PubMed Health⌕ Search

Biomedical subjects

M Exner

Publications and source records attributed to M Exner.

At least 73 records · Page 4Linked to original sources
PubMed1998

Immunochemical characterization of Na+/H+ exchanger isoform NHE4.

Mammalian Na+/H+ exchangers (NHEs) are a family of transport proteins (NHE1-NHE5). To date, the cellular and subcellular localization of NHE4 has not been characterized using immunochemical techniques. We purified a fusion protein containing a portion of rat NHE4 (amino acids 565-675) to use as immunogen. A monoclonal antibody (11H11) was selected by ELISA. It reacted specifically with both the fusion protein and to a 60- to 65-kDa polypeptide expressed in NHE4-transfected LAP1 cells. By Western blot analysis, NHE4 was identified as a 65- to 70-kDa protein that was expressed most abundantly in stomach and in multiple additional epithelial and nonepithelial rat tissues including skeletal muscle, heart, kidney, uterus, and liver. Subcellular localization of NHE4 in the kidney was evaluated by Western blot analysis of membrane fractions isolated by Percoll gradient centrifugation. NHE4 was found to cofractionate with the basolateral markers NHE1 and Na+-K+-ATPase rather than the luminal marker gamma-glutamyl transferase. In stomach, NHE4 was detected by immunoperoxidase labeling on the basolateral membrane of cells at the base of the gastric gland. We conclude that NHE4 is a 65- to 70-kDa protein with a broad tissue distribution. In two types of epithelial cells, kidney and stomach, NHE4 is localized to the basolateral membrane.

Animals↗
PubMed1998

All four putative ligand-binding domains in megalin contain pathogenic epitopes capable of inducing passive Heymann nephritis.

Megalin (gp330) is the main target antigen involved in the induction of Heymann nephritis (HN), a rat model of human membranous nephropathy. Its large extracellular region contains four putative ligand-binding domains separated by spacer regions. Previously, it was reported that the second ligand-binding domain (LBD II) of megalin is involved in the pathogenesis of passive HN because it is capable of binding antibodies in vivo and initiating formation of immune deposits (ID). This study explores the possibility that pathogenic epitopes might also be present in the other putative ligand-binding domains. Recombinant fragments of ligand-binding domains (LBD) I through IV expressed in a baculovirus system were used to generate polyclonal domain-specific antibodies. Antibodies raised against each of the recombinant megalin fragments reacted preferentially with its respective antigen and with whole megalin by immunoblotting. Each of the antibodies also gave a characteristic brush-border staining for megalin by indirect immunofluorescence on rat kidney. When rats were injected with the domain-specific antibodies to test their ability to produce passive HN, glomerular ID were present in kidneys of all injected animals. The staining pattern in glomeruli of rats injected with LBD I, III, or IV was similar to that obtained with antibodies to LBD II. It is concluded that passive HN can be induced with antibodies against LBD I, III, and IV, as well as LBD II, and that each of the ligand-binding domains contains a pathogenic epitope. These findings provide further evidence for the multiple epitope model of HN.

Animals↗
PubMed1997

Pathogenic antibodies inhibit the binding of apolipoproteins to megalin/gp330 in passive Heymann nephritis.

Megalin/gp330 is an endocytic receptor that internalizes multiple ligands including apolipoproteins E (apo E) and B100 (apo B). Megalin is the main antigenic target in passive Heymann nephritis (pHN), where it binds circulating autoantibodies leading to the formation of subepithelial immune deposits (ID)-the hallmark of pHN. Apo E and apo B were found recently to accumulate within these IDs, and evidence was provided that their lipids may undergo peroxidation, causing glomerular basement membrane damage and proteinuria. Here we investigated if ID-forming antimegalin IgG can inhibit the binding and internalization of apo E-betaVLDL (very low density lipoprotein) by megalin, and lead to their accumulation within IDs. By immunoelectron microscopy, apo E and apo B were detected in clathrin-coated pits and multivesicular bodies of podocytes in control rats, suggesting that the uptake of lipoproteins is a constitutive function of the glomerular epithelium. When pHN was induced by intravenous injection of antimegalin IgG, apo E and apo B were found within IDs by immunofluorescence and immunoelectron microscopy. Bound antibodies eluted from glomeruli of rats with pHN were found to inhibit the binding and internalization of apo E-enriched betaVLDL by megalin. These results indicate that pHN-inducing antimegalin IgG is capable of interfering with the uptake of lipoproteins by megalin in vivo during the formation of IDs.

