Partial Depletion of Regulatory T Cells Enhances Host Inflammatory Response Against Acute Pseudomonas aeruginosa Infection After Sepsis

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.

Matrix metalloproteinase-8 regulates dendritic cell tolerance in late polymicrobial sepsis via the nuclear factor kappa-B p65/β-catenin pathway

Background

Tolerogenic dendritic cells (DCs) are associated with poor prognosis of sepsis. Matrix metalloproteinases (MMPs) have been shown to have immunomodulatory effects. However, whether MMPs are involved in the functional reprogramming of DCs is unknown. The study aims to investigate the role of MMPs in sepsis-induced DCs tolerance and the potential mechanisms.

Methods

A murine model of late sepsis was induced by cecal ligation and puncture (CLP). The expression levels of members of the MMP family were detected in sepsis-induced tolerogenic DCs by using microarray assessment. The potential roles and mechanisms underlying MMP8 in the differentiation, maturation and functional reprogramming of DCs during late sepsis were assessed both in vitro and in vivo.

Results

DCs from late septic mice expressed higher levels of MMP8, MMP9, MMP14, MMP19, MMP25 and MMP27, and MMP8 levels were the highest. MMP8 deficiency significantly alleviated sepsis-induced immune tolerance of DCs both in vivo and in vitro. Adoptive transfer of MMP8 knockdown post-septic bone marrow-derived DCs protected mice against sepsis-associated lethality and organ dysfunction, inhibited regulatory T-cell expansion and enhanced Th1 response. Furthermore, the effect of MMP8 on DC tolerance was found to be associated with the nuclear factor kappa-B p65/β-catenin pathway.

Conclusions

Increased MMP8 levels in septic DCs might serve as a negative feedback loop, thereby suppressing the proinflammatory response and inducing DC tolerance.

p53 promotes the expansion of regulatory T cells via DNMT3a- and TET2- mediated Foxp3 expression in sepsis

Background

Immunosuppression is an important characteristic of sepsis and is closely related to poor outcomes. Regulatory T cells (Tregs) contribute to immune suppression by inhibiting effector T cell (Teff) proliferation and differentiation. We aimed to investigate the role of p53 in Treg expansion after sepsis.

Methods

We constructed a sepsis model in wild-type (WT) and p53f/f/CD4-Cre+ mice by cecal ligation and puncture (CLP) and evaluated the proportions of CD4+CD25+ Foxp3+ Tregs by flow cytometry. The expression levels of forkhead/winged helix transcription factor p3 (Foxp3), DNA methyltransferase enzyme (DMNT)3a and ten-eleven translocation (TET)2 were examined using quantitative real-time PCR and Western blot analysis. Treg-specific demethylation region (TSDR) methylation sites in cells were analyzed by bisulfite-sequencing PCR. Furthermore, the direct binding of p53 to the Dnmt3a and TET2 promoters was illustrated using a luciferase assay. The suppressive ability of Tregs was indicated by enzyme-linked immunosorbent assay analysis of cytokine levels and the proliferation of cocultured Teffs. Finally, mortality rates after CLP were compared among WT and p53f/f/CD4-Cre+ mice.

Results

The proportion of CD4+CD25+ Foxp3+ Tregs was significantly reduced in p53f/f/CD4-Cre+ mice compared to WT mice after CLP. The enhanced expression of Foxp3 in WT mice was downregulated in the p53f/f/CD4-Cre+ group. We found decreased DMNT3a and increased TET2 levels after CLP. However, the dysregulation of DNMT3a and TET2 was significantly reversed in p53f/f/CD4-Cre+ mice. TSDR underwent increased demethylation in p53f/f/CD4-Cre+ mice. Luciferase activity indicated direct binding of p53 to the promoter regions of DNMT3a and TET2 to regulate their transcription. Consequently, Tregs from p53f/f/CD4-Cre+ CLP mice exhibited limited suppressive ability, as indicated by the reduced production of transforming growth factor-β and interleukin 10 (IL-10). In the coculture system, Teffs showed preserved production of IL-2, differentiation into Th1 cells and proliferation in the presence of Tregs isolated from p53f/f/CD4-Cre+ CLP mice. Finally, the mortality rate of the p53f/f/CD4-Cre+ group after CLP was significantly reduced in comparison to that of the WT group.

