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Biomedical subjects

C Koch

Publications and source records attributed to C Koch.

At least 217 records · Page 12Linked to original sources
PubMed1996

Monoclonal antibodies against a C-terminal peptide of human brain acetylcholinesterase distinguish between erythrocyte and brain acetylcholinesterases.

Monoclonal antibodies (mAbs) were raised against a peptide of the 10 C-terminal amino acids of human brain acetylcholinesterase (AChE): H-Tyr-Ser-Lys-Gln-Asp-Arg-Cys-Ser-Asp-Leu-OH. Two positive clones (mAbs 190-1 and 190-2) were selected and tested for their ability to distinguish between mammalian brain and erythrocyte AChEs. In a solid-phase enzyme antigen immunoassay as well as by Western- and dot-blot analysis, both antibodies showed clear binding to AChE from human and bovine brain but not to AChE from erythrocytes. MAbs 190-1 and 190-2 reacted with neither AChE from electric eel nor butyrylcholinesterase from human serum. Both antibodies were used in a quantitative assay for AChE in amniotic fluids, where AChE activity could be found only in samples from open neural tube-defect pregnancies, but not in fluids from normal pregnancies or in artificially blood-contaminated samples.

Acetylcholinesterase↗
PubMed1996

Immunocytochemical labelling of aerobic and hypoxic mammalian cells using a platinated derivative of EF5.

The monoclonal antibody ELK3-51 was previously developed to detect adducts of the 2-nitroimidazole EF5. Direct immunofluorescence was used to detect adducts of EF5 or of a platinated derivative cis-[PtCl2(NH3)EF5] in SCCVII cells treated under aerobic or hypoxic conditions. Fluorescence measurements of these cells using both image and flow cytometric methods were compared, giving similar profiles. Platination significantly decreased immunofluorescence levels (approximately 4-fold less than EF5) after 3 h in hypoxia, but also increased levels after exposure in air (approximately 1.5 x) such that the hypoxic ratio decreased from approximately 50 to approximately 13. Platinated EF5 also showed significantly greater cytotoxicity than its parent in both aerobic and hypoxic cells. These results are consistent with targeting of EF5 to DNA, which was confirmed qualitatively by confocal microscopy.

Animals↗
PubMed1995

Recovery of virtually full-length HIV-1 provirus of diverse subtypes from primary virus cultures using the polymerase chain reaction.

In the course of the global pandemic, the human immunodeficiency virus type-1 (HIV-1) has established at least eight distinct genotypes in the main (M), or prevalent, group of isolates, a variety of rare outlier forms, and intergenotypic recombinants of group M viruses. This genotypic diversity has been documented, for the most part, by sequencing of subgenomic segments of the provirus. Using DNA from virus cultures on peripheral blood mononuclear cells (PBMC) and recent improvements of the PCR technique, we have amplified virtually full-length HIV-1 genomes from genetic subtypes A through G of group M viruses and molecularly cloned several of them. Resequencing of the complete genome of a prototype strain after long PCR amplification and cloning has established a PCR error rate of 0.14%. We also report the first complete PCR-derived sequence of a U.S. clinical isolate of genotype B expanded only in primary PBMC; this provirus harbors a uniquely truncated V3 loop.

Amino Acid Sequence↗
PubMed1995

Glucose tolerance in patients with cystic fibrosis: five year prospective study.

