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PubMed1986

2,4-Dinitrophenyl (DNP)-specific continuous B cell lines as a model system for studying B cell activation and tolerance.

Various model systems have been used to study isolated B cell response to receptor cross-linking and to lymphokines. Although each model is useful it is advantageous to have continuous cell lines of nonmalignant antigen-specific B lymphocytes to study antigen-induced B cell function. We further studied the characteristics of the 2,4-dinitrophenyl (DNP)-specific continuous B lymphocyte lines which we previously described (J. Exp. Med. 1983. 157:342). If the cell line lymphocytes are cultured with the antigen DNP-Ficoll without the presence of T cell factors or filler cells they do not produce an immune response above background, but the addition of supernatant from EL4 lymphoma and irradiated normal spleen filler cells results in a 7- to 10-fold increase in plaque-forming cells. The kinetics of the immune response is the same as that seen with normal B cells. Each cell line has a majority of cells which are small surface (s)IgM- lymphocytes which have cytoplasmic IgM and react with 14.8 antibody. There are also large sIgM+-bearing cells, which may be either in the resting or activated state. Some of the sIgM+ cells also bear IgD and Ia antigens but they do not bear IgG. From these studies we conclude that the continuously growing antigen-specific B cell lines can be a useful model to study B cell function.

Animals↗

PubMed2004

Stepwise metastatic human hepatocellular carcinoma cell model system with multiple metastatic potentials established through consecutive in vivo selection and studies on metastatic characteristics.

PURPOSE: To establish a "stepwise metastatic human hepatocellular carcinoma (HCC) cell model system" for in-depth study of the underlying mechanisms of HCC metastasis. METHODS: Using MHCC97- a metastatic human hepatocellular carcinoma (HCC) cell line reported in 1999-as the parent cells, we subsequently established three cell lines (MHCC97-L, HMCC97-H, and HCCLM3) with increasing spontaneous metastatic potential. Now, the fourth cell line with unique multiple metastatic characteristics has been established by six rounds of in vivo selection. RESULTS: This cell line, designated as HCCLM6, is a polygonal epithelial cell with hypotriploid karyotype, the modal chromosomes are 55-58, and marker chromosomal abnormalities include i(1) (q10), i(8)(q10), der (4) t(4;8)(q31;q22), i(X)(q10). The cell population doubling time was 32 h. Fluorescent PCR showed HBV DNA integration in the cellular genome. Thirty-five days after HCCLM6 was injected subcutaneously into BALB/c nude mice, prominent lung metastases occurred in 100% of the recipient animals. When tumor tissue was orthotopically implanted into the liver of nude mouse, widespread loco-regional and pulmonary metastases occurred. Inoculation of this cell into the footpad of nude mice also produced 75% regional lymph node metastasis. Compared with MHCC97-L which was not metastastatic via subcutaneous or footpad inoculation and 40% metastatic via orthotopic inoculation, HCCLM6 had increased expression of matrix metalloproteinase (MMP-2 and MMP-9) and cytokeratin 19 (CK19), and decreased expression of Rb2/p130. The establishment of this new cell line has completed our stepwise metastatic HCC cell mode system, which was characterized by a similar genetic background but with significant differences in spontaneous metastasis behavior. CONCLUSIONS: The study supports the theory that cancer metastasis is a highly selective dynamic process and the cell model system could be a useful platform for the study of HCC metastasis.

Animals↗

PubMed2001

A novel in vitro model system to grow films of oral bacteria for the study of human tooth root surface caries.

AIMS: To develop a simple and flexible novel in vitro model system to grow films of oral bacteria that could be used to study aspects of dental caries. METHODS AND RESULTS: Standardized suspensions of bacteria were inoculated into Ultrafree-CL (Millipore) ultrafiltration units at various densities. These were incubated for varying time intervals with a range of carbon sources. The bacterial films reproducibly achieved between 107 and 108 cfu cm-2, irrespective of the number inoculated and with no significant changes for 14 d. However, Streptococcus mutans grew through membranes with pores of diameter greater than 0.1 microm after 6 d. Culture of films in sucrose or water for 6 d led to a decreased number of colony-forming units, but returning them to broth reversed this. CONCLUSION: Reproducible films of oral bacteria can be cultured in Ultrafree-CL units. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has shown that Ultrafree-CL units can be used as a simple model system to grow biofilms that could be used for dental caries research.

Biofilms↗

PubMed1993

Comparison of uptake characteristics of thymidine and zidovudine in a human intestinal epithelial model system.

