Severe sepsis exacerbates cell-mediated immunity in the lung due to an altered dendritic cell cytokine profile

Metabolic reprogramming and dysregulated IL-17 production impairs CD4 T cell function post sepsis

Sepsis survivors are at high risk for infection-related rehospitalization and mortality for years following the resolution of the acute septic event. These infection-causing microorganisms generally do not cause disease in immunocompetent hosts, suggesting that the post-septic immune response is compromised. Given the importance of CD4 T cells in the development of long-lasting protective immunity, we analyzed their post-septic function. Here we showed that sepsis induced chronic increased and non-specific production of IL-17 by CD4 T cells, resulting in the inability to mount an effective immune response to a secondary pneumonia challenge. Altered cell function was associated with metabolic reprogramming, characterized by mitochondrial dysfunction and increased glycolysis. This metabolic reprogramming began during the acute septic event and persisted long after sepsis had resolved. Our findings reveal cell metabolism as a potential therapeutic target. Given the critical role of cell metabolism in the physiological and pathophysiological processes of immune cells, these findings reveal a potential new therapeutic target to help mitigate sepsis survivors' susceptibility to secondary infections.

The Calm after the Storm: Implications of Sepsis Immunoparalysis on Host Immunity

The immunological hallmarks of sepsis include the inflammation-mediated cytokine storm, apoptosis-driven lymphopenia, and prolonged immunoparalysis. Although early clinical efforts were focused on increasing the survival of patients through the first phase, studies are now shifting attention to the long-term effects of sepsis on immune fitness in survivors. In particular, the most pertinent task is deciphering how the immune system becomes suppressed, leading to increased incidence of secondary infections. In this review, we introduce the contribution of numerical changes and functional reprogramming within innate (NK cells, dendritic cells) and adaptive (T cells, B cells) immune cells on the chronic immune dysregulation in the septic murine and human host. We briefly discuss how prior immunological experience in murine models impacts sepsis severity, immune dysfunction, and clinical relevance. Finally, we dive into how comorbidities, specifically autoimmunity and cancer, can influence host susceptibility to sepsis and the associated immune dysfunction.

Epigenetic biomarkers for human sepsis and septic shock: insights from immunosuppression

Sepsis is a life-threatening condition that occurs when the body responds to an infection damaging its own tissues. Sepsis survivors sometimes suffer from immunosuppression increasing the risk of death. To our best knowledge, there is no 'gold standard' for defining immunosuppression except for a composite clinical end point. As the immune system is exposed to epigenetic changes during and after sepsis, research that focuses on identifying new biomarkers to detect septic patients with immunoparalysis could offer new epigenetic-based strategies to predict short- and long-term pathological events related to this life-threatening state. This review describes the most relevant epigenetic mechanisms underlying alterations in the innate and adaptive immune responses described in sepsis and septic shock, and their consequences for immunosuppression states, providing several candidates to become epigenetic biomarkers that could improve sepsis management and help predict immunosuppression in postseptic patients.

Dendritic cell development in infection

The immune system protects from infections primarily by detecting and eliminating invading pathogens. This is predominantly mediated by innate immune cells like neutrophils, monocytes and dendritic cells (DCs) expressing specific receptors recognizing pathogen-associated molecular patterns. DC activation by pathogens leads to the initiation of antigen-specific adaptive immune responses, thereby bridging the innate and adaptive immune systems. However, various pathogens have evolved immune evasion strategies to ensure their survival. In this review, we highlight recent findings on how various microorganisms or their structural features affect or modulate DC development and whether this has any consequences for a protective immune response.

Immunomodulatory Effects of Genetic Alterations Affecting the Kynurenine Pathway

Several enzymes and metabolites of the kynurenine pathway (KP) have immunomodulatory effects. Modulation of the activities and levels of these molecules might be of particular importance under disease conditions when the amelioration of overreacting immune responses is desired. Results obtained by the use of animal and tissue culture models indicate that by eliminating or decreasing activities of key enzymes of the KP, a beneficial shift in disease outcome can be attained. This review summarizes experimental data of models in which IDO, TDO, or KMO activity modulation was achieved by interventions affecting enzyme production at a genomic level. Elimination of IDO activity was found to improve the outcome of sepsis, certain viral infections, chronic inflammation linked to diabetes, obesity, aorta aneurysm formation, and in anti-tumoral processes. Similarly, lack of TDO activity was advantageous in the case of anti-tumoral immunity, while KMO inhibition was found to be beneficial against microorganisms and in the combat against tumors, as well. On the other hand, the complex interplay among KP metabolites and immune function in some cases requires an increase in a particular enzyme activity for the desired immune response modulation, as was shown by the exacerbation of liver fibrosis due to the elimination of IDO activity and the detrimental effects of TDO inhibition in a mouse model of autoimmune gastritis. The relevance of these studies concerning possible human applications are discussed and highlighted. Finally, a brief overview is presented on naturally occurring genetic variants affecting immune functions via modulation of KP enzyme activity.

Sepsis Induces Prolonged Epigenetic Modifications in Bone Marrow and Peripheral Macrophages Impairing Inflammation and Wound Healing

OBJECTIVE

Sepsis represents an acute life-threatening disorder resulting from a dysregulated host response. For patients who survive sepsis, there remains long-term consequences, including impaired inflammation, as a result of profound immunosuppression. The mechanisms involved in this long-lasting deficient immune response are poorly defined. Approach and Results: Sepsis was induced using the murine model of cecal ligation and puncture. Following a full recovery period from sepsis physiology, mice were subjected to our wound healing model and wound macrophages (CD11b+, CD3-, CD19-, Ly6G-) were sorted. Post-sepsis mice demonstrated impaired wound healing and decreased reepithelization in comparison to controls. Further, post-sepsis bone marrow-derived macrophages and wound macrophages exhibited decreased expression of inflammatory cytokines vital for wound repair (IL [interleukin]-1β, IL-12, and IL-23). To evaluate if decreased inflammatory gene expression was secondary to epigenetic modification, we conducted chromatin immunoprecipitation on post-sepsis bone marrow-derived macrophages and wound macrophages. This demonstrated decreased expression of Mll1, an epigenetic enzyme, and impaired histone 3 lysine 4 trimethylation (activation mark) at NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells)-binding sites on inflammatory gene promoters in bone marrow-derived macrophages and wound macrophages from postcecal ligation and puncture mice. Bone marrow transplantation studies demonstrated epigenetic modifications initiate in bone marrow progenitor/stem cells following sepsis resulting in lasting impairment in peripheral macrophage function. Importantly, human peripheral blood leukocytes from post-septic patients demonstrate a significant reduction in MLL1 compared with nonseptic controls.

