THE V-BETA REPERTOIRE OF MOUSE GUT HOMODIMERIC-ALPHA CD8+ INTRAEPITHELIAL T-CELL RECEPTOR ALPHA/BETA+ LYMPHOCYTES REVEALS A MAJOR EXTRATHYMIC PATHWAY OF T-CELL DIFFERENTIATION

Gut intraepithelial lymphocytes (IEL) contain two independent T cell receptor alpha/beta- T cell populations, with different V-beta repertoires. In DBA/2 mice (Mls(a), IE ), the CD4 and heterodimeric alpha/beta CD8 thymodependent T cell pool shows the same deletion of V-beta-6, 8.1, and 11 cells as found in peripheral lymphoid organs. In contrast, such deletions are not observed in the pool of IEL bearing homodimeric alpha CD8 chains, in which these V-beta families are frequently observed in high amounts. The size of this gut homodimeric alpha CD8 IEL pool and its different V-beta repertoire selection demonstrate the existence of a major extrathymic pathway of T cell differentiation with a gut-restricted localization. The large amount of the thymo-independent, homodimeric alpha CD8 IEl found in the small bowel may contribute to a first line of defense against exogenous superantigens.