How does positive selection impact T cell diversity?

Positive selection is a fundamental process in T cell development that impacts the diversity and functionality of T cells. Occurring in the thymus, this process ensures the emergence of T cells with T cell receptors (TCRs) that are capable of recognizing and binding to major histocompatibility complexes (MHC) while maintaining self-tolerance.

T cells with TCRs that are unable to bind to MHC molecules undergo a type of cell death known as apoptosis. Only those T cells with TCRs that successfully bind to MHC molecules receive survival signals, allowing them to progress in maturation. These cells are considered to be positively selected. 

Positive selection also determines which T cells will develop into CD8+ T cells, which are capable of killing foreign pathogens directly and which will develop into CD4+ T cells, which are helper T cells. 

This process contributes to the overall diversity of T cells, which helps boost the immune system's ability to recognize and respond to a wide range of potential threats.