Positive selection through a motif in the αβ T cell receptor

The two Lineages of T cells, alpha beta and gamma delta, differ in their developmental requirements: only alpha beta cells require major histocompatibility complex recognition, a process known as positive selection, The alpha beta T cell receptor (TCR), but not its gamma delta counterpart, contains a motif within the alpha-chain connecting peptide domain (alpha-CPM) that has been conserved over the Last 500 million years. In transgenic mice expressing an alpha beta TCR Lacking the alpha-CPM, thymocytes were blocked in positive selection but could undergo negative selection. Thus, the alpha-CPM seems to participate in the generation of signals required for positive selection.