OBJECTIVES: To study prevalence and incidence of diabetes mellitus in patients with cystic fibrosis. DESIGN: Five year prospective study with annual oral glucose tolerance tests. SETTING: CF Center Copenhagen, Denmark. SUBJECTS: 191 patients with cystic fibrosis aged above 2 years. MAIN OUTCOME MEASURES: Glucose tolerance, plasma glucose concentrations after fasting and after glucose loading, and haemoglobin A1c levels. RESULTS: Prevalence of diabetes increased from 11% (n = 21) to 24% (n = 46) during study, with annual age dependent incidence of 4-9%. Diabetes was diagnosed at median age of 21 (range 3-40). At diagnosis of diabetes, symptoms of hyperglycaemia were present in 33% of patients, fasting hyperglycaemia (> or = 7.8 mmol/l) was seen in 16%, and increased haemoglobin A1c levels (> 6.4%) were seen in 16%. Impaired glucose tolerance implied higher risk for development of diabetes than normal glucose tolerance (odds ratio 5.6). In 58% of cases with impaired glucose tolerance, however, glucose tolerance was normal at next annual test. Normal glucose tolerance was found in only 37% of patients at all five tests. Within this group of patients, median plasma glucose concentrations after fasting and after glucose loading and haemoglobin A1c levels increased by 6-8% during study. CONCLUSIONS: Prevalence and incidence of diabetes in cystic fibrosis patients was high and increased with age. Since hyperglycaemic symptoms, fasting hyperglycaemia, and increased levels of glycated haemoglobin did not reliably identify diabetes mellitus, we recommend annual oral glucose tolerance tests in all cystic fibrosis patients aged over 10 years.

Adolescent↗
PubMed1995

Recurrent excitation in neocortical circuits.

The majority of synapses in the mammalian cortex originate from cortical neurons. Indeed, the largest input to cortical cells comes from neighboring excitatory cells. However, most models of cortical development and processing do not reflect the anatomy and physiology of feedback excitation and are restricted to serial feedforward excitation. This report describes how populations of neurons in cat visual cortex can use excitatory feedback, characterized as an effective "network conductance", to amplify their feedforward input signals and demonstrates how neuronal discharge can be kept proportional to stimulus strength despite strong, recurrent connections that threaten to cause runaway excitation. These principles are incorporated into models of cortical direction and orientation selectivity that emphasize the basic design principles of cortical architectures.

Animals↗
PubMed1995

Are we aware of neural activity in primary visual cortex?

It is usually assumed that people are visually aware of at least some of the neuronal activity in the primary visual area, V1, of the neocortex. But the neuroanatomy of the macaque monkey suggests that, although primates may be aware of neural activity in other visual cortical areas, they are not directly aware of that in area V1. There is some psychophysical evidence in humans that supports this hypothesis.

Animals↗
PubMed1995

[Transplantation of lung lobe from a mother to a child previously transplanted with her bone marrow].

The lower lobe of the left lung was transplanted from a mother to her child, who previously had received a bone marrow transplant from the mother because of an immune defect. After the bone marrow transplant the child had developed progressive pulmonary fibrosis (obliterative bronchiolitis). The surgical procedure and the early postoperative period has been uncomplicated. Immunosuppression with corticosteroids was only given for a short period, after which no immunosuppressive treatment has been given. The operation and results for both donor and recipient are described. The early results are promising, but rehabilitation is progressing slowly.

Bone Marrow Transplantation↗
PubMed1995

Neonatal isoerythrolysis in mule foals.

Four mule foals received anti-RBC antibody from their dam's colostrum. Two foals developed anemia, 1 developed severe thrombocytopenia, and 1 did not develop any clinical or laboratory abnormalities. All foals had the same donkey sire. Seven mares, including the dams of foals 1 to 4, bred to the donkey sire produced anti-RBC antibody. Two mares produced anti-RBC antibody to the donkey RBC on the first mating. The donkey sire and 18 of its offspring were found to have an RBC antigen unique to mules and donkeys. Thus, all matings of this donkey to horse mares were incompatible. The reason for the high rate of sensitization of mares bred to this donkey is unknown.

Anemia, Hemolytic↗
PubMed1995

Ocular findings in cystic fibrosis patients receiving vitamin A supplementation.

