Human Innate Immune Response Research Articles

Isolation and Chemical Characterization of Lipid A from Gram-negative Bacteria

Lipopolysaccharide (LPS) is the major cell surface molecule of gram-negative bacteria, deposited on the outer leaflet of the outer membrane bilayer. LPS can be subdivided into three domains: the distal O-polysaccharide, a core oligosaccharide, and the lipid A domain consisting of a lipid A molecular species and 3-deoxy-D-manno-oct-2-ulosonic acid residues (Kdo). The lipid A domain is the only component essential for bacterial cell survival. Following its synthesis, lipid A is chemically modified in response to environmental stresses such as pH or temperature, to promote resistance to antibiotic compounds, and to evade recognition by mediators of the host innate immune response. The following protocol details the small- and large-scale isolation of lipid A from gram-negative bacteria. Isolated material is then chemically characterized by thin layer chromatography (TLC) or mass-spectrometry (MS). In addition to matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) MS, we also describe tandem MS protocols for analyzing lipid A molecular species using electrospray ionization (ESI) coupled to collision induced dissociation (CID) and newly employed ultraviolet photodissociation (UVPD) methods. Our MS protocols allow for unequivocal determination of chemical structure, paramount to characterization of lipid A molecules that contain unique or novel chemical modifications. We also describe the radioisotopic labeling, and subsequent isolation, of lipid A from bacterial cells for analysis by TLC. Relative to MS-based protocols, TLC provides a more economical and rapid characterization method, but cannot be used to unambiguously assign lipid A chemical structures without the use of standards of known chemical structure. Over the last two decades isolation and characterization of lipid A has led to numerous exciting discoveries that have improved our understanding of the physiology of gram-negative bacteria, mechanisms of antibiotic resistance, the human innate immune response, and have provided many new targets in the development of antibacterial compounds.

Crimean-Congo hemorrhagic fever virus nucleoprotein suppresses IFN-beta-promoter-mediated gene expression

Crimean-Congo hemorrhagic fever virus (CCHFV) is a member of the family Bunyaviridae and is a causative agent of severe hemorrhagic disease. Knowledge regarding the pathogenesis of CCHFV is limited due to the requirement for high-containment laboratories and the lack of an immunocompetent animal host. Previous studies have shown that CCHFV delays the activation of the human innate immune response, specifically, the type I interferon response. Our study results show that antagonism of the interferon-beta promoter is mediated by the nucleoprotein of CCHFV strain Hoti, while strains IbAr10200 and AP92 do not suppress the activity of the IFN-beta promoter. Our results also suggest that several viral factors may provide antagonistic action against the type I interferon response.

A Distinct Role of Riplet-Mediated K63-Linked Polyubiquitination of the RIG-I Repressor Domain in Human Antiviral Innate Immune Responses

The innate immune system is essential for controlling viral infections, but several viruses have evolved strategies to escape innate immunity. RIG-I is a cytoplasmic viral RNA sensor that triggers the signal to induce type I interferon production in response to viral infection. RIG-I activation is regulated by the K63-linked polyubiquitin chain mediated by Riplet and TRIM25 ubiquitin ligases. TRIM25 is required for RIG-I oligomerization and interaction with the IPS-1 adaptor molecule. A knockout study revealed that Riplet was essential for RIG-I activation. However the molecular mechanism underlying RIG-I activation by Riplet remains unclear, and the functional differences between Riplet and TRIM25 are also unknown. A genetic study and a pull-down assay indicated that Riplet was dispensable for RIG-I RNA binding activity but required for TRIM25 to activate RIG-I. Mutational analysis demonstrated that Lys-788 within the RIG-I repressor domain was critical for Riplet-mediated K63-linked polyubiquitination and that Riplet was required for the release of RIG-I autorepression of its N-terminal CARDs, which leads to the association of RIG-I with TRIM25 ubiquitin ligase and TBK1 protein kinase. Our data indicate that Riplet is a prerequisite for TRIM25 to activate RIG-I signaling. We investigated the biological importance of this mechanism in human cells and found that hepatitis C virus (HCV) abrogated this mechanism. Interestingly, HCV NS3-4A proteases targeted the Riplet protein and abrogated endogenous RIG-I polyubiquitination and association with TRIM25 and TBK1, emphasizing the biological importance of this mechanism in human antiviral innate immunity. In conclusion, our results establish that Riplet-mediated K63-linked polyubiquitination released RIG-I RD autorepression, which allowed the access of positive factors to the RIG-I protein.

