Positive and Negative T-Cell Selection

Question	Answer
T-Cells Before Development	Immature, 'double negative' cells
+ve Selection- Location	Done in the cortex of the thymus
+ve Selection- Role	Removal of weakly binding/non functional T-cells
+ve Selection- Thymic Epithelial Cells	Express both MCHI & MCHII, essentially functioning as antigen presenting cells
+ve Selection- TCR Binding	Binding causes the switching off of aptotic genes- T cells that can bind do not apoptose
+ve Selection- No TCR Binding	Aptotic genes remain functional and weakly/non binding cells apoptose
+ve Selection- T Cells After Selection	Immature 'double +ve' T cells that express both CD4 & CD8
-ve Selection- Location	Corto-medullary junction
-ve Selection- Cells Used	Interdigitating Dendritic Cells
-ve Selection- Antigen Presentation	Interdigitating cells present self antigens to 'double positive' T cells
-ve Selection- Overly Strong Binding	T-cell is actively apoptosed to prevent auto-immune disorders
-ve Selection- Thymic Macrophages	Destroy T-cells that bind too strongly to the 'self' antigens
-ve Selection- Promiscuous Gene Expression	Allows thymic cells to present ALL antigens (even those on other organs or those only expressed at certain times) so the T cell can be tested against the whole body
-ve Selection- End Cells	'Single +ve' cells that only express CD4 or CD8
Creation of Single +ve Cells	Either double +ve cell binds to MCHI by chance and becomes CD4 (or vice versa) or randomly, TCR will upregulate production of one and downregulate other

Resource summary

	Created by gina_evans0312 over 10 years ago