Biomedical subjects

A M Engel

Publications and source records attributed to A M Engel.

At least 19 recordsLinked to original sources

PubMed1997

Hepatitis G virus RNA and hepatitis G virus antibodies in renal transplant recipients: prevalence and risk factors.

BACKGROUND: Hepatitis G virus (HGV/GBV-C) RNA indicating current infection has been frequently isolated from the sera of transplant recipients and other multitransfused individuals. Lifetime exposure to the virus, however, is unknown. We carried out a study to determine the prevalence and risk factors of HGV antibodies and of HGV RNA among renal transplant recipients, and to investigate possible associations between HGV RNA and immunosuppressive treatment. METHODS: HGV RNA was detected by reverse transcriptase-polymerase chain reaction, and HGV antibodies (anti-E2) by a newly developed immunoassay. To assess risk factors for HGV exposure, univariate and multivariate analysis was performed. RESULTS: Of the 221 patients, 14% were HGV RNA positive and 40% had HGV antibodies. Both HGV RNA and anti-HGV were present in only two individuals. Thus, the overall HGV exposure prevalence was 53%. It increased significantly with the number of blood transfusions. In logistic regression, the adjusted HGV exposure prevalence odds ratio was 5.7 (95% confidence interval [CI]: 2.2-15) among patients with > or =10 transfusions (baseline: no transfusions). Other independent risk factors were a longer duration of hemodialysis and a longer time interval since transplantation. HGV viremia was not associated with the type of immunosuppressive treatment. Alanine aminotransferase levels were not significantly increased among HGV RNA-positive patients. CONCLUSIONS: Much higher proportions of renal transplant recipients were exposed to HGV than is suggested by HGV RNA detection alone. The majority of infected individuals apparently eliminate the virus over time. Contaminated blood transfusions have to be regarded as a main risk factor for HGV infection.

Adolescent↗

PubMed1997

Detection of antibodies to a putative hepatitis G virus envelope protein.

BACKGROUND: A flavivirus designated hepatitis G virus (HGV) has been isolated from the serum of patients with non-A-E hepatitis. Hitherto, the presence of HGV RNA in serum has been detected with the reverse transcription-polymerase chain reaction (RT-PCR) amplification method. We have now developed an immunoassay for antibodies against an HGV protein. METHODS: Recombinant HGV envelope protein E2 was used as antigen in an ELISA. 80 blood donors, 99 intravenous-drug users, and 11 patients with acute post-transfusion hepatitis were tested for antibodies to E2. The HGV-RNA status was assessed by RT-PCR. FINDINGS: Anti-E2 seroprevalence was 9% among the blood donors and 41% among the drug users; HGV-RNA prevalence was 2.5% and 38%, respectively. Whereas anti-E2 prevalence increased with the duration of drug use, HGV-RNA prevalence declined in parallel. In each group, the presence of anti-E2 and HGV RNA was almost mutually exclusive: none of the blood donors and only 4% of the drug users were positive for both markers at the same time. Of the 11 post-transfusion patients--who were all HGV-RNA positive and anti-E2 negative at the onset of disease--four developed antibodies to E2 during the following year, and two of the four subsequently became HGV-RNA negative. INTERPRETATION: We conclude that a humoral immune response to E2 is associated with loss of detectable HGV viraemia. Thus, E2-specific antibodies might serve as a useful marker for diagnosing recovery from HGV infections. The immunoassay we describe should facilitate investigation of suspected infections and may be helpful in the elucidation of the clinical significance of HGV.

Antibodies, Viral↗

PubMed1997

Molecular aberrations in the MHC class I-restricted pathway for antigen presentation in methylcholanthrene sarcomas from nude mice: discrepancies between MHC mRNA and surface protein.

