemic infections via their ability to produce crucial immune mediators.

Roles of heat shock proteins and gamma delta T cells in inflammation

Elimination of activated inflammatory cells that infiltrate and damage host organs can reduce morbidity and mortality. A better understanding of the mechanisms by which these processes occur may lead to new approaches to prevent tissue damage. The lungs, gastrointestinal tract, and skin are particularly prone to infection and collateral damage by inflammatory cells. Specialized lymphocytes protect these organs from collateral tissue damage by eliminating neutrophils and macrophages from inflamed tissues. These lymphocytes recognize signals produced by inflammatory cells. One such signal is heat shock protein (Hsp) expressed on the cell surface of inflamed phagocytes. Mammalian Hsp molecules closely resemble their microbial equivalents, and therefore phagocytes decorated with these molecules are recognized as target cells. T lymphocytes bearing the gammadelta T cell receptor (TCR) elicit cytotoxic activity toward macrophages and neutrophils that express Hsp60 and Hsp70, respectively, protecting host organs from collateral tissue damage by phagocytes.

CD4-expressing cells are early mediators of the innate immune system during sepsis

It is well established that the immune response to sepsis is mediated by leukocytes associated with the innate immune system. However, there is an emerging view that T lymphocytes can also mediate this response. Here, we observed a significant depletion of both CD4 and CD8 T cells in human patients after blunt trauma. To determine what effect the loss of these cells may have during a subsequent infection, we obtained CD4- and CD8-deficient mice and subjected them to cecal ligation and puncture (CLP). We observed that CD4 knockout (KO) mice showed increased CLP-induced mortality compared with CD8-deficient and wild-type (WT) mice especially within the first 30 h of injury. CD4 KO mice also exhibited significantly increased IL-6 concentrations after the CLP. The CD4 KO mice had an increased concentration of bacteremia as compared with WT mice. Antibiotic treatment decreased mortality in the CD4 KO mice as compared with no changes in the wild mice after CLP. Neutrophils isolated from septic CD4 KO mice showed decreased spontaneous oxidative burst compared with neutrophils taken from septic controls. We examined the role of IFN-gamma by using mice deficient in this cytokine and found these mice to have significantly higher mortality as compared with WT mice. Finally, we detected a 2-fold increase in CD11b+ cells that exhibited intracellular IFN-gamma staining in the peritoneum of WT mice after CLP. The data suggest that CD4+ cells may facilitate the early clearance of bacteria by regulating neutrophils function possibly through an IFN-gamma-dependent mechanism.

Gammadelta T cells mitigate the organ injury and mortality of sepsis

Sepsis is a difficult condition to treat and is associated with a high mortality rate. Sepsis is known to cause a marked depletion of lymphocytes, although the function of different lymphocyte subsets in the response to sepsis is unclear. gammadelta T cells are found largely in epithelial-rich tissues, and previous studies of gammadelta T cells in models of sepsis have yielded divergent results. In the present study, we examined the function of gammadelta T cells during sepsis in mice using cecal ligation and puncture (CLP). Mice deficient in gammadelta T cells had decreased survival times and increased tissue damage after CLP compared with wild-type mice. Furthermore, bacterial load was increased in gammadelta T cell-deficient mice, yet antibiotic treatment did not change mortality. Additionally, we found that recruitment of neutrophils and myeloid suppressor cells to the site of infection was diminished in gammadelta T cell-deficient mice. Finally, we found that circulating levels of IFN-gamma were increased, and systemic levels of IL-10 were decreased in gammadelta T cell-deficient mice after CLP compared with wild-type mice. gammadelta T cell-deficient mice also had increased intestinal permeability after CLP compared with wild-type mice. Neutralization of IFN-gamma abrogated the increase in intestinal permeability in gammadelta T cell-deficient mice. The intestines taken from gammadelta T cell-deficient mice had decreased myeloperoxidase yet had increased tissue damage as compared with wild-type mice. Collectively, our data suggest that gammadelta T cells modulate the response to sepsis and may be a potential therapeutic target.