Animals↗
PubMed1997

Altered Golgi localization of core 2 beta-1,6-N-acetylglucosaminyltransferase leads to decreased synthesis of branched O-glycans.

Mucin type O-glycans with core 2 branches are distinct from nonbranched O-glycans, and the amount of core 2 branched O-glycans changes dramatically during T cell differentiation. This oligosaccharide is synthesized only when core 2 beta-1, 6-N-acetylglucosaminyltransferase (C2GnT) is present, and the expression of this glycosyltransferase is highly regulated. To understand how O-glycan synthesis is regulated by the orderly appearance of glycosyltransferases that form core 2 branched O-glycans, the subcellular localization of C2GnT was determined by using antibodies generated that are specific to C2GnT. The studies using confocal light microscopy demonstrated that C2GnT was localized mainly in cis to medial-cisternae of the Golgi. We then converted C2GnT to a trans-Golgi enzyme by replacing its Golgi retention signal with that of alpha-2,6-sialyltransferase, which resides in trans-Golgi. Chinese hamster ovary cells expressing wild type C2GnT and the chimeric C2GnT were then subjected to oligosaccharide analysis. The results obtained clearly indicate that the conversion of C2GnT into a trans-Golgi enzyme resulted in a substantial decrease of core 2 branched oligosaccharides. These results, taken together, strongly suggest that the predominance of core 2 branched oligosaccharides in those cells expressing C2GnT is due to the fact that C2GnT is located earlier in the Golgi than alpha-2,3-sialyltransferase that competes with C2GnT for the common substrate. Furthermore, alteration of Golgi localization renders the chimeric C2GnT much less efficient in synthesizing core 2 branched oligosaccharides, indicating the critical role of orderly subcellular localization of glycosyltransferases.

Animals↗
PubMed1997

Identification of the second cluster of ligand-binding repeats in megalin as a site for receptor-ligand interactions.

Megalin is a large cell surface receptor that mediates the binding and internalization of a number of structurally and functionally distinct ligands from the lipoprotein and protease:protease inhibitor families. To begin to address how megalin is able to bind ligands with unique structurally properties, we have mapped a binding site for apolipoprotein E (apoE)-beta very low density lipoprotein (beta VLDL), lipoprotein lipase, aprotinin, lactoferrin, and the receptor-associated protein (RAP) within the primary sequence of the receptor. RAP is known to inhibit the binding of all ligands to megalin. We identified a ligand-binding site on megalin by raising mAb against purified megalin, selected for a mAb whose binding to megalin is inhibited by RAP, and mapped the epitope for this mAb. mAb AC10 inhibited the binding of apoE-beta VLDL, lipoprotein lipase, aprotinin, and lactoferrin to megalin in a concentration-dependent manner. When cDNA fragments encoding the four cysteine-rich ligand-binding repeats in megalin were expressed in a baculovirus system and immunoblotted with AC10, it recognized only the second cluster of ligand-binding repeats. The location of the epitope recognized by mAb AC10 within this domain was pinpointed to amino acids 1111-1210. From these studies we conclude that the binding of apoE-beta VLDL, lactoferrin, aprotinin, lipoprotein lipase, and RAP to megalin is either competitively or sterically inhibited by mAb AC10 suggesting that these ligands bind to the same or closely overlapping sites within the second cluster of ligand-binding repeats.

Animals↗
PubMed1997

A novel variant of lysosomal acid lipase in cholesteryl ester storage disease associated with mild phenotype and improvement on lovastatin.

