scholarly journals The Veto Mechanism Revisited

2001 ◽  
pp. 147-157 ◽  
Author(s):  
Carlos Hervés-Beloso ◽  
Emma Moreno-García
Keyword(s):  
Veto Mechanism

The veto mechanism in transplant tolerance

1991 ◽  
Vol 5 (4) ◽  
pp. 209-229 ◽  
Author(s):  
Judith M. Thomas ◽  
Kathryn M. Verbanac ◽  
Francis T. Thomas
Keyword(s):  
Transplant Tolerance ◽  
Veto Mechanism

Prevention of allogeneic marrow graft rejection by donor T cells that do not recognize recipient alloantigens: potential role of a veto mechanism

Blood ◽  
1996 ◽  
Vol 88 (3) ◽  
pp. 962-969 ◽  
Author(s):  
PJ Martin
Keyword(s):  
T Cells ◽  
Mhc Class I ◽  
Graft Rejection ◽  
Class Ii ◽  
Class I ◽  
Marrow Graft ◽  
Cd8 Cells ◽  
Donor T Cells ◽  
Veto Mechanism ◽  
Allogeneic Marrow

Clinical trials and experimental studies have demonstrated that donor T cells can play a critical role in preventing allogeneic marrow graft rejection. Results of a previous study showed that donor T cells were most effective for preventing rejection when they recognize an alloantigen expressed by recipient T cells and can cause graft-versus- host disease (GVHD). The present study examined models where marrow graft rejection can be prevented by donor T cells that do not recognize host alloantigens and cannot cause GVHD. Donor T cells prevented rejection of major histocompatibility complex (MHC) class I and II- disparate F1 marrow in parental recipients prepared with > or = 800 cGy total body irradiation (TBI) but not in those prepared with < or = 750 cGy TBI. In recipients prepared with high TBI exposures, rejection was mediated entirely by host CD8 cells. With lower TBI exposures, rejection was mediated by host CD4 cells and CD8 cells. These observations suggested the hypothesis that donor T cells prevent rejection mediated by host effectors that recognize donor MHC class I alloantigens but do not prevent rejection mediated by host effectors that recognize donor class II alloantigens. Consistent with this hypothesis, further experiments showed that F1 donor T cells can prevent rejection of MHC class I-disparate marrow in irradiated parental recipients but have no detectable effect on rejection of MHC class II-disparate marrow. We propose that the expression of MHC class I molecules on donor T cells makes it possible for these cells to inactivate the host response against donor class I alloantigens through a veto mechanism, whereas the absence of MHC class II molecules on murine T cells explains why these cells cannot inactivate the host response against donor class II alloantigens. Finally, donor CD4 cells and CD8 cells were equivalently effective for preventing rejection of F1 marrow in parental recipients, suggesting that veto activity is not restricted solely to the CD8 subset of murine T cells. A veto mechanism could enable donor T cells to prevent allogeneic marrow graft rejection without causing GVHD.

Specific and stable CTL tolerance induced by veto mechanism

1986 ◽  
Vol 7 (10) ◽  
pp. 290
Author(s):  
Donald V. Cramer
Keyword(s):  
Veto Mechanism

A ROLE FOR TRANSFORMING GROWTH FACTOR-BETA IN THE VETO MECHANISM IN TRANSPLANT TOLERANCE1,2

1994 ◽  
Vol 57 (6) ◽  
pp. 893-899 ◽  
Author(s):  
KATHRYN M. VERBANAC ◽  
F. Melinda Carver ◽  
CARL E. HAISCH ◽  
JUDITH M. THOMAS
Keyword(s):  
Growth Factor ◽  
Transforming Growth Factor Beta ◽  
Transforming Growth Factor ◽  
Growth Factor Beta ◽  
Veto Mechanism

scholarly journals Modeling Reverse-Phi Motion-Selective Neurons in Cortex: Double Synaptic-Veto Mechanism

2003 ◽  
Vol 15 (4) ◽  
pp. 735-759 ◽  
Author(s):  
Chun-Hui Mo ◽  
Christof Koch
Keyword(s):  
Striate Cortex ◽  
Interaction Analysis ◽  
Cell Model ◽  
Direct Interaction ◽  
Macaque Monkey ◽  
Direction Selectivity ◽  
Excitatory Synapses ◽  
Preferred Direction ◽  
Direction Of Movement ◽  
Veto Mechanism

