CD4 T Cell Responses and the Sepsis-Induced Immunoparalysis State

Immune profile of patients‑a new approach in management of sepsis and septic shock?

The present study was a prospective observational single center study, enrolling 102 patients with sepsis, admitted in the Intensive Care Unit of the County Emergency Clinical Hospital in Târgu Mureș (Mureș, Romania). The main goal of the present study was to compare the changes of the following parameters on day 1 compared with day 5, in sepsis compared with septic shock, as well as in survivors compared with non-survivors: Cell blood count parameters, neutrophil-lymphocyte ratio, platelet-lymphocyte ratio and systemic inflammation index, C reactive protein (CRP), ferritin, procalcitonin (PCT), CD 3+ T cells, CD4+ T cells, CD8+ T cells, CD16+CD56+/CD3-NK cells and CD19+ B cells. The relationship between the subcategories of lymphocytes with the inflammatory markers was evaluated. The serum concentration of CRP and PCT was significantly lower on day 5 compared with day 1 and serum ferritin was significantly higher in patients with septic shock. The percentage of cytotoxic T lymphocytes was significantly decreased and the percentage of NK lymphocytes was significantly increased in patients who developed septic shock. The results indicated a negative significant correlation between the proportion of T lymphocytes and PCT concentration and a positive significant correlation between the proportion of B lymphocytes and PCT concentration.

Epiglottitis Strikes Twice: A Case of Adult Recurrent Epiglottitis

Epiglottitis is an uncommon condition in adults, and recurrent episodes are rare. We report a 58-year-old male who had a second episode of epiglottitis nine years after his first. Our patient's immunologic profile obtained during his hospitalization revealed a significantly low absolute cluster of differentiation 4+ (CD4+) T lymphocyte count of 77 cells/mcL and a low immunoglobulin G (IgG) level of 635 mg/dL. Our patient was successfully managed with broad-spectrum antibiotics and corticosteroids. Given the known ability of short-term corticosteroids and acute inflammation's effect on lymphocyte populations, the significance of these laboratory values remains unclear due to our patient's unwillingness to undergo further diagnostic testing following discharge from our facility. We have considered multiple underlying etiologies for our patient's predisposition to developing this rare, recurrent, infectious manifestation; however, the exact cause is yet to be fully elucidated.

Mouse Models of Sepsis

Human sepsis is a complex disease that manifests with a diverse range of phenotypes and inherent variability among individuals, making it hard to develop a comprehensive animal model. Despite this difficulty, numerous models have been developed that capture many key aspects of human sepsis. The robustness of these models is vital for conducting pre-clinical studies to test and develop potential therapeutics. In this article, we describe four different models of murine sepsis that can be used to address different scientific questions relevant to the pathology and immune response during and after a septic event. Basic Protocol 1 details a non-synchronous cecal ligation and puncture (CLP) model of sepsis, where mice are subjected to polymicrobial exposure through surgery at different time points within 2 weeks. This variation in sepsis onset establishes each mouse at a different state of inflammation and cytokine levels that mimics the variability observed in humans when they present in the clinic. This model is ideal for studying the long-term impact of sepsis on the host. Basic Protocol 2 is also a type of polymicrobial sepsis, where injection of a specific amount of cecal slurry from a donor mouse into the peritoneum of recipient mice establishes immediate inflammation and sepsis without any need for surgery. Basic Protocol 3 describes infecting mice with a defined gram-positive or -negative bacterial strain to model a subset of sepsis observed in humans infected with a single pathogen. Basic Protocol 4 describes administering LPS to induce sterile endotoxemia. This form of sepsis is observed in humans exposed to bacterial toxins from the environment. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Non-synchronous cecal ligation and puncture Basic Protocol 2: Cecal slurry model of murine sepsis Basic Protocol 3: Monomicrobial model of murine sepsis Basic Protocol 4: LPS model of murine sepsis.

Defining Parameters That Modulate Susceptibility and Protection to Respiratory Murine Coronavirus MHV1 Infection

Patients infected with SARS-CoV-2 experience variable disease susceptibility, and patients with comorbidities such as sepsis are often hospitalized for COVID-19 complications. However, the extent to which initial infectious inoculum dose determines disease outcomes and whether this can be used for immunological priming in a genetically susceptible host has not been completely defined. We used an established SARS-like murine model in which responses to primary and/or secondary challenges with murine hepatitis virus type 1 (MHV-1) were analyzed. We compared the response to infection in genetically susceptible C3H/HeJ mice, genetically resistant C57BL/6J mice, and genetically diverse, variably susceptible outbred Swiss Webster mice. Although defined as genetically susceptible to MHV-1, C3H/HeJ mice displayed decreasing dose-dependent pathological changes in disease severity and lung infiltrate/edema, as well as lymphopenia. Importantly, an asymptomatic dose (500 PFU) was identified that yielded no measurable morbidity/mortality postinfection in C3H/HeJ mice. Polymicrobial sepsis induced via cecal ligation and puncture converted asymptomatic infections in C3H/HeJ and C57BL/6J mice to more pronounced disease, modeling the impact of sepsis as a comorbidity to β-coronavirus infection. We then used low-dose infection as an immunological priming event in C3H/HeJ mice, which provided neutralizing Ab-dependent, but not circulating CD4/CD8 T cell-dependent, protection against a high-dose MHV-1 early rechallenge. Together, these data define how infection dose, immunological status, and comorbidities modulate outcomes of primary and secondary β-coronavirus infections in hosts with variable susceptibility.

IL1RAP Exacerbates Sepsis-Induced Pulmonary and Spleen Injury Through Regulating CD4+ T Lymphocyte Differentiation

BACKGROUND

Complex pathophysiological the specific mechanism of sepsis on CD4+ T-cell responses is less well understood. IL1 receptor accessory protein (IL1RAP) was found to be involved in activating host immune responses.

METHOD

Cecum ligation and puncture (CLP) was utilized to build a mouse sepsis model. The experiment was randomly divided into four groups: Sham, CLP, CLP + shNC, and CLP + shIL1RAP group.

RESULTS

qRT-PCR suggested mRNA levels of IL1RAP were decreased when IL1RAP was knocked down with the mRNA levels of IL-1β, NF-κB, and p38 decreased. Histopathology showed severe pathological damage with alveolar integrity lost, red blood cells in the alveoli, massive inflammatory cell infiltration, and the alveolar wall was thickening in the CLP group. The inflammatory cytokine levels of TNF-α, IL-1β, and IFN-γ were elevated in CLP mice by ELISA. The counts of CD4+ T cells were decreased in sepsis mice in peripheral blood, spleen, and BALF by flow cytometry. However, the above was blocked down when using shIL1RAP. Western blot suggested sh IL1RAP inhibited IL-1β, NF-κB, and p38 protein expressions.

CONCLUSIONS

We defined IL1RAP as a new target gene through NF-κB/MAPK pathways regulating CD4+ T lymphocyte differentiation mediated the progression of sepsis, which is potentially exploitable for immunotherapy.

Plasticity and crosstalk of mesenchymal stem cells and macrophages in immunomodulation in sepsis

Sepsis is a multisystem disease characterized by dysregulation of the host immune response to infection. Immune response kinetics play a crucial role in the pathogenesis and progression of sepsis. Macrophages, which are known for their heterogeneity and plasticity, actively participate in the immune response during sepsis. These cells are influenced by the ever-changing immune microenvironment and exhibit two-sided immune regulation. Recently, the immunomodulatory function of mesenchymal stem cells (MSCs) in sepsis has garnered significant attention. The immune microenvironment can profoundly impact MSCs, prompting them to exhibit dual immunomodulatory functions akin to a double-edged sword. This discovery holds great importance for understanding sepsis progression and devising effective treatment strategies. Importantly, there is a close interrelationship between macrophages and MSCs, characterized by the fact that during sepsis, these two cell types interact and cooperate to regulate inflammatory processes. This review summarizes the plasticity of macrophages and MSCs within the immune microenvironment during sepsis, as well as the intricate crosstalk between them. This remains an important concern for the future use of these cells for immunomodulatory treatments in the clinic.