CONCLUSIONS

These data demonstrate that severe sepsis induces stable mixed-lineage leukemia 1-mediated epigenetic modifications in the bone marrow, which are passed to peripheral macrophages resulting in impaired macrophage function and deficient wound healing persisting long after sepsis recovery.

Classical dendritic cells regulate acute lung inflammation and injury in mice with lipopolysaccharide‑induced acute respiratory distress syndrome

Classical dendritic cells (cDCs) are involved in the pathogenesis of inflammatory lung diseases; however, their contributions in acute respiratory distress syndrome (ARDS), which is pathophysiologically inflammatory, remain unknown. The present study aimed to explore the regulatory effects of pulmonary cDCs on acute lung inflammation and injury in lipopolysaccharide (LPS)-induced ARDS. Fms-like tyrosine kinase 3-ligand (FLT3L) and lestaurtinib, a specific activator and an inhibitor of FLT3 signaling respectively, were used separately for the pretreatment of C57BL/6 mice for 5 consecutive days. ARDS was induced by intratracheal injection of LPS, and mice were sacrificed 6 and 24 h later. Flow cytometry was used to measure the aggregation and maturation of pulmonary cDCs. The ratio of lung wet weight to body weight (LWW/BW) and histopathological analyses were assessed to evaluate lung edema and lung injury. Tumor necrosis factor-α and interleukin (IL)-6 levels were measured by ELISA to evaluate acute lung inflammation. The levels of interferon-γ, IL-1β, IL-4 and IL-10, and the expression of the transcription factors T-box-expressed-in-T-cells (T-bet) and GATA binding protein 3, were quantified by ELISA, RT-qPCR and western blotting to evaluate the balance of the Th1/Th2 response. Myeloperoxidase (MPO) activity was measured to evaluate neutrophil infiltration. The results demonstrated that the aggregation and maturation of pulmonary cDCs reached a peak at 6 h after LPS challenge, followed by a significant decrease at 24 h. FLT3L pretreatment further stimulated the aggregation and maturation of pulmonary cDCs, resulting in elevated lung MPO activity and increased T-bet expression, which in turn led to aggravated LWW/BW, acute lung inflammation and injury. However, lestaurtinib pretreatment inhibited the aggregation and maturation of pulmonary cDCs, decreased lung MPO activity and T-bet expression, and eventually improved LWW/BW, acute lung inflammation and injury. The present results suggested that pulmonary cDCs regulated acute lung inflammation and injury in LPS-induced ARDS through the modulation of neutrophil infiltration and balance of the Th1/Th2 response.

Severe Leptospirosis Features in the Spleen Indicate Cellular Immunosuppression Similar to That Found in Septic Shock

Objectives: To compare microscopic and immunologic features in the spleens of patients who died of pulmonary hemorrhage and shock caused by leptospirosis (11 cases) or Gram-positive/-negative bacterial septic shock (10 cases) to those from control spleens (12 cases from splenectomy).

Methodology: Histological features in the red pulp and white pulp were analyzed using archived samples by a semi quantitative score. Immunohistochemistry was used for the recognition of immune cell markers, cytokines, caspase-3 and Leptospira antigens.

Results: The control group differed significantly from the leptospirosis and septic shock patients which demonstrate strong similarities: diffuse congestion in the red pulp with a moderate to intense infiltration of plasma cells and polymorphonuclear cells; follicles with marked atrophy; high density of CD20⁺ cells; low density of NK, TCD4⁺ and active caspase-3 positive cells and strong expression of IL-10; leptospirosis patients had higher S100 and TNF-α positive cells in the spleen than the other groups.

Conclusion: The results suggest that an immunosuppressive state develops at the terminal stage of severe leptospirosis with pulmonary hemorrhage and shock similar to that of patients with septic shock, with diffuse endothelial activation in the spleen, splenitis, and signs of disturbance in the innate and adaptive immunity in the spleen. The presence of leptospiral antigens in 73% of the spleens of the leptospirosis patients suggests the etiological agent contributes directly to the pathogenesis of the lesions. Our results support therapeutic approaches involving antibiotic and immunomodulatory treatments for leptospirosis patients and suggest that leptospirosis patients, which are usually young men with no co-morbidities, form a good group for studying sepsis and septic shock.

Sepsis Induced by Cecal Ligation and Puncture

Despite advances in intensive care unit interventions, including the use of specific antibiotics and anti-inflammation treatment, sepsis with concomitant multiple organ failure is the most common cause of death in many acute care units. In order to understand the mechanisms of clinical sepsis and develop effective therapeutic modalities, there is a need to use effective experimental models that faithfully replicate what occurs in patients with sepsis. Several models are commonly used to study sepsis, including intravenous endotoxin challenge, injection of live organisms into the peritoneal cavity, establishing abscesses in the extremities, and the induction of experimental polymicrobial peritonitis via cecal ligation and puncture (CLP). Here, we describe the surgical procedure of CLP in mice, which has been demonstrated to closely replicate the nature and course of clinical sepsis in human subjects.

Maternal exposure to NO2 enhances airway sensitivity to allergens in BALB/c mice through the JAK-STAT6 pathway

Previous studies have indicated that nitrogen dioxide (NO₂) exposure could increase airway sensitivity to allergens for children. Recently, fetal stress was proposed as a crucial factor for allergic airway response occurring in offspring. Considering that there is inadequate evidence linking maternal NO₂ exposure to offspring airway sensitivity to allergens, pregnant Balb/c mice were exposed daily to 2.5 ppm NO₂ throughout the gestation period; then, the offspring were challenged to an allergen (ovalbumin, OVA) to evaluate airway sensitivity. For air + saline group and air + OVA group, offspring mice were maternally exposed to clean air followed by treatment with saline and OVA, respectively, in adulthood. For NO₂ + saline group and NO₂ + OVA group, offspring mice were maternally exposed to NO₂ followed by treatment with saline and OVA, respectively, in adulthood. The results showed that maternal NO₂ exposure increased the level of OVA-immunoglobulin (Ig) E in serum and caused airway hyper-responsiveness and pathological changes in offspring. Furthermore, maternal NO₂ exposure altered the expression of pro-inflammatory factors and impaired the T helper (Th) 1/Th2 balance. In addition, janus kinase)-signal transducer and activator of transcription 6 pathway participated in OVA-induced airway sensitivity of offspring. Our study showed that the potential risk of airway sensitivity to allergens in offspring is enhanced by maternal NO₂ exposure and proposed a possible mechanism for preventing, alleviating, and evaluating the outcomes in polluted environments.