EP4 and EP2 Receptor Activation of Protein Kinase A by Prostaglandin E2 Impairs Macrophage Phagocytosis of Clostridium sordellii

Clostridium sordellii causes endometrial infections, but little is known regarding host defenses against this pathogen. We tested the hypothesis that the immunoregulatory lipid prostaglandin (PG) E2 suppresses human macrophage clearance of C. sordellii through receptor-induced increases in intracellular cyclic adenosine monophosphate (cAMP). The THP-1 macrophage cell line was used to quantify C. sordellii phagocytosis. PGE2 increased cAMP levels, activated protein kinase A (PKA), and inhibited the class A scavenger receptor-dependent phagocytosis of C. sordellii. Activation of the EP2 and EP4 receptors increased intracellular cAMP and inhibited phagocytosis, with evidence favoring a more important role for EP4 over EP2. This was supported by EP receptor expression data and the use of pharmacological receptor antagonists. In addition, the PKA isoform RI appeared to be more important than RII in mediating the suppression of ingestion of C. sordellii. The endogenous lipid mediator PGE2 impairs human innate immune responses against C. sordellii.

MicroRNA‐130a inhibits HCV replication by restoring the innate immune response

Hepatitis C virus (HCV) infection is a major cause of chronic hepatitis and hepatocellular carcinoma. Currently pegylated interferon (IFN) combined with ribavirin remains the best therapeutic approach, although patients infected with HCV genotype I may benefit from adding protease inhibitors as 'triple therapy'. MicroRNAs (miRNAs) are endogenous small noncoding RNAs that regulate gene expression and have recently been shown to play an important role in human innate immune response and as an antiviral in chimpanzees. We studied the effect of miR-130a on the HCV replication. We found that miR-130a significantly inhibits HCV replication in both HCV replicon and J6-/JFH1-infected cells. Over expression of miR-130a upregulated the expression of type I IFN (IFN-α/IFN -β), ISG15, USP18 and MxA, which are involved in innate immune response and decreased expression of miR-122, a well-defined miRNA promoting HCV production. In conclusion, miR-130a inhibits HCV replication/production by restoring host innate immune responses and/or downregulating pro-HCV miR-122. miR-130a might be a potential drug target by modulating host innate immune responses to combat HCV infection.

Acute liver failure caused by herpes simplex virus in a pregnant patient: Is there a potential role for therapeutic plasma exchange?

A young woman presented with a febrile illness in the third trimester of pregnancy. Laboratory investigation revealed severe acute hepatitis with thrombocytopenia and coagulopathy. Liver injury progressed despite emergent caesarian section and delivery of a healthy infant. Therefore, therapeutic plasma exchange (TPE) was performed on three consecutive days post-partum for a presumed diagnosis of acute liver failure (ALF) associated with pregnancy due to hemolysis, elevated liver enzymes, and low platelets (HELLP) or acute fatty liver of pregnancy (AFLP). Treatment with TPE was followed by biochemical and clinical improvement but during her recovery herpes simplex virus type 2 (HSV-2) infection was diagnosed serologically and confirmed histologically. Changes in the immune system during pregnancy make pregnant patients more susceptible to acute HSV hepatitis, HSV-related ALF, and death. The disease is characterized by massive hepatic inflammation with hepatocyte necrosis, mediated by both direct viral cytotoxicity and the innate humoral immune response. TPE may have a therapeutic role in acute inflammatory disorders such as HSV hepatitis by reducing viral load and attenuating systemic inflammation and liver cell injury. Further investigation is needed to clarify this potential effect. The roles of vigilance, clinical suspicion, and currently accepted therapies are emphasized.