Saa3 promotes pro-inflammatory macrophage differentiation and contributes to sepsis-induced AKI

Sepsis-induced acute kidney injury (SAKI) is a life-threatening condition with complex pathophysiology, often exacerbated by immune cell dysregulation. In this comprehensive study, we leverage publicly available single-cell RNA sequencing (scRNA-seq) datasets to unravel the intricate immune responses occurring during SAKI, shedding light on macrophages as critical players. Specifically, we identify Saa3, a gene primarily expressed in macrophages, as a potent pro-inflammatory cytokine in SAKI. Saa3hi Ccl2hi monocyte-derived infiltrated macrophages (IMs) emerge as a central effector subset, fostering inflammation, and directly engaging with renal cells. Our findings suggest that Saa3 may be a promising predictive marker of SAKI, although further exploration of human homologs is warranted.

Thymopentin plays a key role in restoring the function of macrophages to alleviate the sepsis process

Immune dysfunction is one of the leading causes of death of sepsis. How to regulate host immune functions to improve prognoses of septic patients has always been a clinical focus. Here we elaborate on the efficacy and potential mechanism of a classical drug, thymopentin (TP5). TP5 could decrease peritoneal bacterial load, and reduce inflammatory cytokine levels both in the peritoneal lavage fluid (PLF) and serum, alleviate pathological injuries in tissue and organ, coaxed by cecal ligation and perforation (CLP) in mice, ultimately improve the prognosis of septic mice. Regarding the mechanism, using RNA-seq and flow cytometry, we found that TP5 induced peptidoglycan recognition protein 1 (PGLYRP1) expression, increased phagocytosis and restored TNF-α expression of small peritoneal macrophage (SPM) in the septic mice. This may be increased SPM's ability to clear peritoneal bacteria, thereby attenuates the inflammatory response both in the peritoneal cavity and the serum. It was shown that TP5 plays a key role in restoring the function of peritoneal macrophages to alleviate the sepsis process. We reckon that this is closely relevant to SPM phagocytosis, which might involve increased PGLYRP1 expression and restored TNF-α secretion.

Exploring post-SEPSIS and post-COVID-19 syndromes: crossovers from pathophysiology to therapeutic approach

Sepsis, driven by several infections, including COVID-19, can lead to post-sepsis syndrome (PSS) and post-acute sequelae of COVID-19 (PASC). Both these conditions share clinical and pathophysiological similarities, as survivors face persistent multi-organ dysfunctions, including respiratory, cardiovascular, renal, and neurological issues. Moreover, dysregulated immune responses, immunosuppression, and hyperinflammation contribute to these conditions. The lack of clear definitions and diagnostic criteria hampers comprehensive treatment strategies, and a unified therapeutic approach is significantly needed. One potential target might be the renin-angiotensin system (RAS), which plays a significant role in immune modulation. In fact, RAS imbalance can exacerbate these responses. Potential interventions involving RAS include ACE inhibitors, ACE receptor blockers, and recombinant human ACE2 (rhACE2). To address the complexities of PSS and PASC, a multifaceted approach is required, considering shared immunological mechanisms and the role of RAS. Standardization, research funding, and clinical trials are essential for advancing treatment strategies for these conditions.

T-cell lymphopenia is associated with an increased infecting risk in children after cardiopulmonary bypass

BACKGROUND

children who undergo CPB operations are at an elevated risk of infection due to immunosuppression. This study aims to investigate the association between lymphopenia following CPB and early postoperative infection in children.

METHODS

A retrospective analysis including 41 children under 2 years old underwent CPB. Among them, 9 subjects had an early postoperative infection, and 32 subjects were period-matched without infection. Inflammatory cytokines, serum CRP and PCT values were measured in plasma, additionally, circulating total leucocyte and lymphocyte subpopulations were counted.

RESULTS

Infected subjects exhibited significantly higher levels of inflammatory cytokines, including IL-6, IL-8, IL-10, IL-1β and TNF-α, than non-infected subjects after CPB. Additionally, lower absolute number of lymphocyte and their subpopulations CD3+ T cells, CD4+ T-helper cells and CD8+cytotoxic T-cells, were observed in infected subjects. The impairment of T-cells Immune was found to be associated with higher levels of inflammatory cytokines IL-10. The ROC demonstrated that the absolute number of CD3+ T-cells <1934/ul, CD4+ T helper cells <1203/ul and CD8+cytotoxic T-cells <327/ul were associated with early postoperative infection.

CONCLUSION

Higher levels of inflammatory cytokines resulted in T-cells lymphopenia after CPB, which significantly increasing the risk of postoperative infection in infants and young children.

IMPACT

Infection complications after cardiopulmonary bypass (CPB) in pediatric CHD patients are serious issues, identifing the infection from after CPB remains a challenging. CPB can release numerous inflammatory cytokines associated with T cells lymphopenia, which increases the risk of postoperative infection after surgery. Monitoring T cells lymphopenia maybe more beneficial to predict early postoperative infection than C-reactive protein and procalcitonin.

Immune dysregulation in sepsis: experiences, lessons and perspectives

Sepsis is a life-threatening organ dysfunction syndrome caused by dysregulated host responses to infection. Not only does sepsis pose a serious hazard to human health, but it also imposes a substantial economic burden on the healthcare system. The cornerstones of current treatment for sepsis remain source control, fluid resuscitation, and rapid administration of antibiotics, etc. To date, no drugs have been approved for treating sepsis, and most clinical trials of potential therapies have failed to reduce mortality. The immune response caused by the pathogen is complex, resulting in a dysregulated innate and adaptive immune response that, if not promptly controlled, can lead to excessive inflammation, immunosuppression, and failure to re-establish immune homeostasis. The impaired immune response in patients with sepsis and the potential immunotherapy to modulate the immune response causing excessive inflammation or enhancing immunity suggest the importance of demonstrating individualized therapy. Here, we review the immune dysfunction caused by sepsis, where immune cell production, effector cell function, and survival are directly affected during sepsis. In addition, we discuss potential immunotherapy in septic patients and highlight the need for precise treatment according to clinical and immune stratification.

Soluble CD137: A Potential Prognostic Biomarker in Critically Ill Patients

T cell depletion and functional impairment are characteristics of sepsis. CD137 is a costimulatory receptor on activated T cells, while soluble CD137 (sCD137) inhibits CD137 signaling. This study found elevated sCD137 levels in the plasma of patients with systemic inflammatory response syndrome (SIRS), sepsis, or septic shock compared to healthy controls. The sCD137 levels negatively correlated with the C-reactive protein and positively with procalcitonin and interleukin-6. There was no difference in sCD137 levels based on ventilation, dialysis, or vasopressor treatment. Patients with SARS-CoV-2, Gram-positive, or Gram-negative bacterial infections had similar sCD137 levels as noninfected individuals. Notably, higher plasma sCD137 levels were observed in non-survivors compared to survivors in both the SIRS/sepsis group and the SARS-CoV-2 subgroup. In conclusion, plasma sCD137 levels are associated with severe illness and survival in critically ill patients.

Protective effect of hydrangenol on lipopolysaccharide-induced endotoxemia by suppressing intestinal inflammation

Hydrangenol, a dihydroisocoumarin, isolated from the leaves of Hydrangea serrata, possesses anti-inflammatory, anti-obesity, and anti-photoaging activities. In this study, we investigated the protective effects of hydrangenol (HG) against lipopolysaccharide (LPS)-induced endotoxemia and elucidated the underlying molecular mechanisms of action in C57BL/6 mice. Oral administration of HG (20 or 40 mg/kg) significantly restored the survival rate and population of macrophages, T helper cells (CD3+/CD4+), and Th17 cells (CD3+/CD4+/CCR6+) in the spleens of mice with LPS-induced endotoxemia. HG suppressed the expression of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-1β, and Interferon (IFN)-γ and the mRNA and protein expressions of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) in the intestine and lung of LPS-treated mice. Molecular data showed that HG ameliorated the activation of nuclear factor kappa B (NF-κB) p65, signal transducers and activators of transcription 3 (STAT3), and c-Fos and c-Jun (AP-1 subunits) via the myeloid differentiation primary response 88 (MyD88) dependent toll-like receptor 4 (TLR4) signaling pathway in the LPS-treated mouse intestines. HG treatment caused the recovery of LPS-induced impaired tight junction (occludin and claudin-2) protein and mRNA expressions. Furthermore, HG improved LPS-induced gut dysbiosis in mice. Taken together, our results suggest that HG protects against LPS-induced endotoxemia by restoring immune cells and the capacity of the intestinal barrier, reducing intestinal inflammation, and improving the composition of the gut microbiota.

