N-Glycosylation Of Human ITP Autoantibodies Affects Complement Activation, Platelet Phagocytosis, and Platelet Survival In a Murine Model

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 569-569
Author(s):  
Ulrich J. Sachs ◽  
Kathrin Walek ◽  
Annika Krautwurst ◽  
Mathias J. Rummel ◽  
Gregor Bein ◽  
...  
Keyword(s):  
Complement Activation ◽  
Laser Scanning ◽  
Conflicts Of Interest ◽  
Human Platelets ◽  
Laser Scanning Microscopy ◽  
Platelet Survival ◽  
Scid Mouse Model ◽  
Rapid Clearance

Abstract Introduction Immune thrombocytopenia (ITP) is a bleeding disorder caused by IgG autoantibodies (AAbs) directed against platelets. The IgG effector functions of autoantibodies depend on their Fc-constant region which undergoes posttranslational glycosylation. We investigated the role of Asn279-linked N-glycan of AAbs in vitro and in vivo. Material and Methods AAbs were purified from ITP patients (n=15) and controls (n=10) and N-glycans were enzymatically cleaved by endoglycosidase F. The effects of native AAbs and deglycosylated AAbs (deAAbs) were compared in vitro on enhancement of phagocytosis of platelets by monocytes and complement fixation and activation applying flow cytometry, laser scanning microscopy, and a complement consumption assay. The capability of AAbs and deAAbs to eliminate human platelets in vivo was studied in a NOD/SCID mouse model in presence and absence of a complement source. Results AAb-induced platelet phagocytosis was inhibited by N-glycan cleavage (median phagocytic activity: 8% vs. 0.8%, p=0.004). Seven out of 15 native AAbs bound C1q and induced complement consumption. N-glycan cleavage significantly reduced C1q binding (MFI 16.4 vs. 4.9, p=0.017) and complement consumption. In vivo survival of human PLTs was assessed after cotransfusion with native or deAAbs in NOD/SCID mice. Injection of AAbs resulted in rapid clearance of human platelets compared to control (platelet clearance after 5h (CL5h) 75% vs. 30%, p<0.001). AAbs that were able to activate complement induced more pronounced platelet clearance in the presence of complement compared to the clearance in the absence of complement (CL5h 82% vs. 62%, p=0.003). AAbs lost their ability to destroy platelets in vivo after deglycosylation (CL5h42%, p<0.001). Conclusion Removal of N-glycan from AAbs interferes with Fc-mediated phagocytosis and complement activation and thereby prolongs platelet survival in vivo. Our study provides tools for better characterizing ITP AAbs and sheds light on the heterogeneity of AAbs in ITP. Clinical studies should aim to assess such additional characteristics, since this could lead to the identification of ITP patient subgroups with increased responses to specific or new interventions such as, targetting complement factors. Disclosures: No relevant conflicts of interest to declare.

Glycosylation of autoantibodies: Insights into the mechanisms of immune thrombocytopenia

2013 ◽  
Vol 110 (12) ◽  
pp. 1259-1266 ◽  
Author(s):  
Tamam Bakchoul ◽  
Kathrin Walek ◽  
Annika Krautwurst ◽  
Mathias Rummel ◽  
Gregor Bein ◽  
...  
Keyword(s):  
Immune Thrombocytopenia ◽  
Laser Scanning ◽  
Human Platelets ◽  
Laser Scanning Microscopy ◽  
Effector Functions ◽  
Scid Mouse Model ◽  
Rapid Clearance

SummaryImmune thrombocytopenia (ITP) is a bleeding disorder caused by IgG autoantibodies (AAbs) directed against platelets (PLTs). IgG effector functions depend on their Fc-constant region which undergoes post-translational glycosylation. We investigated the role of Asn279-linked N-glycan of AAbs in vitro and in vivo. AAbs were purified from ITP patients (n=15) and N-glycans were enzymatically cleaved by endoglycosidase F. The effects of native AAbs and deglycosylated AAbs were compared in vitro on enhancement of phagocytosis of platelets by monocytes and complement fixation and activation applying flow cytometry, laser scanning microscopy, and a complement consumption assay. AAb-induced platelet phagocytosis was inhibited by N-glycan cleavage (median phagocytic activity: 8% vs 0.8%, p=0.004). Seven out of 15 native AAbs bound C1q and activated complement. N-glycan cleavage significantly reduced both effects. In vivo survival of human PLTs was assessed after co-transfusion with native or N-glycan cleaved AAbs in a NOD/SCID mouse model. Injection of AAbs resulted in rapid clearance of human platelets compared to control (platelet clearance after 5h (CL5h) 75% vs 30%, p<0.001). AAbs that were able to activate complement induced more pronounced platelet clearance in the presence of complement compared to the clearance in the absence of complement (CL5h 82% vs 62%, p=0.003). AAbs lost their ability to destroy platelets in vivo after deglycosylation (CL5h 42%, p<0.001). N-glycosylation of human ITP AAbs appears to be required for platelet phagocytosis and complement activation, reducing platelet survival in vivo. Posttranslational modification of AAbs may constitute an important determinant for the clinical manifestation of ITP.

