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J D Ebert

Publications and source records attributed to J D Ebert.

At least 19 recordsLinked to original sources
PubMed1985

NIH budget growth.

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National Institutes of Health (U.S.)↗
PubMed1978

Transfer of concanavalin A between responding lymphocytes and syngeneic stimulating cells in cell-mediated mitogenic response.

We have studied the mechanism of the cell-mediated mitogenic response (CMMR), in which proliferative responses are generated in mouse T lymphocytes co-cultivated with syngeneic mitomycin C-treated spleen cells (Mito-SP), when either responder or stimulator cells are briefly pretreated with concanavalin A (Con A) under nonmitogenic conditions. We present evidence that an intact membrane of the stimulator cells is required in CMMR, since the response was abolished by fixation, or by freezing and thawing of stimulator cells. The fate of cell-bound Con A was studied by tracing I-Con A bound to either stimulator or responder. A lymphoblast that developed from untreated CRT stimulated by I-Con A-coated syngeneic Mito-Sp carried about 105 molecules of 125I-Con A. The amount of Con A released into the culture medium was not sufficient for inducing a mitogenic response by itself, nor to bind to cells at the level found in CMMR, suggesting that 125I-Con A was transferred directly from labeled cells to unlabeled cells. Transferred 125I-Con A found in lymphoblasts was undergraded intact Con A, as demonstrated by gel electrophoresis. Autoradiography allowed visualization of the movement of 125I-Con A from stimulator to responder cells within 60 min of cell contact.

Animals↗
PubMed1977

Cell-mediated mitogenic response induced by leukoagglutinin and Lens culinaris lectin in mouse lymphocytes.

The proliferative response of mouse lymphocytes to syngeneic cellular stimulation upon membrane modification with lectins was studied. Brief pretreatment of stimulator cells (mitomycin-C-treated spleen cells) followed by mixed culture with syngeneic cortisone-resistant thymocytes resulted in a significant proliferative response in the thymocytes. This effect was not due to a soluble mediator and was similar to the mitogenic response after Con A-induced membrane modification reported previously. Because of its general characteristics, we refer to this response as cell-mediated mitogenic response (CMMR). Cell contact between stimulator and responder cells was necessary but not sufficient for the induction of the response. The lectins that generated CMMR were T-cell mitogens. CMMR was generated in all the syngeneic combinations tested and even in allogeneic combinations. No detectable cytotoxic activity towards syngeneic targets cells was produced after CMMR. Moreover, CMMR in allogeneic combinations led to the suppression of the generation of specific cytotoxic lymphocytes. Population analysis with antibodies against T or B cells, nylon wool fractionation of stimulator cells, and tests with peritoneal macrophages and with spleen cells from athymic mice revealed that CMMR depends predominantly on the interaction between responder T cells and stimulator Ig-positive lymphocytes.

Agglutination↗
PubMed1977

Accelerated calcium ion uptake in murine thymocytes induced by concanavalin A.

The mechanism of enhancement of Ca2+ uptake by the T cell mitogen concanavalin A (Con A) was studied in murine thymocytes. Native Con A enhanced the rate of Ca2+ uptake as much as 9-fold, an increase being observed within five minutes after Con A addition. The effect of Con A was reversed completely by alpha-methyl mannopyranoside (alpha-MM). Increased Ca2+ uptake was observed with increasing concentrations of Con A, between 2 and 400 microgram/ml, indicating that the stimulation of Ca2+ uptake is not restricted to mitogenic lectin concentrations (0.5-2 microgram/ml). Succinyl Con A exhibits only a slight effect in the same concentration ranges as native Con A. Ca2+ uptake, both in the absence and presence of Con A, is strongly dependent on energy metabolism and is carrier mediated. The augmentation of Ca2+ uptake by native Con A is due to an enhanced Vmax. Uptake of the anion, CrO42-, by thymocytes, found to be a non-saturable process, was also enhanced by Con A. The effect of Con A on CrO42- permeability appears to be independent of its effect on Ca2+ uptake.

Azides↗
PubMed1976

Concanavalin A potentiates syngeneic response in murine lymphocytes.