Expression of proBDNF/p75NTR in peripheral blood lymphocytes of patients with sepsis and its impact on lymphocyte differentiation

OBJECTIVES

Sepsis is a life-threatening organ dysfunction caused by the host's imbalanced response to infection. Due to lack of effective treatments, it has always been the difficulty and focus of clinical treatment of sepsis. Studies have shown that pro-brain-derived neurotrophic factor (proBDNF) binds to the high-affinity total neurotrophic factor p75 neurotrophin receptor (p75NTR), which activates downstream signaling cascades and disrupts immunological inflammation and plays an important role in the progression of sepsis. This study aims to explore the expression changes of lymphocyte-derived proBDNF/p75NTR in patients with sepsis and its effect on lymphocyte differentiation.

METHODS

From the healthy donors (control group, n=40) and sepsis patients (sepsis group, n=40) admitted to the hospital for the first time, peripheral blood samples and blood routine clinical detection indicators were obtained. By using flow cytometry, the proportion of lymphocyte subsets and their expression of proBDNF/p75NTR were examined. The peripheral blood lymphocytes were isolated from the control group and incubated with lipopolysaccharide (LPS). Flow cytometry analysis technology was used to detect the expression of proBDNF/p75NTR on LPS-treated lymphocyte subsets. On this basis, we investigated the effects on lymphocyte differentiation by inhibiting p75NTR.

RESULTS

White blood cell count, neutrophil count, and neutrophil percentage of the patients in the sepsis group at admission were significantly higher than those in the control group; on the contrary, lymphocyte count and lymphocyte percentage in the sepsis group were lower than those in the control group (all P<0.001). The patients in the sepsis group had considerably greater neutrophil/lymphocyte and monocyte/lymphocyte ratios than those in the control group (both P<0.05). In the peripheral blood of sepsis patients, proBDNF expression was upregulated on CD19+ B cells, whereas p75NTR expression was elevated on B cells, CD4+ T cells, and CD8+ T cells (all P<0.05). ProBDNF/p75NTR expression was upregulated by LPS stimulation in vitro in peripheral blood cells of the control group (P<0.05), and this tendency was similar to the expression alterations in peripheral lymphocytes of the sepsis group. Inhibition of p75NTR increased CD4+ T cell and CD19+ B cell percentages, cytokine expression of IL-4 and IL-10, and reduced IL-1β and IL-6 production (all P<0.05).

CONCLUSIONS

The immunosuppressive state of sepsis patients is indicated by a reduction in lymphocyte count and an increase in the proportion of inactive neutrophils. ProBDNF/p75NTR expression is upregulated in the peripheral blood lymphocytes of sepsis patients, and p75NTR inhibition may control lymphocyte differentiation involved in sepsis progression.

CD115+ monocytes protect microbially experienced mice against E. coli-induced sepsis

Uropathogenic E. coli (UPEC) is a primary organism responsible for urinary tract infections and a common cause of sepsis. Microbially experienced laboratory mice, generated by cohousing with pet store mice, exhibit increased morbidity and mortality to polymicrobial sepsis or lipopolysaccharide challenge. By contrast, cohoused mice display significant resistance, compared with specific pathogen-free mice, to a monomicrobial sepsis model using UPEC. CD115+ monocytes mediate protection in the cohoused mice, as depletion of these cells leads to increased mortality and UPEC pathogen burden. Further study of the cohoused mice reveals increased TNF-α production by monocytes, a skewing toward Ly6ChiCD115+ "classical" monocytes, and enhanced egress of Ly6ChiCD115+ monocytes from the bone marrow. Analysis of cohoused bone marrow also finds increased frequency and number of myeloid multipotent progenitor cells. These results show that a history of microbial exposure impacts innate immunity in mice, which can have important implications for the preclinical study of sepsis.

Comparative analysis of peripheral blood immunoinflammatory landscapes in patients with acute cholangitis and its secondary septic shock using single-cell RNA sequencing

BACKGROUND

Acute cholangitis (AC) is a key pathogeny of septic shock, which has a high mortality rate. AC has significant clinical heterogeneity, but no study has analyzed the discrepancies in immunoresponsiveness between AC and its secondary septic shock. The immune inflammatory responses play a critical role in the development of septic shock.

METHODS

We performed single-cell RNA sequencing (scRNA-seq) to analyze the differences of immunocytes in immunoresponse and inflammation between the early stages of AC (A1, A2, and A3) and its secondary septic shock (B1, B2, and B3).

RESULTS

This study has identified seven cell types, including T cells, B cells, plasma cells, neutrophils, monocytes, platelets and erythrocytes. We mainly focused on neutrophils, monocytes, and T cells. Neutrophil subpopulation analysis indicated that neutrophil progenitors (proNeus) were identified in neutrophil subsets. Compared with patients suffering from AC, the gene phenotypes of proNeus (ELANE, AZU1, MPO, and PRTN3) were significantly upregulated in septic shock. The differentiation direction of neutrophil subsets in peripheral blood mononuclear cells (PBMCs) was determined; Moreover, the proNeus in septic shock presented a state of "expansion", with upregulation of neutrophil degranulation and downregulation of monocyte and T cell proliferation. Neutrophils-7 (CCL5, RPL23A, RPL13, RPS19 and RPS18) were mainly involved in the regulation of cellular functions. The neutrophils-7 subpopulation in septic shock were in a state of "exhaustion", and its biological functions showed the characteristics of weakening neutrophil migration and phagocytosis, etc., which maked infection difficult to control and aggravated the development of septic shock. Analysis of monocyte and T cell subpopulations showed that the expression genes and biological functions of subpopulations were closely related to immunoinflammatory regulation. In addition, CCL3 - CCR1, CXCL1 - CXCR2 and other ligand-receptors were highly expressed in neutrophils and monocytes, enhancing interactions between immune cells.

CONCLUSION

ScRNA-seq revealed significant differences in immune cells between AC and its secondary septic shock, which were primarily manifested in the cellular numbers, differentially expressed genes, functions of cellular subsets, differentiation trajectories, cell-cell interactions and so on. We identified many subsets of neutrophil, T cell and monocyte were associated with inflammation and immunosuppression induced by septic shock. These provided a reference for accurately evaluating the pathological severity of patients with AC and discovering the targets for therapy.

TCF7 and LEF-1 downregulation in sepsis promotes immune suppression by inhibiting CD4+ T cell proliferation

BACKGROUND

Previous studies have shown that sepsis is implicated in a reduction in the number and function of CD4+ T cells. TCF7 and LEF-1 facilitate early T cell development and lineage selection of CD4+ T cells. However, the function and mechanism of TCF7 and LEF-1 in sepsis are uncharacterized. This study intended to delineate effect of TCF7 and LEF-1 on sepsis and the impact on proliferation of CD4+ T cells in sepsis.

METHODS

A mouse sepsis model was constructed by cecal ligation and puncture (CLP) method. Expression of TCF7 and LEF-1 in sepsis was investigated using bioinformatics analysis and molecular experiments. We then constructed TCF7 and LEF-1 overexpression cell lines to investigate their effects on proliferation, apoptosis, effector activation, and immunosuppressive molecules of CD4+ T cells in sepsis.

RESULTS

TCF7 and LEF-1 were downregulated in sepsis. As the duration of sepsis induction increased, the levels of TCF7 and LEF-1 gradually decreased, as did the number of CD4+ T cells. Cell experiments showed that overexpression of TCF7 and LEF-1 enhanced proliferation and effector activation of CD4+ T cells, reduced apoptosis, decreased PD-1 and LAG3 expression, and promoted immune response in sepsis.

CONCLUSION

In conclusion, this study confirmed that downregulation of TCF7 and LEF-1 expression in sepsis inhibited proliferation of CD4+ T cells, leading to immune suppression. This finding suggested that TCF7 and LEF-1 were potential biological targets for sepsis and indicated that immunotherapy aimed at improving CD4+ T cell proliferation may be a new strategy for immune therapy in sepsis patients.