scholarly journals Mechanism of Action of Hydroxychloroquine in the Antiphospholipid Syndrome

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 5023-5023
Author(s):  
Nadine Müller-Calleja ◽  
Davit Manukyan ◽  
Wolfram Ruf ◽  
Karl Lackner
Keyword(s):  
Antiphospholipid Syndrome ◽  
Lupus Erythematosus ◽  
Laser Scanning ◽  
Conflicts Of Interest ◽  
Thrombus Formation ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
In Vivo Model

Abstract Objective. The antiphospholipid syndrome (APS) is characterized by thromboembolic events and/or recurrent abortions in the presence of pathogenic antiphospholipid antibodies (aPL). Hydroxychloroquine (HCQ) is recommended for thromboprophylaxis in patients with systemic lupus erythematosus and aPL. We aimed at identifying mechanisms responsible for the beneficial effects of HCQ in the APS. Methods. Monocytic cells were stimulated with human aPL in vitro and expression of tissue factor (TF) and tumor necrosis factor (TNFα) was quantified by qRT-PCR. For intracellular ROS detection, cells were stained with OxyBurst and analyzed by flow cytometry. Live cell imaging was performed by confocal laser scanning microscopy to show translocation of NADPH oxidase 2 (NOX2) and TLR8 on stimulation. Finally, the effect of HCQ was tested in an in vivo model of venous thrombosis. Results. HCQ prevents the induction of TF and TNFα by aPL in MonoMac1 cells, by blocking the activation of endosomal NOX2. This latter effect is not mediated by direct interference with the previously described uptake of aPL into the endosome but by inhibiting the recruitment of the catalytic subunit of NOX2 (gp91phox) into the endosome. Furthermore, HCQ protects mice from aPL induced and NOX2 mediated thrombus formation in vivo. Conclusion. We propose that interference with the assembly of endosomal NOX2 is a major effect of HCQ responsible for its antithrombotic effect in the APS. Since most if not all APS patients harbor aPL that activate endosomal NOX2 this probably explains the well established efficacy of HCQ in APS patients. Disclosures No relevant conflicts of interest to declare.

Vacuoles Induced in Mammalian Cells by Helicobacter Cytotoxin are Acidic Organelles

1990 ◽  
Vol 48 (3) ◽  
pp. 168-169
Author(s):  
M. H. Chestnut ◽  
C. E. Catrenich
Keyword(s):  
Acridine Orange ◽  
Mammalian Cells ◽  
Laser Scanning ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Ulcer Disease ◽  
Gastroduodenal Disease ◽  
H Pylori

Helicobacter pylori is a non-invasive, Gram-negative spiral bacterium first identified in 1983, and subsequently implicated in the pathogenesis of gastroduodenal disease including gastritis and peptic ulcer disease. Cytotoxic activity, manifested by intracytoplasmic vacuolation of mammalian cells in vitro, was identified in 55% of H. pylori strains examined. The vacuoles increase in number and size during extended incubation, resulting in vacuolar and cellular degeneration after 24 h to 48 h. Vacuolation of gastric epithelial cells is also observed in vivo during infection by H. pylori. A high molecular weight, heat labile protein is believed to be responsible for vacuolation and to significantly contribute to the development of gastroduodenal disease in humans. The mechanism by which the cytotoxin exerts its effect is unknown, as is the intracellular origin of the vacuolar membrane and contents. Acridine orange is a membrane-permeant weak base that initially accumulates in low-pH compartments. We have used acridine orange accumulation in conjunction with confocal laser scanning microscopy of toxin-treated cells to begin probing the nature and origin of these vacuoles.

