ER-Mitochondria Communication in Cells of the Innate Immune System

In cells the interorganelle communication comprises vesicular and non-vesicular mechanisms. Non-vesicular material transfer predominantly takes place at regions of close organelle apposition termed membrane contact sites and is facilitated by a growing number of specialized proteins. Contacts of the endoplasmic reticulum (ER) and mitochondria are now recognized to be essential for diverse biological processes such as calcium homeostasis, phospholipid biosynthesis, apoptosis, and autophagy. In addition to these universal roles, ER-mitochondria communication serves also cell type-specific functions. In this review, we summarize the current knowledge on ER-mitochondria contacts in cells of the innate immune system, especially in macrophages. We discuss ER- mitochondria communication in the context of macrophage fatty acid metabolism linked to inflammatory and ER stress responses, its roles in apoptotic cell engulfment, activation of the inflammasome, and antiviral defense.

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NOD-Like Receptors: Guards of Cellular Homeostasis Perturbation during Infection

International Journal of Molecular Sciences ◽

10.3390/ijms22136714 ◽

2021 ◽

Vol 22 (13) ◽

pp. 6714

Author(s):

Gang Pei ◽

Anca Dorhoi

Keyword(s):

Immune System ◽

Innate Immune System ◽

Current Knowledge ◽

Protein Translation ◽

Innate Immune ◽

Cellular Homeostasis ◽

Translation Block ◽

Cytoskeleton Disruption ◽

Molecular Patterns ◽

Fine Tune

The innate immune system relies on families of pattern recognition receptors (PRRs) that detect distinct conserved molecular motifs from microbes to initiate antimicrobial responses. Activation of PRRs triggers a series of signaling cascades, leading to the release of pro-inflammatory cytokines, chemokines and antimicrobials, thereby contributing to the early host defense against microbes and regulating adaptive immunity. Additionally, PRRs can detect perturbation of cellular homeostasis caused by pathogens and fine-tune the immune responses. Among PRRs, nucleotide binding oligomerization domain (NOD)-like receptors (NLRs) have attracted particular interest in the context of cellular stress-induced inflammation during infection. Recently, mechanistic insights into the monitoring of cellular homeostasis perturbation by NLRs have been provided. We summarize the current knowledge about the disruption of cellular homeostasis by pathogens and focus on NLRs as innate immune sensors for its detection. We highlight the mechanisms employed by various pathogens to elicit cytoskeleton disruption, organelle stress as well as protein translation block, point out exemplary NLRs that guard cellular homeostasis during infection and introduce the concept of stress-associated molecular patterns (SAMPs). We postulate that integration of information about microbial patterns, danger signals, and SAMPs enables the innate immune system with adequate plasticity and precision in elaborating responses to microbes of variable virulence.

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CD46 Plays a Key Role in Tailoring Innate Immune Recognition of Apoptotic and Necrotic Cells

Journal of Biological Chemistry ◽

10.1074/jbc.m506579200 ◽

2005 ◽

Vol 280 (43) ◽

pp. 36342-36354 ◽

Cited By ~ 104

Author(s):

Kristina Elward ◽

Mark Griffiths ◽

Masashi Mizuno ◽

Claire L. Harris ◽

Jim W. Neal ◽

...

Keyword(s):

Immune System ◽

Innate Immune System ◽

Apoptotic Cell ◽

Membrane Attack Complex ◽

Factor H ◽

Innate Immune ◽

Immune Recognition ◽

Alternative Pathways ◽

Complement Regulator ◽

Complement C1q

Complement is the canonical innate immune system involved in host defense and tissue repair with the clearance of cell debris. In contrast to the robust armory mounted against microbial nonself-pathogens, complement is selectively activated on altered self (i.e. apoptotic and necrotic cells) to instruct the safe demise by poorly characterized mechanisms. Our data shed new light on the role of complement C1q in sensing nucleic acids (NA) rapidly exposed on apoptotic Jurkat T cell membranes and in driving C3 opsonization but without the lytic membrane attack complex. DNA/RNase-treated apoptotic cells failed to activate complement. We found that several other apoptotic cell models, including senescent keratinocytes, ionophore-treated sperm cells, and CMK-derived platelets, stained for cleaved caspase 3 were rapidly losing the key complement regulator CD46. CD46 from nuclear and membrane stores was found to cluster into blebs and shed into microparticles together with NA, phosphatidylserine, C1q, and factor H. Classical and alternative pathways of complement were involved in the recognition of H2O2-treated necrotic cells. Membrane attack complex was detected on necrotic cells possibly as a result of CD46 and CD59 shedding into soluble forms. Our data highlight a novel and universal paradigm whereby the complement innate immune system is using two synergistic strategies with the recognition of altered self-NA and missing self-CD46 signals to instruct and tailor the efficient removal of apoptotic and necrotic cells in immunoprivileged sites.

