Introduction
T cells are involved adaptive immunity:
Antigen presenting cells (APCs) internally process self and foreign proteins, cut them to short peptides (8-15 amino acids).
The peptides are presented on APC surface, attached to protein MHC.
T cell receptors (TCRs) recognize pathogen peptides by binding to them strongly.
T cell receoptors (TCRs) must be
Self-tolerant: to avoid auto-immune diseases
Diverse: to recognize an evolving landscape of pathogens
Specific: to lock on specific pathogens
The ensemble of T cells is shaped in the thymus gland,
where a diverse repertoire of thymocites (expressing distinct TCRs) is culled by encounters with self-pMHC, via
Positive selection: TCR must bind sufficiently strongly to at least one self pMHC
(implicated in MHC restriction, and sensitivity).
Negative selection: TCR must not bind any self pMHC too strongly
(deleting autoimmune TCR).