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PubMed1988

[Cytometric method of determining the parameters of the interaction of synthetic immunostimulants with the lymphocytic surface].

The cytofluorimetric method was suggested for the determination of parameters of polymer adsorption on the cellular surface. Multiple equilibrium in the homogeneous cellular population with N independent binding sites and in the heterogeneous population of cells with the Poisson distribution of adsorption sites was analysed. A possibility was shown of cytofluorimetric drawing of the adsorption isotherm using mean fluorescence intensity of cells in the equilibrium suspension. The equilibrium association constant and the mean number of binding sites were estimated for adsorption of poly-L-lysin on the surface of human myelogenous leukemic cells (cellular line K-252).

Adjuvants, Immunologic↗

PubMed1977

Quantitative aspects of an in vivo diffusion chamber assay for normal human hemopoietic colony forming units.

The purpose of the present study was to definite some of the quantitative characteristics of the colonies formed by normal human hemopoietic cells in diffusion chambers in vivo. The cells were cultured in fibrin clots in diffusion chambers, which were implanted i.p. into 450 R irradiated mice, reimplanted into newly irradiated mice after 7 days and harvested by a previously described chamber centrifugation technique after a total of 14 days. At low cell doses per chamber, no colonies were observed; however when more than 3-8 X 10(4) cells were inoculated per chamber, the number of granulocytic colonies was proportional to the cell dose. Similar dose-reponse curves were obtained when the cells were harvested in suspensions from the chambers. The granulocytic colonies do not conform to a Poisson distribution when identically prepared chamberbeare compared, but show a more heterogeneous distribution. Evidence is presented that this heterogeneity is not due to technical errors in the process of chamber filling and harvesting. A host factor was found to influence the mean number of cells per neutrophilic colony, but the heterogeneity of the total number of neutrophilic or eosinophilic colonies of more than five cells could not be ascribed to variable host factors. There was a mean of 3.6 granulocytic colonies (of more than 30 cells) per 10(5) cells implanted in a series of 15 normal bone marrows cultured. The mean size of neutrophilic colonies was 23 cells. Determinations in duplicate suggest that the method may serve as an assay for certain classes of colony forming cells, provided the number of chambers in each assay is sufficiently high.

Animals↗

PubMed1987

Risk of neoplastic transformation from cellular DNA: calculations using the oncogene model.

Based on a number of assumptions about oncogene size, frequency, biological integrity, and in vitro as well as in vivo transformation efficiency, estimates are made of the risk that the residual cellular DNA (rcDNA) contaminant in a biological product will cause a neoplastic transformation event. Using a statistical Poisson distribution approach, the probability of such an event is calculated to be at most 10(-6) assuming optimal in vitro conditions with 100 oncogene copies per cell and a 10 pg contaminant. More realistic assumptions using in vivo data suggest that the probability of a transformation event is at most 10(-9) assuming 100 oncogene copies per cell and a contaminant of 1 ng. Imperfections of the model and specific considerations of the human in vivo case are discussed.

Animals↗

PubMed1986

O6-methylguanine mutation and repair is nonuniform. Selection for DNA most interactive with O6-methylguanine.

Mutations were induced in the ampicillinase gene of a bacteriophage f1/pBR322 chimera both by incorporation of O6-methyl-dGTP opposite T during DNA replication in vitro and by site-directed mutagenesis using O6-methylguanine-containing oligonucleotides. After passage of the DNA through Escherichia coli, analysis of 151 O6-methyl-dGTP-induced mutations indicated a significantly greater number of unmutated mutation sites than expected, whereas the mutated sites generally fit a Poisson distribution. The unmutated sites are assumed to be caused by the inability of some sequences to tolerate the presence of a tetrahedral methyl group within the confines of a Watson-Crick helix (Toorchen, D., and Topal, M.D. (1983) Carcinogenesis 4, 1591-1597). A consensus of the DNA sequences surrounding unmutated mutation sites was derived. The consensus sequence had significant similarity to the region of the rat Harvey ras oncogene containing the N-methyl-N-nitrosourea activated site for transformation (Zarbl, H., Sukumar, S., Arthur, A. V., Dionisio, M.-Z., and Barbacid, M. (1985) Nature 315, 382-385). We propose that direct alkylation at O6 of a guanine present within the consensus sequence may produce a DNA conformation less subject to repair. Mutation by O6-methylguanine-containing oligonucleotides demonstrated that repair of the O6-methylguanine lesions varied at least 3-4-fold with position of the lesion.

