Lower Proportion Of Cells Research Articles

Effects of activated serum factor on the induction of Epstein-Barr virus antigens and cell differentiation.

n-Butyrate and 12-0-tetradecanoylphorbol-13-acetate (TPA) have been shown to be potent inducers of Epstein-Barr virus (EBV) antigen synthesis (10, 18) and cell differentiation (1,2). Activated serum factor (SF) has also been reported to induce virus antigen synthesis and moreover it is capable of cooperative action with other inducers (5). We have demonstrated with an EBV-carrying lymphoma cell line (Raji) that activated SF can also induce the appearance of some cellular alterations, specific for early steps of the productive virus cycle in a low proportion of cells. In addition cell differentiation towards plasma cell was noted in about 8 per cent of SF-treated cells. It was confirmed that activated SF enhances the induction of virus antigens by n-butyrate or TPA as detected by the immunofluorescence technique. It was shown that it also potentiates the development of virus-induced changes in cellular morphology and the cell differentiation induced by these drugs. This effect was more pronounced in combination with TPA than with butyrate. Possible relationships between cell differentiation and virus-antigen expression are discussed.

Persistent baculovirus infections: Spodoptera frugiperda NPV and Autographa californica NPV in Spodoptera frugiperda cells.

Establishment of a persistent infection of Spodoptera frugiperda nuclear polyhedrosis virus (NPV) in Spodoptera frugiperda (S.f.) cells occurred in three phases: the first phase was characterised by high levels of cell infection and death, the second phase by decreasing cell infection levels leading to the final phase where less than one per cent of the cells were infected during any subculture. The virus persisted at this level of infection provided the cells were maintained by regular subculturing and incubated at the optimum growth temperature of 27 degrees C. Because of the low proportion of cells infected, cultures of virus-free cells could be selected ('cured') by dilution of the persistent infection without the use of viral antiserum. Unlike the parent S.f. cells, cultures of cured cells were partially resistant to infection with S. frugiperda NPV or infection with an unrelated baculovirus Autographa californica NPV. A. californica NPV, which is cytolytic for the parent S.f. cell line, established a persistent infection in the cured cells. The establishment pattern was similar to that previously found for S. frugiperda NPV and only one to five per cent of the cells were infected at equilibrium. Cured cells from the A. californica NPV persistent infection were highly resistant to infection with both S. frugiperda NPV and A. californica NPV. All attempts to find a viral interference phenomenon to explain the resistance of the cured cells were unsuccessful. All cell types adsorbed virus equally well. Slower growth of S.f. cells cured from the persistent A. californica NPV infection is the only difference so far observed between any of the S.f. cell types.

Quantitative histochemical studies of the effect of levamisole on splenic T-cells in thymectomized Bufo bufo larvae

The ability of levamisole (LVS) to correct the effect of thymectomy on splenic T-cell population in Bufo bufo larvae was tested. Using the nonspecific acid alpha-naphthyl acetate esterase (ANAE) technique, the T-lymphocytes displayed a characteristic reddish brown spot (T-pattern). The total number of white cells per spleen and the number of T-pattern cells per 100 splenic white cells were determined. In addition, differential counts of the T-patterns were made on the basis of the size of their spots. Thymectomized larvae in comparison to sham-operated larvae possessed a lower total number of splenic white cells with a similar proportion of T-pattern cells, but a lower proportion of cells with a large T-pattern. After seven days of LVS treatment, the thymectomized larvae showed an increased total number of splenic white cells and an increased proportion of cells with a large T-pattern, both data falling within normal limits. The effect of LVS appeared marked in thymectomized larvae, but was slight or absent in sham-operated larvae. Differential counts of the large T-pattern cells, based on the size of ANAE reaction product, showed the capacity of LVS to stimulate T-cell maturation. It was concluded that LVS induced proliferation and differentiation of splenic T-cells and that the different sizes of T-pattern reaction represent different maturational stages of T-cells.

Correlation of cell cycle parameters with radiation sensitivity in a series of murine L5178Y cells.