The uptake of a natural nucleoside, thymidine (THY), and one of its deoxynucleoside analogues, zidovudine (AZT), was studied in a newly developed intestinal epithelial model system (CaCO-2). The results of the study indicated that the uptake rate of THY was saturable with a Km of 44.6 microM and maximum rate of 1.73 +/- 0.17 pmol/cm2/s. The uptake of AZT, on the other hand, was not saturable. When various naturally occurring nucleosides were used as inhibitors of THY uptake, it was shown that the uptake was inhibited by various pyrimidine nucleosides (e.g., uridine and cytidine), but not by purine nucleosides (e.g., guanosine). Neither group of nucleosides had any effect on the uptake of AZT. Finally, the uptake of THY was also inhibited by the metabolic inhibitor NaCN and a couple of specific nucleoside transporter inhibitors [i.e., dipyridamole and S-(p-nitrobenzyl-6-thioinosine], whereas none of these compounds had a significant effect on the uptake of AZT. The results showed, for the first time, the existence of a nucleoside carrier in the CaCO-2 cell culture model system. Also the results indicated that the uptake of AZT by the CaCO-2 cell monolayers is mainly via a passive diffusion process.

Cells, Cultured↗

PubMed1995

Hormonal control of apoptosis: the rat prostate gland as a model system.

Because of the large proportion of cells that undergoes apoptosis in response to castration and because of the predictable time in which apoptosis occurs subsequent to castration of an adult male, the rat ventral prostate gland provides a superior model system in which to study the process of apoptosis in vivo. This model system has already proven to be one of the more fertile systems for the identification of specific gene products that have the potential to effect apoptosis. Unfortunately, this in vivo system has limited usefulness for the types of genetic manipulations required to prove the role of any given gene product in the onset and procession of apoptosis. Direct genetic manipulation of a living tissue remains a goal of molecular biology-based therapies, especially for peripheral tissues such as the prostate gland. Appropriate in vitro (cell culture) models in which to study androgen-regulated apoptosis of prostate cells are currently unavailable because prostate epithelial cells, once established in culture, are no longer dependent on androgenic steroids. In the future, genetic approaches involving gene targeting through transgenic mouse technology may provide the kind of information needed to evaluate the role of individual gene products in prostate cell apoptosis.

Androgen Antagonists↗

PubMed1978

A new dynamic model system for the study of capture reactions for diffusable compounds in cytochemistry. I. Description of the model with special attention to phosphate capture in acid phosphatase cytochemistry.

A model system is described for the investigation of the dynamics of precipitation processes in a matrix. In this system a solution containing the molecular species to be precipitated and the precipitating medium are pumped along opposite sides of a polyacrylamide film. The solutions flowing continuously along the film, interact and can form a precipitate inside the film. The applicability of the model was tested on the capture reaction for phosphate ions by the Gomori type medium for acid phosphatase. Precipitation of lead phosphate in the film occurred only at a phosphate concentration above a certain value. The dependence of this minimal phosphate concentration on various parameters was studied and the results were compared with values found in earlier model studies and calculations concerning phosphate concentrations that can be built up in lysosomes during the Gomori reaction. The system seems promising for obtaining fundamental data about other cytochemical enzyme trapping reactions as well as for the matrix facotrs involved in bone calcification and shell formation.

Acid Phosphatase↗

PubMed1983

N,N-dibutylnitrosamine metabolism by rat liver S9 fraction and oxidation by chemical model systems.

Oxidative in vitro metabolism of N,N-dibutylnitrosamine (DBN) by 9000g supernatant fraction (S9 fraction) prepared from rat liver and oxidation of DBN by chemical model systems (Udenfriend and Fenton) were investigated. The products retaining the N-nitroso group of DBN were analyzed by gas-liquid chromatography. Incubation of DBN with the S9 fraction gave hydroxy derivatives of DBN at the omega, omega-1, and omega-2 positions, while the chemical reaction of DBN in the Udenfriend and the Fenton model systems afforded compounds with an oxo group at the same positions. In all cases, omega-1 oxidation was predominant, followed by omega and then by omega-2 oxidations, while omega and omega-1 oxidations were the principal metabolic pathways of DBN in vivo in the rat. The differences in the oxidative transformation of DBN among in vitro enzymatic, non-enzymatic and in vivo systems are discussed.

Animals↗

PubMed2004

Rational design of a bimodular model system for the investigation of heterocyclization in nonribosomal peptide biosynthesis.

Cyclization (Cy) domains in NRPS catalyze the heterocyclization of cysteine and serine/threonine to thiazoline and oxazoline rings. A model system consisting of the first two modules of bacitracin synthetase A fused to the thioesterase (Te) domain of tyrocidine synthetase was constructed (BacA1-2-Te) and shown to be active in production of the heterocyclic IleCys(thiazoline). Based on this model system, the feasibility of Cy domain module fusions was investigated by replacing the BacA2 Cy-A-PCP-module with modules of MbtB and MtaD from the biosynthesis systems of mycobactin and myxothiazol, revealing the formation of novel heterocyclic dipeptides. To dissect the reaction sequence of the Cy domain in peptide bond formation and heterocyclization, several residues of the BacA1-2-Te Cy domain were analyzed by mutagenesis. Two mutants exhibited formation of the noncyclic dipeptide, providing clear evidence for the independence of condensation and cyclization.