BACKGROUND: Vitamin A deficiency with eye symptoms has been reported in patients with cystic fibrosis who received the recommended daily intake of vitamin A. METHODS: We measured serum retinol, dark adaptation, contrast sensitivity, and dry eye status in 35 adult cystic fibrosis patients to ascertain whether they had ocular signs or symptoms. RESULTS: Median serum retinol concentration was 1.95 mumol/l, range 1.08-4.01 mumol/l, with no values indicating vitamin A deficiency. Retinal light sensitivity was normal. Nineteen patients had reduced contrast sensitivity. Conjunctival imprints all showed plenty of goblet cells, but were characteristic of dry eye in 42% of patients (n = 14). Decreased tear film stability was found in 49% (n = 17), tear production was low in 31% (n = 11), and 23% (n = 8) showed an increased amount of dying epithelial cells. Nine patients (26%) had keratoconjunctivitis sicca according to the Copenhagen criteria. CONCLUSION: Our patients had no biochemical or clinical signs of vitamin A deficiency. We speculate that the high incidence of dry eye could be a primary manifestation of cystic fibrosis.

Adolescent↗
PubMed1995

Do neurons have a voltage or a current threshold for action potential initiation?

The majority of neural network models consider the output of single neurons to be a continuous, positive, and saturating firing rate f (t), while a minority treat neuronal output as a series of delta pulses sigma delta (t-ti). We here argue that the issue of the proper output representation relates to the biophysics of the cells in question and, in particular, to whether initiation of somatic action potentials occurs when a certain threshold voltage or a threshold current is exceeded. We approach this issue using numerical simulations of the electrical behavior of a layer 5 pyramidal cell from cat visual cortex. The dendritic tree is passive while the cell body includes eight voltage- and calcium-dependent membrane conductances. We compute both the steady-state (Istatic(infinity)(Vm)) and the instantaneous (I0(Vm)) I-V relationships and argue that the amplitude of the local maximum in Istatic(infinity)(Vm) corresponds to the current threshold Ith for sustained inputs, while the location of the middle zero-crossing of I0 corresponds to a fixed voltage threshold Vth for rapid inputs. We confirm this using numerical simulations: for "rapid" synaptic inputs, spikes are initiated if the somatic potential exceeds Vth, while for slowly varying input Ith must be exceeded. Due to the presence of the large dendritic tree, no charge threshold Qth exists for physiological input. Introducing the temporal average of the somatic membrane potential while the cell is spiking repetitively, allows us to define a dynamic I-V relationship Idynamic(infinity)( ). We find an exponential relationship between and the net current sunk by the somatic membrane during spiking (diode-like behavior). The slope of Idynamic(infinity)( ) allows us to define a dynamic input conductance and a time constant that characterizes how rapidly the cell changes its output firing frequency in response to a change in its input.

Action Potentials↗
PubMed1995

Spatial displacement, but not temporal asynchrony, destroys figural binding.

What are the elementary features that the brain uses to bind spatially distinct parts in a visual scene into an unitary percept of an "object"? The Gestalt psychologists emphasized the extent to which motion, colour, luminance or spatial arrangement contribute towards object formation. Little is known about the role of time per se, rather than motion, in constituting an object. In particular, does the visibility or saliency of an object change if the various parts making up the object are not presented simultaneously? Using a simple experimental design, we show that very small spatial displacements can significantly influence the saliency of an object while large temporal asynchrony has no significant effect.

Form Perception↗
PubMed1995

Immunocytochemical analysis of a monoclonal antibody specific for rainbow trout (Oncorhynchus mykiss) granulocytes and thrombocytes.

A monoclonal antibody against rainbow trout peripheral blood leucocytes was selected for its lack of reactivity with rainbow trout immunoglobulin. Its reactivity with leucocytes from peripheral blood, head kidney and spleen was analysed by flow cytometry and electron microscopy, and compared with that of monoclonal antibodies directed against rainbow trout immunoglobulin, which reacted with B cells, B lymphoblasts and plasma cells. The antibody reacted with 5-20% of the peripheral blood leucocytes, 8-9% of head kidney leucocytes and 5-7% of spleen leucocytes. Electron microscopical immunocytochemistry revealed that the antibody reacted strongly with granulocytes and weakly with thrombocytes, and not with erythrocytes, lymphocytes, monocytes or macrophages. The antibody has possible applications in the identification and isolation of rainbow trout leucocytes, either alone or in combination with other monoclonal antibodies.