Conclusion

p53 appears to be critical for Foxp3 expression and consequent Treg expansion by regulating the induction of DNMT3a and TET2, thereby resulting in Foxp3-TSDR demethylation in the context of sepsis.

Novel evidence on sepsis-inducing pathogens: from laboratory to bedside

Sepsis is a life-threatening condition and a significant cause of preventable morbidity and mortality globally. Among the leading causative agents of sepsis are bacterial pathogens Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pyogenes, along with fungal pathogens of the Candida species. Here, we focus on evidence from human studies but also include in vitro and in vivo cellular and molecular evidence, exploring how bacterial and fungal pathogens are associated with bloodstream infection and sepsis. This review presents a narrative update on pathogen epidemiology, virulence factors, host factors of susceptibility, mechanisms of immunomodulation, current therapies, antibiotic resistance, and opportunities for diagnosis, prognosis, and therapeutics, through the perspective of bloodstream infection and sepsis. A list of curated novel host and pathogen factors, diagnostic and prognostic markers, and potential therapeutical targets to tackle sepsis from the research laboratory is presented. Further, we discuss the complex nature of sepsis depending on the sepsis-inducing pathogen and host susceptibility, the more common strains associated with severe pathology and how these aspects may impact in the management of the clinical presentation of sepsis.

Regulatory T Cells: Angels or Demons in the Pathophysiology of Sepsis?

Sepsis is a syndrome characterized by life-threatening organ dysfunction caused by the dysregulated host response to an infection. Sepsis, especially septic shock and multiple organ dysfunction is a medical emergency associated with high morbidity, high mortality, and prolonged after-effects. Over the past 20 years, regulatory T cells (Tregs) have been a key topic of focus in all stages of sepsis research. Tregs play a controversial role in sepsis based on their heterogeneous characteristics, complex organ/tissue-specific patterns in the host, the multi-dimensional heterogeneous syndrome of sepsis, the different types of pathogenic microbiology, and even different types of laboratory research models and clinical research methods. In the context of sepsis, Tregs may be considered both angels and demons. We propose that the symptoms and signs of sepsis can be attenuated by regulating Tregs. This review summarizes the controversial roles and Treg checkpoints in sepsis.

CD71+ Erythroid Cell Expansion in Adult Sepsis: Potential Causes and Role in Prognosis and Nosocomial Infection Prediction

Background

Immune suppression contributes to nosocomial infections (NIs) and poor prognosis in sepsis. Recent studies revealed that CD71⁺ erythroid cells had unappreciated immunosuppressive functions. This study aimed to investigate the values of CD71⁺ erythroid cells (CECs) in predicting NIs and prognosis among adult septic patients. The potential factors associated with the expansion of CECs were also explored.

Methods

In total, 112 septic patients and 32 critically ill controls were enrolled. The frequencies of CD71⁺ cells, CD71⁺CD235a⁺ cells, and CD45⁺ CECs were measured by flow cytometry. The associations between CECs and NIs and 30-day mortality were assessed by ROC curve analysis and Cox and competing-risk regression models. Factors associated with the frequency of CECs were identified by linear regression analysis.

Results

The percentage of CD71⁺ cells, CECs, and CD45⁺ CECs were higher in septic patients than critically ill controls. In septic patients, the percentages of CD71⁺ cells, CECs, and CD45⁺ CECs were associated with NI development, while CD71⁺ cells and CECs were independently associated with 30-day mortality. Linear regression analysis showed that the levels of interleukin (IL)-6 and interferon (IFN)-γ were positively associated with the frequencies of CD71⁺ cells, CECs, and CD45⁺ CECs, while IL-10 was negatively associated with them. Additionally, the levels of red blood cells (RBCs) were negatively associated with the percentage of CD45⁺ CECs.