Alkylation↗

PubMed1987

Optimal background estimation in EELS.

In quantitative electron energy loss spectrometry, it is desirable to estimate the background law below core edge energy in a way that provides the maximum signal-to-noise ratio. Assuming an inverse power background model and independently Poisson distributed measurements, it is shown how to achieve this goal by using a maximum likelihood (ML) estimation technique which provides unbiased and minimum mean square error estimates of all parameters of interest. An efficient and computationally stable implementation of this procedure is proposed. Standard logarithmic least squares estimations are then compared with the ML approach and the gain in performance due to optimal processing is quantified.

Electrons↗

PubMed1987

Limiting dilution clonal assay of human bone marrow hematopoietic progenitors (granulocytes-macrophages).

We have developed a limiting dilution assay for human bone marrow hematopoietic precursor (granulocytes-macrophages) in microwells. Bone marrow cells were fractionated by discontinuous Percoll gradients and diluted in culture medium containing colony-stimulating factors. They were diluted and cultured in medium containing colony-stimulating factor and 10(-5) M hydrocortisone in microwells over a range of cell densities that allowed calculation of the frequency of growth-inducible precursors. After 10 days, the wells were examined for clonal growth. Clonal proliferation followed the single-hit model of the Poisson distribution. More progenitors were detected in this assay than in simultaneous methylcellulose colony assays or agar cultures. Thymidine suicide experiments led to an increase in the frequency of progenitors detected in this assay, but a decrease in the frequency of methylcellulose colonies. This system may detect additional, less mature progenitors than are detected in semisolid culture systems.

Bone Marrow Cells↗

PubMed1986

Mutational extinction induced by sequential X irradiation and actinomycin D treatments in Chinese hamster ovary cells.

The interactions of sequential X irradiation and actinomycin D (AMD) treatments for mutagenesis to 6-thioguanine resistance were investigated in CHO cells. Cells were exposed to single doses of X rays followed immediately by 1-h treatments with 0.1 or 1 microgram/ml AMD. X Rays alone induced mutagenesis which increased monotonically with dose to at least 8 Gy. AMD-treated control cultures showed slight to moderate cytotoxicity and little induced mutation. X Rays followed by AMD treatment produced bell-shaped mutagenesis dose-response curves with maximal mutation at approximately 5 or 4 Gy for 0.1 or 1.0 microgram/ml AMD, respectively. Induced mutation frequencies then fell to a negligible level at fractional survival levels below 0.10 for either combination treatment. Application of a stochastic Poisson distribution model to these data led to the prediction that two possible components govern induced mutation frequencies. First, X ray +AMD induced mutations may be depleted progressively with dose from the surviving populations by selective lethality, which we term mutational extinction. Second, X ray +AMD treatments were calculated to induce potentially much greater than additive mutagenesis. However, due to the overriding mutational extinction effect, most of these mutations are not recovered as viable colonies. These studies suggest that AMD binding to DNA immediately following irradiation may cause considerably enhanced mutagenic and often lethal DNA damage, and that mutational extinction may occur because these types of damage are statistically correlated in a sensitive subpopulation of exponentially growing CHO cells.

Animals↗

PubMed1979

[Further observations of the course of Plasmodium berghei infection in the mouse].

