Population-Specific Metabolic Alterations in Professional Antigen-Presenting Cells Contribute to Sepsis-Associated Immunosuppression

Evaluation of immune and pyroptosis status in a model of sepsis-induced secondary pneumonia

In recent years, researchers have focused on studying the mechanism of sepsis-induced immunosuppression, but there is still a lack of suitable animal models that accurately reflect the process of sepsis-induced immunosuppression. The aim of this study was to evaluate the immune status at various stages in a model of sepsis-induced secondary pneumonia and to demonstrate whether pyroptosis is one of the modes of immune cell death in sepsis. Firstly, we established a sepsis model in C57BL/6J mice using cecal ligation and puncture (CLP). The surviving mice were treated with a 40 μL suspension of P.aeruginosa (Pa) under anesthesia on day 4 post-CLP to establish a sepsis-induced secondary pneumonia model. Secondly, routine blood tests, serum ALT and PCT levels, gross lung specimens, and H&E staining of the lung and liver tissues were used to assess the successful establishment of this model. Serum levels of TNF-α and IL-6, the CD4+/CD8+ratio in blood, H&E staining of the spleen, and immunohistochemistry of CD4 and CD8 in the spleen were detected to evaluate the immune status of the model mice. Finally, the expression levels of pyroptosis-related proteins in the spleen were detected by Western blot. The expression of GSDMD was assessed using immunohistochemistry, and pyroptosis was directly observed through transmission electron microscopy. The experimental results above confirmed the successful construction of the model for sepsis-induced secondary pneumonia, demonstrating its ability to reflect sepsis-induced immunosuppression. Moreover, the expression of pyroptosis-related proteins, immunohistochemical GSDMD, and transmission electron microscopy of the spleen showed that pyroptosis was one of the modes of immune cell death in sepsis.

Plac8-ERK pathway modulation of monocyte function in sepsis

Sepsis, a life-threatening condition caused by infection, is characterized by the dysregulation of immune responses and activation of monocytes. Plac8, a protein, has been implicated in various inflammatory conditions. This study aimed to investigate the effect of Plac8 upregulation on monocyte proliferation and activation in sepsis patients. Peripheral blood samples were collected from healthy individuals and sepsis patients. Monocytes were stimulated with lipopolysaccharide (LPS) to create an in vitro sepsis model, while a murine sepsis model was established using cecal ligation and puncture (CLP). The levels of monocyte markers, proliferation index (PI), and pro-inflammatory cytokines were assessed using flow cytometry and qPCR, respectively. Plac8 and phosphorylated ERK protein levels were determined by western blot, and TNF-α, IL-6, and IL-10 levels were quantified using ELISA. The CCK-8 assay was used to evaluate PBMC proliferation and activation. The results showed that Plac8 was highly expressed in sepsis models, promoting the survival, proliferation, and activation of monocytes. Plac8 upregulation activated the ERK pathway, leading to increased phosphorylation of ERK protein and elevated levels of CD14, CD16, TNF-α, IL-6, Plac8, and IL-10. In sepsis mice, Plac8 overexpression similarly activated the ERK pathway and promoted the survival, proliferation, and activation of monocytes. In conclusion, the upregulation of Plac8 enhances the activation of the ERK pathway and promotes monocyte proliferation and activation in sepsis patients.

Advances and Challenges in Sepsis Management: Modern Tools and Future Directions

Sepsis, a critical condition marked by systemic inflammation, profoundly impacts both innate and adaptive immunity, often resulting in lymphopenia. This immune alteration can spare regulatory T cells (Tregs) but significantly affects other lymphocyte subsets, leading to diminished effector functions, altered cytokine profiles, and metabolic changes. The complexity of sepsis stems not only from its pathophysiology but also from the heterogeneity of patient responses, posing significant challenges in developing universally effective therapies. This review emphasizes the importance of phenotyping in sepsis to enhance patient-specific diagnostic and therapeutic strategies. Phenotyping immune cells, which categorizes patients based on clinical and immunological characteristics, is pivotal for tailoring treatment approaches. Flow cytometry emerges as a crucial tool in this endeavor, offering rapid, low cost and detailed analysis of immune cell populations and their functional states. Indeed, this technology facilitates the understanding of immune dysfunctions in sepsis and contributes to the identification of novel biomarkers. Our review underscores the potential of integrating flow cytometry with omics data, machine learning and clinical observations to refine sepsis management, highlighting the shift towards personalized medicine in critical care. This approach could lead to more precise interventions, improving outcomes in this heterogeneously affected patient population.