Conclusions

CECs were expanded in sepsis and can serve as independent predictors of the development of NI and 30-day mortality. Low levels of RBCs and high levels of IL-6 and IFN-γ may contribute to the expansion of CECs in sepsis.

Trial Registration

ChiCTR, ChiCTR1900024887. Registered 2 August 2019, http://www.chictr.org.cn/showproj.aspx?proj=38645

Pretreatment with 6-Gingerol Ameliorates Sepsis-Induced Immune Dysfunction by Regulating the Cytokine Balance and Reducing Lymphocyte Apoptosis

Sepsis is characterized by an initial net hyperinflammatory response, followed by a period of immunosuppression, termed immunoparalysis. During this immunosuppressive phase, patients may have difficulty eradicating invading pathogens and are susceptible to life-threatening secondary hospital-acquired infections. Due to progress in antimicrobial treatment and supportive care, most patients survive early sepsis. Mortality is more frequently attributed to subsequent secondary nosocomial infections and multiorgan system failure. 6-Gingerol is the major pharmacologically active component of ginger. Although it is known to exhibit a variety of biological activities, including anti-inflammation and antioxidation, the role of 6-gingerol in sepsis-induced immune dysfunction remains elusive. Thus, we investigated whether 6-gingerol improves septic host response to infections during sepsis. 6-Gingerol-treated mice showed significantly lower mortality in polymicrobial sepsis induced by cecal ligation and puncture LPS via enhanced bacterial clearance in the peritoneum, blood, and organs (liver, spleen, and kidney) and inhibited the production of TNF-α and IL-6 in TLR2 and/or TLR4-stimulated macrophages. In addition, we demonstrated that survival improvement of secondary infection following septic insult was associated with an initial response of enhanced neutrophil numbers and function at the infection site, reduced apoptosis of immune cells, and a shift from a T helper cell type 2 (Th2) to a T helper cell type 1 (Th1) cytokine balance in the hypoinflammation phase. Our overall findings suggest that 6-gingerol potentially restores sepsis-induced immune dysfunction by shifting the balance of Th1/Th2 and by regulating apoptosis of immune cells.

Extract From Tetrastigma hemsleyanum Leaf Alleviates Pseudomonas aeruginosa Lung Infection: Network Pharmacology Analysis and Experimental Evidence

Tetrastigma hemsleyanum Diels & Gilg (T. hemsleyanum) has attracted much attention due to its ability on pneumonia, bronchitis, and immune-related diseases, while its functional components and underlying mechanism of action on pneumonia have not been fully elucidated. Herein, we used a systematic network pharmacology approach to explore the action mechanism of T. hemsleyanum leaf in the treatment of pneumonia. In this study, the results of network pharmacology demonstrated that there were 34 active components and 80 drug-disease targets in T. hemsleyanum leaf, which were strongly in connection with signal transduction, inflammatory response, and the oxidation-reduction process. Subsequently, a mouse model of pneumonia induced by Pseudomonas aeruginosa (P. aeruginosa) was established to validate the predicted results of network pharmacology. In the animal experiments, aqueous extract of T. hemsleyanum leaf (EFT) significantly attenuated the histopathological changes of lung tissue in P. aeruginosa-induced mice and reduced the number of bacterial colonies in BALFs by 96.84% (p < 0.01). Moreover, EFT treatment suppressed the increase of pro-inflammatory cytokines IL-17, IL-6, and TNF-α in lung tissues triggered by P. aeruginosa, which led to the increase of Th17 cells (p < 0.05). High concentration of EFT treatment (2.0 g/kg) obviously increased the anti-inflammatory cytokine levels, accompanied by the enhancement of Treg proportion in a dose-dependent manner and a notable reversal of transcription factor RORγt expression. These findings demonstrated that network pharmacology was a useful tool for TCM research, and the anti-inflammatory effect of EFT was achieved by maintaining Th17/Treg immune homeostasis and thereby suppressing the inflammatory immune response.