Invasion of immature and mature erythrocytes by merozoites of Plasmodium berghei seems to obey the following rules: Merozoites prefer unparasitized immature erythrocytes. Multiple infections of immature erythrocytes occur in conditions of high merozoite production and low concentration of unparasitized immature erythrocytes, when frequently repeated contacts between merozoites and unparasitized or freshly parasitized immature erythrocytes become increasingly probable. Mature erythrocytes are invaded when the relative density of unparasitized immature erythrocytes drops below 0.2--0.5%, in other words, when merozoites do not meet unparasitized immature erythrocytes in 200--500 erythrocytes. Failure to invade mature erythrocytes is obviously not due to inability of the merozoites to penetrate the erythrocyte membranes.--Merozoites of Plasmodium vinckei, on the other hand, show random invasion of parasitized and unparasitized mature erythrocytes, leading to frequencies of unparasitized and singly or multiply parasitized erythrocytes approaching a Poisson distribution.--The Plasmodium berghei infection regularly leads to a lowered density of polychromatophilic erythrocytes in the peripheral blood. This depression of polychromatophilic erythrocytes uses to be of very different duration, form and intensity. The relative density of immature erythrocytes may show pronounced fluctuations in this phase. As has been seen in one animal, even monocytes and polymorphonuclear leucocytes may, alongside with the immature erythrocytes, for some time totally disappear from the peripheral blood. The depression of polychromatophilic erythrocytes evidently goes along with pronounced alterations of the erythropoesis in spleen and bone marrow. Leucocytes in the peripheral blood generally show rather uncharacteristic alterations of their concentration, they may form very high concentration peaks.

Animals↗

PubMed1985

Estimation of cancer mortality rates: a Bayesian analysis of small frequencies.

A Bayesian method is presented for estimating mortality rates of specific diseases when the frequency of deaths over a specified time period is assumed to have a Poisson distribution with mean proportional to the population size. The estimators use information from related populations, each having its own rate which is assumed distributed according to a common prior distribution about which some information is available. The study was motivated by an epidemiological study on the geographic variation of cancer mortality in the state of Missouri. Data from this study are used to illustrate the method and to compare it to a somewhat simpler empirical Bayes method.

Biometry↗

PubMed1985

Some extensions of a linear model for categorical variables.

The Grizzle-Starmer-Koch (GSK) model is extended to include the traditional log-linear model and a general class of Poisson and conditional Poisson distributions. Estimators of the model parameters are defined under general exact and stochastic linear constraints.

Analysis of Variance↗

PubMed1977

[Modeling modification of chemical mutagenesis in human cells. 1. Elimination of chromosomal aberrations].

Elimination of chromosome aberrations was studied in populations of dividing cells. For this purpose, on the basis of the corresponding theory of Carrano-Heddle assuming the Poisson distribution, a theory is advanced by the authors based on geometrical distribution, describing the distribution of lesions caused by the action of tioTEF. Parameters of elimination are obtained observed in case of addition of a protector, aminopropy-laminoethylthiophosphoric acid (APAETF) in a lymphocyte culture of human peripheral blood. It is shown that the addition of the protector diminishes the probability of the transmission of chromosome aberrations to daughter cells.

Cells, Cultured↗

PubMed1974

Immunofluorescence plaque assay for African swine fever virus.

Suitably diluted cell culture adapted African swine fever virus preparations were inoculated on VERO cell monolayers and grown on coverslips. Gum tragacanth was used as an overlay. After three days incubation at 37 degrees C the infected cultures were fixed with acetone and stained with fluorescent antibody conjugate. Fluorescing plaques consisted of 20-30 infected cells. THREE STATISTICAL CRITERIA FOR A QUANTITATIVELY RELIABLE ASSAY WERE MET: the Poisson distribution for plaque counts, linearity of the relationship between the concentration of virus and the plaque count and reproducibility of replicate titrations. The method is suitable for counts up to at least 70 plaques per 5 cm(2) coverslip and computed titers are reproducible within 0.16 log units with a total of 300 plaques enumerated.

African Swine Fever↗

PubMed1983

Reverse plaque formation method for titration of non-cytopathogenic bovine viral diarrhea-mucosal disease virus.

The reverse plaque formation (RPF) method with a semi-micro plate was applied to the titration of a non-cytopathogenic (non-CP) strain of bovine viral diarrhea-mucosal disease (BVD-MD) virus. All the five non-CP strains used in this experiment formed reverse plaques (RP) on bovine testicle cell culture under methyl cellulose overlay. The RPF was inhibited by the pretreatment of a non-CP virus strain with immune rabbit serum to a reference strain. The specificity of the RPF method was demonstrated by the linear test and Poisson distribution test. Comparative titration of commercial BVD-MD vaccines was carried out by the semi-micro RPF method and the tube method based on the exaltation on Newcastle disease virus. The virus titer obtained by the former was slightly higher than that obtained by the latter. The former was proved to be a method of high sensitivity for determining non-CP virus.