[The Immune System of the Critically Ill Patient]

Critically ill patients often experience a dysregulated immune response, leading to immune dysfunction. Sepsis, trauma, severe infections, and certain medical conditions can trigger a state of systemic inflammation, known as the cytokine storm. This hyperactive immune response can cause collateral damage to healthy tissues and organs, exacerbating the patient's condition. On the other hand, some critically ill patients may suffer from immune paralysis which can increase the risk of nosocomial infections.Fever is an evolutionary adaptation that evolved as an effective defense mechanism to fight invading pathogens. By raising body temperature, fever enhances the immune response, inhibits pathogen growth, promotes recovery, and aids in the formation of immune memory. Understanding the role of fever in the context of immune defense is crucial for optimizing medical interventions and supporting the body's natural ability to combat infections.Future Directions: Advancements in immunology research and technology hold promise for better understanding the immune system's complexities in critically ill patients. Personalized medicine approaches may be developed to tailor therapies to individual patients based on their immune profile, optimizing treatment outcomes. Based on recent studies prognostic parameters such as lymphocyte count, IL-10 concentration and mHLA-DR expression can be used to stratify the immunological response pattern in septic patients.Conclusion: The immune system's response in critically ill patients is a multifaceted process, involving intricate interactions between various immune cells, cytokines, and organs. Striking the delicate balance between immune activation and suppression remains a significant challenge in clinical practice. Continued research and therapeutic innovations are vital to improve patient outcomes and reduce the burden of critical illness on healthcare systems.

Destabilisation of T cell-dependent humoral immunity in sepsis

Sepsis is a heterogeneous condition defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. For some, sepsis presents as a predominantly suppressive disorder, whilst others experience a pro-inflammatory condition which can culminate in a 'cytokine storm'. Frequently, patients experience signs of concurrent hyper-inflammation and immunosuppression, underpinning the difficulty in directing effective treatment. Although intensive care unit mortality rates have improved in recent years, one-third of discharged patients die within the following year. Half of post-sepsis deaths are due to exacerbation of pre-existing conditions, whilst half are due to complications arising from a deteriorated immune system. It has been suggested that the intense and dysregulated response to infection may induce irreversible metabolic reprogramming in immune cells. As a critical arm of immune protection in vertebrates, alterations to the adaptive immune system can have devastating repercussions. Indeed, a marked depletion of lymphocytes is observed in sepsis, correlating with increased rates of mortality. Such sepsis-induced lymphopenia has profound consequences on how T cells respond to infection but equally on the humoral immune response that is both elicited by B cells and supported by distinct CD4+ T follicular helper (TFH) cell subsets. The immunosuppressive state is further exacerbated by functional impairments to the remaining lymphocyte population, including the presence of cells expressing dysfunctional or exhausted phenotypes. This review will specifically focus on how sepsis destabilises the adaptive immune system, with a closer examination on how B cells and CD4+ TFH cells are affected by sepsis and the corresponding impact on humoral immunity.

INTRINSIC/EXTRINSIC APOPTOSIS AND PYROPTOSIS CONTRIBUTE TO THE SELECTIVE DEPLETION OF B CELL SUBSETS IN SEPTIC SHOCK PATIENTS

ABSTRACT

The depletion of peripheral blood B cells is associated with immunosuppression and poor prognosis during sepsis, and selective depletion occurs when B cell subsets are specifically targeted. In this study, we examined the mechanisms underlying the selective depletion of B cell subsets in the immunosuppressive phase of septic shock patients. Thirty-two septic shock patients were recruited as a septic shock group and 10 healthy volunteers as a control group. The expression of Bcl-2, CD95, cleaved caspase-9/8, and activated caspase-3/1 in the B cell subsets were measured by flow cytometry. Another 23 septic shock patients were recruited to test the remission of caspase-3 (Z-DEVD-FMK) and caspase-1 (VX-765) inhibitors on B cell subset depletion in vitro . In septic shock patients, the Bcl-2 levels in immature/transitional (IM) B cells decreased and the levels of cleaved caspase-9 in IM B cells increased; the levels of CD95 in IM, naive, resting memory (RM), and activated memory (AM) B cells and the levels of cleaved caspase-8 in IM, RM, and AM B cells increased; the levels of activated caspase-3 and caspase-1 in IM, RM, and AM B cells increased. Activated caspase-1 levels in IM B cells were higher compared with activated caspase-3 in septic shock patients, whereas the levels of activated caspase-1 in AM B cells were lower compared with activated caspase-3. Moreover, in vitro experiments showed that Z-DEVD-FMK and VX-765 could alleviate the depletion of IM, AM, and RM B cells. The selective reduction of circulating B cell subsets in septic shock patients could be attributed to intrinsic and extrinsic apoptosis as well as pyroptosis.