The X-ray dose--response parameters (Do, n and Dq) of 10 strains of murine L5178Y cells spanning a wide range of radiation sensitivities were characterized. The proportions of cells residing in G1, S and G2 + M phases of the cell cycle in exponentially growing cell populations were estimated using DNA microfluorometric techniques. The radiosensitive strains contained a lower proportion of cells in G1 phase and a somewhat larger proporation of cells in S phase than did the radioresistant strains, reflecting a direct correlation between radioresistance and the duration of G1 phase (and possibly an inverse correlation with the duration of the S phase) in these closely related cell strains. These results are discussed in terms of the putative role of G1 in governing radiosensitivity of cells and tumours.

Properties of the K562 cell line, derived from a patient with chronic myeloid leukemia.

The K562 cell line derived from a CML patient in blast crisis was examined for properties of B and T lymphocytes and cell lines. K562 lacks the B markers of immunoglobulins, Epstein-Barr virus (EBV) genome and associated nuclear antigen, and receptors for EBV. A low proportion of cells from rosettes with sheep erythrocytes, the frequency of which is considerably increased after neuraminidase treatment. Unlike B lines but like T lines, K562 cells are lysed rapidly by C'/Fc receptor-positive human blood leukocytes and do not stimulate MLC reactions. On the other hand, K562 lacks T antigen, high radiosensitivity and sensitivity to growth inhibition by thymidine. The cells do not contain N-APase, an enzyme found in all lines derived from lymphoid cells and in lymphoproliferative diseases. By scanning electron microscopy, K562 cells were seen to be rounded and relatively smooth, with small numbers of short microvilli resembling undifferentiated leukemic cells. A few cells had narrow ridge-like profiles and small ruffles similar to granulocytic leukemic cells. K562 is strongly positive for immunoglobuln Fc receptors and pinocytosis, but does not phagocytose or mediate antibody-dependent phagocytosis or cytolysis. Among histochemical stains, K562 is positive for esterase, lipid, and acid phosphatase. There seems to be no doubt that K562 is not a B cell line. While it has some T cell properties, these are not exclusive. Some of its characteristics indicate that it is probably not lymphoid. Due to its low level of differentiation, its nature cannot be stated with certainty. On the basis of the possible presence of the cellular marker of chronic myeloid leukemia, the Ph chromosome, it may be regarded as belonging to the granulocytic series of cells.

Selective cytotoxicity for transformed 3T3 cells

THE therapeutic usefulness of many anti-cancer agents depends on their selective toxicity for cells in the S (DNA synthesising) phase of the cell cycle1. Thus, rapidly proliferating cancer cells are more effectively killed by these agents than are normal cell populations, which have a lower proportion of cells in S. In theory, it should be possible to reduce the toxicity of such agents significantly by further slowing the entry of normal cells into S. We have tested this possibility in vitro by exploiting the ability of cyclic AMP derivatives to inhibit the entry into S phase of 3T3 cells, but not their malignant counterparts, transformed by SV40.

Aspects of the developmental morphology of california encephalitis virus in cultured vertebrate and arthropod cells and in mouse brain

An electron microscopic study was made of the replication of California encephalitis (La Crosse strain) in cultured vertebrate cells (Vero, African green monkey kidney), in a line of cultured mosquito cells (Aedes albopictus), and in brain tissue of suckling mice. Morphologically similar virus particles, approximately 95 nm in diameter, were encountered in all three systems, and a common mode of virus assembly and maturation appeared to obtain. Virus assembly was shown to occur exclusively at internal cytomembrane interfaces, the Golgi complex appearing as the initial assembly site, which site became less focal as infection progressed due to the proliferation of Golgi smooth membranes and the dilation of cisternae and vesicles. The assembly process involved viral budding into cisternal and vesicular lumina, the virion thereby acquiring its limiting membrane. The envelope of such intracellular virions exhibited a poorly defined fringe, approximately 8 nm in width, which appeared to undergo a maturational change as the virions were discharged from the cell, such that, extracellularly, virions displayed a well-developed fringe, approximately 12 nm wide—a change especially noteworthy in the case of virions in infected mouse brain.The presence was noted in infected Vero cells—and in one instance in an infected mosquito cell—of crescent-shaped segments of thickened cisternal membrane, which possibly represented an early phase of viral assembly in which nucleocapsid aligned itself in close apposition to a membrane segment preparatory to the initiation of budding.In areas of the cytoplasm adjacent to sites of viral assembly in neurons, a fine granulofibrillar matrix was frequently found, enmeshed in which were numbers of 50–60 nm spherical structures. In a low proportion of cells from infected mosquito cultures, dense granulofibrillar masses were found in the cytoplasm.In Vero cells, infection with CE virus was cytolytic, while in A. albopictus cells, no gross cytopathic effects were manifest, and persistently infected cultures developed upon subcultivation. However, less than 10% of challenged mosquito cells became productively infected and for a proportion of these, at least as determined by electron microscopy, the infection was lethal.