Depletion of mTOR ameliorates CD4+ T cell pyroptosis by promoting autophagy activity in septic mice

A reduction in the number of CD4+ T cells is a central part of the immunosuppression phase of sepsis and leads to impaired immune defense ability and increased mortality. Pyroptosis, a newly discovered programmed cell death, was confirmed to be an important mechanism of lymphocytopenia in a lot of human diseases and is under the regulation of autophagy. The mammalian target of rapamycin (mTOR) pathway is closely related to CD4+ T-cell survival. Whether the mTOR pathway influences CD4+ T cell pyroptosis by regulating autophagy remains unknown. In this study, a septic mouse model was developed using cecal ligation and puncture (CLP) to explore the degree of pyroptosis and autophagy of CD4+ T cells. T-cell-specific mTOR/TSC1-knockout mice were used to investigate the role of mTOR pathway in the regulation of CD4+ T cell pyroptosis. Bafilomycin, a specific autophagy inhibitor, was used to verify the regulatory effect of autophagy on pyroptosis in septic mice. We observed aggravated pyroptosis in CD4+ T cells in CLP mice accompanied by impaired autophagy activity and an overactivated mTOR signaling pathway. Depletion of mTOR relieved autophagy deficiency and reduced the proportion of pyroptotic CD4+ T cells. In T-cell-specific mTOR-knockout mice treated with bafilomycin, the protective effect of mTOR depletion vanished. This indicated that autophagy negatively regulates CD4+ T cell pyroptosis, which is under the control of the mTOR pathway. Taken together, our findings emphasize the importance of pyroptosis in sepsis-induced lymphopenia and reveal the regulatory effects of the mTOR pathway and the role of autophagy in this regulation.

Sepsis leads to lasting changes in phenotype and function of naïve CD8 T cells

Sepsis, an amplified immune response to systemic infection, is characterized by a transient cytokine storm followed by chronic immune dysfunction. Consequently, sepsis survivors are highly susceptible to newly introduced infections, suggesting sepsis can influence the function and composition of the naïve CD8 T cell pool and resulting pathogen-induced primary CD8 T cell responses. Here, we explored the extent to which sepsis induces phenotypic and functional changes within the naïve CD8 T cell pool. To interrogate this, the cecal ligation and puncture (CLP) mouse model of polymicrobial sepsis was used. In normal, non-septic mice, we show type-I interferon (IFN I)-mediated signaling plays an important role in driving the phenotypic and functional heterogeneity in the naïve CD8 T cell compartment leading to increased representation of Ly6C+ naïve CD8 T cells. In response to viral infection after sepsis resolution, naïve Ly6C+ CD8 T cells generated more primary effector and memory CD8 T cells with slower conversion to a central memory CD8 T cell phenotype (Tcm) than Ly6C- naïve CD8 T cells. Importantly, as a potent inducer of cytokine storm and IFN I production, sepsis leads to increased representation of Ly6C+ naïve CD8 T cells that maintained their heightened ability to respond (i.e., effector and memory CD8 T cell accumulation and cytokine production) to primary LCMV infection. Lastly, longitudinal analyses of peripheral blood samples obtained from septic patients revealed profound changes in CD8 T cell subset composition and frequency compared to healthy controls. Thus, sepsis has the capacity to alter the composition of naïve CD8 T cells, directly influencing primary CD8 T cell responses to newly introduced 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.

Classification of subtypes and identification of dysregulated genes in sepsis

Background

Sepsis is a clinical syndrome with high mortality. Subtype identification in sepsis is meaningful for improving the diagnosis and treatment of patients. The purpose of this research was to identify subtypes of sepsis using RNA-seq datasets and further explore key genes that were deregulated during the development of sepsis.

Methods

The datasets GSE95233 and GSE13904 were obtained from the Gene Expression Omnibus database. Differential analysis of the gene expression matrix was performed between sepsis patients and healthy controls. Intersection analysis of differentially expressed genes was applied to identify common differentially expressed genes for enrichment analysis and gene set variation analysis. Obvious differential pathways between sepsis patients and healthy controls were identified, as were developmental stages during sepsis. Then, key dysregulated genes were revealed by short time-series analysis and the least absolute shrinkage and selection operator model. In addition, the MCPcounter package was used to assess infiltrating immunocytes. Finally, the dysregulated genes identified were verified using 69 clinical samples.

Results

A total of 898 common differentially expressed genes were obtained, which were chiefly related to increased metabolic responses and decreased immune responses. The two differential pathways (angiogenesis and myc targets v2) were screened on the basis of gene set variation analysis scores. Four subgroups were identified according to median expression of angiogenesis and myc target v2 genes: normal, myc target v2, mixed-quiescent, and angiogenesis. The genes CHPT1, CPEB4, DNAJC3, MAFG, NARF, SNX3, S100A9, S100A12, and METTL9 were recognized as being progressively dysregulated in sepsis. Furthermore, most types of immune cells showed low infiltration in sepsis patients and had a significant correlation with the key genes. Importantly, all nine key genes were highly expressed in sepsis patients.

Conclusion

This study revealed novel insight into sepsis subtypes and identified nine dysregulated genes associated with immune status in the development of sepsis. This study provides potential molecular targets for the diagnosis and treatment of sepsis.

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.

Plasminogen System in the Pathophysiology of Sepsis: Upcoming Biomarkers

Severe hemostatic disturbances and impaired fibrinolysis occur in sepsis. In the most serious cases, the dysregulation of fibrinolysis contributes to septic shock, disseminated intravascular coagulation (DIC), and death. Therefore, an analysis of circulating concentrations of pro- and anti-fibrinolytic mediators could be a winning strategy in both the diagnosis and the treatment of sepsis. However, the optimal cutoff value, the timing of the measurements, and their combination with coagulation indicators should be further investigated. The purpose of this review is to summarize all relevant publications regarding the role of the main components of the plasminogen activation system (PAS) in the pathophysiology of sepsis. In addition, the clinical value of PAS-associated biomarkers in the diagnosis and the outcomes of patients with septic syndrome will be explored. In particular, experimental and clinical trials performed in emergency departments highlight the validity of soluble urokinase plasminogen activator receptor (suPAR) as a predictive and prognostic biomarker in patients with sepsis. The measurements of PAI-I may also be useful, as its increase is an early manifestation of sepsis and may precede the development of thrombocytopenia. The upcoming years will undoubtedly see progress in the use of PAS-associated laboratory parameters.

Identification of biomarkers related to sepsis diagnosis based on bioinformatics and machine learning and experimental verification

Sepsis is a systemic inflammatory response syndrome caused by bacteria and other pathogenic microorganisms. Every year, approximately 31.5 million patients are diagnosed with sepsis, and approximately 5.3 million patients succumb to the disease. In this study, we identified biomarkers for diagnosing sepsis analyzed the relationships between genes and Immune cells that were differentially expressed in specimens from patients with sepsis compared to normal controls. Finally, We verified its effectiveness through animal experiments. Specifically, we analyzed datasets from four microarrays(GSE11755、GSE12624、GSE28750、GSE48080) that included 106 blood specimens from patients with sepsis and 69 normal human blood samples. SVM-RFE analysis and LASSO regression model were carried out to screen possible markers. The composition of 22 immune cell components in patients with sepsis were also determined using CIBERSORT. The expression level of the biomarkers in Sepsis was examined by the use of qRT-PCR and Western Blot (WB). We identified 50 differentially expressed genes between the cohorts, including 2 significantly upregulated and 48 significantly downregulated genes, and KEGG pathway analysis identified Salmonella infection, human T cell leukemia virus 1 infection, Epstein-Barr virus infection, hepatitis B, lysosome and other pathways that were significantly enriched in blood from patients with sepsis. Ultimately, we identified COMMD9, CSF3R, and NUB1 as genes that could potentially be used as biomarkers to predict sepsis, which we confirmed by ROC analysis. Further, we identified a correlation between the expression of these three genes and immune infiltrate composition. Immune cell infiltration analysis revealed that COMMD9 was correlated with T cells regulatory (Tregs), T cells follicular helper, T cells CD8, et al. CSF3R was correlated with T cells regulatory (Tregs), T cells follicular helper, T cells CD8, et al. NUB1 was correlated with T cells regulatory (Tregs), T cells gamma delta, T cells follicular helper, et al. Taken together, our findings identify potential new diagnostic markers for sepsis that shed light on novel mechanisms of disease pathogenesis and, therefore, may offer opportunities for therapeutic intervention.