Cholesterol ester storage disease (CESD) is a rare congenital disorder of lipid metabolism, with mutation of the lysosomal acid lipase gene, causing chronic liver disease, usually before adolescence. We here describe three adult siblings with CESD diagnosed by light microscopic demonstration of excessive lysosomal storage of lipids with accumulation of foamy cells in liver biopsies and by a decrease in acid lipase activity (2-3% of controls). One patient (male, 46a) had extensive liver fibrosis, another (female, 58a) had cirrhosis of the liver. The third patient had died from variceal haemorrhage (female, 56a). Using sequence analysis of RT-PCR products of LAL mRNA, the patients were identified as compound heterozygotes for a G-->A substitution at position -1 of the exon 8 splice donor site and a point mutation at the second allele, resulting in a His108-->Pro shift. In two patients, therapy with lovastatin was initiated, which led to normalisation of serum cholesterol and triglyceride levels. After 12 months, liver biopsy demonstrated a significant decrease in vacuolisation of hepatocytes, with fewer and smaller droplets. Semi-automated computer-assisted image analysis of electron microscopic sections demonstrated a decrease in the hepatocellular lysosomal area from 20.5+/-7.1% to 11.7+/-6.5% (p<0.05) and 41.7+/-5.1% to 33.4+/-4.4% (p<0.01). We conclude that in two siblings with a novel LAL variant and mild phenotype of CESD, lovastatin decreased both serum lipid concentrations and hepatocellular lysosomal content.

Anticholesteremic Agents↗
PubMed1997

[Basic principles of infection surveillance].

This paper reviews the ideas of Robert Koch in the context of infection surveillance of typhoid fever in Trier in 1902 and the actual epidemiological situation of infectious diseases in the world. The plan of the EC Commission for a network for surveillance and control of infectious diseases after the treaty Maastricht is presented. Definition, aim and critical points of infectious surveillance are discussed. Problem deficits in Germany associated with infection surveillance are also dealt with.

Communicable Disease Control↗
PubMed1996

Receptor-associated protein and members of the low density lipoprotein receptor family share a common epitope. An extended model for the development of passive Heymann nephritis.

Heymann nephritis is an experimental rat model for human membranous glomerulonephritis. Two target antigens have been identified in the proximal tubule brush border of rat kidneys. One of them is megalin, a 600-kDa membrane protein that belongs to the family of low density lipoprotein receptor (LDLR)-related proteins. The other one is receptor-associated protein (RAP), a polypeptide of 40 kDa that associates with members of the LDLR family. Here we show that antibodies produced against recombinant human RAP strongly cross-react with the chicken oocyte receptor for very low density lipoprotein and vitellogenin (LR8), and with two other members of the LDLR family, LDLR-related protein and megalin. The interaction of this antibody with LR8 showed binding characteristics exactly as those demonstrated for the physiological ligands of this receptor, in that binding of the antibody: (i) is Ca2+-dependent; (ii) is abolished by unfolding of the cysteine-rich binding domain by reduction; and (iii) interferes with the binding of very low density lipoprotein and vitellogenin. Immunopurification of the LR8-specific subpopulation of the polyclonal antiserum yielded an IgG fraction strongly reacting with LR8 as well as with RAP. Using recombinant fragments of RAP and peptide mapping, the cross-reacting epitope(s) could be narrowed down to three short sequences (5-7 residues) in the COOH-terminal part of the protein. After immunization with RAP, anti-LR8 antibodies and anti-RAP antibodies arise simultaneously, indicating that the receptor-specific activity is not due to anti-idiotypic antibodies. These findings suggest the existence of a common epitope(s) on RAP and members of the LDL receptor family. Based on these results, we present an extended molecular model for the development of passive Heymann nephritis.

Animals↗
PubMed1996

Creatine kinase-mb fraction and cardiac troponin T to diagnose acute myocardial infarction after cardiopulmonary resuscitation.