The fate of medial edge epithelial cells during palatal fusion in vitro: an analysis by DiI labelling and confocal microscopy

Development ◽  
1992 ◽  
Vol 114 (2) ◽  
pp. 379-388 ◽  
Author(s):  
M.J. Carette ◽  
M.W. Ferguson
Keyword(s):  
Laser Scanning ◽  
Time Course ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Palatal Fusion ◽  
Morphological Criteria ◽  
Medial Edge ◽  
Mesenchymal Transformation

Fusion of bilateral shelves, to form the definitive mammalian secondary palate, is critically dependent on removal of the medial edge cells that constitute the midline epithelial seam. Conflicting views suggest that programmed apoptotic death or epithelial-mesenchymal transformation of these cells is predominantly involved. Due in part to the potentially ambiguous interpretation of static images and the notable absence of fate mapping studies, the process by which this is achieved has, however, remained mechanistically equivocal. Using an in vitro mouse model, we have selectively labelled palatal epithelia with DiI and examined the fate of medial edge epithelial (MEE) cells during palatal fusion by localisation using a combination of conventional histology and confocal laser scanning microscopy (CLSM). In dynamic studies using CLSM, we have made repetitive observations of the same palatal cultures in time-course investigations. Our results concurred with the established morphological criteria of seam degeneration; however, they provided no evidence of MEE cell death or transformation. Instead we report that MEE cells migrate nasally and orally out of the seam and are recruited into, and constitute, epithelial triangles on both the oral and nasal aspects of the palate. Subsequently these cells become incorporated into the oral and nasal epithelia on the surface of the palate. We hypothesize an alternative method of seam degeneration in vivo which largely conserves the MEE population by recruiting it into the nasal and oral epithelia.

Consequences of topoisomerase II inhibition in early embryogenesis of Drosophila revealed by in vivo confocal laser scanning microscopy

1993 ◽  
Vol 104 (4) ◽  
pp. 1175-1185 ◽  
Author(s):  
P. Buchenau ◽  
H. Saumweber ◽  
D.J. Arndt-Jovin
Keyword(s):  
Confocal Laser Scanning Microscopy ◽  
Laser Scanning ◽  
Topoisomerase Ii ◽  
Metaphase Plate ◽  
Laser Scanning Microscopy ◽  
Confocal Laser Scanning ◽  
Scanning Microscopy ◽  
Confocal Laser

The regulation of DNA topology by topoisomerase II from Drosophila melanogaster has been studied extensively by biochemical methods but little is known about its roles in vivo. We have performed experiments on the inhibition of topoisomerase II in living Drosophila blastoderm embryos. We show that the enzymatic activity can be specifically disrupted by microinjection of antitopoisomerase II antibodies as well as the epipodophyllotoxin VM26, a known inhibitor of topoisomerase II in vitro. By labeling the chromatin of live embryos with tetramethylrhodamine-coupled histones, the effects of inhibition on nuclear morphology and behaviour was followed in vivo using confocal laser scanning microscopy. Both the antibodies and the drug prevented or hindered the segregation of chromatin daughter sets at the anaphase stage of mitosis. In addition, high concentrations of inhibitor interfered with the condensation of chromatin and its proper arrangement into the metaphase plate. The observed effects yielded non-functional nuclei, which were drawn into the inner yolk mass of the embryo. Concurrently, undamaged nuclei surrounding the affected region underwent compensatory division, leading to the restoration of the nuclear population, and thereby demonstrating the regulative capacity of Drosophila blastoderm embryos.

scholarly journals Astrogliosis in an Experimental Model of Hypovitaminosis B12: A Cellular Basis of Neurological Disorders due to Cobalamin Deficiency

Cells ◽  
2020 ◽  
Vol 9 (10) ◽  
pp. 2261
Author(s):  
Zuzanna Rzepka ◽  
Jakub Rok ◽  
Justyna Kowalska ◽  
Klaudia Banach ◽  
Justyna Magdalena Hermanowicz ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Laser Scanning Microscopy ◽  
Cobalamin Deficiency ◽  
Confocal Laser ◽  
In Vivo Model ◽  
Cellular Expression ◽  
Wide Range ◽  
Vitro Model