FRI0351 Modulation of the innate humoral immunity in patients with refractory takayasu arteritis treated with biologic agents.

BackgroundTakayasu arteritis (TA) is a relapsing inflammatory large-vessel panarteritis resulting in vessel stenosis, occlusion or aneurysm formation1,2. Medical therapy with steroids and immunosuppressive agents is the cornerstone of TA treatment...

Molluscum Contagiosum Virus: Persistence Pays Off

The molluscum contagiosum (MC) virus (MCV) is a dermatotropic poxvirus, and the causative agent of MC. Unlike smallpox and human monkeypox diseases, MC is nonlethal, common and worldwide. Additionally, little inflammation is associated with MC papules, and MC can persist for months to years. Such a prolonged infection implies that MCV successfully manipulates the host environment. This review highlights recent findings that reveal how MCV infections manipulate localized host immune responses and which immune response are key for the eventual resolution of MC. Also highlighted here are the MCV proteins that inhibit apoptosis, inflammation and immune cell recruitment or that induce cellular proliferation, with discussion as to how these proteins dampen localized antiviral immune responses. Lastly, this review discusses how the immune evasion tactics of MCV have led to insights about specific functions of the human innate and adaptive immune responses.

Body mass index is not associated with cytokine induction during experimental human endotoxemia

A higher body mass index (BMI) appears to be associated with lower mortality in critically ill patients, possibly explained by an altered innate immune response. However, the precise relationship between BMI and the innate immune response in humans invivo is unknown. We investigated the relationship between BMI and the systemic cytokine response during experimental human endotoxemia. Endotoxemia was induced in 112 healthy male volunteers by intravenous administration of 2 ng/kg Escherichia coli endotoxin. Plasma concentrations of TNF-α, IL-6, IL-10 and IL-1RA were serially determined. The relationship between BMI and the cytokine response, as well as body temperature, was investigated. The BMIs of the participants ranged from 18.3 to 33.6 kg/m(2), (median: 22.7 kg/m(2)). All participants showed a marked increase in plasma cytokine levels [median (interquartile range)] peak levels: TNF-α 509 (353-673) pg/ml; IL-6 757 (522-1098) pg/ml; IL-10 271 (159-401) pg/ml; IL-1RA 4882 (3927-6025) pg/ml; and an increase in body temperature [1.8(1.4-2.2)] during endotoxemia. No significant correlations were found between BMI and levels of any of the cytokines or body temperature. No relationship between BMI and the cytokine response was found in healthy volunteers subjected to experimental endotoxemia. These data question the relationship between BMI and cytokine responses in critical illness.

Reduced Frequency of a CD14+CD16+Monocyte Subset with High Toll-Like Receptor 4 Expression in Cord Blood Compared to Adult Blood Contributes to Lipopolysaccharide Hyporesponsiveness in Newborns

The human innate immune response to pathogens is not fully effective and mature until well into childhood, as exemplified by various responses to Toll-like receptor (TLR) agonists in newborns compared to adults. To better understand the mechanistic basis for this age-related difference in innate immunity, we compared tumor necrosis factor alpha (TNF-α) production by monocytes from cord blood (CB) and adult blood (AB) in response to LAM (lipoarabinomannan from Mycobacterium tuberculosis, a TLR2 ligand) and LPS (lipopolysaccharide from Escherichia coli, a TLR4 ligand). LPS or LAM-induced TNF-α production was 5 to 18 times higher in AB than in CB monocytes, whereas interleukin-1α (IL-1α) stimulated similar levels of TNF-α in both groups, suggesting that decreased responses to LPS or LAM in CB are unlikely to be due to differences in the MyD88-dependent signaling pathway. This impaired signaling was attributable, in part, to lower functional TLR4 expression, especially on CD14(+) CD16(+) monocytes, which are the primary cell subset for LPS-induced TNF-α production. Importantly, the frequency of CD14(+) CD16(+) monocytes in CB was 2.5-fold lower than in AB (P < 0.01). CB from Kenyan newborns sensitized to parasite antigens in utero had more CD14(+) CD16(+) monocytes (P = 0.02) and produced higher levels of TNF-α in response to LPS (P = 0.004) than CB from unsensitized Kenyan or North American newborns. Thus, a reduced CD14(+) CD16(+) activated/differentiated monocyte subset and a correspondingly lower level of functional TLR4 on monocytes contributes to the relatively low TNF-α response to LPS observed in immunologically naive newborns compared to the response in adults.