Aspergillus fumigatus Influences Gasdermin-D-Dependent Pyroptosis of the Lung via Regulating Toll-Like Receptor 2-Mediated Regulatory T Cell Differentiation

Purpose

Aspergillus fumigatus, as an opportunistic fungus, has developed a series of escape mechanisms under the host's immune response to obtain nutrients and promote fungal growth in the hostile environment. The immune escape of pathogens may be through suppressing the inflammatory response mediated by regulatory T cells (Tregs). The aim of this study was to explore whether A. fumigatus influences Gasdermin-D-dependent pyroptosis of the lung by regulating Toll-like receptor 2-mediated regulatory T cell differentiation.

Methods

Collect peripheral blood from patients with A. fumigatus. ELISA kits we used to detect the expression levels of IL-1β, IL-6, IL-2R, and IL-10 in the serum and flow cytometry to detect the percentage of CD4⁺CD25⁺Foxp3⁺ Tregs in the patients' peripheral blood mononuclear cells (PBMCs). The mouse model of A. fumigatus infection was constructed by tracheal instillation. The pathological changes in the lungs of the mice were observed under a microscope. The fungal load in the lung tissue was determined by the plate colony count. ELISA kit was used to detect the lung tissue homogenate proinflammatory cytokines TNF-α, IL-6, CCL2, and VEGF. Q-PCR was used for the detection of the expression of Foxp3 and TLR2 genes in the lung. Western blot was used for the detection of the expression of TLR2, Gasdermin-D (GSDMD), IL-1α, and IL-1β in the lung. Flow cytometry was used to detect splenic CD4⁺CD25⁺FOXP3⁺ Tregs. Using magnetic beads to extract CD4⁺ T cells from mice spleen, the effects of A. fumigatus conidia or TLR2 inhibitor (C29) to differentiate CD4⁺ T cells in vitro were tested.

Results

The expression of Foxp3 and TLR2 in the lung tissue of mice infected with A. fumigatus increased, and we observed that the proportion of Tregs in both A. fumigatus infection patients and mice was upregulated. After using the CD25 neutralizing antibody, the number of Tregs in the mice spleen was significantly reduced. However, lung damage was reduced and the ability to clear lung fungi was enhanced. We found that the Tregs in TLR2^−/− mice were significantly reduced and the nonlethal dose of A. fumigatus conidia did not cause severe lung damage in TLR2^−/− mice. Compared with that of wild-type mice, the fungal burden in the lung of TLR2-deficient mice was reduced and the knockout of TLR2 changed the expression of GSDMD, IL-1α, and IL-1β in A. fumigatus. In in vitro experiments, we found that the inhibition of TLR2 can reduce Treg differentiation.

Conclusions

A. fumigatus triggers CD4⁺CD25⁺FOXP3⁺ Treg proliferation and differentiation by activating the TLR2 pathway, which may be a potential mechanism for evading host defenses in A. fumigatus. This effect can modulate GSDMD-dependent pyroptosis and may partly involve TRL2 signaling.

