Biomedical subjects

A Nel

Publications and source records attributed to A Nel.

27 records · Page 2Linked to original sources

PubMed1993

Intestinal intraepithelial lymphocytes are activated and cytolytic but do not proliferate as well as other T cells in response to mitogenic signals.

Compared with T lymphocytes from other organs, intestinal intraepithelial lymphocytes (IEL) proliferate weakly in response to CD3/TCR ligation, and they do not respond at all to treatment with other mitogenic stimuli. These signals also failed to induce expression of the IL-2R alpha-chain on the surface of most IEL. IEL from germ-free mice, from V gamma 1.1-transgenic mice, and from beta 2-microglobulin-deficient mice also gave a weak proliferative response. Therefore, the low proliferative response is not linked to the level of exposure to gut bacterial flora, the V gamma region expressed by the TCR-gamma delta + IEL, or the presence of class I molecules that may be recognized by CD8+ IEL. The relatively small amount of proliferation in response to TCR signaling, therefore, is not likely to be the result of induction of anergy caused by previous contact with Ag. In contrast, ligation of the CD3/TCR complex could elicit a rapid cytotoxic response and serine esterase release by IEL. The unusual functional capabilities and the activation state of IEL are independent of the TCR isotype expressed by these cells. Freshly isolated IEL have a high intracellular microtubule-associated protein kinase-2 (MAP-2K) activity level, further suggesting that these cells are activated despite their weak proliferative response. Consistent with this, MAP-2K is tyrosine-phosphorylated in both untreated and PMA-treated IEL. In contrast, MAP-2K activation and tyrosine phosphorylation occur in other T cells only when they are activated by PMA or other treatments. MAP-2K activity also is elevated in IEL from germ-free mice, demonstrating that activation does not depend on normal levels of exposure to bacterial flora. The activation of protein kinases such as MAP-2K could reflect the differentiation state of IEL or Ag receptor stimulation of some of these cells by epithelial cells in the preparation.

Animals↗

PubMed1991

Nerve growth factor stimulates the tyrosine phosphorylation of MAP2 kinase in PC12 cells.

NGF treatment of PC12 cells results in the rapid activation of MAP2 kinase. We report here that the induction of enzyme activity was correlated with the phosphorylation of MAP2 kinase, detected by metabolic labeling of the enzyme and with anti-phosphotyrosine antibodies. NGF stimulated the phosphorylation of MAP2 kinase on tyrosine, as well as serine and threonine residues. Western blot analysis using a polyclonal anti-phosphotyrosine antibody demonstrated that the tyrosine phosphorylation of MAP2 kinase was maximal within 2 min following NGF exposure and preceded the induction of MAP2 kinase activity. The NGF-stimulated tyrosine phosphorylation of an identified substrate provides direct evidence for the participation of a tyrosine kinase in the mechanism of action of NGF.

Adrenal Gland Neoplasms↗

PubMed1990

HIV inhibits the early steps of lymphocyte activation, including initiation of inositol phospholipid metabolism.

Mechanisms accounting for HIV-associated suppression of lymphocyte proliferation were investigated. In previous work we demonstrated that purified and inactivated HIV-suppressed lymphoid cell proliferation. In this report we used an inactivated preparation of HIV obtained from infected CEM cells grown in serum free media and demonstrated that this HIV-associated suppression acted in the early steps of activation to inhibit the incorporation of radiolabeled phosphorus into phosphatidylinositol 4,5-bisphosphate and phosphatidic acid. Initially we showed that both purified CD4 and CD8 T lymphocyte subsets were affected and HIV-associated inhibition did not require the CD4 molecule. Impaired lymphocyte blastogenesis (decreased size and granularity and decreased expression of receptors to IL-2 and transferrin) in response to PHA indicated an effect of inactivated HIV on the early steps of activation. This was confirmed by time studies where 1) a 2 min HIV-pretreatment followed by washing before stimulation was sufficient to inhibit PHA induced proliferation of normal lymphocytes, and 2) addition of HIV to PHA prestimulated lymphocytes failed to inhibit proliferation, e.g., there was no effect on preactivated lymphocytes. HIV was mainly inhibitory of lymphocyte proliferation induced by PHA or mAb to the CD3 receptor. In contrast to the effect on the CD3/TiR, responses via the CD2 receptor were not suppressed, e.g., stimulation with the monoclonal antibodies T11(2) + T11(3). Inasmuch as responses by direct A23187 + PMA stimulation of intracellular pathways were also inhibited, it appears that the HIV-induced defect was not (or not only) membrane receptor mediated. The earliest (min) measurable event after stimulation was the initial increase in intracellular Ca2+ which was unaffected by HIV pretreatment. The next measurable event (min to h) of stimulation is a sustained increase in inositol phospholipid turnover. Pretreatment of mononuclear cells with inactivated HIV resulted in a decreased inositol phospholipid turnover as judged from decreased 32P incorporation into phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate. This led to decreased generation of DAG as reflected in the reduced radiolabeling of its metabolite PA. Reduced availability of DAG presumably interferes with pkC activation and leads to decreased expression of receptors for IL-2 and transferrin and impaired proliferation.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1989

Complexing of the CD-3 subunit by a monoclonal antibody activates a microtubule-associated protein 2 (MAP-2) serine kinase in Jurkat cells.

Treatment of Jurkat T-cells with anti-CD-3 monoclonal antibodies resulted in the rapid and transient activation of a serine kinase which utilized the microtubule-associated protein, MAP-2, as a substrate in vitro. The kinase was also activated on treatment of Jurkat cells with phytohaemagglutinin, but with a different time course. The activation of the MAP-2 kinase by anti-CD-3 antibodies was dose-dependent, with maximal activity observed at concentrations of greater than 500 ng/ml. Normal human E-rosette-positive T-cells also exhibited induction of MAP-2 kinase activity during anti-CD-3 treatment. The enzyme was optimally active in the presence of 2 mM-Mn2+; lower levels of activity were observed with Mg2+, even at concentrations up to 20 mM. The kinase was partially purified by passage over DE-52 Sephacel with the activity eluting as a single peak at 0.25 M-NaCl. The molecular mass was estimated to be 45 kDa by gel filtration. The activation of the MAP-2 kinase was probably due to phosphorylation of this enzyme as treatment with alkaline phosphatase diminished its activity. These data demonstrate that the stimulation of T-cells through the CD-3 complex results in the activation of a novel serine kinase which may be critically involved in signal transduction in these cells.

Antibodies, Monoclonal↗

PubMed1986

Inhibitory effect of an antibody against alpha 1-acid glycoprotein (alpha 1-AGP) on autologous mixed lymphocyte reaction and anti-T3 T-lymphocyte activation.

The action of an anti-alpha 1-AGP antibody on AMLR, anti-T3 and PHA T-lymphocyte proliferative response was evaluated. We observed a strong dose-dependent inhibition on T-lymphocyte proliferative responsiveness to autologous non-T cells and to anti-T3 stimulus, whereas PHA activation was unaffected. A lower degree of inhibition of the proliferative response was also observed on pretreating both T and non-T cells with the antibody; the addition of anti-alpha 1-AGP in the culture containing cells pretreated with the antibody showed a further inhibition of thymidine incorporation. The data suggest a direct influence of the antibody on membrane alpha 1-AGP and support a positive role of this glycoprotein (distinct from Ia and T3 antigens) on both anti-T3 and autologous non-T cell T-lymphocyte responsiveness, thus indicating the involvement of alpha 1-AGP in the T3-Ti antigen-specific pathway of T-cell activation.

Adult↗

PubMed1978