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O C Blair

Publications and source records attributed to O C Blair.

10 recordsLinked to original sources
PubMed1991

UV irradiation of lymphocytes triggers an increase in intracellular Ca2+ and prevents lectin-stimulated Ca2+ mobilization: evidence for UV- and nifedipine-sensitive Ca2+ channels.

UV irradiation induces in vitro and in vivo immunosuppression. Because mobilization of intracellular calcium ([Ca2+]i) represents a central step in cell activation and immune response, we investigated the effect of UV irradiation on Ca2+ homeostasis. Using indo-1 and cytofluorometry, [Ca2+]i kinetics in UVC- or UVB-exposed human peripheral blood leukocytes (PBL) and Jurkat cells were determined in parallel with functional assays. Increases in [Ca2+]i were observed within 2-3 h of irradiation; these increases were UV-dose dependent and reached maxima of 240% and 180% above baseline level (130 nM) for UVB and UVC, respectively. The UV-induced [Ca2+]i rise was predominantly due to influx of extracellular calcium, and it was more pronounced in T than in non-T cells. Concurrent with [Ca2+]i shifts following UV treatment, there was a loss of ability to respond to phytohemagglutinin (PHA) or to proliferate or stimulate in mixed leukocyte culture. This loss of function appeared to be related not only to UV-induced calcium shifts, but also to effects of UV irradiation on the plasma membrane. No [Ca2+]i mobilization was induced by gamma irradiation, and gamma-irradiated cells showed a normal [Ca2+]i increase in response to PHA. UV-induced Ca2+ flux into the cells was blocked by nifedipine. These data indicate that UV and gamma irradiation have different effects on lymphocyte membranes and suggest that a disruption of Ca2+ homeostasis may be involved in UV-induced lymphocyte inhibition. The data suggest, furthermore, the presence of Ca2+ channels in lymphocyte membranes that are sensitive to UV irradiation and Ca2+ channel blockers such as nifedipine.

Calcium↗
PubMed1989

Induction of the differentiation of synchronized HL-60 leukemia cells by tiazofurin.

Tiazofurin is an effective inducer of the maturation of HL-60 promyelocytic leukemia cells, as monitored by increased phagocytic ability and the capacity to reduce nitroblue tetrazolium (NBT). The antimetabolite acts as a potent inhibitor of IMP dehydrogenase, which results in a profound depression in the cellular levels of guanine nucleotides. Flow cytometric analysis of DNA histograms indicated that the commitment of HL-60 cells to differentiate when exposed to tiazofurin was preceded by a transient delay in the G1 phase of the cell cycle. HL-60 leukemia cells enriched in the various phases of the cell cycle by centrifugal elutriation were utilized to further characterize the relationship between the phase of the cell cycle and the commitment to enter a pathway of differentiation. Fractions composed mainly of G1 cells demonstrated an increased capacity to mature when exposed to tiazofurin, whereas fractions containing cells from the S and G2 + M phases of the cell cycle had a lower ability to enter a differentiation pathway. The findings suggest that the commitment of HL-60 cells to mature when exposed to tiazofurin is mediated during the G1 phase of the cell cycle.

Cell Cycle↗
PubMed1987

Normal brachial plexus: MR imaging.

Magnetic resonance (MR) imaging of the brachial plexus was performed in the axial, coronal, and sagittal planes in seven volunteers. Normal structures were delineated by comparison with axial and sagittal cadaver sections and with gross dissection. Differentiation of soft tissues with MR imaging enabled the brachial plexus to be defined from surrounding muscle and vascular structures. Multiplanar imaging demonstrated anatomic detail not previously demonstrated with other radiologic modalities and provided excellent delineation of the components of the brachial plexus from the ventral rami to the peripheral nerve branches.

Adult↗
PubMed1987

Cytotoxicity and differentiating actions of adriamycin in WEHI-3B D+ leukemia cells.

The monomyelocytic leukemia WEHI-3B D+ can be induced to differentiate into mature granulocytes in suspension culture when exposed to 40 nM adriamycin. Treated cells underwent approximately two divisions prior to reaching plateau phase, with approximately 55% of the cell population expressing nitro blue tetrazolium positivity (NBT+) by day 3. Decreased cellular proliferation was paralleled by a progressive increase in morphologically mature granulocytic cells. Maturation was also characterized by a 4.4-fold increase in Fc receptors on the cell surface. An increase in the size of adriamycin-treated cells occurred and correlated with residency in the G2M phase of the cell cycle. Adriamycin-induced NBT+ cells, which contained the highest levels of Fc receptors, were also found to reside in G2M. Adriamycin blocked cells in the G2M phase of the cell cycle by 8 hr (125% above control), and this arrest reached its maximum by 20 hr (194% above control). Concomitant with the block in the cell cycle was the commitment by these cells within 8 hr to the granulocytic pathway of differentiation. Fractionation of cells by centrifugal elutriation into enriched phases of the cell cycle was consistent with the hypothesis that induction of the differentiation program was initiated either in G1 or very late in the cell cycle. Immobilized adriamycin, which does not gain access to the cell interior, did not induce the maturation of WEHI-3B D+ cells, nor did it block their replication in a specific phase of the cell cycle; however, immobilized adriamycin was 30-fold more toxic to WEHI-3B D+ cells than free drug. Incubation of WEHI-3B D+ cells with the semisynthetic adriamycin analog N-trifluoroacetyl adriamycin-14-valerate (AD-32) resulted in approximately 50% of the cell population being NBT+ by day 3. The findings suggest that adriamycin must be able to enter cells to induce maturation, and that at least some portion of its toxicity is associated with an effect at the surface membrane. Furthermore, the results obtained with AD-32 imply that intercalation into DNA is not necessary for induction of the differentiated phenotype.