Animals↗

PubMed2006

Primary mouse dermal fibroblast cell cultures as an in vitro model system for the differential pathogenicity of cross-species herpesvirus papio 2 infections.

Infection of mice with herpesvirus papio 2 (HVP2) parallels zoonotic monkey B virus infections. A major benefit of the HVP2/mouse model is the existence of two HVP2 subtypes: HVP2nv rapidly invades and destroys the CNS while HVP2ap produces no clinical signs and mild histopathological lesions. However, in the natural baboon host, no difference in pathogenicity of HVP2 subtypes is evident. Primary dermal fibroblast cells were evaluated as a model system for defining virus-host interactions that influence the outcome of a cross-species infection. No differences in plaque formation or virus replication were observed between HVP2 subtypes in primary baboon dermal fibroblast cultures. In contrast, when primary mouse dermal fibroblasts (PMDF) were infected, HVP2nv replicated to higher titers and was more efficient at shutting down host-cell protein synthesis compared to HVP2ap. HVP2ap-infected PMDF cells produced more IFN-beta compared to HVP2nv, and IFN-beta pretreatment of PMDF cultures inhibited HVP2ap replication but did not affect HVP2nv. The differential pathogenicity of HVP2 subtypes in mice and the lack of such differences in the natural baboon host are recapitulated in the primary dermal fibroblast cell culture system. This model may prove useful in examining early, local, host responses that influence the outcome of cross-species infections.

Animals↗

PubMed1984

Interference in general immune function by parasite infections; African trypanosomiasis as a model system.

Many parasitic diseases are accompanied by an immunosuppression which may affect only parasite-specific responses in some infections or lead to a general dysfunction of the immune system in others. African trypanosomiasis causes a particularly severe disorder of the immune system and this serves as a model system for analysis of the cellular basis of a parasite-induced general immune dysfunction affecting nearly all T- or B-lymphoid cell subpopulations. The nature of the parasite products causing havoc in the immune system may well vary in different infections and still remains to be defined. Trypanosome membrane fractions are active in vitro or in vivo but we have no evidence for a direct action on B- or T-cells. In vitro, both in man and mouse, T-cells are stimulated, but only in the presence of accessory cells. This points to the importance of host-derived immunosuppressive factors in the immune dysfunction. We have evidence that macrophages, after uptake of parasites in the presence of antibodies, are at least one target cell for parasite action. They can mediate immunosuppression and undergo changes in phenotype and mediator release during the course of infection. The macrophages show all the characteristic signs of activation, which can also be induced by other means and other infective agents such as BCG. Thus, macrophage activation would provide a common pathway for induction of a general immunosuppression in different infections.

Animals↗

PubMed1999

A computer-aided approach to the structural analysis and modification of a large circulatory system model.

The purpose of this study is to show an approach to making an intelligent support system for understanding and modifying a large circulatory system model using techniques of system analysis. Structural analysis makes it possible to visualize hierarchies of Coleman's circulatory model Human. Two techniques are successively applied for structural analysis, model reduction and graph analysis by interpretative structural modeling (ISM). First, the analysis for model reduction removes input-output relations with an input-output gain less than a given threshold, and second, the ISM technique applied to the reduced model of Human provides hierarchical directed graphs. The proposed approach: 1) enables visualization of a hierarchy graph of cause and effect relations of the large circulatory model, 2) suggests control and diagnostic information to the model by tracing back a path in the hierarchy, and 3) allows the user to modify the circulatory model. The efficiency and performance of the proposed approach demonstrates technical indications of success in analyzing and justifying experimental evidences with the online help of the system.

Algorithms↗

PubMed1981

The pH dependence of photosensory responses in Stentor coeruleus and model system.

1. Live Stentor coeruleus exhibits a substantially red-shifted fluorescence maximum, corresponding to the anionic species of the photoreceptor chromophore. No change was observed in either the absorption or fluorescence excitation spectrum, indicating an efficient deprotonation of the photoreceptor pigment upon excitation by light. 2 Changes in external pH exhibit a dramatic effect on the pulmonary response of Stentor. Phototaxis is specifically inhibited at pH less than 6, with loss of photosensory perception which is restored when the pH is returned to pH greater than 6. 3. Fluorescence changes of 9-aminoacridine in suspensions of live Stentor indicate the generation of a pH gradient upon irradiation with light. Both pH gradient and phototaxis were inhibited by the addition of nigericin and p-tri-fluoromethoxy carbonyl cyanide phenylhydrazone (FCCP). 4. Incorporation of the Stentor photoreceptor protein in to artificial liposomes demonstrates the ability of the system to generate pH gradients across model membranes as monitored by the quenching of 9-aminoacridine fluorescence. The effect of external pH on net proton movement in the model system is strikingly similar to the pH dependent of the liver Stentor, thus lending support for transient proton flux being an important mode of light signal processing for photosensory transduction.