Understanding the Cellular Origin of the Mononuclear Phagocyte System Sheds Light on the Myeloid Postulate of Immune Paralysis in Sepsis

Sepsis, in essence, is a serious clinical condition that can subsequently result in death as a consequence of a systemic inflammatory response syndrome including febrile leukopenia, hypotension, and multiple organ failures. To date, such life-threatening organ dysfunction remains one of the leading causes of death in intensive care units, with an increasing incidence rate worldwide and particularly within the rapidly growing senior population. While most of the clinical trials are aimed at dampening the overwhelming immune response to infection that spreads through the bloodstream, based on several human immunological investigations, it is now widely accepted that susceptibility to nosocomial infections and long-term sepsis mortality involves an immunosuppressive phase that is characterized by a decrease in some subsets of dendritic cells (DCs). Only recently substantial advances have been made in terms of the origin of the mononuclear phagocyte system that is now likely to allow for a better understanding of how the paralysis of DCs leads to sepsis-related death. Indeed, the unifying view of each subset of DCs has already improved our understanding of the pivotal pathways that contribute to the shift in commitment of their progenitors that originate from the bone marrow. It is quite plausible that this anomaly in sepsis may occur at the single level of DC-committed precursors, and elucidating the immunological basis for such a derangement during the ontogeny of each subset of DCs is now of particular importance for restoring an adequate cell fate decision to their vulnerable progenitors. Last but not least, it provides a direct perspective on the development of sophisticated myelopoiesis-based strategies that are currently being considered for the treatment of immunosenescence within different tissue microenvironments, such as the kidney and the spleen.

Persimmon-derived tannin has bacteriostatic and anti-inflammatory activity in a murine model of Mycobacterium avium complex (MAC) disease

Nontuberculous mycobacteria (NTM), including Mycobacterium avium complex (MAC), cause opportunistic chronic pulmonary infections. Notably, MAC susceptibility is regulated by various factors, including the host immune system. Persimmon (Ebenaceae Diospyros kaki Thunb.) tannin is a condensed tannin composed of a polymer of catechin groups. It is well known that condensed tannins have high antioxidant activity and bacteriostatic properties. However, it is hypothesized that condensed tannins might need to be digested and/or fermented into smaller molecules in vivo prior to being absorbed into the body to perform beneficial functions. In this study, we evaluated the effects of soluble persimmon-derived tannins on opportunistic MAC disease. Soluble tannins were hydrolyzed and evaluated by the oxygen radical absorbance capacity (ORAC) method. The ORAC value of soluble tannin hydrolysate was approximately five times greater than that of soluble tannin powder. In addition, soluble tannin hydrolysate exhibited high bacteriostatic activity against MAC in vitro. Furthermore, in an in vivo study, MAC infected mice fed a soluble tannin-containing diet showed significantly higher anti-bacterial activity against MAC and less pulmonary granuloma formation compared with those fed a control diet. Tumor necrosis factor α and inducible nitric oxide synthase levels were significantly lower in lungs of the soluble tannin diet group compared with the control diet group. Moreover, proinflammatory cytokines induced by MAC stimulation of bone marrow-derived macrophages were significantly decreased by addition of soluble tannin hydrolysate. These data suggest that soluble tannin from persimmons might attenuate the pathogenesis of pulmonary NTM infection.

Polymicrobial Sepsis Diminishes Dendritic Cell Numbers and Function Directly Contributing to Impaired Primary CD8 T Cell Responses In Vivo

Patients surviving acute stages of sepsis often display impaired adaptive-immune responses. Using the cecal ligation and puncture model, we demonstrated that sepsis leads to substantial and long-lasting changes in the naive CD8 T cell repertoire, affecting the capacity of the host to respond to new infections. However, the identity of CD8 T cell-extrinsic factor(s) and mechanism(s) that contribute to impaired CD8 T cell responses after sepsis is unknown. Priming of naive CD8 T cells is critically dependent on the ability of dendritic cells (DCs) to provide Ag, costimulation, and inflammatory signal 3 cytokines; therefore, the sepsis-induced changes in the DC compartment might represent a contributing factor leading to diminished CD8 T cell immunity in septic hosts. In a direct test of this hypothesis, we show that, in addition to numerical decline, sepsis leads to functional impairments in DCs, diminishing their capacity to produce cytokines upon TLR stimulation in vitro or postinfection in vivo. Importantly, we demonstrated a direct link between DC dysfunction and impairments in CD8 T cell immunity after sepsis by directly targeting Ag to DCs. Finally, postsepsis Flt3 ligand treatment increased the number of DCs and improved DC function, including the ability to sense inflammation and produce IL-12, leading to improved primary CD8 T cell responses to newly encountered Ags. Thus, sepsis-induced numerical and functional loss of DCs contributes to the observed defects in CD8 T cell immunity, and therapeutic approaches designed to improve the status of the DC compartment after sepsis might facilitate the recovery of CD8 T cell immunity.

Regulation of Cellular Immune Responses in Sepsis by Histone Modifications

Severe sepsis, septic shock, and related inflammatory syndromes are driven by the aberrant expression of proinflammatory mediators by immune cells. During the acute phase of sepsis, overexpression of chemokines and cytokines drives physiological stress leading to organ failure and mortality. Following recovery from sepsis, the immune system exhibits profound immunosuppression, evidenced by an inability to produce the same proinflammatory mediators that are required for normal responses to infectious microorganisms. Gene expression in inflammatory responses is influenced by the transcriptional accessibility of the chromatin, with histone posttranslational modifications determining whether inflammatory gene loci are set to transcriptionally active, repressed, or poised states. Experimental evidence indicates that histone modifications play a central role in governing the cytokine storm of severe sepsis, and that aberrant chromatin modifications induced during the acute phase of sepsis may mediate chronic immunosuppression in sepsis survivors. This review will focus on the role of histone modifications in governing immune responses in severe sepsis, with an emphasis on specific leukocyte subsets and the histone modifications observed in these cells during chronic stages of sepsis. Additionally, the expression and function of chromatin-modifying enzymes (CMEs) will be discussed in the context of severe sepsis, as potential mediators of epigenetic regulation of gene expression in sepsis responses. In summary, this review will argue for the use of chromatin modifications and CME expression in leukocytes as potential biomarkers of immunosuppression in patients with severe sepsis.

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.

Adoptive transfer of bone marrow-derived dendritic cells decreases inhibitory and regulatory T-cell differentiation and improves survival in murine polymicrobial sepsis

A decrease in the number of dendritic cells (DCs) is a major cause of post-sepsis immunosuppression and opportunistic infection and is closely associated with poor prognosis. Increasing the number of DCs to replenish their numbers post sepsis can improve the condition. This therapeutic approach could improve recovery after sepsis. Eighty C57BL/6 mice were subjected to sham or caecal ligation and puncture (CLP) surgery. Mice were divided into four groups: (i) Sham + vehicle, (ii) Sham + DC, (iii) CLP + vehicle, and (iv) CLP + DC. Bone-marrow-derived DCs (BMDCs) were administered at 6, 12 and 24 hr after surgery. After 3 days, we assessed serum indices of organ function (alanine aminotransferase, aspartate aminotransferase, creatinine, amylase and lipase), organ tissue histopathology (haematoxylin and eosin staining), cytokine [interferon-γ (IFN-γ), tumour necrosis factor-α, interleukin-12p70 (IL-12p70), IL-6 and IL-10] levels in the serum, programmed death-1 (PD-1) expression on T cells, regulatory T-cell differentiation in the spleen, and the survival rate (monitored for 7 days). BMDC transfer resulted in the following changes: a significant reduction in damage to the liver, kidney and pancreas in the CLP-septic mice as well as in the pathological changes seen in the liver, lung, small intestine and pancreas; significantly elevated levels of the T helper type 1 (Th1) cytokines IFN-γ and IL-12p70 in the serum; decreased levels of the Th2 cytokines IL-6 and IL-10 in the serum; reduced expression of PD-1 molecules on CD4(+) T cells; reduced the proliferation and differentiation of splenic suppressor T cells and CD4(+)  CD25(+)  Foxp3(+) regulatory T cells, and a significant increase in the survival rate of the septic animals. These results show that administration of BMDCs may have modulated the differentiation and immune function of T cells and contributed to alleviate immunosuppression, hence reducing organ damage and mortality post sepsis. Hence, the immunoregulatory effect of BMDC treatment has potential for the treatment of sepsis.

Alterations of dendritic cells in sepsis: featured role in immunoparalysis

Sepsis, the leading cause of mortality in intensive care unit, is characterized by hyperinflammatory response in the early stage and followed by a period of immunosuppression. This immune disorder is believed to be the potent factor that is tightly associated with high mortality in sepsis. Dendritic cells (DCs) serve as professional antigen-presenting cells that play a vital role in immune response by activating T lymphocytes. During the progression of sepsis, DCs have been reported to take part in the aberrant immune response and be necessary for survival. Therefore, a better understanding of the DCs pathology will be undoubtedly beneficial for resolving the problems occurring in sepsis. This review discusses effects of sepsis on DCs number and function, including surface molecules expression, cytokines secretion, and T cell activation, and the underlying mechanism as well as some potential therapeutic strategies.

STAT3-mediated IL-17 production by postseptic T cells exacerbates viral immunopathology of the lung

Survivors of severe sepsis exhibit increased morbidity and mortality in response to secondary infections. Although bacterial secondary infections have been widely studied, there remains a paucity of data concerning viral infections after sepsis. In an experimental mouse model of severe sepsis (cecal ligation and puncture [CLP]) followed by respiratory syncytial virus (RSV) infection, exacerbated immunopathology was observed in the lungs of CLP mice compared with RSV-infected sham surgery mice. This virus-associated immunopathology was evidenced by increased mucus production in the lungs of RSV-infected CLP mice and correlated with increased IL-17 production in the lungs. Respiratory syncytial virus-infected CLP mice exhibited increased levels of TH2 cytokines and reduced interferon γ in the lungs and lymph nodes compared with RSV-infected sham mice. In addition, CD4 T cells from CLP mice produced increased IL-17 in vitro irrespective of the presence of exogenous cytokines or blocking antibodies. This increased IL-17 production correlated with increased STAT3 transcription factor binding to the IL-17 promoter in CD4 T cells from CLP mice. Furthermore, in vivo neutralization of IL-17 before RSV infection led to a significant reduction in virus-induced mucus production and TH2 cytokines. Taken together, these data provide evidence that postseptic CD4 T cells are primed toward IL-17 production via increased STAT3-mediated gene transcription, which may contribute to the immunopathology of a secondary viral infection.

Altered MARCH1 ubiquination-regulated dendritic cell immune functions during the early stage of zymosan-induced multiple organ dysfunction syndrome (MODS) in mice

Using a zymosan-induced mouse model of multiple organ dysfunction syndrome (MODS), we previously found profound increases in spleen immune cells' expressions of ubiquitin and MHC-II molecules and increased CD11c+ dendritic cells (DCs) within 24h of zymosan injection. We postulated that the early stage of MODS altered DCs function via an ubiquitination-associated mechanism. We intraperitoneally injected zymosan into 100 male C57BL/6 mice (0.8mg/g) and randomly divided them into 5 groups based on the days after injection (20mice/group): 1d, 3d, 5d, 7d, and 10d. Mice were examined for spleen CD11c+ DC functions at the indicated days. Untreated mice were used for normal spleen tissue and T cell samples. By qPCR, IL-12 and TNF-α mRNA expressions in spleen CD11c+ DCs were significantly increased in MODS 1d mice; on subsequent days post-injection, these mRNA levels gradually returned to control levels. The same patterns were found for MODS mice DCs induction of untreated mouse T cells proliferation and IL-2 and IFN-γ mRNA expressions. When T cell functions were examined using MODS 1d DCs with and without MG132 treatment, an inhibitor of ubiquitinated protein degradation, T cell functional activities were enhanced by DCs treated with MG132. MODS 1d DCs also had significantly reduced MARCH1 mRNA expression, a key ubiquitin ligase that regulates DCs MHC-II expression. Silencing DCs MARCH1 expression with siRNA resulted in enhancing their induction of T cell functional activities. Using co-immunoprecipitation, Western blot, and flow cytometry assays, we deduced that MARCH1 ubiquitinated DC surface MHC-II molecules to regulate DC's immune functions in MODS mice. Our results suggest that aberrant degradation of spleen DCs MARCH1-mediated ubiquitinated proteins is involved during the earliest stage of MODS development.

Sepsis induced by cecal ligation and puncture

Despite advances in intensive care unit interventions, including the use of specific antibiotics and anti-inflammation treatment, sepsis with concomitant multiple organ failure is the most common cause of death in many acute care units. In order to understand the mechanisms of clinical sepsis and develop effective therapeutic modalities, there is a need to use effective experimental models that faithfully replicate what occurs in patients with sepsis. Several models are commonly used to study sepsis, including intravenous endotoxin challenge, injection of live organisms into the peritoneal cavity, establishing abscesses in the extremities, and the induction of polymicrobial peritonitis via cecal ligation and puncture (CLP). Here, we describe the surgery procedure of CLP in mice, which has been proposed to closely replicate the nature and course of clinical sepsis in humans.

How aluminum adjuvants could promote and enhance non-target IgE synthesis in a genetically-vulnerable sub-population

Aluminum-containing adjuvants increase the effectiveness of vaccination, but their ability to augment immune responsiveness also carries the risk of eliciting non-target responses, especially in genetically susceptible individuals. This study reviews the relevant actions of aluminum adjuvants and sources of genetic risk that can combine to adversely affect a vulnerable sub-population. Aluminum adjuvants promote oxidative stress and increase inflammasome activity, leading to the release of IL-1β, IL-18, and IL-33, but not the important regulatory cytokine IL-12. In addition, they stimulate macrophages to produce PGE₂, which also has a role in regulating immune responses. This aluminum-induced cytokine context leads to a T(H)2 immune response, characterized by the further release of IL-3, IL-4, IL-5, IL-9, IL-13, and IgE-potentiating factors such as sCD23. Genetic variants in cytokine genes, such as IL-4, IL-13, IL-33, and IL-18 influence the response to vaccines in children and are also associated with atopy. These genetic factors may therefore define a genetically-vulnerable sub-population, children with a family history of atopy, who may experience an exaggerated T(H)2 immune response to aluminum-containing vaccines. IL-4, sCD23, and IgE are common factors for both atopy and the immune-stimulating properties of aluminum adjuvants. IL-4 is critical in the production of IgE and total IgE up-regulation. IL-4 has also been reported to induce the production of sCD23 and trigger resting sIgM+, sIgD+ B-cells to switch to sIgE+ B-cells, making them targets for IgE-potentiating factors. Further, the actions of IgE-potentiating factors on sIgE+ B-cells are polyclonal and unrestricted, triggering their differentiation into IgE-forming plasma cells. These actions provide a mechanism for aluminum-adjuvant promotion and enhancement of non-target IgE in a genetically vulnerable sub-population. Identification of these individuals may decrease the risk of adverse events associated with the use of aluminum-containing vaccines.

A historical perspective on sepsis

In North America, approximately 700,000 cases of sepsis occur each year, with mortality ranging between 30% and 50%. The American Journal of Pathology has featured numerous articles on the topic, revealing mechanistic insights gleaned from both experimental rodent models and human sepsis. Nonetheless, there remains urgent need to determine the basis for sepsis-related complications and how they can be avoided, as well as how they can be most effectively treated once recognized. This historical perspective reviews what we currently understand about the mechanisms of sepsis, as well as the barriers that remain in our treatment strategies.

Modulation of FLT3 signaling targets conventional dendritic cells to attenuate acute lung injury

Conventional dendritic cells (cDCs) have been reported to participate in the pathophysiology of acute lung injury (ALI). Fms-like tyrosine kinase 3 (FLT3) signaling represents a highly specific pathway for the manipulation of cDCs in vivo. The purpose of this study was to clarify the effect of FLT3 signaling on the accumulation and maturation of pulmonary cDCs, and whether inhibition of FLT3 signaling may attenuate acute lung inflammation and lung injury. C57BL/6 mice were pretreated with FLT3-ligand (FLT3L) and lestaurtinib separately for five consecutive days. A murine model of ALI was subsequently generated by intra-tracheal instillation of lipopolysaccharide (LPS) and lung specimens were harvested 24 h later. Flow cytometry was conducted to measure the accumulation and maturation of pulmonary cDCs. IL-6, IFN-γ, IL-4, MPO activity and transcription factor T-bet/GATA-3 mRNA ratio were quantified to evaluate lung inflammation. Lung injury was estimated by lung wet weight/body weight ratio (LWW/BW) and histopathological analysis. LPS challenge resulted in rapid accumulation and maturation of pulmonary cDCs. FLT3L pretreatment further stimulated the accumulation and maturation of pulmonary cDCs, leading to a markedly increased LWW/BW and aggravated lung histopathology. Meanwhile, lung MPO activity, T-bet/GATA-3 mRNA ratio and concentrations of IL-6 and IFN-γ were elevated by FLT3L administration. In contrast, lestaurtinib pretreatment inhibited the accumulation and maturation of pulmonary cDCs, leading to a significantly decreased LWW/BW and improved lung histopathology. Lestaurtinib administration also suppressed lung MPO activity, T-bet/GATA-3 mRNA ratio and production of IL-6 and IFN-γ. Our findings show that FLT3 signaling ameliorates ALI by regulating the accumulation and maturation of pulmonary cDCs, suggesting an innovative pharmacotherapy for ALI.

Sepsis leads to a reduced antigen-specific primary antibody response

Immunosuppression, impaired cytokine production and high susceptibility to secondary infections are characteristic for septic patients, and for mice after induction of polymicrobial septic peritonitis by sublethal cecal ligation and puncture (CLP). Here, we demonstrate that CLP markedly altered subsequent B-cell responses. Total IgG and IgM levels, as well as the memory B-cell response, were increased in septic mice, but antigen-specific primary antibody production was strongly impaired. We found that two days after CLP, CD11b(+) splenocytes were activated as demonstrated by the increased expression of activation markers, expression of arginase and production of NO by immature myeloid cells. The in vivo clearance of a bacterial infection was not impaired. DCs demonstrated reduced IL-12 production and altered antigen presentation, resulting in decreased proliferation but enhanced IFN-γ production by CD4(+) cells. CD4(+) T cells from mice immunized on day 2 after CLP showed reduced Th1 and Th2 cytokine production. In addition, there was an increase in Treg cells. Interestingly, levels of immature B cells decreased but levels of mature B cells increased two days after CLP. However, adoptive transfer of naïve CD4(+) T cells, naïve B cells, or naïve DCs did not rescue the antigen-specific antibody response.

Therapeutic DNA vaccine reduces schistosoma mansoni-induced tissue damage through cytokine balance and decreased migration of myofibroblasts

Helminths are known to elicit a wide range of immunomodulation characterized by dominant Th2-type immune responses. Our group previously showed that a DNA vaccine encoding the mycobacterial 65-kDa heat shock protein (DNA-hsp65) showed immunomodulatory properties. We also showed, using a helminth-tuberculosis (TB) co-infection model, that the DNA-hsp65 vaccine protected mice against TB. We next investigated the mechanistic role of the vaccine during helminth-TB co-infection. Clinically, helminth infection causes type 2 granulomas in the lung. Mice were immunized with DNA-hsp65 while they were submitted to the type 2 granuloma induction protocol by Schistosoma mansoni eggs infusion. In this work we investigated the effects of DNA-hsp65 on the pathology and immune response during the development of type 2 granuloma induced by S. mansoni eggs. Histologic analyses of lung parenchyma showed that the DNA-hsp65 vaccine protected mice against exacerbated fibrosis induced by Schistosoma eggs, and decreased the size of the granulomas. These changes were correlated with a reduction in the number of T cells specific for the egg antigens in the lung and also with modulation of Th2 cytokine expression. Taken together, our results showed that the adjuvant properties of the DNA-hsp65 vaccine regulated the immune response in this Th2 model, and resulted in a preserved lung parenchyma.

Dysregulated cytokine expression by CD4+ T cells from post-septic mice modulates both Th1 and Th2-mediated granulomatous lung inflammation

Previous epidemiological studies in humans and experimental studies in animals indicate that survivors of severe sepsis exhibit deficiencies in the activation and effector function of immune cells. In particular, CD4+ T lymphocytes can exhibit reduced proliferative capacity and improper cytokine responses following sepsis. To further investigate the cell-intrinsic defects of CD4+ T cells following sepsis, splenic CD4+ T cells from sham surgery and post-septic mice were transferred into lymphopenic mice. These recipient mice were then subjected to both TH1-(purified protein derivative) and TH2-(Schistosoma mansoni egg antigen) driven models of granulomatous lung inflammation. Post-septic CD4+ T cells mediated smaller TH1 and larger TH2 lung granulomas as compared to mice receiving CD4+ T cells from sham surgery donors. However, cytokine production by lymph node cells in antigen restimulation assays indicated increased pan-specific cytokine expression by post-septic CD4+ T cell recipient mice in both TH1 and TH2 granuloma models. These include increased production of T(H)2 cytokines in TH1 inflammation, and increased production of T(H)1 cytokines in TH2 inflammation. These results suggest that cell-intrinsic defects in CD4+ T cell effector function can have deleterious effects on inflammatory processes post-sepsis, due to a defect in the proper regulation of TH-specific cytokine expression.

GSK-3β-induced ASK1 stabilization is crucial in LPS-induced endotoxin shock

Glycogen synthase kinase-3β (GSK-3β), a multifunctional kinase, is a regulator of lipopolysaccharide (LPS)-mediated septic shock. Apoptosis signal-regulating kinase 1 (ASK1) is also required for LPS-induced activation of p38, which is a crucial determinant for the production of pro-inflammatory cytokines via Toll-like receptor 4 (TLR4) in endotoxemia. Here, we show that attenuation of endotoxemia induced by GSK-3 inhibition is caused by the ASK1 reduction-mediated inhibition of p38, a representative downstream kinase of ASK1. LPS-stimulated activation of p38 was blocked by the reduction of ASK1 via the knockdown of GSK-3β. In addition, compared with L929 control cells, ASK1 protein was reduced in L929 cells stably expressing Wnt-3a and in which β-catenin was active, due to the inhibition of GSK-3β activity. GSK-3β inhibition-mediated ASK1 reduction was also confirmed by reduced ASK1 in GSK-3β-deficient mouse embryo fibroblasts (MEFs) and MCF7 GSK-3β siRNA cells. Furthermore, ASK1 protein stability was also attenuated in MCF7 GSK-3β siRNA cells compared with GFP control cells. Consistent with stability data, a much stronger ubiquitination of ASK1 was observed in cells in which GSK-3β was knocked down. These findings suggest that GSK-3β crosstalks with p38 kinase via the regulation of ASK1 protein stability in endotoxemia.

Epigenetic regulation of immune cell functions during post-septic immunosuppression

Studies in humans and animal models indicate that profound immunosuppression is one of the chronic consequences of severe sepsis. This immune dysfunction encompasses deficiencies in activation of cells in both the myeloid and lymphoid cell lineages. As a result, survivors of severe sepsis are at risk of succumbing to infections perpetrated by opportunistic pathogens that are normally controlled by a fully functioning immune system. Recent studies have indicated that epigenetic mechanisms may be one driving force behind this immunosuppression, through suppression of proinflammatory gene production and subsequent immune cell activation, proliferation and effector function. A better understanding of epigenetics and post-septic immunosuppression can improve our diagnostic tools and may be an important potential source of novel molecular targets for new therapies. This review will discuss important pathways of immune cell activation affected by severe sepsis, and highlight pathways of epigenetic regulation that may be involved in post-septic immunosuppression.

Modulation of dendritic cell differentiation in the bone marrow mediates sustained immunosuppression after polymicrobial sepsis

Murine polymicrobial sepsis is associated with a sustained reduction of dendritic cell (DC) numbers in lymphoid organs and with a dysfunction of DC that is considered to mediate the chronic susceptibility of post-septic mice to secondary infections. We investigated whether polymicrobial sepsis triggered an altered de novo formation and/or differentiation of DC in the bone marrow. BrdU labeling experiments indicated that polymicrobial sepsis did not affect the formation of splenic DC. DC that differentiated from bone marrow (bone marrow-derived DC [BMDC]) of post-septic mice released enhanced levels of IL-10 but did not show an altered phenotype in comparison with BMDC from sham mice. Adoptive transfer experiments of BMDC into naive mice revealed that BMDC from post-septic mice impaired Th1 priming but not Th cell expansion and suppressed the innate immune defense mechanisms against Pseudomonas bacteria in the lung. Accordingly, BMDC from post-septic mice inhibited the release of IFN-γ from NK cells that are critical for the protection against Pseudomonas. Additionally, sepsis was associated with a loss of resident DC in the bone marrow. Depletion of resident DC from bone marrow of sham mice led to the differentiation of BMDC that were impaired in Th1 priming similar to BMDC from post-septic mice. Thus, in response to polymicrobial sepsis, DC precursor cells in the bone marrow developed into regulatory DC that impaired Th1 priming and NK cell activity and mediated immunosuppression. The absence of resident DC in the bone marrow after sepsis might have contributed to the modulation of DC differentiation.

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.

Hemozoin from Schistosoma japonicum does not affect murine myeloid dendritic cell function

Hemozoin (Hz) formation is a byproduct of hemoglobin digestion in some hematophagous organisms. Although Hz produced by Plasmodium falciparum (PfHz) has been shown to affect development and activities of human dendritic cells (DCs), the effects of Schistosoma Hz on DCs have not been elucidated. Our data presented in this report demonstrated that native Schistosoma japonica Hz (SjHz) did not affect the differentiation of murine bone marrow cells into immature DCs (imDCs). Maturation and stimulatory activities to T cells by imDCs induced by LPS were not altered in the presence of SjHz; whereas purified PfHz induced a slight increase in CD40 expression and enhanced IL-12p40 secretion. Lastly, SjHz treatment did not significantly affect the phagocytic activities of DCs. These data suggested that SjHz failed to exert any significant effects on the development and activities of murine myeloid DCs. The mechanisms of different effects on DCs by SjHz and PfHz remain to be elucidated.