Cell Cycle↗
PubMed1986

Differentiation of HL-60 promyelocytic leukemia cells: simultaneous determination of phagocytic activity and cell cycle distribution by flow cytometry.

Phagocytosis of fluorescent microspheres by HL-60 promyelocytic leukemia cells following induction of differentiation with dimethyl sulfoxide (DMSO) was monitored using flow cytometry. Initiation of phagocytic capability following initiation of differentiation with 1.5% DMSO coincided with the attainment of respiratory burst activity as measured by NBT (nitro blue tetrazolium) reduction; the degree of phagocytic activity was dependent upon parameters such as microsphere size, microsphere number, and exposure time. Ingestion of fluorescent microspheres did not interfere with the measurement of DNA content using propidium iodide; thus, simultaneous determination of phagocytic activity and the cell cycle phase was possible. Accumulation of cells in the G1/G0 phase of the cell cycle following DMSO treatment was correlated with the acquisition of the capacity to phagocytize. Analysis of two-parameter correlated data also indicated that phagocytosis is coupled with residence in the G1/G0 phase of the cell cycle, further suggesting that the ability to phagocytize fluorescent microspheres is associated with end-stage differentiation.

Cell Cycle↗
PubMed1986

Alterations in glycoprotein synthesis and guanosine triphosphate levels associated with the differentiation of HL-60 leukemia cells produced by inhibitors of inosine 5'-phosphate dehydrogenase.

The synthetic "C" nucleoside, tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide), its selenium analogue selenazofurin, and the related inhibitor of inosine 5'-phosphate (IMP) dehydrogenase, mycophenolic acid, are effective inducers of the terminal differentiation of HL-60 promyelocytic leukemia cells. The inhibition of cellular replication and the induced maturation produced by these agents appears to be a consequence of the inhibition of IMP dehydrogenase, since growth inhibition is partially reversed and differentiation is completely prevented by the simultaneous exposure of cells treated with inhibitors of IMP dehydrogenase to exogenous guanosine, which serves to circumvent the effects of the blockage of IMP dehydrogenase. The exposure of HL-60 leukemia cells to inhibitors of IMP dehydrogenase caused a marked reduction in the incorporation of [3H]mannose into both cellular glycoproteins and their lipid-linked oligosaccharide precursors; these effects are presumably due to the pronounced decrease in intracellular levels of guanosine triphosphate produced by blockage of IMP dehydrogenase. Maximum effects on glycoprotein biosynthesis occurred within 8 h of exposure to the inhibitors of IMP dehydrogenase. The simultaneous incubation of cells with guanosine and these inducers of differentiation partially prevented the reduction in [3H]mannose incorporation into glycoproteins, supporting a relationship between glycoprotein biosynthesis and guanosine triphosphate formation in the induction of differentiation by inhibitors of IMP dehydrogenase.

Cell Cycle↗
PubMed1986

Differentiation of WEHI-3B D+ monomyelocytic leukemia cells by retinoic acid and aclacinomycin A.

WEHI-3B D+ monomyelocytic leukemia cells were induced to differentiate to mature granulocytes when treated with either 30 nM aclacinomycin A or 7 microM retinoic acid. Differentiation was assessed by the appearance of mature granulocytic phenotypes, as measured by the ability to reduce nitro blue tetrazolium, morphological changes, an increase in cell surface Fc receptors, as well as the loss of proliferative capacity. Maximum differentiation occurred 3 days after drug exposure. Analysis of DNA histograms of treated cells indicated that cells accumulated in the G1 phase of the cell cycle after 8 h of exposure to either inducer, with maximum accumulation occurring by 20 h; this arrest was observed prior to the phenotypic appearance of mature cells. The minimum interval of time necessary to commit cells to a differentiation pathway, which was less than one doubling time (9.2 h), closely paralleled the initial accumulation of cells in the G1 phase of the cell cycle. Since drug exposure for more than one cell division was required for maximum differentiation, the observed kinetics of maturation is consistent with a stochastic model. These studies support the idea that this cell line would be a particularly good model for extrapolation of findings with differentiating agents in culture to therapeutic monitoring in animals, since WEHI-3B D+ leukemia cells can be readily propagated in vivo in BALB/c mice.

Aclarubicin↗
PubMed1985

Differentiation of HL-60 promyelocytic leukemia cells monitored by flow cytometric measurement of nitro blue tetrazolium (NBT) reduction.

Reduction of nitro blue tetrazolium (NBT) to insoluble blue formazan granules occurs during the stimulus-induced respiratory burst of mature granulocytes and is routinely used as an indicator of the extent of granulocytic differentiation of HL-60 acute promyelocytic leukemia cells. In the present study, the differentiation of HL-60 leukemia cells induced by dimethylsulfoxide (DMSO) or retinoic acid was monitored by flow cytometric (FCM) measurement of forward and 90 degree light scatter of NBT treated cells. Two-parameter correlated analysis permitted a distinction between cells with increased forward and decreased 90 degree light scatter (NBT-), and cells with decreased forward and increased 90 degree light scatter (NBT+). Fixation of NBT treated cells with 1% paraformaldehyde facilitated flow cytometric analysis, and allowed differences in NBT reduction to be quantitated. DMSO-induced cells expressed an all-or-none reduction of NBT to formazan, compared with retinoic acid treated cells that exhibited a graded response. Three parameter flow cytometric analysis of HL-60 leukemia cells stained with propidium iodide in combination with NBT allowed the determination of the cell cycle distribution of NBT-treated cells.

Cell Differentiation↗