Immune surveillance by the liver Jenne, Craig N; Kubes, Paul
Nature immunology,
10/2013, Letnik:
14, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Receiving both portal vein blood and arterial blood, the liver is an important and critical component in the defense against blood-borne infection. To accomplish this role, the liver contains ...numerous innate and adaptive immune cells that specialize in detection and capture of pathogens from the blood. Further, these immune cells participate in coordinated immune responses leading to pathogen clearance, leukocyte recruitment and antigen presentation to lymphocytes within the vasculature. Finally, this role in host defense must be tightly regulated to ensure that inappropriate immune responses are not raised against nonpathogenic exogenous blood-borne molecules, such as those derived from food. It is this balance between activation and tolerance that characterizes the liver as a frontline immunological organ.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
During the systemic inflammatory response of severe sepsis, neutrophils accumulate in the liver microcirculation, but their functional significance is largely unknown. We show that neutrophils ...migrate to liver sinusoids during endotoxemia and sepsis where they exert protective effects by releasing neutrophil extracellular traps (NETs), which are DNA-based structures that capture and eliminate microbes. NETs released into the vasculature ensnare bacteria from the bloodstream and prevent dissemination. NET production requires platelet-neutrophil interactions and can be inhibited by platelet depletion or disruption of integrin-mediated platelet-neutrophil binding. During sepsis, NET release increases bacterial trapping by 4-fold (beyond the basal level provided by resident intravascular macrophages). Blocking NET formation reduces the capture of circulating bacteria during sepsis, resulting in increased dissemination to distant organs. Thus, NETs ensnare circulating bacteria and provide intravascular immunity that protects against bacterial dissemination during septic infections.
► Neutrophils release intravascular NETs in liver sinusoids during endotoxemia/sepsis ► Production of NETs requires integrin-dependent interactions with platelets ► Intravascular NETs capture circulating bacteria 4× better than Kupffer cells alone ► Intravascular NETs protect against bacterial dissemination during sepsis
Neutrophil extracellular traps (NETs; webs of DNA coated in antimicrobial proteins) are released into the vasculature during sepsis where they contribute to host defense, but also cause tissue damage ...and organ dysfunction. Various components of NETs have also been implicated as activators of coagulation. Using multicolor confocal intravital microscopy in mouse models of sepsis, we observed profound platelet aggregation, thrombin activation, and fibrin clot formation within (and downstream of) NETs in vivo. NETs were critical for the development of sepsis-induced intravascular coagulation regardless of the inciting bacterial stimulus (gram-negative, gram-positive, or bacterial products). Removal of NETs via DNase infusion, or in peptidylarginine deiminase-4–deficient mice (which have impaired NET production), resulted in significantly lower quantities of intravascular thrombin activity, reduced platelet aggregation, and improved microvascular perfusion. NET-induced intravascular coagulation was dependent on a collaborative interaction between histone H4 in NETs, platelets, and the release of inorganic polyphosphate. Real-time perfusion imaging revealed markedly improved microvascular perfusion in response to the blockade of NET-induced coagulation, which correlated with reduced markers of systemic intravascular coagulation and end-organ damage in septic mice. Together, these data demonstrate, for the first time in an in vivo model of infection, a dynamic NET–platelet–thrombin axis that promotes intravascular coagulation and microvascular dysfunction in sepsis.
•In vivo imaging reveals a NET–platelet–thrombin axis that promotes intravascular coagulation in sepsis.•Inhibition of NETs during sepsis reduces intravascular coagulation, improves microvascular perfusion, and reduces organ damage.
Kupffer cells (KCs), the vast pool of intravascular macrophages in the liver, help to clear blood-borne pathogens. The mechanisms by which KCs capture circulating pathogens remain unknown. Here we ...use intra-vital imaging of mice infected with Staphylococcus aureus to directly visualize the dynamic process of bacterial capture in the liver. Circulating S. aureus were captured by KCs in a manner dependent on the macrophage complement receptor CRIg, but the process was independent of complement. CRIg bound Staphylococcus aureus specifically through recognition of lipoteichoic acid (LTA), but not cell-wall-anchored surface proteins or peptidoglycan. Blocking the recognition between CRIg and LTA in vivo diminished the bacterial capture in liver and led to systemic bacterial dissemination. All tested Gram-positive, but not Gram-negative, bacteria bound CRIg in a complement-independent manner. These findings reveal a pattern recognition role for CRIg in the direct capture of circulating Gram-positive bacteria from the bloodstream.
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•Kupffer cells (KCs) capture circulating S. aureus in the liver•Macrophage receptor CRIg, but not complement, is required for pathogen capture by KCs•CRIg directly binds Gram-positive bacteria via lipoteichoic acid (LTA) recognition•CRIg-LTA recognition is required for clearance of circulating Gram-positive bacteria
Liver macrophages called Kupffer cells (KCs) capture circulating pathogens. Using intravital imaging to visualize bacterial capture by KCs, Zeng et al. discover that CRIg functions as a pattern recognition receptor on KCs to directly bind Gram-positive bacteria via lipoteichoic acid (LTA). CRIg-LTA recognition is required for clearance of circulating bacteria.