DRYBP Contributes to the Negative Regulation of the Drosophila Imd Pathway

The Drosophila humoral innate immune response fights infection by producing antimicrobial peptides (AMPs) through the microbe-specific activation of the Toll or the Imd signaling pathway. Upon systemic infection, the production of AMPs is both positively and negatively regulated to reach a balanced immune response required for survival. Here, we report the function of the dRYBP (drosophila Ring and YY1 Binding Protein) protein, which contains a ubiquitin-binding domain, in the Imd pathway. We have found that dRYBP contributes to the negative regulation of AMP production: upon systemic infection with Gram-negative bacteria, Diptericin expression is up-regulated in the absence of dRYBP and down-regulated in the presence of high levels of dRYBP. Epistatic analyses using gain and loss of function alleles of imd, Relish, or skpA and dRYBP suggest that dRYBP functions upstream or together with SKPA, a member of the SCF-E3-ubiquitin ligase complex, to repress the Imd signaling cascade. We propose that the role of dRYBP in the regulation of the Imd signaling pathway is to function as a ubiquitin adaptor protein together with SKPA to promote SCF-dependent proteasomal degradation of Relish. Beyond the identification of dRYBP as a novel component of Imd pathway regulation, our results also suggest that the evolutionarily conserved RYBP protein may be involved in the human innate immune response.

Whole-exome sequencing links caspase recruitment domain 11 (CARD11) inactivation to severe combined immunodeficiency

Primary immunodeficiencies represent model diseases for the mechanistic understanding of the human innate and adaptive immune response. They are clinically highly relevant per se because in patients with severe combined immunodeficiency (SCID), infections caused by opportunistic pathogens are typically life-threatening early in life. We aimed at defining and functionally characterizing a novel form of SCID in an infant of consanguineous parents who presented with life-threatening Pneumocystis jirovecii pneumonia using a comprehensive immunologic and whole-exome genetic diagnostic strategy. Analysis of leukocyte subpopulations was performed by using multicolor flow cytometry and was combined with stimulation tests for T-cell function. The search for a disease-causing mutation was performed with diagnostic whole-exome sequencing and systematic variant categorization. Reconstitution assays were used for validating the loss-of-function mutation. The novel entity of SCID was characterized by agammaglobulinemia and profoundly deficient T-cell function despite quantitatively normal T and B lymphocytes. Genetic analysis revealed a single pathogenic homozygous nonsense mutation of the caspase recruitment domain 11 (CARD11) gene. In reconstitution assays we demonstrated that the patient-derived truncated CARD11 protein is defective in antigen receptor signaling and nuclear factor κB activation. We show that an inactivating CARD11 mutation links defective nuclear factor κB signaling to a novel cause of autosomal recessive SCID.

Heat Shock Proteins and Disease Control in Aquatic Organisms

Four families of heat shock proteins (Hsps), including the small heat shock proteins (sHsps), Hsp70, Hsp90 and Hsp60, are synthesized under normal physiological conditions and in response to stress. sHsps protect proteins from irreversible denaturation independently of ATP. The remaining ATP-responsive Hsps fold nascent proteins, shield proteins from irreversible denaturation during stress and aid protein refolding. Several observations indicate that Hsps contribute to disease resistance in aquatic organisms, the first being that these proteins are produced in finfish, shellfish and bivalves upon infection with viral and bacterial pathogens. Induction of Hsp synthesis by heat shock and incubation with chemicals such as Pro-Tex® boosts resistance to pathogens, as does administration of exogenous Hsps to host organisms. The extent of Hsp accumulation and the increase in disease tolerance are generally correlated with one another. Not only do Hsps protect against pathogens by functioning as molecular chaperones, but they are thought to mediate humoral and cellular innate immune responses. Hsp70 is highly immunogenic and serves as a ligand for Toll-like receptors. Hsps elicit cytokine production and they deliver peptides to antigen presenting cells via major histocompatibility complexes (MHC). Vaccines have been produced for use in aquaculture by employing Hsps, either alone or fused to antigens obtained from pathogens. Hsps offer several advantages over current methods for the treatment of disease in commercially important organisms and they are being increasingly exploited as their roles in protein chaperoning and immune modulation are better understood.

