• Multiple Vα segments;60 Jα
segmentsè higher
chance for successive Vα to Jα rearrangements
to take place
• Continued rearrangement on both
chromosomes can produce several different α chains with the same ß chain because expression of the T cell receptor is not
in itself
sufficient to shut off gene rearrangement.
3-4 days; ceases only when positive selection occurs or cell dies.
• expression of functional TcRα chain is NOT SUFFICIENT for
allelic exclusion.
• POSITIVE SELECTION ensures that each T cell
has only a single functional specificity