Soluble CD4 effectively prevents excessive TLR activation of resident macrophages in the onset of sepsis

T lymphopenia, occurring in the early phase of sepsis in response to systemic inflammation, is commonly associated with morbidity and mortality of septic infections. We have previously shown that a sufficient number of T cells is required to constrain Toll-like receptors (TLRs) mediated hyperinflammation. However, the underlying mechanisms remains unsolved. Herein, we unveil that CD4⁺ T cells engage with MHC II of macrophages to downregulate TLR pro-inflammatory signaling. We show further that the direct contact between CD4 molecule of CD4⁺ T cells or the ectodomain of CD4 (soluble CD4, sCD4), and MHC II of resident macrophages is necessary and sufficient to prevent TLR4 overactivation in LPS and cecal ligation puncture (CLP) sepsis. sCD4 serum concentrations increase after the onset of LPS sepsis, suggesting its compensatory inhibitive effects on hyperinflammation. sCD4 engagement enables the cytoplasmic domain of MHC II to recruit and activate STING and SHP2, which inhibits IRAK1/Erk and TRAF6/NF-κB activation required for TLR4 inflammation. Furthermore, sCD4 subverts pro-inflammatory plasma membrane anchorage of TLR4 by disruption of MHC II-TLR4 raft domains that promotes MHC II endocytosis. Finally, sCD4/MHCII reversal signaling specifically interferes with TLR4 but not TNFR hyperinflammation, and independent of the inhibitive signaling of CD40 ligand of CD4⁺ cells on macrophages. Therefore, a sufficient amount of soluble CD4 protein can prevent excessive inflammatory activation of macrophages via alternation of MHC II-TLR signaling complex, that might benefit for a new paradigm of preventive treatment of sepsis.

Inflammation durably imprints memory CD4+ T cells

Adaptive immune responses are induced by vaccination and infection, yet little is known about how CD4+ T cell memory differs when primed in these two contexts. Notably, viral infection is generally associated with higher levels of systemic inflammation than is vaccination. To assess whether the inflammatory milieu at the time of CD4+ T cell priming has long-term effects on memory, we compared Spike-specific memory CD4+ T cells in 22 individuals around the time of the participants' third SARS-CoV-2 mRNA vaccination, with stratification by whether the participants' first exposure to Spike was via virus or mRNA vaccine. Multimodal single-cell profiling of Spike-specific CD4+ T cells revealed 755 differentially expressed genes that distinguished infection- and vaccine-primed memory CD4+ T cells. Spike-specific CD4+ T cells from infection-primed individuals had strong enrichment for cytotoxicity and interferon signaling genes, whereas Spike-specific CD4+ T cells from vaccine-primed individuals were enriched for proliferative pathways by gene set enrichment analysis. Moreover, Spike-specific memory CD4+ T cells established by infection had distinct epigenetic landscapes driven by enrichment of IRF-family transcription factors, relative to T cells established by mRNA vaccination. This transcriptional imprint was minimally altered following subsequent mRNA vaccination or breakthrough infection, reflecting the strong bias induced by the inflammatory environment during initial memory differentiation. Together, these data suggest that the inflammatory context during CD4+ T cell priming is durably imprinted in the memory state at transcriptional and epigenetic levels, which has implications for personalization of vaccination based on prior infection history.

Study on immune status alterations in patients with sepsis

Sepsis, characterized by cytokine-mediated hyper-inflammation and a consistent decline in immune responsiveness, is associated with a high risk of death in the intensive care unit (ICU). Here, we for the first time investigated the changes in immune and inflammatory responses to understand the interactions between immune and inflammatory biomarkers and their association with patient outcomes. The cytokine and lymphocyte subset levels were analyzed in healthy donors (HD) and patients with sepsis upon admission to the ICU (D0), D3, D7, D14, and D28 using flow cytometry. The primary endpoint was mortality on day 90. The trends in lymphocyte subsets and cytokine levels in all patients (n = 47), HD (n = 27), and patient subgroups (surviving, n = 30; dead, n = 17) were analyzed using an independent sample t-test and principal component analysis. Age, steroids (steroids used > 48 h), secondary infection, acute heart failure, acute kidney injury, coagulopathy, hypohepatia, organ transplant and septic shock (when transferred to the ICU) were associated with mortality. Absolute lymphocyte counts and lymphocyte subsets levels were reduced in most patients with sepsis. The proportion of Tregs in the patients increased with disease progression and was associated with immunosuppression. In conclusion, sepsis downregulated adaptive immunity, and induced the transition of the patients to prolonged immune suppression. The study suggests that while cellular immunity recovered within 2 weeks of admission, humoral and innate immunity recovery takes longer. These findings may assist in developing appropriate therapeutic approaches to improve the immune responses in patients with sepsis.

Immune dysregulation and RNA N6-methyladenosine modification in sepsis

Sepsis is defined as life-threatening organ dysfunction caused by the host immune dysregulation to infection. It is a highly heterogeneous syndrome with complex pathophysiological mechanisms. The host immune response to sepsis can be divided into hyper-inflammatory and immune-suppressive phases which could exist simultaneously. In the initial stage, systemic immune response is activated after exposure to pathogens. Both innate and adaptive immune cells undergo epigenomic, transcriptomic, and functional reprogramming, resulting in systemic and persistent inflammatory responses. Following the hyper-inflammatory phase, the body is in a state of continuous immunosuppression, which is related to immune cell apoptosis, metabolic failure, and epigenetic reprogramming. Immunosuppression leads to increased susceptibility to secondary infections in patients with sepsis. RNA N6-Methyladenosine (m6A) has been recognized as an indispensable epitranscriptomic modification involved in both physiological and pathological processes. Recent studies suggest that m6A could reprogram both innate and adaptive immune cells through posttranscriptional regulation of RNA metabolism. Dysregulated m6A modifications contribute to the pathogenesis of immune-related diseases. In this review, we summarize immune cell changes and the potential role of m6A modification in sepsis. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > RNA Editing and Modification.

Uridine Alleviates Sepsis-Induced Acute Lung Injury by Inhibiting Ferroptosis of Macrophage

Uridine metabolism is extensively reported to be involved in combating oxidative stress. Redox-imbalance-mediated ferroptosis plays a pivotal role in sepsis-induced acute lung injury (ALI). This study aims to explore the role of uridine metabolism in sepsis-induced ALI and the regulatory mechanism of uridine in ferroptosis. The Gene Expression Omnibus (GEO) datasets including lung tissues in lipopolysaccharides (LPS) -induced ALI model or human blood sample of sepsis were collected. In vivo and vitro, LPS was injected into mice or administered to THP-1 cells to generate sepsis or inflammatory models. We identified that uridine phosphorylase 1 (UPP1) was upregulated in lung tissues and septic blood samples and uridine significantly alleviated lung injury, inflammation, tissue iron level and lipid peroxidation. Nonetheless, the expression of ferroptosis biomarkers, including SLC7A11, GPX4 and HO-1, were upregulated, while lipid synthesis gene (ACSL4) expression was greatly restricted by uridine supplementation. Moreover, pretreatment of ferroptosis inducer (Erastin or Era) weakened while inhibitor (Ferrostatin-1 or Fer-1) strengthened the protective effects of uridine. Mechanistically, uridine inhibited macrophage ferroptosis by activating Nrf2 signaling pathway. In conclusion, uridine metabolism dysregulation is a novel accelerator for sepsis-induced ALI and uridine supplementation may offer a potential avenue for ameliorating sepsis-induced ALI by suppressing ferroptosis.

Whole transcriptome analysis to explore the impaired immunological features in critically ill elderly patients with sepsis

BACKGROUND

Sepsis is a frequent complication in critically ill patients, is highly heterogeneous and is associated with high morbidity and mortality rates, especially in the elderly population. Utilizing RNA sequencing (RNA-Seq) to analyze biological pathways is widely used in clinical and molecular genetic studies, but studies in elderly patients with sepsis are still lacking. Hence, we investigated the mortality-relevant biological features and transcriptomic features in elderly patients who were admitted to the intensive care unit (ICU) for sepsis.

METHODS

We enrolled 37 elderly patients with sepsis from the ICU at Taichung Veterans General Hospital. On day-1 and day-8, clinical and laboratory data, as well as blood samples, were collected for RNA-Seq analysis. We identified the dynamic transcriptome and enriched pathways of differentially expressed genes between day-8 and day-1 through DVID enrichment analysis and Gene Set Enrichment Analysis. Then, the diversity of the T cell repertoire was analyzed with MiXCR.

