Question

2 Describe the mechanisms of central T lymphocyte tolerance (negative selection and development of Tregs).

Answer 1

Central tolerance is the process of eliminating developing T or B lymphocytes that are reactive to self .it ensures immunity does not attack self Peptides.

Mechanisms of T cell tolerance

It occurs in thymus ( positive or negative selection) a) positive selection B) negative selection .

A) During T cell positive selection , T cells are checked for their ability to bind peptide MHC complexes with affinity.

B) During negative selection : T cells are tested to their affinity if they bind to a slef peptide the are signaled to apoptosis ( clonal deletion). If they bind antigen they goes to secondary lymphoid organs as spleen .

- the thymic epithelium cells display self antigen to the T cells. To test their affinity for self.

- Transcriptional regulators AIRE and Fezf2 play important roles in the. Expression of self tissue antigen on the thymic epithelium cells in the thymus .

- Negative selection occur in cortico medullary junction and in the thymic medulla. T cells undergo apoptosis .

If, the T cell that do not bind to self ,but recognize antigen /MHC Complexes , and are either. CD4+ , CD8+ , migrate to Secondary lymphoid. Organs ( spleen) As a mature naive T cells.

TREGS OR REGULATORY T CELLS are another type of T cells That mature In the thymus . Selection of T reg cell occur in thymus medulla accompanied by the transcription of FOXP3 . In thymus CD4+,CD8+ T cells undergo negative selection and become mature t Treg cells through IL -2,IL-15 ,TGF -beta signals .

T reg cells are important for regulating. Automimmunity. By suppressing. Thee immune system when it should not be active.

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