In a previous study, we demonstrated that eight sarcomas induced by chemical carcinogenesis in nude mice were rejected by syngeneic immunocompetent recipients at a much higher rate than eight sarcomas induced with the same method in syngeneic immmunocompetent mice. In the present study, we investigated these 16 sarcomas for structural and quantitative aberrations in components of the MHC class I-restricted antigen-processing and -presentation pathway. Considerable discrepancies between mRNA levels and cell surface protein expression of MHC class I (Kd, Dd and Ld) molecules were observed almost exclusively in the tumours derived from nude mice. Several of the nude mouse-derived tumours also displayed incongruent levels of heavy chain mRNA and beta2-microglobulin mRNA. These findings are taken as indications of abnormal regulation of gene transcription in nude mouse tumours, and if this abnormal regulation extends to the entire genome, it may explain the pronounced immunogenicity of these tumours. Proteasome composition, heat shock protein expression, TAP-molecule inducibility and intercellular adhesion molecule-1 expression were investigated in the same tumours. We found no indications of structural defects or quantitative differences in these molecules between the two groups of tumours.

Animals↗

PubMed1997

The susceptibility to cytotoxic T lymphocyte mediated lysis of chemically induced sarcomas from immunodeficient and normal mice.

A panel of sarcomas induced with 3-methylcholanthrene in normal and immunodeficient mice was studied for their capacity to present antigen by the endogenous, MHC class I restricted pathway. Lymphocytic choriomeningitis virus was used to infect cultured tumour cells, and the infected cells were tested for susceptibility to cytolysis by virus specific cytotoxic T cells. Tumour cells originating from tumours induced in immunocompetent C.B.-17 mice presented virus antigen more efficiently than tumour cells from immunodeficient SCID mice. No significant difference in virus antigen presentation was found between tumours from nude and nu/+ BALB/c mice. The sensitivity of target cells from the individual tumours to cytotoxic T lymphocyte (CTL) mediated lysis correlated negatively with their sensitivity to natural killer (NK) cell mediated lysis. There was a positive correlation between the sensitivity to CTL mediated lysis and surface expression of the MHC class I molecule Ld of the tumour cells. Tumour cells incapable of in vitro presentation of viral antigen to specific cytotoxic T cells originated from tumours known from previous experiments to be readily accepted after transplantation to immunocompetent, histocompatible recipients.

Animals↗

PubMed1997

MCA sarcomas induced in scid mice are more immunogenic than MCA sarcomas induced in congenic, immunocompetent mice.

With the aim of studying possible T-cell mediated selection of the cells in growing tumours, 108 mice of the C.B-17 strain, either immunocompetent C.B-17 mice or histocompatible immunodeficient C.B-17 severe combined immune deficiency (scid) were treated with 3-methylcholanthrene (MCA) in two different dosages. A total of 51 tumours were obtained, 44 of which were established as uncloned tumour cell lines, and used for further study. Tumour incidence correlated with carcinogen-dosage in that more tumours developed in groups treated with a high MCA dose than in groups treated with a low MCA dose, but not with immune status of the tumour host. No significant difference in the level of MHC class I molecule expression was found between the two groups of tumours. The rate of rejection after transplantation to syngeneic immunocompetent hosts was significantly higher for the scid tumours than for the non-scid tumours. The authors suggest that this reflects an immunoselection performed by T cells in the immunocompetent host in which the tumour originated, which has eliminated highly immunogenic tumour cells, leaving non-immunogenic tumour cells to grow.

Animals↗

PubMed1996

Chemically induced sarcomas from nude mice are more immunogenic than similar sarcomas from congenic normal mice.

To detect possible differences in immunogenicity between tumors induced in T cell-deficient mice and phenotypically normal congenic mice, 16 sarcomas, 8 having developed in nude BALB/c mice and 8 having developed in congenic normal (nu/+) mice, were transplanted to normal BALB/c recipients and the rates of rejection or acceptance were registered. The 16 tumors were chosen randomly from a panel of 39 sarcomas induced with 0.5% or 0.1% 3-methylcholanthrene and maintained as cell lines in culture. Out of the tumors originating from nude mice, 66% were rejected by the normal BALB/c recipients, while only 30% of the tumors originating from normal mice were rejected. Tumors with short induction times from normal mice were more readily accepted than tumors with long induction times. Tumors originating from nude mice had significantly longer mean latency times after transplantation to both normal and nude recipients than tumors originating from normal mice. Contrary to what has been reported by others, there was no correlation between the rejection rates of the individual tumors and their Kd, Dd or Ld major histocompatibility complex (MHC) class I surface expression as measured by flow cytometric analysis of cultured tumor cells. The Kd, Dd and Ld proteins of the transplanted tumor lines were analyzed by isoelectric focusing for the occurrence of mutations resulting in altered charge of the MHC protein. No such mutations were found, ruling out MHC mutations of that kind as the source of immunogenicity in the cell lines used in these experiments. Our results suggest the existence of a T cell-mediated selection in the original tumor cell mass of tumors induced in normal mice, adapting the tumor to growth in a host with a functional T cell system, but apparently there is no connection between this loss of immunogenicity and loss of MHC class I expression.

