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Biomedical subjects

T Leanderson

Publications and source records attributed to T Leanderson.

At least 73 records · Page 4Linked to original sources
PubMed1990

Phorbol ester treatment down-regulates immunoglobulin RNA steady-state levels in B type chronic lymphocytic leukemia and non-Hodgkin's lymphoma cells.

The human B-lymphoma cell lines BJAB and Daudi, as well as the human pre-B cell line KM3, were found to down-regulate steady-state immunoglobulin RNA levels 2- to 4-fold after stimulation with phorbol 12-myristate-13-acetate (PMA) for 24 hr. No down-regulation of the transcriptional rate of a kappa promoter could be observed in any of these cell lines upon transient expression transfection. The observed down-regulation of steady-state immunoglobulin RNA affected both the secretory and the membrane form of the mu transcript equally. When freshly isolated chronic lymphocytic leukemia (CLL) cells where tested for their response to PMA, three of four isolates responded by down-regulating their steady-state immunoglobulin RNA levels.

Animals↗
PubMed1989

Regulation of interleukin 2 gene expression: discrepancy between enhancer activity and endogenous gene expression.

A 630-bp fragment of the human interleukin 2 (IL 2) promoter (+51 to -584) permitted expression of a reporter gene transfected into a mouse T cell lymphoma line (EL4) upon induction with phorbol ester. In contrast, when a human T cell lymphoma (Jurkat) was transfected with the same plasmid and subsequently induced with phorbol ester together with phytohemagglutinin, a very low expression of the transfected gene was observed. The endogenous IL 2 gene was equally well expressed in both cell lines upon induction. Thus, the expression of the endogenous and the transfected gene did not correlate in Jurkat cells. An SV 40 enhancer element cloned 5' of the IL 2 promoter did not result in constitutive expression after transfection to either cell line, rather the IL 2 promoter retained the need for induction. The addition of an enhancer element increased the induced expression of the transfected gene in Jurkat cells into proximity of that observed in induced EL4 cells, indicating that additional sequence elements not contained in the 630-bp fragment are needed for proper expression of the IL 2 gene in Jurkat cells.

Animals↗
PubMed1989

Regulation of immunoglobulin gene expression in trans by phorbol esters.

Lipopolysaccharide-stimulated B cell cultures treated with phorbol-12,13-dibutyrate have been shown to down-regulate their steady state levels of microseconds RNA while the microns RNA remained constant. In contrast, the steady state levels of delta RNA was up-regulated by the same treatment. By using mice transgenic for a rearranged mu or delta gene, it could be shown that the down-regulatory effect acts in trans on a defined DNA stretch and is independent of isotype. Thus, the positive effect on endogenous delta RNA steady-state levels must be regulated at the level of RNA processing. In addition, a DNA construct containing 1.5 kb of a kappa promoter 5' of, and an IgH enhancer 3' of, a chloramphenicol acetyl transferase reporter gene could be down-regulated in trans by anti-mu- or phorbol-12,13-dibutyrate treatment, showing that transcriptional control of Ig promoter elements can readily be observed in non-transformed B lymphocytes.

Animals↗
PubMed1989

Transcriptional regulation of immunoglobulin expression in a chronic lymphocytic leukemia cell line.

A cell line derived from a B-type chronic lymphocytic leukemia, Corinna II, was found to down-regulate its steady-state level of IgM mRNA after treatment with phorbol 12-myristate 13-acetate while the proliferative capacity of the cell line was unaffected. No changes in the splicing pattern of the IgM transcript could be observed after treatment. The down-regulatory effect on IgM RNA expression was found to be inhibited by cycloheximide, suggesting that functional protein synthesis was needed for the effect. Transfection experiments showed that the down-regulatory effect of phorbol myristate acetate was exerted at the level of transcriptional initiation. The DNA element mediating the down-regulatory effect was found to be present within 140 bp 5' of the mRNA cap site in an immunoglobulin promoter.

B-Lymphocytes↗
PubMed1989

Substitution of asparagine324 with aspartic acid in the Fc portion of mouse antibodies reduces their capacity for C1q binding.

The sequence of the heavy chain C region of mouse mutant IgG2a antibodies with reduced capacity for C1q binding but with retained ability for Fc receptor-mediated functions was determined by cDNA cloning and by mRNA sequencing. The specific mutation was found to be the substitution of asparagine324 with aspartic acid. Asparagine324 represents a new residue relating to the C1q-binding sites previously described.

Amino Acid Sequence↗
PubMed1988

Effects of phorbol esters on B-cell gene expression.