Cobalamin deficiency affects human physiology with sequelae ranging from mild fatigue to severe neuropsychiatric abnormalities. The cellular and molecular aspects of the nervous system disorders associated with hypovitaminosis B12 remain largely unknown. Growing evidence indicates that astrogliosis is an underlying component of a wide range of neuropathologies. Previously, we developed an in vitro model of cobalamin deficiency in normal human astrocytes (NHA) by culturing the cells with c-lactam of hydroxycobalamin (c-lactam OH-Cbl). We revealed a non-apoptotic activation of caspases (3/7, 8, 9) in cobalamin-deficient NHA, which may suggest astrogliosis. The aim of the current study was to experimentally verify this hypothesis. We indicated an increase in the cellular expression of two astrogliosis markers: glial fibrillary acidic protein and vimentin in cobalamin-deficient NHA using Western blot analysis and immunocytochemistry with confocal laser scanning microscopy. In the next step of the study, we revealed c-lactam OH-Cbl as a potential non-toxic vitamin B12 antagonist in an in vivo model using zebrafish embryos. We believe that the presented results will contribute to a better understanding of the cellular mechanism underlying neurologic pathology due to cobalamin deficiency and will serve as a foundation for further studies.

Hepatocytes Ingest Longterm Refrigerated Platelets: A Novel Platelet Clearance Mechanism.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1523-1523 ◽  
Author(s):  
Viktoria Rumjantseva ◽  
Emma C. Josefsson ◽  
Hans Wandall ◽  
John H. Hartwig ◽  
Thomas P. Stossel ◽  
...  
Keyword(s):  
Cold Storage ◽  
Fluorescent Microscopy ◽  
Hepatic Clearance ◽  
Human Platelets ◽  
Lectin Domain ◽  
Clearance Mechanism ◽  
Rapid Clearance

Abstract We previously reported that the lectin domain of αMβ2 receptors on hepatic macrophages mediates rapid clearance of washed murine platelets transfused after refrigeration for 2 hours, recognizing exposed βN-acetylglucosamine (βGlcNAc) residues of N-linked glycans on clustered platelet GPIbα molecules and that the same receptors elicit phagocytosis of refrigerated human platelets human macrophages in vitro. A platelet-associated galactosyltransferase catalyzes the covering of βGlcNAc residues with galactose in the presence of UDP-galactose, thereby blocking clearance of cold mouse platelets in vivo and phagocytosis of human platelets in vitro. These intriguing findings contradicted earlier evidence that refrigeration of human platelets procured for transfusion only promotes their rapid clearance after prolonged (>8h) incubation and also are inconsistent with the well-known recognition system for exposed galactose residues through asialoglycoprotein (ASGP) receptors. Reconciling these contradictions, we report that the absence of plasma during storage accounts for the differences in time of exposure to cold to promote clearance and that mouse platelets cold-stored in plasma also only clear rapidly after long-term (48h) storage. We also found that hepatic clearance of long-term cold-stored (LTCS) mouse platelets occurs in hepatocytes. Streptavidin-POD staining revealed abundant LTCS biotinylated platelets in hepatocyte phagosomes. Furthermore, cells of the hepatocyte HepG2 line avidly ingest fluorescently-labeled LTCS human platelets (7-fold above the baseline of room-temperature-stored platelets), as evidenced by flow cytometry, fluorescent microscopy and by time-laps video microscopy. Long-term cold storage increases by ~1.7-fold platelet binding of the galactose-specific lectin RCA I, implying that with long-term cold storage, exposed galactose residues cluster sufficiently to induce recognition by hepatocyte ASGPR receptors. The results define a new clearance mechanism, representing the first example of blood cell removal by a non-myeloid cell. Since we find that human platelets also express a cell surface sialotransferase that adds sialic acid to galactose residues, we suggest that a combination of sialylation and glactosylation, achievable by addition of sugar substrates alone, might accommodate long-term cold storage of platelets for transfusion.

Dynamics of Cytokine Capture Within Hemoadsorption Beads Used to Treat Sepsis

2009 ◽  
Author(s):  
Jeremy D. Kimmel ◽  
Morgan V. DiLeo ◽  
Isabella E. Valenti ◽  
Gregory A. Gibson ◽  
Simon C. Watkins ◽  
...  
Keyword(s):  
Inflammatory Cytokines ◽  
Laser Scanning ◽  
Medical Condition ◽  
Ex Vivo ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Adsorption Dynamics ◽  
The Us ◽  
Rapid Clearance