Animals↗

PubMed1996

Detection of the hepatitis G virus genome among injecting drug users, homosexual and bisexual men, and blood donors.

The recently identified hepatitis G virus (HGV) is parenterally transmitted; the impact of sexual transmission is unknown. Moreover, it is unclear what proportion of HGV-infected persons may develop persistent viremia. Sera from injecting drug users (IDUs), non-drug-injecting homosexual and bisexual men with high levels of sexual risk behavior, and blood donors were tested for HGV RNA and hepatitis C virus (HCV) RNA by reverse transcriptase-polymerase chain reaction and for antibodies to human immunodeficiency virus, hepatitis B virus, and HCV. HGV RNA was detected in 33% of IDUs (n = 130), 11% of homosexual and bisexual men (n = 101), and 2% of blood donors (n = 90). HGV RNA seroprevalence significantly decreased with increasing time since first drug injection, whereas the seroprevalences of both HCV RNA and anti-HCV antibody increased. Thus, a high proportion of HGV-infected persons may clear the virus and develop protective antibodies. The relatively high HGV RNA prevalence among non-drug-injecting homosexual and bisexual men indicates that sexual contact may be another important route of HGV transmission.

Adult↗

PubMed1996

Methylcholanthrene-induced sarcomas in nude mice have short induction times and relatively low levels of surface MHC class I expression.

In order to study the role of the T-cell-mediated immune defense in tumor development, a total of 93 sarcomas were induced using different doses (8 micrograms (0.1%), 40 micrograms (0.5%) and 400 micrograms (5%)) of 3-methylcholanthrene in athymic nude Balb/c mice and phenotypically normal immunocompetent Balb/c mice. A shorter tumor induction time and a higher tumor incidence after treatment with low doses of methylcholanthrene were seen in nude mice than in immunocompetent mice, indicating that they have a lower resistance to the carcinogen. Contrary to expectations we found that the MHC class I expression of tumors from nude mice was lower than that of tumors from normal mice. Higher surface expression of MHC class I was demonstrated on high dose tumors from normal mice than on low dose tumors from normal mice. The cellular composition of the individual tumors raised in nude mice was more heterogeneous with respect to MHC class I expression. Since the mice differ genetically only with respect to the nu gene, these results indicate that a lack of T-cell-mediated defense mechanisms may confer upon the bearer a lower resistance to 3-methylcholanthrene and a different MHC profile of the ensuing tumor.

Animals↗

PubMed1996

Reverse transcription-PCR detection of hepatitis G virus.

Hepatitis G virus (HGV) was recently identified as a new member of the Flaviviridae, but its clinical significance is still unclear. Since no immunoassay for the diagnosis of HGV is available, we developed a sensitive reverse transcription-PCR (RT-PCR) assay to facilitate the detection of the viral genome by mass screening in the clinical laboratory. Sequences within the 5'-noncoding region and within the putative NS5a region are independently amplified in the presence of digoxigenin-11-dUTP and are detected by hybridization with biotinylated capture probes binding to a streptavidin-coated matrix. Semiquantitative Enzymun-Test DNA detection via chemiluminescence can be performed either in a microtiter plate format or on fully automated ES 300 machines. We were able to detect at least 8 x 10(2) genome equivalents per ml of serum using both primer pairs. HGV was shown to be present in 43 of 130 (33%) serum samples from intravenous drug abusers with a high risk of parenteral exposure. However, only two of the patients were positive when the NS5a primers only were used, and only one patient was positive when only the 5'-noncoding region primers were used, demonstrating the increased sensitivity of HGV detection with two sets of primers. Among these patients, there was no obvious correlation with other viral infections like hepatitis B virus, hepatitis C virus, or human immunodeficiency virus. Within a blood donor panel, 3 of 92 (3%) samples were found to be HGV positive, suggesting that donated blood may need to be screened for HGV.

