C5a regulates IL-12+ DC migration to induce pathogenic Th1 and Th17 cells in sepsis

Dysregulated dendritic cells in sepsis: functional impairment and regulated cell death

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Studies have indicated that immune dysfunction plays a central role in the pathogenesis of sepsis. Dendritic cells (DCs) play a crucial role in the emergence of immune dysfunction in sepsis. The major manifestations of DCs in the septic state are abnormal functions and depletion in numbers, which are linked to higher mortality and vulnerability to secondary infections in sepsis. Apoptosis is the most widely studied pathway of number reduction in DCs. In the past few years, there has been a surge in studies focusing on regulated cell death (RCD). This emerging field encompasses various forms of cell death, such as necroptosis, pyroptosis, ferroptosis, and autophagy-dependent cell death (ADCD). Regulation of DC's RCD can serve as a possible therapeutic focus for the treatment of sepsis. Throughout time, numerous tactics have been devised and effectively implemented to improve abnormal immune response during sepsis progression, including modifying the functions of DCs and inhibiting DC cell death. In this review, we provide an overview of the functional impairment and RCD of DCs in septic states. Also, we highlight recent advances in targeting DCs to regulate host immune response following septic challenge.

Th17/Treg balance: the bloom and wane in the pathophysiology of sepsis

Sepsis is a multi-organ dysfunction characterized by an unregulated host response to infection. It is associated with high morbidity, rapid disease progression, and high mortality. Current therapies mainly focus on symptomatic treatment, such as blood volume supplementation and antibiotic use, but their effectiveness is limited. Th17/Treg balance, based on its inflammatory property, plays a crucial role in determining the direction of the inflammatory response and the regression of organ damage in sepsis patients. This review provides a summary of the changes in T-helper (Th) 17 cell and regulatory T (Treg) cell differentiation and function during sepsis, the heterogeneity of Th17/Treg balance in the inflammatory response, and the relationship between Th17/Treg balance and organ damage. Th17/Treg balance exerts significant control over the bloom and wanes in host inflammatory response throughout sepsis.

Complement Inhibition and COVID-19: The Story so Far

Acute respiratory distress syndrome (ARDS) is the most severe complication of COVID-19, a disease caused by severe acute respiratory syndrome coronavirus (SARS CoV) 2. The mechanisms underlying the progression from asymptomatic disease to pneumonia and ARDS are complex and by far unelucidated. As for bacterial sepsis, the release of damage associated molecular patterns and pathogen associated molecular patterns triggers activation of the complement cascade. Subsequently, overexpressed anaphylatoxins recruit inflammatory cells in the lung and other organs and contribute initiating and amplifying a vicious circle of thromboinflammation causing organs damage and eventually death. Preclinical and observational studies in patients with COVID-19 provided evidence that complement inhibition effectively may attenuate lung and systemic inflammation, restore the coagulation/fibrinolysis balance, improve organs function and eventually may save life. Ongoing Phase 2/3 trials should elucidate the benefit to risk profile of complement inhibitors and may clarify the optimal targets in the complement cascade.

Immunotherapy in Solid Tumors and Gut Microbiota: The Correlation-A Special Reference to Colorectal Cancer

Simple Summary

Immunotherapy and immune checkpoint inhibitors have become the breakthrough treatment with extended responses and survival rates in various neoplasms. They use the immune system to defeat cancer, while gut microbiota seems to play a significant role in that attempt. To date, colorectal cancer patients have gained little benefit from immunotherapy. Only mismatch repair-deficient/microsatellite-unstable tumors seem to respond positively to immunotherapy. However, gut microbiota could be the key to expanding the use of immunotherapy to a greater range of colorectal cancer patients. In the current review study, the authors aimed to present and analyze the mechanisms of action and resistance of immunotherapy and the types of immune checkpoint inhibitors (ICIs) as well as their correlation to gut microbiota. A special reference will be made in the association of immunotherapy and gut microbiota in the colorectal cancer setting.

Abstract

Over the last few years, immunotherapy has been considered as a key player in the treatment of solid tumors. Immune checkpoint inhibitors (ICIs) have become the breakthrough treatment, with prolonged responses and improved survival results. ICIs use the immune system to defeat cancer by breaking the axes that allow tumors to escape immune surveillance. Innate and adaptive immunity are involved in mechanisms against tumor growth. The gut microbiome and its role in such mechanisms is a relatively new study field. The presence of a high microbial variation in the gut seems to be remarkably important for the efficacy of immunotherapy, interfering with innate immunity. Metabolic and immunity pathways are related with specific gut microbiota composition. Various studies have explored the composition of gut microbiota in correlation with the effectiveness of immunotherapy. Colorectal cancer (CRC) patients have gained little benefit from immunotherapy until now. Only mismatch repair-deficient/microsatellite-unstable tumors seem to respond positively to immunotherapy. However, gut microbiota could be the key to expanding the use of immunotherapy to a greater range of CRC patients.