Studies on the division cycle of mammalian cells III. Preparation of synchronously dividing cell populations by isotonic sucrose gradient centrifugation

Abstract A method of preparing synchronous cell cultures is presented which is based on a selection of postmitotic cells by density gradient centrifugation. Gradients were prepared by appropriate mixing of normal culture medium with medium in which NaCl was replaced by sucrose at a concentration providing for isotonicity. The cells sedimenting most slowly (2–5% of the original cell number) were collected, suspended in sucrose-free medium and cultured under conditions of an optimal steady state. Cell viability, as determined by the capacity of cells to form macroscopically visible colonies in a semisolid medium, was not altered by this treatment. Rhythmic variations of mitotic activity were observed, with a first maximum at 8 h after collection of postmitotic cells. The percentage of cells in the S period was determined at regular time intervals by pulse labeling with 3H-thymidine. A high proportion of DNA-synthesizing cells was found during low mitotic activity, while a low proportion of cells in S phase was observed at the time of maximum mitotic activity.

The arbovirus carrier state in tissue cultures

1. The methods employed for the establishment of latently infected arbovirus carrier cultures have been described. 2. Once established the carrier cultures appeared to be similar to one another in their properties. These included the ability to resist superinfection with homologous and heterologous viruses, slower growth rates than uninfected cells, morphological similarity to uninfected cell populations, and low proportion of cells actually carrying virus. No evidence has been found of a lysogenic relationship similar to that occurring with temperate phages and bacteria. 3. Evidence is presented which indicates that interferon is intimately associated with the maintenance of the carrier state, and that conditions which interfere with the level of interferon could result in an increase in CPE and virus output.

On the specificity of the desoxyribonucleic acid which induces streptomycin resistance in Hemophilus.

Streptomycin resistance of a high degree has been induced in sensitive populations of Hemophilus influenzae and Hemophilus parainfluenzae by desoxyribonucleic acids (DNA's) derived from streptomycin (SM)-resistant cells of at least one heterologous species of Hemophilus. The specificity of the DNA which controls SM resistance has been studied within and among species of Hemophilus by comparing, in a given population, the proportion of cells transformed to SM-resistant by DNA's derived from highly resistant cells of heterologous type or species with the proportion changed by the DNA derived from SM-resistant cells of the homologous type or species. The ratio resulting from this comparison correlates in general with the degree of kinship between recipient and donor cells suggested by accepted methods of bacteriologic classification. The numerical value of the ratio is much lower when the species of the recipient population and donor of the DNA differ than when they are of the same species. The data suggest that this ratio is of value as an index of degree of kinship of recipient and donor cells. Comparison of the activity of heterologous and homologous DNA's shows differences within species and degrees of differences among species not brought out by other available methods. The data suggest that H. influenzae is more closely related to H. parainfluenzae than to H. suis and that the relationship between H. parainfluenzae and H. suis is remote. Within the species H. influenzae and H. parainfluenzae the ratio of hetero-specific transformants to homospecific transformants appears to be relatively constant for a given recipient population. This ratio also appears to be independent of the type or group source of the heterologous species SM resistance DNA. The low proportion of cells in H. influenzae populations which are transformed to SM-resistant by DNA's derived from SM-resistant H. parainfluenzae and vice versa has been increased 4- to 15-fold by the replication of the heterologous species SM resistance DNA in the heterologous species. An alteration of the heterologous DNA by the host is suggested.