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Biomedical subjects

M Popescu

Publications and source records attributed to M Popescu.

At least 55 records · Page 3Linked to original sources
PubMed1982

Procedure for titration of interleukin-2 based on direct observation of factor-dependent growth of cells.

A semi-quantitative procedure for titration of interleukin-2 (IL-2) without the use of radioactive labeling of IL-2 target cells was developed. The procedure is based on the observation that those cells cultivated in round-bottom wells formed visible cultures and that the dimension of these cultures decreased at higher dilutions of IL-2 in the medium. The end-point of the titration can be easily established by observing the cultures with a concave mirror placed under the titration plate. The procedure has been used for the determination of IL-2 during its purification and characterization.

Animals↗
PubMed1982

Multiplication of lymphocytic choriomeningitis virus in thymocytes during its persistence in mice.

Persistence of lymphocytic choriomeningitis (LCM) virus in mice infected in utero or neonatally is due to impairment of the specific subsets of thymus-dependent lymphocytes which, in the adult normal mouse, are involved in elimination of LCM virus. Virus-thymocyte interactions were studied since it was likely that this impairment takes place in the thymus. Using an infectious centre assay, we found that about 1% of the thymocytes from foetal and neonatal mice were productively infected by the virus while thymocytes from older mice were refractory to infection. The infected cells were Thy 1-positive and agglutinated by peanut lectin together with immature lymphocytes. Later, when virus persistence was established, the number of infected thymocytes declined to about 0.1% and these cells were not agglutinated by lectin. The results are compatible with the assumption that thymic precursor T-cells capable of elimination LCM virus are chronically infected by the virus and rendered non-functional.

Aging↗
PubMed1979

Infectious lymphocytes in lymphocytic choriomeningitis virus carrier mice.

The infectivity of blood and lymphoid organs of mice persistently infected with lymphocytic choriomeningitis virus was found to be predominantly associated with lymphocytes and both T and B cells were infectious. A hypothesis is presented in which it is assumed that lymphocytes in carrier mice are infected via their LCM virus-specific antigen receptors, thereby leading to their antigen-triggered clonal expansion followed by infection and functional inactivation.

Animals↗
PubMed1976

Diversity of lymphocytic choriomeningitis virus: variation due to replication of the virus in the mouse.

Depending on passage history, strain WE infectious LCM virus either damages L cells more or less severely or leaves them morphologically intact. Correspondingly, the plaques which are formed on L cell monolayers are of different appearance, ranging from intensely turbid to clear. Multiplication of LCM virus in certain mouse organs profoundly affects plaque characteristics. The brain, for instance, favours lytic variants while the spleen supports the replication of virus which forms turbid plaques. This statement holds if virus taken from organs of persistently infected mice or virus passaged from mouse to mouse is analysed and is true also if the initial preparation contains virus forming predominantly either clear or turbid plaques on L cell monolayers. Selection is not rapid and not absolute. It may take months of multiplication before a final state is reached, and even then the number of characteristic plaques is usually in great excess of the rest but never reaches 100%. Cloning procedures may alter the proportions, but with our experimental conditions no plaque has ever been isolated which would retain its characteristics upon passage. Differences of plaque type morphology were not reflected in differences of pathogenic properties, and both clear and turbid variants caused persistent infection if used to infect newborn mice and led to disease with signs of neurological involvement and death if inoculated intracerebrally into adult animals.

Animals↗
PubMed1976

Homologous interference of lymphocytic choriomeningitis virus: detection and measurement of interference focus-forming units.

Lymphocytic choriomeninigitis (LCM) virus defective interfering (DI) particles form foci of protected cells in a monolayer under an agarose-containing overlay medium. Foci originate from one cell dually infected with at least 1 interference focus-forming unit and infectious virus. As a result, an interfering factor is produced and released which interacts with neighboring cells, thereby protecting them against cytopathic lysis by challenge virus. The property of individual LCM virus DI particles to induce countable foci has been made the basis of quantitative assay that is comparable in every respect to the plaque assay of infectious virus and is much more sensitive and probably more accurate than other procedures used to measure LCM virus DI particles. LCM virus was passaged, undiluted, 10 times in cell cultures. When yields were analyzed as to concentrations of PFU and interference focus-forming units, both entities were found to fluctuate with the pattern expected from theoretical considerations.

Cell Line↗
PubMed1976

Dynamics of the changes in the tissular levels of cyclic AMP after cobalt-60 gamma-irradiation.

