T cell receptors are the sensing molecules for alloantigens
The immune receptors for T cells, or T cell receptors, possess the inherent capacity to bind to MHC molecules bearing peptide antigens, and they are the sensing elements to discriminate self from non-self. T cell receptor genes have the capacity to undergo recombination and other molecular events for the generation of a vast T cell receptor repertoire, able to bind and respond to virtually any given antigen in the universe. However, the infinity of T cell receptor specificities generated must undergo a series of selective processes in the thymus to ensure exported T cells would carry T cell receptor able to bind foreign peptide antigens presented on self-MHC molecules on the surface of peripheral antigen-presenting cell, while unable to react autoreactively to self antigens born by self-MHC molecules. The set of MHC alleles of a given individual shapes the T cell receptor specificities to be selected through these processes, creating an immunoreactive T cell repertoire to foreign antigens presented by antigen-presenting cell in the periphery, which is both self-MHC-restricted and self tolerant.