RESULTS

Overall, 37 patients had sepsis, and responders and non-responders were grouped through principal component analysis. Significantly higher SOFA scores at day-7, longer ventilator days, ICU lengths of stay and hospital mortality were found in the non-responder group, than in the responder group. On day-8 in elderly ICU patients with sepsis, genes related to innate immunity and inflammation, such as ZDHCC19, ALOX15, FCER1A, HDC, PRSS33, and PCSK9, were upregulated. The differentially expressed genes (DEGs) were enriched in the regulation of transcription, adaptive immune response, immunoglobulin production, negative regulation of transcription, and immune response. Moreover, there was a higher diversity of T-cell receptors on day-8 in the responder group, than on day-1, indicating that they had better regulated recovery from sepsis compared with the non-response patients.

CONCLUSION

Sepsis mortality and incidence were both high in elderly individuals. We identified mortality-relevant biological features and transcriptomic features with functional pathway and MiXCR analyses based on RNA-Seq data; and found that the responder group had upregulated innate immunity and increased T cell diversity; compared with the non-responder group. RNA-Seq may be able to offer additional complementary information for the accurate and early prediction of treatment outcome.

Glutamine alleviates intestinal injury in a murine burn sepsis model by maintaining intestinal intraepithelial lymphocyte homeostasis

Intestinal intraepithelial lymphocytes (IELs) play a sentinel role in the mucosal immune system because of their unique anatomical location in the epithelial layer. The disruption of IEL homeostasis is implicated in driving the intestinal injury of many typical inflammatory disorders, such as inflammatory bowel disease (IBD) and sepsis. Therefore, it is meaningful to alleviate intestinal injury by restoring IEL homeostasis in disease conditions. This study explores the effects of glutamine on intestinal IEL homeostasis in a murine model of burn sepsis. We report that glutamine inhibits inflammatory response and reduces injury in the small intestine of burn septic mice. This effect is attributed to the maintaining of IEL homeostasis by suppressing apoptosis and restoring the disrupted subpopulation balance induced by burn sepsis. Mechanistically, we show that glutamine does not affect the IL-15 dependent mechanisms that drive the maintenance and differentiation of IELs. Instead, glutamine sustains IEL homeostasis by upregulate aryl hydrocarbon receptor (AHR) and interleukin (IL)-22 transcription and expression. Consistently, the protective roles of glutamine in burn septic mice were repressed by further supplement with an AHR antagonist CH-223191. Collectively, our study reveals a new role of glutamine to maintain IEL homeostasis by activating the AHR signaling pathway, which in turn ameliorates intestinal injury in burn sepsis.

Inhibition of DDX3X ameliorated CD4+ T cells pyroptosis and improves survival in septic mice

Over-expression of DDX3X mRNA is associated with T cell loss in septic patients. This study aimed to investigate the molecular mechanism of DDX3X on T cell reduction in sepsis. The sepsis model was established using lipopolysaccharide stimulation in vitro and cecal ligation and puncture (CLP) surgery in vivo. Results showed that the expression of DDX3X was significantly upregulated in CD4⁺ T cells in sepsis. RK-33, the inhibitor of DDX3X, was found to dramatically increase CD4⁺ T cell counts and prolong the survival rate of mice with sepsis. The results also showed that the expression of caspase-1/GSDMD in CD4⁺ T cells was significantly increased in vitro and in vivo, and RK-33 can substantially reduce CD4⁺ T cell pyroptosis through inhibiting NLRP3/caspase-1/GSDMD. Globally, our results suggest that DDX3X is involved in the loss of CD4⁺ T cells partly through activating the pyroptotic pathway during sepsis, which may provide potential targets for therapeutic interventions in this highly lethal disease.

Inefficient Recovery of Repeatedly Stimulated Memory CD8 T Cells after Polymicrobial Sepsis Induction Leads to Changes in Memory CD8 T Cell Pool Composition

Long-lasting sepsis-induced immunoparalysis has been principally studied in primary (1°) memory CD8 T cells; however, the impact of sepsis on memory CD8 T cells with a history of repeated cognate Ag encounters is largely unknown but important in understanding the role of sepsis in shaping the pre-existing memory CD8 T cell compartment. Higher-order memory CD8 T cells are crucial in providing immunity against common pathogens that reinfect the host or are generated by repeated vaccination. In this study, we analyzed peripheral blood from septic patients and show that memory CD8 T cells with defined Ag specificity for recurring CMV infection proliferate less than bulk populations of central memory CD8 T cells. Using TCR-transgenic T cells to generate 1° and higher-order (quaternary [4°]) memory T cells within the same host, we demonstrate that the susceptibility and loss of both memory subsets are similar after sepsis induction, and sepsis diminished Ag-dependent and -independent (bystander) functions of these memory subsets equally. Both the 1° and 4° memory T cell populations proliferated in a sepsis-induced lymphopenic environment; however, due to the intrinsic differences in baseline proliferative capacity, expression of receptors (e.g., CD127/CD122), and responsiveness to homeostatic cytokines, 1° memory T cells become overrepresented over time in sepsis survivors. Finally, IL-7/anti-IL-7 mAb complex treatment early after sepsis induction preferentially rescued the proliferation and accumulation of 1° memory T cells, whereas recovery of 4° memory T cells was less pronounced. Thus, inefficient recovery of repeatedly stimulated memory cells after polymicrobial sepsis induction leads to changes in memory T cell pool composition, a notion with important implications in devising strategies to recover the number and function of pre-existing memory CD8 T cells in sepsis survivors.

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 exaggerates multiple organ injury, inflammation, and immune cell imbalance by activating the NF-κB pathway in sepsis

Objective

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) modulates the inflammatory immune response and organ dysfunction, which are closely implicated in sepsis pathogenesis and progression. This study aimed to explore the role of MALT1 in sepsis-induced organ injury, immune cell dysregulation, and inflammatory storms.

Methods

Septic mice were constructed by intraperitoneal injection of lipopolysaccharide, followed by overexpression or knockdown of MALT1 by tail vein injection of the corresponding lentivirus. Mouse naïve CD4⁺ T cells and bone marrow-derived macrophages were treated with MALT1 overexpression/knockdown lentivirus plus lipopolysaccharide.

Results

In the lungs, livers, and kidneys of septic mice, MALT1 overexpression exaggerated their injuries, as shown by hematoxylin and eosin staining (all p < 0.05), elevated cell apoptosis, as reflected by the TUNEL assay and cleaved caspase-3 expression (p < 0.05 in the lungs and kidneys), and promoted macrophage infiltration, as illustrated by CD68 immunofluorescence (p < 0.05 in the lungs and kidneys). Meanwhile, in the blood, MALT1 overexpression reduced T-helper (Th)1/Th2 cells, increased Th17/regulatory T-cell ratios (both p < 0.05), promoted systematic inflammation, as revealed by tumor necrosis factor-α, interleukin-6, interleukin-1β, and C-reactive protein (all p < 0.05), elevated oxidative stress, as shown by nitric oxide (p < 0.05), superoxide dismutase, and malondialdehyde (p < 0.05), and enhanced liver and kidney dysfunction, as revealed by an automatic animal biochemistry analyzer (all p < 0.05 except for aspartate aminotransferase). However, MALT1 knockdown exerted the opposite effect as MALT1 overexpression. Ex vivo experiments revealed that MALT1 overexpression promoted the polarization of M1 macrophages and naïve CD4⁺ T cells toward Th2 and Th17 cells (all p < 0.05), while MALT1 knockdown attenuated these effects (all p < 0.05). Mechanistically, MALT1 positively regulated the nuclear factor-κB (NF-κB) pathway both in vivo and ex vivo (p < 0.05).

Conclusion

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 amplifies multiple organ injury, inflammation, oxidative stress, and imbalance of macrophages and CD4⁺ T cells by activating the NF-κB pathway in sepsis.