The total amounts of cyclic AMP in liver, brain and intestinal mucosa have been measured in rats, at constant intervals, up to 18 days after whole body exposure to either a unique moderate dose (500 rd) or a unique lethal dose (750 rd) of cobalt-60 gamma-radiation. This radiation, even in a lethal dose, was found to induce no significant changes in the hepatic levels of cAMP. In contrast, an abrupt short-lasting increase in the levels of cAMP was observed in brain and intestinal mucosa after a 500-rd-irradiation, and a progressive long-lasting increase in its levels in the intestinal mucosa and, especially, in the brain was found after a 750-rd-irradiation. It is concluded that these organs contain different cAMP systems, which would explain, at least in part, their dissimilar responses to the ionizing rays.

Adenosine Triphosphate↗
PubMed1975

The in situ localization of folic acid.

A histochemical azo-coupling method for localizing folic acid in situ is described. Cat and rat liver, kidney, bone marrow and brain were found to be rich in folic acid; stomach, intestine, salivary glands, and blood contained less. Folic acid was localized in the cytoplasm of tissues having a very active metabolism, but in the nucleus of highly specialized cells such as neurons.

Animals↗
PubMed1975

Use of iodinated organic compounds for the density gradient centrifugation of viruses.

Use of Urografin and Conray for the equilibrium centrifugation of viruses is described. These pharmaceuticals, which consist of iodinated arylic compounds, reach densities of 1.6 g/cm3 and have low intrinsic viscosities. Poliovirus, Newcastle disease virus, and lymphocytic choriomeningitis virus were centrifuged to equilibrium in gradients made of these substances. Viral infectivities were not measurably affected, which is especially noteworthy in the case of the very labile lymphocytic choriomeningitis virus. Buoyant densities were found to be significantly lower than densities obtained with gradients made of CsCl and sucrose.

Centrifugation, Density Gradient↗
PubMed1975

LCM virus infection of cells in vitro.

Most mammalian cells cultivated in vitro can be infected with lymphocytic choriomeningitis (LCM) virus. In addition to infectious virus, the cells produce antigenic material that fixes complement in the presence of antibody and is precipitated by antiserum. Intracellular antigen can also be demonstrated by the immunofluorescence procedure. When infected cells are viewed with the electron microscope, viral structures are seen either budding from or in association with the cell membranes. Immunoelectron microscopy, immunofluorescence, and cytotoxicity tests reveal virus-specific antigens on the surface of intact cells. Virus multiplication may be succeeded by cytolysis. Two LCM virus-specific antigens (or antigenic groups) can at present be distinguished. One corresponds to the infectious virus; the other is the complement-fixing "soluble" antigen. This extractable complement-fixing activity is produced by infected cells and is also a structural component of the infectious virus. It is not represented on the surface of either the virion or the infected cell. The cytolytic potential of LCM virus varies and is dependent on its previous passage history. Cytolytic and "attenuated" variants are able to initiate persistent infection of Mus musculus.Together with infectious virus, particles are produced that temporarily protect cells against standard virus. They appear to be by-products of virus multiplication, not in the sense of deletion mutants but of virus structures insufficiently equipped for their own active or passive replication, though capable of interfering with infectious virus. No evidence has been found for the generation of "defective interfering" particles, though their presence has not yet been excluded.

Animals↗
PubMed1975

Cholinergic innervation of the human stomach.

A histochemical method for the acetylcholinesterase activity was used to establish the parasympathetic components of the gastric coats in man. The four gastric layers contain a rich cholinergic innervation. In the mucosa the positive nerve fibers are located around the gastric glands and between the muscles of the muscularis mucosae. In the submucosa rich interconnected nerve fibers, rare large nerve trunks, and scarce ganglia cells show a strong cholinergic reaction. The muscular layer contains the highest density of cholinergic nerve fibers, isolated or in large bundles. Auerbach's plexus has a strong acetylcholinesterase activity in the nerve cell bodies. The subserous layer is very rich in cholinergic nerve fibers, rarely isolated, but interconnected. The vessels of each gastric layer exhibit a rich cholinergic innervation in the adventitia and the outside part of media.

Acetylcholinesterase↗
PubMed1975

Folate metabolism in normal peripheral leukocytes in children.

The activity of dihydrofolate dehydrogenase by histochemical method in children leukocytes was investigated. Blood leukocytes have a positive enzymic activity. Except monocytes a large enzymic variability was observed in neutrophils, eosinophils, and lymphocytes in puberty and at the onset of the adolescence. Enzymic activity varies with blood cellular type, the age, in males and females and from one child to another.

Adolescent↗