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In immunology, clonal deletion is the process of removing T and B lymphocytes from the immune system repertoire. [1] [2] The process of clonal deletion helps prevent recognition and destruction of the self host cells, making it a type of negative selection. Ultimately, clonal deletion plays a role in central tolerance. [3]
Positive selection occurs in the thymic cortex with the help of thymic epithelial cells that contain surface MHC I and MHC II molecules. During negative selection, T cells are tested for their affinity to self. If they bind a self peptide, then they are signaled to apoptose (process of clonal deletion).
Self reactive cells are subject to clonal deletion or clonal diversion. Both processes of peripheral tolerance control the presence and production of self reactive immune cells. [3] Deletion of self-reactive T cells in the thymus is only 60-70% efficient, and naive T cell repertoire contains a significant portion of low-avidity self-reactive T ...
However, these discoveries, and the host of allograft experiments and observations of twin chimerism they inspired, were seminal for the theories of immune tolerance formulated by Sir Frank McFarlane Burnet and Frank Fenner, who were the first to propose the deletion of self-reactive lymphocytes to establish tolerance, now termed clonal ...
AICD (activation-induced cell death) is programmed cell death caused by the interaction of Fas receptors (Fas, CD95) and Fas ligands (FasL, CD95 ligand). [1] AICD is a negative regulator of activated T lymphocytes that results from repeated stimulation of their T-cell receptors (TCR) and helps to maintain peripheral immune tolerance. [2]
In immunology, clonal selection theory explains the functions of cells of the immune system (lymphocytes) in response to specific antigens invading the body. The concept was introduced by Australian doctor Frank Macfarlane Burnet in 1957, in an attempt to explain the great diversity of antibodies formed during initiation of the immune response .
Autoreactive T cells must be eliminated from the body or skewed into the T Regulatory cells (TRegs) lineage to prevent manifestations of autoimmunity. mTECs possess the ability to deal with these autoreactive clones via mediation of the processes of central tolerance, namely clonal deletion or T regulatory cells selection, respectively. N.B.:
Clonal ignorance theory, according to which autoreactive T cells that are not represented in the thymus will mature and migrate to the periphery, where they will not encounter the appropriate antigen because it is inaccessible tissues. Consequently, auto-reactive B cells, that escape deletion, cannot find the antigen or the specific helper T cell.