Abstract
Although platelets are traditionally recognized for their central role in hemostasis, many lines of research clearly demonstrate these rather ubiquitous blood components are potent immune ...modulators and effectors. Platelets have been shown to directly recognize, sequester and kill pathogens, to activated and recruit leukocytes to sites of infection and inflammation, and to modulate leukocyte behavior, enhancing their ability to phagocytose and kill pathogens and inducing unique effector functions, such as the production of Neutrophil Extracellular Traps (NETs). This multifaceted response to infection and inflammation is due, in part, to the huge array of soluble mediators and cell surface molecules expressed by platelets. From their earliest origins as primordial hemocytes in invertebrates to their current form as megakaryocyte-derived cytoplasts, platelets have evolved to be one of the key regulators of host intravascular immunity and inflammation. In this review, we present the diverse roles platelets play in immunity and inflammation associated with autoimmune diseases and infection. Additionally, we highlight recent advances in our understanding of platelet behavior made possible through the use of advanced imaging techniques that allow us to visualize platelets and their interactions, in real-time, within the intact blood vessels of a living host.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Neutrophils mediate bacterial clearance through various mechanisms, including the release of mesh-like DNA structures or neutrophil extracellular traps (NETs) that capture bacteria. Although ...neutrophils are also recruited to sites of viral infection, their role in antiviral innate immunity is less clear. We show that systemic administration of virus analogs or poxvirus infection induces neutrophil recruitment to the liver microvasculature and the release of NETs that protect host cells from virus infection. After systemic intravenous poxvirus challenge, mice exhibit thrombocytopenia and the recruitment of both neutrophils and platelets to the liver vasculature. Circulating platelets interact with, roll along, and adhere to the surface of adherent neutrophils, forming large, dynamic aggregates. These interactions facilitate the release of NETs within the liver vasculature that are able to protect host cells from poxvirus infection. These findings highlight the role of NETs and early tissue-wide responses in preventing viral infection.
► Systemic virus challenge induces neutrophil and platelet recruitment to the liver ► Platelets bind adherent neutrophils, generating large dynamic aggregates ► Viral infection induces the release of NETs within the liver microvasculature ► NETs can protect host cells from viral infection in vivo
In some studies, using highly pathogenic strains of influenza, neutrophils have been demonstrated to be critical in limiting viral replication and disease progression during the early phases of ...infection 4, 5, whereas others have reported that neutrophil recruitment to the lung in response to viral infection is associated with increased epithelial cell death, fibrin deposition, and a worse prognosis 3, 6, 7. To date, no single specific signal has been identified as responsible for NET release, but rather this effector response has been attributed to a wide variety of stimuli including TLR-ligands, phorbol esters, complement, and the binding of activated platelets to neutrophils. ...a number of viruses induce NET formation, including influenza A, HIV-1, myxoma and encephalomyocarditis virus 14-17.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Well established for their central role in hemostasis, platelets have increasingly been appreciated as immune cells in recent years. This emerging role should not come as a surprise as the central ...immune cells of invertebrates, hemocytes, are able to phagocytose, secrete soluble mediators and promote coagulation of hemolymph, blurring the line between immunity and hemostasis. The undeniable evolutionary link between coagulation and immunity becomes even clearer as the role of platelets in inflammation is better understood. Platelets exert a range of immune-related functions, many of which involve an intimate interplay with leukocytes. Platelets promote leukocyte recruitment via endothelial activation and can serve as "landing pads" for leukocytes, facilitating cellular adhesion in vascular beds devoid of classic adhesion molecules. Moreover, platelets enhance leukocyte function both through direct interactions and through release of soluble mediators. Among neutrophil-platelets interactions, the modulation of neutrophil extracellular traps (NETs) is of great interest. Platelets have been shown to induce NET formation; and, in turn, NET components further regulate platelet and neutrophil function. While NETs have been shown to ensnare and kill pathogens, they also initiate coagulation via thrombin activation. In fact, increased NET formation has been associated with hypercoagulability in septic patients as well as in chronic vascular disorders. This review will delve into current knowledge of platelet-neutrophil interactions, with a focus on NET-driven coagulation, in the context of infectious diseases. A better understanding of these mechanisms will shed a light on the therapeutic potential of uncoupling immunity and coagulation through targeting of NETs.
Neutrophil extracellular traps (NETs) composed of DNA decorated with histones and proteases trap and kill bacteria but also injure host tissue. Here we show that during a bloodstream infection with ...methicillin-resistant Staphylococcus aureus, the majority of bacteria are sequestered immediately by hepatic Kupffer cells, resulting in transient increases in liver enzymes, focal ischaemic areas and a robust neutrophil infiltration into the liver. The neutrophils release NETs into the liver vasculature, which remain anchored to the vascular wall via von Willebrand factor and reveal significant neutrophil elastase (NE) proteolytic activity. Importantly, DNase although very effective at DNA removal, and somewhat effective at inhibiting NE proteolytic activity, fails to remove the majority of histones from the vessel wall and only partly reduces injury. By contrast, inhibition of NET production as modelled by PAD4-deficiency, or prevention of NET formation and proteolytic activity as modelled in NE(-/-) mice prevent collateral host tissue damage.
Highlights • Platelets play a critical role in the host immune response as an immune cell. • Platelets contribute neutrophil extracellular trap production, maximize inflammation. • Uncontrolled NET ...production drives harmful effect on various inflammatory diseases. • NETs and their components also largely culminate in platelet activation.
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