Intestinal microbiota: a new force in cancer immunotherapy

Cancer displays high levels of heterogeneity and mutation potential, and curing cancer remains a challenge that clinicians and researchers are eager to overcome. In recent years, the emergence of cancer immunotherapy has brought hope to many patients with cancer. Cancer immunotherapy reactivates the immune function of immune cells by blocking immune checkpoints, thereby restoring the anti-tumor activity of immune cells. However, immune-related adverse events are a common complication of checkpoint blockade, which might be caused by the physiological role of checkpoint pathways in regulating adaptive immunity and preventing autoimmunity. In this context, the intestinal microbiota has shown great potential in the immunotherapy of cancer. The intestinal microbiota not only regulates the immune function of the body, but also optimizes the therapeutic effect of immune checkpoint inhibitors, thus reducing the occurrence of complications. Therefore, manipulating the intestinal microbiota is expected to enhance the effectiveness of immune checkpoint inhibitors and reduce adverse reactions, which will lead to new breakthroughs in immunotherapy and cancer management. Video abstract.

Effect of TIPE1 on Immune Function of Dendritic Cells and Its Signaling Pathway in Septic Mice

Dendritic cell (DC) dysfunction plays a pivotal role in sepsis-induced immunosuppression. Tumor necrosis factor α (TNF-α)-induced protein 8 like-1 (TIPE1), a new member of the tumor necrosis factor α-induced protein 8 family, may be related to cell death. The aim of the present study was to elucidate the effect of TIPE1 on the immune function of DCs and its regulatory mechanism via PD-L1/PD-1 signaling in mice. Sepsis was induced in adult C57BL/6 male mice via cecal ligation and puncture. In vitro, we found that expression of CD80, CD86, and major histocompatibility complex class II in DCs and levels of cytokines, including tumor necrosis factor α and interleukin 12p40, were elevated; similarly, T-cell proliferation and differentiation were promoted when the gene expressing TIPE1 was silenced. Next, we examined the in vivo role of TIPE1 in a cecal ligation and puncture animal model system. Flow cytometry of the immune functional status in DCs revealed negative regulation of TIPE1 on DC maturation, as well as activation. Moreover, changes in PD-L1/PD-1 levels confirmed the negative effect of TIPE1 in DCs. Collectively, we report that TIPE1 might exert negative regulation in sepsis, at least in part by inhibiting DC maturation and subsequent T-cell-mediated immunity via PD-L1/PD-1 signaling.

Crosstalk between Dendritic Cells and Immune Modulatory Agents against Sepsis

Dendritic cells (DCs) play a critical role in the immune system which sense pathogens and present their antigens to prime the adaptive immune responses. As the progression of sepsis occurs, DCs are capable of orchestrating the aberrant innate immune response by sustaining the Th1/Th2 responses that are essential for host survival. Hence, an in-depth understanding of the characteristics of DCs would have a beneficial effect in overcoming the obstacle occurring in sepsis. This paper focuses on the role of DCs in the progression of sepsis and we also discuss the reverse sepsis-induced immunosuppression through manipulating the DC function. In addition, we highlight some potent immunotherapies that could be used as a novel strategy in the early treatment of sepsis.

IL-17A activated by Toll-like receptor 9 contributes to the development of septic acute kidney injury

Toll-like receptor 9 (TLR9), which is activated by endogenously released mtDNA during sepsis, contributes to the development of polymicrobial septic acute kidney injury (AKI). However, downstream factors of TLR9 to AKI remain unknown. We hypothesized that IL-17A activated by TLR9 may play a critical role in septic AKI development. To determine the effects of TLR9 on IL-17A production in septic AKI, we used a cecal ligation and puncture (CLP) model in Tlr9 knockout (Tlr9KO) mice and wild-type (WT) littermates. We also investigated the pathway from TLR9 activation in dendritic cells (DCs) to IL-17A production by γδT cells in vitro. To elucidate the effects of IL-17A on septic AKI, Il-17a knockout (Il-17aKO) mice and WT littermates were subjected to CLP. We further investigated the relationship between the TLR9-IL-17A axis and septic AKI by intravenously administering recombinant IL-17A or vehicle into Tlr9KO mice and assessing kidney function. IL-17A levels in both plasma and the peritoneal cavity and mRNA levels of IL-23 in the spleen were significantly higher in WT mice after CLP than in Tlr9KO mice. Bone marrow-derived DCs activated by TLR9 induced IL-23 and consequently promoted IL-17A production in γδT cells in vitro. Knockout of Il-17a improved survival, functional and morphological aspects of AKI, and splenic apoptosis after CLP. Exogenous IL-17A administration aggravated CLP-induced AKI attenuated by knockout of Tlr9. TLR9 in DCs mediated IL-17A production in γδT cells during sepsis and contributed to the development of septic AKI.