Beyond RV144 Efficacy Results: An Update

The RV144 efficacy trial conducted in Thailand provided the first evidence that an HIV vaccine could provide a modest level of protection against HIV acquisition (31.2% at 42 months of follow-up) in populations at low risk for HIV infection. Vaccine efficacy appeared to be higher (60%) at 12 months post vaccination, suggesting an early, but nondurable, vaccine effect. This breakthrough finding led to identification of immune correlates of risk, antibodies directed against the V2 loop, paving the way to new vaccine designs and clinical trials to better characterization of the vaccine-induced adaptive and innate humoral and cell-mediated immune responses in peripheral and mucosal compartments. Whether the RV144 correlates of risk are universal and apply to other populations at higher risk for HIV acquisition and other modes of transmission (rectal, injecting drug users) is unknown and remains to be explored. Future efficacy trials using a similar vaccine concept tested in high-risk heterosexual populations and in men having sex with men are planned.

Editorial: Gazing forward while looking back

Discussion of how transcriptional responses of neutrophils contribute to the resolution of inflammation, and direct studies of human innate immune responses.

Respiratory Syncytial Virus Regulates Human MicroRNAs by Using Mechanisms Involving Beta Interferon and NF-κB

ABSTRACTRespiratory syncytial virus (RSV) is the most common viral cause of severe lower respiratory tract illness in infants and children. The virus replicates in polarized epithelial cells in the airway and, to a lesser extent, infects airway antigen-presenting cells, such as dendritic cells (DCs). RSV possesses a number of expressed genes that antagonize the effect of type I interferons and other related host factor pathways that inhibit replication efficiency. Virus infection alters host gene transcription and the translation of host transcripts through specific antagonism of the function of host proteins, through induction of RNA stress granules, and through induction of altered patterns of host gene expression. In healthy cells, microRNAs (miRNAs) regulate gene expression by targeting the noncoding region of mRNA molecules to cause silencing or degradation of transcripts. It is not known whether or not RSV infection alters the level of microRNAs in cells. We profiled the pattern of expression of host cell microRNAs in RSV-infected epithelial cells or DCs and found that RSV did alter microRNA expression but in a cell-type-specific manner. The studies showed that let-7b was upregulated in DCs, while let-7i and miR-30b were upregulated in epithelial cells in a process that required viral replication. Interestingly, we found that the RSV nonstructural genes NS1 and NS2 antagonized the upregulation of let-7i and miR-30b. RSV appears to manipulate host cell gene expression through regulation of expression of miRNAs related to the interferon response. The data suggest a new mechanism of virus-host cell interactions for paramyxoviruses.

The bitter taste of infection

The human innate immune response to pathogens is complex, and it has been difficult to establish the contribution of epithelial signaling in the prevention of upper respiratory tract infection. The prevalence of chronic sinusitis in the absence of systemic immune defects indicates that there may be local defects in innate immunity associated with such mucosal infections. In this issue of the JCI, Cohen and colleagues investigate the role of the bitter taste receptors in airway epithelial cells, and find that these are critical to sensing the presence of invading pathogens.