Regulatory T cell populations in sepsis and trauma

Sepsis syndrome remains the leading cause of mortality in intensive care units. It is now believed that along with the body's hyperinflammatory response designated to eliminate the underlying pathogen, mechanisms are initiated to control this initial response, which can become deleterious and result in immune dysfunctions and death. A similar state of immune suppression has been described after numerous forms of severe trauma/injury. Although the evidence for immune dysfunctions after sepsis has grown, much remains to be understood about mechanisms underpinning its development and how it acts to increase the morbid state of the critically ill patient. In this context, although the majority of clinical and basic science conducted so far has focused on the roles of myeloid cell populations, the contribution of T lymphocytes and in particular, of regulatory T cells has been somewhat ignored. The studies presented here support the concept that regulatory T lymphocytes (CD4+CD25+ regulatory, gammadelta, and NK T cells) play a role in the control of immune responses and are affected by injury and sepsis. This may be related to their capacity to interact with components of the innate and adaptive immune responses and to their ability to be activated nonspecifically by bacterial products and/or cytokines and to regulate through direct cell-cell and/or soluble mediators. It is our hope that a better understanding of the mechanism through which those rare lymphocyte subsets exert such a profound effect on the immune response may help in improving our ability not only to diagnose but also to treat the critically ill individual.

Thermal injury-plus-sepsis contributes to a substantial deletion of intestinal mesenteric lymph node CD4 T cell via apoptosis

Thermal injury (TI) with septic complications continues to be a serious clinical problem. One of the main concerns in such patients is immunosuppression related to functional derangements in intestinal CD4⁺ T lymphocytes. Extensive previous studies in thermal injury/septic patients and animal models of thermal injury/sepsis have shown decreased responsiveness of intestinal CD4⁺ T cells to antigen/mitogen. This hyporesponsiveness could significantly contribute to increase injured host susceptibility to pathogens including those translocating from host's gut lumen. Our previous studies indicated that while thermal injury or sepsis alone lead to suppressed proliferation and IL-2 production of intestinal CD4⁺ T cells, this study showed a substantial deletion via apoptosis of the Mesenteric Lymph Nodes (MLN) CD4⁺ T cells. Hence, thermal injury-plus-sepsis contributes not only to suppressed CD4⁺ T proliferation/IL-2 production but also to a substantial modulation of CD4⁺ T cell survivability. These findings allow us to conclude that while thermal injury alone can produce attenuated cell mediated responses without an overt change in CD4⁺ T cell survival, thermal injury with septic complications causes CD4⁺ T cell death and an irreversible loss of cell-mediated responses. The latter happening could be responsible for high morbidity and mortality in the injured host afflicted with thermal injury plus a critical infection.

CD6 binds to pathogen-associated molecular patterns and protects from LPS-induced septic shock

CD6 is a lymphocyte receptor that belongs to the scavenger receptor cysteine-rich superfamily. Because some members of the scavenger receptor cysteine-rich superfamily act as pattern recognition receptors for microbial components, we studied whether CD6 shares this function. We produced a recombinant form of the ectodomain of CD6 (rsCD6), which was indistinguishable (in apparent molecular mass, antibody reactivity, and cell binding properties) from a circulating form of CD6 affinity-purified from human serum. rsCD6 bound to and aggregated several Gram-positive and -negative bacterial strains through the recognition of lipoteichoic acid and LPS, respectively. The Kd of the LPS-rsCD6 interaction was 2.69 +/- 0.32 x 10(-8) M, which is similar to that reported for the LPS-CD14 interaction. Further experiments showed that membrane CD6 also retains the LPS-binding ability, and it results in activation of the MAPK signaling cascade. In vivo experiments demonstrated that i.p. administration of rsCD6 before lethal LPS challenge significantly improved mice survival, and this was concomitant with reduced serum levels of the proinflammatory cytokines TNF-alpha, IL6, and IL-1beta. In conclusion, our results illustrate the unprecedented bacterial binding properties of rsCD6 and support its therapeutic potential for the intervention of septic shock syndrome or other inflammatory diseases of infectious origin.