Complement After Trauma: Suturing Innate and Adaptive Immunity

The overpowering effect of trauma on the immune system is undisputed. Severe trauma is characterized by systemic cytokine generation, activation and dysregulation of systemic inflammatory response complementopathy and coagulopathy, has been immensely instrumental in understanding the underlying mechanisms of the innate immune system during systemic inflammation. The compartmentalized functions of the innate and adaptive immune systems are being gradually recognized as an overlapping, interactive and dynamic system of responsive elements. Nonetheless the current knowledge of the complement cascade and its interaction with adaptive immune response mediators and cells, including T- and B-cells, is limited. In this review, we discuss what is known about the bridging effects of the complement system on the adaptive immune system and which unexplored areas could be crucial in understanding how the complement and adaptive immune systems interact following trauma.

Effect of tumor necrosis factor-α induced protein 8 like-2 on immune function of dendritic cells in mice following acute insults

Tumor necrosis factor-α induced protein 8 like-2 (TNFAIP8L2, TIPE2) is a lately discovered negative regulator of innate immunity and cellular immunity. The present study was designed to investigate whether naturally occurring dendritic cells (DCs) could express TIPE2 mRNA/protein and its potential significance. Expressions of co-stimulatory molecules on DC surface and cytokines were analyzed to assess the functional role of TIPE2 in controlling DC maturation as well as activation. The activated DCs were assessed for their capacity to stimulate the proliferation and differentiation of T cells. It was found that TIPE2 was a cytoplasmic protein expressed in DCs, and the percentage of DCs which expressed co-stimulatory molecules and cytokines were obviously up-regulated when TIPE2 gene silenced by siRNA in vitro and in vivo. DCs undergone TIPE2 knockdown were found to promote the maturation of DCs, T-cell proliferation as well as differentiation, and they were significantly elevated IL-2 level and intranuclear NF-AT activation. Conversely, in over-expressing TIPE2 DC cells, it could inhibit T-cell proliferation and differentiation, and markedly down-regulate IL-2 expression and intranuclear NF-AT activation after scald injury. The results suggested that TIPE2 appeared to be a critical immunoregulatory molecule which affected DC maturation and subsequent T-cell mediated immunity.

Dendritic Cells in Sepsis: Pathological Alterations and Therapeutic Implications

Sepsis is the leading cause of death for critically ill patients in recent years. Dendritic cells (DCs) are important antigen-presenting cells and play a key role in immune response by regulating the innate and adaptive immunity. The number of DCs, the differentiation of monocytes into DCs, and the levels of surface molecules associated with the function of DCs are changed in the development of sepsis. There are many mechanisms involved in the alterations of DCs during sepsis, including the induction of apoptosis, reactive oxygen species generation, activation of the Wnt signaling pathway, epigenetic regulation, and variation in Toll-like receptor-dependent signaling. In this review, we present the classifications of DC subsets and mechanisms involved in the alterations of DCs in sepsis, as well as further discuss the therapeutic strategies targeting DCs in sepsis to improve the aberrant immune response and prolong the life during sepsis progression.

Attenuation of cGVHD by C5a/C5aR blockade is associated with increased frequency of Treg

C5aR signaling plays an important role in the regulation of T cell activation and alloimmune responses in chronic graft-versus-host disease (cGVHD). However, direct evidence of this modulation and the efficacy of C5aR blockade in the treatment of cGVHD have not been demonstrated. We observed higher expression of C5aR on both monocytes and T cells of patients with cGVHD compared with healthy controls and non-GVHD patients after allogeneic hematopoietic stem cell transplantation. Our data also demonstrated a significant negative correlation between C5aR expression and regulatory T cells (Treg) frequency in cGVHD patients, indicating a potential role of C5aR in the generation and regulation of Treg. In addition, an in vitro experiment revealed C5aR deficiency promoted the development of Treg whereas C5a activation abolished the differentiation of Treg. Importantly, we found C5aR blockade by PMX53 attenuated the pathology of cGVHD and improved the survival of cGVHD mice. PMX53 had a direct regulatory effect on Treg commitment and increased TGF-β1 expression. Thus, C5aR signaling may induce and intensify cGVHD by down-regulating Treg induction. The modulation of C5aR activation by PMX53 may provide a potential therapy for cGVHD.