Base Sequence↗

PubMed1995

Model structure of the Omp alpha rod, a parallel four-stranded coiled coil from the hyperthermophilic eubacterium Thermotoga maritima.

Omp alpha is an outer-membrane protein that spans the periplasmic space of the hyperthermophilic eubacterium Thermotoga maritima. The molecule contains a globular head with an apparent diameter of 8 nm and a rod-shaped tail of 40 nm length. The sequence of the globular domain is homologous to a conserved region of cell wall-bound proteins and probably attaches Omp alpha to the peptidoglycan. The sequence of the rod domain resembles that of coiled coil proteins and ends in a transmembrane segment that anchors Omp alpha to the outer membrane. We have analysed Omp alpha by scanning transmission electron microscopy (STEM) and by statistical sequence analysis methods. The Omp alpha rod is a tetramer with an unusual periodicity of hydrophobic residues close to 3.6 that differs from the 3.5 periodicity of canonical coiled coils. This is due to periodic omissions of three residues in the heptad repeat pattern ("stutters") whose effect is to locally distort the packing of hydrophobic layers in the core of the coiled coil. Residues in position alpha are shifted to occupy a position halfway between positions alpha and d (x layers) and residues in positions d and e are shifted so that both participate in core packing interactions (da layers). Such distorted layers are frequently found in helical bundles and are characteristic of helices that do not undergo supercoiling. The only homo-oligomeric coiled coil of known structure which contains x and da layers is the three-stranded coiled coil of influenza haemagglutinin. Using geometric constraints derived from this structure, we have built a model for the Omp alpha rod in which the helices have a crossing angle of less than 15 degrees and maintain a residual degree of supercoiling with a pitch of approximately 40 nm. Our analysis of distorted layers in the hydrophobic core of coiled coils and helical bundles shows that stutters must not be viewed as discontinuities but rather as a departure from the canonical "knobs-into-holes" packing that allows helices to interact at a low angle without supercoiling. Although stutters have been considered to weaken helical interactions, their occurrence in a rigid, highly thermostable coiled coil indicates that this may not be generally true. Our analysis also indicates that skips and stutters are two different conventions for describing the same underlying structural feature.

Amino Acid Sequence↗

PubMed1995

Characterization of the hormone binding site of natriuretic peptide receptor-C.

The hormone binding site of rat and human natriuretic peptide clearance receptor (NPR-C), a single transmembrane receptor, has been further refined by mutagenesis. In addition to residue 188 (rat Ala, human Ile), which completely inverts the pharmacology of the rat and human receptors [Engel et al. (1994) J. Biol. Chem. 269, 17005-17008], we report a second key residue at position 205 (rat Tyr, human Asn) which modulates affinity to a limited number of ligands. Orthologous mutation of both residues results in tighter binding for human and weaker binding for rat NPR-C. The ligand binding fold of the receptor is formed by at least the first half of the extracellular domain containing two intramolecular disulfide loops, with the two affinity-modulating residues 188 and 205 in the second loop.

Animals↗

PubMed1994

The disulfide linkages and glycosylation sites of the human natriuretic peptide receptor-C homodimer.

The natriuretic peptide receptor-C (NPR-C) constitutes greater than 95% of the natriuretic peptide binding sites in vivo. This cell surface glycoprotein is a disulfide-linked homodimer with a subunit molecular weight of 68,000. Two sources and types of ANP affinity-purified human NPR-C were used to map disulfide linkages and glycosylation sites of this receptor by mass spectrometry: the extracellular domain obtained by papain cleavage of a receptor-IgG fusion protein expressed in Chinese hamster ovary cells, and a baculovirus/Sf9-expressed cytoplasmic truncation mutant in which 34 of 37 cytoplasmic domain amino acids were deleted. Two intramolecular disulfide bonded loops were found in the 435 amino acid extracellular domain (C63-C91, C168-C216). The juxtamembrane residues C428 and C431 are involved in homodimer formation, confirmed by site-directed mutagenesis of full-length NPR. Three of the four potential Asn-linked glycosylation sites are occupied: N41 (complex), N248 (high mannose), and N349 (complex; partial occupancy). These data describe the intra- and intermolecular linkages in NPR-C, providing a model for the homologous guanylyl cyclase receptors, NPR-A and NPR-B; both of the cyclase receptors likely contain the first amino-terminal 29 amino acid loop, but only NPR-A possesses the second 49 amino acid loop in common with NPR-C.