Multisite Metagenomic Next-Generation Sequencing Improved Diagnostic Performance for Sepsis-Associated Lymphopenia Patients

A precise and efficient microbiological diagnosis is essential for sepsis. Metagenomic next-generation sequencing (mNGS) is a novel technique for the diagnosis of infectious diseases, but its current application in multisite sampling and interpretation remains controversial. Therefore, this study was undertaken to evaluate the reliability of multisite mNGS tests and the efficiency of plasma mNGS based on lymphocyte subset counts. A prospective observational study was performed on the intubated patients with sepsis-associated lymphopenia from January 2020 to February 2022. During the study period, data on 71 patients with sepsis-induced lymphopenia were collected. Among the 125 mNGS tests, 95 were positive for pathogens, whereas of the 166 conventional microbiological tests (CMTs), 91 were positive. The comparison showed that 38 patients (53.5%) had at least one matched pair of plasma mNGS and CMT results, while for multisite sampling, 47 patients (66.2%) had at least one. Lymphocyte subset analysis showed that T lymphocyte (577 ± 317 versus 395 ± 207, P = 0.005) and CD4⁺ T lymphocyte (333 ± 199 versus 230 ± 120, P = 0.009) counts were lower in the matched group. According to receiver operating characteristic (ROC) analysis, a CD4⁺ T lymphocyte count lower than 266 cells/mm³ was predictive of a match result. For sepsis-associated lymphopenia patients, we found that multisite mNGS tests showed a higher positivity rate. With plasma mNGS, a lower CD4⁺ T lymphocyte count predicted a better match result with CMT. The lymphocyte subset analysis may promote the clinical interpretation of mNGS results. IMPORTANCE This study was undertaken to evaluate the reliability of pathogenic diagnoses based on multisite mNGS detection at the clinically suspected sites and to analyze the efficiency of plasma mNGS detection based on lymphocyte subset counts in patients with sepsis-associated lymphopenia.

Clinical improvement of sepsis by extracorporeal centrifugal leukocyte apheresis in a porcine model

BACKGROUND

Extracorporeal blood purification therapies targeting removal of the downstream products of the inflammatory cascade in sepsis have failed to improve mortality. As an upstream process of the inflammatory cascade, activated white blood cells should be a potential therapeutic target for sepsis, and the effect of removing such cells by extracorporeal centrifugal leukocytapheresis (LCAP) is worth considering.

METHODS

Fourteen peritonitis-induced septic pigs were randomly assigned to receive a sham operation (control group, n = 7) or one session of LCAP at 12 h after sepsis induction (treatment group, n = 7). Samples from peripheral blood at various time-points and from LCAP collection were tested. All pigs were euthanized at 48 h, and lung, kidney, liver and spleen tissues were obtained for histopathological examination.

RESULTS

Two pigs died in accidents before the induction of sepsis, and 12 pigs were finally included for the statistical analysis. A significant clinical improvement was present in the treatment group relative to the control group in terms of the mean arterial blood pressure (MAP), oxygen tension (PaO2), lactic acid level, oxygenation index (PaO2/FiO2), and carbon dioxide tension (PaCO2, P < 0.05). Flow cytometry tests showed that a mixture of B cells, dendritic cells, T helper cells, cytotoxic T cells, monocytes and neutrophils were removed from the circulation by LCAP, resulting in sepsis-induced change trends in the control cells; these change trends were all flattened in the treatment group, although nonsignificantly.

CONCLUSIONS

LCAP may exert a wide-spectrum and bidirectional immunomodulatory effect on sepsis, accompanied by improvements in hemodynamics and oxygenation status.

Residual persistence of cytotoxicity lymphocytes and regulatory T cells in patients with severe coronavirus disease 2019 over a 1-year recovery process

Aim

To clarify the immune cellular changes in critically ill patients recovering from coronavirus disease 2019 (COVID‐19).

Methods

The immune response of peripheral blood mononuclear cells from patients with severe COVID‐19 in different stages of recovery (3, 6, and 12 months from hospitalization) was evaluated by single‐cell mass cytometry. Immunological changes in patients were compared with those in age‐matched healthy donors.

Results

Three patients with severe COVID‐19 were compared with four healthy donors. In the patients, there was an increase in the cell density of CD4‐ and CD8‐positive T lymphocytes, and B cells, over the course of the recovery period. CD4‐ and CD8‐positive T lymphocytes expressing T‐bet and granzyme B (Gzm B) in patients were abundant during all recovery periods. The level of regulatory T cells remained high throughout the year. The levels of natural killer (NK) cells in patients were higher than in those in the healthy donors, and the frequency of CD16⁺ NK cells expressing Gzm B increased throughout the year.

Conclusion

Patients recovering from severe COVID‐19 showed persistence of cytotoxic lymphocytes, NK cells, and regulatory T cells throughout the posthospitalization year of recovery.

T cell dysregulation in inflammatory diseases in ICU

Severe inflammatory diseases, including sepsis, are characterized by an impaired host adaptive and innate immunity which results in immunosuppression, responsible for secondary infections and increased morbidity and mortality in critically ill patients. T cells are major actors of the immune system. During post-aggressive immunosuppression, lymphopenia, reduction of innate T cells, changes in T helper cell polarization and regulatory T cell increase are observed. The main mechanisms involved in T cell dysregulation are T cell apoptosis, autophagy deficiency, T cell anergy, T cell exhaustion and T cell metabolic reprogramming. In this review, we describe the alterations of T cell regulation, their mechanisms, and their association with clinical outcomes in severe inflammatory diseases, foremost of which is the sepsis.

This review focuses on the alterations of T cell regulation and their mechanisms in severe inflammatory ICU diseases. Lymphopenia, reduction of innate T cells, changes in T helper cell polarization and regulatory T cell increase contribute to secondary immunosuppression in ICU patients.

Of mice and men: Laboratory murine models for recapitulating the immunosuppression of human sepsis

Prolonged immunosuppression is increasingly recognized as the major cause of late phase and long-term mortality in sepsis. Numerous murine models with different paradigms, such as lipopolysaccharide injection, bacterial inoculation, and barrier disruption, have been used to explore the pathogenesis of immunosuppression in sepsis or to test the efficacy of potential therapeutic agents. Nonetheless, the reproducibility and translational value of such models are often questioned, owing to a highly heterogeneric, complex, and dynamic nature of immunopathology in human sepsis, which cannot be consistently and stably recapitulated in mice. Despite of the inherent discrepancies that exist between mice and humans, we can increase the feasibility of murine models by minimizing inconsistency and increasing their clinical relevance. In this mini review, we summarize the current knowledge of murine models that are most commonly used to investigate sepsis-induced immunopathology, highlighting their strengths and limitations in mimicking the dysregulated immune response encountered in human sepsis. We also propose potential directions for refining murine sepsis models, such as reducing experimental inconsistencies, increasing the clinical relevance, and enhancing immunological similarities between mice and humans; such modifications may optimize the value of murine models in meeting research and translational demands when applied in studies of sepsis-induced immunosuppression.

Inhibition of endoplasmic reticulum stress and the downstream pathways protects CD4+ T cells against apoptosis and immune dysregulation in sepsis

BACKGROUND

Immunosuppression mediated by CD4⁺ T cell apoptosis and dysfunction is a key factor in promoting the progression of sepsis. Endoplasmic reticulum (ER) stress participates in the apoptosis and dysfunction of immune cells.

AIM

We aimed to investigate the role of ER stress inhibition in CD4⁺ T cells in both in vitro and in vivo models of sepsis.

METHODS

In vitro model of sepsis was established with lipopolysaccharide (LPS) and the rat model of sepsis was established using cecal ligation and puncture (CLP). After the LPS treatment or CLP, ER stress inhibitors including 4-PBA, SNJ-1945, and SP600125 were used to treat cells or rats, and the CD4⁺ T cells were obtained by magnetic bead sorting. The effects of ER stress inhibitors on apoptosis and the function of CD4⁺ T cells were evaluated.

RESULTS

After the LPS stimulation or CLP, the levels of ER stress and downstream markers (PERK, eIF2α, IRE-1α, ATF6, ATF4, XBP-1s, GRP78, CHOP, and p-JNK) were increased in CD4⁺ T cells at the beginning of sepsis. Meanwhile, the number of apoptotic CD4⁺ T cells markedly increased. In addition, sepsis impaired the function of CD4⁺ T cells, manifested by the increased population of Th1, Th2, Th17, and Treg, as well as the production of TNF-α, interleukin (IL)-6, IL-4, and IL-10. However, inhibitors of ER stress, JNK, and calpain all decreased the induction of Th1 and Th17, enhanced the increase of Th2 and Treg, decreased the production of TNF-α and IL-6, and enhanced the production of IL-4 and IL-10.

CONCLUSION

Our findings indicate that ER stress inhibitors may play a protective role by reducing CD4⁺ T cell apoptosis and maintaining CD4⁺ T cell function, which may be useful for enhancing the immune function and poor prognosis of patients with sepsis.