OBJECTIVES: This study sought to evaluate the diagnostic value of the biochemical markers creatine kinase (CK), creatine kinase-MB fraction (CK-MB) and cardiac troponin T (cTNT) to diagnose acute myocardial infarction (AMI) after cardiopulmonary resuscitation (CPR). BACKGROUND: Elevations of CK and CK-MB after CPR are a frequent finding and might be associated with ischemic myocardial injury, as well as physical trauma to the chest. METHODS: Patients who had cardiac arrest and primary successful resuscitation were included in the study. The diagnosis of AMI was confirmed or ruled out by means of typical electrocardiographic findings, thallium-201 myocardial scintigraphy or autopsy, if death occurred during the hospital period, in 39 primary survivors of sudden cardiac death. In 24 patients (62%) the diagnosis of AMI was established. Serum cTNT, CK and CK-MB were measured, and the CK-MB/CK ratio was calculated on admission and after 12 h. RESULTS: On admission all markers of myocardial injury proved to be weak methods for the diagnosis of AMI. After 12 h cTNT as well as CK-MB exhibited a similar diagnostic performance; CK and the CK-MB/CK ratio proved to be worthless. Sensitivity and specificity for a cTNT cutoff value of 0.6 ng/ml, 12 h after cardiac arrest, were 96% and 80%, respectively. For a CK-MB cutoff value of 26 U/liter, sensitivity was 96% and specificity was 73%. CONCLUSIONS: Cardiac TNT and CK-MB are valuable tools in detecting AMI as the cause of sudden cardiac death. However, there is a considerable lack of sensitivity and specificity. Cardiac injury is probably caused not only by AMI, but also by myocardial damage related to CPR efforts.

Animals↗
PubMed1996

Induction of passive Heymann nephritis with antibodies specific for a synthetic peptide derived from the receptor-associated protein.

Passive Heymann nephritis (pHN) is an experimental rat model for human membranous glomerulopathy. In pHN, the formation of subepithelial immune deposits (ID) involves as antigenic targets the membrane glycoprotein gp330/megalin and the 44-kD receptor-associated protein (RAP). A single binding site for ID- inducing antibodies (Abs) was previously mapped to the 86 NH2-terminal amino acids of RAP (RAP1-86). To further narrow this epitope, Abs eluted from the glomeruli were immunoblotted on membranes that were loaded with overlapping synthetic peptides representing the amino acid sequence of RAP (SPOTs system). Two adjacent Ab-binding domains with the sequences PVRLAF, (amino acids 39-44) and HSD-LKIQE (amino acids 46-53), which were separated by a single L residue at amino acid 45, were detected. Rabbit Abs raised against synthetic peptides containing these domains individually (P31-44 and P46-53) failed to procedure glomerular IDs. By contrast, Abs raised against a larger composite peptide (P31-53) induced IDs within 3d that were firmly cross linked to the glomerular basement membrane. These data suggest that Ab binding in vivo depends on the conformation of the antigenic target sequence that is preserved in the synthetic peptide P31-53, which covers the entire Ab-binding domain of RAP but not in its subdomains, P31-44 and P46-53. Collectively, these results locate the sole ID-inducing epitope of RAP to amino acids 39-53.

Amino Acid Sequence↗
PubMed1996

Elevated levels of soluble CD14 in serum of patients with acute Plasmodium falciparum malaria.

Serum sCD14, tumour necrosis factor-alpha (TNF-alpha), IL-6, and endotoxin were analysed in 45 patients with complicated malaria, in 14 patients with Gram-negative septicaemia and in 24 healthy subjects by ELISA. Malaria patients with renal failure (n = 16) had higher levels than patients without renal failure (n = 29) (8116 + 1440 micrograms/l versus 9453 + 1017 micrograms/l; P < 0.05) and both had higher levels than patients with septicaemia (6155 + 1635 micrograms/l) and normal subjects (2776 + 747 micrograms/l). A significant correlation between sCD14 and IL-6 (r = 0.756) and TNF (r = 0.822) existed. However, no relation between sCD14 and serum endotoxin or indices of clinical disease severity (parasitaemia, fever, parasite or fever clearance time) was seen. Although the role of sCD14 in malaria remains to be determined, elevated levels may participate in the inflammatory response in complicated malaria.