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The Role of the Immune System in Obesity and Insulin Resistance

Journal of Obesity ◽

10.1155/2013/616193 ◽

2013 ◽

Vol 2013 ◽

pp. 1-9 ◽

Cited By ~ 68

Author(s):

Payal S. Patel ◽

Eric D. Buras ◽

Ashok Balasubramanyam

Keyword(s):

Insulin Resistance ◽

Adipose Tissue ◽

Immune System ◽

Stress Responses ◽

Innate Immune System ◽

Metabolic Diseases ◽

Innate Immune ◽

Metabolic Dysfunction ◽

Adipose Tissue Inflammation ◽

Tissue Inflammation

The innate immune system provides organisms with rapid and well-coordinated protection from foreign pathogens. However, under certain conditions of metabolic dysfunction, components of the innate immune system may be activated in the absence of external pathogens, leading to pathologic consequences. Indeed, there appears to be an intimate relationship between metabolic diseases and immune dysfunction; for example, macrophages are prime players in the initiation of a chronic inflammatory state in obesity which leads to insulin resistance. In response to increases in free fatty acid release from obese adipose depots, M1-polarized macrophages infiltrate adipose tissues. These M1 macrophages trigger inflammatory signaling and stress responses within cells that signal through JNK or IKKβpathways, leading to insulin resistance. If overnutrition persists, mechanisms that counteract inflammation (such as M2 macrophages and PPAR signaling) are suppressed, and the inflammation becomes chronic. Although macrophages are a principal constituent of obese adipose tissue inflammation, other components of the immune system such as lymphocytes and mast cells also contribute to the inflammatory cascade. Thus it is not merely an increased mass of adipose tissue that directly leads to attenuation of insulin action, but rather adipose tissue inflammation activated by the immune system in obese individuals that leads to insulin resistance.

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Neutrophils—From Bone Marrow to First-Line Defense of the Innate Immune System

Frontiers in Immunology ◽

10.3389/fimmu.2021.767175 ◽

2021 ◽

Vol 12 ◽

Author(s):

Richard Felix Kraus ◽

Michael Andreas Gruber

Keyword(s):

Immune System ◽

Innate Immune System ◽

Current Knowledge ◽

Immune Defense ◽

Innate Immune ◽

Human Organism ◽

Polymorphonuclear Cells ◽

Target Tissue ◽

First Line

Neutrophils (polymorphonuclear cells; PMNs) form a first line of defense against pathogens and are therefore an important component of the innate immune response. As a result of poorly controlled activation, however, PMNs can also mediate tissue damage in numerous diseases, often by increasing tissue inflammation and injury. According to current knowledge, PMNs are not only part of the pathogenesis of infectious and autoimmune diseases but also of conditions with disturbed tissue homeostasis such as trauma and shock. Scientific advances in the past two decades have changed the role of neutrophils from that of solely immune defense cells to cells that are responsible for the general integrity of the body, even in the absence of pathogens. To better understand PMN function in the human organism, our review outlines the role of PMNs within the innate immune system. This review provides an overview of the migration of PMNs from the vascular compartment to the target tissue as well as their chemotactic processes and illuminates crucial neutrophil immune properties at the site of the lesion. The review is focused on the formation of chemotactic gradients in interaction with the extracellular matrix (ECM) and the influence of the ECM on PMN function. In addition, our review summarizes current knowledge about the phenomenon of bidirectional and reverse PMN migration, neutrophil microtubules, and the microtubule organizing center in PMN migration. As a conclusive feature, we review and discuss new findings about neutrophil behavior in cancer environment and tumor tissue.

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Acute-phase responses and adipocytokines

10.1093/med/9780199642489.003.0058 ◽

2013 ◽

Author(s):

Elena Neumann ◽

Klaus Frommer ◽

Ulf Müller-Ladner

Keyword(s):

Adipose Tissue ◽

Immune System ◽

Chronic Inflammation ◽

Acute Phase ◽

Innate Immune System ◽

Current Knowledge ◽

Cell Types ◽

Innate Immune ◽

Bioactive Substances ◽

Different Cell Types

Adipokines, also called adipocytokines, are highly bioactive substances mainly expressed by adipose tissue. In addition to adipocytes, different cell types resident in various tissues produce adipokines under pathophysiological conditions. Adipokines include a growing number of pluripotent molecules such as adiponectin, resistin, leptin, and visfatin. Since distinct effects of adipokines on inflammation have been described, their influence on the (innate) immune system has been investigated in rheumatology, gastroenterology, and endocrinology. This review gives an overview on the current knowledge about the influence which adipokines have on the immune system and chronic inflammation in rheumatic diseases.

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