Allelic exclusion of the T cell receptor alpha-chain: developmental regulation of a post-translational event

Allelic exclusion of the alpha and beta chains of the T cell receptor is ma intained by different mechanisms. Exclusion of the beta-chain is primarily by allowing the successful rearrangement of only one of the two beta-chain loci. In the case of the alpha-chain, rearrangement on both chromosomes is very common, as is expression of alpha-chain mRNA and protein encoded by bo th loci. For the most part, however, functional alpha-chain allelic exclusi on is maintained at the cell surface after positive selection in the thymus . The mechanism by which this is accomplished is not yet Known, but recent evidence indicates that it is an active process coupled to signalling throu gh the T cell receptor.