The Diagnostic Value of Mitochondrial Mass of Peripheral T Lymphocytes in Early Sepsis

Background

Studies have shown that lymphocyte dysfunction can occur during the early stages of sepsis and that cell dysfunction is associated with mitochondrial dysfunction. Therefore, quantifying the mitochondrial function of lymphocytes in patients with sepsis could be valuable for the early diagnosis of sepsis.

Methods

Seventy-nine patients hospitalized from September 2020 to September 2021 with Sepsis-3 were retrospectively analyzed and subsequently compared with those without sepsis.

Results

Univariate analysis showed statistical differences between the data of the two groups regarding age, neutrophil/lymphocyte, procalcitonin (PCT), C-reactive protein, total bilirubin, serum creatinine, type B natriuretic peptide, albumin, prothrombin time, activated partial thromboplastin time, lactic acid, single-cell mitochondrial mass (SCMM)-CD3, SCMM-CD4, SCMM-CD8, and Acute Physiology and Chronic Health Evaluation II score (P < 0.05). Multivariate logistic regression analysis performed on the indicators mentioned above demonstrated a statistical difference in PCT, lactic acid, SCMM-CD4, and SCMM-CD8 levels between the two groups (P < 0.05). The receiver operating characteristic curves of five models were subsequently compared [area under the curve: 0.740 (PCT) vs. 0.933 (SCMM-CD4) vs. 0.881 (SCMM-CD8) vs. 0.961 (PCT + SCMM-CD4) vs. 0.915 (PCT+SCMM-CD8), P < 0.001].

Conclusion

SCMM-CD4 was shown to be a better diagnostic biomarker of early sepsis when compared with the traditional biomarker, PCT. Furthermore, the value of the combination of PCT and SCMM-CD4 in the diagnosis of early sepsis was better than that of SCMM-CD4 alone.

Chronic critical illness and post-intensive care syndrome: from pathophysiology to clinical challenges

Background

Post‐intensive care syndrome (PICS) encompasses physical, cognition, and mental impairments persisting after intensive care unit (ICU) discharge. Ultimately it significantly impacts the long‐term prognosis, both in functional outcomes and survival. Thus, survivors often develop permanent disabilities, consume a lot of healthcare resources, and may experience prolonged suffering. This review aims to present the multiple facets of the PICS, decipher its underlying mechanisms, and highlight future research directions.

Main text

This review abridges the translational data underlying the multiple facets of chronic critical illness (CCI) and PICS. We focus first on ICU-acquired weakness, a syndrome characterized by impaired contractility, muscle wasting, and persisting muscle atrophy during the recovery phase, which involves anabolic resistance, impaired capacity of regeneration, mitochondrial dysfunction, and abnormalities in calcium homeostasis. Second, we discuss the clinical relevance of post-ICU cognitive impairment and neuropsychological disability, its association with delirium during the ICU stay, and the putative role of low-grade long-lasting inflammation. Third, we describe the profound and persistent qualitative and quantitative alteration of the innate and adaptive response. Fourth, we discuss the biological mechanisms of the progression from acute to chronic kidney injury, opening the field for renoprotective strategies. Fifth, we report long-lasting pulmonary consequences of ARDS and prolonged mechanical ventilation. Finally, we discuss several specificities in children, including the influence of the child’s pre-ICU condition, development, and maturation.

Conclusions

Recent understandings of the biological substratum of the PICS’ distinct features highlight the need to rethink our patient trajectories in the long term. A better knowledge of this syndrome and precipitating factors is necessary to develop protocols and strategies to alleviate the CCI and PICS and ultimately improve patient recovery.

Beyond QuantiFERON-TB Results, the Added Value of a Weak Mitogen Response

Introduction

While QuantiFERON-TB gold (QFT) is frequently used, little attention is paid to the mitogen response. How it could be impacted and associated with outcomes is poorly known.

Methods

Retrospective, case-control study in hospitalized patients who underwent QFT testing in two hospitals between 2016 and 2019. We defined two groups of cases with either negative [interferon (IFN)-γ ≤ 0.5 IU/ml, official threshold] or weak (0.5–2 IU/ml) mitogen response, and one group of controls with normal (>2 IU/ml) mitogen response.

Results

A total of 872 patients were included. An ongoing infection was independently associated with both a negative (RR = 4.34; 95% CI = 2.94–6.41) and a weak mitogen response (RR = 2.44; 95% CI = 1.66–3.58). Among tuberculosis patients, a weak mitogen response was associated with a false-negative QFT result (75%) compared to a normal response (20%). Decreasing mitogen response (normal, weak and negative, respectively) was associated with increasing length of hospital stay [median (interquartile range) 5 (3–13), 11 (5–21) and 15 (10–30) days; p < 0.001] and increasing hospital mortality (3, 7, and 15%; p < 0.001).

Conclusion

Clinicians should take notice of the mitogen response since IFN-γ concentrations lower than <2 IU/ml were associated with false-negative QFT results in tuberculosis patients, independently associated with ongoing infections, and could be associated with worse prognosis.

Role of extracellular vesicles in severe pneumonia and sepsis

INTRODUCTION

Extracellular vesicles (EV) released constitutively or following external stimuli from structural and immune cells are now recognized as important mediators of cell-to-cell communication. They are involved in the pathogenesis of pneumonia and sepsis, leading causes of acute respiratory distress syndrome (ARDS) where mortality rates remain up to 40%. Multiple investigators have demonstrated that one of the underlying mechanisms of the effects of EVs is through the transfer of EV content to host cells, resulting in apoptosis, inflammation, and permeability in target organs.

AREAS COVERED

The current review focuses on preclinical research examining the role of EVs released into the plasma and injured alveolus during pneumonia and sepsis.

EXPERT OPINION

Inflammation is associated with elevated levels of circulating EVs that are released by activated structural and immune cells and can have significant proinflammatory, procoagulant, and pro-permeability effects in critically ill patients with pneumonia and/or sepsis. However, clinical translation of the use of EVs as biomarkers or potential therapeutic targets may be limited by current methodologies used to identify and quantify EVs accurately (whether from host cells or infecting organisms) and lack of understanding of the role of EVs in the reparative phase during recovery from pneumonia and/or sepsis.

Advances in Immune Monitoring Approaches for Sepsis-Induced Immunosuppression

Sepsis represents a life-threatening organ dysfunction due to an aberrant host response. Of note is that majority of patients have experienced a severe immune depression during and after sepsis, which is significantly correlated with the occurrence of nosocomial infection and higher risk of in-hospital death. Nevertheless, the clinical sign of sepsis-induced immune paralysis remains highly indetectable and ambiguous. Given that, specific yet robust biomarkers for monitoring the immune functional status of septic patients are of prominent significance in clinical practice. In turn, the stratification of a subgroup of septic patients with an immunosuppressive state will greatly contribute to the implementation of personalized adjuvant immunotherapy. In this review, we comprehensively summarize the mechanism of sepsis-associated immunosuppression at the cellular level and highlight the recent advances in immune monitoring approaches targeting the functional status of both innate and adaptive immune responses.

EGFR promotes the apoptosis of CD4+ T lymphocytes through TBK1/Glut1 induced Warburg effect in sepsis

INTRODUCTION

Sepsis-induced apoptosis leads to lymphopenia including the decrease of CD4⁺ T cells thus favoring immunosuppression.

OBJECTIVES

Although epidermal growth factor receptor (EGFR) inhibitors significantly improve the survival rate of septic mice, the effect of EGFR on the function and metabolism of CD4⁺ T cells in sepsis remained unknown.

METHODS

CD4⁺ T cells from septic mice and patients were assessed for apoptosis, activation, Warburg metabolism and glucose transporter 1 (Glut1) expression with or without the interference of EGFR activation.

RESULTS

EGFR facilitates CD4⁺ T cell activation and apoptosis through Glut1, which is a key enzyme that controls glycolysis in T cells. EGFR, TANK binding kinase 1 (TBK1) and Glut1 form a complex to facilitate Glut1 transportation from cytoplasm to cell surface. Both the levels of membrane expression of EGFR and Glut1 and the activation levels of CD4⁺ T cells were significantly higher in patients with sepsis as compared with healthy subjects.

CONCLUSION

Our data demonstrated that through its downstream TBK1/Exo84/RalA protein system, EGFR regulates Glut1 transporting to the cell surface, which is a key step for inducing the Warburg effect and the subsequent cellular activation and apoptosis of CD4⁺ T lymphocytes and may eventually affect the immune functional status, causing immune cell exhaustion in sepsis.