C5a of Cynoglossus semilaevis has anaphylatoxin-like properties and promotes antibacterial and antiviral defense

Activation of the complement system leads to the cleavage of component factor C5 into C5a and C5b. C5a can induce chemotaxis and inflammatory responses in mammals. The function of C5a in fish is poorly understood. In this study, we report the identification and analysis of a C5 homologue, CsC5, from tongue sole (Cynoglossus semilaevis). CsC5 is composed of 1683 amino acid residues that include an anaphylatoxin homologous domain. Expression of CsC5 could be detected in a variety of tissues and was up-regulated by bacterial or viral pathogen infection. Purified recombinant CsC5a (rCsC5a) could bind to peripheral blood leukocytes (PBL) and stimulate PBL chemotaxis, proliferation, respiratory burst, acid phosphatase activity, and phagocytosis. Tongue sole administered rCsC5a exhibited enhanced resistance against bacterial and viral infections. These results indicate that CsC5a is an anaphylatoxin with a role in innate immune defense against bacterial and viral infections.

Antiseptic effect of sea cucumber (Holothuria atra) against multi-organ failure induced by sepsis: Molecular and histopathological study

Sepsis is a systemic inflammatory response to infection and severe sepsis patients can develop acute lung and liver injury. The aim of the present study was to evaluate the efficacy of Holothuria atra methanolic body wall extract (HaE), as an antioxidant and anti-inflammatory agent against induced sepsis in a cecal ligation and puncture (CLP) rat model. In total, 30 males albino rats were divided into three groups (n=10 each) as follows: Sham (Sh), which was used as negative control; sepsis (Se), which was used as a positive control and was subjected to CLP surgery; and Ho, which was subjected to CLP and fed with 200 mg/kg (body weight) of HaE, once daily for 7 days. Subsequently, the expression of various genes was detected by polymerase chain reaction, while liver and lung tissues were examined by immunohistochemistry. The expression of Caspase-3 was significantly reduced in liver and lung tissues in the Ho group, while the expression levels of Gsta2, Cat and Sod1 genes were slightly reduced in the Ho group, when compared with the Se group. In addition, expression levels of tumor necrosis factor, interferon-γ, liver interleukin (IL)1b and lung IL1a were reduced in the Ho group compared with the Se group. Furthermore, histopathological changes were observed in liver tissues of the Se group, including congestion of hepatoportal blood vessel and focal hepatic necrosis, while lung tissues showed marked edema, hemorrhage and alveolar septal thickening. The Ho group showed apparent normal hepatic parenchyma and slight interstitial pneumonia. Immunohistochemical staining of caspase-3 in liver and lung tissues showed no expression in the Sh group, strong expression in the Se group and moderate expression in the Ho group. In conclusion, HaE demonstrated beneficial effect against induced sepsis, which may be attributed to its antioxidant and antiapoptotic activities.

Activated Complement Factors as Disease Markers for Sepsis

Sepsis is a leading cause of death in the United States and worldwide. Early recognition and effective management are essential for improved outcome. However, early recognition is impeded by lack of clinically utilized biomarkers. Complement factors play important roles in the mechanisms leading to sepsis and can potentially serve as early markers of sepsis and of sepsis severity and outcome. This review provides a synopsis of recent animal and clinical studies of the role of complement factors in sepsis development, together with their potential as disease markers. In addition, new results from our laboratory are presented regarding the involvement of the complement factor, mannose-binding lectin, in septic shock patients. Future clinical studies are needed to obtain the complete profiles of complement factors/their activated products during the course of sepsis development. We anticipate that the results of these studies will lead to a multipanel set of sepsis biomarkers which, along with currently used laboratory tests, will facilitate earlier diagnosis, timely treatment, and improved outcome.

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.