Animals↗

PubMed1982

Model system oxidations supporting the crystal growth model of ferritin iron uptake.

Fe2+ is oxidized and taken up by ferritin or ápoferritin in the presence of dioxygen. Iodate causes Fe2+ oxidation and uptake by ferritin, but not by apoferritin. Synthetic iron polymer facilitates Fe2+ oxidation by either dioxygen or iodate. Nitrilotriacetic acid or iminodiacetic acid facilitate oxidation of Fe2+ by oxygen but not by iodate. These results support the crystal growth model of ferritin iron uptake, with iron polymer serving as a model for the ferritin core and aminocarboxylic acids mimicking the metal-binding sites of apoferritin.

Apoferritins↗

PubMed1991

A bacterial model system for chromosomal targeting.

A system that permits efficient site-specific chromosomal targeting of foreign DNA on the Escherichia coli chromosome has been developed, using the FLP site-specific recombination system derived from the yeast 2 mu plasmid. The system demonstrates the feasibility of using site-specific recombination for this purpose, and provides a means to gather information on parameters that may affect chromosomal targeting to guide efforts to establish similar systems in higher eukaryotes. In this model system, the efficiency of integration of foreign DNA is affected by the location of the target site in the chromosome, and the structure of the recombination sites.

Base Sequence↗

PubMed2001

Hibiscus acid as an inhibitor of starch digestion in the Caco-2 cell model system.

Hibiscus acid, an alpha-amylase inhibitor isolated from roselle tea, and its derivatives were compared in an inhibition test for starch digestion. An alpha-amylase-added Caco-2 system was established as a useful model to evaluate the effects of alpha-glucosidase inhibitors on starch digestion. Hibiscus acid showed weak inhibition in this model system, and the methyl ester derivatives showed even weaker or no acitivity.

Animals↗

PubMed2006

Using a human visual system model to optimize soft-copy mammography display: influence of veiling glare.

RATIONALE AND OBJECTIVES: This project evaluated human observer performance and that of a human visual system model (JNDmetrix) to assess whether the veiling glare of a digital display influences observer performance during soft-copy interpretation of mammographic images for the detection of masses. MATERIALS AND METHODS: A set of 160 mammographic images, half containing a single mass, was processed to simulate four levels of veiling glare: none, comparable to a medical grade monochrome curved-screen cathode ray tube (CRT) display, double that of the CRT and quadruple that of the CRT. The images were shown to six observers in a randomized presentation order on a liquid crystal display (LCD) that had essentially no veiling glare. The images were also analyzed using the JNDmetrix human visual system model. RESULTS: Observer performance as measured using receiver operating characteristic techniques declined with increasing veiling glare (F = 6.884, P = .0035), with quadruple veiling glare yielding significantly lower performance than the lower veiling glare levels. The JNDmetrix model did not show a large reduction in performance as a function of veiling glare, and correlation with the human observer data was modest (0.588). CONCLUSIONS: Soft-copy display veiling glare can influence observer performance, but only at extreme levels. The impact of veiling glare on performance may be more pronounced for less experienced readers.

Glare↗

PubMed1998

The dog as a model system to study epididymal gene expression.

Advances in understanding the role of the epididymis in human sperm maturation and fertility are dependent upon the availability of appropriate model systems in which to examine regulatory mechanisms and functions in a controllable fashion. Of a number of mammalian species studied by us and others, we suggest that the dog epididymis offers an excellent compromise in terms of the similarity of the specific genes expressed to those in the human, their mode of regulation, and the availability of tissues suitable for cell culture studies. We have developed a set of important tools in the form of epididymis-specific canine cDNA clones and cell culture methods, with which to examine the functioning of the epididymal epithelial cells in vitro, as well as the expression of specific genes in vivo, under normal and pathological conditions (e.g. cryptorchidism). Using this model system, we have elaborated the regional patterns of gene expression in vivo for several of the major secretory protein genes of the canine epididymis, and we have examined the importance of androgens and temperature on gene expression in vitro.

Animals↗

PubMed2003

A colloidal model system with an interaction tunable from hard sphere to soft and dipolar.

Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics--such as glass transitions and crystal nucleation. But to date, no quantitative real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension--poly(methyl methacrylate) spheres in a mixture of cycloheptyl (or cyclohexyl) bromide and decalin--where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behaviour, with several unusual colloidal (liquid) crystalline phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concentration; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external electric field ranging from a small perturbation to the point where it completely determines the phase behaviour. We also demonstrate that the electric field can be used as a pseudo-thermodynamic temperature switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheological fluids.

Journal Article↗