Reverse-phi motion is the illusory reversal of perceived direction of movement when the stimulus contrast is reversed in successive frames. Livingstone, Tsao, and Conway (2000) showed that direction-selective cells in striate cortex of the alert macaque monkey showed reversed excitatory and inhibitory regions when two different contrast bars were flashed sequentially during a two-bar interaction analysis. While correlation or motion energy models predict the reverse-phi response, it is unclear how neurons can accomplish this. We carried out detailed biophysical simulations of a direction-selective cell model implementing a synaptic shunting scheme. Our results suggest that a simple synaptic-veto mechanism with strong direction selectivity for normal motion cannot account for the observed reverse-phi motion effect. Given the nature of reverse-phi motion, a direct interaction between the ON and OFF pathway, missing in the original shunting-inhibition model, it is essential to account for the reversal of response. We here propose a double synaptic-veto mechanism in which ON excitatory synapses are gated by both delayed ON inhibition at their null side and delayed OFF inhibition at their preferred side. The converse applies to OFF excitatory synapses. Mapping this scheme onto the dendrites of a direction-selective neuron permits the model to respond best to normal motion in its preferred direction and to reverse-phi motion in its null direction. Two-bar interaction maps showed reversed excitation and inhibition regions when two different contrast bars are presented.

scholarly journals Inactivation of human immunodeficiency virus (HIV)-1 envelope-specific CD8+ cytotoxic T lymphocytes by free antigenic peptide: a self-veto mechanism?

1996 ◽  
Vol 183 (3) ◽  
pp. 879-889 ◽  
Author(s):  
H Takahashi ◽  
Y Nakagawa ◽  
G R Leggatt ◽  
Y Ishida ◽  
T Saito ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
The Other ◽  
Viral Escape ◽  
Common Mechanism ◽  
Lymphocyte Function ◽  
Partial Recovery ◽  
Free Peptide ◽  
Immunodeficiency Virus ◽  
Veto Mechanism ◽  
Hiv 1

Free peptide has been found to inhibit cytotoxic T lymphocyte (CTL) activity, and veto cells bearing peptide-major histocompatibility complex (MHC) complexes have been found to inactivate CTL, but the two phenomena have not been connected. Here we show that a common mechanism may apply to both. CD8+ CTL lines or clones specific for a determinant of the human immunodeficiency virus (HIV) 1 IIIB envelope protein gp160, P18IIIB, are inhibited by as little as 10 min exposure to the minimal 10-mer peptide, I-10, within P18IIIB, free in solution, in contrast to peptide already bound to antigen-presenting cells (APC), which does not inhibit. Several lines of evidence suggest that the peptide must be processed and presented by H-2Dd on the CTL itself to the specific T cell receptor (TCR) to be inhibitory. The inhibition was not killing, in that CTL did not kill 51Cr-labeled sister CTL in the presence of free peptide, and in mixing experiments with CTL lines of different specificities restricted by the same MHC molecule, Dd, the presence of free peptide recognized by one CTL line did not inhibit the activity of the other CTL line that could present the peptide. Also, partial recovery of activity could be elicited by restimulation with cell-bound peptide, supporting the conclusion that neither fratricide nor suicide (apoptosis) was involved. The classic veto phenomenon was ruled out by failure of peptide-bearing CTL to inactivate others. Using pairs of CTL lines of differing specificity but similar MHC restriction, each pulsed with the peptide for which the other is specific, we showed that the minimal requirement is simultaneous engagement of the TCR and class I MHC molecules of the same cell. This could occur in single cells or pairs of cells presenting peptide to each other. Thus, mechanistically, the inhibition is analogous to veto, and might be called self-veto. As a clue to a possible mechanism, we found that free I-10 peptide induced apparent downregulation of expression of specific TCR as well as interleukin 2 receptor, CD69, lymphocyte function-associated antigen 1, and CD8. This self-veto effect also has implications for in vivo immunization and mechanisms of viral escape from CTL immunity.

scholarly journals Legal Nature of the “Veto” in Ukraine and the World: historical and comparative essay.

2021 ◽  
pp. 142-151
Author(s):  
Anastasiia Ivanova
Keyword(s):  
Decision Making ◽  
Political Process ◽  
Balance Of Power ◽  
Executive Branch ◽  
The Political ◽  
Eastern European ◽  
European Tradition ◽  
Legal Nature ◽  
Western European ◽  
Veto Mechanism

On classical sources, the author traced and compared the history of the formation and development of the institution of veto in ancient Rome, in medieval England, France, the Commonwealth. Particular attention is paid to the development of the institution of veto on Ukrainian lands. The author comes to the conclusion about the different legal nature of the veto in the medieval Western European and Eastern European traditions. The Eastern European tradition corresponds to the veto, the peculiarity of which is consensual in nature and the use of the legislature. The principle of consensual decision-making is inherent in the Western European tradition - in the English Parliament, decision-making by consensus has always been desirable. However, in Eastern European practice, it has become mandatory. In medieval society, consensus could exist as long as it was not denied by a minority. Historical experience has demonstrated the shortcomings of this approach and the dangers to the political and legal system in the case of its instrumentalization. Subsequently, the principle of consensus evolved towards the development of the majority principle. The second type of veto should be considered in the context of ensuring a balance of power, it is part of the mechanism of checks and balances, a tool to limit the legislature and strengthen the executive branch. The purpose of this mechanism is to find a balance of power between different spheres of power, which will correspond to the balance of power in a particular society at the moment. Therefore, there is no and obviously cannot be an ideal veto mechanism - in different states the forms of its implementation differ, depending on the distribution of powers between participants in the political process.

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