Tripterygium glycoside improves regulatory T cells and attenuates acute organ dysfunction in septic mice

Sepsis is a fatal infectious disease accompanied by multiple organ failure. Immune dysfunction and inflammatory response play an important role in the progression of the disease. Tripterygium glycoside (TG) has immune suppression and anti-inflammatory effects. Here, we investigated the effects of TG on cecal ligation and puncture (CLP)-induced sepsis. Septic mice model was induced by cecal ligation and puncture(CLP), after administration of TG, specimens are collected at designated time points. Histopathology changes of lung tissues and Kidney tissues were observed under light microscope, magnetic microbeads were used to isolate splenic CD4+CD25+ regulatory T cells (Tregs), and phenotypes were then analyzed by flow cytometry. ELISA method was employed to detect the concentrations of plasma TNF-α, IL-6, and IL-10. Nuclear p-NF-κB and Cytoplasmic IkB-a was detected by western blot. TG administration significantly alleviated lung and kidney inflammatory injury and improved the survival of septic mice. Furthermore, the suppressive function of regulatory T cells was enhanced and plasma expression of IL-10 was increased following TG treatment. The NF-B signaling pathway and secretion of plasma TNF-α and IL-6 was notably inhibited in septic mice treated with TG. TG exerts protective effects through improving regulatory T cells and attenuating pro-inflammatory cytokines in septic mice.

Lymphocyte Immunosuppression and Dysfunction Contributing to Persistent Inflammation, Immunosuppression, and Catabolism Syndrome (PICS)

ABSTRACT

Persistent Inflammation, Immune Suppression, and Catabolism Syndrome (PICS) is a disease state affecting patients who have a prolonged recovery after the acute phase of a large inflammatory insult. Trauma and sepsis are two pathologies after which such an insult evolves. In this review, we will focus on the key clinical determinants of PICS: Immunosuppression and cellular dysfunction. Currently, relevant immunosuppressive functions have been attributed to both innate and adaptive immune cells. However, there are significant gaps in our knowledge, as for trauma and sepsis the immunosuppressive functions of these cells have mostly been described in acute phase of inflammation so far, and their clinical relevance for the development of prolonged immunosuppression is mostly unknown. It is suggested that the initial immune imbalance determines the development of PCIS. Additionally, it remains unclear what distinguishes the onset of immune dysfunction in trauma and sepsis and how this drives immunosuppression in these cells. In this review, we will discuss how regulatory T cells (Tregs), innate lymphoid cells, natural killer T cells (NKT cells), TCR-a CD4- CD8- double-negative T cells (DN T cells), and B cells can contribute to the development of post-traumatic and septic immunosuppression. Altogether, we seek to fill a gap in the understanding of the contribution of lymphocyte immunosuppression and dysfunction to the development of chronic immune disbalance. Further, we will provide an overview of promising diagnostic and therapeutic interventions, whose potential to overcome the detrimental immunosuppression after trauma and sepsis is currently being tested.

Histone Deacetylation Inhibitors as Modulators of Regulatory T Cells

Regulatory T cells (T_regs) are important mediators of immunological self-tolerance and homeostasis. Being cluster of differentiation 4⁺Forkhead box protein3⁺ (CD4⁺FOXP3⁺), these cells are a subset of CD4⁺ T lymphocytes and can originate from the thymus (tT_regs) or from the periphery (pT_regs). The malfunction of CD4⁺ T_regs is associated with autoimmune responses such as rheumatoid arthritis (RA), multiple sclerosis (MS), type 1 diabetes (T1D), inflammatory bowel diseases (IBD), psoriasis, systemic lupus erythematosus (SLE), and transplant rejection. Recent evidence supports an opposed role in sepsis. Therefore, maintaining functional T_regs is considered as a therapy regimen to prevent autoimmunity and allograft rejection, whereas blocking T_reg differentiation might be favorable in sepsis patients. It has been shown that T_regs can be generated from conventional naïve T cells, called iT_regs, due to their induced differentiation. Moreover, T_regs can be effectively expanded in vitro based on blood-derived tT_regs. Taking into consideration that the suppressive role of T_regs has been mainly attributed to the expression and function of the transcription factor Foxp3, modulating its expression and binding to the promoter regions of target genes by altering the chromatin histone acetylation state may turn out beneficial. Hence, we discuss the role of histone deacetylation inhibitors as epigenetic modulators of T_regs in this review in detail.

