Simulations were performed for TCRs of length N=5, with amino-acid compositions typical of human proteome.

Selected fraction:

(Typical number of peptide encounters in thymus is 1,000-10,000)

The selection process biases the composition of amino-acids in mature TCRs:

Negative selection leads to a preference for weaker amino-acids.

This is more or less consistent with the limited available crystallographic data from TCR/peptide interfaces.

Specificity of TCRs and transgenic mice: