Breaking the co-operation between bystander T-cells and natural killer cells prevents the development of immunosuppression after traumatic skeletal muscle injury in mice.

Nosocomial infections represent serious complications after traumatic or surgical injuries in intensive care units. The pathogenesis of the underlying immunosuppression is only incompletely understood. In the present study, we investigated whether injury interferes with the function of the adaptive immune system in particular with the differentiation of antigen-specific T helper (Th)-cell responses in vivo. We used a mouse model for traumatic gastrocnemius muscle injury. Ovalbumin (OVA), which served as a foreign model antigen, was injected into the hind footpads for determination of the differentiation of OVA-specific Th-cells in the draining popliteal lymph node (pLN). The release of interferon (IFN)-γ from OVA-specific Th-cells was impaired within 24 h after injury and this impairment persisted for at least 7 days. In contrast, the proliferation of OVA-specific Th-cells remained unaffected. Injury did not modulate the function of antigen-presenting cells (APCs) in the pLN. Adoptive transfer of total T-cells from pLNs of injured mice inhibited IFN-γ production by OVA-specific Th-cells in naive mice. Suppressed Th1 priming did not occur in lymphocyte-deficient mice after injury but was restored by administration of T-cells before injury. Moreover, the suppression of Th1 differentiation required the presence of natural killer (NK) cells that were recruited to the pLN after injury; this recruitment was dependent on lymphocytes, toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88). In summary, upon traumatic skeletal muscle injury T-cells and NK cells together prevent the development of protective Th1 immunity. Breaking this co-operation might be a novel approach to reduce the risk of infectious complications after injury.

Interaction with mesenchymal stem cells provokes natural killer cells for enhanced IL-12/IL-18-induced interferon-gamma secretion.

Tissue injury induces an inflammatory response accompanied by the recruitment of immune cells and of mesenchymal stem cells (MSC) that contribute to tissue regeneration. After stimulation with interleukin- (IL-) 12 and IL-18 natural killer (NK) cells secrete the proinflammatory cytokine interferon- (IFN-) γ. IFN- γ plays a crucial role in the defense against infections and modulates tissue regeneration. In consideration of close proximity of NK cells and MSC at the site of injury we investigated if MSC could influence the ability of NK-cells to produce IFN-γ. Coculture experiments were performed with bone marrow-derived human MSC and human NK cells. MSC enhanced the ability of IL-12/IL-18-stimulated NK cells to secrete IFN- γ in a dose-dependent manner. This activation of NK cells was dependent on cell-cell contact as well as on soluble factors. The increased IFN- γ secretion from NK cells after contact with MSC correlated with an increased level of intracellular IFN- γ. Alterations in the IL-12 signaling pathway including an increased expression of the IL-12ß1 receptor subunit and an increased phosphorylation of signal transducer and activator of transcription 4 (STAT4) could be observed. In conclusion, MSC enhance the IFN- γ release from NK cells which might improve the defense against infections at the site of injury but additionally might affect tissue regeneration.

Profiling the dysregulated immune response in sepsis: overcoming challenges to achieve the goal of precision medicine.

Sepsis is characterised by a dysregulated host immune response to infection. Despite recognition of its significance, immune status monitoring is not implemented in clinical practice due in part to the current absence of direct therapeutic implications. Technological advances in immunological profiling could enhance our understanding of immune dysregulation and facilitate integration into clinical practice. In this Review, we provide an overview of the current state of immune profiling in sepsis, including its use, current challenges, and opportunities for progress. We highlight the important role of immunological biomarkers in facilitating predictive enrichment in current and future treatment scenarios. We propose that multiple immune and non-immune-related parameters, including clinical and microbiological data, be integrated into diagnostic and predictive combitypes, with the aid of machine learning and artificial intelligence techniques. These combitypes could form the basis of workable algorithms to guide clinical decisions that make precision medicine in sepsis a reality and improve patient outcomes.

Lipopeptides rather than lipopolysaccharide favor the development of dendritic cell dysfunction similar to polymicrobial sepsis in mice.

OBJECTIVE: We investigated whether the dysfunction of dendritic cells (DC) that develops during polymicrobial sepsis is mimicked by systemic administration of the Toll-like receptor (TLR) 4 agonist lipopolysaccharide (LPS) or of the TLR2 agonist Pam3-Cys-Ser-Lys4 (P3CSK4). MATERIALS AND METHODS: BALB/c mice underwent cecal ligation and puncture (CLP) or sham operation or received a single i.p. injection of LPS (30 mg/kg body weight), P3CSK4 (10 mg/kg body weight), or saline as control. Purified splenic DC and in-vitro-generated DC from bone marrow were analyzed in terms of surface marker expression, cytokine secretion, and antigen-specific T-cell activation in vivo. RESULTS: Splenic DC were suppressed in IL-12 secretion 12 h after LPS and P3CSK4 administration but released increased levels of IL-12 4 days after TLR agonist application, unlike DC from CLP mice. Polymicrobial sepsis and TLR agonists caused a loss of DC in the spleen but led to the expansion of diverse DC subsets. DC that differentiated from bone marrow after P3CSK4 but not after LPS application resembled DC from CLP mice regarding cytokine secretion and impaired Th1-cell polarization. CONCLUSIONS: The development of DC dysfunction during sepsis is at least partly mimicked by TLR2 agonists rather than TLR4 agonists.

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.

TLR2-induced CD8+ T-cell deactivation shapes dendritic cell differentiation in the bone marrow during sepsis.

Sepsis is associated with profound immune dysregulation that increases the risk for life-threatening secondary infections: Dendritic cells (DCs) undergo functional reprogramming due to yet unknown changes during differentiation in the bone marrow (BM). In parallel, lymphopenia and exhaustion of T lymphocytes interfere with antigen-specific adaptive immunity. We hypothesized that there exists a link between T cells and the modulation of DC differentiation in the BM during murine polymicrobial sepsis. Sepsis was induced by cecal ligation and puncture (CLP), a model for human bacterial sepsis. At different time points after CLP, the BM and spleen were analyzed in terms of T-cell subpopulations, activation, and Interferon (IFN)-γ synthesis as well as the number of pre-DCs. BM-derived DCs were generated in vitro. We observed that naïve and virtual memory CD8+ T cells, but not CD4+ T cells, were activated in an antigen-independent manner and accumulated in the BM early after CLP, whereas lymphopenia was evident in the spleen. The number of pre-DCs strongly declined during acute sepsis in the BM and almost recovered by day 4 after CLP, which required the presence of CD8+ T cells. Adoptive transfer experiments and in vitro studies with purified T cells revealed that Toll-like receptor 2 (TLR2) signaling in CD8+ T cells suppressed their capacity to secrete IFN-γ and was sufficient to change the transcriptome of the BM during sepsis. Moreover, the diminished IFN-γ production of CD8+ T cells favored the differentiation of DCs with increased production of the immune-activating cytokine Interleukin (IL)-12. These data identify a novel role of CD8+ T cells in the BM during sepsis as they sense TLR2 ligands and control the number and function of de novo differentiating DCs.

BMP signaling balances proliferation and differentiation of muscle satellite cell descendants.

BACKGROUND: The capacity of muscle to grow or to regenerate after damage is provided by adult stem cells, so called satellite cells, which are located under the basement lamina of each myofiber. Upon activation satellite cells enter the cell cycle, proliferate and differentiate into myoblasts, which fuse to injured myofibers or form new fibers. These processes are tightly controlled by many growth factors. RESULTS: Here we investigate the role of bone morphogenetic proteins (BMPs) during satellite cell differentiation. Unlike the myogenic C2C12 cell line, primary satellite cells do not differentiate into osteoblasts upon BMP signaling. Instead BMP signaling inhibits myogenic differentiation of primary satellite cells ex vivo. In contrast, inhibition of BMP signaling results in cell cycle exit, followed by enhanced myoblast differentiation and myotube formation. Using an in vivo trauma model we demonstrate that satellite cells respond to BMP signals during the regeneration process. Interestingly, we found the BMP inhibitor Chordin upregulated in primary satellite cell cultures and in regenerating muscles. In both systems Chordin expression follows that of Myogenin, a marker for cells committed to differentiation. CONCLUSION: Our data indicate that BMP signaling plays a critical role in balancing proliferation and differentiation of activated satellite cells and their descendants. Initially, BMP signals maintain satellite cells descendants in a proliferating state thereby expanding cell numbers. After cells are committed to differentiate they upregulate the expression of the BMP inhibitor Chordin thereby supporting terminal differentiation and myotube formation in a negative feedback mechanism.

Major Surgical Trauma Impairs the Function of Natural Killer Cells but Does Not Affect Monocyte Cytokine Synthesis.

Major traumatic and surgical injury increase the risk for infectious complications due to immune dysregulation. Upon stimulation with interleukin (IL) 12 by monocyte/macrophages, natural killer (NK) cells release interferon (IFN) γ that supports the elimination of the pathogen. In the present study, we investigated the impact of invasive spine surgery on the relationship between monocytes and NK cells upon exposure to Staphylococcus aureus. Mononuclear cells and serum were isolated from peripheral blood of patients before and up to 8 d after surgery and stimulated with inactivated S. aureus bacteria. NK cell and monocyte function were determined by flow cytometry. NK cells continuously lost their ability to produce IFN-γ during the first week after surgery independently from monocyte-derived IL-12 secretion. IFN-γ synthesis was minimal on day 8 and was associated with decreased expression of the IL-12 receptor and activation of transcription factors required for IFNG gene transcription. Addition of recombinant IL-12 could at least partially restore NK cell function. Pre-operative levels of growth/differentiation factor (GDF) 15 in the serum correlated with the extent of NK cell suppression and with hospitalization. Thus, NK cell suppression after major surgery might represent a therapeutic target to improve the immune defense against opportunistic infections.

TLR4 Transactivates CD8+ T Lymphocytes upon Acute Sterile Tissue Injury.

Acute major tissue injury induces immune dysregulation that is characterized by the development of systemic sterile inflammation and an increased risk for opportunistic infections. Although the contribution of the innate immune system has been examined in detail, research on the impact of acute sterile tissue damage on the T cell compartment remains limited. In the current study, we used a clinically relevant mouse model for traumatic skeletal muscle injury to investigate the impact of sterile tissue damage on diverse subpopulations of CD4+ Th and CD8+ cytotoxic T cells in systemic and local lymphoid organs. For the first time, to our knowledge, we provide evidence that injury selectively induced the expression of the activation marker CD69 on naive and central/virtual memory CD8+ T cells in the lymph nodes but not in the spleen of male mice. CD4+ Th cells remained unaffected in both organs. The activation of CD8+ T cells was dependent on signaling through TLR4. Within a few hours, injury triggered the expression of IL-12 in the lymph nodes in a TLR4-dependent manner. Blocking of IL-12 prevented the activation of naive and central memory CD8+ T cells after injury. Thus, early after traumatic tissue damage, TLR4 transactivates naive and central/virtual memory CD8+ T cells through innate cytokines in local lymph nodes, where they might modulate forthcoming local immune responses.

Bridging animal and clinical research during SARS-CoV-2 pandemic: A new-old challenge.

Many milestones in medical history rest on animal modeling of human diseases. The SARS-CoV-2 pandemic has evoked a tremendous investigative effort primarily centered on clinical studies. However, several animal SARS-CoV-2/COVID-19 models have been developed and pre-clinical findings aimed at supporting clinical evidence rapidly emerge. In this review, we characterize the existing animal models exposing their relevance and limitations as well as outline their utility in COVID-19 drug and vaccine development. Concurrently, we summarize the status of clinical trial research and discuss the novel tactics utilized in the largest multi-center trials aiming to accelerate generation of reliable results that may subsequently shape COVID-19 clinical treatment practices. We also highlight areas of improvement for animal studies in order to elevate their translational utility. In pandemics, to optimize the use of strained resources in a short time-frame, optimizing and strengthening the synergy between the preclinical and clinical domains is pivotal.

The COVID-19 puzzle: deciphering pathophysiology and phenotypes of a new disease entity.

The zoonotic SARS-CoV-2 virus that causes COVID-19 continues to spread worldwide, with devastating consequences. While the medical community has gained insight into the epidemiology of COVID-19, important questions remain about the clinical complexities and underlying mechanisms of disease phenotypes. Severe COVID-19 most commonly involves respiratory manifestations, although other systems are also affected, and acute disease is often followed by protracted complications. Such complex manifestations suggest that SARS-CoV-2 dysregulates the host response, triggering wide-ranging immuno-inflammatory, thrombotic, and parenchymal derangements. We review the intricacies of COVID-19 pathophysiology, its various phenotypes, and the anti-SARS-CoV-2 host response at the humoral and cellular levels. Some similarities exist between COVID-19 and respiratory failure of other origins, but evidence for many distinctive mechanistic features indicates that COVID-19 constitutes a new disease entity, with emerging data suggesting involvement of an endotheliopathy-centred pathophysiology. Further research, combining basic and clinical studies, is needed to advance understanding of pathophysiological mechanisms and to characterise immuno-inflammatory derangements across the range of phenotypes to enable optimum care for patients with COVID-19.

Isolated closed minor-muscle injury of the lower leg did not cause an obvious systemic immune response.

OBJECTIVE: A common consequence in patients with blunt trauma is a deterioration of the immune system. The specific impacts of a frequently occurring isolated soft tissue trauma on the immune response are described. However, the dimension of trauma needed to cause systemic effects has not been definitely elucidated. METHODS: Mice were traumatized on the lower leg. The extent of soft tissue trauma was quantified by determination of the wet/dry ratio, magnetic resonance imaging (MRI), and serum content of muscle proteins. Five minutes, 3, 24, 36, 48, and 72 h after trauma (a.t.) the ex vivo cytokine-expression of immune-competent cells were measured. RESULTS: Trauma resulted in an early edema that could be quantified by MRI and wet/dry ration. Release of muscle-specific proteins was detected 5 min a.t. The trauma did not cause significant changes of TNF-alpha response of isolated cells to endotoxin. IL6-response of splenocytes to endotoxin was slightly increased 72 h a.t., while IL6-response of peritoneal macrophages to endotoxin was decreased 36 h a.t. CONCLUSION: We describe a standardized trauma model for minor soft tissue injury in mice. Systemic effects on the immune system by traumatized lower leg were not found on the level of circulating cytokines or cellular responses to endotoxin.

An Inverse Relationship Between c-Kit/CD117 and mTOR Confers NK Cell Dysregulation Late After Severe Injury.

Major trauma-induced tissue injury causes a dysregulation of the immune system. Severe systemic inflammation occurs early after the insult. Later on, an enhanced risk for life-threatening opportunistic infections develops that culminates at the end of the first week after trauma. CD56bright Natural killer (NK) cells play a key role in the defense against infection due to their rapid release of Interferon (IFN) γ in response to Interleukin (IL) 12. NK cells are impaired in IFN-γ synthesis after severe injury due to a disturbed IL-12/IFN-γ axis. Thereby, a circulating factor mediates extrinsic suppression of NK cells. Yet unknown cell-intrinsic mechanisms manifest by day 8 after trauma and render NK cells unresponsive to stimulatory cytokines. In the present study, we investigated the origin of such late NK cell-intrinsic suppression after major trauma. Peripheral blood mononuclear cells (PBMC) were isolated from patients 8 day after severe injury and from healthy control subjects and were stimulated with inactivated Staphylococcus aureus. The expression of diverse cytokine receptors, intracellular signaling molecules, and the secretion of IFN-γ by CD56bright NK cells were examined. After stimulation with S. aureus, NK cells from patients expressed enhanced levels of c-kit/CD117 that inversely correlated with IFN-γ synthesis and IL-12 receptor (IL-12R) ß2 expression. Supplementation with IL-15 and inhibition of the transforming growth factor receptor (TGF-ßR) I reduced CD117 expression and increased the level of IL-12Rß2 and IFN-γ. NK cells from patients showed reduced phosphorylation of mammalian target of rapamycin (mTOR). Addition of IL-15 at least partly restored mTOR phosphorylation and increased IL-12Rß2 expression. The reduced mTOR phosphorylation after severe injury was cell-intrinsic as it was not induced by serum factors. Inhibition of mTOR in purified NK cells from healthy donors by rapamycin decreased the synthesis of IFN-γ. Thus, impaired mTOR phosphorylation in response to a microbial challenge contributes to the cell-intrinsic mechanisms that underlie NK cell dysregulation after trauma. Restoration of the mTOR phosphorylation capacity along with inhibition of the TGF-ßRI signaling in NK cells after severe injury might improve the immune defense against opportunistic infections.

SARS-CoV-2/COVID-19: Evolving Reality, Global Response, Knowledge Gaps, and Opportunities.

Approximately 3 billion people around the world have gone into some form of social separation to mitigate the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. The uncontrolled influx of patients in need of emergency care has rapidly brought several national health systems to near-collapse with deadly consequences to those afflicted by Coronavirus Disease 2019 (COVID-19) and other critical diseases associated with COVID-19. Solid scientific evidence regarding SARS-CoV-2/COVID-19 remains scarce; there is an urgent need to expand our understanding of the SARS-CoV-2 pathophysiology to facilitate precise and targeted treatments. The capacity for rapid information dissemination has emerged as a double-edged sword; the existing gap of high-quality data is frequently filled by anecdotal reports, contradictory statements, and misinformation. This review addresses several important aspects unique to the SARS-CoV-2/COVID-19 pandemic highlighting the most relevant knowledge gaps and existing windows-of-opportunity. Specifically, focus is given on SARS-CoV-2 immunopathogenesis in the context of experimental therapies and preclinical evidence and their applicability in supporting efficacious clinical trial planning. The review discusses the existing challenges of SARS-CoV-2 diagnostics and the potential application of translational technology for epidemiological predictions, patient monitoring, and treatment decision-making in COVID-19. Furthermore, solutions for enhancing international strategies in translational research, cooperative networks, and regulatory partnerships are contemplated.

Surgical vacuum filter-derived stromal cells are superior in proliferation to human bone marrow aspirate.

BACKGROUND: During joint replacement, surgical vacuum suction guarantees a sufficient overview on the situs. We assume high concentrations of mesenchymal stromal cells (MSCs) on surgical vacuum filters. We compared the in vitro proliferative and differentiation potency of cells from the following: (i) bone marrow (BM), (ii) cancellous bone (CB), (iii) vacuum filter (VF), and (iv) cell saver filtrate reservoir (SF) in 32 patients undergoing elective total hip replacement. METHODS: Mononuclear cells (MNC) were isolated, and cell proliferation and colony-forming units (CFU) were measured. Adherent cells were characterized by flow cytometry for MSC surface markers. Cells were incubated with osteogenic, adipogenic, and chondrogenic stimuli. Cells were cytochemically stained and osteoblastic expression (RUNX-2, ALP, and BMP-2) investigated via qPCR. RESULTS: Dependent on the source, initial MNC amount as well as CFU number was significantly different whereas generation time did not vary significantly. CFU numbers from VF were superior to those from SR, BM, and CB. The resulting amount of MSC from the respective source was highest in the vacuum filter followed by reservoir, aspirate, and cancellous bone. Cells from all groups could be differentiated into the three mesenchymal lines demonstrating their stemness nature. However, gene expression of osteoblastic markers did not differ significantly between the groups. CONCLUSION: We conclude that surgical vacuum filters are able to concentrate tissue with relevant amounts of MSCs. A new potent source of autologous regeneration material with clinical significance is identified. Further clinical studies have to elucidate the regenerative potential of this material in an autologous setting.

Circulating growth/differentiation factor 15 is associated with human CD56bright natural killer cell dysfunction and nosocomial infection in severe systemic inflammation.

BACKGROUND: Systemic inflammation induced by sterile or infectious insults is associated with an enhanced susceptibility to life-threatening opportunistic, mostly bacterial, infections due to unknown pathogenesis. Natural killer (NK) cells contribute to the defence against bacterial infections through the release of Interferon (IFN) γ in response to Interleukin (IL) 12. Considering the relevance of NK cells in the immune defence we investigated whether the function of NK cells is disturbed in patients suffering from serious systemic inflammation. METHODS: NK cells from severely injured patients were analysed from the first day after the initial inflammatory insult until the day of discharge in terms of IL-12 receptor signalling and IFN-γ synthesis. FINDINGS: During systemic inflammation, the expression of the IL-12 receptor ß2 chain, phosphorylation of signal transducer and activation 4, and IFN-γ production on/in NK cells was impaired upon exposure to Staphylococcus aureus. The profound suppression of NK cells developed within 24 h after the initial insult and persisted for several weeks. NK cells displayed signs of exhaustion. Extrinsic changes were mediated by the early and long-lasting presence of growth/differentiation factor (GDF) 15 in the circulation that signalled through the transforming growth factor ß receptor I and activated Smad1/5. Moreover, the concentration of GDF-15 in the serum inversely correlated with the IL-12 receptor ß2 expression on NK cells and was enhanced in patients who later acquired septic complications. INTERPRETATION: GDF-15 is associated with the development of NK cell dysfunction during systemic inflammation and might represent a novel target to prevent nosocomial infections. FUND: The study was supported by the Department of Orthopaedics and Trauma Surgery, University Hospital Essen.

Current gaps in sepsis immunology: new opportunities for translational research.

Increasing evidence supports a central role of the immune system in sepsis, but the current view of how sepsis affects immunity, and vice versa, is still rudimentary. The European Group on Immunology of Sepsis has identified major gaps that should be addressed with high priority, such as understanding how immunological alterations predispose to sepsis, key aspects of the immunopathological events during sepsis, and the long-term consequences of sepsis on patient's immunity. We discuss major unmet topics in those three categories, including the role of key immune cells, the cause of lymphopenia, organ-specific immunology, the dynamics of sepsis-associated immunological alterations, the role of the microbiome, the standardisation of immunological tests, the development of better animal models, and the opportunities offered by immunotherapy. Addressing these gaps should help us to better understand sepsis physiopathology, offering translational opportunities to improve its prevention, diagnosis, and care.

Origin of immunomodulation after soft tissue trauma: potential involvement of extracellular heat-shock proteins.

Severe injury may lead to immunosuppression, multiple organ failure, and death. The aim of the study was to investigate the direct impact of soft tissue destruction on the development of trauma-associated immunomodulation. Hip surgery was considered to represent an isolated soft tissue trauma that allowed for the examination of changes taking place locally at the site of trauma or systemically with regard to monocyte function and leukocyte redistribution. Peripheral blood and wound fluid collected from the drains of 21 patients after hip surgery were analyzed to determine the cellular composition and/or the responsiveness of mononuclear cells (MNCs) to lipopolysaccharide (LPS). Different factors present in the wound fluids were tested for their capacity to modulate the MNC of healthy individuals with regard to cytokine and chemokine secretion. We found that various factors, including heat-shock protein (HSP) 60 and HSP70, were locally released at the site of soft tissue trauma and could be detected in wound fluids. The wound fluid-derived MNC (but not the peripheral blood-derived MNC) showed an impaired capacity to release TNF-alpha after LPS stimulation. Cell-free wound fluid suppressed in healthy individuals the LPS-induced TNF-alpha secretion by MNC. After surgery, granulocytosis was found in peripheral blood and in wound fluids, but monocytopenia was restricted to wound fluids. In parallel, wound fluids induced in healthy individuals the release by MNC of distinct chemokines specific for granulocytes and monocytes. These wound fluid-mediated effects of TNF-alpha suppression and chemokine induction could be mimicked by recombinant human HSP70 and, in part, by HSP60. Thus, tissue-derived factors, such as HSP70 released after injury, suppress monocyte function and, therefore, might favor the development of immunosuppression after severe injury.

Dendritic cells during polymicrobial sepsis rapidly mature but fail to initiate a protective Th1-type immune response.

Polymicrobial sepsis is associated with immunosuppression caused by the predominance of anti-inflammatory mediators and profound loss of lymphocytes through apoptosis. Dendritic cells (DC) are potent antigen-presenting cells and play a key role in T cell activation. We tested the hypothesis that DC are involved in sepsis-mediated immunosuppression in a mouse cecal ligation and puncture (CLP) model, which resembles human polymicrobial sepsis. At different time-points after CLP, DC from the spleen and peripheral lymph nodes were characterized in terms of expression of costimulatory molecules, cytokine synthesis, and subset composition. Splenic DC strongly up-regulated CD86 and CD40 but not CD80 as soon as 8 h after CLP. In contrast, lymph node DC equally increased the expression of CD86, CD40, and CD80. However, this process of maturation occurred later in the lymph nodes than in the spleen. Splenic DC from septic mice were unable to secrete interleukin (IL)-12, even upon stimulation with CpG or lipopolysaccharide+CD40 ligand, but released high levels of IL-10 in comparison to DC from control mice. Neutralization of endogenous IL-10 could not restore IL-12 secretion by DC of septic mice. In addition, the splenic CD4+CD8- and CD4-CD8+ subpopulations were lost during sepsis, and the remaining DC showed a reduced capacity for allogeneic T cell activation associated with decreased IL-2 synthesis. Thus, during sepsis, splenic DC acquire a state of aberrant responsiveness to bacterial stimuli, and two DC subtypes are selectively lost. These changes in DC behavior might contribute to impaired host response against bacteria during sepsis.

Toll-like receptor 2 and 4 expression after severe injury is not involved in the dysregulation of the innate immune system.

BACKGROUND: Severe injury after trauma is associated with a diminished production of different proinflammatory cytokines after stimulation with bacterial cell wall components. The cellular mechanisms, leading to a decreased responsiveness especially of monocytes after multiple injuries have not yet been elucidated in detail. The expression of Toll-like receptors (TLR) on leukocytes is essential for recognition of bacterial components. We investigated the expression of TLR2 and 4 in correlation with gram-negative and gram-positive stimuli-dependent cytokine liberation after severe injury in comparison with that in healthy volunteers. METHODS: In a prospective clinical experimental study, 12 trauma patients with an Injury Severity Score above 21 points and 14 healthy volunteers were analyzed. Heparinized whole blood samples of patients were collected within 48 hours after trauma and incubated in vitro with or without lipopolysaccharide (LPS) and peptidoglycan (PGN). TLR2 and TLR4 expression on monocytes was analyzed by flow cytometry. LPS- and PGN-induced tumor necrosis factor alpha (TNFalpha) and interleukin-8 production was measured by means of enzyme-linked immunosorbent assay. RESULTS: Both LPS- and PGN-induced TNFalpha liberation were significantly reduced in severely injured patients. The surface expression of TLR2 was also significantly decreased on monocytes collected from trauma patients, whereas the expression of TLR4 remained unchanged. There was only a negative correlation between TLR2 expression and the liberation of TNFalpha after stimulation with LPS or PGN. CONCLUSIONS: We conclude that diminished cytokine production after trauma cannot be explained simply by changes in TLR2 or TLR4 expression and that subsequent signaling cascades or additional receptors are involved in the blunted cytokine response after trauma.