Data compression: 8-dimensional flow cytometric data processing with 28K addressable computer memory

Computational models in immunological methods: an historical review

The utilization of computational models in immunology dates from the birth of the science. From the description of antibody-antigen binding to the structural models of receptors, models are utilized to bring fundamental understandings of the processes together with laboratory measurements to uncover implications of these data. In this review, an historical view of the role of computational models in the immunology laboratory is presented, and short mathematical descriptions are given of fundamental assays. In addition, the range of current uses of models is explored -- especially as seen through papers which have appeared in the Journal of Immunological Methods from volume 1 (1971/1972) to volume 208 (1997). Each paper which introduced a new mathematical, statistical, or computer simulation model, or introduced an enhancement to an instrument through a model in those volumes is cited and the type of computational model noted.

Multiparameter flow cytometric analysis of a novel cytotoxin (factor 2) induced tumor cell membrane permeability

An improved twin-probe multiparameter flow cytometric technique was applied to examine a novel cytotoxin, Factor (F2), induced tumor cell permeability. Ability to retain preloaded intracellular bis-carboxyethyl carboxyfluorescein (BCECF, green fluorescence) and to exclude extracellular propidium (red fluorescence) was measured simultaneously with forward and right-angle scatter. In addition to the two expected cell populations which were stained green negative, red positive ("membrane-damaged" and "non-viable", Region 2), and green positive, red negative ("membrane intact" and "viable", Region 3), a third population was seen which fluoresced neither green nor red and displayed intermediate light scatter characteristics (Region 1). K562 cells progressed from Region 3 to Region 1, and then from Region 1 to Region 2 after treatment with F2. These results suggest that sequential changes in membrane structure lead to increased permeability, first with respect to intracellular BCECF and then in turn to extracellular propidium. Flow cytometric changes caused by F2 were detectable 10 min after treatment with 2.5 U/ml of F2, and 5 min after 10 or 40 U/ml of F2. Flow cytometric analysis showed that F2-induced tumor cell lysis and growth inhibition were accompanied by rapid alternations in tumor cell membrane permeability. Flow cytometric analysis also distinguished F2 cytotoxicity from phorbol myristate acetate (PMA) associated cytotoxicity to K562 cells and determined that F2 produced spontaneously or induced by PMA and/or ciprofloxacin had a similar ability to induce tumor cell membrane permeability change.

Multiparameter flow-cytometric quantitation of epidermal growth factor receptor and c-erbB-2 oncoprotein in normal and neoplastic tissues of the female genital tract

A novel multiparameter flow-cytometric method was used to quantify the expression of epidermal growth factor receptor (EGFR) and c-erbB-2 oncoprotein on 85 cryopreserved normal tissues (30 ovary, 29 endometrium, 16 cervix) and 67 carcinomas (31 ovarian, 18 cervical, 15 endometrial, 3 vulvar). Overexpression of the EGFR and c-erbB-2 oncoproteins was found in respectively 3/31 (9%) and 10/31 (32%) ovarian carcinomas, 13/18 (72%) and 7/18 (38%) cervical carcinomas, and 2/15 (13%) and 2/15 (13%) endometrial carcinomas. Oncoprotein expression was significantly higher in the malignant tumors (for all tumor sites) than in the corresponding normal tissues (P less than 0.034 for all combinations). Aneuploid tumors expressed levels of EGFR and c-erbB-2 oncoprotein significantly higher than those of DNA diploid tumors (P = 0.042 and P = 0.048, respectively). Oncoprotein could be detected in nearly all normal tissues: expression was higher in premenopausal than in postmenopausal patients (EGFR, P = 0.07; c-erbB-2, P less than 0.001). The present study supports the idea that EGFR and c-erbB-2 may play an important role in the autocrine, paracrine, and/or endocrine growth control and differentiation of normal tissues. Alteration in the expression of these oncoproteins is probably involved in malignant transformation and tumorigenesis.

Detection of multidrug resistance and quantification of responses of human tumour cells to cytotoxic agents using flow cytometric spectral shift analysis of Hoechst 33,342-DNA fluorescence

We describe the application of a flow cytometric technique for assessing the radiation or drug sensitivity characteristics of human tumour cells. The technique makes use of the phenomenon that a red shift occurs in the fluorescence emission spectrum of a DNA-specific dye (Hoechst 33,342) as an increasing number of dye molecules bind to nuclear DNA. Intact, viable cells undergo a time-dependent spectral shift that can be distinguished from the rapid shift observed in cells with damaged membranes by the use of multiparametric flow cytometry. The responses of various human cell lines were compared, namely, those of normal and ataxia-telangiectasia (A-T) lymphoblastoid lines, a small-cell lung carcinoma line and its (in vitro) derived multidrug-resistant variants. A close correlation was found between dye toxicity and the degree of DNA binding of Hoechst 33,342 independent of cellular DNA content, with lymphoblastoid and multidrug-resistant small-cell lung cancer cells showing enhanced and restricted dye-binding rates, respectively. VP16- and radiation-induced cell kill was found to result in a quantifiable increase in the fraction of cells undergoing a rapid spectral shift and was capable of detecting the increased radiation sensitivity of A-T-derived cells. Spectral shift analysis provides a rapid method for assessing the responses of tumour cells to cytotoxic agents and for determining the general ability of cells to protect cellular DNA from a model DNA-binding agent (Hoechst 33,342) that participates in the multidrug resistance phenotype.

