Cluster analysis of flow cytometric list mode data on a personal computer

A cluster analysis algorithm, dedicated to analysis of flow cytometric data is described. The algorithm is written in Pascal and implemented on an MS-DOS personal computer. It uses k-means, initialized with a large number of seed points, followed by a modified nearest neighbor technique to reduce the large number of subclusters. Thus we combine the advantage of the k-means (speed) with that of the nearest neighbor technique (accuracy). In order to achieve a rapid analysis, no complex data transformations such as principal components analysis were used. \ud Results of the cluster analysis on both real and artificial flow cytometric data are presented and discussed. The results show that it is possible to get very good cluster analysis partitions, which compare favorably with manually gated analysis in both time and in reliability, using a personal computer

A new principle of cell sorting by using selective electroporation in a modified flow cytometer

When a strong electric field pulse of a few microseconds is applied to biological cells, small pores are formed in the cell membranes; this process is called electroporation. At high field strengths and/or long pulse durations the membranes will be damaged permanently. This eventually leads to cell kill. \ud We have developed a modified flow cytometer in which one can electroporate individual cells selected by optical analysis. The first experiments with this flow cytometer were designed to use it as a damaging sorter; we used electric pulses of 10 s and resulting field strengths of 2.0 and 3.2 X 106 V/m to kill K562 cells and lymphocytes respectively. The hydrodynamically focused cells are first optically analyzed in the usual way in a square flow channel. At the end of this channel the cells are forced to flow through a small Coulter orifice, into a wider region. If optical analysis indicates that a cell is unwanted, the cell is killed by applying a strong electric field across the Coulter orifice. The wanted living cells can be subsequently separated from the dead cells and cell fragments by a method suitable for the particular application (e.g., centrifugation, cell growth, density gradient, etc.). \ud The results of these first experiments demonstrate that by using very simple equipment, sorting by selective killing with electric fields is possible at rates of 1,000 cells/s with a purity of the sorted fraction of 99.9%

A flow cytometric study of the membrane potential of natural killer and k562 cells during the cytotoxic process

This study demonstrates that it is possible to investigate the membrane potential of interacting cells during the cytotoxic process using flow cytometry. Changes in the membrane potential of NK and K562 cells, involved in a cell-mediated cytotoxic process, were studied by standard and slit-scan flow cytometry, using the membrane potential sensitive fluorescent probe DiBAC4(3). The NK cells were labeled with a membrane marker (TR-18 or DiI) prior to incubation with K562 cells and the conjugates that were formed could be identified on the basis of the membrane marker fluorescence and light scattering signals. With a slit-scan technique we measured the membrane potential of each cell in a conjugate separately. The results show that depolarization of the K562 cell occurs as a consequence of the cytotoxic activity of the NK cell. This depolarization appears to be an early sign of cell damage because the cell membrane still remains impermeable to propidium iodide. Our data also indicate that depolarization of the NK cell occurs as a result of its cytotoxic activity

Raman spectroscopy for guidance of vulvar cancer surgery:A pilot study

For vulvar squamous cell carcinoma (VSCC), the mainstay of treatment is surgical removal with tumour-free margins. Surgeons still operate without objective tools that provide margin-status. This study assesses Raman spectroscopy potentiality for distinguishing ex-vivo VSCC from healthy tissue in 11 patients. Grid-based Raman maps were obtained from processed spectra. Water content and C-H band ratio (2,910-2,966 cm(-1) / 2810-2890 cm(-1)) were calculated per spectrum and used as linear discriminant parameters. Healthy tissue was differentiated from VSCC with 0.90 discriminative power, 0.79 sensitivity and 0.86 specificity.This is an important step towards the development of objective tools for VSCC surgical guidance

Competition for imperfect consumers

This lecture provides a selective discussion of some issues in the economics of competition for imperfect consumers. Limited consumer awareness – about what deals are on offer, or about the consequences of purchasing decisions – is a central feature of many markets. Consumer imperfection can give rise to market power, but can also co-exist with strong rivalry between firms, and then is more for ‘consumer policy’ than competition policy. Two recent court cases illustrate some of the issues involved. The lecture then reviews a line of theoretical work on competition for imperfect consumers. The analysis highlights some policy tradeoffs, and a key theme is how patterns of consumer awareness matter for patterns of competition among firms