Amino Acid Sequence↗

PubMed1994

A single residue determines the distinct pharmacology of rat and human natriuretic peptide receptor-C.

We report the cloning and expressing of rat natriuretic peptide receptor-C (NPR-C), which binds naturally occurring and synthetic ligands with higher affinity than human NPR-C. Using rat/human hybrids and site-directed mutagenesis, we identified residue 188, Ala for rat and Ile for human, which modulates hormone binding. Orthologous mutagenesis at position 188 for either rNPR-C or hNPR-C results in a complete reversal of the pharmacology. To our knowledge, this is the first example of a single transmembrane domain receptor for which a single residue dictates the ligand binding properties; previous examples are limited to seven transmembrane receptors.

Amino Acid Sequence↗

PubMed1994

Comparison between sodium cromoglycate (MDI: metered-dose inhaler) and beclomethasone dipropionate (MDI) in treatment of adult patients with mild to moderate bronchial asthma. A double-blind, double-dummy randomized, parallel-group study.

This study compared the efficacy and tolerability of sodium cromoglycate (SC) and beclomethasone dipropionate (BDP) in adult patients with bronchial asthma inadequately treated with bronchodilators alone. The study was a double-blind, randomized, double-dummy, parallel-group study. Patients with mild to moderate symptomatic asthma, inadequately treated with bronchodilators only, were, after a 2-week run-in (base-line) period, randomized to 8 weeks of treatment with either SC 10 mg four times daily or BDP 100 micrograms four times daily. Salbutamol metered-dose inhaler was given as relief medication. A total of 37 patients were randomized for treatment, 19 patients in the SC group and 18 patients in the BD group. Efficacy and safety were determined by daily record card data: morning and evening peak-expiratory-flow rates (PEFR), daytime and nighttime asthma symptom scores, and rescue salbutamol use. At clinic visits, FEV1 and FVC were measured, as were the physician's and the patient's assessment of the medication at the end of the study. The safety and tolerability of the trial medication were assessed by monitoring adverse events throughout the study. A clinically and statistically significant improvement of the asthma in FEV1, symptom scores, rescue medication, and global opinion of efficacy was observed, and both groups provided equivalent efficacy. The morning PEFR as well as the evening PEFR for both groups improved, but was statistically significant only for the BDP group (M-PEFR). Both drugs were well tolerated with only a few minor adverse events. This trial shows that SC and BDP are equally effective anti-inflammatory treatments for mild to moderate bronchial asthma in adults.

Adult↗

PubMed1994

Salmeterol in two different doses in the treatment of nocturnal bronchial asthma poorly controlled by other therapies.

This study compared the efficacy of inhaled salmeterol (SM) 50 micrograms twice a day with SM 100 micrograms once a day (at night) and placebo in patients with poorly controlled nocturnal asthma despite treatment with corticosteroids, oral long-acting bronchodilators, or both. This was a two-center, double-blind, randomized, crossover study with three treatment periods, each of 3 weeks' duration. The first treatment period was preceded by two 1-week run-in periods, and the last treatment period was followed by a 2-week follow-up period. In the three treatment periods, patients received either SM 50 micrograms twice a day, SM 100 micrograms nightly, or placebo, in randomized order. Salbutamol metered-dose inhaler was given as relief medication. Of the 41 randomized patients, 38 were evaluable for more than one treatment period. Efficacy and safety were determined by daily record card data: morning and evening peak expiratory flow rates (PEFR), daytime and nighttime asthma symptom scores, and rescue salbutamol use. At clinic visits, FEV1 and FVC were measured, and the physicians' and the patients' respective assessments of the study mediation were noted. The study showed that the two doses, SM 50 micrograms twice a day and SM 100 micrograms nightly, were equally effective in controlling nocturnal asthma symptoms and were significantly better than placebo. SM was well tolerated, and no unexpected problems were revealed. The adverse events reported during this study were related either to the patient's underlying disease or to an intercurrent respiratory infection.