Ginsenoside metabolite compound K suppresses T-cell priming via modulation of dendritic cell trafficking and costimulatory signals, resulting in alleviation of collagen-induced arthritis

Ginsenoside metabolite compound K (CK; 20-O-d-glucopyranosyl-20(S)-protopanaxadiol), a novel ginsenoside metabolite, belongs to the dammarane-type triterpene saponins, according to its structure. The anti-inflammatory activity of CK has been identified in several studies. Our study demonstrated that CK exerted an anti-inflammatory effect in collagen-induced arthritis (CIA) and adjuvant-induced arthritis animal models, and this effect was due to inhibition of the abnormal activation and differentiation of T cells. However, the mechanism of CK in suppressing T-cell activation remains unclear. In this study, CK had a therapeutic effect in mice with CIA, decreased the percentage of activated T cells and dendritic cells (DCs), and increased the percentage of naive T cells in lymph nodes. The inhibitory effect on T-cell activation of CK was related to suppression of accumulation of DCs in lymph nodes. CK decreased CCL21 levels in lymph nodes and CCR7 expression in DCs and suppressed CCL21/CCR7-mediated migration of DCs, thus reducing accumulation of DCs in lymph nodes. In addition, signals for T-cell activation including major histocompatibility complex class II and costimulatory molecules, such as CD80 and CD86, were suppressed by CK, and the proliferation of T cells induced by DCs was inhibited by CK. In conclusion, this study demonstrated that CK downregulated DC priming of T-cell activation in CIA, and suppression of CCL21/CCR7-mediated DC migration and signaling between T cells and DCs might be the potential mechanism. These results provide an interesting, novel insight into the potential mechanism by which CK contributes to the anti-inflammatory effect in autoimmune conditions.

Therapeutic effects of micheliolide on a murine model of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease and collagen-induced arthritis (CIA) is an animal model for RA. Micheliolide (MCL) is a novel compound with strong anti-inflammatory effects. The present study was conducted to evaluate the therapeutic effects of MCL on RA. Mice were randomly divided into four groups and the CIA model mice were treated with methotrexate (MTX), MCL and dimethyl sulfoxide. A score associated with the severity of arthritis was assigned on alternate days from the 22nd day for 60 days. Histopathological changes and the serum levels of cytokines were measured on day 85. The results demonstrated that the MCL treatment group had arthritis scores lower than the CIA group and higher than the MTX group; compared with the CIA group, MCL and MTX significantly reduced the swelling of the paws and suppressed the degeneration of articular cartilage. Expression levels of macrophage colony-stimulating factor (M-CSF), tissue inhibitors of metalloproteinases-1 (TIMP-1) and complement component 5a (C5/C5a) were lower in the mice with arthritis compared with normal mice, however, following treatment with MCL and MTX, all the mice exhibited significant recovery to differing degrees. Unlike the MTX group, the MCL group failed to recover the level of soluble intercellular adhesion molecule-1. In addition, the cytokine of B-lymphocyte chemoattractant (BLC) solely presented in the MCL group. These results suggest that MCL may be considered for use as a novel therapeutic treatment against RA and that changes in the expression of cytokines C5/C5a, TIMP-1, M-CSF and BLC may underlie the mechanism by which MCL effects changes in this disease.

T-cell autophagy deficiency increases mortality and suppresses immune responses after sepsis

BACKGROUND

Although the role of autophagy in sepsis has been characterized in several organs, its role in the adaptive immune system remains to be ascertained. This study aimed to investigate the role of autophagy in sepsis-induced T cell apoptosis and immunosuppression, using knockout mice with T cell specific deletion of autophagy essential gene Atg7.

METHODS AND RESULTS

Sepsis was induced in a cecal ligation and puncture (CLP) model, with T-cell-specific Atg7-knockout mice compared to control mice. Autophagic vacuoles examined by electron microscopy were decreased in the spleen after CLP. Autophagy proteins LC3-II and ATG7, and autophagosomes and autolysosomes stained by Cyto-ID Green and acridine orange were decreased in CD4+ and CD8+ splenocytes at 18 h and 24 h after CLP. This decrease in autophagy was associated with increased apoptosis of CD4+ and CD8+ after CLP. Moreover, mice lacking Atg7 in T lymphocytes showed an increase in sepsis-induced mortality, T cell apoptosis and loss of CD4+ and CD8+ T cells, in comparison to control mice. This was accompanied by suppressed cytokine production of Th1/Th2/Th17 by CD4+ T cells, reduced phagocytosis in macrophages and decreased bacterial clearance in the spleen after sepsis.

CONCLUSION

These results indicated that sepsis led to down-regulation of autophagy in T lymphocytes, which may result in enhanced apoptosis induction and decreased survival in sepsis. Autophagy may therefore play a protective role against sepsis-induced T lymphocyte apoptosis and immunosuppression.