Tissue preparation for simultaneous flow cytometric quantitation of tumour associated antigens and DNA in solid tumours

A multiparameter flow cytometric assay for the simultaneous study of tumour associated antigens (TAA) and DNA in fresh solid tumours was devised. Cell suspensions were prepared by disaggregating unfixed solid tumour samples mechanically over a stainless steel mesh. Indirect immunofluorescence was used to identify the TAA, and DNA was stained with propidium iodide. Cell morphology was well preserved, cell clumping was negligible, and high quality indirect immunofluorescence quality indirect immunofluorescence and DNA staining were obtained. The technique is simple, rapid, and reproducible. Multiparameter assays can be developed to study prognostic indicators such as membrane oncoproteins, receptors, and multidrug resistance in solid tumours. With a suitable panel of antibodies the technique might become an aid in the differential diagnosis and biochemical diagnosis of some solid tumours.

Caffeine overcomes a restriction point associated with DNA replication, but does not accelerate mitosis

Mitotic chromosome condensation is normally dependent on the previous completion of replication. Caffeine spectacularly deranges cell cycle controls after DNA polymerase inhibition or DNA damage; it induces the condensation, in cells that have not completed replication, of fragmented nuclear structures, analogous to the S-phase prematurely condensed chromosomes seen when replicating cells are fused with mitotic cells. Caffeine has been reported to induce S-phase condensation in cells where replication is arrested, by accelerating cell cycle progression as well as by uncoupling it from replication; for, in BHK or CHO hamster cells arrested in early S-phase and given caffeine, condensed chromosomes appear well before the normal time at which mitosis occurs in cells released from arrest. However, we have found that this apparent acceleration depends on the technique of synchrony and cell line employed. In other cells, and in synchronized hamster cells where the cycle has not been subjected to prolonged continual arrest, condensation in replication-arrested cells given caffeine occurs at the same time as normal mitosis in parallel populations where replication is allowed to proceed. This caffeine-induced condensation is therefore "premature" with respect to the chromatin structure of the S-phase nucleus, but not with respect to the timing of the normal cycle. Caffeine in replication-arrested cells thus overcomes the restriction on the formation of mitotic condensing factors that is normally imposed during DNA replication, but does not accelerate the timing of condensation unless cycle controls have previously been disturbed by synchronization procedures.

An improved method for the detection of cell surface antigens in samples of low viability using flow cytometry

A high non-specific background fluorescence signal was observed when cell surface antigen analysis was carried out using flow cytometry on a cell sample which contained a high proportion of dead and dying cells. To overcome this problem it was necessary to analyse the cells in three stages. First the intact cells were identified by their forward (FWD) and 90 degree scatter profile. These cells were gated-on, then analysed on the basis of their FWD scatter and propidium iodide (PI) signal, allowing the dead PI positive cells to be gated out. The PI negative cells were then displayed using their 90 degree scatter and fluorescence signals following staining with the irrelevant antibody control. This revealed a population of dead cells, which despite being PI negative, were non-specifically binding antibody molecules. Such multiparameter analysis permitted the successful analysis of cell surface antigens in preparations of low viability by gating out the high background fluorescence associated with dead PI positive and negative cells.

Multiparametric analysis of cell membrane permeability by two colour flow cytometry with complementary fluorescent probes

We describe an improved twin-probe multiparameter flow cytometric technique to examine cell membrane permeability. Ability to retain preloaded intracellular bis-carboxyethyl carboxy fluorescein (BCECF, green fluorescence) and to exclude extracellular propidium (red fluorescence) is measured, simultaneously with forward and right-angle scatter. This has significant advantages over an earlier method using fluorescein together with ethidium. In addition to the two expected cell populations which were stained green positive, red negative (by convention membrane "intact" and "viable," Region 1) and green negative, red positive ("membrane-damaged" and "non-viable," Region 3), a third population was seen which fluoresced neither green nor red and displayed intermediate light scatter characteristics (Region 2). This was true for each of 9 cell types in vitro. For EMT6 mouse mammary tumour cells held under sub-optimal conditions or treated with membrane-active drugs, progression from Region 1 to Region 2 was observed, followed by further progression from Region 2 to Region 3. Cells eventually accumulated in Region 3. These results suggest that sequential changes in membrane structure lead to increased permeability, first with respect to intracellular BCECF and in turn to extracellular propidium.