POSITIVE SELECTION OF THYMOCYTES BEARING ALPHA-BETA-T-CELL RECEPTORS

The past year has been marked by the application of new technologies t o study thymocyte development. These studies have shown that positive selection affects a surprisingly large proportion of thymocytes, and n ow are beginning to investigate the affinities/avidities of the reacti ons involved. The lengthy controversy over how thymocytes decide wheth er to express CD4 or CD8 has taken a new turn with the discovery that levels of expression of the fate-determining protein Notch may affect the decision.