Animals↗

PubMed1983

Patterns of isotype commitment in human B cells: limiting dilution analysis of Epstein Barr virus-infected cells.

The frequency of Epstein Barr virus- (EBV) inducible IgM, IgG, and IgA-secreting cells in human peripheral blood and tonsil was determined by performing limiting dilution experiments in suspension culture. We devised a method of propagating small numbers of EBV-infected B cells with irradiated umbilical cord blood cells as a feeder layer. Precursor cell frequencies can be derived from these experiments; we have shown by statistical analysis that they conform to the single hit model of the Poisson distribution. By using this technique, a significant percentage of surface immunoglobulin-bearing lymphocytes are activated to secrete immunoglobulin in vitro. On the average, 8 to 38% of B cells in peripheral blood and tonsil can be propagated and the secreted immunoglobulin from the clonal progeny can be analyzed. Neither the EBV immune status of the donor nor the source of the umbilical cord blood feeder layer could account for the variations in cloning efficiency observed among donors. A surprisingly high frequency of B cells secreted IgA in vitro and we have shown that a small proportion of B cell clones in tonsil and peripheral blood secrete both IgM and IgA during the 4-wk culture period. Other B cells, including all those that produce IgG, appear to be committed to the secretion of a single isotype. Thus, these studies establish methodology for the analysis of the secreted products of human B cells at the single cell level and demonstrate that the progeny of at least some clones can secrete more than one isotype in vitro.

Adult↗

PubMed1984

[Wiener analysis of transmission of signals of identified mollusk neurons].

Mathematical model of spike train transmission by identified neurons of the mollusc Planorbis corneus was obtained by means of Wiener analysis. Poisson distributed sequences of near-threshold stimuli were used as input trains for construction and testing. It was shown that addition of terms sensitive to the nonlinear properties of the synapse-neuron system to the model decreased the model error from 25% to 16%. When comparing the mean square error value of the predicted model responses to testing stimuli and the real neuron responses to the same stimuli, the prediction error with allowance for nonlinear properties was established not to exceed 21%. Some questions connected with choosing adequate criteria for comparing model and experimental results are discussed.

Animals↗

PubMed1984

On the effect of the discrete nature of the photoelectric emission in the thermoluminescence measurements (pulse counting method).

The discrete nature of the photoelectric emission cannot be neglected at low reading levels. The effect of A/D conversion after photomultiplication were both calculated and measured. The reading and its standard deviation were considerably different from those expected on the basis of a simple Poisson distribution and this should be taken into account at low reading levels. The authors describe a simple method which permits the experimental determination of photoelectron/digit conversion factor necessary for the prediction of the variation coefficient of TL measurements.

Analog-Digital Conversion↗

PubMed1983

The estimation of age, period and cohort effects for vital rates.

In models for vital rates which include effects due to age, period and cohort, there is aliasing due to a linear dependence among these three factors. This dependence arises both when age and period intervals are equal and when they are not. One solution to the dependence is to set an arbitrary constraint on the parameters. Estimable functions of the parameters are invariant to the particular constraint applied. For evenly spaced intervals, deviations from linearity are estimable but only a linear function of the three slopes is estimable. When age and period intervals have different widths, further aliasing occurs. It is assumed that the number of deaths in the numerator of the rate equation has a Poisson distribution. The calculations are illustrated with data on mortality from prostate cancer among nonwhites in the U.S.

Age Factors↗

PubMed1983

On Ewens' equivalence theorem for ascertainment sampling schemes.

The usual likelihood formulations for segregation analysis of a genetic trait ignore both the at-risk but unobservable families and the demographic structure of the surrounding population. Families are not ascertained if, by chance, they have no affected members or if the affected members are not ascertained. Ewens has shown that likelihoods which take into explicit account both unobservable families and demographic parameters lead to the same maximum likelihood estimates of segregation and ascertainment parameters as the usual likelihoods. This paper provides an alternative proof of Ewens' theorem based on the Poisson distribution and simple continuous optimization techniques.

Genetics, Population↗