[Dendritic cells in sepsis: an approach to post-infectious immunosuppression]

Dendritic cells (DCs) play a decisive role in the immune system, especially in the initial events that determine coordination between the innate and adaptive response. Moreover, they are antigen-presenting cells which, through contact with T cells, determine the type of immune responses towards inflammatory or anti-inflammatory. Currently, the hypothesis that attributes importance to the development of a post-infectious immunosuppression in the prognosis of the septic patient is growing stronger. It has been possible to verify the role played by these cells in this type of immunosuppression by the significant decrease in the number of DCs and by the dysfunctions in the functional capacity that include, on the one hand, the abnormal cytokine production and, on the other hand, the alterations in communication between the DCs and T cells that constitute an essential immunological fact. Further research into the knowledge regarding the DCs, in the context of severe infection, may help to consolidate some encouraging data that indicate these cells as: 1) an effective tool for monitoring the acute infection, 2) a discriminatory variable that may help determine the risk of nosocomial infection and 3) in a longer term, a treatment target that would restore the immunological abnormalities that occur in sepsis.

Dendritic cells modulate lung response to Pseudomonas aeruginosa in a murine model of sepsis-induced immune dysfunction

Host infection by pathogens triggers an innate immune response leading to a systemic inflammatory response, often followed by an immune dysfunction which can favor the emergence of secondary infections. Dendritic cells (DCs) link innate and adaptive immunity and may be centrally involved in the regulation of sepsis-induced immune dysfunction. We assessed the contribution of DCs to lung defense in a murine model of sublethal polymicrobial sepsis (cecal ligature and puncture, CLP). In this model, bone marrow-derived DCs (BMDCs) retained an immature phenotype, associated with decreased capacity of IL-12p70 release and impaired priming of T cell lymphocytes. Eight days after CLP surgery, we induced a secondary pulmonary infection through intratracheal instillation of 5 x 10(6) CFUs of Pseudomonas aeruginosa. Whereas all sham-operated mice survived, 80% of post-CLP mice died after secondary pneumonia. Post-CLP mice exhibited marked lung damage with early recruitment of neutrophils, cytokine imbalance with decreased IL-12p70 production, and increased IL-10 release, but no defective bacterial lung clearance, while systemic bacterial dissemination was almost constant. Concomitant intrapulmonary administration of exogenous BMDCs into post-CLP mice challenged with P. aeruginosa dramatically improved survival. BMDCs did not improve bacterial lung clearance, but delayed neutrophil recruitment, strongly attenuated the early peak of TNF-alpha and restored an adequate Il-12p70/IL-10 balance in post-CLP mice. Thus, adoptive transfer of BMDCs reversed sepsis-induced immune dysfunction in a relevant model of secondary P. aeruginosa pneumonia. Unexpectedly, the mechanism of action of BMDCs did not involve enhanced antibacterial activity, but occurred by dampening the pulmonary inflammatory response.

Molecular and cellular aspects of sepsis-induced immunosuppression

Sepsis is a significant cause of death worldwide. Although the prevailing theory of the sepsis syndrome has been that of a condition of uncontrolled inflammation in response to infection, sepsis is increasingly being recognized as an immunosuppressive state. The immune modulations of sepsis result in altered innate and adaptive immune responses, thereby rendering the septic host susceptible to secondary infections. In this review, we present an overview of the clinical and experimental evidence for sepsis-induced immunosuppression and outline the mechanisms that underlie this phenotype. With an improved understanding of how host immune states may be altered during sepsis, better immunomodulatory therapies may be developed to address the immune derangements observed in patients with sepsis.

Diversity of interferon gamma and granulocyte-macrophage colony-stimulating factor in restoring immune dysfunction of dendritic cells and macrophages during polymicrobial sepsis

The development of immunosuppression during polymicrobial sepsis is associated with the failure of dendritic cells (DC) to promote the polarization of T helper (Th) cells toward a protective Th1 type. The aim of the study was to test potential immunomodulatory approaches to restore the capacity of splenic DC to secrete interleukin (IL) 12 that represents the key cytokine in Th1 cell polarization. Murine polymicrobial sepsis was induced by cecal ligation and puncture (CLP). Splenic DC were isolated at different time points after CLP or sham operation, and stimulated with bacterial components in the presence or absence of neutralizing anti-IL-10 antibodies, murine interferon (IFN) gamma, and/or granulocyte macrophage colony-stimulating factor (GM-CSF). DC from septic mice showed an impaired capacity to release the pro-inflammatory and Th1-promoting cytokines tumor necrosis factor alpha, IFN-gamma, and IL-12 in response to bacterial stimuli, but secreted IL-10. Endogenous IL-10 was not responsible for the impaired IL-12 secretion. Up to 6 h after CLP, the combined treatment of DC from septic mice with IFN-gamma and GM-CSF increased the secretion of IL-12. Later, DC from septic mice responded to IFN-gamma and GM-CSF with increased expression of the co-stimulatory molecule CD86, while IL-12 secretion was no more enhanced. In contrast, splenic macrophages from septic mice during late sepsis responded to GM-CSF with increased cytokine release. Thus, therapy of sepsis with IFN-gamma/GM-CSF might be sufficient to restore the activity of macrophages, but fails to restore DC function adequate for the development of a protective Th1-like immune response.

[Clinical usefulness of plasma interleukin-6 and interleukin-10 in disseminated intravascular coagulation]

BACKGROUND

Disseminated intravascular coagulation (DIC) is a syndrome characterized by a systemic activation of coagulation leading to the intravascular deposition of fibrin and the simultaneous consumption of coagulation factors and platelets. Inflammatory cytokines can activate the coagulation system. This study investigated the diagnostic and prognostic usefulness of the plasma level of interleukin-6 (IL-6) and interleukin-10 (IL-10) for predicting DIC.

METHODS

The study populations were 15 healthy controls and 81 patients who were clinically suspected of having DIC and were requested to perform DIC battery tests. The presence of overt DIC was defined by the International Society on Thrombosis and Haemostasis Subcommittee cumulative score of 5 or above. The 28 day mortality was used to assess the prognostic outcome. The plasma levels of the cytokines were measured by ELISA.

RESULTS

The plasma levels of IL-6 and IL-10 in patients (N=81) were higher than those of control (N=15). IL-6 and IL-10 levels of overt DIC group (N=31) were 3 times and 1.5 times higher than those, respectively, of non-overt DIC group (N=50). In infection group (N=48), IL-6 and IL-10 levels of overt DIC group (N=18) were 5 times and 3 times higher than those, respectively, of non-overt DIC group (N=30). The diagnostic efficiency of IL-6 (optimal cut off >40.4 pg/mL) and IL-10 (>9.7 pg/mL) for the diagnosis of overt DIC were 67% and 69%, respectively, which were similar to that of D-dimer. Plasma levels of IL-6 and IL-10 were also higher in non-survivors than in survivors. The patients with higher levels of IL-6 and IL-10 showed a poorer prognosis.