Effects of regulatory T cells on glyceraldehyde-3-phosphate dehydrogenase vaccine efficacy against Schistosoma japonicum

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a candidate subunit vaccine that induces protective immunity and elicits partial resistance to Schistosoma japonicum upon mouse and livestock vaccination. This study aimed to evaluate the effect of regulatory T cells (Tregs), which were defined as CD4⁺CD25⁺Foxp3⁺ cells, on the efficacy of a GAPDH vaccine against S. japonicum. BALB/c female mice were randomly divided into five groups as follows: normal, infected control, anti-CD25 monoclonal antibody (anti-CD25 mAb), GAPDH group, and co-treated with anti-CD25 mAb and GAPDH group. The worm reduction and liver egg reduction rates in the GAPDH group were 32.46% and 35.43%, respectively, which increased to 60.09% and 58.78%, respectively, after anti-CD25 mAb administration. Compared with those in the infected control group, the percentage of Tregs in the spleen decreased significantly when GAPDH and anti-CD25 mAb were used either alone or in combination. Furthermore, secretions associated with the Th1 response increased in splenocytes of the anti-CD25 mAb group, whereas the Th1 and Th2 responses increased in splenocytes of the GAPDH and co-treated groups. Compared to that in the infected control group, granuloma diameter in the GAPDH and co-treated groups increased slightly, but there were no significant differences among the groups. Our results indicate that the protective effect of the GAPDH vaccines can be improved by decreasing Tregs and enhancing the Th1- and Th2-type immune responses. Therefore, anti-CD25 mAb and GAPDH might exert synergistic effects to clear parasites by decreasing the frequency of Tregs and increasing the Th1- and Th2-type immune responses.

Effect of regulatory T cells on the efficacy of the fatty acid-binding protein vaccine against Schistosoma japonicum

Schistosomiasis is one of the most devastating parasitic diseases, making it imperative to develop efficient vaccines to control the causative flatworms called schistosomes. Regulatory T cells (Tregs) and the Th1 immune response have been implicated in the effectiveness of vaccines to control schistosomiasis, but the mechanisms underlying their effects are unclear. In this study, we evaluated the role of Tregs on the efficacy of the 14 kDa FABP (fatty acid-binding protein) vaccine against Schistosoma japonicum. BALB/c female mice were randomly divided into five groups: an uninfected group, infected control group, anti-CD25 monoclonal antibody (anti-CD25 mAb) group, FABP group, and combined anti-CD25 mAb and FABP group. Compared with FABP alone, a combined treatment with FABP and anti-CD25 mAb increased the rate of S. japonicum inhibition in mice from 30.3 to 56.08% and decreased the number of eggs per gram of liver. Compared with that of the infected control group, the percentage of Tregs in the spleen decreased significantly after single or combined treatment with FABP and anti-CD25 mAb, while it increased gradually in the anti-CD25 mAb group. Further, the secretion of Th1 cytokines, IFN-γ, and IL-2 increased in splenocytes in the anti-CD25 mAb group. Our results indicate that anti-CD25 mAb partially blocks Tregs and concomitantly enhances the Th1 type immune response, thereby enhancing the protective effect of the FABP vaccine.

The role of regulatory T cells in pathogenesis and therapy of human papillomavirus-related diseases, especially in cancer

Human papillomavirus (HPV) is the most common sexually transmitted agent in the world. It can cause condyloma acuminatum, anogenital malignancies, and head and neck cancers. The host immune responses to HPV involve multiple cell types that have regulatory functions, and HPV-mediated changes to regulatory T cells (Tregs) in both the local lesion tissues and the circulatory system of patients have received considerable attention. The role of Tregs in HPV infections ranges from suppression of effector T cell (Teff) responses to protection of tissues from immune-mediated injury in different anatomic subsites. In this review, we explore the influence of Tregs in the immunopathology of HPV-related diseases and therapies targeting Tregs as novel approaches against HPV.