In an attempt to modulate the recognition processes that occur on lymphocyte membranes in mixed lymphocyte culture, responding cortisone resistant thymocytes or stimulating spleen cells (treated with mitomycin C) were pretreated with native concanavalin A (N-Con A) or succinyl-Con A (S-Con A). Highly significant cell proliferation was observed in syngeneic combinations when either the responding cells or the stimulating cells were so treated with Con A, although Con A pretreatment alone was never mitogenic. In allogeneic combinations the proliferative response with Con A pretreatment of either partner on day 3 was five to seven times higher than in the normal mixed lymphocyte reactions. The triggering of proliferation was dependent on two factors: (a) The presence of spleen cells as the stimulating cells (thymocytes were much less effective). (b) The binding of Con A molecules to either one of the partners, the effect being abrogated by the specific inhibitor of Con A, alpha-mannopyranoside. The optimal concentration of S-Con A was about twice that of N-Con A. Even more striking was the observation that cultures in which either one of the partners was pretreated with Con A in allogeneic combinations showed a strong suppression (60-80% inhibition) in the subsequent generation of the cytotoxic lymphocytes (CL). The Con A concentration required to trigger a proliferative response corresponded to that for suppressing the generation of CL. Con A pretreatment did not result in a cytotoxic activity toward syngeneic tumor cells.

Animals↗
PubMed1975

The effect of potassium on the cell membrane potential and the passage of synchronized cells through the cell cycle.

The cell membrane potential of cultured Chinese hamster cells is known to increase at the start of the S phase. The putative role of the cell membrane potential as a regulator of cell proliferation was examined by following the cell cycle traverse of synchronized Chinese hamster cells in the presence or absence of high exogenous levels of potassium. An increase in external potassium levels results in a depressed membrane potential and a reduced rate of cell proliferation. A potassium concentration of 115 mM was used in experiments with synchronized cells since at that level cell proliferation is almost completely halted, recovery of growth is rapid and complete, and the membrane potential is reduced to a level well below that normally found in cells in the G1 phase. A mitotic population was divided into four aliquots and plated in either control medium or medium containing 115 mM K+. Cells placed directly into high K+ medium were retarded in their exit from mitosis and displayed a delayed and abnormal entry into the S phase. If control medium was added after two hours, cell cycle traverse was normal, but delayed by two hours compared to control cells. If the mitotic cells were plated directly into control medium and two hours later were shifted to high K+ medium, the cells entered the S phase in the absence of the normally observed increase in membrane potential and proceeded to the next mitosis normally. It was concluded that the increase in membrane potential observed at the start of the S phase in isolated synchronized cells is not a requirement for the initiation of DNA synthesis. In addition, sensitivity to the high potassium regimen was found at two different times during the cell cycle. In one case, cells were impeded in their transit through mitosis. Such cells displayed an altered chromosome structure which may account for the partial mitotic block. In the second case, synchronized cells displayed a sensitivity to the high potassium regimen in early G1 which appeared to be separate from the block in mitosis and independent of a change in the membrane potential.

Animals↗
PubMed1975

Pretreatment of murine thymocytes by phytohemagglutinin inhibits the binding of H-concanavalin A.

The binding of H-concanavalin A (Con A) to cortisone-resistant and normal mouse thymocytes, which greatly differ in mitogenic responsiveness, was compared. Almost equal numbers of 3H-Con A molecules (7 x 10(5) molecules per cell) were found to bind to both cell types, and the rates of H-Con A binding were nearly identical. The binding capacity of thymocytes for H-Con A decreased rapidly after removal from the thymus and incubation in protein free synthetic medium. Similarly, mitogenic responsiveness droped rapidly after cells were exposed to this medium. H-Con A molecules bound to cells were dissociated from them after a brief incubation, about 30 percent of radioactivity being lost in 2 hr with increasing radioactivity being found in the supernatant. When cells were pretreated with PHA-P, which is a T cell mitogen, their mitogenic responsiveness to Con A was suppressed along with H-Con A binding to the cells. In contrast, a B cell mitrogen, LPS, that has a synergistic effect on the Con A mitogenic response in thymocytes had no effect on binding of H-Con A to thymocytes.

Anhydrides↗
PubMed1972

Potassium: effect on DNA synthesis and multiplication of baby-hamster kidney cells: (cell cycle-membrane potential-synchronization-transformation).

The relations between DNA synthesis, cell multiplication, and external potassium concentration have been investigated in cultured baby-hamster kidney cells. When the potassium concentration was raised from 8 mM to 114 mM by equimolar replacement of sodium, DNA synthesis and cell multiplication were almost completely inhibited. This inhibition was reversible even after 72 hr of incubation in medium with a high concentration of potassium. There is a consistent difference between the cultured cells and polyoma virus-transformed cells in response to high-potassium medium, a higher-potassium concentration being required to inhibit multiplication of polyoma virus-transformed cells to the same extent as that of the nontransformed cells.

Animals↗