Acute Disease↗
PubMed1996

Detection of anti-neutrophil cytoplasmic antibodies after acute Plasmodium falciparum malaria.

Four of 30 patients with Plasmodium falciparum infection in Bangkok, Thailand, were positive for anti-neutrophil cytoplasmic antibodies by indirect immunofluorescence 1 month after antimalarial therapy. No myeloperoxidase, proteinase 3, lactoferrin, or elastase reactivity was found. Since no evidence of vasculitis was seen in these patients, anti-neutrophil cytoplasmic antibody production in malaria-infected susceptible patients probably represents a secondary response, indicating neutrophil activation.

Acute Disease↗
PubMed1996

[Transmission of pathogenic human viruses by foods: hepatitis A epidemic caused by baked goods in the Euskirchen district)].

In the last few years many reports have documented that human pathogenic viruses are transmitted via food and can cause epidemics. Between November 1994 and February 1995 a HAV epidemic was recorded in the village and agricultural area of Euskirchen (Germany). 49 persons with HAV infections were registered. It seems that the epidemic started in a bakery and was caused by an employee who had spent his holidays in the Dominican Republic and came back already excreting the virus via his faeces. Two weeks later he developed a symptomatic illness. HAV is transmitted via a fecal-oral cycle. Lack of hygiene in food production and distribution cause the risk of secondary virus contamination. Virus transmission via food is first of all a problem in uncooked food. To ensure success in food safety in respect of foodborne human pathogenic viruses it is important to establish personal hygienic education, cleaning and disinfection plans and preventive measures such as immunization to avoid viruses in the food.

Disease Outbreaks↗
PubMed1996

Lipoproteins accumulate in immune deposits and are modified by lipid peroxidation in passive Heymann nephritis.

Proteinuria in passive Heymann nephritis is primarily caused by reactive oxygen species that are produced by glomerular cells. Reactive oxygen species apparently exert their damaging effects on the glomerular filter by lipid peroxidation and subsequent adduct formation on matrix proteins of glomerular basement membranes. This raised the question as to the source of polyunsaturated fatty acids required as substrates for lipid peroxidation. Here we have localized by immunocytochemistry rat apolipoprotein E and apolipoprotein B within subepithelial immune deposits. Moreover, apolipoprotein B extracted from isolated glomeruli of proteinuric passive Heymann nephritis rats shows degradation and lipid peroxidation adduct formation, similar to apoproteins of oxidized lipoproteins in atherosclerotic lesions. These data provide evidence that lipoproteins accumulate within immune deposits and suggest that their lipids generate lipid-peroxidation-derived reactive compounds.

Animals↗
PubMed1996

[Risk assessment and risk prevention in infectious diseases].

The purpose of risk assessment is to provide source data to state and local health agencies and other administrative departments to aid in the development of approaches for risk management and preventive strategies. In respect of the far reaching consequences it is necessary to have evaluated and accepted measures for the risk assessment. The system of risk assessment was developed in the USA for the assessment of chemical substances and includes the identification of the hazard, the exposure assessment, the dose-response-assessment and the risk assessment. Basis for the risk assessment are detailed information of the chemical substance or the pathogen and epidemiologic data. Preventive strategies and risk management like the stop of production have great social and economic consequences. Risk management must be highly effective. In a historic review it is described that in the past of the former centuries infectious diseases were tried to prevent or control in a wrong manner in consequence of the lack of knowledge about the etiology of infectious diseases. Since Robert Koch there was the beginning of an effective risk assessment and management of infectious diseases. Long time in this century it was thought that infectious diseases wouldn't play any role for the public health. Now it is clear that infectious diseases remain the leading cause of death and disability in the developed and underdeveloped countries and that the risk potential is increasing. Therefore risk-assessment and risk-management developed formerly for chemical substances are necessary for infectious diseases. Specific criteria for-the risk assessment for infectious diseases which are different to chemical substances are discussed like illness related, pathogen related, host related, transmission related factors and general aspects. The most important measures for risk management are discussed.

Communicable Disease Control↗