Adult↗

PubMed1994

MHC class II-bound self-peptides can be effectively separated by isoelectric focusing and bind optimally to their MHC class II restriction elements around pH 5.0.

More than 90% of the major histocompatibility complex (MHC) class II molecules on antigen-presenting cells (APC) have in their binding site a peptide derived from an extracellular protein ingested by the APC or from a protein of the APC itself. These self-peptides can be eluted from affinity-purified MHC class II molecules by acid elution, and have been studied with a variety of techniques. We show here that the self-peptides eluted from the mouse MHC class II molecules Ad, Ed and Ek bind specifically to MHC class II molecules of the allelic type from which they were derived. The pH optimum for binding is around 5.0, i.e. the same optimum at which synthetic peptides representing sequences of foreign antigens bind to MHC class II molecules. This suggests that the physiological compartment where MHC class II molecules bind self-peptides may be very late in the endocytic pathway. The chemical properties of the eluted and labelled MHC class II peptides were studied by isoelectric focusing. This method was able to separate the peptides very efficiently, and enabled a rapid comparison of peptides eluted from different MHC molecules. The 125I-labelled peptides displayed a broad range of isoelectric points with values predominantly below neutral. This suggests that such peptides bind to MHC in a predominantly non-charged state.

Amino Acid Sequence↗

PubMed1993

The protective effect of inhaled levomepromazine (Nozinan) on histamine-induced bronchial constriction.

The effect of inhaled levomepromazine (Nozinan, Veractil) on bronchial responsiveness to inhaled histamine was investigated in asthmatics. In a double blind, randomized controlled study, 12 asthmatics (FEV1% pred 52-96%, and PC20 histamine 1.01 mg/ml (geometric mean)) were challenged before and after inhalation of levomepromazine in three different doses. Before and after each inhalation of levomepromazine, PC20, FEV1, the continuous reaction time (CRT) and the subjective sedation score (VAS) were determined. A dose-dependent increase in PC20 was observed after inhalation of levomepromazine. PC20 was increased by up to 4.02 two-fold concentration differences (doubling), i.e. up to a 38-fold increase from the basic values. Inhalation of the two higher doses of levomepromazine had a small sedative effect evaluated from an increase in CRT and the VAS-score and corresponding to the plasma concentrations. We conclude that inhaled levomepromazine has a dose-dependent protective effect on histamine-induced bronchial hyperresponsiveness in asthmatics and that inhalation of levomepromazine was well tolerated. The mechanism by which levomepromazine acts on histamine-induced bronchial hyperresponsiveness is not known but it could be partly explained by the antihistaminic effect. In this respect levomepromazine bears comparison with the most potent second generation antihistamines. The plasma concentrations of levomepromazine measured corresponded to those seen after oral intake of 5-10 mg levomepromazine.

Administration, Inhalation↗

PubMed1993

Expression of beta 2-microglobulin by premalignant epithelium.

Many human tumors express low amounts of HLA class I molecules relative to the normal cells from which they are derived. From experimental work it is clear that the malignant behavior of a tumor cell may depend on its MHC class I expression. Therefore, it is of obvious interest to study the HLA class I expression of human tumors in their various stages. We have studied the HLA class I expression by the cells in premalignant epithelial lesions and invasive carcinoma of the bladder and uterine cervix using immunoperoxidase staining for beta 2-microglobulin of paraffin-embedded tissue. We here assume that beta 2-microglobulin expression by malignant and premalignant cells equals HLA class I expression. Thirty-two of the 36 invasive tumors expressed less overall beta 2-microglobulin than cells from the normal epithelium. In contrast, approximately two-thirds of 34 premalignant bladder epithelia and 47 premalignant cervix epithelia displayed higher overall beta 2-microglobulin expression than the normal epithelium. Thus, a systematic large-scale elimination of HLA class I high-expressing tumor cell variants may take place only after the tumor penetrates the basement membrane.

Carcinoma in Situ↗