Targeting the Granulocytic Defense against A. fumigatus in Healthy Volunteers and Septic Patients

Neutrophil granulocytes (NGs) are among the key players in the defense against Aspergillus fumigatus (A. fumigatus). To better elucidate a pathophysiological understanding of their role and functions, we applied a human cell model using NGs from healthy participants and septic patients to evaluate their inhibitory effects on the growth of A. fumigatus ex vivo. Conidia of A. fumigatus (ATCC^® 204305) were co-incubated with NGs from healthy volunteers or septic patients for 16 h. A. fumigatus growth was measured by XTT assays with a plate reader. The inhibitory effect of NGs on 18 healthy volunteers revealed great heterogeneity. Additionally, growth inhibition was significantly stronger in the afternoon than the morning, due to potentially different cortisol levels. It is particularly interesting that the inhibitory effect of NGs was reduced in patients with sepsis compared to healthy controls. In addition, the magnitude of the NG-driven defense against A. fumigatus was highly variable among healthy volunteers. Moreover, daytime and corresponding cortisol levels also seem to have a strong influence. Most interestingly, preliminary experiments with NGs from septic patients point to a strongly diminished granulocytic defense against Aspergillus spp.

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.

Fucoxanthin Alleviates Lipopolysaccharide-Induced Inflammation and Immunosuppression in RAW264.7 Macrophages

Fucoxanthin (FX) has been reported to reduce mortality in mouse models of sepsis, but its exact cause remains to be determined. In the present study, we evaluated the immunomodulatory properties of FX in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Our results showed that FX could not only suppress the immune activation responses caused by LPS primary stimulation, but also antagonize LPS restimulation-induced immunosuppression in macrophages. The immunomodulatory capabilities of FX was mainly demonstrated by regulating the production of the inflammatory mediator under different LPS stimuli. Furthermore, we found that adenosine monophosphate-activated protein kinase (AMPK) activation was required for FX's anti-inflammatory and anti-immunosuppressive activities. Our results complement existing data supporting the clinical potential for FX in treating sepsis.

Insights into the Roles of B Cells in Patients with Sepsis

Sepsis is a life-threatening yet common disease, still posing high mortality worldwide. Sepsis-related deaths primarily occur during immunosuppression; the disease can hamper the numbers and function of B cells, which mediate innate and adaptive immune responses to maintain immune homeostasis. Dysfunction of B cells, along with aggravated immunosuppression, are closely related to poor prognosis. However, B cells in patients with sepsis have garnered little attention. This article focuses on the significance of B-cell subsets, including regulatory B cells, in sepsis and how the counts and function of circulating B cells are affected in patients with sepsis. Finally, potential B-cell-related immunotherapies for sepsis are explored.

The emerging roles and therapeutic potential of B cells in sepsis

Sepsis is a life-threatening syndrome caused by anomalous host response to infection. The pathogenesis of sepsis is complex, and immune dysfunction is the central link in its occurrence and development. The sepsis immune response is not a local and transient process but a complex and continuous process involving all major cell types of innate and adaptive immunity. B cells are traditionally studied for their ability to produce antibodies in the context of mediating humoral immunity. However, over the past few years, B cells have been increasingly recognized as key modulators of adaptive and innate immunity, and they can participate in immune responses by presenting antigens, producing cytokines, and modulating other immune cells. Recently, increasing evidence links B-cell dysfunction to mechanisms of immune derangement in sepsis, which has drawn attention to the powerful properties of this unique immune cell type in sepsis. Here, we reviewed the dynamic alterations of B cells and their novel roles in animal models and patients with sepsis, and provided new perspectives for therapeutic strategies targeting B cells in sepsis.

