Treml4 receptor is a master regulator of inflammation and innate immune cell death during polymicrobial sepsis.
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ABSTRACT:
SUBMITTER: Hamsa Puthalakath
PROVIDER: S-BSST399 | biostudies-other |
REPOSITORIES: biostudies-other
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Project description:OBJECTIVES:Cell death in lymphatic organs, such as the spleen, is in part responsible for immunosuppression and contributes to mortality during sepsis. An early and noninvasive detection of lymphoid cell death could thus have significant clinical implications. Here, we tested in vivo imaging of lymphoid cell death using a near-infrared annexin V (AV-750). DESIGN:Animal study. SETTING:Laboratory investigation. SUBJECTS:C57BL/6J wild-type and toll-like receptor 3 knockout mice. INTERVENTIONS:Mild and severe polymicrobial sepsis was induced with cecum ligation and puncture. Serum cytokines and acute kidney injury markers were tested by immunoassay and quantitative reverse transcription-polymerase chain reaction, respectively. Sepsis-induced lymphoid cell death was detected by fluorescent AV-750 accumulation in the thorax and abdomen (in vivo), in isolated organs (ex vivo), and in isolated cells (flow cytometry). Caspase-3 cleavage/activity and terminal deoxynucleotidyl transferase dUTP nick-end labeling staining were tested for apoptosis. MEASUREMENTS AND MAIN RESULTS:Severe sepsis induced marked apoptosis in the thymus, spleen, and liver as demonstrated by cleaved caspase-3 and an increase in caspase-3 activity and terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells. A significant increase in fluorescent AV-750 signal was seen in the thoracic and upper abdominal fields and associated with the severity of sepsis. The in vivo thoracic and abdominal AV-750 fluorescent signal was attributed to the thymus, liver, and spleen as determined by ex vivo imaging and highly correlated with the levels of cell death in thymocytes and splenocytes, respectively, as measured by flow cytometry. Compared with wild-type septic mice, toll-like receptor 3 septic mice had attenuated abdominal AV-750 fluorescent signal, reduced ex vivo fluorescence in the spleen, and decreased splenocyte cell death. CONCLUSIONS:In vivo AV-750 fluorescent imaging provides spatially resolved and organ-specific detection of lymphoid cell death during polymicrobial sepsis. The AV-750 fluorescent intensity in the thoracic and abdominal fields is associated with sepsis severity and well correlated with sepsis-induced cell death in the thymus and spleen, respectively.
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Project description:Sepsis, a leading cause of death in the United States, has poorly understood mechanisms of mortality. To address this, our model of cecal ligation and puncture (CLP) induced sepsis stratifies mice as predicted to Live (Live-P) or Die (Die-P) based on plasma IL-6. Six hours post-CLP, both Live-P and Die-P groups have equivalent peritoneal bacterial colony forming units and recruitment of phagocytes. By 24 h, however, Die-P mice have increased bacterial burden, despite increased neutrophil recruitment, suggesting Die-P phagocytes have impaired bacterial killing. Peritoneal cells were used to study multiple bactericidal processes: bacterial killing, reactive oxygen species (ROS) generation, and phagocytosis. Total phagocytosis and intraphagosomal processes were determined with triple-labeled Escherichia coli, covalently labeled with ROS- and pH-sensitive probes, and an ROS/pH-insensitive probe for normalization. Although similar proportions of Live-P and Die-P phagocytes responded to exogenous stimuli, Die-P phagocytes showed marked deficits in all parameters measured, thus suggesting immunosuppression rather than exhaustion. This contradicts the prevailing sepsis paradigm that acute-phase sepsis deaths (<5 d) result from excessive inflammation, whereas chronic-phase deaths (>5 d) are characterized by insufficient inflammation and immunosuppression. These data suggest that suppression of cellular innate immunity in sepsis occurs within the first 6 h.
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Project description:The lung is a primary organ for gas exchange in mammals that represents the largest epithelial surface in direct contact with the external environment. It also serves as a crucial immune organ, which harbors both innate and adaptive immune cells to induce a potent immune response. Due to its direct contact with the outer environment, the lung serves as a primary target organ for many airborne pathogens, toxicants (aerosols), and allergens causing pneumonia, acute respiratory distress syndrome (ARDS), and acute lung injury or inflammation (ALI). The current review describes the immunological mechanisms responsible for bacterial pneumonia and sepsis-induced ALI. It highlights the immunological differences for the severity of bacterial sepsis-induced ALI as compared to the pneumonia-associated ALI. The immune-based differences between the Gram-positive and Gram-negative bacteria-induced pneumonia show different mechanisms to induce ALI. The role of pulmonary epithelial cells (PECs), alveolar macrophages (AMs), innate lymphoid cells (ILCs), and different pattern-recognition receptors (PRRs, including Toll-like receptors (TLRs) and inflammasome proteins) in neutrophil infiltration and ALI induction have been described during pneumonia and sepsis-induced ALI. Also, the resolution of inflammation is frequently observed during ALI associated with pneumonia, whereas sepsis-associated ALI lacks it. Hence, the review mainly describes the different immune mechanisms responsible for pneumonia and sepsis-induced ALI. The differences in immune response depending on the causal pathogen (Gram-positive or Gram-negative bacteria) associated pneumonia or sepsis-induced ALI should be taken in mind specific immune-based therapeutics.
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Project description:IntroductionVarious immune cell types play critical roles in sepsis with numerous distinct subsets exhibiting unique phenotypes even within the same cell population. Single-cell RNA sequencing (scRNA-seq) enables comprehensive transcriptome profiling and unbiased cell classification. In this study, we have unveiled the transcriptomic landscape of immune cells in sepsis through scRNA-seq analysis.MethodsWe induced sepsis in mice by cecal ligation and puncture. 20 h after the surgery, the spleen and peritoneal lavage were collected. Single-cell suspensions were processed using a 10× Genomics pipeline and sequenced on an Illumina platform. Count matrices were generated using the Cell Ranger pipeline, which maps reads to the mouse reference transcriptome, GRCm38/mm10. Subsequent scRNA-seq analysis was performed using the R package Seurat.ResultsAfter quality control, we subjected the entire data set to unsupervised classification. Four major clusters were identified as neutrophils, macrophages, B cells, and T cells according to their putative markers. Based on the differentially expressed genes, we identified activated pathways in sepsis for each cell type. In neutrophils, pathways related to inflammatory signaling, such as NF-κB and responses to pathogen-associated molecular patterns (PAMPs), cytokines, and hypoxia were activated. In macrophages, activated pathways were the ones related to cell aging, inflammatory signaling, and responses to PAMPs. In B cells, pathways related to endoplasmic reticulum stress were activated. In T cells, activated pathways were the ones related to inflammatory signaling, responses to PAMPs, and acute lung injury. Next, we further classified each cell type into subsets. Neutrophils consisted of four clusters. Some subsets were activated in inflammatory signaling or cell metabolism, whereas others possessed immunoregulatory or aging properties. Macrophages consisted of four clusters, namely, the ones with enhanced aging, lymphocyte activation, extracellular matrix organization, or cytokine activity. B cells consisted of four clusters, including the ones possessing the phenotype of cell maturation or aging. T cells consisted of six clusters, whose phenotypes include molecular translocation or cell activation.ConclusionsTranscriptomic analysis by scRNA-seq has unveiled a comprehensive spectrum of immune cell responses and distinct subsets in the context of sepsis. These findings are poised to enhance our understanding of sepsis pathophysiology, offering avenues for targeting novel molecules, cells, and pathways to combat infectious diseases.
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