Consequences of self and foreign superantigen interaction with specific VB elements of the murine TCR aB

The aB T-cell receptor (TCRaB) recognizes a ligand composed of an antigen fragment complexed with a product of the major histocompatibility complex (MHC). The repertoire of receptors is limited both by the germ line of receptor variable elements and by selective events that take place during T-cell development. The current view is that the germ-line repertoire is expressed in the thymus randomly but that only those T cells bearing receptors that successfully interact with MHC molecules expressed on thymic cortical epithelial cells are allowed to mature (Bevan and Fink 1978; Zinkernagel et al. 1978; Kisielow et al. 1988; Sha et al. 1988). Furthermore, during the process of establishing tolerance to self-antigens, this positively selected population is further reduced by the deletion or inactivation of clones whose receptors continue to interact with self-antigen/MHC ligands (Kappler et al. 1987a, 1988; MacDonald et al. 1988; Pullen et al. 1988). Thus, positive and negative selections reduce expressed receptor repertoire in the periphery to a fraction of the germ-line repertoire.