CONCLUSIONS

The proinflammatory cytokine, IL-6 and anti-inflammatory cytokine, IL-10 were useful for the diagnosis of overt DIC and the prediction of its prognosis. These results also showed the evidence of a close interaction between coagulation and inflammation.

Epigenetic regulation of dendritic cell-derived interleukin-12 facilitates immunosuppression after a severe innate immune response

Patients who survive sepsis have significant deficiencies in their immune responses caused by poorly understood mechanisms. We have explored this phenomenon by studying dendritic cells (DCs) recovered from animals surviving severe peritonitis-induced sepsis, using the well-established cecal ligation and puncture (CLP) model. Immediately after the initiation of sepsis there is a depletion in DCs from the lung and spleen, which is followed by repopulation of these cells back to the respective organs. DCs recovered from surviving animals exhibited a significant and chronic suppression of interleukin-12 (IL-12), a key host defense cytokine. The suppression of DC-derived IL-12 persisted for at least 6 weeks after CLP and was not due to immunoregulatory cytokines, such as IL-10. Using chromatin immunoprecipitation (ChIP) techniques, we have shown that the deficiency in DC-derived IL-12 was due to epigenetic alterations. Specifically, IL-12 expression was regulated by stable reciprocal changes in histone H3 lysine-4 trimethylation (H3K4me3) and histone H3 lysine-27 dimethylation (H3K27me2), as well as changes in cognate histone methyltransferase (HMT) complexes on the Il12p35 and Il12p40 promoters. These data implicate histone modification enzymes in suppressing DC-derived IL-12, which may provide one of the mechanisms of long-term immunosuppression subsequent to the septic response.

TLR9 activation is a key event for the maintenance of a mycobacterial antigen-elicited pulmonary granulomatous response

Type 1 (Th1) granulomas can be studied in mice sensitized with mycobacterium antigens followed by challenge of agarose beads covalently coupled to purified protein derivative. TLR9 is known to play a role in the regulation of Th1 responses; thus, we investigated the role of TLR9 in granuloma formation during challenge with mycobacterium antigens and demonstrated that mice deficient in TLR9 had increased granuloma formation, but a dramatically altered cytokine phenotype. Th1 cytokine levels of IFN-gamma and IL-12 in the lungs were decreased in TLR9(-/-) mice when compared to wild-type mice. In contrast, Th2 cytokine levels of IL-4, IL-5, and IL-13 were increased in TLR9(-/-) mice. The migration of CD4(+) T cells in the granuloma was impaired, while the number of F4/80(+) macrophages was increased in TLR9(-/-) mice. Macrophages in the lungs of the TLR9-deficient animals with developing granulomas expressed significantly lower levels of the classically activated macrophage marker, nitric oxide synthase, but higher levels of the alternatively activated macrophage markers such as 'found in inflammatory zone-1' antigen and Arginase-1. These results suggest that TLR9 plays an important role in maintaining the appropriate phenotype in a Th1 granulomatous response.

Dendritic cells at the interface of innate and acquired immunity: the role for epigenetic changes

Dendritic cells (DC) are known to be essential immune cells in innate immunity and in the initiation of adaptive immunity. The shaping of adaptive immunity by innate immunity is dependent on DC unique cellular functions and DC-derived effector molecules such as cytokines and chemokines. Thus, it is not surprising that numerous studies have identified alterations in DC number, function, and subset ratios in various diseases, such as infections, cancers, and autoimmune diseases. Recent evidence has also identified that immunosuppression occurring after severe systemic inflammation, such as found in sepsis, is a result of depletion in DC numbers and a later dysfunction in DC activity. This correlation suggests that the sustained DC dysfunction initiated by life-threatening inflammation may contribute to the subsequent immunoparalysis, potentially as a result of the long-term maintenance of an abnormal gene expression pattern. In this review, we summarized the present information regarding altered DC function after a severe, acute inflammatory response and propose a mechanism, whereby epigenetic changes can influence long-term gene expression patterns by DC, thus supporting an immunosuppression phenotype.

Changes in dendritic cell function in the immune response to sepsis. Cell- & tissue-based therapy

Sepsis represents a complex clinical syndrome of significant morbidity and mortality. This continues to be the case in intensive care units around the world, despite extensive use of antibiotics, aggressive surgical intervention and optimization of nutritional support. Furthermore, the failure of > 30 anti-inflammatory mediator therapeutic trials implies, beyond the issue of trial design, there remains the necessity to develop a better understanding of the evolving pathophysiology of this syndrome. Studies indicate that the development of marked immune suppression in sepsis is more often associated with morbid outcome. Dendritic cells, a critical immune cell type bridging the innate and adaptive immune response, not only are affected (killed) by the systemic inflammatory response but also contribute to (by impaired function) the development of immune suppression during sepsis. Here the authors attempt to review emerging data indicating the key role dendritic cells may play in sepsis-induced immune suppression. Undoubtedly, a better understanding of the dendritic cell's response during sepsis will be critical to developing novel strategies for fighting this deadly disease.

Murine gammaherpesvirus-68 productively infects immature dendritic cells and blocks maturation

Many viruses have evolved mechanisms to evade host immunity by subverting the function of dendritic cells (DCs). This study determined whether murine gammaherpesvirus-68 (gamma HV-68) could infect immature or mature bone-marrow-derived DCs and what effect infection had on DC maturation. It was found that gamma HV-68 productively infected immature DCs, as evidenced by increased viral titres over time. If DCs were induced to mature by exposure to LPS and then infected with gamma HV-68, only a small percentage of cells was productively infected. However, limiting-dilution assays to measure viral reactivation demonstrated that the mature DCs were latently infected with gamma HV-68. Electron microscopy revealed the presence of capsids in the nucleus of immature DCs but not in mature DCs. Interestingly, infection of immature DCs by gamma HV-68 did not result in upregulation of the co-stimulatory molecules CD80 and CD86 or MHC class I and II, or induce cell migration, suggesting that the virus infection did not induce DC maturation. Furthermore, gamma HV-68 infection of immature DCs did not result in elevated interleukin-12, an important cytokine in the induction of T-cell responses. Finally, lipopolysaccharide and poly(I : C) stimulation of gamma HV-68-infected immature DCs did not induce increases in the expression of co-stimulatory molecules and MHC class I or II compared with mock-treated cells, suggesting that gamma HV-68 infection blocked maturation. Taken together, these data demonstrate that gamma HV-68 infection of DCs differs depending on the maturation state of the DC. Moreover, the block in DC maturation suggests a possible immunoevasion strategy by gamma HV-68.