Sepsis is a serious medical condition characterized by systemic inflammation caused by infection, and affects more than 750,000 individuals per year in the US, with a mortality rate of approximately 30% [1]. The pathophysiology of sepsis is complex and not entirely understood, but is believed to be related to the dysfunction of multiple interdependent humoral mediator pathways, including redundant release of inflammatory cytokines [2]. Removal of both pro- and anti-inflammatory cytokines from the circulating blood is believed to be a promising therapy for severe sepsis [3]. We are developing an extracorporeal hemoadsorption device to remove cytokines from the blood using a novel, biocompatible, sorbent bead technology. A simple model was developed to characterize cytokine adsorption within hemoadsorption beads [4]. Despite rapid clearance of cytokines with hemoadsorption in an ex vivo murine sepsis model [5], our model analysis predicted that only the outer 20μm of each sorbent bead (avg diam = 450μm) adsorbed cytokine. In this work, we used in vitro column capture experiments and confocal laser scanning microscopy (CLSM) to examine cytokine adsorption dynamics within hemoadsorption beads.

scholarly journals Enhancement of Vancomycin Activity against Biofilms by Using Ultrasound-Targeted Microbubble Destruction

2011 ◽  
Vol 55 (11) ◽  
pp. 5331-5337 ◽  
Author(s):  
Nianan He ◽  
Jian Hu ◽  
Huayong Liu ◽  
Tao Zhu ◽  
Beijian Huang ◽  
...  
Keyword(s):  
Staphylococcus Epidermidis ◽  
Laser Scanning ◽  
Rabbit Model ◽  
Antibiotic Activity ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Content Type ◽  
Implanted Medical Devices

ABSTRACTTreating biofilm infections on implanted medical devices is formidable, even with extensive antibiotic therapy. The aim of this study was to investigate whether ultrasound (US)-targeted microbubble (MB) destruction (UTMD) could enhance vancomycin activity againstStaphylococcus epidermidisRP62A biofilms. Twelve-hour biofilms were treated with vancomycin combined with UTMD. The vancomycin and MB (SonoVue) were used at concentrations of 100 μg/ml and 30% (vol/vol), respectively, in studiesin vitro. After US exposure (0.08 MHz, 1.0 W/cm2, 50% duty cycle, and 10-min duration), the biofilms were cultured at 37°C for another 12 h. The results showed that many micropores were found in biofilms treated with vancomycin combined with UTMD. Biofilm densities (A570values) and the viable counts ofS. epidermidisrecovered from the biofilm were significantly decreased compared with those of any other groups. Furthermore, the highest percentage of dead cells was found, using confocal laser scanning microscopy, in the biofilm treated with vancomycin combined with UTMD. The viable counts of bacteria in biofilms in anin vivorabbit model also confirmed the enhanced effect of vancomycin combined with UTMD. UTMD may have great potential for improving antibiotic activity against biofilm infections.

scholarly journals Characterization of a mucoid-like Pseudomonas aeruginosa biofilm

Fine Focus ◽  
2015 ◽  
Vol 1 (2) ◽  
pp. 121-137
Author(s):  
Brandon M. Bauer ◽  
Lewis Rogers ◽  
Monique Macias ◽  
Gabriella Iacovetti ◽  
Alexander M. Woodrow ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Laser Scanning ◽  
Growth Conditions ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Chronic Infections ◽  
Planktonic Bacteria ◽  
The Difference

Pseudomonas aeruginosa biofilms are implicated in chronic infections. A key element of P. aeruginosapathogenicity is the formation of a biofilm, a community of bacteria encased in an exopolymeric substance (EPS) that shields the bacteria from the host immune response and antibiotic treatment. A crucial step in biofilm production is a switch in motility from freely swimming, planktonic bacteria to twitching movement and then to attached and sedentary bacteria that develop into a mature pillar-shaped biofilm. A mucoid biofilm produces an excess of alginate and is clinically the most pathogenic and the most resistant to antibiotics. Biofilms from patients exhibit a wide variety of structure, motility, and levels of attachment. In vitrobiofilms do not exhibit such a wide variety of structure and physiology. The difference between in vivo and in vitro biofilms has made the translation of in vitro studies into in vivo treatments difficult. Under different growth conditions in our lab, the P. aeruginosa strain PAO1 demonstrates two phenotypes: a non-mucoid and a mucoid-like phenotype. Confocal laser scanning microscopy (CLSM) indicates the mucoid-like phenotype is intermediate in height to the non-mucoid phenotype and biofilms formed in a once-flow-through chamber. Both mucoid-like and non-mucoid phenotypes exhibit a significant increase in twitching between 24 and 72 hours of development. The mucoid-like phenotype had greater attachment at 72 hours compared to non-mucoid phenotype. Therefore, the two phenotypes observed in our lab may represent the effect of environment to stimulate development of two types of biofilms by PAO1.

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