Splenic B lymphocytes were stimulated with lipopolysaccharide alone or in combination with phorbol-12,13-dibutyrate, a protein kinase C-activating phorbol ester. The effect of the treatment was analysed at the single cell level with in situ RNA/RNA hybridization. Hybridization with a kappa light chain probe revealed that the whole population had shifted towards a low, but significant, expression of immunoglobulin mRNA. Analysis at the population level was performed by DNA/RNA and RNA/RNA hybridization experiments. It was found that the steady-state levels of mRNA for kappa light chain, IgM heavy chain and J chain were reduced by phorbol ester treatment, while the steady-state level of mRNA for IgD heavy chain was increased. Steady-state levels of mRNA for Ia antigen and alpha-actin were marginally affected.

Actins↗
PubMed1988

Regulation of growth and differentiation of pre-activated B lymphocytes.

The differential effects of H-2 IAk-specific T helper cells, their soluble factors and Sepharose-coupled anti-mu antibodies on the growth and differentiation of pre-activated B cells were studied. It was found that the prolonged growth of pre-activated B cells required activation signals from major histocompatibility complex (MHC)-restricted T helper cells or Sepharose-coupled anti-mu antibodies. The MHC-restricted T helper cells induced both prolonged growth and differentiation of activated B cells. Anti-mu antibodies together with T helper cell-derived soluble factors induced prolonged growth of activated B cells, but no differentiation into Ig secretion was detected. The inhibition of Ig secretion in anti-mu cultures could be overcome to some extent by either MHC-restricted T helper cells or lipopolysaccharide together with soluble factors. It was also observed that T helper cell interactions were needed for long-term in vitro culture of pre-activated B lymphocytes.

Animals↗
PubMed1988

Heterogeneity in the specificities of an alloreactive T helper cell line.

Heterogeneity in antigen recognition of an alloreactive helper T-cell line was studied by repeated limiting dilution cloning. Analysis of the fine specificities of these clones showed that the gain of reactivity to new antigens by the T-cell line included the generation of non-cross-reactive T cells specific to new major histocompatibility (MHC) antigens. Analysis of function revealed that all the T-cell clones studied had similar cell surface antigens and secreted interleukin 4 (IL-4) and IL-5/IL-3 but not IL-2 or gamma interferon (IFN-gamma). The T-cell clones served as helper cells for B cells expressing the appropriate MHC antigens to both clonal proliferation and differentiation into antibody-producing cells.

Animals↗
PubMed1987

Transient gene expression in untransformed lymphocytes.

Conditions for transfection of normal, freshly isolated and mitogen-stimulated spleen cells were established. A sharp optimum of plasmid at 10 micrograms per 1.5 X 10(7) transfected spleen cells per transfection was observed. The Ig promoter and the IgH enhancer activity was found to be restricted to cells of the B lineage also in normal, freshly isolated lymphocytes in vitro.

Acetyltransferases↗
PubMed1987

Prolonged growth of activated B lymphocytes requires interaction with helper T cells.

Resting B lymphocytes acquire upon activation responsiveness to soluble factors that support their growth and differentiation. We have studied the growth requirements of anti-mu pre-activated B lymphocytes in vitro. We found that activated B lymphocytes did respond to soluble factors from helper T cells by entering the cell cycle but cell-cell contact with specific helper T cells was required for prolonged growth of activated B lymphocytes. Thus, activated B lymphocytes must receive activation signals from helper T cells in order to stay in the proliferative phase of the cell cycle.

Animals↗
PubMed1987

Regulation of immunoglobulin transcription rates and mRNA processing in proliferating normal B lymphocytes by activators of protein kinase C.

Immunoglobulin gene expression in normal splenic B lymphocytes stimulated with lipopolysaccharide was selectively down-regulated by anti-IgM antibodies and a protein-kinase C-activating phorbol ester, phorbol 12,13-dibutyrate. This control was concomitant with a decreased rate of transcription of the IgM gene while "polymerase pausing" was induced in the IgD gene. The suppression was resistant to treatment with cycloheximide, indicating that it was not caused by a labile repressor protein. The down-regulation of immunoglobulin gene expression affected only the secretory form of immunoglobulin, while the mRNA levels for the membrane-bound form of immunoglobulin remained unaltered. We conclude that the mechanisms controlling immunoglobulin gene expression in untransformed B lymphocytes differ from those operating in tumors derived from the same cell lineage.

Animals↗
PubMed1987

Neither interleukin 2 nor gamma interferon directly promote growth or differentiation of mouse B cells.

The roles of interleukin 2 (IL-2) and gamma interferon (IFN-gamma) as direct mediators of B-cell growth and differentiation were analysed. Products of cloned genes were used in both cases. The use of flow cytometric assays coupled with density fractionation of responding splenic B-cell populations enabled both the characterization of B cells responding to various stimuli and the estimation of their frequency. B cells responding to non-IL-2 related lymphokines promoting growth and differentiation were restricted to low buoyant density fractions. In addition, these cells expressed densities of IL-2 receptor determinants comparable to those found on T cells, although, IL-2 did not support their growth or differentiation. The inability to demonstrate any direct effect of either IL-2 or IFN-gamma on B cells in any state of activation suggests that their physiological roles are mediated through additional cell types.