Animals↗
PubMed1995

Monoclonal antibodies for the direct detection of influenza-A virus by ELISA in clinical specimens from patients with respiratory infections.

BACKGROUND: Monoclonal antibody technology provides antibody reagents of known specificity, high titres and unlimited availability, that form ideal reference antibodies for use in specific viral antigen-detection methods. OBJECTIVES: To produce mouse monoclonal antibodies against antigenic sites of influenza-A virus, and evaluate their use as diagnostic reagents in a sandwich ELISA. STUDY DESIGN: (1) Production and characterization of monoclonal antibodies against influenza-A virus; (2) application of these antibodies in an ELISA method for direct antigen detection; and (3) evaluation of the ELISA as routine procedure. RESULTS: Four monoclonal antibodies (A1-A4) from mice immunized intranasally with influenza-A virus were selected according to their specific reactivity with either nucleoprotein or matrix protein antigens as demonstrated by Western blot analysis. These antibodies lacked haemagglutination inhibition and neutralization properties and recognized both H1N1 and H3N2 strains of influenza-A virus equally. A sandwich ELISA using unlabelled antibodies for antigen capture and biotin-labelled antibodies for antigen detection was used to analyse nasopharyngeal secretions or nasal swabs from culture-confirmed influenza-A-infected patients and comparable specimens from patients with other viral respiratory infections. Only influenza-A virus (strains H1N1 and H3N2) could be detected in samples from patients with known influenza-A and influenza-B infections, and also after re-isolation of such viruses in conventional cultures of MDCK cells or embryonated hens' eggs. The antigen-detection assay showed a diagnostic sensitivity of 100% and a specificity of 98.3% compared with conventional culture methods. CONCLUSION: The reported ELISA appears to be a rapid and inexpensive method for diagnosis and epidemiological studies of influenza-A infections.

Journal Article↗
PubMed1995

Monoclonal antibodies for the rapid diagnosis of influenza-B virus infections by ELISA: production and characterization.

BACKGROUND: Monoclonal antibodies directed against conserved epitopes of viral proteins have substantially improved the accuracy of several immunochemical methods in diagnostic virology. OBJECTIVES: To characterize mouse monoclonal antibodies directed against structural protein antigens of influenza-B virus and evaluate their use as diagnostic reagents for the direct detection of such antigens in clinical specimens from patients with respiratory infections of unknown aetiology. STUDY DESIGN: (a) Production and characterization of monoclonal antibodies against influenza-B viral antigens, and (b) their use in two different ELISA systems for detecting influenza-B antigen either directly in clinical specimens or after confirmation by rapid culture in MDCK cells. RESULTS: Four monoclonal antibodies were selected for their specificity for the nucleoprotein antigen as demonstrated by Western blot analysis. The specificity of these antibodies for different epitopes of the nucleoprotein was demonstrated by competition experiments, using unlabelled and biotin-labelled purified antibodies in a sandwich assay. All four antibodies belong to the mouse IgG(2a) isotype, lack haemagglutination inhibition and neutralization properties and exhibit titres as high as 10(-6) in ELISA with as little as 30 ng purified influenza-B virus. ELISA methods using these antibodies detected only influenza-B viral antigens in direct testing of clinical specimens from patients with known influenza-B or influenza-A infections, or after reisolating virus from such specimens in tissue culture of MDCK cells. CONCLUSION: The antibodies were suitable for the direct detection and typing of influenza-B virus in clinical specimens or for use in rapid confirmation cultures.

Journal Article↗