Cellular and Exosomal Regulations of Sepsis-Induced Metabolic Alterations

Sepsis is a sustained systemic inflammatory condition involving multiple organ failures caused by dysregulated immune response to infections. Sepsis induces substantial changes in energy demands at the cellular level leading to metabolic reprogramming in immune cells and stromal cells. Although sepsis-associated organ dysfunction and mortality have been partly attributed to the initial acute hyperinflammation and immunosuppression precipitated by a dysfunction in innate and adaptive immune responses, the late mortality due to metabolic dysfunction and immune paralysis currently represent the major problem in clinics. It is becoming increasingly recognized that intertissue and/or intercellular metabolic crosstalk via endocrine factors modulates maintenance of homeostasis, and pathological events in sepsis and other inflammatory diseases. Exosomes have emerged as a novel means of intercellular communication in the regulation of cellular metabolism, owing to their capacity to transfer bioactive payloads such as proteins, lipids, and nucleic acids to their target cells. Recent evidence demonstrates transfer of intact metabolic intermediates from cancer-associated fibroblasts via exosomes to modify metabolic signaling in recipient cells and promote cancer progression. Here, we review the metabolic regulation of endothelial cells and immune cells in sepsis and highlight the role of exosomes as mediators of cellular metabolic signaling in sepsis.

Screening of Key Genes of Sepsis and Septic Shock Using Bioinformatics Analysis

Objective

Sepsis is a disease associated with high mortality. We performed bioinformatic analysis to identify key biomarkers associated with sepsis and septic shock.

Methods

The top 20% of genes showing the greatest variance between sepsis and controls in the GSE13904 dataset (children) were screened by co-expression network analysis. The differentially expressed genes (DEGs) were identified through analyzing differential gene expression between sepsis patients and control in the GSE13904 (children) and GSE154918 (adult) data sets. Intersection analysis of module genes and DEGs was performed to identify common DEGs for enrichment analysis, protein-protein interaction network (PPI network) analysis, and Short Time-series Expression Miner (STEM) analysis. The PPI network genes were ranked by degree of connectivity, and the top 100 sepsis-associated genes were identified based on the area under the receiver operating characteristic curve (AUC). In addition, we evaluated differences in immune cell infiltration between sepsis patients and controls in children (GSE13904, GSE25504) and adults (GSE9960, GSE154918). Finally, we analyzed differences in DNA methylation levels between sepsis patients and controls in GSE138074 (adults).

Results

The common genes were associated mainly with up-regulated inflammatory and metabolic responses, as well as down-regulated immune responses. Sepsis patients showed lower infiltration by most types of immune cells. Genes in the PPI network with AUC values greater than 0.9 in both GSE13904 (children) and GSE154918 (adults) were screened as key genes for diagnosis. These key genes (MAPK14, FGR, RHOG, LAT, PRKACB, UBE2Q2, ITK, IL2RB, and CD247) were also identified in STEM analysis to be progressively dysregulated across controls, sepsis patients and patients with septic shock. In addition, the expression of MAPK14, FGR, and CD247 was modified by methylation.

Conclusion

This study identified several potential diagnostic genes and inflammatory and metabolic responses mechanisms associated with the development of sepsis.

The Metabolic Basis of Immune Dysfunction Following Sepsis and Trauma

Critically ill, severely injured and high-risk surgical patients are vulnerable to secondary infections during hospitalization and after hospital discharge. Studies show that the mitochondrial function and oxidative metabolism of monocytes and macrophages are impaired during sepsis. Alternatively, treatment with microbe-derived ligands, such as monophosphoryl lipid A (MPLA), peptidoglycan, or β-glucan, that interact with toll-like receptors and other pattern recognition receptors on leukocytes induces a state of innate immune memory that confers broad-spectrum resistance to infection with common hospital-acquired pathogens. Priming of macrophages with MPLA, CPG oligodeoxynucleotides (CpG ODN), or β-glucan induces a macrophage metabolic phenotype characterized by mitochondrial biogenesis and increased oxidative metabolism in parallel with increased glycolysis, cell size and granularity, augmented phagocytosis, heightened respiratory burst functions, and more effective killing of microbes. The mitochondrion is a bioenergetic organelle that not only contributes to energy supply, biosynthesis, and cellular redox functions but serves as a platform for regulating innate immunological functions such as production of reactive oxygen species (ROS) and regulatory intermediates. This review will define current knowledge of leukocyte metabolic dysfunction during and after sepsis and trauma. We will further discuss therapeutic strategies that target leukocyte mitochondrial function and might have value in preventing or reversing sepsis- and trauma-induced immune dysfunction.