Correct option is C
The correct answer is self-antigens in association with self-MHC molecules, which is the basis of positive selection of T cells in the thymus. Positive selection ensures that only T cells whose T cell receptors (TCRs) can moderately recognize self-MHC molecules are allowed to survive and mature. This process occurs in the cortex of the thymus, where cortical thymic epithelial cells present self-peptides on self-MHC molecules to developing T cells.
T cells that fail to recognize self-MHC at all undergo apoptosis (death by neglect), while those that recognize self-MHC with moderate affinity are positively selected to become MHC-restricted mature T cells. This process ensures that all functional T cells can recognize antigens only when presented by self-MHC molecules.
Information Booster:
- Positive selection occurs in the thymic cortex, mainly on cortical epithelial cells.
- It allows T cells with TCRs that recognize self-MHC molecules to survive.
- The process helps establish MHC restriction, a fundamental property of T cells.
- T cells that do not recognize self-MHC undergo apoptosis (death by neglect).
- Only T cells that pass positive selection proceed to negative selection in the medulla.
- Negative selection removes T cells that bind too strongly to self-antigens, preventing autoimmunity.
- Positive selection determines whether a T cell will become CD4+ (MHC II restricted) or CD8+ (MHC I restricted).
Additional Information:
- (a) Foreign antigens with self-MHC: Incorrect — This occurs in peripheral tissues during immune responses, not in thymic selection.
- (b) Self-antigens with foreign-MHC: Incorrect — Foreign MHC is never used during thymic selection; this would lead to non-self recognition.
- (d) Foreign antigens with TLR ligands: Incorrect — TLRs (Toll-like receptors) are part of innate immunity, not involved in T cell selection.