The Lysozyme-Induced Peptidoglycan N -Acetylglucosamine Deacetylase PgdA (EF1843) Is Required for Enterococcus faecalis Virulence

Lysozyme is a key component of the innate immune response in humans that provides a first line of defense against microbes. The bactericidal effect of lysozyme relies both on the cell wall lytic activity of this enzyme and on a cationic antimicrobial peptide activity that leads to membrane permeabilization. Among Gram-positive bacteria, the opportunistic pathogen Enterococcus faecalis has been shown to be extremely resistant to lysozyme. This unusual resistance is explained partly by peptidoglycan O-acetylation, which inhibits the enzymatic activity of lysozyme, and partly by d-alanylation of teichoic acids, which is likely to inhibit binding of lysozyme to the bacterial cell wall. Surprisingly, combined mutations abolishing both peptidoglycan O-acetylation and teichoic acid alanylation are not sufficient to confer lysozyme susceptibility. In this work, we identify another mechanism involved in E. faecalis lysozyme resistance. We show that exposure to lysozyme triggers the expression of EF1843, a protein that is not detected under normal growth conditions. Analysis of peptidoglycan structure from strains with EF1843 loss- and gain-of-function mutations, together with in vitro assays using recombinant protein, showed that EF1843 is a peptidoglycan N-acetylglucosamine deacetylase. EF1843-mediated peptidoglycan deacetylation was shown to contribute to lysozyme resistance by inhibiting both lysozyme enzymatic activity and, to a lesser extent, lysozyme cationic antimicrobial activity. Finally, EF1843 mutation was shown to reduce the ability of E. faecalis to cause lethality in the Galleria mellonella infection model. Taken together, our results reveal that peptidoglycan deacetylation is a component of the arsenal that enables E. faecalis to thrive inside mammalian hosts, as both a commensal and a pathogen.

Apolipoprotein B100 is a suppressor of Staphylococcus aureus‐induced innate immune responses in humans and mice

Plasma lipoproteins such as LDL (low-density lipoprotein) are important therapeutic targets as they play a crucial role in macrophage biology and metabolic disorders. The impact of lipoprotein profiles on host defense pathways against Gram-positive bacteria is poorly understood. In this report, we discovered that human serum lipoproteins bind to lipoteichoic acid (LTA) from Staphylococcus aureus and thereby alter the immune response to these bacteria. Size-exclusion chromatography and solid-phase-binding analysis of serum revealed the direct interaction of LTA with apolipoproteins (Apo) B100, ApoA1, and ApoA2. Only ApoB100 and the corresponding LDL exerted biological effects as this binding significantly inhibited LTA-induced cytokine releases from human and murine immune cells. Serum from hypercholesterolemic mice or humans significantly diminished cytokine induction in response to S. aureus or its LTA. Sera taken from the patients with familial hypercholesterolemia before and after ApoB100-directed immuno-apheresis confirmed that ApoB100 inhibited LTA-induced inflammation in humans. In addition, mice in which LDL secretion was pharmacologically inhibited, displayed significantly increased serum cytokine levels upon infection with S. aureus in vivo. The present study identifies ApoB100 as an important suppressor of innate immune activation in response to S. aureus and its LTA.

Defensin like peptide from Panulirus argus relates structurally with beta defensin from vertebrates

Naturally occurring antimicrobial peptides take place in the first line of host defense against pathogen as part of the humoral innate immune response. β-defensins are among the most abundant antimicrobial peptides in mammals, and thought to be solely found in vertebrates until a recent report describing the cloning and sequencing of defensin like peptides in the spiny lobster Panulirus japonicus. In the current study, we cloned and sequenced two genes from the hemocytes of the spiny lobster Panulirus argus encoding for two isoforms of defensin-like peptides, thus confirming the presence of this protein in the Panulirus genus. The 44 amino acids mature peptides showed the conservation of cysteine pattern characterizing the β-defensins, as well as known amino acids residues critical to exert their antimicrobial activity. They are also amphipathics, hydrophobics, and display an overall positive charge (+1) located at the C-terminus. The tertiary structure obtained by homology modeling indicated that likely conformations of lobster peptides are highly similar to β-defensins from vertebrates. The phylogenetic study carried out by probabilistic methods confirmed the relation with ancestral β-defensin from vertebrates. The finding of a putative defensin-like peptide in the expressed sequence tag (EST) of the lobster Homarus americanus with high homology with those of P. argus described in this study, would indicate the presence of this peptides in Palinuridae family. Taking into account all similarities between these peptides with β-defensins from vertebrates, it is conceivable to further support the finding of a new family of β-defensins in invertebrate.