Animals↗
PubMed1987

The role of gamma interferon in B-cell activation.

This study evaluates the role of gamma interferon in in vitro B-cell activation. Two clones of an alloreactive helper T-cell line were equally effective in activating B cells polyclonally to proliferate and to mature to immunoglobulin secretion. One of these clones produced high levels of gamma interferon, while the other clone did not. From these data we conclude that gamma interferon plays no limiting role in T-dependent B-cell activation.

Animals↗
PubMed1986

Mouse B cells do not proliferate in human interleukin 2.

By pre-activation with a monoclonal anti-IgM antibody coupled to Sepharose, either in the absence or presence of low doses of lipopolysaccharide, mouse B cell populations were rendered responsive to recombinant DNA derived human interleukin 2 (IL 2). However, if the B cell populations were subjected to separation based on their buoyant density before pre-activation, only low but not high buoyant density cells became responsive to IL 2. Both cell populations subsequent to anti-IgM pre-activation were equally responsive to a Sephadex G-100 fraction of supernatants from rat spleen cells stimulated with concanavalin A. Furthermore, the differences in the IL 2 titration curves on T and B cell populations indicate that only a subpopulation of cells are responding to IL 2 in the B cell populations. In B cell populations that did respond to IL 2, a population of Thy-1.2-positive cells appeared. The proportion of IL 2-responsive T cells needed to give a significant signal when admixed with nonresponding B cell populations was quantitated to be less than 1%.

Animals↗
PubMed1986

Chicken T-cell growth factor: use in the generation of a long-term cultured T-cell line and biochemical characterization.

Supernatants from concanavalin A (Con A)-stimulated chicken spleen cells were used to generate a long-term cultured cell line from antigen-primed chicken peripheral blood leukocytes. This line has been kept in continuous proliferation in vitro for more than 25 weeks. Morphologically these cells were lymphoblastoid and expressed class I and class II antigens of the major histocompatibility complex as well as T-cell (but not B-cell or macrophage) antigens. In addition they contained no peroxidase or non-specific esterase activity, neither were they phagocytic. Proliferation of the line was totally dependent on exogenous T-cell growth factor (TCGF) activity provided by the Con-A-stimulated spleen cell supernatant, comparable with the proliferation of Con-A-induced T-cell blasts. TCGF activity from the supernatant was absorbed both by the long-term cultured T cells and by Con A blasts, demonstrating the presence of receptors for the same TCGF species on the two populations. We have used the long-term cultured cell line to characterize chicken TCGF further. The molecular weight of the biologically active fractions found by gel filtration on Sephadex G-100 was approximately 13,000 and isoelectric focusing showed chicken TCGF to have a pI of pH 5.9. We propose that the TCGF described here is the chicken analogue to the mammalian interleukin 2.

Animals↗
PubMed1985

Anti-IgM treatment influences immunoglobulin heavy and light chain mRNA levels in mitogen-stimulated B lymphocytes.

The mechanism by which soluble anti-IgM inhibits plaque formation by lipopolysaccharide-stimulated B cells was investigated. Since lower amounts of immunoprecipitable mu heavy and kappa light chains were found in cell lysates, this indicated that soluble anti-IgM was inhibiting not only secretion. Subsequently, Northern blot analysis of poly(A+) RNA showed that the steady state levels of mRNA for immunoglobulin heavy and light chain from B cells stimulated with lipopolysaccharide were reduced if the cultures were treated with soluble anti-IgM. The steady-state levels of class I major histocompatibility complex antigen RNA were unaffected by anti-IgM treatment. Addition of supernatants from mouse spleen cells stimulated with concanavalin A at day 2 of culture partially reversed the effect of soluble anti-IgM on immunoglobulin expression.

Animals↗
PubMed1985

Characterization of activities inducing polyclonal maturation of activated B lymphocytes to immunoglobulin secretion.

Supernatants from long-term in vitro-propagated helper T-cell clones were analysed for their ability to induce polyclonal maturation of B lymphocytes under conditions that ensured activation and proliferation of the target cells. In gel filtration analysis, three peaks of activity appeared corresponding to molecular weights of about 100 kD, 60 kD, and 30 kD. When the same supernatants were run on sodium dodecyl sulphate gels under reducing conditions, only the last two peaks of activity could be detected. Flat-bed isoelectric focusing gave two peaks of activity corresponding to isoelectric points of pH 5-6 and pH 8-9. These peaks of activity were devoid of any activity supporting proliferation of either T or B cells, and they induced the expression of several heavy-chain isotypes. Furthermore, when the same analysis was performed on the B-cell line WEHI 279.1, only one peak was obtained (molecular weight of about 60 kD; isoelectric point, approximately pH 5-6), a result suggesting alternate pathways of induction of B cells to high-rate secretion cells.

Animals↗